Cementing & cement evaluation.pdf
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26/06/2013
المعھد الجزائري للبترول INSTITUT ALGERIEN DU PETROLE
School of Boumerdes UFR: Drilling and Production
Cementing & cement evaluation PREPARED BY: A.NACEF DRILLING INSTRUCTOR
Contents Introduction
2
Types of cementing Primary cementing Methods of primary cementing Primary cementing-casing Designing a cement job Casing & cementing accessories Cementing additives Remedial cementing Plug cementing Squeeze cementing Cement chemistry and additives Cement evaluation
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Introduction 3
A critical Well Construction process used worldwide Cementing is an important steps in the well’s finishing
process. Cementing is done by pumping a slurry of cement and
water at a strategic point around the casing to bind these up to the formation
Types of cementing 4
When drilling oil and gas wells, several different cementing methods can be needed:
Primary Cementing : is the introduction of cementacious material into the annulus between casing and open hole
Remedial jobs : to repair primary cementing jobs (Squeeze cementing, Cement plug)
Other cementing: plugs for abandonment, sidetracking, loss zones …etc
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Primary cementing 5
The placement of a cement slurry into the annulus between the casing
and the formation exposed to the wellbore (open hole) or previous casing. The most important objective of primary cementing is to provide zonal
isolation (that is, to prevent communications between the different zones in a well). In addition, the cement provides support for the several casing strings run in a well.
Zonal Isolation 6
Poor Zonal Isolation:
improper reservoir evaluation crossflow of unwanted fluids corrosion of pipe and scale production annular pressure and environmental hazards more than $45 Billion/year spent on unwanted produced water
management
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Purpose of primary cementing 7
Fasten the casing to the formation Reduce the possibility of blowout from high pressure zones Protect all Production zones Prevent fluid movement between different formations, or between
formation and the surface Strengthen and protect casing/tubing against corrosion Support the borehole
Methods of primary cementing 8
Thru-Drill Pipe Cementing (Stab-in) Outside Cementing (Top Job) Single stage cementing ( two plugs cementing) Two Stage Cementing
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Primary Cementing - Casing 9
Conductor Surface Intermediate Production Liners
Conductor Casing (stove pipe) 10
Confines circulating fluids Prevents washing out under rig Provides elevation for flow nipple and bell nipple BOP are usually not attached to conductor casings.
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Conductor Casing (stove pipe) 11
Set from 40 to 100 feet Casing is large; 36/42 inches inches
diameter Hole may be eroded severely. Casing can be pumped out easily and must be tied down. Large excess Stab-in cementing common Accelerated neat cement
Surface casing 12
Protect water sands. Case unconsolidated formations. Provides primary pressure control.
(BOP usually nippled up on surface casing) Supports subsequent casings. Case off loss circulation zones.
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Surface casing 13
Characteristics: (Set from 100 to 3000 feet) Casing may stick easily in unconsolidated formations. Loss of circulation may be a problem. Most areas require that cement be circulated. Guide shoe, or float shoe, and stab-in shoe commonly used. 18 5/8 ‘’ casing in 26 ‘’ hole Light weight lead and neat tail slurries or Large excess ( 50 - 150 %) 13 3/8” casing in 17 ½” hole @ 100 ft – 3000 ft
Surface casing 14
Characteristics: Often cemented through drill pipe with
stinger. Top plug should be prepared for any failure to seal with stinger. Shoe Bottom joints should be centralized and thread locked to prevent loss down hole. Cemented to surface /top job
18 5/8 ‘’ casing in 26 ‘’ hole or 13 3/8” casing in 17 ½” hole @ 100 ft – 3000 ft
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Itermediate casing 15
Cases off loss circulation zones, water flows, etc. Isolates salt sections Protects open hole from increase in mud weight Prevents flow from high-pressure zones if mud weight must
be reduced Basic pressure control casing BOP always installed Supports subsequent casings
Intermediate casing 16
3000 to 10,000 ft (vertical or deviated) 13 3/8” casing in 16” or 17 ½” hole 9 5/8” casing in 12 ¼” hole Guide shoe, or float shoe, and float collar commonly used. Cement volumes usually largest in well
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Intermediate casing 17
Potential problems: over-pressured, loss zones, salt formations
or heaving shales Narrow pressure window, between pore @ bottom & frac @ top Long casing string may need a two-stage job Best cementing practices are required Cemented to surface or to previous casing shoe Typically filler slurries followed by high compressive tail Specialized slurries (light, heavy, salt etc)
Production casing 18
Conduit for Completion String Provides pressure control Cover worn or damaged intermediate casing Setting depth through producing zone Common sizes 4 1/2 ”and 7 " casing Generally cemented back to intermediate casing Good cement job is vital to successful completion. Can be a liner
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Production Liner 19
Isolates the pay zone from other
formations and the fluids in them. Protective housing for production
equipment. usually cemented and perforated
Common sizes: 3 ½ ,4 ½”, 7’’,
Can be blanked or slotted
Liners 20
• Key Points:
Pump Down Plug “Dart”
• Requires less casing
Liner Hanger
• Deeper wells
Liner Wiper Plug
• Small annular clearance
Liner Over Lap
• Specialized equipment
Previous Shoe
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Methodes of primary cementing 21
Thru-Drill Pipe Cementing (inner string cementing) Outside Cementing (Top Job) Single stage cementing ( two plugs cementing) Two Stage Cementing
Thru-Drill Pipe Cementing (Stab-in) 22
Key Points: Less cement contamination Less channelling Small displacement volume Pump until cement to surface Less job time (rig time) Less cement
Stinger.exe
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Inner string cementing 23
Operational Sequence for running & cementing 18 5/8” Prepare and measure the 18 5/8” string (prepare the landing joint according to section TD). Remove the 30" conductor pipe raiser, respecting all the time the safety procedures. Run 18 5/8” casing in the hole circulating from the cellar with a jet pump. Connect last casing joint with the minimum torque. Center the 18 5/8” string (see figure 1) with metal rig-made slips. Install the IPN in the top of the cellar, perpendicular to the 18 5/8” casing. Install the 18 5/8” casing elevator between the IPN and the next joint couple. The side door elevator needs to be landing on top of the IPN. Land casing.
