Chapter 3 Water Based Mud

Agip KCO G

R

O

U

P

WELL AREA OPERATIONS DRILLING SUPERVISOR TRAINING COURSE

WATER BASED MUDS

Cod.: RPWA2021A

Date: 01/03/2005

Rev: 00

Page: 132

Code RPWA2021A Date: 01/03/2005 Page 2 of 132

Agip KCO

INDEX

1.0

INTRODUCTION

8

2.0

NON INHIBITING FLUIDS

12

2.1

Service waters (clean waters)

12

2.2

Muds with formation shale (native muds)

13

2.3

Bentonite-water (spud mud)

16

2.4

Lignite/lignosulfonate mud

18

3.0

INTRODUCTION

25

4.0

FORMATION DAMAGE CONTROL

26

5.0

DRILLABILITY

26

6.0

COMPATIBILITY WITH COMPLETION PROCEDURES AND EQUIPMENT

27

7.0

FORMATION DAMAGE MECHANISMS

27

7.1

Plugging by solids

28

7.2

Hydration of formation shales (migration)

28

7.3

Emulsion blocking

29

7.4

Scaling

29

8.0

TYPES AND APPLICATIONS OF DRILL IN FLUIDS

30

8.1

Clear fluids without viscous cushions

30

8.2

Fluids with HEC

30

8.3

Calibrated salt systems (salt size)

30

8.4

Oil base systems

31

8.5

Synthetic base systems

32

9.0

INTRODUCTION

33

10.0

FLUID DENSITY (MUD WEIGHT)

33

10.1 Instruments

33

10.2 Mud balance 10.2.1 Description

33 33 Well Area Operations

Code RPWA2021A Date: 01/03/2005 Page 3 of 132

Agip KCO

10.2.2 10.2.3

11.0

12.0

13.0

14.0

Calibration Procedure

34 34

VISCOSITY

36

11.1 Instruments

36

11.2 Marsh funnel viscometer 11.2.1 Description 11.2.2 Calibration 11.2.3 Procedure

36 36 36 37

11.3 Rotational viscometer 11.3.1 Description 11.3.2 Specifications: Direct reading viscometers 11.3.3 Procedure to determine apparent viscosity, plastic viscosity and the yield point 11.3.4 Procedure to determine gel strengths (at 10” and 10’) 11.3.5 Taking care of the viscometer

37 37 38 39 40 41

FILTRATION

42

12.1 Description

42

12.2 Instruments

42

12.3 API fluid loss 12.3.1 Procedure

43 43

12.4 High temperature high pressure (HTHP) filtration - MB style (API #II) HTHP filter press 12.4.3 Description 12.4.4 Procedure 12.4.5 API # I HTHP filter press 12.4.6 Description 12.4.7 Filter cake compressibility

44 44 45 47 47 50

SAND CONTENT

51

13.1 Instruments

51

13.2 Sand content testing kit 13.2.1 Description 13.2.2 Procedure

51 51 51

SOLID AND LIQUID CONTENT

52

14.1 Instruments

52

14.2 Description of the distiller 53 14.2.1 Procedure 53 14.2.2 Percentage from analysing the volume of solids, weight method (calculating the difference in weight using a conventional distiller). 54 14.2.3 Equipment 54 14.2.4 Procedure 55 Well Area Operations

Code RPWA2021A Date: 01/03/2005 Page 4 of 132

Agip KCO

15.0

16.0

14.3 Methylene blue capacity test 14.3.1 Equipment 14.3.2 Reagents 14.3.3 Procedure

56 56 56 57

14.4 Methylene blue capacity of clay 14.4.1 Methylene blue capacity (bentonite equivalent) 14.4.2 Cation exchange capacity of clays 14.4.3 Procedure

58 58 58 58

CONCENTRATION OF HYDROGEN IONS (PH)

59

15.1 Scope

59

15.2 Litmus (or pH) papers 15.2.1 Description 15.2.2 Procedure

59 59 59

15.3 pH meter 15.3.1 Description 15.3.2 Equipment 15.3.3 Procedure 15.3.4 Cleaning 15.3.5 Principle of equivalent solutions

60 60 60 60 61 62

CHEMICAL ANALYSIS OF WATER IN MUDS

63

16.1 Alkalinity (Pf , Mf , Pm) and lime content 16.1.1 Equipment 16.1.2 Procedure to test filtrate alkalinity (Pf and Mf) 16.1.3 Procedure to test mud alkalinity (Pm) 16.1.4 Procedure to test calcium content (excess lime) 16.1.5 Filtrate alkalinity: P1 and P2 16.1.6 Equipment 16.1.7 Procedure

63 63 64 65 65 66 66 67

16.2 GARRETT GAS TRAIN (GGT) test for carbonates 16.2.1 Scope 16.2.2 Equipment 16.2.3 Procedure 16.2.4 Selecting the Dräger tube

68 68 68 69 72

16.3 Chlorides (Cl–) 16.3.1 Scope 16.3.2 Equipment 16.3.3 Light coloured filtrates 16.3.4 Procedure 16.3.5 Dark coloured filtrates 16.3.6 Procedure

73 73 73 73 73 75 75

16.4 Calcium – qualitative testing 16.4.1 Scope 16.4.2 Equipment

77 77 78

Well Area Operations

Code RPWA2021A Date: 01/03/2005 Page 5 of 132

Agip KCO

16.4.3

17.0

Procedure

78

16.5 Total hardness 16.5.1 Calcium plus magnesium – Quantitative testing 16.5.2 Equipment 16.5.3 Procedure (total hardness) 16.5.4 Calcium and magnesium separately

78 79 79 80 82

16.6 Hardness in dark filtrates 16.6.1 Total hardness in dark filtrates – Quantitative testing 16.6.2 Scope 16.6.3 Equipment 16.6.4 Calcium and magnesium, separately

83 83 83 84 86

16.7 Sulphate 16.7.1 Qualitative testing 16.7.2 Scope 16.7.3 Equipment 16.7.4 Procedure 16.7.5 Availability of calcium sulphate 16.7.6 Scope 16.7.7 Equipment 16.7.8 Procedure

87 87 87 87 87 88 88 88 88

16.8 Potassium (K+) 16.8.1 Procedure I — Potassium 200°F). NOTE: Never put the part with measurements in water.

Well Area Operations

Code RPWA2021A Rev. 00 – Date 01/03/2005 Page 42 of 132

Agip KCO

12.0 FILTRATION 12.1

Description Filtration, or the capacity of a mud to produce filter cake, is determined by a filter press. In this test, the rate at which a fluid is forced through a filter press is determined. The test is carried out in specific time, temperature and pressure conditions. The thickness of the solid panel which deposits is measured after the test. The filter press must conform to API standards and should be used following API specifications. The API fluid loss test is carried out at a pressure of 100 psi and fluid loss is recorded as the quantity in millilitres lost in 30 minutes minus the filtering surface which equals 7.1 square inches.

12.2

Instruments The instrument in figure 5 comprises a mud cell assembly, a pressure regulator and pressure gauge assembled above the container. The cell is connected to the regulator by an adaptor, with the cell simply fitted in the filter press receptacle, which is then rotated 1.4 times clockwise. Some cells may not have a device to secure them. In this case simply fit the cell in the receptacle.

Close the cell at the bottom with the lid containing a filter. Firmly push the

lid against the paper filter and turn to the right to tighten. This will push the paper filter against the O-ring at the base of the cell. At this point, the cell is pressurised by a carbon dioxide cylinder.

A bleeder valve releases pressure

before disassembly. Do not use N2O (nitrogen oxide) for this step.

Well Area Operations

Code RPWA2021A Rev. 00 – Date 01/03/2005 Page 43 of 132

Agip KCO

Cell

Graduated Cylinder

Cell Carbone dioxide cartridges Figure 5: A filter press.

12.3

API fluid loss 12.3.1

Procedure 1.

Ensure a pressure of 100 psi (7 Kg/cm2) with gas or air.

2.

Remove the lid from the bottom of the clean, dry cell. Fit the O-ring making sure the seating is not damaged, then turn over. Any mechanical flaw may affect the seal of the cell. Cover the hole with a finger.

3.

Fill the cell with mud to 1.4” from the O-ring housing. Put the paper filter (Whatman No. 50 or equivalent) above the O-ring. Put the lid on the paper filter with the flanges between the flanges of the cell, then turn clockwise and close. Turn the cell upside down and fit the male cell in the female cell of the filter press and turn in both directions to close.

4.

Put a graduated cylinder below the filtrate outlet to collect filtrate.

Well Area Operations

Code RPWA2021A Rev. 00 – Date 01/03/2005 Page 44 of 132

Agip KCO

5.

Open the valve to pressurise the cell. The needle on the pressure gauge will immediately move, probably indicating higher pressures during pressurisation. The needle will then stabilise at 100 psi.

6.

API recommends a 30 minute test time. Close the valve after the test to stop pressure at source. Bleeding will be automatic. Remove the cell.

7.

Record the fluid loss in millilitres (unless otherwise requested).

8.

Remove the cell, remove the mud and carefully remove the paper filter, making sure the filter cake is not damaged. Wash the cake carefully to eliminate excess mud. Measure the panel thickness in 32”.

12.4

High temperature high pressure (HTHP) filtration - MB style (API #II) HTHP filter press 12.4.3

Description The system in figure 6 comprises a heating jack with thermostat, cell assembly and primary and final pressure sensor. The mud cell has a 160 ml capacity and a filtering area of 3.5 square inches. The filtrate receiver has a 15 cm3 capacity and the glass tube can withstand a final pressure of up to 100 psi. If a higher pressure is necessary, stainless steel rather than glass tubes will have to be used in routine tests with a temperature of 300°F and differential pressure of 500 psi. High temperature filtrate should be recorded as a dual value in relation to the number of millilitres lost in 30 minutes. Filtering area = 3.5 square inches.

Well Area Operations

Code RPWA2021A Rev. 00 – Date 01/03/2005 Page 45 of 132

Agip KCO

Figure 6: HTHP Filter Press.

12.4.4

Procedure 1.

Turn on the heating unit and wait for the system to reach the pre-heating temperature.

Put the thermometer in its housing and adjust the

thermostat to obtain a temperature which is 10 °F higher than the value required. 2.

Close the cell inlet valve and turn the cell upside down.

3.

Collect mud from the flow line. Put it inside the container up to 0.2” below the O-ring housing and wait for expansion.

4.

Put a paper filter in the housing and the O-ring on top. Use a Whatman no. 50 filter or equivalent.

5.

Put the lid on top of the paper filter and secure.

6.

Secure lids manually and close the blowdown valve.

Well Area Operations

Code RPWA2021A Rev. 00 – Date 01/03/2005 Page 46 of 132

Agip KCO

7.

With the lid on the bottom of the cell, put the cell in the oven, making sure all valves are closed. Put the thermometer in its housing.

8.

Insert the CO2 cylinder in the primary pressure inlet, and tighten until it opens. Make sure the regulator and bleeder valve are closed.

9.

Raise the stop ring, put the primary pressure unit in the upper housing and let the stop ring close.

10.

Apply a pressure of 100 psi to the top valve, then open to pressurise the unit.

This pressure will minimise

boiling when the sample is being

heated. 11.

If the test temperature is equal to or above boiling point, always use a bleeder collector to prevent the filtrate from vaporising. Fit and activate the CO2 cylinder in the bleeder unit.

12.

Put the bleeder unit in its housing.

13.

Apply a pressure of 100 psi to the bottom unit, while the valve is still closed.

14.

After reaching the required temperature (300°F), (shown on the thermometer), increase the pressure in the top cell regulator from 100 to 600 psi, keeping a pressure of 100 psi with the bottom regulator. Open the valve (turn once) of the bottom cell and start the test.

15.

Maintain a pressure of 100 psi on the receiver during the test.

If

pressure increases, discharge a small amount of the filtrate and maintain a differential pressure of 500 psi. Keep the temperature at ±5°F. 16.

After 30 minutes of filtration, close the bottom cell valve and then the top cell valve.

17.

Loosen both T-screws in the regulator and release pressure from both regulators.

18.

Discharge the filtrate into the graduated cylinder and record the volume. Remove the receiver.

Well Area Operations

Code RPWA2021A Rev. 00 – Date 01/03/2005 Page 47 of 132

Agip KCO

19.

Disconnect the primary pressure unit; lift the stop ring and remove the unit. WARNING: the cell is pressurized.

20.

Keep the cell in an upright position and leave to cool at room temperature, then release the pressure. Do not let mud come out from the valve.

21.

Turn the cell upside down, loosen the screws on the lid (use an Allen key if necessary) and disassemble. Clean and dry the parts.

12.4.5

API # I HTHP filter press The HTHP fluid loss test is carried out with a temperature of 300°F (148°C) and differential pressure of 500 psi.

12.4.6

Description 1.

Oven on a stand.

2.

Cell for samples, to work at a pressure of 1000 psi. (filter surface area 3.5 square inches).

3.

Thermometer or electronic thermocouple (readings < 500°F [260°C]).

4.

Top regulator suitable for adjusting pressure up to 1000 psi, starting from any pressure source.

5.

Filtrate receiver (recommended capacity - 100 cm3) tested to work at a pressure of at least 500 psi.

6.

Graduated cylinder to recover the sample (METAL)

NOTE: Take great care when carrying out an HTHP test. equipment is kept in safe conditions.

Well Area Operations

Make sure all

Code RPWA2021A Rev. 00 – Date 01/03/2005 Page 48 of 132

Agip KCO

Tests at temperatures equal to or below 300°F (149°C) 1.

Connect the oven to the mains, make sure the voltage is appropriate. Put the thermometer in its housing.

2.

