长沙岭转换带构造演化特征及其与油气的关系

Tectonic evolution in Changshaling transfer zone and its relation with hydrocarbon accumulation

长沙岭构造带发育复杂断块-岩性油气藏,受多期构造运动影响,断裂发育、切割关系复杂,且断裂发育带地震资料成像品质较差,导致断裂识别难度大、发育期次认识不清、成藏规律认识不系统。为此,在前人研究基础上,通过分析构造演化史精细解释构造,分析断裂期次和圈闭特征,研究构造控砂、断裂与油气运聚关系,明确了油气富集规律。获得以下认识:①长沙岭转换带的断裂主要形成于早白垩世拉张断陷期的两期伸展构造运动,早期为基底卷入伸展构造运动,主要发育西倾正断层,晚期为盖层滑脱伸展构造运动,主要发育东倾犁式正断层,对早期断层切割强烈。②早期西倾同沉积断层形成多级断阶带,控制沉积体系的平面展布;调节断层控制形成"断槽"、"断梁"相间的古地貌;白垩系下沟组沉积时期,具有"断槽输砂、古地貌控砂"沉积特征。③早期西倾断层对油气主要起封堵、保存作用,晚期东倾断层主要起运移、输导作用,在两期断层共同控制作用下形成断垒块油气藏,具有"构造控油、一块一藏、高块富集"的特点。

Fault block-lithologic reservoirs in Changshaling transfer zone exhibit complicated fault-formation intersections due to the occurrence of multiphase tectonic movements,and it is hard to investigate the fault system and hydrocarbon accumulation using seismic data with poor quality.Based on preceding studies,we focus on tectonic evolution history,structure interpretation,episodes of faulting,and trap features to establish the relations among structures,sands,faults,and hydrocarbon migration and accumulation.We conclude that(1)Changshaling transfer zone is the product of twophase extensional tectonic movements in the Early Cretaceous extension and fault depression period.Basement-convolved extensional tectonic movement occurred at the early stage,when west-inclined normal faults came into being.Overburden-slippage extensional tectonic movement occurred at the late stage,when east-inclined plough-type normal faults appeared and intersected early faults;(2)early west-inclined syndepositional faults gave rise to fault-bench belts and thus dominate the lateral distribution of sedimentary systems.Accommodation faults gave birth to an ancient land form with fault troughs alternating with fault ridges.Sands migration was dominated by fault troughs,and sands distribution was dominated by the ancient land form at the depositional stage of the Cretaceous Xiagou Formation;(3)early west-inclined faults played a role in hydrocarbon preservation,and late east-inclined faults played a role in hydrocarbon migration.Fault-horst reservoirs are the product of these two-phase faulting activities.In summary,hydrocarbon accumulation is dominated by structures;each fault block has a reservoir;oil and gas concentrate in the structural highs.