Inner string cementing 24
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Inner string cementing 25
Disconnect landing joint. Check the condition of the “O” rings of the cementing stinger nipple. Use 18 5/8'' X 5 1/2'' DP Centralizer Run in hole stinger string. Set stinger in casing shoe. circulate through the cement stinger, and
ensure the stinger seal is not leaking. R/U CMT head, R/U cementing lines. Well Service flush lines with water and test lines to 3000 psi Have enough cement and additives on location for 100% excess over required volume Conduct a pump efficiency test and report the results on the daily drilling report
Stinger 26
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Inner string cementing 27
Inner string cementing 28
Cement 18 5/8” casing, pump cement slurries (lead then tail) While cementing closely monitor any return from DP X Csg annulus. Observe returns from the well for any indication of hole losses or
instability Displace cement, check for mud return Disconnect stinger from float shoe, flush & POOH the stinger string, Proceed to weld the centralizing slips. Cut 18 5/8” casing as detailed in the procedures to install casing head housing. Install casing head housing.
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Outside Cementing (Top Job) 29
Key points:
Bring cement to surface Macaroni tubing used Max. depth 250-300 ft High friction pressures Non-standard connections
Tubing moved during job
Single stage cementing ( two plugs cementing) 30
It is conventional method The most method used in drilling Long pumping times High pump pressures
SingleStage.exe
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Single stage cementing ( two plugs cementing) 31
Run 13 3/8" to TD w/Circulation. Adjust column R/D WFT running gear & LA Fleur Offline Verify the cement top & bottom plugs type and load it on the
plug holder perform pump efficiency tests and record it in the daily drilling report R/U CMT head and lines Pressure test lines to 4000 psi Circulate prior cementing: Circulate to cool down, hole clean and break gelled up mud. Reciprocate casing gently and continuously at 3m up and 3m down. Meanwhile mix cement. Mud conditioning (low viscosity = good mobility) is the most important variable in achieving good cement placement behind the casing.
Single stage cementing ( two plugs cementing) 32
Pump spacer ahead Release bottom plug Pump cement Release top plug Pump spacer With rig pump displace cement, wait for bottom plug bump Record final displacement pressure, bump top plug and continue
pressure up to 3000 psi If the plug does not bump after finished theoretical displacement
volume do not over displace at all (max half shoe track volume) In case of float equipment not holding back press keep the CMT head
valve closed till CMT set R/D CMT head, Unscrew & hang BOP'S, Set casing hanger, Cut,
Beveled and L/D L.Jt
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Two Stage Cementing 33
The cementing of a string of casing in 02 Stages, using a stage collar
Stage Collar
1st Stage
Two Stage Cementing 34
Why? Potential Casing Collapse due to Hydrostatic Pressure of a full column
of Cement Lost circulation zone or low Frac gradient Cement very long intervalle (time/volume limitations) Reduce use of expensive slurries due to special well problems (salt zone, gas zone) Incomplet fill up (Can leave zone in the annulus uncemented)
TwoStage.exe
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Two Stage Cementing 35
Hardware Stage collar Plugs • First stage wiper plug (bottom plug is optional) • Opening plug/bomp • Closing plug
Stage collar 36
CLOSING PLUG SHEAR PINS
Running in Position
OPENING
OPENING
BOMB
BOMB
Cementing Position
Closed Position
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Two Stage Cementing 37
Where to place stage collar? Problematic formations (lost circulation, salt zone …etc) Inside previous casing to: • Avoid jetting effect on the formation while circulating cement • To ensure that if the collar fails to open, at least the open hole section is cemented
Two Stage Cementing 38
Some other points The stage collar is eventually drilled out leaving the same
drift as the rest of the casing 3 stages cementing is the same as 2 stages, but with 2 stage collars A stage collar is considered to be a weak point in the casing by many clients and so avoid using them. Alternatives: use of lightweight slurries (foam cement)
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Two Stage Cementing job procedure 39
Pressure test lines Pump wash/spacer Pump slurry Drop first stage plug Slowdown when the first stage plug passes the stage collar Displace, bump plug, check returns Drop bomb, wait allocated time (rule of Thumb 200ft/min) Pressure up to open stage collar Circulate (W.O.C if required) Pump wash/spacer then pump slurry Drop closing plug Displace close stage collar Check for returns
Two Stage Cementing examples 40
Calculate First stage cement and displacement volume Second stage cement and displaced volume
13 3 3//8” 68 lb/ft Casing
Top of cement at 2461 feet
4 13 3 3//8” shoe at 2789 feet 3
9 5/ 5/8” Stage collar at 4265. 4265.3 feet 12 1 1//4” O.H. 9 5/ 5/8” 53. 53.50 lb/ft Casing
1
9 5/ 5/8” Float collar at 6348. 6348.8 feet 2 9 5/ 5/8” Shoe at 6398 feet
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Two Stage Cementing examples 41
