黔北凤冈地区牛蹄塘组页岩气勘探与开发潜力

黔北凤冈地区为页岩气重要目的层——下寒武统牛蹄塘组的典型分布区块之一,为分析其页岩气储集与开采条件,以该组页岩样品为研究对象,采用X射线衍射、扫描电镜、液氮低温吸附和核磁共振等方法进行实验测试。结果表明:(1)黔北凤冈地区下寒武牛蹄塘组页岩矿物组成以石英为主,脆性矿物含量高,黏土矿物含量低,黏土矿物以伊利石为主;(2)页岩孔隙以有机质纳米级孔、矿物溶蚀孔、矿物晶间孔、铸模孔为主,大量发育闭合—半闭合微裂隙;(3)液氮吸附实验表明页岩的比表面积和孔体积都较大,吸附脱附曲线存在H_2型滞后环,页岩内部存在大量"墨水瓶"形孔隙,微孔是页岩比表面积和孔体积的主要贡献者;(4)核磁共振实验反映页岩孔隙的连通性差,所测的页岩孔径分布与液氮吸附实验孔径分布具有一致性,即页岩孔径主要分布在3~10 nm之间。结论认为,黔北牛蹄塘组储层条件有利于页岩气储集与压裂,页岩气开采条件较好。

Exploration and development potential of Niutitang Fm shale gas in Fenggang area,North Guizhou

Fenggang area in North Guizhou is one of the typical blocks where the Lower Cambrian Niutitang Fm—an important shale gas payzone is located. In this paper, samples from Lower Cambrian Niutitang Fm were experimentally tested by means of X-diffraction, scanning electron microscope (SEM), liquid-nitrogen cryogenic adsorption and nuclear magnetic resonance (NMR) to analyze its accumulation and recovery conditions of shale gas. The X-diffraction results show that the Lower Cambrian Niutitang Fm shale in Fenggang area contains quartz as the main mineral. Its brittle mineral content is high and clay mineral (mainly illite) content is low. The SEM results show that shale pores are mainly composed of nanometer organic matter pores, mineral dissolution pores, mineral intercrystal pores and moldic pores, as well as a large number of closed and semi-closed microcracks. The liquid nitrogen absorption experiments show that the specific surface area and pore volume of shale are large, and micropores are the main contributor to the specific surface area and pore volume of shale. H2 type hysteresis loop is presented in adsorption and desorption curves and there are a lot of "ink bottle" type pores in the shale. The NMR experiments show that shale pores are poorly connected, and that the pore size distribution measured by the NMR is consistent with that in liquid nitrogen absorption experiments, mainly ranging between 3 and 10 nm. It is finally concluded that the reservoir conditions of the Niutitang Fm in North Guizhou are favorable for shale gas accumulation and fracturing, suggesting a good potential of shale gas recovery.