 # Question 1 A volumetric gas field has an initial pressure of 4200 ...

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Question 1 A volumetric gas field has an initial pressure of 4200 psia, a porosity of 17.2%, and connate water of 23%. The gas volume factor at 4200 psia is 0.003425 cu ft/SCF and at 750 psia it is 0.01852 cu ft/SCF. a. Calculate the initial in-place gas in standard cubic feet on a unit basis. b. Calculate the initial gas reserve in standard cubic feet on a unit basis, assuming an abandonment pressure of 750 psia. c. Explain why the calculated initial reserve depends on the abandoned pressure selected. d. Calculate the initial reserve of a 640-acre unit whose average net productive formation thickness is 34 ft, assuming an abandonment pressure of 750 psia. e. Calculate the recovery factor based on an abandonment pressure of 750 psia. Question 2 a. Consider the following reservoir explored and developed using two wells Based on the logs at wells W1 and W2, a fault is determined that seals the reservoir in the north. From expert geological interpretation, it is determined that the reservoir is dome shaped. The contour plot of depth to layer top has circular shaped contour lines. The cross-section of the reservoir is ellipse shaped. Both wells W1 and W2 do not intersect the GWC. A Drill Stem Test was performed on the well W1 and the reservoir pressure at a depth of 7053.5ft was determined to be 3200 psi. The specific gravity of the gas was determined to be 0.7. Using this information and assuming air = 16.457 lb/cu.ft and a normal pressured reservoir, with hydrostatic pressure given by: Pw = 0.45 D + 14.8 where D is the depth in ft. And correspondingly: Pg = D C dD dP gas         where C is a constant Determine the depth to the Gas Water contact. Given the contour plots above and the cross-section compute the bulk volume of the reservoir (i.e. the volume upto the Gas Water Contact). For this task you need to use the trapezoid equation with areas A1, A2 etc.. are areas of the half-circle in the contour plot. In order to compute the radii of these circles you will need to use the cross-section W1 W2 Depth7043.5 ft. 7083.5 ft. 7073.5 ft. 7063.5 ft. 7053.5 ft. 727 ft 40 N ft GWC = ? Ellipse shaped 7043.5 ft. W1 a b plot and the fact that the cross section is a ellipse. Equation of an ellipse: 1 2 2 2 2   b y a x where a is the major axis (see figure) and b is the minor axis (see figure). Given the following production data: Pressure (psia) Cumulative Gas Production MM SCF Gas Volume Factor cu. Ft/SCF 3200 0 0.0052622 2925 79 0.0057004 2525 221 0.0065311 2125 452 0.0077360 The initial average reservoir pressure is 3200 psia and the bottom hole temperature is 220oF. Standard conditions are 14.7 psia and 60oF. a) Calculate the initial gas in place using the production data at the end of each production interval, assuming volumetric behaviour. b) Do the calculated Gas in place indicate a water drive c) Show that a water drive exists by plotting the cumulative production vs. P/z d) Using the material balance equations for water influx and the graphical technique for fitting an aquifer We, determine the strength of the aquifer. Assume aquifer(water+void) is a weak function of pressure and is 1*10-6 psi-1 at 2925 psia, 1.8*10-6 psi-1 at 2525 psia and 3.8*10-6 psi-1 at 2125 psia. This increase in compressibility is basically to account for the fact that the pores in the aquifer are losing water that is an incompressible fluid and air occupies the voids. What is the initial gas in place predicted by the material balance calculation? How does this compare with the gas in place from the earlier volumetric calculations? Comment Question 3 A well produces 45.3 bbl of condensate and 742 MSCF of sales gas daily. The condensate has a molecular weight of 121.2 and a gravity of 52.0 oAPI at 60oF. a. What is the gas-oil ratio on a dry gas basis? b. What is the liquid content expressed in barrels per million standard cubic feet on a dry gas basis? c. What is the liquid content expressed in GPM on a dry gas basis? d. Repeat parts (a), (b) and (c) expressing the figures on a wet or gross gas basis. Question 4 The initial daily production from a gas-condensate reservoir is 186 STB of condensate, 3750M SCF of high-pressure gas and 95 M SCF of stock tank gas. The tank oil has a gravity of 51.2 oAPI at 60oF. The specific gravity of the separator gas is 0.712 and of the stock tank gas, 1.30. The initial reservoir pressure is 3480 psia, and the reservoir temperature is 220oF. Average hydrocarbon porosity is 17.2% and connate water saturation is 0.2. Assume standard conditions of 14.7 psia and 60oF. a. What is the average gravity of the produced gases? b. What is the initial gas-oil ratio? c. Estimate the molecular weight of the condensate. d. Calculate the specific gravity (air = 1.00) of the total well production. e. Calculate the gas deviation factor of the initial reservoir fluid (vapor) at initial reservoir pressure. f. Calculate the initial moles in place per acre-foot. g. Calculate the mole fraction that is gas in the initial reservoir fluid. h. Calculate the initial (sales) gas and condensate in place per acre-foot

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