断陷盆地弱构造区地质特征与油气成藏——以冀中坳陷为例

断陷盆地总体构造活动强烈，断裂带、褶皱带、背斜带等强构造区十分发育，是断陷盆地中主要的油气富集区，也是早期勘探的主要对象。但随着强构造区勘探程度的不断提高，已很难再有大的发现，油气勘探必须向弱构造区转移。通过对断层落差面密度、地层曲率、地层厚度变化率导数3个表征构造活动强度指标的统计、分析，划分出冀中坳陷的弱构造区，并分析其地质特征。通过对比强、弱构造区成藏条件的差异性，解剖油气成藏实例，总结弱构造区的油气成藏特征及富集规律。发现弱构造区主要分布在洼槽和斜坡地区，油气成藏主要受控于烃源岩、输导体系等，以发育岩性油气藏为主，在油气源充足条件下具有大面积、连片含油的成藏特点，可形成规模油气富集。以冀中坳陷蠡县斜坡为例，北部油源充足，且具有有效的输导体系，发育大面积多源供烃、断—砂输导的岩性油气藏。

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 large-scale lithologic reservoirs with multiple hydrocarbon sources and fault-sand migration ways.