Chapter 2 Dry Gas Reservoir: Example 1 [PDF]

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CHAPTER 2 DRY GAS RESERVOIR Example 1 The following data are given for the Bell Gas Field: Area = 160 acres Øavg = 22% Swi = 23% Sgr after water displacement = 34% Bgi (3250psia) = 0.00533 ft3/SCF Bg (2500 psia) = 0.00667 ft3/SCF Bg (500 psia) = 0.03623 ft3/SCF h = 40 ft a) b) c) d) e) f) g) h) i)



Initial gas in place Gas in place after volumetric depletion to 2500 psia Gas in place after volumetric depletion to 500 psia Gas in place after water invasion at 3250 psia Gas in place after water invasion at 2500 psia Gas in place after water invasion at 500 psia Gas reserve by volumetric depletion to 500 psia Gas reserve by full water drive; i.e. at 3250 psia Gas reserve by partial water drive; i.e. at 2500 psia



Example 2 A gas reservoir has the following characteristic; A = 3000 acres T = 150oF



h = 30 ft zi = 0.82



Ø = 0.15 Swi = 20% P, psia



Pi = 2600 psia z



2600 0.82 1000 0.88 400 0.92 Calculate the cumulative gas production and recovery factor at 1000 and 400 psia.



Example 3 The following pressures and cumulative production data is available for a natural-gas reservoir; P, psia z Gp, MMMSCF 2080 0.759 0 1885 0.767 6.873 1620 0.787 14.002 1205 0.828 23.687 888 0.866 31.009 645 0.900 36.207 a) Estimate the initial gas in place b) Estimate the recoverable reserve at an abandonment pressure of 500 psia. Assume za = 1 c) What is the recovery factor at the abandonment pressure of 500 psia. Example 4 Time, years 0 0.5 1 1.5 2 Ø = 13% Swi = 0.52



Pressure, psia 1798 1680 1540 1428 1335 h = 54 ft T = 164oF



z 0.869 0.87 0.88 0.89 0.9 A = 1060 acres



Calculate the GIIP volumetrically and from MBE. Example 5 Pressure, psia 6000 5300 4520 3640 3100 2600 2120 2028 1760 1570



Gp , SCF 0 7737328.244 13536207.06 23488811.39 30905455.55 38671313.90 47318522.34 49122795.64 53512916.85 58302139.98



Estimate; a) Gas initial in place b) Recoverable amount of gas at 1358 psia.



z 1.0135 1.0006 0.9627 0.8972 0.863 0.8502 0.8525 0.855 0.8617 0.8765



Gp (MMMSCF) 0 0.96 2.12 3.21 3.92



Example 6 After producing 360 MMSCF of gas from a volumetric gas reservoir, the pressure has declined from 3200 psia to 3000 psia. Bg3200 psia = 0.005278 ft3/SCF Bg3000 psia = 0.005390 ft3/ SCF Calculate GIIP. Example 7 The M Sand is a small gas reservoir with an initial pressure of 3200 psia and temperature of 220oF. Pressure – production history and gas volume factor are given as follow; P, psia 3200 2925 2525 2125



Gp, MMSCF 0 79 221 452



Gas FVF, ft3/SCF 0.0052622 0.0057004 0.0065311 0.007736



a) Show that this reservoir is producing under water drive. b) Volumetric calculation on the M Sand showed that the initial gas in place is 1018 MMSCF. If the san d is under partial water drive, what is the volume of water encroached at the end of each period? There is no appreciable water production. Example 8 A volumetric gas field has an initial pressure of 4200 psia, porosity of 17.2% and connate water of 23%. Gas FVF at 4200 and 750 psia are 0.003425 and 0.01852 ft3/SCF, respectively. Estimate; a) GIIP (SCF/ ac-ft) b) Initial gas reserves assuming the abandonment pressure of 750 psia (SCF/ac-ft) c) Initial reserves of a 640 acres unit whose average net production thickness is 34 ft, assuming an abandonment pressure of 750 psia. d) Recovery factor based on an abandonment pressure of 750 psia.



