“源热共控”北部湾盆地福山凹陷油气的形成

Formation of oil and gas in the Fushan sag of Beibuwan Basin under the co-control of source and heat

基于大量地球化学、地质资料以及"源热共控"的思想,深入研究了北部湾盆地福山凹陷油气的形成。结果表明,福山凹陷的"源"为古新世流沙港组烃源岩,该烃源岩有机碳丰度分布范围宽,有机碳含量TOC为0.4%~6.0%,但有机质类型主要为腐殖—腐泥型(Ⅱ2型)烃源岩,属于"源够"型凹陷;"热场"研究表明,福山凹陷经历过多期构造热事件,火成岩侵入导致烃源岩有明显热异常,促使东部地区烃源岩快速成熟生气,故凹陷热场类型定为"热足"型。"源够热足"型耦合作用促成了福山凹陷油气的形成,该成果进一步丰富了"源热共控"理论,揭示富油气凹陷烃源岩成熟及油气富集机理,进而指导油气勘探。

Based on plenty of geochemical and geological data and the idea of "co-control of source and heat", an in-depth study is performed on the formation of oil and gas in the Fushan sag of Beibuwan Basin. The results show that Fushan sag is originated from the Paleozoic Liushagang Formation source rock. The source rock has a wide distribution range of organic carbon abundance, and the TOC content of 0.4%-6.0%;however, it is dominated by the humic-sapropelic type(type II2) organic matter. Thus, Fushan sag is characterized with sufficient source. The thermal field study shows that the Fushan sag experienced multiple tectonic heat events;the igneous intrusion caused a significant thermal anomaly in the source rocks, prompting the maturation of source rocks in the eastern part to generate gas, so the thermal field of the sag is characterized with sufficient heat. The coupling effect of sufficient source and sufficient heat promoted the formation of oil and gas in Fushan Sag. This result further enriches the theory of "co-control of source and heat", reveals the maturation of source rocks and mechanism of hydrocarbon enrichment in hydrocarbon-rich sags, and guides the oil and gas exploration.