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TECHNICAL AND VOCATIONAL EDUCATION
TECHNICAL AND VOCATIONAL EDUCATION
Sample Questions & Worked Out
Sample Questions & Worked Out Examples
Examples
For
For
PE-04025
PE-04025
RE
RES
SE
ERV
RVOI
OI R E
R ENGI
NGI NE
NEE
ERI
RI NG
NG (( II ))
B.Tech(Second Year)
B.Tech(Second Year)
Petroleum Engineering
Petroleum Engineering
Ministry of Science and Technology
Department of Technical and Vocational Education Petroleum Engineering
Sample Questions for
PE 04025 RESERVOIR ENGINEERING I Chapter 1
1.*** The following experimental data were taken in determining the gas constant. An evacuated glass flask weighs 50g. Filled with pure nitrogen at 14.40 psia and 60°F, it weighs 51.16g. Filled with distilled water at 60° F, it weights 1050g. Calculate the gas constant from these data.
(5 marks) 2.* Calculate the volume of one pound mole of ideal gas will occupy at (a) 14.7 psia and 60°, (b) 14.7 psia and 32°F, (c) 14.7 psia plus 10 oz and 80°,and (d) 15.025 psia and 60°F.
(10 marks) 3.* A 1000 cubic-foot tank is filled with air to a pressure of 25 psia at 140°F. Calculate and place in tabular form for comparison, the molecular weight, specific gravity, pound moles in the tank, pound in the tank, molecules in the tank, SCF at 14.7 psia and 60°F, SCF at 14.7 psia and 32°, SCF at 14.7 psia +10oz and 80°F, and SCF at 15.025 psia and 60°F, for air, carbon dioxide, methane, and propane. (10 marks )
4.** A 500 cubic-foot tank contains 10 lb of ethane at 90°F. (a) How many moles are in the tank? (b) What is the pressure of tank in psia ? (c) What is the molecular weight of mixture. (d) What is the specific gravity of mixture. (10 marks)
5.*** Calculate the molecular weight of air if it contains 78.06 per cent nitrogen, 21.0 per cent oxygen, and 0.94 per cent argon by volume. ( 5 marks )
6.*** What are the molecular weight and specific gravity of a gas which contains one third each of methane, ethane, and propane by volume. (5 marks)
7.** A ten-pound block of Dry Ice (solid CO2) is placed in a 50 cubic-foot tank which contains
air at atmospheric pressure 14.7 psia and 75°F. What will be the final pressure of the sealed tank when all the Dry Ice has evaporated and cooled the gas to 45°F? (5 marks )
8.* (a) A 55,000 bbl (nominal) pipe line tank has a diameter of 110 ft and a height of 35 ft. It contains 25 ft of oil at the time suction is taken on the oil with pumps which handle 20,000 bbl per day. The breather and safety valves have become clogged so that a vacuum is drawn on the tank. If the roof is rated to withstand ¾ oz per sq in. pressure ,how long will it be before the roof collapses? Barometric pressure is 29.1 inches. Neglect the fact that the roof is peaked and that there may be some leak. (b) Calculate the total force on the roof at the time of collapse. (c) If the tank had contained more oil, would the collapse time have been greater or less? Explain.
(20 marks) 9.* What is the molecular weight of a gas which contains 50 per cent C1, 30 per cent C2, and
20 per cent C3by weight? (5 marks )
10.* What volume will 100 lb of a gas of 0.75 specific gravity ( air = 1.0 ) at 100 psia and 100°F ? (5 marks )
11.* A 10 cubic-foot tank contains ethane at 25 psia surrounding a balloon 2 ft in diameter filled with methane at 35 psia. Neglecting the volume of the rubber in the balloon and assuming isothermal conditions, calculate the final pressure when the balloon is burst. (10 marks )
12.** (a) What per cent methane by weight does a gas of 0.65 specific gravity contain which composed only of methane and ethane? What per cent by volume. (b) Explain why the per cent by volume is greater than the per cent by weight? ( 5 marks )
13.* (a) A 1500 cubic-foot tank contains methane at 30 psia and 80°F. To it are added: 1.80 moles of ethane at 14.4 psia and 60°F, 25 lb of butane at 75°F, 4.65×1026molecules of propane at 30°F, and 500 SCF(14.7 psia and 60°F) of nitrogen. If the final temperature of the mixture is 60°F, what is the final pressure of the tank? (b) Of what significance are the temperature given in the part (a), with the mole of ethane, the pound of butane, and the molecules of propane? Explain.
