Abstract

The production of fluids from a reservoir often reduces pore pressure such that there is an increase in its effective stresses. During water flooding orgas injection the equilibrium rock stresses can also be altered in a similar dynamic manner. An understanding of these changes are of fundamental importance to performance prediction and management of the stress sensitive reservoirs.

Conventional laboratory methods for studying permeability under simulated burial conditions involve hydrostatic stresses, or sometimes anisotropic triaxial loading in which two of the principal stresses are equal. However, such conditions are rarely encountered in hydrocarbon reservoirs, and true-triaxial stresses are more representative. Whilst previous investigators have utilized true triaxial stresses on cylindrical and prismatic samples, such studies have been restricted by the limited deviatoric stress magnitudes which could be achieved with the test systems. In this investigation, laboratory equipment is being utilized to measure rock properties whilst applying the three principal boundary stresses independently using cubic samples. The apparatus uses closed-loop control, and can achieve deviatoric stresses in excess of 200 MPa and pore pressures to 70 Mpa.

This paper reports the experimental system and work which was carried out to examine the permeability hysteresis effect under hydrostatic, triaxial, and true triaxial stress conditions. The experimental data are being incorporated into a reservoir simulator to investigate the changes in hydrocarbon recovery under different stress conditions. The main objectives are to integrate important petrophysical properties such as permeability and porosity with rock mechanics, to investigate how permeability alteration under in situ stress conditions might affect hydrocarbon recovery.

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