Impact of fluid adsorption on geomechanical properties of shale gas reservoir and shale gas recovery rate

Shale gas reservoirs comprise of various minerals like clay and organic matters. After hydraulic fracturing, large number of water together with CH4 remains in reservoirs. In this case, fluid adsorption is one of obvious fluid-shale interactions and affects geomechanical properties of shale which are important for shale gas production. In this paper, experimental observations of shale property change due to fluid adsorption were illustrated and discussed. It was suggested that those experimental observations result from the internal strain between different minerals and microcracks initiation inside shale. Based on the poroelastic theory and rock damage theory, models of Young's modulus and permeability were established to consider effects of those physical processes. Those models were verified by over ten groups of experimental results. Meanwhile, an experimental method was proposed to identify the impact of gas adsorption on permeability. Finally, the impact of fluid adsorption on recovery rate of shale gas reservoirs was analysed through numerical simulations. The results illustrate that the fluid adsorption strongly affect the recovery rate, and indicate that those factors need to be seriously considered for shale gas production design.