Abstract:

The objective of this study is to outline the best possible way to determine the pore-volume compressibility as input to reservoir engineering simulations. The best manner to determine the pore volume compressibility from core measurements is to apply the conditions as they are in-situ in the reservoir: Total stresses, stress changes and pore pressure changes over time, reservoir temperature, reservoir fluids and direct measurement of pore volume changes. In the article we discuss the possibilities and consequences of the mitigation of these requirements. One obvious mitigation is the application of effective stresses and loading under constant pore pressure. Two clear advantages are that the total stresses become much lower and that the pore volume changes can be measured more accurately under constant pore pressure. The drawback of the method is that the interpretation of these test results requires knowledge of Biot’s effective stress coefficient, which usually is stress-dependent. We derive expressions for the equivalent reservoir pressure, a concept allowing for interpretation of non-linear pore volume compressibility data. Finally we present and interpret laboratory data to demonstrate the power of the concept.

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