Formation Evaluation Exam

Course:- 28117 Class:- 289FE HERIOT WATT UNIVERSITY DEPARTMENT OF PETROLEUM ENGINEERING Examination for the Degree of Meng in Petroleum Engineering

Formation Evaluation Section A Monday 7th January 2002 09.30 - 11.30 NOTES FOR CANDIDATES 1.

This is a Closed Book Examination.

2.

15 minutes reading time is provided from 09.15 – 09.30.

3.

Examination Papers will be marked anonymously. See separate instruction for completion of Script Book front covers and attachment of loose pages. Do not write your name on any loose pages which are submitted as part of your answer.

4.

Attempt ALL Questions. Answer in the blue books provided.

5. Return all logs with your Answer Books. 6.

Marks for each Question are given in brackets.

7.

This examination represents 100% of the Class assessment.

8.

State clearly any assumptions used and intermediate calculations made in numerical questions. No marks can be given for an incorrect answer if the method of calculation is not presented. When the result is obtained using a chart book figure, give the number of the figure (eg, Rint-2a, CP-18, Gen-7).

22/10/13

This exam is in two main parts, Section A (closed-book), a series of general questions on formation evaluation and Section B (open-book), a specific log based problem. Section A The questions in this section require a short answer, which may be numerical. Be clear and concise. If you consider a question ambiguous, please record this in the form of notes. Alternatively, clarification may be sought from the invigilator. A1. In a wellbore, we ran a logging string consisting of resistivity logs and both neutron and density porosity devices. What physico-chemical properties of the clay minerals present in the sandstone formation of interest may influence the formation evaluation and why? Give an example in each case.

(4)

A2. The porosity measured in a formation is dependent upon the physical properties of the rock fabric making up the formation. Detail the principal controls on porosity (3) In the same formation, detail how porosity and permeability might be affected by the presence of fractures.

(3)

A3. The minerals that make up reservoir rocks give off Natural Gamma radiation. What are the three radioisotopes that we commonly detect using the spectral gamma method?

(3)

What minerals may be principally responsible for these responses? Name two of the commonest sources of radiation of each spectral type.

(3)

A4. Array Acoustic or Sonic tools can capture the full-waveforms of compressional, shear and Stoneley arrivals. What are the three principal uses of these waveform data?

(3)

A5. The invasion of the drilling fluid into the formation results in a fluid distribution profile when we log a well. Sketch the resultant resistivity profile in terms of its distance away from the well bore, and show the relative resistivity of deep, medium and shallow investigation logs, when run in the following fluids:

Fresh mud, Salt-water zone. Salty mud, Hydrocarbon zone



(4)

A6. Given: Rw Rt ∆t ρb ρma ρf

= 0.04 ohm-m at FT = 27 ohm-m at FT in the zone of interest = 84 µsec/ft in the zone of interest = 2.31 g/cm3 = 2.67 g/cm3 = 1.00 g/cm3

In a sandstone matrix, with an acoustic velocity of 5400 ft/sec in the fluid and 18,000 ft/ sec in the matrix, calculate porosity using the two weighted average equations provided, one for density one for acoustics, (Wyllie).



φ =

ρma − ρb ρma − ρf

φ =

∆t log − ∆t ma ∆t f − ∆t ma



(4)

continued

22/10/13

A6. continued Is the value for porosity about the same for both the density and acoustic models? Using the calculated density porosity, calculate fluid saturation from the Archie relationship where ‘a’ = 1.37, ‘m’ = 1.80 and ‘n’ = 1.65. If the critical Sw is 45% is this zone hydrocarbon productive? Sw = n

a 1 ⋅ Rw ⋅ m φ Rt



(4)

(1)

A7. We have drilled a well into an apparent water bearing formation of moderate porosity. The drilling fluid is fresh water based and an SP run shows a deflection of -71 millivolts (i.e. to the left). Rmf is 0.55 ohm.m at the formation temperature of 140°F. Determine the Rw of the formation from the relationships: SSP = −(61 + 0.133 ⋅ T°F )log(

Rmfeq ) Rweq

Rmfeq = Rmf × 0.85

Rw = −



Rweq + 0.131 × 10 −0.5Rweq + 10

  1  −2  log( T ° F / 19.9 ) 

  0.0426    log( T ° F / 50.8 ) 

or chart SP 2

Use Chart Gen-9 to determine the NaC1 equivalent ppm

(5)

Now propose the most appropriate logging tool suite for this well to obtain lithology, porosity and formation fluid saturations. Minimise cost while maximising information. Justify your choice.

