Seepage behaviors in shale gas affect the recovery significantly.However,previous studies on the seepage are often done under different confining pressure,and studied findings fail to reveal the intermediate principal stress affecting permeability.So,by employing a self-developed true tri-axial liquid-solid coupling system with multiple functions,many coupling experiments were conducted on the cubic samples from shale outcrop of the Silurian Longmaxi Formation,Fuling shale gas block.Moreover,matching with the Klinkenberg equation,experimental data were adopted to analyze how different intermediate principal stress impacts on both seepage behaviors and slippage effect.Results show that(i)this principal stress has a little influence on permeability evolution at smaller deviatoric stress,while an incremental effect along with the increasing deviatoric stress cannot be ignored;(ii)after fitting the relation of slippage factor to inherent permeability with experimental data,a better correlation is found,which can be used to predict this factor for shale in the same block;and(iii)when the deviatoric stress is less than or equal to 35 MPa,the slippage contribution is above 65%,indicating that the slippage effect dominates gas seepage in shale.
Intermediate principal stressSeepage behaviors in shale gasTrue triaxialSlippage ContributionDeviatoric stress
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