Course:- 28117Class:- 289FE

HERIOT WATT UNIVERSITYDEPARTMENT OF PETROLEUM ENGINEERING

Examination for the Degree ofMeng in Petroleum Engineering

Formation Evaluation Section A

Monday 7th January 200209.30 - 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 forcompletion of Script Book front covers and attachment of loose pages. Do notwrite 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 innumerical questions. No marks can be given for an incorrect answer if the methodof calculation is not presented. When the result is obtained using a chart bookfigure, give the number of the figure (eg, Rint-2a, CP-18, Gen-7).

This exam is in two main parts, Section A (closed-book), a series of general questionson 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 clearand concise. If you consider a question ambiguous, please record this in the form ofnotes. Alternatively, clarification may be sought from the invigilator.

A1.In a wellbore, we ran a logging string consisting of resistivity logs and both neutron anddensity porosity devices. What physico-chemical properties of the clay minerals presentin 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 therock 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 thepresence of fractures.

(3)

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

(3)

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

(3)

A4.Array Acoustic or Sonic tools can capture the full-waveforms of compressional, shearand 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 profilewhen we log a well. Sketch the resultant resistivity profile in terms of its distance awayfrom the well bore, and show the relative resistivity of deep, medium and shallowinvestigation logs, when run in the following fluids:

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

(4)

A6.Given:

Rw = 0.04 ohm-m at FTRt = 27 ohm-m at FT in the zone of interest∆t = 84 µsec/ft in the zone of interestρ

b= 2.31 g/cm3

ρma

= 2.67 g/cm3

ρf

= 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).

,

φρ ρρ ρ

φ

t t

t t

ma b

ma f

log ma

f ma

=−−

=−

−

∆ ∆

∆ ∆

(4)

continuedA6. 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 Archierelationship where ‘a’ = 1.37, ‘m’ = 1.80 and ‘n’ = 1.65.If the critical Sw is 45% is this zone hydrocarbon productive?

(4)

Swa

RwRtm

n= ⋅ ⋅φ

1

(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 T FRmfeqRweq

Rmfeq Rmf

RwRweq

Rweq

or chart SPT F

T F

= − + ⋅ °

= ×

= −+ ×

− +

°

−

°

( . ) log( )

.

.

.

log( / . )

.

log( / . )

61 0 133

0 85

0 131 10

0 5 10

2

1

19 92

0 0426

50 8

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 porespace? What use would you make of NMR data in an appraisal well?

(5)

(Enclosures: Gen-9 and SP-2)

Course:- 28117Class:- 289FE

HERIOT WATT UNIVERSITYDEPARTMENT OF PETROLEUM ENGINEERING

Examination for the Degree ofMeng in Petroleum Engineering

Formation Evaluation Section B

Monday 7th January 200212.30 - 14.30

NOTES FOR CANDIDATES

1. This is a Closed Book Examination.

2. 15 minutes reading time is provided from 12.15 – 12.30.

3. Examination Papers will be marked anonymously. See separate instruction forcompletion of Script Book front covers and attachment of loose pages. Do notwrite 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 innumerical questions. No marks can be given for an incorrect answer if the methodof calculation is not presented. When the result is obtained using a chart bookfigure, give the number of the figure (eg, Rint-2a, CP-18, Gen-7).

Section B

This Section deals with a suite of down-hole logs, attached. The information you re-quire 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(FMud properties are:Mud Density is 11.0 ppg,Rm = 0.248 ohm.m @60˚ FRmf = 0.159 ohm.m @60˚ FRmc = 0.355 ohm.m @60˚ F

B9Zone 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 answerbook.

(15)

B10Determine the probable lithology within the intervals 11,410; 11,510,11,655 and 12,165feet by plotting 1 data point per depth on both a Neutron-Density cross-plot and a M&NPlot. (Blank plots attached)

If any ambiguity is seen, suggest potential causes and at least one solution.

(25)

B11Determine the appropriate Rw at 12,165 feet using the Rwa method and the Humbleequation. Determine a neutron-density porosity. Highlight any possible sources of error

(3)

B12Determine the invasion profile and Rt from the attached Tornado chart and the

resistivity profile between 11,590 and 11,600 feet.

(5)

B13Determine the Gamma ray shale index (IGR ) at 11,890, using a “clean” value at 12,180feet 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 thecalculation of Rw from Rwa?

(5)

(Enclosures: Logs, 2 pages, N - D X-plot template, M & N Plot template, and tornadochart, also Gen-9 and SP-2)

Page 1 of 2

Gamma Ray (GR)0 150 (GAPI)

Caliper (CALI)6 1 6 (in)

M. D

EP

TH

(ft)

11450

11500

11550

11600

11650

11700

11750

SONI140 40 (us/f)

Compensated Neutron Log (CNL)45 -15 (%)

DENS1.95 2.95 (g/cc)

LL9S0.2 2000 (ohmm)

LL9D0.2 2000 (ohmm)

Flushed zone resistivity (RX0)0.2 2000 (ohmm)

11800

11850

11900

11950

12000

12050

12100

12150

12200