Frac Gradient: 0.8 psi/ft MW = 12 ppg
1. Would you recommend a 2-stage ?
Why ? 2. What depth would the Collar be? 3. What is the maximum density of
slurry possible during the first stage 2400’
(assume cmt to stage collar)? 4. Where would the TOC be for the first
5500’
salt zone
salt zone 5850’
stage TD:8400’
Two Stage Cementing examples 42
4100’
Frac Gradient: 0.8 psi/ft MW = 11.2 ppg weak formation
7100 -7250 FG: 0.6 psi/ft
weak formation
8400 - 8450 FG:0.68 psi/ft
TD:10200’
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Liners 43
Any string of casing whose top is located below the
surface, hung inside the previous casing and is run to its setting depth by drill pipe.
LINER HANGER
OVERLAP 50 - 500 FT
CASING SHOE
Liners 44
Way liners? Prime reason: Save money (Cost of 1 Joint of Casing can be $3,000!) Cover Corroded/Damaged Casing Cover: • Lost Circulation Zones. • Shale or Plastic Formations • Salt Zones Deep Wells: Rig Unable to Lift Long String of Casing
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Types of liners 45
Production: • Most common • Save$$ • Slotted liner • Blanked liner Intermediate/drilling: • Cover problem zone in order to be able to continue drilling Tie-back/liner complement: • From top of existing liner to surface, or further up casing to cover
corroded or damaged zone.
Types of liners 46
Tie-Back (Liner Complement) This is often done if production is commercially viable or there is damage to casing above the liner
TIE BACK STINGER WITH SEALS
LINER
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Liners 47
Procedure for Setting Liner 48
RIH hole with drill pipe At liner hanger depth, condition mud (Reciprocation / Rotation) Release slips (liner hanger) (Rotation - mechanical pressure
hydraulic) Set slips, release liner weight, check to see if running tool is free Pump mud - to ensure free circulation Cement/ Displace/ Bump plug/ Bleed off Release setting tool POOH above TOC and circulate
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Liner cement job procedure 49
Pressure test lines. Pump wash/spacer. Pump slurry. Drop "Pump Down" plug (or drill pipe wiper dart). Displace • To running tool and slow down the rate • Shear "Wiper Plug“ • Displace to Float Collar. Slow down while approaching end of
displacement Bump plug/checkf or returns. Release tool. Pull up to T.O.C. and reverse circulate / circulate
Liner.exe
Liner overlap 50
Cementing the liner "lap" is critical. Too much cement above the liner hanger is not recommended So make sure that "uncontaminated" cement is present at the liner lap -
washes and spacers / WELLCLEAN If not, there is communication from the annulus to the formation
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Recommendations for Liner Cementing 51
Ensure rheology of cement System is adequate for 100% mud removal Turbulent flow, if possible Consider 5 -10 min. "contact time" at liner lap Batch mix cement Minimize U-tubing effect Adequate mud conditioning prior to cementing
Liner example: well data 52
1) Well Information: • 9-5/8" 47 Ib/ft intermediate casing surface to 6500‘ • 7" 29 Ib/ft intermediate liner 6200 ft to 10,500‘ • 6“OH to TD at 14,500‘ • DP 3-1/2" 13.30 Ib/ft G105 • 4-1/2" 16.90 Ib/ft liner required 14,400' to 400' inside 7" liner. • FC 80' above shoe. 2) Cement required to TOL with 20% excess in OH 3) Calculate Slurry and displacement volumes 4) Give Job Procedure
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Liner exemple: well schematic 53 9 5/8” casing 47 lb/ft 3 1/2” drill pipe 13.3 lb/ft 9 5/8” casing shoe at 6,500 ft 7” liner 29 lb/ft Top at 6,200 ft 7” liner shoe at 10,500 ft 6” Open hole + 20% Excess 4 1/2” liner 16.6 lb/ft top @ 10,100ft ; collar @ 14,320 ft 4 1/2” liner shoe at 14,400 ft
Designing a Cement Job 54
Compute fluid volumes Slurry Wash, Spacer, displacement volumes based on : Hole capacity Casing capacity Annular length
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Designing a Cement Job 55
Check that well security is respected:
Simulate cement pumping process to compute hydrostatic and dynamic pressures and compare them to : • pore pressure • Fracture pressure • Tubular burst pressure
Ensure well security when Running In Hole Check Temperature and thickening time
Designing a Cement Job 56
Check for an efficient mud removal to prevent
mud channeling and to ensure good zonal isolation • Optimize fluid properties • Optimize the pumping rate • Optimize casing centralization Ensure good wall cleaning •
Optimize pre-flushes volume, and flow rate
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Parameters required 57
WELL PARAMETERS
FLUID PARAMETERS
Hole size and depth Casing tally PP and FP Temperature Centralization
Densities Rheology, PV and Ty Cement additives
Cement calculations 58
Prior to a cement job, the following calculations are made
Cement volume requirements 2. Cement displacement volume 3. Cement slurry composition calculations 1.
