Laboratory Observation of Fluid Flow in Depleted Shale Gas Reservoir: Coupling Effect of Sorbing and Non-sorbing Gas on Stress, Slippage, Flow Regime in Anisotropic and Fractured Shales
Abinash Bal, Santanu Misra
Abstract
Understanding gas flow in depleted unconventional reservoirs is crucial but limited, particularly in organic-rich shale with ultrafine nanopores and high matrix compressibility. Here, we assess the apparent permeability ( k app ) along perpendicular and parallel to bedding, as well as through fractures─using shale samples from three petroliferous basins in India. Our experiments simulate depleted reservoir conditions with varying mean pore pressures ( P m ), using both sorbing (N 2, CO 2 ) and nonsorbing (He, Ar) gases, and the results are compared to nanopore structures determined through low-pressure gas sorption and He-pycnometer. We further explored the gas fluid dynamic behavior, intrinsic permeability ( k ∞ ), stress sensitivity, and effective stress coefficients and correlated between experimental variables and shale properties. We found that gas type and shale anisotropy significantly influence k app . He, exhibits the highest k app, followed by Ar, N 2, and the lowest for CO 2 due to varying adsorption affinities. At lower effective stress (σ eff < 15 MPa), bedding parallel gas flow results in higher k app, while at higher stress, perpendicular flow increases permeability. Bedding perpendicular flow is matrix-dominated, while bedding parallel flow contains stress-sensitive microfractures serving as flow conduits. CO 2 in parallel bedding and fractured samples show a nonlinear relationship between slippage factor ( b ) and σ eff, indicating higher sensitivity compared to bedding perpendicular samples. Gas type exerts a stronger impact on b than σ eff . Notably, CO 2 with higher adsorption affinity, low k app, and enhanced penetration capacity in complex nanopores, emerges as a practical candidate for carbon storage and enhanced oil/gas recovery.