查干凹陷下白垩统有效烃源岩识别及其控藏作用

Identification of effective source rocks of Lower Cretaceous and its controlling on hydrocarbon accumulation in Chagan Depression

有效烃源岩识别是沉积盆地油气成藏研究的基础,其分布对油气成藏具有重要的控制作用。结合烃源岩生排烃特征,分析烃源岩中可溶有机质氯仿沥青"A"和热解参数S1与TOC含量的关系,认为对查干凹陷下白垩统油气藏的形成具有重大贡献的烃源岩,其TOC质量分数均在1.0%以上。利用测井Δlog R法预测单井TOC含量,并以TOC含量下限值作为评价标准进一步确定不同探井有效烃源岩的厚度及其平面展布特征。结果表明,查干凹陷有效烃源岩主要发育于缓坡带,深洼陷有效烃源岩厚度较小甚至不发育,油气藏也主要位于缓坡带附近或其上倾方向。通过源藏叠合、油源对比和生烃期与成藏期匹配等分析,认为缓坡带有效烃源岩所生成烃类在原地或经砂体和断层等输导体系近距离运移至圈闭并聚集成藏,缓坡带有效烃源岩的分布对研究区油气成藏具有重要的控制作用。

Identification of effective source rocks is the basis of research on hydrocarbon reservoir-forming in sedimentary basins, and the distribution of effective source rocks has important controls on hydrocarbon accumulation.Based on the characteristics of hydrocarbon generation and expulsion of source rocks, this paper fully considered the control functions of expulsion on hydrocarbon accumulation and analyzed the relations of TOC content with chloroform bitumen ＂A＂ and pyrolysis parameter S1. It is considered that the real contributors to hydrocarbon reservoir of Lower Cretaceous are the source rocks whose TOC content is over 1.0%. The logging Δlog R method was used to predict TOC content in single well. The lowest limit of TOC content was chose as evaluation criteria to determine the thickness and the plane distribution characteristics of effective source rocks in different prospecting wells. The study result shows that effective source rocks mainly distributed in gentle slope belt in Chagan Depression. The thickness of effective source rocks in trough is even thinner. Hydrocarbon reservoirs are mainly enriched in the updip direction of gentle slope belt rather than deep trough. Through the analysis of the superimposition of source-reservoir distribution, oilsource correlation and the match of hydrocarbon generation and accumulation stage, it is believed that hydrocarbon which is generated by effective source rocks in gentle slope belt migrates to trap and forms reservoir through sand bodies and fault. The distribution of effective source rocks in gentle slope belt has significant control on hydrocarbon accumulation in Chagan Depression.