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Cement calculations 59
The following categories are involved: Cement volume (annular volume) Amount of water to make the cement Cement density and yield Displacement for landing top plug Pumping pressure for landing top plug Hydrostatic pressure on the formation Pressure for casing axial force during pressure test after the top cement
plug is bumped
Cement calculations 60
Cement slurry volume Before a cementing job can be carried out, volume calculations are
needed. Depending on the drilling fluid program and types of formation, the
hole diameter will be somewhat larger than the drill bit diameter. Annular volume is calculated to determine the amount of cement to be mixed. The amount is decided by making calculations based on the drill bit diameter, plus an extra amount based on experience or what is known about the formations in that particular area or caliper log. This forms the basis for the cement company's calculation of the total time needed for mixing and pumping the required.
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Cement calculations 61
Cement slurry volume After the casing is put into place, this calculated amount will normally
be adjusted, based on data collected via the caliper log. The caliper log does not give completely reliable results, and is usually used to find out whether the calculated cement volume, based on the drill bit diameter, is satisfactory. We normally use between 1.25 and 2 times the cement volume which was calculated by using drill bit diameter, this to compensate for washout in the well
Cement calculations 62
Cement slurry volume This is especially important with regard to deviation drilling, as these
wells have a tendency to become oval, and so excess cement is needed. This can often vary up to as much as 50% of the calculated hole volume. The ratio of fullness in the annulus will vary somewhat, depending on practice in the different companies, and the demands from the authorities. The two upper casings are always cemented back to the surface. Normal cement volume is 100-200% more than calculated volume, based on ideal diameters. 12 1/4" and 8 1/2" sections often have 30-50 % excess.
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Cement calculations 63
Cement slurry volume The required volume of cement slurry is based on the following factors: Length of open hole Diameter of the open hole (drill bit diameter and degree of washout) External and internal diameter in the particular casing Top of cement in the well
Cement calculations 64
Cement slurry composition calculations are based on kilos or liters per
100 kg cement powder. Slurry composition is characterized by: 1. 2. 3. 4. 5. 6.
Slurry Density Thickening time Ultimate cement strength Slurry permeability Slurry viscosity (Pressure loss) Fluid loss
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Cement calculations 65
A 7" liner cementation require 43 m3 cement slurry volume. From cementing company laboratory • The slurry density is 1,90 kg/liter • Slurry yield is 96,88 LHK Additives • Micro Block: (Gas Block Additive) • CFR3L: (Thinner) • SCR-100L (Retarder) • HALAD (Fluid loss reducer) • NF-5 ( De-foamer) • Fresh Water
18 LHK 1,15 LHK 2,0 LHK 6,5 LHK 0,1 LHK 37,38 LHK
Cement calculations 66
Step 1 : Calculate cement requirements: Cernent Requirement = CementVolume.x.100/slurry yield (LHK)
= 43000 x 100/96.88 = 44.39 ton
LHK = Litre per Hundred Kilo Cement
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Additive calculations 67
Additive calculations exercise 68
A 9 5/8" casing cement job require 123 m3 cement slurry volume.
Calculate cement and mix water and liquid additives per measuring tank. From cementing company laboratory • The slurry density is 1,92 kg/litre • Slurry yield is 95,88 LHK Additives • CFR3L: (Thinner) 1,27 LHK • SCR-100L (Retarder) 1,40 LHK • HALAD (Fluid loss reducer) 5,70 LHK • NF-5 (De-foamer) 0,15 LHK • Fresh Water 35,38 LHK
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Cement calculations 69
Displacement Volume After the cement is mixed and pumped into the well it is
displaced down the casing and up the annulus The displacement volume is the volume needed to send the top plug from the cement head to the float collar. This is normally done by multiplying the length with the capacity for the string. A pump efficiency is used for these calculations This capacity varies normally between 96% - 99%
Pumping Pressure to Charge Top Plug 70
When the cement leaves the casing shoe and start to move up in the
annulus we will notice the u -tube effect by the heavier slurry in the annulus. Example
A casing is cemented with 1,90 sg slurry and displaced with 1, 35 sg. Top Of Cement, TOC, is at 1000 m. Cement shoe is at 2000 m and the float collar is at 1976 m. What is the differential pressure just before the top plug lands (ignore friction) AP = (1976 -1000) x 0,0981 x (1,90 - 1,35) = 52,7 bar
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Hydrostatic Pressure 71
To ensure we are not fracturing the formation during the cement job, it
is necessary to calculate the hydrostatic pressure in the cement slurry to be used. Get an idea of whether there is a risk of the well fracturing when we are cementing. We must calculate pressure at different levels in the well, based on the geological conditions. In very weak zones, we must take extra care with regard to friction pressure, in addition to the hydrostatic pressure.