Heat the oven to 10°F higher than the test temperature and maintain at this temperature, adjusting the thermometer if necessary. Check and replace the O-rings if necessary.

3.

Agitate the sample for 10 minutes and pour into the cell, making sure the cell valve is closed. The cell should not be filled up more than 1.2 inches from the edge.

4.

Put a paper filter (Whatman no. 50 or equivalent) on the edge.

5.

Put the lid on, align and tighten the Allen screws. Make sure the valves are closed and put the cell in the oven. Screw the cell down on the stand. NOTE: the cell is fitted on the stand with the end containing the filter facing downwards.

6.

Install the thermometer in its housing.

7.

Put the pressure sensor in the top valve and secure.

8.

Install the low pressure receiver in the bottom valve and secure (figure 7).

9.

Apply 100 psi to both pressure units and open the top valve, turning it 90 degrees anticlockwise.

10.

After the test temperature has been reached, increase the pressure in the top unit to 600 psi, open the bottom valve 90° clockwise to start filtration. Recover the filtrate in a graduated container for 30 minutes.

11.

The temperature should be kept within ±5°F during the test. Discharge the filtrate until external pressure is above 100 psi.

Well Area Operations

Code RPWA2021A Rev. 00 – Date 01/03/2005 Page 49 of 132

Agip KCO

12.

After 30 minutes, close both valves and loosen the safety screws on the regulator.

Discharge the filtrate and release the pressure from the

bottom valve and remaining pressure from the top valve. Disassemble the regulator and valve. Remove the cell from the oven and leave to cool to room temperature, in an upright position.

Be careful of residual

pressure inside the cell. 13.

When cooling the cell, measure the amount of recovered filtrate and record a value which is twofold the result.

Record the filtrate in

millimetres, along with the test temperature and differential pressure. 14.

After cooling the cell, carefully release the pressure from the top part, i.e. the opposite part from the paper filter. Close the valve, then carefully open the opposite part, to release the pressure. Make sure all pressure has been released from the cell and sample before disassembly.

Table 8: Steam pressure and water volume expansion between 212° and 450°F with recommended external pressure

Test temperature

Steam pressure

°F

°C

kPa

Psi

212

100

101

14.7

250

121

207

300

149

350

Water expansion volume coefficient at saturation pressure

Recommended external pressure kPa

psi

1.04

689

100

30

1.06

689

100

462

67

1.09

689

100

177

931

135

1.12

1104

160

400

205

1703

247

1.16

1898

275

450

232

2917

422

1.21

3105

450

Note: Do not exceed the pressure, volume and temperature limits recommended in the user’s manual.

Well Area Operations

Code RPWA2021A Rev. 00 – Date 01/03/2005 Page 50 of 132

Agip KCO

Figure 7: HTHP filter press with CO2 pressurization (sectioned) Testing at temperatures from 300 - 400°F (149°C - 233°C) The same procedures are used, apart from the following cases when a 500 ml cell should be used, pressurising the manifold with nitrogen: 1.

Heat the sample and pressurize both units to 450 psi. Start the test; the upper pressure will increase to 950 psi, while the lower pressure will remain at 450 psi.

2.

A porous stainless steel disk (Dynalloy X5 or equivalent) should be used instead of a paper filter when temperatures range from 350°F to 400°F (see API RP 13B-1 and 13B-2).

3.

The sample should not be heated for more than 1 hour. 12.4.3

Filter

cake compressibility 12.4.7

Filter cake compressibility The same procedure for temperatures of 300°F (149°C) is used, but a pressure of 200 psi is applied to the cell and of 100 psi to the bottom receiver. The differential values for 100 and 500 psi are then compared.

Well Area Operations

Code RPWA2021A Rev. 00 – Date 01/03/2005 Page 51 of 132

Agip KCO

13.0 SAND CONTENT 13.1

Instruments Sand content in mud is estimated using a sand sieve. The sieve test is widely used at rigsites as it is simple.

13.2

Sand content testing kit 13.2.1

Description The sand content testing kit (figure 8) has a 21.2 inch diameter opening, a 200 mesh (74 micron) screen, a funnel below the screen and a graduated glass container to measure mud volume, and consequently the percentage of sand on the bottom of the container, which is graduated from 0 to 20%.

13.2.2

Procedure 1.

Fill the glass container with mud up to the first mark. Add water to bring the volume up to the second mark. Put your thumb over the container opening and strongly agitate.

2.

Pour the mixture onto the sieve. Pour more water into the container, agitate and pour onto the sieve. Continue until the water is clean. Wash the sand retained on the sieve.

3.

Put the funnel above the opening. Insert the funnel end in the opening of the glass container. Wash the sand from the sieve and let it run into the container, with a little water. Leave the sand to decant. Read the sand percentage from the graduation marks at the bottom of the container.

Well Area Operations

Code RPWA2021A Rev. 00 – Date 01/03/2005 Page 52 of 132

Agip KCO

Elutiometer

Figure 8 : Sand content testing kit

14.0 SOLID AND LIQUID CONTENT 14.1

Instruments Mud can be distilled by heating (see figure 9) in order to determine the amounts of liquids and solids present (10-, 20- or 50- cm3 distillers). Distillers with an internal probe are not recommended. Fill the container to the top with the mud sample, then put the lid on, letting a little liquid leak out to ensure the volume is exact. Heat up until the liquid components have vaporised. The vapours will be conveyed through the condenser to a graduated cylinder, which usually indicates the percentage, so the volume of liquid – the oil and water – is measured as a percentage. Suspended and dissolved solids are then determined deducting 100% or recording the empty space at the top of the cylinder.

Well Area Operations

Code RPWA2021A Rev. 00 – Date 01/03/2005 Page 53 of 132

Agip KCO

Figure 9 : Oil and mud distillation kit

Retort Assembly

Retort Condenser

14.2

Description of the distiller 14.2.1

Procedure 1.

Leave the mud to cool to room temperature.

2.

Disassemble the distiller and lubricate the thread of the cup with grease suitable for high temperatures. Fill the cup with mud nearly to the top. Put the lid on, rotate strongly and let any excess fluid flow out, to obtain a mud volume or 10, 20 or 50 cm3. Dry any traces of mud.

3.

Fill the top expansion chamber with steel wool. The chamber will retain the solids left after the mud has been boiled. Keep the assembly in an upright position, to make sure the mud does not flow down the outlet.

4.

Fit or tighten the outlet in the hole at the end of the condenser. Put the graduated cylinder, which is calibrated to record the percentage, in the condenser.

Well Area Operations

Code RPWA2021A Rev. 00 – Date 01/03/2005 Page 54 of 132

Agip KCO

5.

Connect to the mains and keep on until distillation is finished. This might take up to 25 minutes, depending on the characteristics of the oil, water and solids.

6.

Allow the distillate to cool to room temperature.

7.

Read the % of water, oil and solids. A few drops of aerosol solution will help to define the oil-water interface; read the percentage of solids.

8.

Cool the distiller after the test, then clean and dry.

9.

Carefully clean the condenser hole and outlet with a small pig. NOTE: make sure the outlet is not obstructed in any way.

14.2.2

Percentage from analysing the volume of solids, weight method (calculating the difference in weight using a conventional distiller).

14.2.3

Equipment 1.

Conventional balance

2.

Conventional 20 cm3 distiller (with oven).

3.

Analytical scales with a 0.01 g accuracy.

1.

Record the following values: A.

Mud weight.

B.

Distiller weight (including steel wool and cup)

C.

Distiller weight with whole mud.

D.

Distiller weight with mud solids.

Well Area Operations

Code RPWA2021A Rev. 00 – Date 01/03/2005 Page 55 of 132

Agip KCO

14.2.4

Procedure 1.

Prepare the distiller with the steel wool and cup. Record the weight (in grams). Value B.

2.

Disassemble the distiller and fill the cup with mud. The volume or lid do not have to be determined, as volumes are calculated with the weighin/out procedure. Weigh and disassemble the distiller. Value C.

3.

Use the distiller as normal (water and traces of oil).

4.

Cool and weigh the distiller again. Value D.

Calculations Calculate: 1.

The mud density (g/cm3); SGMUD = mud density (lb/gal) x 0.11994.

2.

Grams of mud in the distiller: g of mud = Value C – Value B.

3.

Grams or cm3 of distilled water: Value C – Value D. Calculate the volume (%) of solids. The solids fraction = [(C – B) – SGMUD x (C – D)] / (C – B) % solids = 100 x solids fraction volume

Example: With four measurements from a rigsite mud: A) 12.70 lb/gal B) 317.45 g C) 348.31 g D) 332.69 g i.e. : #1 = 12.70 lb/gal [0.1194

g / cm 3 ] = 1.523 g/cm3 lb / gal

Well Area Operations

Code RPWA2021A Rev. 00 – Date 01/03/2005 Page 56 of 132

Agip KCO

#2 = 348.31 – 317.45 = 30.86 g of mud #3 = 348.31 – 332.69 = 15.62 g of water The volume of the solids fraction = [30.86 – (1.52 x 15.62) ] / (30.86) = 7.12 / 3086 = 0.2307 % solids = 100 x 0.2307 = 23.07%

14.3

Methylene blue capacity test Rigsite procedure to determine cation exchange capacity. 14.3.1

14.3.2

Equipment 1.

3 cm3 syringe, 10 cm3 burette.

2.

0.5 cm3 micro pipette.

3.

250 cm3 graduated Erlenmeyer flask, with rubber cap.

4.

10 cm3 burette or pipette.

5.

50 cm3 graduated cylinder.

6.

Mixing blade.

7.

Hot plate

8.

Whatman no. 1 or equivalent paper filter, 11 cm in diameter.

Reagents 1.

Methylene blue solution: 1 cm3 = 0.01 milliequivalents 3.74 g of methylene blue, USP grade (C16H18N3SCl•3H2O) per litre.

2.

Hydrogen peroxide (3% solution).

3.

5 N sulphuric acid solution.

Well Area Operations

Code RPWA2021A Rev. 00 – Date 01/03/2005 Page 57 of 132

Agip KCO

14.3.3

Procedure 1.

Add 2 cm3 of mud (or a suitable mud volume for 2 - 10 cm3 of reagent) to 10 cm3 of water in the Erlenmeyer flask. Add 15 cm3 of hydrogen peroxide (3% solution), 0.5 cm3 of 5 N sulphuric acid solution and mix with a blender before heating.

2.

Boil on simmer for 10 minutes.

Dilute with water to 50 cm3. NOTE:

besides bentonite, drillings fluids contain other substances which absorb methylene blue. Using hydrogen peroxides allows the effect of organic materials such as CMC, polyacrylates, lignosulfonates and lignins to be neutralised. 3.

Use a burette or pipette to add 0.5 cm3 of methylene blue solution at a time.

4.

After each dose, put the rubber cap on and agitate for approximately half a minute.

5.

Use a glass rod to collect a drop while the solids are still suspended

6.

and place on the paper filter. Titration is finished when a greenish blue streak appears around the solids deposited on the filter.

7.

As soon as the greenish blue colour appears, shake the ampoule bottle for another 2 minutes and repeat the test putting another drop on the paper filter.

8.

If the greenish blue streak is strong, the end point has been reached. If the streak does not appear, continue until it develops.

9.

Record the cm3 of methylene blue solution used.

10.

Methylene blue capacity of mud; MBC imperial system (lb/bbl) = (of methylene blue/cm3 of mud) x 5 MBC metric system (kg/m3) = (cm3 of methylene blue/cm3 of mud) x 14 CEC (cation exchange capacity )= cm3 methylene blue / cm3 mud.

Well Area Operations

Code RPWA2021A Rev. 00 – Date 01/03/2005 Page 58 of 132

Agip KCO

14.4

Methylene blue capacity of clay 14.4.1

Methylene blue capacity (bentonite equivalent) MBC imperial system (lb/bbl) = CEC x 5 MBC metric system (kg/m3) = CEC x 14

14.4.2

Cation exchange capacity of clays Carefully weigh 1 g of dried, ground gypsum. Put in an Erlenmeyer flask and add 50 cm3 of deionised water. Boil on a low heat for 10 minutes with 0.5 cm3 5 N of sulphuric acid. Leave to cool and titrate, adding 0.5 cm3 at a time of 0.01 N blue methylene solution. CEC in milliequivalents/100 g of gypsum = (cm3 of methylene blue) / (g of titrated gypsum) FLOCCULATION EFFICIENCY TEST

14.4.3

Procedure 1.

Measure 100 cm3 of service water, collected from the drilling rig flow line, in a graduated cylinder.

2.

Add 1 cm3 of 1%* flocculating solution to the graduated cylinder.

3.

Slowly turn the cylinder upside down, 3 or 4 times, then rest on a flat surface.

4.

Record the time (seconds) it takes for flakes to form and leave to decant to the 40 cm3 mark in the graduated cylinder.

5.

Repeat for each flocculant.

If flakes do not form, a flocculent is not

necessary. Repeat the test at least every two days. 6.

The quickest acting flocculant should be used.

Well Area Operations

Code RPWA2021A Rev. 00 – Date 01/03/2005 Page 59 of 132

Agip KCO

15.0 CONCENTRATION OF HYDROGEN IONS (PH) 15.1

Scope Recording and adjusting the pH of mud (or filtrate) is fundamental in controlling drilling fluids. Interactions with clay, the solubility of various components and effectiveness of additives depend on the pH; this also applies when acid and sulphate-induced corrosion. Two methods are used to detect and measure the pH of filtrate in muds: litmus papers and the potentiometric method, using a pH meter with glass electrode.

15.2

Litmus (or pH) papers 15.2.1

Description Litmus papers (figure 10) are treated so that their colour changes depending on the pH of the fluid soaking the papers. The kit includes a complete colour palette for the entire pH range, for easier correlation.

