Study on experiment conditions of marine shale gas seepage law

Abstract

In order to discover the conditions suitable for testing shale gas seepage law, marine shale gas cores were taken from southern China. Samples were tested by using the differential pressure-flow rate method with actual gas under two modes (e.g. constant confining pressure and constant net confining pressure). Moreover, influences of the different confining pressure modes on the experimental results were analyzed. The results show that under constant confining pressure or constant net confining pressure mode, the gas seepage law curve has two sections. One is the curve section and the other is the pseudo linear section. Features of non-linear seepage were observed with the inflection points of 1 MPa and 1.3 MPa, as well as the average permeability damage rate of 52.41% and 40.56% respectively. The slip effect generated different influences. In the constant confining pressure mode, the change of injection pressure may cause stress sensitivity, which is not consistent with the actual situation in the reservoir development. The influence of the slip effect on seepage law was more substantial than stress sensitivity under the condition of low effective stress. In the constant net confining pressure mode a complete seepage law curve was obtained to simulate the seepage of the actual reservoir in a certain extent. The confining pressure effect had an insignificant influence on gas seepage. Comprehensive analysis shows that net confining pressure mode is the best way to test the seepage law of marine shale gas core in southern China.

Keywords

• Seepage law
• Constant confining pressure
• Constant net confining pressure
• Slip effect
• Effective stress
• Confining pressure effect