湘西北牛蹄塘组页岩气形成条件及有利区预测

The Reservoir Characteristics and Favorable Areas of Shale Gas in Northwestern Hunan Lower Cambrian Niutitang

基于野外露头和剖面资料,应用薄片观察、有机岩石学分析、扫描电镜、压汞、比表面和等温吸附实验等分析测试成果,研究了湘西北地区下寒武统牛蹄塘组形成条件及其有利区分布情况。研究表明:牛蹄塘组黑色页岩具有沉积面积广、厚度大、有机碳含量高(平均1.87%)和成熟度较高(大于1.0%以上)等特点。在储层物性方面,页岩孔隙度变化差异大(0.2%～25.9%),平均孔径12.5±3.0 nm,分选性好,有利于含气页岩储层改造后的运移;孔隙结构以微小孔为主,比表面积大,吸附甲烷能力较强,具有较好的含气潜力;对比美国五大盆地页岩气选区参数,认为永顺—桑植和慈利—石门一带为页岩气形成有利区带。

Through outcrop observation and cross section measured,together with analytic results like microscope observation,geochemical parameters,pore structure,surface area and methane adsorption isotherm experiments,the geological accumulation characteristics and physical properties of the shale gas were investigated in detail in this article. Results show that the shale is characterized with wide distribution area,a great thickness,high organic content（an average of 1.87%）,and high organic thermal evolution degree（above 1.0%）. At the same time,a large variation in porosity（0.2%～25.9%）,with an average size of 12.5±3.0 nm,and good sorting is conducive to shale reservoir reconstruction after migration. Pore structure is mainly dominated by tiny pores,but due to larger specific surface area and strong methane adsorption ability,a large amount of methane adsorbed on the shale surface. According to contrast with the shale constituency parameters of American 5 basins,we suggest that Yongshun–Sangzhi and Cili–Shimen Area are favorable shale gas accumulation zones.