15.2.2

Procedure 1.

Put a litmus paper in the mud or filtrate, and wait for the colour to stabilise, which should take less than a minute. Rinse the paper with distilled water but do not dry.

2.

Compare the colour of the paper with the kit colour palette to estimate the pH of the mud.

3.

Record the pH of the mud, rounding the value up or down by 0.5.

Figure 10 : Litmus paper.

Well Area Operations

Code RPWA2021A Rev. 00 – Date 01/03/2005 Page 60 of 132

Agip KCO

15.3

pH meter 15.3.1

Description The recommended method for accurately measuring the pH of drilling fluids is to use a pH meter with electronic electrode (figure 11). This is an precise and reliable way to determine pH values, without interference. Readouts are easy, quick and self-adjusting with temperature variations.

15.3.2

Equipment The portable pH meter consists of a probe and digital read out. The probe has: -

a glass electrode

-

a standard reference electrode

-

a temperature sensor (optional)

Figure 11 : ph Meter. 15.3.3

Procedure The following method is recommended for recording the pH: (1) Calibrate the instrument, (2) Determine the pH of a sample, (3) Clean and store the probe.

Well Area Operations

Code RPWA2021A Rev. 00 – Date 01/03/2005 Page 61 of 132

Agip KCO

1.

Remove the cap and rinse the probe with distilled water. Dry carefully.

2.

Let the mud reach the temperature of the probe and buffers; this should be around 75±5°F (24±3°C).

3.

Measure the buffer temperature with a pH of 7. Put the probe in the buffer solution with a pH of 7 and start the reader. Wait for the reading to stabilise.

4.

Adjust the knob to a temperature corresponding to a buffer solution pH of 7. Adjust the knob to calibrate the reader.

5.

Rinse the electrode with distilled water and dry delicately.

6.

Repeat steps 4 and 5 using a buffer with a pH of 4 and 10. Select the buffer closest to the pH of the sample (usually for muds with a pH of 10). If the pH reading is not correct, adjust the calibration knob accordingly. Rinse the electrode with distilled water and dry carefully. Put the probe back in the buffer solution with a pH of 7 and then retest the pH. If the same pH is recorded, turn the calibration screw to adjust the pH reading to the correct value. Repeat step 6 until values are correct.

7.

Complete the calibration with the two buffers, rinse the probe and dry carefully. Put the probe back in the sample and agitate carefully. Wait for the value to stabilise.

8.

Record the temperature of the sample in °F or °C. Record the pH of the sample to the nearest decimal point.

9.

Disconnect the equipment.

Wash the probe with distilled water.

Saturate the cotton in the cap with a buffer that has a pH of 4. Put the cap back on the probe. 10. 15.3.4

Turn off the equipment and put in its case.

Cleaning 1.

Electrodes must be cleaned regularly, and particularly when particles of oil or gypsum have stuck on the surface of the glass electrode or on porous electrode surfaces. Clean the electrodes with a soft brush and mild detergent.

Well Area Operations

Code RPWA2021A Rev. 00 – Date 01/03/2005 Page 62 of 132

Agip KCO

2.

Electrodes should be reconditioned if there is too much build up.

3.

To recondition the electrodes, put in 0.1 molar HCl solution for 10 minutes, rinse thoroughly with water, put in 0.1 molar NaOH solution for 10 minutes and rinse with water.

4.

Test the electrodes again, following the calibration procedure.

5.

Only qualified personnel should carry out the next step. If no reaction takes places, put the electrode in a solution with 10% NH4F HF for a maximum of 2 minutes. (WARNING: this acid is extremely corrosive and hazardous). Repeat the calibration steps.

6.

If this procedure does not work, replace the electrode system and recondition the electrodes.

15.3.5

Principle of equivalent solutions 1.

A solution is defined as equivalent when one litre contains an amount of salt (in grams) which is equal to the equivalent weight; for example NaCl= 58.44 grams (molecular weight/valence).

2.

The equivalent weight is given by: the molecular weight/valence, for example AgNO3 = 169.89/2 g = 84.94 g

3.

Equivalent solutions are “corresponding” i.e.: 1 litre of AgNO3 N/1 (containing 84.94 g), reacts in the exactly the same way as one litre of NaCl n/1 (containing 58.44 g), according to the reaction

4.

AgNO3+NaCL = NaNO3+AgCL (white precipitate)

Well Area Operations

Code RPWA2021A Rev. 00 – Date 01/03/2005 Page 63 of 132

Agip KCO

16.0 CHEMICAL ANALYSIS OF WATER IN MUDS 16.1

Alkalinity (Pf , Mf , Pm) and lime content 16.1.1

Equipment The following materials and products are required to determine the alkalinity of mud and its lime content: 1.

Standard acid solution, 0.02 N (N/50); nitric or sulphuric acid

(NOTE: A 0.1N (N/10) acid solution can be used as an alternative, but should be converted to the equivalent of ml 0.02 N multiplied by 5). 2.

Phenolphthalein solution indicator.

3.

Methyl orange/bromocresol green as an indicator.

API recommends

methyl orange (from yellow to pink). 4.

A 100 – 150 cm3 titration beaker, preferably white.

5.

Graduated pipettes: from 1 cm3 - 10 cm3.

6.

Stirring rod.

7.

A 1 cm3 syringe.

8.

A pH meter with glass electrode (optional, but recommended).

Well Area Operations

Code RPWA2021A Rev. 00 – Date 01/03/2005 Page 64 of 132

Agip KCO

16.1.2

Procedure to test filtrate alkalinity (Pf and Mf) 1.

Measure 1 cm3 of filtrate in the titration beaker, then add 5 cm3 of deionised water.

2.

Add 2 or more drops of phenolphthalein indicator. The solution will turn pink.

3.

Add N/50 acid, in drops, agitate until the pink has disappeared. If the colour of the sample is so strong that it cannot be defined, the endpoint should be recorded when the pH has dropped to below 8.3, recorded using a pH meter with glass electrode (the sample can be diluted with distilled water).

4.

Record the alkalinity of the phenolphthalein of the filtrate, Pf, in cm3 of 0.02 N acid required for every cm3 of filtrate to reach the endpoint.

5.

Add 3 to 4 drops of methyl orange/bromocresol green indicator to the sample used to measure the Pf;

6.

The reaction will produce a green colour.

7.

Titrate with 0.02 N acid until the solution turns yellow (at a pH of 4.3).

8.

The Mf is recorded as the amount in millilitres of acid used for the Pf in addition to the last titration.

Example: If you use 0.5 cm3 of acid to titrate the endpoint of phenolphthalein the Pf will be 0.5 Procedure BaCl2: 1.

Measure 1 cm3 of filtrate in a titration beaker.

2.

Add 2 drops of 10% barium chloride solution (NOTE: BaCl2 is poisonous; do not aspirate with the pipette).

3.

Repeat steps 2 to 4 to titrate the Pf.

Well Area Operations

Code RPWA2021A Rev. 00 – Date 01/03/2005 Page 65 of 132

Agip KCO

4.

As a basic rule, carbonate contamination is present if the alkalinity of the BaCl2 is one and a half times, or less, the previous titration of the Pf.

Example: If you use 1 cm3 of acid to titrate the Pf, the Pf is equal to 1.0. If you use 0.5 cm3 of acid to titrate the alkalinity endpoint with BaCl2, the value of BaCl2 will be 0.5. So carbonate contamination is present, as the value of BaCl2 is less than half the Pf. 16.1.3

Procedure to test mud alkalinity (Pm) 1.

Measure 1 cm3 of mud in the titration beaker, using a syringe. Dilute the sample with 25 cm3 of distilled water. Add 5 drops of phenolphthalein indicator, agitate and quickly titrate with 0.02 N or 0.1 N acid until the pink colour has completely disappeared.

2.

If the change cannot be determined because the colour is so strong, record the endpoint when the pH has dropped below 8.3, as recorded from the measurement taken with the glass electrode (ph meter).

3.

Record the alkalinity of the phenolphthalein in the mud, Pm, as the cm3 3

of 0.02 N (N/50) acid required for every cm of mud. If 0.1 N acid is used, 3

3

Pm = 5 x cm of 0.1 N acid per cm of mud. 16.1.4

Procedure to test calcium content (excess lime) Determine the Pf and Pm, as follows. Determine the fraction of the water volume in mud, Fw (decimal fractions of water), using the values recorded in the retort test (mud still). Record the lime content in the mud in lb/bbl, calculated from the following formula: Lime (lb/bbl) = 0.26 x (Pm -FwPf). Or lime (Kg/mc)=0.742(Pm-FwxPf) manual. 1996

Well Area Operations

AGIP

Code RPWA2021A Rev. 00 – Date 01/03/2005 Page 66 of 132

Agip KCO

16.1.5

Filtrate alkalinity: P1 and P2

16.1.6

Equipment 1.

Standardized solution of 0.02 N (N/50) sulphuric acid.

2.

0.1 N (N/10) sodium hydroxide solution.

3.

10% barium chloride solution.

4.

Phenolphthalein indicator.

5.

Deionized water.

6.

Litmus papers or glass electrode indicator.

7.

100 to 150 cm3 titration beaker, preferably white.

8.

Pipette: one 1- cm3, one 2-ml and one 10- cm3 pipette.

9.

Graduated cylinder, one 25 cm3 and one 5 or 10 cm3 cylinder.

10.

Stirring rod. Procedure: P1 - P2

Well Area Operations

Code RPWA2021A Rev. 00 – Date 01/03/2005 Page 67 of 132

Agip KCO

16.1.7 Procedure Measure 1 cm3 of filtrate in the titration beaker and add 24 cm3 of

1.

deionized water. Add 2 cm3 of 0.1 N sodium hydroxide and agitate. Measure the pH with

2.

a litmus paper or glass electrode pH meter. If the pH is the same as or above 11.4 continue with the next step. If the pH is less than 11.4, add a further 2 ml of 0.1 N sodium hydroxide. Measure 2 cm3 of barium chloride using the graduated cylinder and add

3.

to the titration beaker. Add 2 to 4 drops of phenolphthalein and agitate. NOTE: Do not aspirate from the pipette; barium chloride is poisonous. 4.

Titrate immediately with sulphuric acid, as soon as the purple colour disappears (or when you record a pH of 8.3 using the pH meter). If the colour reappears after a short time, continue with titration. Record the alkalinity, P1, as the amount in cm3 of 0.02 sulphuric acid

5.

required to titrate to the phenolphthalein endpoint. Procedure P2 1.

Put the filtrate on one side, or repeat the procedure for P1 using exactly the same amounts of water and reagents. Titrate following the same procedure used for P1.

2.

Record the alkalinity, P2, in ml of 0.02 N sulphuric acid required to titrate to the phenolphthalein endpoint.

Calculations Within limits, ion alkalinities can be calculated as follows: Where P1 > P2 OH– (mg/l) = 340 x (P1 – P2) 2–

CO3 (mg/l) = 1,200 x [Pf – (P1 – P2)]

Well Area Operations

Code RPWA2021A Rev. 00 – Date 01/03/2005 Page 68 of 132

Agip KCO

Where P1 < P2 –

HCO3 (mg/l) = 1,220 x (P2 – P1) 2–

CO3 (mg/l) = 1,200 x Pf 16.2

GARRETT GAS TRAIN (GGT) test for carbonates 16.2.1

Scope The Garrett Gas Train test is used to analyse soluble carbonates in mud filtrate. A CO2 Dräger tube reacts to the gas and turns purple. The length of the stain indicates the concentration of CO2 as well as the rate and volume of gas passing through the tube. However the gas must be captured in a 1 litre bag so the CO2 can mix uniformly with the gas.

The CO2 Dräger tube may give incorrect

readings, if not used properly. The filtrate must not contain solids and the first jet of filtrate must not be used as it contains CaCO3; this could lead to excessively high values. Apply 10 strokes of the Dräger hand pump to covey the contents of the bag through the Dräger tube. This will make 1 litre of gas flow through the tube. 16.2.2

Equipment 1.

Deionized water.

2.

Octyl alcohol defoamer.

3.

Approximately 5 N sulphuric acid.

4.

Garrett Gas Train (figure 12).

5.

Dräger tube for CO2 analysis, “CO2 100/a” marked from 100 to 3,000 ppm. Factor = 2.5 (make sure the factor does not change).

6.

1 litre #762425 Dräger bag.

7.

Dräger hand pump for the multigas detector vacuum.

8.

Two-way 8 mm graduated tube.

Well Area Operations

Code RPWA2021A Rev. 00 – Date 01/03/2005 Page 69 of 132

Agip KCO

9.

Hypodermic syringes: one 10 cm3 syringe, with 21 needles suitable for acid, one 5 cm3 syringe and one 2.5 cm3 syringe.

10.

Cartridges for N2O recharging. Nitrogen or helium may also be used.

Figure 12 : Garrett Gas Train 16.2.3

Procedure 1.

Make sure equipment is clean and resting on a flat surface.

2.

Install the N2O cartridge and activate, with the regulator set to zero. Do not use CO2 cartridges or compressed air.

3.

Add 20 cm3 of deionized water to Chamber 1.

4.

Add 5 drops of defoamer to Chamber 1.

5.

Put the cover on the gas train and tighten uniformly to seal the O-rings.

6.

Turn the regulator knob anti-clockwise to prevent pressurisation. Connect the tubing to the dispersion tube in Chamber 1. Install and activate the N2O cartridge.

7.

Adjust the bleed line in chamber 1, so it is ¼” from the end.

Well Area Operations

Code RPWA2021A Rev. 00 – Date 01/03/2005 Page 70 of 132

Agip KCO

8.

