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Molecular Insights into Kerogen Deformation Induced by CO₂/CH₄ Sorption: Effect of Maturity and Moisture

Huang, Liang, Ning, Zhengfu, Wang, Qing, Qi, Rongrong, Cheng, Zhilin, Wu, Xiaojun, Zhang, Wentong, Qin, Huibo
Energy & fuels 2019 v.33 no.6 pp. 4792-4805
carbon dioxide, carbon sequestration, deformation, methane, molecular dynamics, nanopores, physicochemical properties, porosity, shale, shale gas, sorption, water content
Kerogen is the source of hydrocarbons in shale. As a soft nanoporous matter, kerogen constantly experiences mechanical deformation induced by subsurface stress environment and interplay with geofluid, significantly affecting the percolation and production of hydrocarbons. However, the associated coupling deformation of kerogen in reservoir conditions remains poorly understood. Here we quantify the kerogen coupling deformation induced by moisture uptake, CH₄ and CO₂ sorption, and mechanical compression using the combination of molecular simulations and poromechanics theory. The effects of kerogen maturity and preloaded moisture are discussed in detail. Our results show that moisture induced deformation is governed by the dynamic distribution of water molecules and the physicochemical characteristics of kerogen. Moisture induced volumetric strain increases with decreasing kerogen maturity or rising moisture content. The porosity of kerogen skeleton increases upon moisture uptake, although the residual porosity accessible for fluid presents a linearly decreasing trend. The coupling deformation upon gas sorption results from the combined effect of sorption swelling and mechanical compression. The coupling volumetric strain increases with rising kerogen maturity or declining moisture content, contrary to results for moisture uptake. The total deformation, coupling sorption–pressure–moisture effect, rises with increasing kerogen maturity. The evolution the total deformation follows with moisture content depends on the kerogen maturity. Results of this work can help improve the estimation of fluid-in-place in a shale gas reservoir and the understanding of the chemomechanical coupling associated with CO₂ sequestration and CO₂ fracturing.