A universal nanoscopic swell behavior model for gas shales

Hydraulic fracturing to tap unconventional shale gas reservoirs causes a volume change of the active clay minerals matrix in the gas shale structure, resulting in the clogging of the tiny nanopores and consequently undermining the production of the shale gas. Due to the complex natural structure and fabric of clay and non-clay minerals associated with high in-situ stresses at pre and post-fracking and the practical difficulties in the replication of the field stress conditions in the lab testing facilities, swell potential from the macro and micro investigations do not provide reliable and universally applicable results. None of the existing macro level and few molecular-level studies incorporate simulations cover natural structure of gas shales. In this study, we present comprehensive molecular level simulations based volume change constitutive model for clay minerals combining the effects of cation exchange capacity, density, water content, in-situ stress state, exchangeable-cations type and proportion, pore fluids, and the dissolved salts. Although in this paper, the developed protocol have been demonstrated for the gas shales, it can equally be used for several other fields involving the use of clay minerals such as agriculture, medicine, petroleum, environment, and geotechnical engineering.