PETROLEUM ENGINEERING 310 SECOND EXM October 23, 2002 Ground Rules Do all your work on the test paper and the space provided for the answer, do no write on the back. Grading will be based on approach and answers. Remember to show all your work!!!! nswers with no evidence of calculations where they are required will not be graded. The point value of each question or problem is provided in parentheses after the question or problem statement. Read the problem statement very carefully and do exactly what is required and the way it is required. For example: if I request labels you MUST label, if I require units you MUST provide units. Time allotted for the test is 120 minutes. Only interpretation questions are allowed. This examination is open book, no homework is allowed. You can have two cheat sheets with formulas if you wish. You cannot discuss this test with your neighbor. Statement When you have finished the exam. Read and sign the statement below, then return in the examination booklet. I pledge that I have neither given nor received aid in completing this exam. I have followed the strictures of the Texas &M University ggie Code of honor during this exam. Signature: 1/10
2 1. Two identical cells ( and B) with a volume of 600 cm 3 each can be connected trough a valve (v a ). core sample with a bulk volume of 79 cm 3 is placed in cell B and vacuum is pulled in the cell by opening valve v b and closing valve v a. Cell contains helium at 200 psia. fter evacuation of cell B, valve v b is closed and valve v a is opened. fter equilibration the final cell pressure is 105 psia. The temperature was kept constant at 75 o F. You need to determine de porosity of this core sample and the volume of the rock (10 points) Pressure Gauges Vacuum Pump v a v b Cell Cell B Page 2/10
3 2. cylinder with 0.36 ft 3 capacity is filled with 5 lb of a dry gas mixture with 95 moles % of C 1 and 5 moles % of C 2. The pressure in the vessel is 4,500 psia and the temperature is 75 o F. What is the z-factor of this gas? (10 points) 3. To make reasonable gas recovery predictions, estimates of the initial gas in place in each reservoir must be made. In natural gas reservoir engineering applications the following formula is used to estimate the gas in place in a reservoir G = 7,758 V p (1- S wi ) /Bg Where G is the initial gas in place in SCF, V p the reservoir pore volume, and 7,758 is a conversion factor, bbl/acre-ft. Standard conditions are p=15.025 psia and T=60 o F. Estimate the gas in place (G) of a reservoir with an areal extent of 5,000 acres, average formation thickness (h) of 30 ft, average porosity of 15% and interstitial water saturation (S wi ) of 30%. The reservoir temperature is 200 o F and the initial reservoir pressure is 4,000 psia. (15 points) The following data for the natural gas is available. Page 3/10
4 Gas Specific Gravity 1.2 Molar fraction of H 2 S 0.08 Molar fraction of CO 2 0.05 Determine the gas in place. Show intermediate calculations and write the results in the space provided in the following table. Write down the equations and/or figures used to evaluate this problem. Property Value Units T pc P pc T pr P pr z B g G Page 4/10
5 4. Sketch on a single plot the behavior of the oil viscosity, the oil formation volume factor (B o ), and the solution gas oil ratio (R s ) versus pressure for an oil with PI gravity of 20 and another oil B with PI gravity of 45. Label all pertinent points. Both oils are at the same temperature. (10 points) Page 5/10
6 5. wet gas is produced through a separator at 400 psia and 150 o F to a stock tank at 70 o F. The separator gas oil ratio is 70,000 scf/stb and the stock tank vents 2,500scf/STB. The oil PI gravity is 60. Determine the recombination molar ratios for the stock tank and for the separator. For the compositions of the separator liquid and the reservoir fluid it is sufficient that you make the calculations only for methane (the rest is repetitive). Show the equations used. (15 points). Mole Fraction Separator Gas y i SEP Mole Fraction Stock Tank Gas y i STO Mole Fraction Stock Tank Oil x i STO M wi C 1 0.8814 0.4795 0.0026 16.043 C 2 0.073 0.1769 0.0054 30.07 C 3 0.0297 0.1755 0.0194 44.097 C 4 0.0099 0.0956 0.0341 58.123 C 5 0.004 0.0515 0.0605 72.15 C 6 0.0016 0.019 0.0902 86.177 C 7 + 0.0004 0.002 0.7878 135 Mole Fraction Separator Oil x i SEP Mole Fraction Reservoir Gas z i Page 6/10
7 Show all intermediate work 6. Estimate the isothermal compressibility of a dry gas for use at 4,200 psia using the following data taken at 195 o F (10 points) Pressure (psia) Z - factor 6000 1.1252 5600 1.0736 5200 1.0222 4800 0.9711 4400 0.9207 4000 0.8715 3600 0.8243 3200 0.7952 2800 0.7824 2600 0.781 Page 7/10
8 7. The ggie Brazos Reservoir is producing a 50 o PI stock tank oil and a 0.9 specific gravity separator gas. The field separator conditions are 200 psia and 70 o F. Estimate the solution gas oil ratio at the bubble point and the bubble point pressure of this reservoir. The production history is plotted below. (10 points) Production Data - ggie Field Producing Gas Oil Ratio (scf/stb) 2000 1800 1600 1400 1200 1000 800 600 400 200 GOR (scf/stb) verage Production Pressure 3800 3600 3400 3200 3000 2800 2600 2400 2200 Pressure (psia) 0 0 1000 2000 3000 4000 5000 6000 Cumulative Oil Production (MSTB) 2000 Page 8/10
9 8. The following differential liberation test has been provided to you from the laboratory. You need to determine the following reservoir engineering properties. Oil Formation Volume Factors (B od )(5 points) Solution gas oil ratios in SCF/STB (R sd ) (15 points) Differential Depletion Test: Stinky Oil Well Temperature = 180 o F Pressure (psig) cm 3 oil cm 3 gas Gas z factor 2777.0 53.5 0.0 2600.0 52.3 2.4 0.879 2350.0 50.8 3.4 0.869 2100.0 49.5 3.4 0.868 1850.0 48.1 3.8 0.869 1600.0 46.9 4.3 0.876 1350.0 45.8 4.9 0.887 1100.0 44.6 6.0 0.900 850.0 43.4 7.8 0.918 600.0 42.1 11.4 0.939 350.0 40.8 22.2 0.963 184.0 39.4 33.5 0.980 0.0 34.6 716.4 1.000 0 @ 60 o F 31.5 0.0 B od (bbl/stb) R sd (SCF/STB) Show all your work. Useful Information 1 bbl = 158987.3 cc 1 ft 3 = 28316.85 cc (ft 3 = cu ft) T sc = 60 o F p sc = 14.7 psia B g zt = 0. 0282 p 1bbl = 5. 615cu ft cu ft scf Page 9/10
10 The following table may help you to organize your calculations Differential Depletion Test: Stinky Oil Well Temperature = 180 o F Pressure (psig) 2777.0 2600.0 2350.0 2100.0 1850.0 1600.0 1350.0 1100.0 850.0 600.0 350.0 184.0 0.0 0 @ 60 o F B od (bbl/stb) R sd (SCF/STB) Page 10/10