湖南省保靖地区下寒武统牛蹄塘组页岩气成藏条件分析

Analysis of shale gas accumulation conditions in Niutitang Formation of Lower Cambrian in Baojing area of Hunan Province

为评价湖南省保靖地区寒武系牛蹄塘组页岩气勘探潜力,利用野外地质调查及页岩气井勘探成果资料,结合钻井岩芯样品测试结果,研究了保靖地区牛蹄塘组页岩储层发育特征及其分布规律。保靖下寒武统牛蹄塘组发育被动大陆边缘浅海深水碎屑岩陆棚相黑色碳质页岩、深灰色泥岩、深灰色钙质粉砂岩。该页岩层系分布稳定,厚度较大(90m),有机质丰度较高(1.48%~3.49%),为I型干酪根,成熟度较高(3.90%~4.86%),处于过成熟阶段;脆性矿物含量较高(38.4%~50.5%),具较好的破裂潜力;成岩作用较深,黏土矿物以伊利石和伊蒙混层为主;页岩孔隙度中等(0.50%~4.24%),渗透率极低(0.0005×10^-3~0.0146×10^-3μm^2)。储集空间有晶体矿物晶面溶蚀孔、矿物边缘溶蚀孔、有机质溶蚀孔、黄铁矿晶间孔、成岩作用解理缝和构造裂缝。综合分析认为,湖南省保靖地区下寒武统牛蹄塘组具有较好的页岩气成藏地质条件,裂缝发育区可促进页岩气聚集,在保靖县东部昂洞—泽碧一带可以加大勘探力度。

In order to evaluate the exploration potential of shale gas in Cambrian Niutitang Formation in Baojing area of Hunan Province, using the data of field geological survey and gas well exploration results, combined with drilling core sample test results, the authors studied the reservoir characteristics and distribution of Niutitang Formation in Baojing area of Hunan Province. The black shale, dark grey mudstone and dark grey calcareous siltstone of passive continental margin deepwater shelf was deposited at Lower Cambrian Niutitang Formation in Baojing area of Hunan Province. The shale layer was stable in distribution, large in thickness (90 m), high in organic matter (1.48%~3.49%) with I type kerogen, high in maturity (3.90%~4.86%) at over mature stage. The content of brittle minerals in reservoir was high (38.4%~ 50.5%), and it had better fracture potential. Diagenesis was deeper and clay minerals were mainly illite and illite mixed layers. The shale porosity was medium (0.50%~4.24%), and the permeability was very low ((0.0005 ~ 0.0146)×10^-3 μm^2). The reservoir spaces included crystal faces corrosion pores of crystal minerals, mineral marginal dissolution pores, organic matter dissolution pores, pyrite intergranular pores, cleavage joints by diagenesis and structural fractures. Through comprehensive analysis, the authors believed that Niutitang Formation in Baojing area of Hunan Province has good geological condition of shale gas and the fracture developed area can promote shale gas accumulation, so exploration efforts in Angdong-Zebi area in eastern Baojing County showld be increased.