(92d) From the Fundamentals of Porous Carbons Poromechanics to Applications for CO2 Sequestration and Gas-Shale

Coal is made of a microporous carbonaceous solid matrix and exhibits a high adsorption capacity. Gas-shale are in their matured state very close to coal. Adsorption of fluids in microporous carbons is known to induce dimensional changes. Understanding of adsorption-induced strain is critical for the industrial development of Enhanced Coal Bed Methane recovery (ECBM) and for gas-shale production. In this work, we present a general poro-mechanics modeling valid for microporous solids under adsorption and the application of this modeling to the specific case of carbon dioxide (CO2) and methane (CH4) adsorption in coal and kerogen.

We derived extended poro-mechanics constitutive equations valid whatever the size and morphology of pores i.e. valid for disordered microporous carbons such as coal. We then performed molecular simulations of adsorption of CH4 adsorption in a flexible molecular model of disordered microporous carbon representative of a kerogen/coal matrix. According to these molecular simulations, the adsorbed amount depends almost linearly on the strain of the solid. Therefore, we proposed a simplified poro-mechanics modeling in which adsorption in coal is assumed to depend linearly on the strain. We then applied this poro-mechanics modeling of coal (i) to estimate the so called ‘differential swelling’ induced by ECBM in coal beds at different geological depths (ii)  to determine the thermodynamics of confined CH4 in coal pores in ground conditions akin to gas shale production.