Numerical Modeling of Multiphysics Constitutive Relations Governing Water Migration into Variably Saturated Sorptive Shale

The water invasion within shales easily causes damage to the hydrocarbon flow. However, the water imbibition mechanisms are still unclear, and the mathematical connection between stress-dependent permeability and water imbibition was rarely known. As a result, in this paper, a numerical simulation model coupled with water imbibition, shale deformation, and shale permeability alteration was established to analyze how water imbibition lead to an alteration in geomechanical properties and shale gas permeability. The results showed that the proposed model was validated with the high pressure imbibition experimental data of shale samples. Moreover, more comprehensive water imbibition mechanisms included in the model can improve the prediction accuracy for the water imbibition process. Furthermore, the water imbibition distance was demonstrated to be a power function of water imbibition duration and clay mineral content, an exponential expression of initial matrix permeability, and a positively linear equation of the injection pressure difference. Last but not least, the elastic modulus after hydration is negatively related to matrix permeability, clay mineral content, and injection pressure difference. These bigger control factors will result in clay swelling and cementation weakening during the water imbibition, finally enhancing stress sensitivity and decreasing permeability. Finally, the cores with a high clay mineral content and injection pressure difference are likely to enhance stress sensitivity, obeying the positive power function and linear function, respectively. The findings can provide a scientific basis to study the water-sensitive damage to flow capacity and stress sensitivity for unconventional formations in a water environment.