渤海湾盆地济阳拗陷沙三段页岩气地质条件分析

Analysis of geological condition of the formation of Shahejie shale gas in Jiyang Depression in Bohai Bay Basin

沙河街组三段的湖相富有机质泥页岩是济阳拗陷常规油气的主力烃源岩,也是该拗陷页岩气勘探的重点研究层系.分析沙三段暗色泥页岩的地球化学指标、页岩储层特征、含气性等,探讨济阳拗陷沙河街组湖相泥页岩形成页岩气的地质条件.结果表明:沙河街组湖相泥页岩沉积厚度大,平均大于200m;有机碳含量高,干酪根类型好,以Ⅰ型为主,Ⅱ1和Ⅱ2为辅;成熟度以成熟—高熟为主,与美国产气页岩和中国南方上扬子地区海相富有机质页岩地球化学特征具有可比性.湖相泥页岩脆性矿物质量分数高,石英与碳酸盐岩所占比例大,黏土矿物质量分数为10%～30%,页岩储层裂缝类型多样.由于砂泥岩互层频繁,粉砂或砂质夹层孔隙可以有效改善页岩储层储集性能,为页岩气提供有效的储集空间.泥页岩层段气测显示异常,指示其良好的含气性.沙三段富有机质泥页岩是济阳拗陷页岩气勘探的优选层系,具有良好的页岩气勘探潜力.

The Lacustrine organic-rich shale of Es3 is not only the main source rock of the conventional hydrocarbon,but also the important layer of shale gas exploration in Jiyang Depression.This paper focuses on the analysis of geochemical indicators,shale reservoir characteristics,gas-bearing of sets of dark shale,and discusses the geological condition of the formation of Shahejie.It is believed that Shahejie Lacustrine shale in Jiyang Depression is of great thickness of sediments with high abundances of organic matter and the main kerogen type is Ⅰ;the maturity of organic matter is from mature to high mature stage.It is comparable with geochemical characteristics of American's shale and the organic-rich marine shale in Upper Yangtze region in China.The content of brittle mineral in shale of Bohai Bay Basin is high,especially the quartz and carbonate rock are large proportion and the content of clay minerals is low.The fracture types include tectonic fracture,interlayer bedding fracture,rock convergent and abnormal pressure fractures.It not only provides effective shale gas reservoir space,reviewing the old well shows that shale segment has abnormal gas test and good indication of its gas-bearing.Comprehensive analysis shows that lower the 3rd member of the Shahejie Formation is preferred layer of shale gas exploration and development in Jiyang Depression and the potential is large.