Refer to table 3, to the carbonate scale and Dräger tube, for the volume required.

9.

Turn the regulator knob clockwise for 1 minute, to release air from the system and bleed the transport gas.

Make sure there are no leaks.

Close the gas valve. 10.

Connect to the gas bag and close the hand pump valve. Use a reject Dräger tube for the connection and empty the bag.

11.

Lift the hand pump entirely and compress again. The pump will stay raised for several minutes when completely empty and if there are no leaks. If there are leaks, intercept them, inspecting all connections, as explained below. If there is a leak in the bag, replace.

Note: Insert a Dräger tube, closed at one end, in the pump and lower the membrane to check the pump. If there are no leaks, the membrane will stay lowered. 12.

Make sure the bag is entirely compressed, then fit the rubber tubing from the valve and from the bag to the outlet of chamber 3. Close the valve.

13.

Use a hypodermic syringe with needle to inject the filtrate without solids into chamber 1 via the rubber membrane. Measure the volume.

14.

3

Use a hypodermic syringe with needle to slowly inject 10 cm of sulphuric acid into chamber 1 via the rubber membrane. Gently shake the gas receptacle to mix the acid with the sample in chamber 1.

15.

Remove the tube from the outlet of chamber 3.

Break off the ends

(make sure the arrow indicates the direction of the flow), then fit on the side upstream the CO2 Dräger tube. Connect the Dräger hand pump to the other end of the Dräger tube. 16.

Open the bag valve. Slowly open the N2O cartridge to fill the bag, then close and close the valve. Immediately go on to step 17.

Well Area Operations

Code RPWA2021A Rev. 00 – Date 01/03/2005 Page 71 of 132

Agip KCO

Figure 13 : Check losses into gas pocket.

Figure 14: GGT with gas bag for carbonate testing.

17.

Remove the tube from the outlet of chamber 3.

Break off the ends

(make sure the arrow is in the direction of the flow), then fit on the side upstream the CO2 Dräger tube. Connect the small pump to the opposite end of the Dräger tube 18.

Open the bag valve. Lower the pump lever, then let the gas flow out of the bag via the Dräger tube. 10 pump strokes should be sufficient to empty the gas bag.

Well Area Operations

Code RPWA2021A Rev. 00 – Date 01/03/2005 Page 72 of 132

Agip KCO

19.

A pinkish deposit inside the tube indicates the presence of CO2. Record the length, in line with the graduated scale, including the slight blue shade.

16.2.4

Selecting the Dräger tube Table 9: Volume of samples and type of tube to use to define carbonate scales 1 Carbonate scale (mg/l)

2 Volume Sample (cm3)

3 Selecting the Dräger tube

4 Tube factor

25 - 750

10

CO2 100/a

2.5*

50 - 1,500

5

CO2 100/a

2.5*

100 - 3,000

2.5

CO2 100/a

2.5*

250 - 7,500

1

CO2 100/a

2.5*

*NOTE: The tube factor “2.5” refers to new CO2 100/a tubes (cat. no. 8101811) with a 100 - 3,000 scale. Use a factor of 25,000 with a scale from 0.01 to 0.3% for old tubes. Calculations Measure the sample volume, the length of the purple deposit in the Dräger tube and tube factor of 2.5 (Table 9) to calculate the soluble carbonates in the filtrate of the sample, with the following formula: 2–

3

CO (mg/l) = (length in the tube x 2.5) / cm of filtrate NOTE: the gas train must be cleaned after use to prevent acid-induced corrosion. Remove the tubing and top. Wash the chambers with lukewarm water, a mild detergent and brush. Use a small pig to clean the ducts between the chambers. Wash, rinse and jet air to eliminate residues. Do not use nitric oxide for any other test, not even as a gas as it may cause explosions if used incorrectly.

Well Area Operations

Code RPWA2021A Rev. 00 – Date 01/03/2005 Page 73 of 132

Agip KCO

16.3

Chlorides (Cl–) 16.3.1

Scope Chloride testing is very important in zones where salt may contaminate the mud. The chloride ion content is an excellent indicator when drilling, for example, salt formations or salt water zones, and is also suitable for checking the quality of service water. -

Chloride ions (Cl ) are analyzed by titrating the sample of filtrate, using silver +

(Ag ), to reach a red colour from the endpoint of silver chromate with potassium chromate as an indicator. 16.3.2

Equipment The following items are required to determine the concentration of chloride ions in the filtrate. 1.

Silver nitrate solution, 0.0282N or 0.282N (strong) AgNO3, stored in an opaque bottle. A strength of 0.1N and 1N is used by ENI, Italy.

2.

Potassium chromate indicator solution.

3.

0.02 sulphuric or nitric acid solution.

4.

Distilled water.

5.

Two graduated pipettes: one 1 cm and one 10 cm pipette.

6.

A 100 - 150 cm titration beaker, preferably white.

7.

Small glass spatula.

3

3

16.3.3

Light coloured filtrates

16.3.4

Procedure 1.

Measure 1 cm3 of filtrate in the titration beaker.

2.

Add 2-3 drops of phenolphthalein indicator.

Well Area Operations

3

Code RPWA2021A Rev. 00 – Date 01/03/2005 Page 74 of 132

Agip KCO

3.

If the indicator turns pink, agitate with the glass spatula and add 0.02N (N/50) sulphuric acid in drops until the colour disappears.

4.

Add 50 cm3 of deionized water and 10 drops of potassium chromate.

5.

Add silver nitrate solution (0.0282N for chlorides 10,000 mg/L.) and agitate until the yellow turns to orange red and stays this colour for 30 seconds.

Record the cm3 of silver nitrate required to reach the endpoint.

If the

concentration of chloride ions in the filtrate is < 10,000 mg/l, use 0.0282N silver –

nitrate solution equivalent to 0.001 g Cl ions per cm3. Record the concentration of chloride ions in the filtrate in mg/l, calculated as follows: –

Cl (mg/l) = cm3 of 0.0282 N silver nitrate x 1,000 / cm3 of filtrate for any normal silver nitrate or 0.1N (frequently used by ENI): –

Cl (mg/l) = (N x 35,000 x cm3 used) / (cm3 of filtrate of sample) CL(mg/l) = (0.1Nx3500x cm3 used/( cm3 of filtrate of sample). As salinity is expressed as NaCL (mg/l), the factors will be 58000 and 5800 rather than 35000 and 3500.

Well Area Operations

Code RPWA2021A Rev. 00 – Date 01/03/2005 Page 75 of 132

Agip KCO

Table 10 Chloride titration

Chlorides (Cl) – Light coloured filtrates Column 1 Column 2 3 1 cm of filtrate 1 cm3 of filtrate 25-50 cm3 No No No 2-3 drops of 8-10 drops of potassium phenolphthalein chromate 0.028N AgNO3 or 0.282N 0.02 (N/50) H2SO4 AgNO3 * (silver nitrate) (sulphuric acid)

Chemical analysis Sample Deionized water Buffer Colour indicator Titrated with: (Titrator)

Filtrate, from pink to original

Colour change

From yellow to orange red

Record

No

(cm3 of 0.0282 N AgNO3 x 1,000) / cm3 of filtrate or (cm3 of 0.282 N AgNO3 x 10,000 ) / cm3 of filtrate

Note:

Go to col. 2

*Chlorides: 10,000 mg/l if < use: 0.0282 N AgNO3 if > use: 0.282 N AgNO3

16.3.5

Dark coloured filtrates

16.3.6

Procedure 1.

Measure 1 cm3 of filtrate in a titration beaker.

2.

Add 2-3 drops pf phenolphthalein. If the solution is too dark, add 2 cm3 of 0.02N (N/50) sulphuric acid and agitate.

3.

Add 1 g of calcium carbonate to this solution and agitate, adding 50 cm3 of deionized water and 10 drops of potassium chromate solution.

4.

Continue to agitate.

Add silver nitrate using a pipette (0.0282N for

chlorides 10,000 mg/l) until the yellow turns to orange red and stays this colour for approximately 30 seconds. 5.

Record the cm3 of silver nitrate solution to reach the endpoint. Calculations

Well Area Operations

Code RPWA2021A Rev. 00 – Date 01/03/2005 Page 76 of 132

Agip KCO

Record the concentration of chloride ions in the filtrate in mg/l.

If the

concentration is 10,000 mg/l, use 0.0282N silver nitrate –

solution or equivalent to 0.001 g Cl ions per cm3. –

Cl (mg/l) = (cm3 of 0.282 N silver nitrate x 10,000 ) / cm3 of filtrate

Well Area Operations

Code RPWA2021A Rev. 00 – Date 01/03/2005 Page 77 of 132

Agip KCO

Table 11 Chloride titration chart

Chemical analysis Sample Deionized water Buffer Colour indicator

Chlorides (Cl) – Dark coloured filtrates Column 1 Column 2 1 cm3 of filtrate 1 cm3 of filtrate 25-50 cm3 No 1 g CaCO3 (calcium carbonate) Non 2-3 drops of phenolphthalein

Titrated with: (Titrator)

0.02 (N/50) H2SO4 (sulphuric acid)

Colour change

From yellow to the original colour

Record

Note:

16.4

5-10 drops of potassium chromate 0.028N AgNO3 o 0.282N AgNO3 * (silver nitrate) From yellow to orange red (cm3 of 0.0282 N AgNO3 x 1,000) / cm3 of filtrate or (cm3 of 0.282 N AgNO3 x 10,000 ) / cm3 of filtrate

No

*Chlorides : 10,000 mg/l if < use: 0.0282 N AgNO3 if > use: 0.282 N AgNO3

Go to Col. 2

Calcium – qualitative testing 16.4.1

Scope Hard water is water with a high mineral content, and particularly a high calcium and magnesium content. The simplest example which shows that household water is soft is when soap does not foam very much.

Hard water is normally

present at rigsites. When drilling, clays are not very efficient if mixed with hard water. The harder the water is, the more bentonite is required to obtain an acceptable drilling mud. In more extreme cases, it is cheaper to treat water chemically before making up mud, but this practice is not usually recommended for purely economic reasons.

If several types of water are available at the

rigsite, a test should be done to select the softest water. Rigsite engineers are well aware of mud reactions when drilling through anhydrite (calcium sulphate) or gypsum formations. Calcium can also

Well Area Operations

Code RPWA2021A Rev. 00 – Date 01/03/2005 Page 78 of 132

Agip KCO

contaminate cement, when running in cement plugs or drilling shale formations with lime. The main reason why calcium contaminates mud is a major increase in water loss and the mud developing a high gel strength (increase in filtrate). 16.4.2

Equipment The following items are required to effectively determine the presence of calcium and/or magnesium.

16.4.3

1.

Test tube

2.

Dropper with saturated ammonium oxalate solution.

Procedure Put 1 - 3 cm3 of filtrate in the test tube. Add a few drops of ammonium oxalate. Record whether weak, medium or strong.

16.5

Total hardness Water or mud filtrate hardness is mainly due to the presence of calcium (Ca++) and magnesium (Mg++) ions. The harder the water is, the more difficult it will be for the chemical products used to react and the efficiency of bentonite shales is affected in particular. Moreover water hardness makes most polymer products less effective. Hardness is analysed by titrating bivalent cations in the filtrate, using a standard versenate reagent with an indicator that will change from a red wine to blue endpoint. In dark coloured filtrates, there will be a greyish blue endpoint.

Well Area Operations

Code RPWA2021A Rev. 00 – Date 01/03/2005 Page 79 of 132

Agip KCO

16.5.1

Calcium plus magnesium – Quantitative testing

16.5.2

Equipment 1.

Standard Versenate solution (EDTA) 0.01 M (1 ml = 400 mg Ca++ or 1,000 mg CaCO3).

2.

Strong buffer solution (ammonium hydroxide/ammonium chloride).

3.

Versenate solution as a hardness indicator (eriochrome black t)

4.

100 to 150 cm3 titration plate, preferably white.

5.

Three graduated pipettes: one, 1 cm3, one 5 cm3 and one 10 cm3pipette.

6.

50 cm3 graduated cylinder.

7.

Distilled water.

8.

Rod.

9.

8N NaOH or KOH solution.

10.

Calcon or Calver II indicator.

11.

Porcelain spatula.

12.

Masking agent: 1:1:2 triethanolamine, tetraethylenepentamine: water (API).

The total hardness of water or the filtrate can be determined following the procedure described in 16.5.4, calculating the total hardness of calcium, in pm, which is then recorded in the mud report. Magnesium sometimes has to be tested as well, determined from the difference between two titrations. Caustic soda, which is otherwise known as the buffer solution, makes magnesium precipitate as a hydroxide, while the calcium is titrated with a specific calcium indicator.

Well Area Operations

Code RPWA2021A Rev. 00 – Date 01/03/2005 Page 80 of 132

Agip KCO

16.5.3

Procedure (total hardness) 1.

Add 50 cm3 of deionized water to the titration beaker; add 2 cm3 (20 drops) of versenate buffer solution (NH4OH base).

2.

Add 10 drops of versenate hardness indicator solution (eriochrome black t). If the deionized water contains calcium and/or magnesium, it will turn wine red, otherwise it will stay blue.

3.

While agitating the solution, titrate with standard versenate (EDTA) until the colour changes from wine red to blue.

DO NOT EXCEED THE

ENDPOINT. Note: Steps 1-3 will eliminate the hardness of deionized water, if present. 4.

Add 1 cm3 of filtrate to the deionized water. If the water contains calcium and /or magnesium, it will turn wine red. While agitating the solution, titrate with standard versenate (add in drops) until the colour changes from wine red to blue.

5.

Note the cm3 of versenate used (if the magnesium is measured following the procedure in 16.5.4, record the value as “A” cm3) and calculate the hardness in mg/l.

