应用高温甲烷吸附实验研究川东北地区五峰组页岩甲烷吸附能力

页岩甲烷吸附能力是决定页岩气井开采方案的重要参数,对评估页岩气藏潜力意义重大。干酪根类型、总有机碳含量、矿物组成、成熟度和孔径等是影响页岩吸附性能的因素,但针对高温高压下过剩吸附现象对页岩甲烷吸附能力影响的研究还需开展进一步的探索。为揭示四川盆地东北地区五峰组页岩甲烷吸附能力,本文通过场发射扫描电镜、低温氮气吸附和高压甲烷吸附实验,研究了高温高压下页岩的甲烷吸附能力,并分析了页岩孔隙结构等对页岩吸附能力的影响。结果表明:①五峰组页岩孔隙结构非均质性强,发育有机孔隙、粒(晶)间孔隙、粒(晶)内孔隙和粒(晶)间溶孔等多种孔隙;②比表面积平均为19.1282m^2/g;孔体积平均为0.0195cm^3/g;孔径平均为5.2226nm;③修正后的饱和吸附气量为2.56m^3/t;④五峰组页岩甲烷吸附性能受控于比表面积、孔体积;有机质含量越大、有机质热演化程度越低,其甲烷吸附性能越强;⑤孔隙结构是影响页岩甲烷吸附能力的重要内因。同时指出低压条件下的实验吸附曲线不适合直接评价页岩甲烷吸附能力。

Application of High-temperature Methane Adsorption Experiment to Study the Adsorption Capacity of Methane in Shales from the Wufeng Formation, Northeast Sichuan

BACKGROUND: Shale 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.
OBJECTIVES: To 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.
METHODS: Based 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.
RESULTS: The 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.
CONCLUSIONS: The experimental adsorption curve under low pressure is not suitable for directly evaluating the shale methane adsorption capacity.