北大巴山地区鲁家坪组页岩地球化学特征及勘探意义

Geochemical characteristics and exploration significance of shale of Lujiaping Formation in northern Dabashan area

为揭示北大巴山地区下寒武统暗色页岩的生烃潜力,以该区鲁家坪组野外露头区样品的分析数据为基础,分析鲁家坪组烃源岩的地球化学特征,并探讨其页岩气勘探意义。结果表明:北大巴山地区鲁家坪组烃源岩有机质丰度高,样品TOC质量分数为0.182%~9.063%,平均值为3.21%;有机质类型为Ⅰ—Ⅱ1型,有机质主要来源于低盐度浅水中的菌藻类微生物;镜质体反射率(RO)值为1.36%~2.56%,平均值为1.86%,岩石热解峰温(Tmax)为418~530℃,平均值为460℃,烃源岩已进入高成熟—过成熟阶段,表明处于生湿气或干气阶段,原始生烃潜力较好;北大巴山地区鲁家坪组暗色页岩厚度大,热演化程度高,烃源岩中的裂隙、溶孔可成为页岩气的吸附储集空间,构造改造较弱区及侧向封堵良好的断层下盘有望形成页岩气富集的有利区。

In order to reveal the hydrocarbon generating potential of the dark shale of Lower Cambrian Lujiaping Formation in northern Dabashan area,based on the geochemical analysis data of the samples of Lujiaping Formation in the outcrop area,the geochemical characteristics of the source rocks and the exploration significance of shale gas were discussed.The results show that the source rocks of Lujiaping formation in northern Dabashan area have high organic matter abundance,and the TOC content of the samples ranges from 0.182%to 9.063%with an average value of 3.21%.The organic matter is typeⅠ-Ⅱ1,and mainly comes from bacteria and algae in low salinity shallow water.The vitrinite reflectance(Ro)ranges from 1.36%to 2.56%with an average value of 1.86%,and the peak temperature of rock pyrolysis(Tmax)ranges from 418℃to 530℃with an average value of 460℃.The source rocks have entered a high-maturity to over-maturity stage,indicating that it is in the stage of generating moisture or dry gas,and the original hydrocarbon generation potential is good. The dark shale of Lujiaping Formationin northern Dabashan area is thick with high degree of thermal evolution. The fissures and dissolved poresin the source rocks can become the adsorption storage space of shale gas. Favorable areas for shale gas enrichmentare expected to be formed when having weak structural area or footwall with good lateral sealing.