Example 9 Fifty billion standard cubic feet of gas has been produced from a dry gas reservoir since its discovery. The reservoir pressure during this production has dropped to 3600 psia. The company which operates the field has decided to use the reservoir as a gas storage reservoir. A gas with a gravity of 0.75 is to be injected until the average pressures reaches 4800 psia. Assume the reservoir behaves volumetrically, determine the amount of SCF of the gas that must be injected to raise the reservoir pressure from 3600 to 4800 psia. The initial pressure and temperature of the reservoir were 6200 psia and 280 oF, respectively and the specific gravity of the reservoir gas is 0.75. Example 10 The following information is available on a volumetric gas reservoir; Initial reservoir temperature, Ti = 115oF Initial reservoir pressure, Pi = 3500 psia Specific gravity of gas, γg = 0.65 (air = 1) Thickness of reservoir, h = 20 ft Porosity of the reservoir, Ø = 10% Initial water saturation, Swi = 25% After producing 300 MMSCF, the reservoir pressure declined to 2500 psia. Estimate the areal extent of this reservoir. Example 11 a) The gas cap of the St. John Oil Field had a bulk volume of 17000 ac-ft when the reservoir pressure had declined to 634 psi. Core analysis shows an average porosity of 18% and average interstitial water of 24%. It is desired to increase the recovery of oil from the field by repressuring the gas cap to 1100 psi. Assuming that no additional gas dissolves in the oil during repressuring, calculate the SCF required. The deviation factors for both the reservoir gas and the injected gas are 0.86 at 634 psi and 0.78 at 1100 psia, respectively, both at 130oF. b) If the injected gas has a deviation factor of 0.94 at 634 psi and 0.88 at 1100 psi, and the reservoir gas deviation factors are as in (a), recalculate the injected gas required. Example 12 The following production data are available from a gas reservoir produced under volumetric control; Pressure, psia 5000 4000



Cumulative Gas Production, MMMSCF 200 420



The initial reservoir temperature was 237oF and the reservoir gas gravity is 0.7. a) What will be the cumulative gas production at 2500 psia? b) What fraction of the initial reservoir gas will be produced at 2500 psia? c) What was the initial reservoir pressure? Example 13 The initial volume of gas in place in the P Sand reservoir of the Holden Field is calculated from electric log and core data to be 200 MMMSCF underlying 2250 productive acres, at an initial pressure of 3500 psia and 140oF. The pressure-productive history is Pressure, psia



Production , MMMSCF



3500 (initial) 2500



0.0 75.0



Gas Deviation Factor at 140oF 0.85 0.82



a) What is the initial volume of gas in place as calculated from the pressure-production history, assuming no water influx? b) Assuming uniform sand thickness, porosity, and connate water, if the volume of gas in place from pressure-production data is believed to be correct, how many acres of extension to the present limits of the P Sand are predicted? c) If, on the other hand, the gas in place calculated from the log and core data is believed to be correct, how much water influx must have occurred during the 75MMMSCF of production to make the two figures agree? Example 14 A gas-producing formation has uniform thickness of 32 ft, a porosity of 19%, and a connate water saturation of 26%. The gas deviation factor is 0.83 at the initial reservoir pressure of 4450 psia and reservoir temperature of 175oF. a) Calculate the initial in-place gas per acre-foot of bulk reservoir rock. b) How many years will it take a well to deplete by 50% a 640 acre unit at the rate of 3 MMSCF/day? c) If the reservoir is under an active water drive so that the decline in reservoir pressure is negligible, and during the production of 50.4 MMMSCF of gas water invades1280 acres, what is the percentage of recovery by water drive? d) What is the gas saturation as a percentage of total pore space in the portion of the reservoir invaded by water?



Pseudo critical properties of miscellaneous natural gases and condensate well fluids



The Z−factor correlation chart of Standing and Katz