Analysis of Reservoir Performance kg/ko Curves and a Laboratory kg/ko Curve Measured on a Core Sample
- T.D. Mueller (California Research Corp.) | J.E. Warren (California Research Corp.) | W.J. West (California Research Corp.)
- Document ID
- Society of Petroleum Engineers
- Transactions of the AIME
- Publication Date
- December 1955
- Document Type
- Journal Paper
- 128 - 131
- 1955. Original copyright American Institute of Mining, Metallurgical, and Petroleum Engineers, Inc. Copyright has expired.
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Published in Petroleum Transactions, AIME, Volume 204, 1955, pages 128-131.
Two methods are used to obtain the relationship between ratio of gas to oil permeability and gas saturation. One method is to calculate a curve from field measurements of reservoir behavior: the other is to measure the relationship on a core sample in the laboratory. The curves resulting from these two methods are often compared and seldom found to agree. The most important reason for the nonagreement is often overlooked. This reason is that the performance kg/ko curve is calculated with the assumption of uniform pressure and saturation throughout the reservoir. To show the difference between performance type kg/ko curves and laboratory type kg/ko curves, two performance type kg/ko curves for two different production rates were calculated from the production performance of a hypothetical reservoir for which a laboratory type curve was assumed. Production performance of the hypothetical reservoir was calculated by use of International Business Machine's 701 Computer. The performance type kg/ko curves differed from the laboratory curve for the hypothetical reservoir. The performance type curve for the lowest production rate most nearly coincided with the laboratory curve.
Predictions of oil reservoir performance are often made with the aid of complex numerical calculations. An important quantity required in these calculations is the ratio of gas permeability to oil permeability (kg/ko) at a particular gas saturation. Two methods are used to obtain a relationship between this ratio and gas saturation. The curves resulting from these two methods are called performance kg/ko curves and laboratory kg/ko curves.
The performance curve is obtained from field measurements of reservoir behavior. Particular kg/ko values are calculated from the producing gas-oil ratio, the cumulative reservoir withdrawals, the original oil in place. the average reservoir pressure and the PVT properties of the reservoir fluids. The particular kg/ko values are then plotted against the average reservoir gas saturations for the entire history period. In order to use this derived kg/ko relationship for performance predictions, a curve through these points is extrapolated to higher gas saturations.
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