下扬子宣泾地区二叠系大隆组页岩含气量主控因素分析--以港地1井为例

The main controlling factors of the gas content in the Permian Dalong Formation of the Xuanjing area,the lower Yangtze region:a case study of Gangdi 1 Well

下扬子地区发育了寒武系、志留系和二叠系3套有利成藏的页岩,资源潜力大,但存在页岩含气量主控因素不明确的问题。为此,以下扬子宣泾地区港地1井为依托,钻遇的70.1 m厚上二叠统大隆组富有机质页岩为目的层,对岩心系统取样并应用对比分析法,在纵向上连续动态地进行包括矿物成分、孔隙结构、总有机碳(Total Organic Carbon,TOC)、镜质体反射率(vitrinite reflectance,Ro)和有机质类型等研究工作,深入分析TOC、Ro和有机质类型等地球化学指标与含气量之间的对应关系,从而厘定了影响含气量的关键地球化学参数。分析结果表明:TOC与页岩含气量之间存在强正相关关系;在有机质成熟阶段中期,Ro与含气量之间相关性偏弱,对含气量变化没有明显的影响;有机质类型对页岩含气量有重要影响,但是两者的相关性弱于TOC。通过对大隆组页岩从顶部到底部的系统分析,探索了用一套完整页岩在纵向上分析含气量影响因素的新方法。

There are three favorable shale reservoirs developed in Cambrian,Silurian and Permian in the lower Yangtze region.Even though with great gas potential,the main controlling factors of shale gas content are not yet clear.Therefore,based on the Gangdi 1 Well in the Xuanjing area of the Lower Yangtze region,we took the drilled 70 m shale of the Late Permian Dalong Formation as the target layer for core sampling,and made continuous and dynamic studies on mineral composition,pore structure,Total Organic Carbon,vitrinite reflectance(Ro)and organic matter types in vertical direction by comparative analysis.The corresponding relationship between gas content and geochemical indicators,namely TOC,Ro and organic matter type were further researched and accordingly the key geochemical parameters affecting the gas content were determined.Analysis results show a strong positive correlation between TOC and shale gas content,and a relatively weak correlation between Ro and gas content in the middle process of organic matter maturation,which less affected the gas content change.At the same time,organic matter type has an important impact on shale gas content,but the correlation is weaker than that with TOC.Through systematic analysis on Dalong Formation shale from top to bottom,we figure out a new method to analyze the factors that affect gas content in the vertical direction.