西湖凹陷西斜坡断层-岩性圈闭形成条件探讨

Discussion on Formation Conditions of Fault-Lithologic Traps in West Slope of Xihu Sag

随着勘探程度的深入,西湖凹陷西斜坡全面进入了岩性圈闭勘探阶段,西斜坡主要勘探层系始新统经历了强烈的断陷-断拗转换期,断层相关的断层-岩性圈闭为主要的岩性圈闭类型,为了寻找规模岩性油气藏富集区,需要认识到断层-岩性圈闭的形成条件。此文通过针对断层-岩性圈闭的构造沉积演化及控砂模式研究,认为斜坡带西高东低的地貌背景造成物源自西向东推进,形成的潮坪-潮控三角洲共生的沉积环境下发育的三角洲分支河道、潮坪砂和潮道等多种类型的砂体,在断裂和地貌的控制下形成顺向主断裂下降盘陡坡砂岩上倾尖灭-断层侧翼封堵圈闭、多级顺向断层下降盘断层上倾封堵-砂岩侧翼尖灭圈闭、反向断层下降盘砂岩上倾尖灭-断层侧翼封堵圈闭、反向断层上升盘断层上倾封堵-砂岩侧翼尖灭圈闭四种类型的断层-岩性圈闭。

West Slope of Xihu Sag has entered the exploration stage of lithologic traps with the development of exploration.The main exploration strata of Eocene Series in West Slope experienced a period of strong fault subsidence-depression transition.The fault-lithologic traps related to faults are the main types of lithologic traps.In order to find the rich areas of large-scale lithologic oil and gas reservoirs,it is necessary to recognize the formation conditions of fault-lithologic traps.In this paper,through the study of the tectonic sedimentary evolution of fault-lithologic traps and the combination of sand control models,it is considered that various types of sand bodies such as delta branch channels,tidal flat sands and tidal channels are developed in the sedimentary environment of tidal flat and tide-dominate delta intergrowth,which is formed for the reason that the slope belt with the geomorphic background of low eastern part and high western part caused the provenance to advance from west to east.Four types of fault-lithologic traps are formed under the control of faults and landforms,those are traps of the up dip pinch out zone of sandstone on the downthrown side slope of the consequent main fault and the block zone from the flank of the fault,traps of the up dip block of the downthrown side of the multilevel consequent fault and the pinch out zone of sandstone on the flank,traps of the up dip pinch out zone of sandstone on the downthrown side of the antithetic fault and the block zone from the flank of the fault,and traps of the up dip block of the upthrown side of the antithetic fault and the pinch out zone of sandstone on the flank.