青藏高原北部东昆仑地区三叠系页岩成岩作用及其对储层的影响

青藏高原北部东昆仑地区八宝山盆地作为高原页岩气成藏特征探索的典型区域之一,对影响储层储集性能的关键因素——成岩作用的研究程度很低,不足以更大限度地发挥其勘探价值。基于岩性观察及薄片、铸体薄片、扫描电镜、X-射线衍射等实验分析资料,对该区三叠系页岩成岩作用及对储层的影响开展研究,结果显示,三叠系八宝山组页岩成岩作用共有6类:压实、胶结、黏土矿物转化、交代、溶蚀及有机质热成熟作用。综合有机质成熟度、岩石热解最高峰温、伊蒙混层比中蒙皂石占比、黏土矿物组合、孔隙类型等指标得出:研究区页岩处于中成岩B期-晚成岩阶段。结合各成岩作用对储层孔隙度的影响,研究区压实作用、胶结作用、黏土矿物转化作用易于造成孔隙度的减小,溶蚀作用、有机质热成熟作用易于孔隙度的增大,而交代作用对孔隙影响小。

Diagenesis of Triassic Shale and Its Influence on Reservoir in East Kunlun,Northern Qinghai-Tibetan Plateau

As a typical area to study shale gas reservoir characteristics in the east Kunlun (northern Qinghai-Tibetan Plateau), the research on shale diagenesis for the reservoir properties is inadequate with limiting its exploration potential. Based on petrographic observation and experimental analyses including thin section microscopy, cast thin section, scanning electron microscope (SEM) and X-ray diffraction (XRD), we studied the Triassic shale diagenesis and its impact on reservoir characteristics. The results show six types of Babaoshan Formation shale diagenesis: compaction, cementation, clay mineral transformation, metasomatism, dissolution, and thermal maturation of organic matter. Based on indicators such as organic matter maturity, rock pyrolysis peaks, smectite ratio in illite-montmorillonite mixed layer, clay mineral assemblage and pore type, we concluded that the studied shale is in the middle diagenetic stage B-late diagenetic stage. Combined with the influence of diagenetic on reservoir, compaction, cementation and clay mineral transformation can readily reduce porosity, dissolution and thermal maturation of organic matter can increase up porosity, while metasomatism has little effect on porosity.