Casing & cementing Accessories 72
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Guide Shoe 73
Attached to first length of casing to be lowered into hole Guides casing into borehole and around obstructions Can be drilled out with the bit
Float collar 74
• Float Collar: – This is set about two-three joints above the casing shoe, and act as a one way valve, – When it is used, the cement plugs land on top of it.
Ball Type
Flapper Type
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Wiper Plugs 75
To Separate Fluids, (cement/wash/spacer/mud) Wiping the casing clean, Top Plug (Solid)
Surface indication of
Bottom Plug (pump through)
placement
Others 76
Centralizer: to centre casing in bore hole to promote even distribution of cement around casing
Cementing Basket: to minimize losses in weak zones.
Scratchers; to scratch off the mud cake to improve cement bond
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Cement Heads 77
Conventional cement head
Equipment On-Shore 78
Bulk Plant Silos, WBB, Compressor, Dust Collector
Batch Mixer
Fill
Diesel Engine
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Equipment Off-Shore 79
Batch Mixer CPS
LAS Liquid Addtive System
Cement Pump Skid
Slurry Chief
Cement Head
Mixing System
(Sub Sea System)
Mixing & Surface equipment 80
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Mixing & Surface equipment 81
Casing String Components from bottom up 82
Float shoe – guide and check valve to prevent cement back flow 2 Casing joints – to capture any contaminated cement
Cement Head
Rig Floor Ground Level
Drilling Fluid Cement
Float collar
Casing
Centralizer
Centralizers Scratchers
Float Collar
Float Shoe
Figure 9 Typical cementing equipment.
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REMEDIAL CEMENTING
What is remedial cementing? 84
Why do we do it? Plugs
Squeeze
Lost circulation Kick off Abandonment Primary cement job repair Unwanted Water Production High Gas-Oil Ratio (GOR) Casing Splits or Leaks Nonproductive or Depleted Zones
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PLUG CEMENTING
Plug Cementing 86
Purposes • To side track above a fish or to initiate directional drilling. • To plug back a zone • To plug back a well (abandonment or later re-entry) • To solve a lost-circulation problem during the drilling phase • To provide an anchor for OH tests.
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Side Track and Directional Drilling 87
Design considerations
Kick Off Point
CEMENT PLUG
NEW HOLE
• High compressive strength, typically with high density • Length should be enough to kick off
Plug Back a Depleted Zone 88
Design considerations
Cement Plug
Depleted Zone
• Sufficient length to provide a long term barrier • Legal requirements dictated by authorities • Reservoir zones may require additional additives
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Lost Circulation 89
Design considerations • Sufficient length to cover the thief zone • Successive treatments may be required, depending on losses • Lower density to minimise hydrostatic pressure
CEMENT CEMENT PLUG PLUG
ThiefZone
Abandonment 90
Design considerations CEMENTPLUG
CEMENTPLUG
CEMEN PLUG T
• Sufficient length to provide a long term barrier • Legal requirements dictated by authorities • Reservoir zones may require additional additives
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Test Anchor 91
Design considerations Test String
• Sufficient compressive strength to withstand pressure testing • Reservoir zones may require additional additives
Zone to be Tested CEMENT PLUG
Weak Formation
Cement Plugs - design 92
Design criteria 1. Quality • Cement hardness • Cement weight • Cement permeability 2. Time
Cement setting time (Pumping time): The minimum thickening time should be the job time plus a safety factor 2. Cement hardening time (ultimate strength) For kick off plugs the ultimate setting time should be achieved prior kick off operation
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Cement Plugs - design 93
Cement testing should be carried out using samples of the
actual materials to be used during the job (samples of mix water and lead/tail slurries) Calculate the hydrostatic pressures throughout the job and
check that the formation is never under balanced. Weighted spacers or mud must be used to maintain primary well control at all times.
Cement Plugs – string design 94
Wherever possible run a slim tubing stinger below the main
pipe. The minimum stinger length should be the plug length plus 30m. The natural tendency for cement slurry is to travel downwards when it leaves the string, since the slurry will generally be heavier than the drilling fluid. This can be avoided by spotting a viscous pill below the plug setting interval.
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Slurry Properties 95
Compressive Strength
Density
lighter for Lost Circulation heavier for Sidetracking homogeneous - batch mixing
Rheology
higher for Sidetracking less important for Lost Circulation minimum 500 psi for drill out
Thickening Time
higher for Lost Circulation Optimum (mud removal) for Sidetracking lower for placement with Coiled Tubing
enough for placement, POOH & circulating clean
Optimising Cement Plugs - Slurry mixing/placement 96
1. 2. 3. 4. 5. 6. 7.
8.
Pump a spacer ahead of the slurry to give a separation between the drilling mud and the cement slurry. Cement slurry should be batch mixed. A slight under-displacement is required in order to pull a dry string Pump a spacer behind the slurry to give a separation between the drilling mud and the cement slurry. Displace at maximum rates If possible rotate the string during the slurry placement and displacement. Pull back slowly above the plug and circulate out excess cement. At the same time the inside of the drill pipe will be cleaned for cement. Do not run back into the cement plug after pulling clear
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Reasons for Cement Plug Failures 97
Lack of hardness (sidetracking).
