RECENT ADVANCES IN THE MEASUREMENT OF PORE VOLUME COMPRESSIBILITY OF RESERVOIR ROCKS

摘要

The compressibility of a reservoir at different pressures is an important parameter affecting reserve forecasts and field development strategies.Among the four definitions proposed by Zimmerman(1991,2000),the pore volume compressibility,C_(pc) affects the reservoir engineering calculations the most,as it serves as a major energy source for reservoirs.The most commonly-used technique involves using liquid-saturated core plugs connected to a laboratory setup which controls the confining pressure and the pore pressure,and monitors the fluid volume changes in order to derive an average value of C_(pc).Computerized Tomography(CT) scanners have been used by the petroleum industry for calculating among others,the porosity of core plugs.The changes in the X-ray attenuation coefficient as a function of pressure at different slice locations can be used to calculate the pore volume compressibility.This paper presents a fast new technique involving dual-energy CT-scanning in order to determine the pore volume compressibility.Several tests were conducted on actual core plugs taken from a Middle-Eastern carbonate reservoir and results were compared against those from conventional pore volume compressibility measurements on the same plugs and they matched very well within the range of repeatability of such tests.The results also matched published results(Hariri et al.,1995) on cores taken from the same reservoir.Some of the advantages of the CT-based technique are also discussed in the paper which include the generation of multiple C_(pc) curves,each at a different slice location,the’visualization’of the changes,the possibility of using either hydrostatic or triaxial cells to make the test more case specific,the possibility of measuring permeability under different stress conditions before,during and after the test and the possibility of observing the failure of the rock under stress if there is a mechanical failure.