A = total hardness; B = hardness of calcium ; A-B = hardness of magnesium. Calculations ++

Total hardness as Ca (mg/l) = (cm3 of versenate x 400) / (cm3 of sample) CaCO3 (mg/l) = (cm3 of versenate x 1,000) / (cm3 of sample) Occasionally, dark filtrates may not be easily visible at their endpoint, making it hard to determine total hardness. The following method is recommended to better define the endpoint. Calculations are the same. 1.

Add 20 cm3 of distilled water to the titration beaker.

2.

Add 1 cm3 of filtrate to the titration plate (up to 0.5 cm3 measured

,

accurately; if necessary a sample >1 cm3 to reach the endpoint).

Well Area Operations

Code RPWA2021A Rev. 00 – Date 01/03/2005 Page 81 of 132

Agip KCO

3.

Add 1 cm3 of masking agent.

4.

Add 1 cm3 of strong buffer solution.

5.

Add 6 drops of versenate indicator and agitate.

6.

Use a pipette and titrate with a standard versenate solution until the colour changes to blue/green.

Record the ml needed for the

determination, as in the previous procedure.

Table 12 Total hardness – Titration chart

Total Hardness

Chemical analysis

Column 1

Column 2

Sample

No

1 cm3 of filtrate

50 cm3

No

Deionized water Buffer Colour indicator Titrate with: Colour change

2 cm3 buffer, versenate hardness

No

10 drops versenate hardness indicator

No

Standard versenate From wine red to blue. Do not exceed the endpoint

Record

No

Note:

Go to column 2

Well Area Operations

Standard versenate From wine red to blue (cm3 of versenate x 400)/ (cm3 of sample)

Code RPWA2021A Rev. 00 – Date 01/03/2005 Page 82 of 132

Agip KCO

16.5.4

Calcium and magnesium separately Calcium is obtained titrating the filtrate, using versenate as the reagent, then a strong pH buffer so that the magnesium ions precipitate and only the calcium ions are analysed. 1.

3

3

Add 50 cm of deionized water to the titration beaker, then add 1 cm of strong buffer solution for the calcium.

2.

Add a small amount of indicator. If calcium is present, a wine red colour will develop.

3.

While agitating the solution, titrate with versenate (add in drops) until the colour changes from wine red to blue.

DO NOT EXCEED THE

ENDPOINT. 4.

3

Add 1 cm of deionized water filtrate. If the water contains calcium, a wine red colour will develop. While agitating the solution, titrate with versenate (add in drops), until the colour changes from wine red to blue. DO NOT EXCEED THE ENDPOINT.

5.

3

3

Record the cm of versenate (note as “B” in cm ) and calculate the calcium in mg/l, as explained in 8.5.2.1:

A= total hardness; B= hardness of calcium; A - B = hardness of magnesium Calculations 3

3

3

Calcium (mg/l) = (cm of versenate x 400) / (cm of sample) = (B x 400) / (cm of sample) The concentration of magnesium ions is determined from the difference of the total hardness minus the calcium, multiplied by a factor of 0.6. Magnesium in mg/L = [(Total hardness mg/L) – (Calcium mg/L)] (0.6) 3

or magnesium (mg/l) = (A – B) x 243) / (cm of sample)

Well Area Operations

Code RPWA2021A Rev. 00 – Date 01/03/2005 Page 83 of 132

Agip KCO

Table 13 Hardness of calcium/magnesium – Titration chart Calcium Chemical analysis Sample Deionized water

Colour indicator

Titrated with: Colour change

Record

Column 2

No

1 cm3 of filtrate

No

50 cm3

No

No

A small amount of indicator

Versenate From wine red to blue. Do not exceed the endpoint. No

Note:

16.6

Column 1

1 cm3 of versenate buffer for the hardness of calcium

Buffer

Magnesium (Mg++)

No No

No No Versenate

No No

From wine red to blue (cm3 of EDTA x 400)/ (cm3 of sample)

Go to column 2

Total Hardness – Calcium x 243 The calculation is based on the results of total hardness and on calcium tests.

Hardness in dark filtrates 16.6.1

Total hardness in dark filtrates – Quantitative testing

16.6.2

Scope Problems may occur when titrating dark filtrates, due to the unpredictability of the filtrate colour change when the endpoint is reached. The following method

Well Area Operations

Code RPWA2021A Rev. 00 – Date 01/03/2005 Page 84 of 132

Agip KCO

has therefore been developed and should only be used if the previous method is not successful. 16.6.3

Equipment 1.

Glacial acetic acid: (care should be taken).

2.

Indicator (specific for Ca++).

3.

Sodium hypochlorite 5.25%

4.

Calmagite indicator

5.

Sodium hydroxide; 8N NaOH.

6.

Masking agent.

7.

0.01 molar versenate solution.

8.

Strong buffer solution.

9.

100 cm3 beaker.

10.

Two, 10 cm3 graduated cylinders. 10 cm3 graduated pipette.

11.

Hot plate.

12.

1 cm3 volumetric pipette.

13.

Porcelain spatula.

Method I (includes all metals titrated with versenate) WARNING: Make sure the area is well airy. 1.

Use a 1 cm3 volumetric pipette to transfer 1 cm3 of filtrate into a 100 cm3 beaker.

2.

Add 10 cm3 of chlorine (make sure it is fresh, and has not deteriorated). Whisk to mix.

Well Area Operations

Code RPWA2021A Rev. 00 – Date 01/03/2005 Page 85 of 132

Agip KCO

3.

Add 1 cm3 of acetic acid, whisk to mix.

4.

Bring to the boil; boil at a high temperature for 5 minutes. Add deionised water to top up the volume.

5.

Remove the beaker from the hot plate and leave to cool at room temperature. Carefully wash the outside of the beaker with deionised water. 3

6.

Add 1 cm of strong buffer solution; whisk to mix.

7.

Add 6 drops of calmagite and mix. If the filtrate is hard, it will turn red.

8.

Use a pipette to titrate with a versenate solution, while agitating, until the sample has turned blue, without any traces of red. In the case of dark filtrates, the colour will vary from purple to dark grey. Note the quantity in ml of versenate solution used.

Calculations Total hardness Ca++ (mg/l) = cm3 versenate x 400 ++

Method II (includes calcium and magnesium, recorded as Ca ) 1.

Use a 1 cm3 volumetric pipette to transfer 1 cm3 of filtrate into a 100 cm3 beaker.

2.

Add 10 cm3 of chlorine. Whisk to mix.

3.

Add 1 cm3 of acetic acid and mix.

4.

Bring to the boil; boil at a high temperature for 5 minutes. Add deionised water to top up the volume.

5.

Remove the beaker from the hot plate and leave to cool at room temperature. Carefully wash the outside of the beaker with deionised water.

Well Area Operations

Code RPWA2021A Rev. 00 – Date 01/03/2005 Page 86 of 132

Agip KCO

6.

Add a strong buffer solution = 1 cm3 and whisk to mix.

7.

Add 1 cm3 of masking agent and mix.

8.

Add 6 cm3 of calmagite and mix.

If calcium and/or magnesium are

present, the filtrate will turn wine red. 9.

Use a pipette to titrate with a versenate solution, while agitating, until the sample has turned blue, without any traces of red. Note the quantity in ml of versenate solution used. This is value A.

Calculations ++

Total hardness Ca (mg/l) = A x 400 16.6.4

Calcium and magnesium, separately 1.

Use a 1 cm3 volumetric pipette to transfer 1 cm3 of filtrate into a 100 cm3 beaker.

2.

Add 10 cm3 of chlorine. Whisk to mix.

3.

Add 1 cm3 of acetic acid and mix.

4.

Bring to the boil; boil at a high temperature for 5 minutes. Add deionised water to top up the volume.

5.

Remove the beaker from the hot plate and leave to cool at room temperature. Carefully wash the outside of the beaker with deionised water.

6.

Add 1 cm3 of sodium hydroxide (buffer) and mix (Mg2+ precipitate)

7.

Add 1 cm3 of masking agent and mix.

8.

Add 1.4 spoonfuls (0.2 g) of indicator and mix. If calcium is present, a wine red colour will develop.

9.

Titrate with versenate until the indicator develops a wine red to blue colour, without any traces of red. Record the ml of versenate required. This will be value B.

Well Area Operations

Code RPWA2021A Rev. 00 – Date 01/03/2005 Page 87 of 132

Agip KCO

Calculations Calcium (mg/l) = B x 400 Magnesium (mg/l) = (A - B) x 243 16.7

Sulphate 16.7.1

Qualitative testing

16.7.2

Scope Sulphate ions are present in a large number of natural waters because of the dissolving action of water on minerals. Anhydrites (calcium sulphate) are slightly soluble salts which can be encountered when drilling for a few hours.

The

sulphate ion content in filtrate often needs to be checked. A concentration of sulphate ions above 2,000 mg/l may cause viscosity and fluid loss problems. 16.7.3

Equipment The following items are required to determine the calcium sulphate content: 1.

Test tube

2.

Decanter with 10% barium chloride solution.

(WARNING: THIS

SOLUTION IS POISONOUS. Do not inhale). 3. 16.7.4

Decanter with strong nitric acid.

Procedure Pour 3 ml of filtrate in a test tube. Add a few drops of barium chloride solution. The formation of white precipitate indicates that sulphates and/or carbonates are present.

Add a few drops of concentrated nitric acid.

If the precipitate

dissolves, carbonate is present. If it does not dissolve, sulphate is present. Note the amount of precipitate as slight, average or strong, after treatment with acid.

Well Area Operations

Code RPWA2021A Rev. 00 – Date 01/03/2005 Page 88 of 132

Agip KCO

16.7.5

Availability of calcium sulphate

16.7.6

Scope When gypsum muds are used, the excess amount of gypsum in the mud must be assessed.

16.7.7

Equipment 1.

Masking agent: 1:1:2 mixture of triethanolamine, tetraethylenepentamine and water

16.7.8

2.

Deionized water.

3.

Calmagite indicator.

4.

0.01 molar versenate solution.

5.

Strong buffer solution.

6.

400 cm3 beaker.

7.

250 cm3 calibrated beaker.

8.

Electric hotplate.

9.

1 cm3, 2 cm3 and 10 cm pipettes. 5 cm3 syringe.

10.

100 - 150 cm3 titration beaker, preferably white.

11.

Mud still

Procedure 1.

Add 5 cm3 of mud to the calibrated beaker, then add 245 cm3 of water to top up to 250 cm3.

2.

Heat to 160°F and agitate for 15 to 20 minutes. Heat while agitating if possible. (If this is not possible, heat then agitate for 30 minutes).

3.

Cool while agitating, top up with water to 250 cm3

4.

Filter with a filter press; throw away the first cloudy part of the filtrate and only keep the clear part.

Well Area Operations

Code RPWA2021A Rev. 00 – Date 01/03/2005 Page 89 of 132

Agip KCO

5.

Add 10 cm3 of filtrate, 1 cm3 of strong buffer and 6 drops of Calmagite indicator.

6.

Titrate with versenate solution, agitate constantly until the sample turns blue (or green if the filtrate is dark without any traces of red). Record the amount of versenate used = Vt.

7.

Clean the titration beaker and add approximately 20 cm3 of water.

8.

Add 1 cm3 of filtrate from the mud.

9.

Add 1 cm3 of strong buffer solution.

10.

Add 1 cm3 of masking agent.

11.

Add 6 drops of Calmagite and mix with a spatula.

12.

Titrate with versenate solution, agitate constantly until the sample turns blue (or green for dark filtrates) without any traces of red.

13.

Record the ml of versenate solution used = Vf

Calculations CaSO4 available (lb/bbl) = 2.38 x Vt – [0.2 x (Fw x Vf)] Where: Vt = Amount in cm3 of standard versenate solution used to titrate 10 cm3 of clear filtrate in step 6. Vf = Amount in cm3 of standard versenate solution used to titrate 1 cm3 of filtrate in step 13. Fw = fresh water should be fractioned with mud in static conditions. /100 = Fw.

Well Area Operations

% water

Code RPWA2021A Rev. 00 – Date 01/03/2005 Page 90 of 132

Agip KCO

16.8

Potassium (K+) The purpose of potassium ions in mud is to stabilize water-sensitive clays, while maintaining an appropriate potassium concentration to optimize the quality of potassium base muds. Either of the following procedures can be used to determine potassium ion concentration. Procedure I can be used for any potassium ion concentration, while procedure II, which is quick, can only be used for high concentrations.

16.8.1

Procedure I — Potassium 100,000

Add 1 ml of filtrate to 9 cm of distilled 3 water. Mix and measure 1 cm of solution.

50,000 - 100,000

Add 1 ml of filtrate to 9 cm of distilled 3 water. Mix and measure 2 cm of solution.

20,000 - 50,000

Add 1 ml of filtrate to 9 cm of distilled 3 water. Mix and measure 5 cm of solution.

10,000 - 20,000 4,000 - 10,000 2,000 - 4,000

Collect 1 cm of undissolved filtrate. 3 Collect 2 cm of undissolved filtrate. 3 Collect 5 cm of undissolved filtrate.

250 - 2,000

Collect 10 cm of undissolved filtrate.

Filtrate (cm )

3

0.10

3

0.20

3

0.50

3

3

1.00 2.00 5.00 10.00

NOTE: The concentration of QAS should be checked against the concentration 3

of STPB at monthly intervals. To determine the QAS equivalent, dilute 2 cm of 3

STPB solution in a titration beaker with 50 cm of distilled water. Add 1 ml of sodium hydroxide solution and 10 – 20 drops of bromophenol blue indicator. Titrate with the QAS solution until the colour changes from purple blue to light blue. 16.8.4

Procedure II — Potassium ≥ 5,000 mg/l (sodium perchlorate method)

16.8.5

Equipment 1.

