Coupling Characteristics and Sensitivity Differences of Coal Porosity and Permeability with Stress in Different Wellfields of Fukang Mining Area

Abstract

Quantifying how coal porosity and permeability vary with effective stress is essential for forecasting coalbed methane (CBM) deliverability, yet the coupled stress response of low-rank coals and its variation among wellfields remain poorly constrained. Nine cores from three wellfields of the Fukang mining area─Kuangou (KG), Wudong (WD), and Donggou (DG)─were tested under stepwise hydrostatic loading of 2.07–15.86 MPa while porosity and permeability were measured simultaneously. Both properties decrease exponentially with stress, but permeability declines far more strongly: at maximum loading, the porosity damage ratio ranges from 15.9% to 69.55%, whereas the permeability damage ratio reaches 82.2–96.7%, and permeability sensitivity across wellfields follows DG ≈ WD > KG. A porosity–permeability ratio (e = φ/k) and a relative sensitivity parameter (R) were introduced to quantify the storage–seepage mismatch, with e rising continuously along the loading path. Fracture density, aperture, pore-throat connectivity, and mineral infilling jointly govern the heterogeneous response. The results provide quantitative criteria for staged depressurization and fracturing design in low-rank CBM development.