Hydro-mechanical interactions in CO2 storage: Critical parameters influencing coal mine at Shenhua's CCS site

Abstract

The co-development of saline aquifers and coal seams in sedimentary basins results in geomechanical conflicts when concurrently exploited in shared subsurface strata. However, reliable assessments of CO₂ storage effects on coal mines are limited by uncertainties associated with the mechanical and physical characteristics of deep rock formations. Studies have developed advanced hydraulic-mechanical (HM) coupling frameworks for CO₂ storage in saline aquifers or coal seams; however, no study has quantitatively linked parameter uncertainties to coal mine stability thresholds under CO₂ injection pressures, a gap addressed in this study. This study investigated the critical parameters governing coal mine stability under CO₂ injection at the Shenhua CCS site. A coupled MRST-FLAC3D model was developed to simulate HM interactions, and Tornado analysis and response surface methodology were performed to evaluate 17 parameters, with $F$-values quantifying their significance. Predictive models for CO₂ plume radius ($R$) and vertical displacement ($U$) were established, revealing three key findings: (1) reservoir porosity had the dominant effect on $R$ variations (73.6), exceeding the influences of reservoir permeability (34.16) and reservoir thickness (0.95) by orders of magnitude; (2) $U$ was most sensitive to the caprock Poisson's ratio (1, 240.22), followed by the caprock Young's modulus (1, 019.59), Biot's coefficient (707.8), interbedded mudstone-sandstone Poisson's ratio (367.22), and reservoir permeability (289.45); (3) the $R$ and $U$ models robustly predicted CO₂ migration and stratum deformation across diverse geological conditions. These findings provide a quantitative framework for optimizing CO₂ storage integrity and coal mine safety in tectonically active basins, with implications for global CCS projects facing similar resource conflicts.