鄂西仙女山断裂构造演化及其对长阳背斜圈闭性的影响

Tectonic evolution of Xiannüshan fault and its influence on hydrocarbon traps in Changyang anticline,Western Hubei fold belt

位于中扬子地区的湘鄂西褶皱带是我国南方油气勘探的重点接替区域,仙女山断裂位于湘鄂西褶皱带东北部,与褶皱带内长阳背斜成交切关系,是影响长阳背斜油气圈闭性的重要构造。受限于深部资料的缺乏,仙女山断裂的几何形态和演化历史始终未能得到准确刻画,其构造演化对油气有利保存构造的影响也尚未得到分析。通过解释仙女山断裂中部最新的地震剖面,在结合浅表地质分析的基础上,刻画了仙女山断裂的拟三维形态,分析了仙女山断裂的形成过程,并结合区域地质演化与油气成藏过程,分析了断裂形成、演化过程中对长阳背斜油气保存单元的影响,认为:(1)仙女山断裂带是一条北段西倾,中段、南段东倾的断裂带;(2)仙女山断裂带形成于晚侏罗世湘鄂西褶皱带向北递进变形的过程中,经历了晚白垩世的伸展作用和古近纪末期的挤压逆冲作用形成现今的形态;(3)仙女山断裂晚侏罗世的走滑活动有利于长阳背斜内部油气的运移,晚白垩世伸展活动则破坏了长阳背斜的构造圈闭条件,是该区油气散失的主要原因。湘鄂西地区发生过类似断裂活动的地区,其油气勘探潜力可能均受到了不利影响。

The Western Hubei fold belt is an important oil and gas exploration area in South China.Located in the northeast of the fold belt,the Xiannüshan fault intersects the Changyang anticline,and has an important influence on the hydrocarbon traps in the Changyang anticline.However,the geometrical morphology and evolution history of the Xiannüshan fault has not been well studied due to the lack of accurate depth information,and the influence on hydrocarbon trap evolution was still unclear.Based on the interpretation of the latest seismic section in the central part of the fault,the quasi-three-dimensional shape and the formation process of the Xiannüshan fault were analyzed.Combined with the regional geological evolution and hydrocarbon accumulation process,the influence of the formation and evolution of faults on the preservation units in the Changyang anticline was analyzed.(1)The Xiannüshan fault belt can be divided into three parts.The northern part is dipping westwards,while the middle and southern parts are dipping eastwards.(2)The Xiannüshan fault was first formed during the Late Jurassic as a strike slip fault,pulling apart during the Late Cretaceous,and thrusted during the Middle and Late Paleogene.(3)The strike slip of the Xiannüshan fault in the Late Jurassic was favorable for hydrocarbon migration in the Changyang anticline.However,the stretching of the Xiannüshan fault in the Late Cretaceous destroyed tectonic traps in the Changyang anticline,leading to hydrocarbon loss.In areas where similar faults have occurred in the western Hubei,the potential for oil and gas exploration may have been adversely affected.