MSc Pet Geo 2019 exam - Final PDF

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IMPERIAL COLLEGE LONDON

Metals and Energy Finance (MSc)

Petroleum and Mineral Geoscience

Petroleum Engineering

Tuesday 8th January 2019, 14.00 to 15.00

Answer EITHER Questions 1 OR Question 2

DO NOT OPEN THIS EXAMINATION PAPER UNTIL INSTRUCTED TO DO SO BY THE INVIGILATOR

Imperial College London

Answer EITHER Questions 1 OR Question 2 QUESTION 1 Material balance for a gas field

(i) Define the difference between the producing gas/oil ratio, the solution gas/oil ratio and the cumulative gas/oil ratio. Show a phase diagram for a black oil that illustrates the meaning of the solution gas/oil ratio. (12 marks)

(ii) You have the following production data for a gas field that might be produced by a natural water drive. Gp Pressure Bg (106 scf) (MPa) (rb/scf) 0 38 0.000605 75 37 0.000624 160 36 0.00066 235 35 0.000702 310 34 0.000755 33 0.00735 32 0.00779 31 0.00824 30 0.00892 The initial water saturation is 0.15 and the residual gas saturation, from laboratory measurements, is 0.26. The material balance equation is:  Bg i  We  G p  G1    Bg B g  

Assuming a simple aquifer model, make an approximate estimate of the original gas in place and the value of the aquifer size times the aquifer compressibility. You may neglect the compressibility of the connate water and rock in the gas field itself. (18 marks) (iii) What is the recovery factor now? What is the average gas saturation in the field? What fraction of the recovery to date can be attributed to water drive, and what to gas expansion? What is the pressure drop necessary for water influx to invade the whole field? What is the likely final recovery factor? Explain your working carefully.

(20 marks) Total: 50 marks

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QUESTION 2 You measure the following from appraisal wells in an oilfield:

Depth (m) 3,482 3,739 3,862

Fluid and density (kg.m-3) Gas, 410 Oil, 530 Water, 1,020

Pressure (MPa) 34.54 35.65 36.72

The acceleration due to gravity = 9.81 ms-2. surface. (i)

Depths are measured from the

Is the reservoir normally pressured, over pressured or under pressured? Explain your answer. (4 marks)

(ii)

Find the depths of the free oil and free water levels. Hence find the height of the oil column. (18 marks)

(iii)

Explain carefully the concept of capillary pressure: in equilibrium, how does the capillary pressure vary above the free water level? (4 marks)

(iv)

The top of the field is located at 3,450m. What is the capillary pressure between gas and water at the top of the field? (14 marks)

(v)

The average horizontal cross-sectional area of the field is 14 km2, while the average porosity and water saturation in the hydrocarbon-bearing zones are 0.17 and 0.28 respectively. The oil formation volume factor is 1.3. The net-to-gross is 0.72. Estimate the original oil in place. (10 marks)

Total: 50 marks

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