Assignment

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EXAMINATION 2023 (homework assignment) FUNDAMENTALS OF OIL AND GAS ENGINEERING 1. Material balance for a gas field (50 marks total) (i) 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 40 0.012 26 38 0.0132 52 36 0.0148 75 34 0.0166 93 32 0.0185 The initial water saturation is 0. 20 and the residual gas saturation, from laboratory measurements, is 0.25. The material balance equation is: g e g gi p B W B BGG +      −= 1 Assuming the pot aquifer model, plot a graph and use this to 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) (ii) What is the recovery factor now? What is the average gas saturation in the field? What is the relative contribution of gas expansion and aquifer drive to production? How would you produce this field? Explain your working carefully. (20 marks) (iii) What is the pressure at which the aquifer sweeps the entire reservoir leaving just the residual gas saturation behind? Comment on this value. (12 marks) 2. You measure the following from appraisal wells in a small oilfield: (50 marks total) Depth (m) Pressure (MPa) Fluid and density (kg.m-3) 2,971 32.14 Gas, 420 2,995 32.23 Oil, 780 3,015 32.41 Water, 1,040 The acceleration due to gravity = 9.81 ms-2. Depths are measured from the surface. (i) Is the reservoir normally pressured, over pressured or under pressured? (2 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 why the oil pressure should be close to the bubble point. How would you…