(20 marks) 14.* A 50 cubic-foot of tank contains gas at 50 psia and 50°F. It is connected to another tank which contains gas at 25 psia and 50°F. When the valve between the two is opened, the pressure is equalizes at 35 psia at 50°F. What is the volume of other tank ? (5 marks )
15.** A high-pressure cell has a volume of 0.330 cu ft and contains gas at 2500 psia and 130°F, at which conditions its deviation factor is 0.75. When 43.6 SCF measured at 14.7 psia and 60°F are bled from the cell through the wet test meter, the pressure dropped to 1000 psia , the temperature remaining at 130°F. What is the gas deviation factor at 1000 psia and 130°F?
(10 marks) 16.* (a) Calculate the bulk volume of the gas cap of a reservoir whose aerial extent is 940 acres, i.e., the area enclosed by the zero thickness contour. The areas enclosed by the 4,8,12,16,and 20-ft isopach lines are 752 ,526,316,142, and 57 acres, respectively. The greatest thickness within the 20-ft isopach line is 23 ft . (b) Show that when the ratio of the area enclosed by two successive contours is 0.50, the error introduced by using the trapezoidal formulae is 2 per
cent greater than the pyramidal formula. (c) What error is introduced by using the trapezoidal formula instead of the pyramidal formula when the ratio of the areas is 0.333? (20 marks) 17.** A volumetric gas field has an initial pressure of 4200 psia, a porosity of 17.2 per cent , and connate water of 23 per cent. The gas volume factor at 4200 psia is 292 SCF/cu ft and at 750 psia is 54 SCF/cu ft. (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 . ( 10 marks )
18.* A volumetric gas field has an initial pressure of 4350 psia, a porosity of 16.75 per cent , and connate water of 20 per cent. The gas volume factor at 4350 psia is 285 SCF/cu ft and at 755 psia is 57.5 SCF/cu ft. (a) Calculate the initial reserve of a 640-acre unit whose average net productive formation thickness is 34 ft, assuming an abandonment pressure of 755 psia. (b)
Calculate the recovery factor based on abandonment pressure of 755 psia. (10 marks)
19.* The “M” Sand is a small gas reservoir with an initial bottom-hole pressure of 3200 psia and bottom-hole temperature of 220°F. It is desired to inventory the gas in placed at three production intervals. The pressure production history and gas volume factor in cu ft/SCF at
standard condition of 14.7 psia and 60°F are as follows;
Pressure Cumulative gas Production Gas volume factor
psia MM CF cu ft / SCF
3200 0 0.0052622
2925 79 0.0057004
2525 221 0.0065311
2125 452 0.0077360
(c) Calculate the initial gas in place using production data at the end of each of the production intervals, assuming volumetric behavior. (b) Explain why the calculations of the part
20.** The gas cap of the “ S.J ”oil field had a bulk volume of 17000 ac-ft when the reservoir pressure had declined to the 634 psig. Core analysis shows an average porosity of 18 per cent, and
average interstitial water of 24 per cent. It is desired to increase the recovery of oil from the field by repressuring the gas cap to 1100 psig. Assuming that no additional gas dissolves in the oil
during repressuring, calculate the SCF (14.7psia and 60°F) required. The deviation factor for both the reservoir gas and the injected gas are 0.86 at 634 psig and 0.78 at 1100 psig, both at 130°F.
