engineering Homework
Jim_Ak
hw_17_oil_compressibility_probs1.docxPetr 3520 Homework 17
Oil Compressibility Problems
Assigned: Sun, March 8, 2015 Name:
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Oil Compressibility Equations |
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(Thermodynamic) Definition of Isothermal Compressibility [Eqn (1)] (units are 1/pressure; for petroleum engineers, usually 1/psi) |
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In terms of ordinary derivative (understanding that T = const) [Eqn (2)] |
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In terms of V and p….(this is a(n) (useful) approximation) [Eqn (3)] |
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Integrated form of Eqn (2) [Eqn (4)] |
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Integrated form of Eqn (3) [Eqn (5)] |
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Expansion (V) of fluid of volume V which has undergone an average p (over the entire volume V) (rearranged Eqn (3)) [Eqn (6)] |
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Series representation of ex….. |
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1. Draw a p-V diagram for a pure component with one isotherm. Label the liquid, two-phase, and vapor regions. Explain how the concept of compressibility (both for liquid and vapor) is represented in that picture.
2. Give four examples of volume changes that occur in an oil/free gas/water reservoir as pressure drops.
3. Draw a Bo vs. p curve. Explain which part of the curve illustrates isothermal compressibility. What is the slope of this part of the curve? What feature on this picture illustrates thermal expansion (volume change due to temperature change)?
4. At bubble point pressure pBP = 4450 psi, B0BP = 1.5 RVB/STB, and co = 8.8·10-6 psi-1. Find Bo at p = 5000 psi using (a) Eqn.(4) and (b) Eqn. (5). (c) Draw the Bo vs. p curve for this oil. [ Bo = 1.49 RVB/STB ]
5. Equations (4) and (5) look different but give essentially the same answer. Why?
6. Is co constant for an oil above its bubble point?
7. An oil reservoir (with a fluid filled pore volume of 85 million bbls) is discovered at an initial average pressure pi = 6000 psi. Fluid tests indicate that the oil has a bubble point of 4860 psi. The averaged compressibility of both the connate water and the oil present is c = 8.8·10-6 psi-1. Assume the rock and formation pore volume remains constant. As oil is produced from the reservoir, assume that pressure changes occur instantly over the entire reservoir. (Not true, since pressures will be lower near wells.) When the average pressure in this reservoir has dropped to the bubble point (4860 psi), how many RVB of oil have been removed from the reservoir? If Bo = 1.30 RVB/STB and Rs = 800SCF/STB for this oil, how many STB of oil have been removed? How many MCF of gas has been produced at the surface? (Hint: Use Eqn. (6)) [ RVB produced = 852.7·103 RVB oil; Np = 655.9·103 STB; Gp = 524.75 MMCF gas ]
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