BACKGROUNDShale methane adsorption capacity is not only a significant parameter to determine the exploration and exploitation plan, but also a critical criterion to evaluate the potential of a shale gas reservoir. Types of kerogen, total organic carbon content, mineral composition, maturity, and pore size are factors that affect shale adsorption performance; however, not enough attention is being focused on the influence of excess adsorption under high temperature and high pressure on shale methane adsorption capacity.

OBJECTIVESTo reveal the influence of excess adsorption under high temperature and high pressure on the adsorption capacity of methane from the Wufeng Formation shale in Northeast Sichuan.

METHODSBased on methods of field emission scanning electron microscopy, low-temperature nitrogen adsorption test, and high-pressure methane adsorption test, the shale methane adsorption capacity under high temperature and pressure was studied, and the influence of shale pore structure on the shale adsorption capacity was analyzed.

RESULTSThe types of pore structure in the Wufeng Formation shale were diverse, including organic, intergranular, intercrystalline, and intergranular dissolved pore. The average specific surface area was 19.1282m²/g, while average pore volume and pore diameters were 0.0195cm³/g and 5.2226nm, respectively. The corrected adsorption capacity of shale in the Wufeng Formation was 2.56m³/t. The Wufeng Formation shale methane adsorption performance was controlled by specific surface area and pore volume. The larger the organic matter content, the lower the thermal evolution of organic matter and the stronger its methane adsorption performance. Pore structure was an important internal factor affecting the shale methane adsorption capacity.

CONCLUSIONSThe experimental adsorption curve under low pressure is not suitable for directly evaluating the shale methane adsorption capacity.