(5)

A8. The T2 response of the NMR log has been correlated with what aspect of the pore space? What use would you make of NMR data in an appraisal well?

(Enclosures: Gen-9 and SP-2)

22/10/13

(5)



22/10/13

Course:- 28117 Class:- 289FE HERIOT WATT UNIVERSITY DEPARTMENT OF PETROLEUM ENGINEERING Examination for the Degree of Meng in Petroleum Engineering

Formation Evaluation Section B Monday 7th January 2002 12.30 - 14.30 NOTES FOR CANDIDATES 1.

This is a Open Book Examination.

2.

15 minutes reading time is provided from 12.15 – 12.30.

3.

Examination Papers will be marked anonymously. See separate instruction for completion of Script Book front covers and attachment of loose pages. Do not write your name on any loose pages which are submitted as part of your answer.

4.

Attempt ALL Questions. Answer in the blue books provided.

5. Return all logs with your Answer Books. 6.

Marks for each Question are given in brackets.

7.

This examination represents 100% of the Class assessment.

8.

State clearly any assumptions used and intermediate calculations made in numerical questions. No marks can be given for an incorrect answer if the method of calculation is not presented. When the result is obtained using a chart book figure, give the number of the figure (eg, Rint-2a, CP-18, Gen-7).

22/10/13

Section B This Section deals with a suite of down-hole logs, attached. The information you require is as follows: You have a suite of logs comprising, CALI (Caliper in inches), GAPI (Gamma ray), SONI (Sonic/acoustic), DENS (Bulk Density), CNL (Neutron Porosity), LL9S (Laterolog Shallow), LL9D (Laterolog Deep), RXO (Flushed zone - shallow resistivity) The bit-size is 8.5 inches and the mud is water-based. The zones of interest are from 11,430 - 12,190 feet. The Bottom Hole temperature at 12,924 ft is 240˚ F, Mean surface temperature is 60(F Mud properties are: Mud Density is 11.0 ppg, Rm = 0.248 ohm.m @60˚ F Rmf = 0.159 ohm.m @60˚ F Rmc = 0.355 ohm.m @60˚ F B9 Zone the log putting the zone boundaries in track 1. Indicate: (a) The possible/probable lithology and, (b) Where permeable, the potential/probable fluid contents. Mark a maximum of 5 zones, including shales and hand this log back with your answer book.

(15)

B10 Determine the probable lithology within the intervals 11,410; 11,510,11,655 and 12,165 feet by plotting 1 data point per depth on both a Neutron-Density cross-plot and a M&N Plot. (Blank plots attached) If any ambiguity is seen, suggest potential causes and at least one solution.

(25)

B11 Determine the appropriate Rw at 12,165 feet using simplified Archie’s equation, Humble formula and Tornado chart’. Determine a neutron-density porosity. Highlight any possible sources of error (3) B12 Determine the invasion profile and Rt from the attached Tornado chart and the resistivity profile between 11,590 and 11,600 feet.

(5)

B13 Determine the Gamma ray shale index (IGR ) at 11,890, using a “clean” value at 12,180 feet and your choice of the most appropriate maximum shale value on the log. What implications does this have for the choice of water saturation equation and the calculation of Rw from Rwa?

(5)

(Enclosures: Logs, 2 pages, N - D X-plot template, M & N Plot template, and tornado chart, also Gen-9 and SP-2) Page 1 of 2

22/10/13

22/10/13

22/10/13

0

Gamma Ray (GR) (GAPI)

6 150

M. DEPTH (ft)

6

Caliper (CALI) 1 (in)

11450

11500

11550

11600

11650

11700

11750

22/10/13

1.95

DENS (g/cc)

45

Compensated Neutron Log (CNL) (%)

140

SONI (us/f)

2.95 -15 40

0.2

Flushed zone resistivity (RX0) (ohmm)

2000

0.2

LL9D (ohmm)

2000

0.2

LL9S (ohmm)

2000

11800

11850

11900

11950

12000

12050

12100

12150

12200