Poor isolation (plug back, abandonment).
Wrong Depth.
Not in place due to sinking to the bottom .
Not in place due to loss to thief zone.
Balanced Plug Placement 98
• Most commonly used method. • Set using drill pipe and stinger
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Balanced Plug Placement 99
Balanced Plug Placement 100
Water or other fluid of different density from that hole is run ahead
and behind cement slurry. The volume of fluid ahead and behind slurry is calculated so that height in casing is same as height inside the string.
mud water cement water
hW Height of plug with pipe in place
Height of plug after pulling pipe
mud
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Balanced Plug Placement 101
Procedure: 1. 2. 3. 4. 5. 6. 7.
Pump required spacer volume Mix and pup required cement volume Pump spacer behind cernent inside stinger Displace with mud POOH above cement plug Circulate POOH
Balanced Plug Placement 102
Example When the cement stinger is pulled above the plug, The last "drop" of cement is leaving the stinger, Then the displacement volume is: V = Stinger capacity X distance to top plug. 5"DP19,5# -> 9,15lpm V= 9,15 x 1450 = 13267 Litre mud + 50 m Spacer = 457 litre Total displacement volume: 13724 litre
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Balanced Plug Placement 103
Exercise: Set 200m balanced cement plug inside 12 14" hole. Use 3 ½” 13,3 Ibs/ft DP, cap. 3,86 lpm. 50 m spacer between DP and open hole Bottom of plug at 3000 m Calculate 1. Required plug cement volume, 2. Spacer volumes ahead and behind 3. Displacement volume.
Balanced Plug Placement 104
Question
If the mud density is greater than the cement density should you over displace or under displace?
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SQUEEZE CEMENTING
Squeeze Cementing - Definition 106
• Injection of Cement Slurry into
packer
the voids behind the casing tubing FORMATION
• Dehydration of cement requires:
fluid-loss, porous (permeable) matrix, differential pressure, time. • Injection below or above
fracture pressure
casing DEHYDRATED CEMENT
cement slurry
cement nodes
PRIMARY CEMENT CHANNEL BEHIND CASING
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Squeeze Cementing - Applications 107
• • • • •
Primary cement job repair Unwanted Water Production High Gas-Oil Ratio (GOR) Casing Splits or Leaks Non-productive or Depleted Zones
Squeeze Cementing - Methods 108
Squeeze techniques:
High pressure - above formation frac pressure Low pressure - below formation frac pressure
Pumping techniques:
Hesitation Running
Placement techniques:
Packer/Cement Retainer Bradenhead
Coiled tubing
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Low Pressure Squeeze 109
Squeeze pressure below fracture pressure Best way to squeeze the pay zone Use small volume of slurry Applicable for : Multiple zones Long intervals Low BHP wells Naturally fractured formations
High Pressure Squeeze 110
Fracturing is necessary to place cement in the void Requires placement of large volumes of slurry Wash or acid ahead to minimize pump rates required to
initiate fracture
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Running Squeeze 111
Continuous pumping until final squeeze pressure is attained Clean fluid in the hole Large slurry volumes without fluid loss control Low or high pressure squeeze Applications
Water flow Abandon perforations Increase cement top Casing shoes Liner tops Block squeeze Lost circulation zones
Hesitation Squeeze 112
Intermittent pumping Low pump rates Small slurry volumes Long job times Applications
Channel repair Long perforated interval Long splits in casing Lost circulation
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Bradenhead Squeeze 113
Done through tubing or drill
pipe without packer Advantages No tools are used (simplicity) Cost Disadvantages Casing and wellhead are exposed to pressure
BO P
CEMEN T Sand BRIDGE PLUG
Packer with Tailpipe Squeeze 114
• Downhole Isolation tool • Casing and wellhead
protection • Tailpipe for placement or setting a bridge plug • Long intervals
Packer Tail Pipe
CEMENT
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Cement Retainer Squeeze 115
Drillable Isolation Tool Similar to packer without tailpipe Applications Squeeze pressure trapped
CEMENT RETAINER CEMENT Sand BRIDGE PLUG
Coiled Tubing Squeeze 116
Applications Producing wells Through tubing Advantages Cost Accurate placement
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Cement Chemistry & Additives
The Clinker and Its Components 118
Cement is made of Limestone and clay or shale mixed in
the right proportions Each run may be slightly different due to impurities Cement is heated in a rotary kiln from 2600 to 2800 degrees F What comes out of the kiln is called clinker
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The Clinker and Its Components 119
The clinker is the mixture formed by the clinkering process.