(10 marks) 21.** (a)A well drilled in to a gas cap for recycling purposes is found to be in an isolated fault block. After injecting 50MM SCF (14.7psia and 60°F), the pressure increased from 2500 to 3500psia. Deviation factors for the gas are 0.90 at 3500 and 0.80 at 2500 psia and the bottom hole temperature is160°F. What the cubic feet of gas storage space in the fault block? (b) If the average porosity is 16 per cent, average connate water is 24 per cent, and average sand thickness is 12 ft,
what is the aerial extent of the fault block? (10 marks)
22.* A gas reservoir under partial water drive produced 12.0MMM SCF (14.7psia and •
60 F) when the average reservoir pressure had dropped from 3000psia to 2200psia. During the same interval an estimated 5.20MM bbl of water entered the reservoir based on the volume of the invaded area. If the gas deviation factor at 3000psia and bottom-hole temperature of •
170 F is 0.88 and at 2200psia is 0.78, what is the initial volume of gas in place measured at 14.7psia and •
60 F? ( 10 marks ) 23.** A gas-producing formation has a uniform thickness of 32 ft, a porosity of 19 per cent, and connate water saturation of 26 percent. The gas deviation factor is 0.83 at the initial reservoir pressure of 4450psia and reservoir temperature of •
175 F. (S.C. 14.7psia and •
60 F) (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 percent a 640-acre unit at the rate of 3MM
SCF/day? (10 marks )
24.** Calculate the daily gas production including the condensate and water gas equivalents for a reservoir with the following daily production.
Separator gas production = 6MM SCF Condensate production = 100 STB Stock tank gas production = 21M SCF Fresh water production =10bbl
Initial reservoir pressure = 6000psia Current reservoir pressure = 2000psia Reservoir temperature =225 F•
Water vapor content at 6000psia and •
225 F = 0.86 bbl/MM SCF Condensate gravity = ο
50 API (10 marks )
25.* A gas condensate reservoir initially contains 1300 MSCF of residue ( dry or sale gas ) per ac-ft and 115 bbl of condensate. Gas recovery is calculated to be 85 per cent and condensate recovery 58 per cent by depletion performance. Calculate the value of initial gas and condensate reserves per ac-ft if the condensate sells for $ 2.50/bbl and the gas sells for 20 cent / MSCF.
(10 marks) 26.** 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 gravity of 52.0° API at 60F. (a) What is the gas oil ratio on dry gas basis? (b) What is the liquid content expressed in bbl/MMSCF on a dry gas basis?
(c) What is the liquid content expressed in GPM on a dry gas basis? (10 marks)
27.* The initial daily production from a gas-condensate reservoir is 186 bbl of condensate, 3750 MSCF of high pressure gas, and 95 MSCF 0f stock tank gas. The tank oil has a gravity of 51.2° API at 60° F. The specific gravity of the separator is 0.712 and of the stock tank gas, 1.30.
The initial reservoir pressure is 3480 psia and reservoir temperature is 220°F. Average hydrocarbon porosity is 17.2 per cent . Assume standard condition of 14.7 psia and 60°F.
(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? (10 marks) 28.** In a PVT study of a gas-condensate fluid 17.5 cu cm of wet gas (vapor) measured at cell pressure of 2500 psia and temperature of 195°F was displaced into an evacuated low-pressure
receiver of 5000 cu cm volume which was maintained at 250°F to insure that on liquid phase developed in the expansion. If the pressure of the receiver rose to 620mm Hg, what is the deviation factor of the gas in the cell at 2500 psia and 195°F, assuming the gas in the receiver behaved ideally? (10 marks )
29.** Calculate the contents of a tank of ethane in moles, pounds, molecules, and SCF. Data are as a 500 cu ft tank of ethane at 100 psia and 100°F. (5 marks )
30.* Calculate the gas deviation factor of the Bell Field gas from its specific gravity. Use the Fig.1.2 and Fig.1.3 of textbook. The required data are as follows:
Specific gravity = 0,665 (air =1.0) , CO2content = 0.10 mole per cent
N2 content = 2.07 mole per cent, Reservoir temperature = 213°F
Reservoir pressure = 3250 psia (10 marks )
31.** Calculate the net volume of an idealized reservoir from the isopachous map data (planimetered areas):
Area (acres) A0 A1 A2 A3 A4 A5 A6
450 375 303 231 154 74 0 Interval (ft) - 5 5 5 5 5 4
( 5 marks )
32.* Calculate the initial gas reserve of a 160 acre unit of the Bell Gas Field by volumetric depletion and under partial and complete water drive. The required data are given as follows:
