江汉盆地江陵凹陷复兴场背斜盐构造特征与成因

Characteristics and genetic mechanism of salt structure in Fuxingchang anticline,Jiangling Sag,Jianghan Basin

复兴场盐背斜是江汉盆地江陵凹陷重要的含油构造,其构造演化及成因机制认识不清,制约了精细勘探。因此,对复兴场盐背斜构造演化及形成机制的分析,不仅有助于理解盐层在不同应力背景下的流动对背斜形成演化的影响,对理解油气成藏过程也有重要意义。通过对三维地震资料的精细解析,结合关键构造层的平衡恢复技术及生长地层分析技术,研究复兴场背斜的构造特征及成因机制。结果显示,复兴场背斜为一构造特征走向上变化显著,受多期次断层改造、多种变形机制复合而成的盐背斜;背斜初始于早始新世新沟咀组沉积期—晚始新世早期的正断层作用,形成滚筒状褶皱并造成盐层的聚集;在晚始新世晚期—渐新世,沉积地层的差异负载作用驱使盐层自西向东流动,造成构造整体西倾,形成单斜构造,并在渐新世晚期抬升剥蚀;背斜定型于新近纪—第四纪,发生构造反转,演化为一挤压型盐背斜,伴生逆断层和膝折构造。复兴场背斜的形成和演化受区域应力背景、沙市组盐层、东倾正断层及盐下古构造等因素的综合作用。复兴场盐背斜形成的构造圈闭略早于烃源岩的主要排油期,并且在主要排油期,构造处于拗陷阶段,断层活动弱,有利于早期圈闭油气的成藏。

The Fuxingchang salt anticline is an important oil-bearing structure in the Jiangling Sag of the Jianghan Basin,while its structural evolution and formation mechanism are unclear,which restricts the delicate exploration of oil and gas.Therefore,the analysis of structural evolution and formation mechanism of the Fuxingchang salt anticline is not only helpful to understand the influence of salt bed flow under different stress backgrounds on the formation and evolution of the anticline,but also important to understand the process of petroleum accumulation.The structural characteristics and genetic mechanism of Fuxingchang anticline were studied by analyzing 3D seismic data and combining with the techniques of balance restoration of key structural layers and growth strata analysis.The results show that the Fuxingchang anticline is a salt anticline with significant structural features that vary along strike,resulting from multiple stages of fault reconstruction and complex deformation mechanisms.The anticline was initially formed during normal faulting in the sedimentary period from Early Eocene Xingouzui Formation to the early period of Late Eocene,which formed roller fold and caused the accumulation of salt layer.From the late period of Late Eocene to Oligocene,the differential loading of sedimentary strata drove salt beds to flow from west to east,resulting in the westward dip of the whole structure and the formation of monoclinal structure,which was uplifted and denudated in the late period of Oligocene.The anticline was finalized from Neogene to Quaternary,and evolved into a compressional salt anticline,associated with reverse faults and kink-band structures.The formation and evolution of Fuxingchang anticline are influenced by the combined effects of regional stress background,salt layer of Shashi Formation,the east-dipping normal faults,sub-salt paleostructures,etc.The structural trap formed by Fuxingchang salt anticline occurred slightly earlier than the main oil expulsion period of source rocks,and during the main oil expulsion period,the structure was in the depression stage,with weak fault activity,which was conducive to the early accumulation of trapped oil and gas.