A Compositional Model for CO2 Storage in Deformable Organic-Rich Shales
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AbstractIncreased development of resource shales near industrial areas is spawning interests in storing CO2 generated from the neighboring industries in depleted organic-rich resource shales. This work presents a compositional model for the flow of a multi-component hydrocarbon gas and CO2 in a deformable porous medium consisting of an inorganic and an organic matrix. The fully-coupled equations for fluid transport and geomechanics are solved using the Control Volume Finite Element Method.This work presents a mathematical model for CO2 storage in shales. The model accounts for the dispersed nature of kerogen in shale and can describe the advective and diffusive transport of the hydrocarbon components and CO2. The pressure- dependence of diffusion is modeled using the Maxwell-Stefan model, while desorption of the hydrocarbon species and adsorption of CO2 in kerogen is modeled with the Extended Langmuir Isotherm. The governing equations are solved implicitly for coupled geomechanics and flow. The developed simulator is used to model the primary depletion of a representative Barnett shale-gas reservoir, as well as the storage of CO2 in this depleted reservoir under various conditions.The simulation results from this work indicate that the storage capacity of organic-rich shales could be overestimated if we do not account for the pore-volume reduction due to the pore space occupied by the adsorbed gas. During primary recovery from organic-rich shales, the pore-pressure drops and some of the gases adsorbed on the surface of the organic pore walls are produced. This results in an increase in the pore volume available for subsequent CO2 storage. However, the pore-pressure drop also results in an increased effective stress, which could lead to a reduction in fracture conductivity and cumulative production. The model and simulator presented is capable of modeling the relative contributions of these coupled phenomena and the attending effect on CO2 storage.