Average porosity = 22 %, Connate water = 23 % , Areas = 160 acres , Net productive thickness = 40 ft, Bgi =188.0 SCF/ cu ft at pi =3250 psia
Bg =150.0 SCF/ cu ft at 2500 psia and 27. 6 SCF/ cu ft at 500 psia,
Residual gas saturation after water displacement = 34 % (10 marks )
33.* Calculate the initial gas in place and the initial reserve of a gas reservoir from pressure production data for a volumetric reservoir. Required data are as follows:
Initial pr. = 3250 psia , Reservoir temp. = 213°F , Standard pr. =15.025 psia , Standard temp. = 60°F , Cumulative production = 1.0 × 109SCF, Avg. res. pr. = 2864 psia ,
Gas deviation factor at 3250 psia =0.910 , Gas deviation factor at 2864 psia =0.888 , Gas deviation factor at 500 psia = 0.951 . (10 marks)
34.** Calculate the water influx and residual gas saturation in water drive reservoir. Required data are as follows:
Average porosity = 0.172 , Average connate water = 0.25 ,
Initial pressure = 3200 psia, Final pressure = 2925 psia, Bw = 1.03 bbl/STB ,
G p = 935.4 MMSCF at 14.7 psia and 60°F ,
Bgi = 0.005262 cu ft/SCF,14.7 psia and 60°F ,
Bgf = 0.005700 cu ft/SCF, 14.7 psia and 60°F,
Cumulative water production = 15200 bbl (surface) ,
Bulk reservoir volume, initial = 415.3 MMCF, (10 marks)
35.* Calculate the total daily gas production including the gas equivalents of water and condensate. Required data are as follows:
Initial reservoir pressure = 4000 psia , Reservoir temperature = 220°F ,
Current reservoir pressure = 1500 psia, Condensate gravity = 55°API (0.759 sp. gr) Daily gas saperator production = 3.25 MMSCF, Daily stock tank gas =10 MSCF , Daily stock tank condensate = 53.2 STB , Daily fresh water production = 5.5 bbl
(10 marks) 36.** The “M” Sand is a small gas reservoir with an initial bottom-hole pressure of 3200 psia and bottom-hole temperature of 220°F. It is desired to inventory the gas in placed at three production intervals. The pressure production history and gas volume factor in cu ft/SCF at
standard condition of 14.7 psia and 60°F are as follows;
Pressure Cumulative gas Production Gas volume factor
psia MM CF cu ft / SCF
3200 0 0.0052622
2925 79 0.0057004
2525 221 0.0065311
2125 452 0.0077360
(a) Show that a water drive exists by plotting the cumulative production versus p/z. (b) Based on electric log and core data , volumetric calculations on the “ M “ Sand showed that initial volume of gas in place is 1018 MMSCF . If the sand is under the partial water drive, what is the volume of water encroached at the end of each of the periods? There was no appreciable water production.
( 20 marks ) 37.** The gas cap of the “ S.J ”oil field had a bulk volume of 17000 ac-ft when the reservoir pressure had declined to the 634 psig. Core analysis shows an average porosity of 18 per cent, and
average interstitial water of 24 per cent. It is desired to increase the recovery of oil from the field by repressuring the gas cap to 1100 psig. Assuming that no additional gas dissolves in the oil
during repressuring, calculate the SCF (14.7psia and 60°F) required. The deviation factor for both the reservoir gas and the injected gas are 0.86 at 634 psig and 0.78 at 1100 psig, both at 130°F. If injected gas has a deviation factor 0.94 at 634 psig and 0.88 at 1100 psig, and the reservoir gas deviation factors are as above, recalculate the injected gas required. (20 marks)
38.** The initial daily production from a gas-condensate reservoir is 200 bbl of condensate, 3700 MSCF of high pressure gas, and 100 MSCF 0f stock tank gas. The tank oil has a gravity of 51.2° API at 60° F. The specific gravity of the separator is 0.712 and of the stock tank gas, 1.30. The initial reservoir pressure is 3475 psia and reservoir temperature is 223°F. Average hydrocarbon porosity is 17.5 per cent . Assume standard condition of 14.7 psia and 60°F. (a)Calculate the specific gravity (air = 1.0) of the total well production. (b)Calculate the gas deviation factor of the initial reservoir fluid at initial reservoir pressure. (c)Calculate the initial moles in place per ac-ft. (10 marks )
39.** Calculate the initial gas reserve of a 225 acre unit of the “ X “ gas field by volumetric depletion and under partial and complete water drive. The required data are given as follows:
Average porosity = 18.75 %, Connate water = 22.35 % , Areas = 225 acres , Net productive thickness = 30 ft, Bgi =188.0 SCF/ cu ft at pi =3250 psia
Bg =150.0 SCF/ cu ft at 2500 psia and 27. 6 SCF/ cu ft at 500 psia,
Residual gas saturation after water displacement = 27.5 % (10 marks ) 40.* Calculate the initial oil and gas in place per acre-foot for a gas condensate reservoir.
