Study on Stress Sensitivity of Longmaxi Formation Shales in East Sichuan

Abstract

 Depletion development is the main way of shale gas reservoir development. The stress sensitivity of shale will have made a great impact on the correct evaluation of shale gas productivity. At the time that the shale gas reservoir in Fuling is on development, the study of stress sensitivity of shale gas reservoir gas formation, Longmaxi formation, will make a great significance to the high efficient development of shale gas reservoir in Fuling even to the shale gas development in our country. This article uses the Longmaxi formation outcrop in east Sichuan and the PDP-200 pulse decay permeameter applied for the evaluation of stress sensitivity of shale permeability. Two different plans, constant confining pressure-decreasing inner pressure test and constant internal pressure-increasing confining test, are adopted to do the permeability experiments of the same core with horizontal bedding. The results show that with the increase of effective stress affected on the shale, the permeability of shale decreases exponentially in tests, and according to decline index that decreasing process is divided into two sections. It respectively embodies the stress sensitivity of shale fracture permeability and shale matrix permeability. At the same time, the tests show permeability hysteresis when compare two tests: constant confining pressure test and constant internal pressure test. And the fracture closing pressure showed in the internal pressure test is lower than the confining pressure test result.