Standard sodium perchlorate solution: 150.0 g of NaClO4 per 100 ml of distilled water. NOTE: When in a dry state, sodium perchlorate can explode if heated to high temperatures or if it comes in contact with organic reducing reagents. Perchlorate is not hazardous if hydrated with water and will break down harmlessly if disposed in water.

2.

Standard potassium chloride solution, 14.0 g KCl mixed with 100 ml of distilled water.

Well Area Operations

Code RPWA2021A Rev. 00 – Date 01/03/2005 Page 93 of 132

Agip KCO

3.

10 ml centrifuge tubes, usually Kolmer; Corning 8360 tubes.

4.

Electric or manually horizontal rotation centrifuge, with a 1,800 RPM capacity (figure 15).

5.

Standard calibration curve for potassium chloride.

Figure 15 16.8.6

Preparation 1. a.

Calibrate the centrifuge If you are using an electric centrifuge, adjust the rheostat to calibrate the centrifuge to 1,800 RPM.

b.

If you are using a manual centrifuge, maintain a constant RPM of 1,800 as follows:

- Determine the number of revolutions transmitted to the rotor with each turn of the crank; start turning the crank slowly to make it easier to determine the number of rotor revolutions for each turn of the crank. - Determine the number of crank revolutions to have 1,800 rotor revolutions. - To maintain a constant rotation speed for 1 minute, count the number of crank revolutions and divide by 12.

The number you obtain is the number of

revolutions required in 5 seconds.

Well Area Operations

Code RPWA2021A Rev. 00 – Date 01/03/2005 Page 94 of 132

Agip KCO

- Turn the crank quickly for 5 seconds. If you turn the crank more than 10 times, slow down a little and count the turns in 5 seconds again. Continue to adjust the rotation speed. 2.

Prepare a standard potassium chloride curve.

A standard calibration curve is required for each centrifuge. prepared as follows.

This can be

You will need at least three points (3.5, 10.5, and 17.5

lb/bbl KCl) ( Figure 16).= Kg/mc 9.90 – 29.7 – 49 for an accurate diagram.

Table 15 Filtrate volumes for various concentrations of KCl Concentration scale KCl (lb/bbl)

Filtrate volume (cm3)

K+ (mg/L)

3.5-18

5,250-27,000

7.0

18-35

27,000-52,500

3.5

35-70

52,500-105,000

2.0

> 70

> 105,000

1.0

a. Prepare a test to cover scales from 1 a 8% KCl adding an appropriate amount (ml=) of standard potassium chloride solution (0.5 ml for every 3.5 lb/bbl) to the centrifuge tube. Dilute with 7 ml of distilled water. b. Add 3 ml of sodium perchlorate solution to each tube. c. Centrifuge for 1 minute at 1,800 RPM and immediately record the amount of precipitate (volume). d. Wash the tube and dispose of the liquid. e. Record the ml of precipitate versus the potassium chloride content (lb/bbl) and plot a graph.

Well Area Operations

Code RPWA2021A Rev. 00 – Date 01/03/2005 Page 95 of 132

Agip KCO

Figure 16: Example of a concentration curve for KCI concentration

16.8.7

Procedure 1.

Measure 7 ml of filtrate in a centrifuge tube.

Add 3 ml of sodium

perchlorate solution (if potassium if present, precipitation will be sudden). DO NOT AGITATE. Centrifuge at a constant speed of 1,800 RPM for 1 minute and immediately record the amount of precipitate (volume). Rinse the precipitate thoroughly with water. NOTE: Add 2 to 3 drops of sodium perchlorate to the centrifuge tube at the end of the procedure, to make sure there are no more traces of potassium.

If

precipitate has formed, the total amount of potassium ions is not measured and the sample is diluted as explained in note 2. 2.

Determine the potassium chloride concentration comparing the amount of measured precipitate with the relative diagram. (see Figure 16).

3.

Record the potassium concentration as lb/bbl KCl or kg/m3

Well Area Operations

Code RPWA2021A Rev. 00 – Date 01/03/2005 Page 96 of 132

Agip KCO

Calculations The potassium concentration can also be recorded as the weight of KCI (percentage). KCl (wt %) = (lb/bbl) / 3.5 +

K (mg/l) = 1,500 x KCl (lb/bbl) NOTE 2: These two calculations are based on filtrate with a specific weight of 1.00. If the KCI concentration is above 21 lb/bbl, the precision can be improved using a dilution which keeps the test result between 3.5 and 21 lb/bbl. The volume in the tube must not exceed 7 ml with distilled water and should be agitated before adding the sodium perchlorate solution. If volumes of filtrate are not 7 ml, the KCI concentration should be calculated as follows: KCl (lb/bbl) = 7 / ml of filtrate (values from a standard diagram) This is a typical rigsite method and should be used as such. The purpose of the procedure is to keep potassium ions in mud filtrate at a higher level. The best results can be achieved when the potassium ion concentration is >5,000 mg/l (KCl>9500 mg/l). 16.9

Nitrate ion concentration 16.9.1

Scope Identifying filtrate and formation water from formation fluids sampled during a DST can be problematic, and using nitrate ion in the filtrate as a tracer provides for a better evaluation.

Well Area Operations

Code RPWA2021A Rev. 00 – Date 01/03/2005 Page 97 of 132

Agip KCO

16.9.2

Equipment Nitrate testing kit (A.J. Chemicals), a spoon to measure lime.

16.9.3

Procedure 1.

Measure a 5 ml sample of colourless or nearly colourless filtrate in a test tube. If the filtrate is coloured, eliminate by dilution or treat with lime (see Note 1 and Table 9).

2.

Add an ampoule bottle of NO3 and agitate for 3 minutes.

3.

Leave to decant in another test tube.

4.

Add an ampoule bottle of NO3 . Leave to decant in another test tube.

5.

Agitate then leave for 10 minutes until the colour has fully developed.

6.

Pour the sample into a graduated 10 ml test tube and add deionised water to make up to 10 ml. Agitate carefully.

7.

Put the sample in the second test tube.

8.

Prepare a test tube with a 5 ml sample that has been treated following step 1; add 5 ml of deionised water to dilute as indicated in step 6.

9.

Put the unknown sample in the right-hand hole of the comparison box.

10.

Put the sample to test in the left-hand hole of the box.

11.

Observe the samples through the holes, turn the colour wheel until the right colour intensity has been reached. If the colour of the sample is darker than the colour of the wheel marked no. 80 (note 2) estimate the dilution required (Table 16) to reduce the concentration of nitrate ions to the colour scale of the wheel and repeat the test.

12.

Record the value.

Well Area Operations

Code RPWA2021A Rev. 00 – Date 01/03/2005 Page 98 of 132

Agip KCO

16.9.4

Calculations Clear filtrates: –

mg/l NO3 = (reading x dilution factor) / 10 Coloured filtrate requiring calcium treatment: ––

mg/l NO3 = [(reading x dilution factor / 10] – (6 x mg/1 NO3 in calcium*) Coloured filtrate requiring two calcium treatments: ––

mg/l NO3 =[(reading x dilution factor) / 10] – 1 – (42 x mg/l NO3 in calcium*) *Read this value on the calcium container. NOTE 1: The 5 ml sample collected in step 1 does not necessarily have to be colourless. A slight colouring is possible, provided that the container conforms to the specifications in step 8.

A very dark filtrate should however be

decoloured. To decolour the filtrate, dilute 5 mil of filtrate with deionised water, add a spoon of calcium hydroxide, agitate as required and filter through a funnel, for a dilution factor of 6. If the filtrate is too dark, take 1 ml and dilute to 5 ml with deionized water to see whether the sample reacts as in point 1. If the sample does not react, take 5 ml and repeat using the same dilution ratio and treatment, then filter again, for a dilution factor of 36. Further discolouring should not be necessary. However further discolouring with deionised water (Table 11) might be required, and this can be verified after step 11. NOTE 2: Readings >80 on the colour wheel are not accurate and should always be rechecked. [ Memo : 1 ml = 1 cc = 1 cm3 = 1/1000 litre]

Well Area Operations

Code RPWA2021A Rev. 00 – Date 01/03/2005 Page 99 of 132

Agip KCO

16.9.5. Dilution table This table is a guide to choosing the right dilution ratio for the original filtrate (except for calcium treatments) or further dilution after calcium, if the approximate concentration of NO3 in mud filtrates is known. The dilution factor column indicates the amount of filtrate used and final volume which is diluted with deionized water.

Well Area Operations

Code RPWA2021A Rev. 00 – Date 01/03/2005 Page 100 of 132

Agip KCO

Treatment without lime Dilution (ml)

Dilution factor

NO3 – (mg/l) 0–8

None

1

8 – 20

2–5

2.5

20 – 40

1–5

5

40 – 80

1 – 10

10

80 – 200

1 – 25

1025

200 - 500

1 - 50

50

Treatment with calcium (1) NO3 – (mg/l)

Dilution (ml)

Dilution factor

0 - 20

None

6

20 - 100

2-5

15

100 - 200

1-5

30

200 - 450

1 - 10

60

Treatment with calcium (2) NO3 – (mg/l)

Dilution (ml)

Dilution factor

0 - 120

None

36

120 - 550

2-5

90

Table 16

Well Area Operations

Code RPWA2021A Rev. 00 – Date 01/03/2005 Page 101 of 132

Agip KCO

16.10 PHPA polymer concentration 16.10.1 Scope PHPA polymers are added to mud to help stabilize clays in the borehole. The following tests make it possible to determine free polymers and polymers that can be absorbed by the well sidewalls. 16.10.2 Equipment 1.

Electric hotplate/electric whisk with magnetic wires.

2.

Two, 125 cm3 raduated Erlenmeyer flasks.

3.

Distilled water.

4.

Boric acid solution, 2% in weight.

5.

Methyl orange indicator (methyl red).

6.

6 N sodium hydroxide solution.

7.

2 – 3 ft Tygon tubing, 0.25 in. ID.

8.

6 rubber stoppers with a 0.25 in hole.

9.

0.02 N sulphuric acid solution.

10.

Polymer defoamer (such as Dow-Corning 84 AFC-78).

11.

Small glass tube, 0.25-in. OD— (2 tubes, 3 – 4 in. long).

Well Area Operations

Code RPWA2021A Rev. 00 – Date 01/03/2005 Page 102 of 132

Agip KCO

16.10.3 Procedure 1.

Connect the two small glass tubes to the two ends of the Tygon tubing. Put one end inside the rubber stopper so it reaches the bottom of the stopper.

2.

Pour 25 cm3 of boric acid solution into an Erlenmeyer flask, add 6 drops of methyl orange indicator. The original colour should be red/pink, but not yellow.

3.

Pour into another graduated flask (not into the reaction flask), add 50 ml of distilled water, 2 cm3 of silicone defoamer and 10 cm3 of mud; if the concentration of active polyacrylamide (PHPA with a high molecular weight) is >1.5 lb/bbl, or if polyacrylamide (PHPA with a high molecular weight) IS > 4.5 lb/bbl, use 5 cm3 of mud, then double the result.

4.

Put the reaction flask with the mud on the electric hotplate and start stirring. Add 3 ml of sodium hydroxide solution and immediately connect the flask to the rubber stopper.

5.

Put the other end of the tubing (Pasteur pipette) into the methyl orange and 2% boric acid solution and bring to the boil. The condensation in the flask (volume) should be approximately 25 cm3, with the colour varying from pink to yellow.

6.

Adjust to a medium heat so the fluid can be removed. Turn the plate to “off”. As the solution cools, the boric acid can be sucked up from the flask. After collecting 25 cm3, remove the stopper and empty the flask entirely. Titrate the contents with 0.02 N H2SO4 until the colour returns to the original red/pink and record the amount of acid used.

7.

The concentration of Polyacrylamide – with high molecular weight PHPH can be determined using an accurate diagram. Double the result if a 5 cm3 sample has been used.

Well Area Operations

Code RPWA2021A Rev. 00 – Date 01/03/2005 Page 103 of 132

Agip KCO

16.10.4 Additional guidelines and trouble shooting 1.

The glass tube must be washed when the bottom part is still inside the rubber stopper.

If the tube is sticking out of the stopper, the caustic

solution will collect around the lower part of the tube as it is distilled. As a result it will be sucked up and dispersed in the boric acid solution. 2.

Make sure methyl orange is used as the indicator. It will change from a pale amber yellow to pink/dark red depending on the pH. Moreover, the boric acid solution will change the colour to pink rather than yellow. If the colour does not turn pink, use a fresh sample of boric acid. If this is not possible, use 0.02 N sulphuric acid solution and add in drops until the solution goes pink. Use this solution to collect the distillate.

By following this procedure, only the acid to titrate ammonia will be measured during final titration.

Any addition of acid to correct the boric acid is not

considered. 3.

If the mud foams, increase the amount of defoamer and try to estimate the active polymer scale of use, to determine amounts to use in actual operating contexts.

4.

The distillation temperature should be chosen so that the solution does not boil for too long (as this would make the test result void). The solution should be left to boil on a gentle heat, so that water distillation (or the distillate) condensates at the top of the tube. As a result, the mud inside the receiver ampoule bottle will not boil, but the distillate will thicken in the tube, reaching the boric acid solution. NOTE: the temperature should be adjusted to ensure the solution boils gently and consistently and to prevent the ampoule bottle with the mud cooling due to the boric acid being sucked up by the bottle.

5.

Make sure the bottom end of the tube is below the level of the boric acid solution. A Pasteur pipette should be used instead of the glass tube. As it has a smaller opening, it is less likely that ammonia will leak.