Given:
Initial pressure 2740 psia Reservoir temperature 215°F Average porosity 25% Average connate water 30% Daily tank oil 242bbl Oil gravity , 60°F 48°API Daily separator gas 3100MCF Separator gas gravity 0.650
Daily tank gas 120MCF Tank gas gravity 1.20 (10 marks ) 41.* The initial daily production from a gas-condensate reservoir is 200 bbl of condensate, 3700 MSCF of high pressure gas, and 100 MSCF 0f stock tank gas. The tank oil has a gravity of 51.2° API at 60° F. The specific gravity of the separator is 0.712 and of the stock tank gas, 1.30. The initial reservoir pressure is 3475 psia and reservoir temperature is 223°F. Average hydrocarbon porosity is 17.5 per cent . Assume standard condition of 14.7 psia and 60°F.(a) Calculate the more fraction which is gas in the initial reservoir fluid. (b) Calculate the initial (sales) gas and condensate in place per acre-foot. (10 marks )
42.*** Gas was contracted at 5.5 cents per MCF at contract conditions of 14.4 psia and 80°F. What is the equivalent price at a legal temperature of 60°F and pressure of 15.025 psia?
(5 marks ) 43.** A gas producing formation has a uniform thickness of 32 ft, a porosity of 19%, and connate water saturation of 26%. The gas deviation factor is 0.83 at the initial reservoir pressure of 4450 psia and reservoir temperature of 175°F.(S.C.14.7 psia and 60°F ). (a) If the reservoir is under an active water drive so that the decline in reservoir pressure is negligible, and during the production of 50.4MMM SCF of gas, measured at 14.7psia and •
60 F, water invades 1280 acres, what is the per cent recovery by water drive? (b) What is the gas saturation as per cent of total pore space in the water invaded portion of the reservoir? (10 marks )
44.* 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 200MMMSCF (14.7 psia and 60°F) underlying 2250 productive acres, at the initial pressure of 3500 psia and 140°F. The pressure-production history is
Pressure, psia Production ( MMMSCF ) Gas deviation factor at 140°F
3500 ( initial ) 0.0 0.85
2500 75.0 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?
(20 marks) 45.** Calculate the contents of a tank of ethane in moles, pounds, molecules, and SCF. Given a 1500 cu-ft tank of ethane at 325 psia and 120°F. (10 marks )
46.** Calculate the gas deviation factor of the Bell Field gas from its specific gravity. Given data are the following. Specific gravity 0.75, CO2 content is 0.15 moles per cent, N2content is 2.2 moles per cent, reservoir temperature 200°F, reservoir pressure 3500 psia. Used the Fig.1.2 and Fig.1.3. (10 marks )
47.* Calculate the gas deviation factor for the gas-condensate fluid whose composition at 5280 psia and 265°F is given as follows:
Component C1 C2 C3 C4 C5 C6 C+7
Gas condensate 87.07 4.39 2.29 1.74 0.83 0.60 3.80 Mol. wt C+7 225 181 112 157 …
Tank gravity, API 34.3 50.1 60.8 54.7 (10 marks)
48.* Calculate the gas deviation factor for the " Z " Field gas from its composition given below. Used the Fig.1.2 and 1.3.
Component Comp: Mole Fraction Mol: wt Pc Tc
Methane 0.8612 16.04 673 343 Ethane 0.0591 30.07 708 550 Propane 0.0358 44.09 617 666 Butane 0.0172 58.12 550 766 Pentane 0.0050 72.15 490 846 CO2 0.0010 44.01 1070 548 N2 0.0207 28.02 492 227 (20 marks ) 49.** Calculate the initial oil and gas in place per acre-foot for a gas condensate reservoir. Given data are as follows:
Initial pressure ………2740psia Reservoir temperature ……… ο
215 F Average porosity………..25 per cent Average connate water……….30 per cent Daily tank oil………242 bbl Oil gravity, 60ο F ……… ο
0 .