The clinker has four components: C3S, C2S, C3A, and C4AF The letters in the clinker names are not chemical formulas. Instead, the letters represent abbreviations of chemical formulas: C – CaO S – SiO2 A – Al2O3 F – Fe2O3
The Clinker and Its Components 120
Clinker
Scientific Name
Chemical Formula
Properties in Cement
C3S
Tricalcium silicate
3CaO . SiO2
Major component (50 to 60%) Strength development
C2S
Dicalcium silicate
2CaO . SiO2
Final compressive strength
C3A
Tricalcium aluminate
3CaO. AlO3
Sets rapidly Controlled by gypsum Early strength development
C4AF
Tetracalcium aluminoferrite
4CaO . Al2O3. Fe2O3 Little influence
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Portland Cement 121
After the clinker is formed and cooled, it is moved to a second grinding
mill where it is combined with 1.5% to 5% gypsum (CaSO4. 2H2O), by weight of clinker. When added in this amount (generally +/- 3%), gypsum prevents "flash set" by controlling the hydration of C3A. If more than 5% gypsum is added to the clinker, the cement undergoes
a "false set." Excess gypsum causes false set because it tends to hydrate quicker than the cement. The clinker and gypsum mixture is ground and blended to form Portland cement. Cement reactivity to water depends a lot on surface area, which is
related to the size of the cement grains. Cement grain size ranges from 1 to 100 microns (average size around 30 microns).
API Cement Classes 122
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API Cement Classes 123
Cement Additives 124
Cement must be placed in wells ranging from shallow to
very deep Additives are used to adjust cement properties and tailor the cement to specific needs
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Cement Additives 125
Extenders Lightweight additives or extenders are used to decrease
the density of cement Excess mix water can be used to decrease the density to a limited extent Excess water increases thickening time, increases free water and reduces compressive strength
Cement Additives 126
Extenders • • • •
Bentonite is the most common light weight additive Bentonite will tie up extra mix water reducing density Light weight cements have as much as 12% bentonite Adding bentonite thickens the cement slurry and it must be thinned by adding a thinner or friction reducer
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Cement Additives 127
Extenders Perlite is volcanic glass bubbles that has some times been
used in geothermal wells because of its insulating properties Perlite is considerably more expensive Gilsonite and kolite are used to reduce density; however, their primary function is as a lost circulation material Gilsonite is a black asphalt Kolite is crushed coal
Cement Additives 128
Extenders Foamed cements are also used to reduce the density of the
slurry In a foamed cement, nitrogen is added to the cement mixture Very low densities can be obtained with foamed cement but they are more expensive
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Cement Additives 129
Weighting Agents Hematite is one of the more common additive for high
density cement due to its high specific gravity For smaller increases in density, barite can be used Barite is ground fine and requires more mix water to keep the slurry pumpable Sand can be added to increase the density due to low mix water requirements
Cement Additives 130
Densified slurries can be used up to 17.5 ppg A densified slurry is produced by reducing the mix water
and adding a dispersant to make it thin enough to pump Salt can be used to increase the density of a slurry Salt increases the density of the liquid phase
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Cement Additives 131
At low temperatures, it would
take too long for the cement to set up so accelerators are added to the cement Decrease the thickening time
of cement for shallow, low temperature applications
Cement Additives 132
As a rule of thumb,
accelerators are inorganic compounds
Calcium chloride is the most common accelerator It is used in concentrations from 1 to 3%
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Cement Additives 133
A little salt will
accelerate A lot of salt will retard the cement
Cement Additives 134
Retarders Increase the thickening time of cement for deeper, hotter applications Typically retarders are organic compounds
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Cement Additives 135
Retarders One of the most common retarders is calcium
lignosufonate Sodium Chloride is a retarder at high concentrations As bottomhole temperatures change, the type of retarder will change
Cement Additives 136
Friction loss additives (Dispersants): are used to
thin the cement slurry •
Organic acids
•
Lignosulfonate
•
Alky aryl sulfonate
•
Phosphate
•
Salt
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Cement Additives 137
Lost circulation material • Granular material such as gilsonite, kolite, perlite and
walnut hulls • Organic compounds can
retard the cement
Other Additives 138
Antifoam/ defoamer agents Bonding agents Gas migration control additives, etc. Fluid Loss Control
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139
Cement Evaluation
Cement evaluation 140
Cement bond logs are used to: •
• • •
Determine hydraulic isolation between zones of interest Locate cement top Determine feasibility of a cement squeeze Evaluate the quality of the cement
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Cement evaluation 141
Pipe to Cement Bond Directly related to surface finish of the pipe. A clean surface greatly enhances the bond potential.ie, no
grease, oil spots or paint on the pipe exterior. The pipe to cement bond was formerly the top priority. Today
the cement to formation is now considered more critical.
Cement evaluation 142
Cement to Formation Bond Generally determines whether there will be gas or liquid
communication in the annulus. Hydraulic bond across permeable zones is largely influenced by
the presence or absence of mud filter cake. Permeable formations will leach fluids so cement with water
loss additives must be used in these conditions.
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Cement evaluation 143
Two types of cement evaluation tools : The
Sonic Tools The Cement Bond Log The Radial Bond Tool
The Ultrasonic Tools The Circumferential Acoustic Scanning Tools
Acoustic Bond Logs 144
Acoustic cement bond logs do not directly measure hydraulic seal. Instead they measure the loss of acoustic energy as it propagates
through casing. This loss of acoustic energy can be related to the fraction of the
casing perimeter covered with cement.