6.

When carrying out final titration, make sure you titrate to the original colour of the boric acid solution. If a light pink colour develops, do not continue titrating to try and obtain a darker pink.

Well Area Operations

Code RPWA2021A Rev. 00 – Date 01/03/2005 Page 104 of 132

Agip KCO

17.0 CHEMICAL ANALYSES FOR CORROSION 17.1

Zinc oxide (ZnO) and basic zinc carbonate (ZnCO3•Zn(OH)2) 17.1.1

Scope Zinc oxide and zinc carbonate can be used to neutralise H2S in drilling muds. To determine the concentration of ZnO or ZnCO3 in mud, use the following:

17.1.2

Equipment 1.

Glacial acetic acid.

2.

10% ammonium fluoride.

3.

Concentrated ammonium hydroxide.

4.

Masking agent.

5.

Deionized water.

6.

4% formaldehyde solution.

7.

Calmagite indicator solution.

8.

Standard versenate solution.

9.

150 cm3 beaker.

10.

One 10 cm3, one 25 cm3 and one 100 cm3 graduated cylinder.

11.

Whisk with magnetic wires.

12.

One 10 cm3 and one 20 cm3 syringe.

13.

Plastic, 4 in. funnel.

14.

Cone paper filters (S & S No. 588 - 18.5 cm).

15.

Litmus papers.

16.

One 10 cm3 and one 20 cm3 volumetric pipette.

Well Area Operations

Code RPWA2021A Rev. 00 – Date 01/03/2005 Page 105 of 132

Agip KCO

17.1.3

Procedure 1.

Agitate the mud sample and measure 10 cm3 with a syringe.

2.

Transfer into a 150 cm3 beaker.

3.

Dilute to 40 cm3 with deionized water.

4.

Add 10 cm3 of glacial acetic acid (WARNING: use protective equipment).

5.

Agitate for 10 minutes.

This longer time is necessary, because the

reaction is quite slow. 6.

Add 15 cm3 of ammonium hydroxide (ATTENTION).

7.

Check the pH. If it is >9, go on to the next step. If it is 9.

8.

Add 3 cm3 of masking agent.

9.

Add 10 cm3 of ammonium fluoride solution.

NOTE: as ammonium

fluoride is poisonous, do not aspirate with the pipette and never mix with an acid solution. 10.

Transfer the solution to a 100 cm3 graduated cylinder and dilute with deionised water up to 100 cm3.

11.

Mix well and filter into a clean beaker.

12.

Take 20 cm3 of filtrate and pour into a clean beaker.

13.

Dilute with deionized water to approximately 40 cm3.

14.

Add 6 drops of calmagite indicator. If the solution is blue, go directly to step 15. If the solution is red, slowly titrate with standard versenate to a blue endpoint. The amount of versenate indicator does not have to be recorded.

15.

Add 5 cm3 of ammonium hydroxide.

16.

Check the pH, which should be between 10 and 11. If the pH is 15 ppm, the mud needs to be diluted further. Use 1 ml of mud and 24 cm3 of deionized water for concentrations ranging from 15 to 125 ppm and multiply the ppm of H2S obtained from the paper by 25. For concentrations from 125 to 1,250 ppm, mix 1 cm3 of mud in 9 cm3 of deionized water in a small beaker. Take 1 cm3 of the mixture and add 24 cm3 of deionized water for the test, multiply the ppm of H2S, obtained from the paper, by 250.

Well Area Operations

Code RPWA2021A Rev. 00 – Date 01/03/2005 Page 109 of 132

Agip KCO

17.3.5

Procedure 2: Garrett Gas Train (GGT)

17.3.6

Scope H2S is immediately ionized in alkaline mud, as it is neutralized and transformed into sulphur (S) and bisulphite (HS) ions. When mud filtrate is put in a GGT and acidified, the H2S reforms, is released and measured using the Dräger tube inside the GGT.

17.3.7

Equipment Section 1: Garrett Gas Train and accessories (figure 17). Section 2. Dräger tubes for H2S analysis: A) Low scale-H2S 100/a (labelled from 100 to 2,000) Factor = 0.12. B) High scale H2S 0.2%/A (labelled from 0.2 to 7%) Factor = 1,500. Section 3. Cartridges for CO2 (or other gases inert to H2S provided they do not contain air or oxygen, such as nitrogen). Section 4. Lead acetate paper strips (optional). Section 5. Approximately 5 N sulphuric acid. Section 6. Optanol defoamer. Section 7. One, 10 cm3 hypodermic syringe with needle for acid (21 gauge), one 40 cm3 and one 5 cm3 hypodermic syringe

17.3.8 Procedure 1.

The gas train must be clean, dry and put on a flat surface. Tubing etc. must not be obstructed, or damp as this would obstruct the flow and invalidate results.

2.

Fit a new CO2 cartridge.

3.

Add 20 ml of deionized water to chamber 1

4.

Add 5 drops of defoamer to chamber 1 (figure 18).

Well Area Operations

Code RPWA2021A Rev. 00 – Date 01/03/2005 Page 110 of 132

Agip KCO

5.

Select the exact volume for the sample and the Dräger tube, with an appropriate scale for sulphide, in line with table 17.

6.

Break off both ends of the tube (figure 19).

Figure 17 : Garret Gas Train assemblied.

Well Area Operations

Code RPWA2021A Rev. 00 – Date 01/03/2005 Page 111 of 132

Agip KCO

Figure 18: Preparing the GGT for sulphide analysis.

Well Area Operations

Code RPWA2021A Rev. 00 – Date 01/03/2005 Page 112 of 132

Agip KCO

Figure 19: Breaking off the ends of the Dräger tube.

Figure 20 : Drager tube installed on the base of GGT.

Broken ends

Receptacles

Well Area Operations

Code RPWA2021A Rev. 00 – Date 01/03/2005 Page 113 of 132

Agip KCO

7.

Wash the chambers with a mild detergent and soft brush. Use a small pig. Put the tube with the arrow pointing downwards, in the receptacle in the corner . After cleaning and drying the tube, install the flow meter with the word “TOP” facing upwards, and ball in the channel at the side facing downwards at the bottom. Make sure the O-rings seal the tubes.

8.

Measure the samples in chamber 1. Chambers 2 and 3 will be empty and are used as “traps” for the foam.

9.

Put the O-rings in the grooves and assemble the top part of the gas train. Tighten all screws uniformly.

10.

Connect the dispersion tube to the Dräger tube.

11.

Adjust the dispersion tube so it is 0.5 cm from the bottom.

12.

Slowly inject CO2 for 15 minutes to remove air from the system. Activate the gas flow gently to avoid the ball coming out of the flow meter tube. Apply gentle pressure to the tube, to check air is being eliminated and prevent the ball coming out.

13.

Slowly inject 10 ml of sulphuric acid into chamber 1, through the rubber top.

14.

Restore the CO2 flow and adjust so that the ball is between the small 3

red lines (from 200 - 400 cm /min). A CO2 cartridge should guarantee a 15 to 20 minute flow at this rate. 15.

Continue gas flow for 15 minutes. Record the maximum length of the stain. Note: if sulphites appear in the top part of the Dräger tube, an orange colour produced by the SO2 may form in front of the black part. The orange part should be ignored. Only record the dark part. Note: the length of the stain, which should cover more than half the length of the tube, is the most accurate way to evaluate the Dräger tube.

16.

The gas train must be thoroughly cleaned after use, as the acid could cause damage. To clean the train, remove the flexible tube and upper part of the GGT. Remove the flow meter and Dräger tube then cover

Well Area Operations

Code RPWA2021A Rev. 00 – Date 01/03/2005 Page 114 of 132

Agip KCO

the holes with stoppers to prevent damp getting in. Rinse with deionised water and leave to drain.

Calculations Referring to the sample volume, maximum length of the stain in the Dräger tube and factor (table 17) calculate the sulphides in the sample: Sulphides (mg/l) = (length of stain x tube factor) / (cm3 of sample volume).

Table 17: Selecting the Dräger tube and ranges. Volume of samples and tube factor to use for various sulphide ranges

Sulphide range (mg/l)

Sample volume (cm3)

Selecting the Dräger tube

Tube factor

1.2 - 24

10.0

H2S 100/a (100 2,000 range)

0.12*

2.4 - 48

5.0

H2S 100/a (100 2,000 range)

0.12*

4.8 - 96

2.5

H2S 100/a (100 2,000 range)

0.12*

30 - 1,050

10.0

H2S 0.2%/A

1,500**

60 - 2,100

5.0

H2S 0.2%/A

1,500**

120 - 4,200

2.5

H2S 0.2%/A

1,500**

* The tube factor of 0.12 is for new H2S 100/a tubes (Cat. No. CH-291-01), with a 100 - 2,000 range. Use a factor of 12.0 for old tubes with a 1 or 2 – 20 range. ** The tube factor of 1,500 is for new H2S 0.2%/A tubes (Cat. No. CH-281-01), with a 0.2 - 7.0% range. Use a factor of 600 multiplied by a batch factor/0.40 ratio for old tubes with a 1 – 17 cm range.

Well Area Operations

Code RPWA2021A Rev. 00 – Date 01/03/2005 Page 115 of 132

Agip KCO

17.4

Phosphate 17.4.1

Scope The active ingredient in inhibitors is an organic phosphate. However organic phosphates may be found in drilling muds, so analysis must differentiate between organic and inorganic phosphates.

17.4.2

Procedure 1 : Using a Hach Direct Reading Colorimeter

17.4.3

Equipment 1.

Deionized water.

2.

Phenolphthalein indicator.

3.

PhosVer III pillows.

4.

Potassium persulphate pillows.

5.

8 N NaOH sodium hydroxide.

6.

5 N H2SO4 sulphuric acid.

7.

50 cm3 Erlenmeyer flask.

8.

25 cm3 graduated cylinder.

9.

Hach direct reading colorimeter.

10.

Electric hotplate.

11.

Pipettes: one 1 cm3, one 5 cm3 and one 10 cm3 pipette.

a) Inorganic phosphate 1.

Use a pipette to transfer 5 - 10 cm3 of filtrate into a 50 cm3 flask. Add deionized water up to the 20 cm3 mask.

2.

Add 1 cm3 of sulphuric acid.

Well Area Operations

Code RPWA2021A Rev. 00 – Date 01/03/2005 Page 116 of 132

Agip KCO

3.

Boil for 15 minutes, making sure the volume stays at approximately 20 cm3.

4.

Cool.

5.

Add a drop of phenolphthalein indicator.

6.

Add sodium hydroxide in drops until the sample starts to turn pink. If you add too much sodium hydroxide the pink colour will remain. Add sulphuric acid in drops until the pink has disappeared.

7.

Pour the sample into a 25 cm3 graduated cylinder and add deionised water up to the 25 cm3 mark.

8.

Pour into a square mixing bottle.

9.

Add the contents of a PhosVer III pillow. AGITATE and leave for 1 to 2 minutes (do not leave for more than 2 minutes).

10.

Put the deposit measuring device in the Hach colorimeter and use a 2407 colour filter.

11.

Fill another square colorimeter bottle with filtrate that has not been treated in the receptacle (blank). Make sure the concentration is the same as the sample. If you used 5 cm3 for the sample volume, use 5 cm3 of filtrate diluted to 25 cm3 for the sample.

12.

Put the blank in the colorimeter. Adjust the control light for a 0 mg/l or 100% reading (transmittance depending on which scale is being used).

13.

Pour the sample into the colorimeter and read the PO43- (phosphate) in 3–

mg/l or transmittance (%). If the value for PO4

is >2.0 mg/l or if the

transmittance is 2.0 mg/l or if the

transmittance is 1 cm3 1.

Use a pipette to transfer 2 cm3 of iodine solution to each of the two 125 3

cm Erlenmeyer flasks. 2.

Add 20 cm3 of deionized water to each flask.

3.

Use a pipette to transfer 1 cm3 of filtrate to both flasks. Flask 1 is then covered. Use a sheet of white paper as a background to see the colour change better.

4.

Add 4 drops of HCl to flask 2, and 5 drops of starch indicator solution. The solution will develop a blackish blue colour.

5.

Titrate the sodium thiosulphate drop by drop until the blackish blue colour fades to the same shade as the solution in flask 1.

Calculations SO32- (mg/l) = [cm3 of iodine solution – (factor x cm3 of thiosulphate solution)] x 320.2 / cm3 of filtrate

Well Area Operations

Code RPWA2021A Rev. 00 – Date 01/03/2005 Page 123 of 132

Agip KCO

18.0 RESISTIVITY Mud, filtrate and filter cake resistivity is often fundamental for evaluating electric logs. 18.1

18.2

Equipment 1.

Mud, filtrate and filter cake.

2.

Resistivity meter for direct mud readings.

3.

Calibrated resistivity cell.

4.

32 - 220°F thermometer.

Procedure 1.

Fill the clean resistivity cell with filtrate and mud that has been recently agitated. Try to eliminate the air bubbles. Fill the cell to the right volume, in line with the recommended procedure.

2.

Connect the cell to the gauger.

3.

Measure the resistance in ohms-meter with direct readout. The value should be calibrated in ohms if this is not used.

4.

Record the detected temperature.

5.

Clean the cell, wash with deionized water and dry.

Calculations 1.

Record the resistivity Rm or resistivity of the filtrate Rmf in ohm-meters, with the value closest to 0.01.

2.

Note the mud temperature in °F.

3.

If the value is recorded in ohms, convert in ohm-meters as follows:

4.

