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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 (kapp) 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 (Pm), using both sorbing (N2, CO2) 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 kapp. He, exhibits the highest kapp, followed by Ar, N2, and the lowest for CO2 due to varying adsorption affinities. At lower effective stress (σeff < 15 MPa), bedding parallel gas flow results in higher kapp, 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. CO2 in parallel bedding and fractured samples show a nonlinear relationship between slippage factor (b) and σeff, indicating higher sensitivity compared to bedding perpendicular samples. Gas type exerts a stronger impact on b than σeff. Notably, CO2 with higher adsorption affinity, low kapp, and enhanced penetration capacity in complex nanopores, emerges as a practical candidate for carbon storage and enhanced oil/gas recovery.
Bal et al. (Mon,) studied this question.