48 API Daily separator gas………3100 MCF Separator gas gravity……….0.650 Daily tank gas ………120 MCF Tank gas gravity……….1.20
Use the Fig.1.2 and 1.3. (10 marks)
50.* A 725 cubic-foot tank contains 12.5-lb of methane and 21.5-lb of ethane at 95°F. (c) How many moles are in the tank?
(d) What is the pressure of the tank in psia ? psig ? (e) What is the molecular weight of the mixture?
(f) What is the specific gravity of the mixture? (10 marks)
Ministry of Science and Technology
Department of Technical and Vocational Education Petroleum Engineering
Worked Out Examples for
PE 04025 RESERVOIR ENGINEERING I
1. Calculate the contents of a tank of ethane in moles, pounds, molecules, and SCF. Data are as a 500 cu ft tank of ethane at 100 psia and 100°F.
Solution: Assuming ideal gas behavior,
Moles = 8.324 7 . 559 732 . 10 500 100 = × × Pounds = 8.324×30.07 =250.3 Molecules = 8.324 × 2.733× 1026 = 2.275 × 1027 At 14.7 psia and 60°F, SCF = 8.324×379.4 = 3158 (or) SCF = 7 . 14 7 . 559 7 . 519 500 100 × × × = 3158 (or) SCF = 7 . 14 7 . 519 73 . 10 324 . 8 × × = p nRT = 3157
2. Calculate the gas deviation factor of the Bell Field gas from its specific gravity. Use the Fig.1.2 and Fig.1.3 of text book. The required data are as follows:
Specific gravity = 0,665 (air =1.0) , CO2content = 0.10 mole per cent
N2 content = 2.07 mole per cent , Reservoir temperature = 213F
Reservoir pressure = 3250 psia
Solution: From the Fig .1.2 the critical pressure and temperature corrected for CO2and N2
are
pc = 669 – ( 2.07× 1.7 ) + (0.10× 4.4 )
= 666 psia
Tc= 378 – ( 2.07 ×2.5 ) - ( 0.10 ×0.8 )
= 373°R
For 3250 psia and 213°F, pseudoreduced pressure and pseudoreduced temperature are
pr = c p p = 666 3250 = 4.88 , Tr = c T T + 460 = 373 213 460+ = 1.80
Enter Fig.1.3 with the values of pr = 4.88, and Tr = 1.80 . Then we obtain the
value of z = 0.90 .
3. Calculate the gas deviation factor for the " Z " Field gas from its composition given below. Used the Fig.1.2 and 1.3.
Component Comp: Mol: wt Pc Tc
Mole Fraction Methane 0.8612 16.04 673 343 Ethane 0.0591 30.07 708 550 Propane 0.0358 44.09 617 666 Butane 0.0172 58.12 550 766 Pentane 0.0050 72.15 490 846 CO2 0.0010 44.01 1070 548 N2 0.0207 28.02 492 227 Solution :
Mole Fraction×Mol: wt Mole Fraction×Pc Mole Fraction×Tc
13.81 579.59 295.39 1.78 41084 32.51 1.58 22.08 23.84 1.00 9.46 13.18 0.36 2.45 4.23 0.04 1.07 0.55 0.58 10.18 4.70 ... ... ... 19.15 666.67 374.40
The specific gravity may be obtained from the sum 19.15 , which is the average molecular weight of the gas , 661 . 0 97 . 28 15 . 19 = = SG
The sum 666.67 and 374.40 are the pseudocritical pressure and temperature, respectively. Then at 3250 psia and 213°F, the pseudocritical pressure and temperature
87 . 4 67 . 666 3250 = = r P 80 . 1 4 . 374 673 = = r T
The gas deviation factor using Fig. 1.3 is z = 0.91
4. Calculate the initial gas reserve of a 160-acre unit of the Bell Gas Field by volumetric depletion and under partial and complete water drive.
