保靖地区龙马溪组高成熟海相页岩吸附气量及其影响因素

Gas adsorption capacity of Longmaxi Formation high-maturity marine shale in Baojing area and its influential factors

页岩吸附气量是含气性评价和资源潜力预测的关键参数,保靖地区志留系龙马溪组海相页岩热演化程度高,页岩吸附气量尚未查明,成为亟待研究的关键问题。采集研究区BY-1井龙马溪组页岩岩心样品12个,开展了页岩TOC、热成熟度(R_o)、X射线衍射、场发射扫描电镜、低压液氮吸附和高压甲烷等温吸附等分析测试。结果表明,研究区海相页岩有机质丰度高,TOC范围是0.57%~2.16%;热演化程度高,R_o的范围为2.86%~3.76%;矿物组分中石英含量为33.7%~73.9%,斜长石含量为0.7%~16.9%,黏土矿物含量为15.8%~54.4%;页岩中纳米级孔隙发育,以粒间孔和有机质孔为主;低压液氮吸附实验结果展示页岩孔径分布范围宽,以2~50nm的中孔为主;高压等温吸附实验揭示保靖地区龙马溪组页岩的吸附气量较高,为0.82~3.56m3/t,平均为1.93m3/t。保靖地区页岩吸附气量主要受到有机质丰度和中孔、微孔比表面积的控制,龙马溪组页岩有机质处于高成熟阶段,有机质热演化产生大量的微孔和中孔,二者比表面积较大,为页岩气吸附提供了较大的空间,页岩的吸附气量大。

Gas adsorption capacity of shale is a key parameter of gas potential evaluation and resource potential prediction. The marine shale of Silurian Longrnaxi Formation in the Baojing area is high in thermal evolution degree, and its gas adsorption capacity is unclear and will be a focus to be figured out. In this paper, 12 core samples of Longmaxi Formation shale in Well BY-1 in the study area were collected and tested in terms of total organic carbon （TOC）, thermal maturity （Ro）, X-ray diffraction, field emission scanning electron microscopy （FE- SEM）, low-pressure liquid nitrogen adsorption and high-pressure isothermal methane adsorption. The results show that the marine shale in the study area is high in organic abundance and thermal maturity with TOC and Ro in the range of 0.57%-2.16% and 2.86%-3.76%, respectively. The mineral composition includes quartz （33.7%-73.9%）, plagioclase （0.7%-16.9%）, and clay mineral （15.8%-54.4%）. Nano-scale pores are developed in shale dominantly in the forms of intergranular pore and organic pore. According to the low-pressure liquid nitrogen adsorption test, the pore diameter of shale is in a large range and mesopores （2-50 nm） are dominant. The high-pressure isothermal methane adsorption test revels that the gas adsorption capacity of Longmaxi Formation shale in the Baojing area is high - 0.82-3.56 m^3/t, averaging 1.93 m^3/t. The gas adsorption capacity is mainly controlled by the organic abundance and the specific areas of mesopores and micropores. The organic matter in the Longmaxi Formation shale is of high maturity. With the thermal evolution of organic matter, abundant micropores and mesopores are generated and their specific area is large, providing large space for shale gas adsorption, resulting in high gas adsorption capacity of shale.