Multi-Scale Evaluation of the Elastic Properties of Clay-Rich Rocks under Competitive CO2/CH4 Adsorption

ABSTRACT: CO2 injection into clay-rich gas reservoirs alters their mechanical properties, potentially causing injection complications and instabilities in the long-term sealing efficiency. There remains a significant gap in reliably quantifying the extent of mechanical degradation due to CO2 injection in clay-rich gas reservoirs. This paper aims to reliably quantify the impacts of (i) clay type, (ii) clay volumetric concentration, (iii) spatial distribution of clay minerals, and (iv) volumetric concentrations of water, CO2, and CH4 on the mechanical properties of clay minerals and clay-rich rocks at the molecular and core scales. We deployed molecular dynamics (MD) simulations to quantify the impact of fluids on the mechanical properties of clay minerals including illite, kaolinite, and sodium-montmorillonite. We upscaled the outcomes of MD simulations to core-scale synthetic clay-rich samples using finite-element modeling and evaluate their effective mechanical properties under different clay inclusion type, volumetric concentration, spatial distribution, and fluid composition. Results suggested that among all fluids, water had the highest impact on the mechanical properties of clay minerals and clay-rich synthetic samples. The extent of mechanical degradation by CO2 was controlled by the rock water content. Finally, clay volumetric concentration significantly affected the Young's modulus of the samples while the Poisson's ratio was primarily controlled by clay type and clay sedimentation.