Given
Average porosity = 22 per cent Connate Water = 23 per cent
Residual gas saturation after water displacement = 34 per cent Bgi = 188.0 SCF / cuft at Pi = 3250 psia
Bg = 150.0 SCF / cuft at 2500 psia
= 27.6 SCF / cuft at 500 psia Area = 160 acres
Net productive formation = 40 ft
Solution :
Pore Volume = 43560 × 0.22 ×160 × 40 = 61.33 ×106cu ft
Initial gas in place ;
G1= 61.33 ×106 ×( 1- 0.23 ) ×188.0
= 8878 MMSCF
Gas in place after volumetric depletion to 2500 psia ; G2= 61.33 ×106×( 1- 0.23 ) ×150.0
= 7084 MMSCF
Gas in place after volumetric depletion to 500 psia ; G3= 61.33 ×106×( 1- 0.23 ) × 27.6
= 1303 MMSCF
Gas in place after water invasion at 3250 psia; G4= 61.33 ×106×0.34 ×188.0
= 3920 MMSCF
Gas in place after water invasion at 2500 psia; G5= 61.33 ×106×0.34 ×150
= 3128 MMSCF
Initial reserve by depletion to 500 psia ; G1– G3= ( 8878 – 1303 ) ×106
= 7575 MMSCF
Initial reserve by water drive at 3250 psia ; G1– G4= ( 8878 – 3920 ) ×106
= 4958 MMSCF
Initial reserve by water drive at 2500 psia ; ( G1– G2 ) + ( G2– G5 ) = ( G1– G5 )
= ( 8878 – 3128 ) ×106 = 5750 MMSCF
2 1 ( G – G ) = 2 1 ( 8878 – 3920 ) × 106 = 2479 MMSCF
5. Calculate the initial gas in place and the initial reserve of a gas reservoir form pressure- production data for a volumetric reservoir.
Given;
Initial Pressure = 3250 psia Reservoir temperature = 213°F Standard temperature = 60°F Standard pressure = 15.025 psia Cumulative production = 1.00×109SCF Average reservoir pressure = 2864 psia Gas deviation factor at 3250 psia = 0.910 Gas deviation factor at 2864 psia = 0.888 Gas deviation factor at 500 psia = 0.951
Solution;
The reservoir gas pore volume Vi
673 888 . 0 2864 673 910 . 0 3250 520 10 00 . 1 025 . 15 9 × − × × = × × V i V i Vi= 56.17 MM cu ft
The initial gas in place is
MMSCF p T T z V P G sc sc i i i 32 . 10 025 . 15 673 910 . 0 520 10 17 . 56 3250 6 = × × × × × = × =
The gas remaining at 500 psia abandonment pressure is
MMSCF p T T z V P G sc sc a i a a 1.52 025 . 15 673 951 . 0 520 10 17 . 56 500 6 = × × × × × = × =
The initial gas reserve based on a 500 psia abandonment pressure is the difference between the initial gas in place and remaining at 500 psia or
Gr = G - Ga
= (10.32 – 1.52 ) ×109 = 8.80 MMSCF
6. Calculate the water influx and residual gas saturation in water drive reservoir. Required data are as follows:
Average porosity = 0.172 , Average connate water = 0.25 , Initial pressure = 3200 psia, Final pressure = 2925 psia,
G p = 935.4 MMSCF at 14.7 psia and 60°F ,
Bgf = 0.005700 cu ft/SCF, 14.7 psia and 60°F,
Bw = 1.03 bbl/STB ,
Cumulative water production = 15200 bbl (surface) , Bulk volume invaded by water at 2925 psia = 13.04 MMCF.
Bulk reservoir volume, initial = 415.3 MMCF,
Solution:
Initial gas in place = G =
005262 . 0 ) 25 . 0 1 ( 172 . 0 10 3 . 415 × 6 × × − = 10180 MMSCF at 14.7 psia and 60°F We= 935.4×106× 0.005700 - 10,108 ×106 = ( 0.005700 – 0.005262 ) + 15200 × 1.03×5.615 = 960400 cu ft
This much water has invaded 13.04 MM cu ft of bulk rock, which initially contained 25 per cent connate water. Then the final water saturation of the flooded portion of the
reservoir is Porespace lux Water er Connatewat S w = + inf = 172 . 0 10 04 . 13 960400 ) 25 . 0 172 . 0 10 04 . 13 ( 6 6 × × + × × × = 0.68 or 68 percent
Then the residual gas saturation Sgr is 32 per cent.
---7. Calculate the initial oil and gas in place per acre-foot for a gas condensate reservoir. Given data are as follows:
Initial pressure ………2740psia Reservoir temperature ………215 Fο Average porosity………..25 per cent Average connate water……….30 per cent Daily tank oil………242 bbl Oil gravity, ο F
60 ……… ο
0 .