Resistivity (ohm-meters) = R (ohms) x K (cell constant, m2/m)

Well Area Operations

Code RPWA2021A Rev. 00 – Date 01/03/2005 Page 124 of 132

Agip KCO

19.0 PROCEDURE FOR ANALYSING GLYCOL Rig site procedure to determine the glycol content in a mud 19.1

Refractometer 19.1.1

Equipment 1.

Refractometer to determine the percentage of glycol per volume used in

mud systems. Different types of refractometer are available and the most widely used measure glycol on a scale from 0 to 10%.

Follow the manufacturer’s

directions if you need to measure values over this scale. 2. 19.1.2

10, 20 or 50 cm3 retort, clean steel wool, glassware.

Reagents Glycol used in the mud. Deionized water. Graduated cylinders and receptacles for samples.

19.1.3

Procedure 1 1.

Prepare a calibration diagram for water and glycol.

This curve is

obtained adding the percentages of glycol in deionized water (usually from 1% to 6% of the volume used). Put each mixture into the retort and plot values on graph paper, which includes the corresponding BRIX vs. the percentage of added glycol.

BRIX is the refraction unit of

measurement to determine the glycol. 2.

Distil the mud.

3.

Record the fluid volume (percentage).

4.

Agitate the liquid, so it flows from the graduated cylinder to the retort.

5.

Put 2 to 4 drops of liquid from the retort onto the clean surface of the refractometer prism.

Make sure the entire surface of the prism is

covered by the liquid and close the lid.

Well Area Operations

Code RPWA2021A Rev. 00 – Date 01/03/2005 Page 125 of 132

Agip KCO

Observe through the refractometer window with the prism facing a light source (figure 21). 6.

Record the BRIX value, using the glycol calibration diagram, then convert to the glycol volume in the mud (percentage).

7.

Glycol percentage in the mud = percentage of glycol from the calibration diagram x liquid fraction of the mud. The liquid fraction of the mud = Fw.

19.2

Dual-temperature retort analysis for glycol systems Glycol is a primary inhibitor which neutralises in water systems with polyglycol as it is absorbed by clays, so the concentration of glycol in mud has to be measured and controlled.

This procedure applies to all types of glycol.

Although it is not an API

procedure, an API retort procedure is employed. 19.2.1

Equipment API retort test kit (a 50 cm3 kit is recommended for accuracy). Make sure it has a thermostat to heat up to 302°F (150°C) and 950°F (510°C).

19.2.2

Procedure 2 1. Measure a mud sample and put in the bottom beaker of the cell in the retort. The air in the mud must be reduced to the minimum. Put fine, clean steel wool in the top part of the cell. Lubricate the threads with grease suitable for high temperatures when assembling the cells, to minimise leaks. 2. Adjust the thermostat to 302°F (150°C). Heat the retort until all the water has been recovered (approximately 90 minute). Record as the value V1. 3. Adjust the thermostat to 950°F (510°C), and continue distillation of the remaining liquid phase. Record the final volume as the value V2.

Volume of glycol (%) = (V2 – V1) x 100 / (Volume of mud sample) NOTE: liquids with a high boiling point, such as lubricating oils, may alter the results of this test.

Well Area Operations

Code RPWA2021A Rev. 00 – Date 01/03/2005 Page 126 of 132

Agip KCO

19.3

Determining the amount of glycol (kilos) with a centrifuge 19.3.1

Procedure 1. Pour 8 cm3 of filtrate into the tube of a centrifuge. 2. Add 3 g of NaCl to the tube and agitate until entirely dissolved. 3. Centrifuge for 3 minutes. 4. The glycol will separate from the NaCl solution, forming a layer above it. Record the volume of the layer (V) referring to the graduated scale. Volume of the glycol (%) in the filtrate = V x 100 / volume of the filtrate (cm3) Volume of the glycol (%) in the mud = volume of the glycol (%) in the filtrate x fraction of liquid mud (Fw). Where the fraction of liquid mud (Fw) is equal to %/100 of the mud and obtained from the retort.

Well Area Operations

Code RPWA2021A Rev. 00 – Date 01/03/2005 Page 127 of 132

Agip KCO

20.0 PROCEDURE TO ANALYSE PLUGGED PERMEABILITY 20.1

Equipment 1. Cylindrical cell, with a ¼” thick porous disk. 2. Resistance. 3. Thickness. 4. Caps for the ends (one with a filter for the hydraulic part). 5. Two rods: one rod with a quick fit attachment for the hydraulic line and the other with a valve above the cell. 6. Pump with a quick fit attachment. 7. Hydraulic oil. 8. Piston with O-rings to keep the mud and hydraulic oil separate. 9. T-wrench to position the piston. 10. Cell for the bleeder valve. 11. Connection for the counter pressure regulator. 12. Two thermometers. 13. Two half cocks.

20.2

Procedure 1. Heat the resistance to the selected temperature. Open the cell and check the O-rings; replace if damaged. Cover the parts around the O-rings with a thin layer of silicone lubricant. Tighten the floating piston on the T-wrench and put the piston at the bottom of the cell. Reciprocate to check that the piston moves freely. NOTE: the bottom of the cell is the part with the shorter recessed end. Put the piston at the bottom of the cell and tighten the T-wrench. This is the access part.

Well Area Operations

Code RPWA2021A Rev. 00 – Date 01/03/2005 Page 128 of 132

Agip KCO

2. Before loosening the T-wrench, put the end of the piston close to the recessed part. Fit the O-rings. Put in the hydraulic cell and bottom cap in the part accessing the cell. Apply a thin layer of silicone to make installation easier. Insert the adjustment screws, check alignment with the mark and tighten slightly. Use tempered stop screws and grease with a high temperature lubricant to make it easier to tighten and loosen the screws. Use the opposite end of the T-wrench to push the floating cap downwards and expel the air. 3. Fit the stem of the quick fit access valve. Fill the stem then open the pump bleeder valve and use the opposite end of the T-wrench to push the floating cap downwards and expel the air. 4. Put the cell in an upright position and fill with 300 cm3 of mud. Put an O-ring in the top part of the cell. Insert the hydraulic tube in the hand pump, pump the mud to fill the system and put the disk above the _ring, then disconnect the tube. NOTE: Put the disk in fresh water for 5 to 10 minutes before using it to analyse the mud. If you analyse a synthetic oil base mud, the disk should be put for 5 – 10 minutes in a fluid which is compatible with the mud to be analysed. Never use disks more than once. 5. Fit the cap in the bottom. Put a thin layer of silicone grease on the O-ring to make assembly easier. Make sure the adjustment screw housings are perfectly aligned with the screws. Assemble the outlet valve, with bleeder valve, then assemble the parts and put the cell in the heating unit until the cycle is completed. Turn the cell clockwise until it stops in the locked position at the bottom of the heating unit. 6. Put a metal thermometer in the housing above the cell. Pour the filtrate in the receptacle above the valve, check the O-ring then secure. Assemble the bleeder valve and secure. Connect the hydraulic pump quick fit attachment to the valve inlet before pressurisation. Pressurise the cell to 200 psi and close the valve. When the cell is heated the pressure inside will increase as the hydraulic oil heats up. Activate the pump valve to release pressure and maintain a value of 200 psi. 7. Heat the cell to 150°F (temperature for these analyses). Record the time required to reach the temperature. Close the bleeder valve on the pump and activate the pump to pressurise to the required value. Operate the hydraulic pump to increase to an operating pressure of 1500 psi.

NOTE: Always wear safety goggles when working with a

pressurised cell at temperature.

When the mud and/or filtrate are close to the test

temperature, slowly open the bleeder valve.

Well Area Operations

Code RPWA2021A Rev. 00 – Date 01/03/2005 Page 129 of 132

Agip KCO

8. After applying the required pressure, pressurise behind without exceeding 50 psi and slowly open the bleeder valve. After 30 seconds slowly open the discharge valve and recover the mud and/or filtrate which flows out in a small beaker, until the cell is entirely empty. 9. Close the valve and maintain the required pressure in the cell using the hydraulic pump. The pressure will decrease as the mud is filtered, so it needs to be kept stable. Maintain pressure in the cell for 30 minutes, and discharge the liquid collected at regular intervals. After 30 minutes note the total volume recovered (excluding any spurt losses). Close the blowdown valve and open the pump bleeder valve. Keep the pressure behind and open the bleeder valve. This will move the floating piston downwards so hydraulic oil in the pump can be recovered. Turn off the resistance. 10. After recovering the oil, close the safety valve. Remove the hydraulic tube quick fit attachment from the cell. Close the pressure inlet behind the receptacle and bleed. If there is no residual pressure in the receptacle, remove the safety catch, remove the device and pressurise behind the receptacle. 11. Leave the cell to cool when it is still inside the heater, or remove it carefully and cool in water. After cooling, position so the safety valve is facing towards you. Carefully open and bleed the remaining pressure. Remove the top cover of the cell and turn the cell upside down in a sink. Remove the cover from the hydraulic part (bottom) and uncover the floating piston. Tighten the T-wrench and push downwards, to make the mud and disk come out from the opposite end. 12. Recover the disk and filter cake and rinse with freshwater or a base oil if using an oil base mud. Measure the thickness of the filter cake in 32”/inches. The total fluid is calculated as follows: Total fluid loss (cm3) = spurt losses (cm3) + 2 x (fluid recovered in 30 min. (cm3).

Well Area Operations

Code RPWA2021A Rev. 00 – Date 01/03/2005 Page 130 of 132

Agip KCO

21.0 COUPON RING FOR DRILL PIPE CORROSION This system for determining drill pipe corrosion is important but hardly used nowadays, so we shall give a brief overview. The rings, in bronze, are put between the threads of the drill pipes before they are run into the well. The rings are then removed after some 100 hours. They are carefully examined to determine the cause and rate of corrosion. From this information, the type of inhibitors and products to use to prevent or minimise corrosion can be selected. 21.1

Monitoring corrosion rings 1.

The rings should stay in the drill string for at least 40 hours, as a shorter time

would give inaccurate data. The standard time is around 100 hours. The rings are assembled in pairs; the first on the surface, in the Kelly Saver Sub, and the second in the last drill pipe, above the drill collars. 2.

The ring is put in a bag after it is removed from the drill string. The form on the

bag should be carefully filled in, with the name of the oil company, well name and number, contacts, type of mud and products used in it, string metallurgy, depth, period of use and removal date. 21.2

Laboratory test 1. Before evaluating corrosion, the ring needs to be washed with detergent and rinsed and prior to this it should be weighed to compare the vale with the original weight on the packaging. Use drops of reagent to check for any residual carbonates from dissolved H2S, CO2 or other substances. 2. The ring should be washed with mild detergent and a hard bristle brush, then put in a 15% hydrochloric acid solution with an inhibitor, once or twice, to remove corrosion products. The ring should be cleaned each time it has been put in the acid solution and rinse with service water, followed by anhydride acetone or methyl alcohol to make sure it is dry (always follow safety recommendations when using these chemical products). 3. Weigh the ring again (to the milligram) and calculate any weight loss (corrosion). Any significant metal loss caused by mechanical damage should be recorded in the ring report. The corrosion value is obtained multiplying the weight loss (g) by the K-factor, divided by the total number of hours the sample was downhole.

Well Area Operations

Code RPWA2021A Rev. 00 – Date 01/03/2005 Page 131 of 132

Agip KCO

4. Visual inspection Corrosion which is evident when the sample is removed from the drill string may be caused by a general attack or pitting. The corrosion value is the weight loss of a general attack.

The pitting value cannot be determined from the weight loss of the ring.

Mechanical damage may consist of cuts on the metal, or metal which has been removed from the surface. In some cases, the ring will have wear marks, which mean that the ring and housing have moved considerably during drilling and manoeuvres. As the coupon rings are exposed to mud circulation, the mud loss includes circulation corrosion and erosion. Inspection of the rings may reveal deep pitting with a fairly low weight loss.

This

indicates a corrosion problem which goes beyond general surface corrosion. The pH and Pf should be maintained at optimal levels for all water base muds. If these values tend to increase, an organic inhibitor may be necessary.

Bacteriological

problems also need to be considered as these may cause a number of problems for the mud. The corrosion values for freshwater and mud are usually 2 lb/ft2-y or less, without any deviations. Values towards the top end of this scale should be further evaluated by adding chemical treatments. 21.3

Calculating the degree of corrosion Coupons for determining corrosion are available from service companies. These are usually numbered, pre-weighed and packed in water-repellent paper. The coupon number is on the packaging along with the K-factor calculation. The degree of corrosion is obtained from the weight difference of a coupon before and after the test, multiplied by the K factor and divided by the total number of hours. For qualitative purposes, coupons should be weighted extremely carefully before and after the test. The test should preferably be carried out at another laboratory.

Well Area Operations

Code RPWA2021A Rev. 00 – Date 01/03/2005 Page 132 of 132

Agip KCO

1. If the K factor is not available, the degree of corrosion can be calculated in lb/ft2 per year (lb/ft2-y) using the following formula: lb/ft2-y = (weight loss (mg) x 144 x 365) / (453,600 x *area (in2) x days of exposure ** or = (weight loss (mg) x 2,781) / (*area (in2) x hours of exposure**) kg/m2-y = (weight loss (mg) x 10,000 x 365) / (1,000,000 x area (cm2) x days of exposure**) or = (weight loss (mg) x 87.60) / (*area (cm2) x hours of exposure**) * The total surface area of the ring is used for this calculation. ** Time based on the total period of use of the string. 2. The conversion rates between various units for steel follow: mpy = 24.62 x lb/ft2-y mpy = 5.03 x kg/m2-y lb/ft2-y = 0.04 x mpy lb/ft2-y = 0.20 x kg/m2-y kg/m2-y = 0.20 x mpy kg/m2-y = 4.90 x lb/ft2-y

Well Area Operations