湘中涟源—邵阳凹陷上二叠统大隆组页岩气储层特征

Reservoir characteristics of shale gas of Upper Permian Dalong Formation in Lianyuan-Shaoyang depression, central Hunan

为评价湘中涟源—邵阳凹陷上二叠统大隆组页岩气的勘探潜力,分析其泥页岩的有机碳含量、矿物组成、孔隙及裂隙的微观特征、孔隙度和渗透率等,系统研究了页岩气的储层特征。研究区上二叠统大隆组岩石的有机碳含量与岩性关系密切,其中硅质泥岩的有机碳含量最高,平均质量分数大于3%,表明沉积环境是控制有机碳含量的最主要因素;硅质泥岩中石英等脆性矿物平均质量分数为67.7%,与美国Barnett硅质页岩基本相当,脆性矿物含量较高;硅质泥岩中构造裂缝较发育,其形成主要与其脆性矿物含量较高及地质构造较发育等因素有关;有机碳含量较高的硅质泥岩,其有机质微孔隙也是基质孔隙及裂隙的主要组成部分;硅质泥岩的孔隙度和渗透率均较低,分别小于5%和0.01 m D,构造裂缝发育程度是影响硅质泥岩孔隙度和渗透率的最主要因素。

To evaluate shale gas exploration potential in Upper Permian Dalong Formation in Lianyuan-Shaoyang depression, central Hunan, the reservoir characteristics of shale gas were investigated by the analysis of total organic carbon （TOC） content, mineral composition, microscopic characteristics of pores and fractures, porosity and permeability of shale. The results show that the TOC content has close relationship with lithology, the TOC content of siliceous mudstones were the highest, with an average value over 3%, which shows that it is obviously controlled by sedimentary environment. The brittle mineral contents in the siliceous mudstones were 67.7% on average, which is essentially the same as the brittle mineral contents in Barnett siliceous shale of America. The tectonic fractures developed well, and they are related to the brittle mineral contents and geological structure. The organic micropore is the main composition of pore-fracture system in the siliceous mudstones with higher TOC content. The porosity and permeability of siliceous mudstones were both low, being lower than 5% and 0.01 mD respectively. Fracture development degree is the dominant factor for influencing porosity and permeability of siliceous mudstones.