48 API Daily separator gas………3100 MCF Separator gas gravity……….0.650 Daily tank gas ………120 MCF Tank gas gravity……….1.20 Use the Fig.1.2 and 1.3.
Solution:
Average gas gravity = 0.670 120 3100 20 . 1 120 650 . 0 3100 = + × + ×
7883 . 0 5 . 131 0 . 48 5 . 141 = + = o γ 5 . 144 9 . 5 0 . 48 6084 = − = o M bbl SCF R 1000 13300 / 242 120 3100 = × + = 893 . 0 5 . 144 / 7883 . 0 132800 13300 7883 . 0 4584 670 . 0 13300 = × + × + × = w γ
From Fig. 1.2 , Tc = 425°R , Pc = 652 psia using the condensate curves. Then Tr = 1.59
and Pr = 4.20 , from which, using Fig. 1.3, the gas deviation factor is 0.82 at 2740 psia
and 215°F. Then the total initial gas in place per ac-foot of bulk reservoir rock is 1334 675 73 . 10 82 . 0 ) 30 . 0 1 ( 25 . 0 43560 2740 4 . 379 4 . 379 = × × − × × × × = = zRT pV G MCF/ac ft
Since the volume fraction equals the mole fraction in the gas state, the fraction of the total which is produced on the surface as gas is
9483 . 0 5 . 144 / 7883 . 0 350 4 . 379 / 4 . 379 / = × + = + = R R n n n f o g g g Then,
Initial gas in place = 0.9483×1334 = 1265 MCF/ac ft Initial oil in place = 95.1bbl /acft
13300 10 1265 3
= ×
8. A gas condensate reservoir initially contains 1300 MSCF of residue ( dry or sale gas ) per ac-ft and 115 bbl of condensate. Gas recovery is calculated to be 85 per cent and condensate recovery 58 per cent by depletion performance. Calculate the value of initial gas and condensate reserves per ac-ft if the condensate sells for $ 2.50/bbl and the gas sells for 20 cent / MSCF.
Solution: The value of initial condensate reserve = 115 × 0.58 = 66.7 bbl = 66.7× 2.5
= $ 166.75
The value of initial gas reserve = 1300 ×0.85 = 1105 MSCF = 1105× 0.20
9. 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 gravity of 52.0° API at 60F. (a) What is the gas oil ratio on dry gas basis? (b) What is the liquid content expressed in bbl/MMSCF on a dry gas basis? (c) What is the liquid content expressed in GPM on a dry gas basis?
Solution: Gas production rate = 742MSCF
Condensate production rate = 45.3 bbl
(c) Gas-Oil ratio on a dry gas basis = 16380 3 . 45 10 742 3 = × SCF/bbl
(d) Liquid content in barrel per million standard cu ft on a dry gas basis
Liquid content = bbl millionSCF SCF bbl / 05 . 61 16380 1 = (c) Liquid content in GPM = 1000 2.56 1 42 16380 1 = × × bbl gal SCF bbl GPM
10. The initial daily production from a gas-condensate reservoir is 186 bbl of condensate, 3750 MSCF of high pressure gas, and 95 MSCF 0f stock tank gas. The tank oil has a gravity of 51.2° API at 60° F. The specific gravity of the separator is 0.712 and of the stock tank gas, 1.30. The initial reservoir pressure is 3480 psia and reservoir temperature is 220°F. Average hydrocarbon porosity is 17.2 per cent . Assume standard condition of 14.7 psia and 60°F.
(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?
Solution: Initial daily production of condensate = 186 bbl Stock tank gas = 95 M SCF High pressure gas = 3750 M SCF S.G of separator gas = 0.712
S.G of tank gas = 1.3
API = 52.1°, T = 60°F, Pi= 3480 psia , Ti= 220°F , Φ =17.2% (c) Average gas gravity =
3750 95 712 . 0 3750 3 . 1 3 . 95 + × + × = 0.727 (d) Initial GOR = 186 10 ) 3750 95 ( + × 3 = 20672 SCF/bbl
(c) Molecular weight of condensate Mo =
9 . 5 6084 − API = 9 . 5 2 . 51 6084 − = 134.3
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