湘鄂西地区下志留统龙马溪组页岩吸附能力主控因素

Main controlling factors on shale adsorption capacity of the Lower Silurian Longmaxi Formation in western Hunan-Hubei area

利用实验测试手段剖析了湘鄂西地区龙马溪组页岩的有机质特征、矿物特征、孔隙特征以及甲烷吸附特征,发现龙马溪组页岩的甲烷吸附能力较强,在恒温30℃时平均饱和吸附气量为2.46 cm3/g,具有良好的储气能力。通过相关性分析,认为有机碳含量、适中的有机质成熟度、干酪根镜质组和惰质组含量、黄铁矿含量和微、中孔的体积与吸附能力正相关性较强,是吸附能力主要的内部控制因素。温度和压力作为外部控制因素分别与吸附能力呈负相关和正相关性,而该区构造抬升幅度大,对温度和压力具有较大影响。研究认为,构造抬升对吸附能力的影响具有阶段性特征:当地层在高压区内抬升时,温度对吸附气的影响大于压力对吸附气的影响,构造抬升使得页岩的吸附能力增强;当地层抬升幅度很大、地层进入低压区时,压力对吸附气的影响大于温度对吸附气的影响,会使得吸附气量迅速下降。

Various laboratorial techniques are applied for dissecting the characteristics of the Longmaxi Formation shale in Western Hunan-Hubei Area, including organic carbon, mineral, porosity and methane adsorption. It is found that the Longmaxi Formation shale has good methane adsorption capacity with an average saturated adsorption gas content of 2.46 cm3/g under constant temperature 30 ℃, thus has favorable gas capacity storage. Correlation analysis reveals that the content of organic carbon, appropriate maturity, contents of vitrinite and inertinite, content of pyrite as well as the volume of micropores and mesopores, as the major internal controlling factors, are positively correlated with gas adsorption capacity, while temperature and pressure, as the external controlling factors, have negative and positive relationships with adsorption capacity, respectively. The tectonic uplifting produced a considerable influence on temperature and pressure due to its relatively high intensity. It is suggested that the influence of tectonic uplifting on adsorption capacity can be di- vided into two stages. When the strata are uplifted within high pressure zone, the impact of temperature on gas adsorption is greater than that of pressure, enhancing adsorption capacity. In contrast, when the strata enter into low pressure zone due to strong tectonic uplifting, the influence of pressure on gas adsorption is greater than that of temperature, rapidly lowering adsorption capacity.