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Travel Time (Transit Time) 145
For free-pipe, the travel time should match the expected time for that
casing size. For bonded pipe the travel time should increase as it triggers later
arrivals. If the travel time decreases below casing arrival time and the
amplitude drops then suspect eccentralization. If the travel time decreases below casing arrival time and the
amplitude increases suspect fast formations. The travel time difference between the 3ft and 5ft receivers should be
114 µs. If it less than this suspect fast formations.
Amplitude 146
For bonded pipe the amplitude should be low. For free-pipe the amplitude will be high. If the amplitude is intermediate cross check with the cement
map to see if it’s due to cement channeling or low compressive strength cement.
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Decentralized Tools String 147
Centring of the Tool is critical for valid measurements. If the tool is eccentered there are 2 paths for the sonic signal to take the travel time will be less than the expected travel time and the amplitude will be low which will falsely indicate good bonding.
CBL Tool 148
Advantage: Widely Used Method to Evaluate the Cement Job. Used to Evaluate the Zonal Isolation, Bonding to Casing, Bonding to
Formation, and Cement Compressive Strength. Tool Response Characterized and Well Documented.
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CBL Tool 149 Casing
Formation
B
Cement
TRANSMITTER
A
C
D
G 3 FT RECEIVER
E
F 5 FT RECEIVER
CBL Log 150
Free Pipe
Partial Bond
Good Bond
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CBL Tool 151
Disadvantage: Affected by tool centralization, fluid attenuation, pressure and
temperature. Affected by fast formations, thin cement sheath. Gives only qualitative cement-formation bonding information. Omni-directional signal- Assumes uniform distribution of cement
in the annulus. Cannot evaluate the radial placement of cement materials in the
casing formation annulus. Does not provide positive channel identification.
Sector Tool (Radial Bond Tool) 152
Measures the quality of the cement bond laterally around
the circumference of the casing. It has a single omni-directional transmitter The 3 foot near spaced receiver is divided into 8 radial segments measure 45° increments to produce cement map for channel identification. The receiver located at 5 feet is the traditional omni-directional sensing. The amplitude of the received acoustic signal in each of the segments represents radial variations in material in the casing-formation annulus. These radial variations in the signal amplitude could be possible channels or voids in the cement
GR
Electronics
Transmitter
3 Ft. Receiver & 8 Radials
5 Ft. Receiver
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Sector Tool (Radial Bond Tool) 153
Advantages Less affected by heavy drill fluids. Can log in #18 ppg mud Not affected by oil based mud. Identifies channels. Not affected by casing thickness. Good in wells with corrosion. Centralized very easily in deviated wells up to 60°
Sector Tool (Radial Bond Tool) 154
Disadvantages Three foot spacing will be affected by fast formation arrivals. Reads incorrect amplitudes in presence of micro annulus( unless run
under pressure) The RBT has sensors with 60 degree or 45 degree azimuthal resolution which cannot resolve the detection of small azimuthal channels.
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Ultrasonic Tools 155
Use a single rotating transducer combined
transmitter and receiver. Acquire ultrasonic waveform data for both cement
evaluation and casing evaluation in the same logging run or pass. The sampling rate of the rotating transducer can
provide 100% azimuthal coverage of the casing. Allows to distinguish cement, liquid, and gas in the
casing-formation annular space, based on the acoustic properties of the received waves
Ultrasonic Tools 156
Ultrasonic transducer is located 1.25” to
2.5” from the casing wall
Sends a beam of ultrasonic energy in the
500 kHz band.
Ultrasonic energy causes the casing to
vibrate or “ring”
Frequency and decay rate of return
signal is measured
Casing thickness and impedance of
cement sheath is calculated
By measuring the energy of the vibration
the presence or absence of cement can be detected.
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Ultrasonic Theory of Measurement 157
Ultrasonic transducer acts as transmitter & receiver • Transmits short pulse of acoustic energy • Receives multiple echoes from the casing, cement & formation Casing Resonates Casing resonance dampened in the presence of cement Transducer
Mud
Casing
Cement
Formation
Acoustic Impedance 158
The Impedance of a material defines the sound properties for that material. It is a product of the density of the medium and the velocity of sound of the medium. Z= p x c • Where Z = Impedance in MRayls • P = the density in kg/m3 • C = speed of sound in m/s • Example: Zwater = 1000 kg/m3 * 1500 m/sec = 1.5 MRayls • At any bed boundary (Z1 / Z2) with different Impedances, sound energy will be reflected and refracted. • Acoustic impedance of steel: Zsteel = 45 MRayls
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Ultrasonic Technique 159
The amplitude of the signal is proportional to the acoustic
impedance of the material behind pipe
Color
Acoustic Impedance
Material Behind Casing
White
0.00-0.38
Gas
Light Blue - Dark Blue
0.39-2.30
Liquid Gas - Fresh Water
Yellow - Light Brown
2.31-2.70
Heavy Drilling Fluid – Light Cement
Light Brown - Dark Brown
2.71-3.85
Low Impedance Cement
Dark Brown
3.86-5.00
Medium Impedance Cement
Black
> 5.00
High Impedance Cement
Acoustic Impedance Map 160
White color = Z < 1.4 Mrayls Blue color = 1.4
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