大巴山山前带油气成藏条件与勘探方向

位于四川盆地边缘的大巴山山前带由于构造变形较为强烈，地表地震地质情况复杂，给地震资料采集和处理带来诸多困难，目前该区勘探程度还较低。为预测其油气勘探前景，从生储盖组合、烃源岩条件、储层条件、盖层条件等几个方面分析了该区油气成藏条件，发现其原始成藏条件优越，存在3套成藏组合和多种类型的勘探目的层。古油藏解剖结果表明，山前带二、三叠系油气主力烃源岩为上二叠统，油气成藏分为3个阶段：①晚三叠世-早侏罗世开始变形，形成宽缓背斜，形成古油藏；②中侏罗世-早白垩世进一步变形，圈闭构造定型，部分古油藏裂解，形成油气藏；③古近纪喜山运动对先期构造进行了强烈的改造，造成古油气藏的调整与破坏。综合评价该区构造变形样式、储层分布和油气显示特征后认为：南大巴山西北部镇巴断裂至铁溪-巫溪隐伏断裂是油气勘探有利区，应以二叠系长兴组和三叠系飞仙关组礁滩相储层勘探为主展开工作；东南部鸡鸣寺断裂至铁溪-巫溪断裂为二、三叠系出露区，应以落实寒武系膏盐岩下伏地层的保存条件为主进行勘探部署。

Hydrocarbon pooling conditions of the foothill belt of the Dabashan Mountain and exploration direction

Seismic acquisition and processing are challenging in the foothill belt of the Dabashan Mountain in the marginal area of the Sichuan Basin due to strong tectonic deformation and complex surface seismic geologic conditions,so the exploration maturity is still very low in the study area at present.In order to predict the potential of petroleum exploration,we analyzed the hydrocarbon pooling conditions in this area in respect of source-reservoir-seal combination,source rocks,reservoir and sealing conditions.The original hydrocarbon pooling conditions are favorable and there are 3 plays and various types of exploration pay zones.The analysis of the paleo-reservoir in this study area shows that the major source rocks contributing hydrocarbons to the Permian and Triassic reservoirs in the foothill belt are mainly in the Upper Permian formations,where the hydrocarbon pooling is divided into 3 stages.The first stage is at the Late Triassic-Early Jurassic,when tectonic deformation initiated and paleo-pools were formed in wide and gentle anticlines.The second stage is at the Middle-Jurassic-Early-Cretaceous,when tectonic deformation continued,traps finalized,and crude oil in some palaeo-pools cracked to form oil/gas reservoirs.The third stage is at the Paleogene,when the Himalayan movement strongly transformed the existing traps,which resulted in the adjustment and destruction of the palaeo-pools.The comprehensive analysis of tectonic deformation style,reservoir distribution and oil/gas displaying characteristics reveals that the favorable exploration area is from the Zhenba Fault to the Tiexi-Wuxi buried fault in the northwestern part of South Dabashan Mountain,where the major targets are the Permian Changxing Formation and the Triassic Feixianguan Formation reservoirs of reef-bank facies.In addition,it indicates that preservation conditions of the presalt Cambrian reservoirs should be the focus of research in the southeastern part of South Dabashan Mountain,where the Permian and Triassic are outcropped from the Jimingshi Fault to the Tiexi-Wuxi Fault.