Geological Characteristics and Hydrocarbon Accumulation of Weak Tectonic Zone in Rift Basin:A Case Study from Jizhong Depression

Rift basin develops intensive tectonic activities,where strong tectonic zones are well developed such as fault belt,fold belt,anticline belt and so on.They are major hydrocarbon-rich regions and the main target of early exploration in rift basin.But with the increase of exploration degree,it is difficult to have big progress in strong tectonic zones,so oil and gas exploration must be transferred to the weak tectonic zones.Through the statistics and analysis of stratigraphic curvature,derivative of stratigraphic thickness changing rate,and the density of fault throw surface,weak tectonic zones are divided in the Jizhong Depression.The differences of accumulation conditions between strong and weak zones were analyzed,the reservoir profile was dissected,and the hydrocarbon accumulation characteristics and enrichment regularities of weak tectonic zones were summarized.It is found that weak tectonic zones mainly distribute in subsags and slope areas,and their hydrocarbon accumulation is mainly controlled by source rocks,petroleum migration pathways,etc.It mainly developed lithologic reservoirs and the large-scale oil-gas accumulation was formed in the area with sufficient oil and gas source.For example,the Lixian slope in Jizhong Depression,where there is sufficient oil and gas source in the northern part,has effective migration pathways,so it develops largescale lithologic reservoirs with multiple hydrocarbon sources and fault-sand migration ways.