克拉通内走滑断裂成因与控藏机制研究进展——以塔里木盆地北部为例

Advances in research on the genetic mechanisms of intracratonic strike-slip fault system and their control on hydrocarbon accumulation:A case study of the northern Tarim Basin

近年来,在中国多个克拉通盆地腹部识别出成体系发育的走滑断裂系统,这是克拉通盆地内部一种重要的构造样式。针对塔里木盆地北部走滑断裂体系,应用断裂构造解析、断裂发育演化离散元数值模拟、断裂形变有限元数值模拟及断裂核-带结构解剖等技术方法,结合油气井生产动态资料,分析了走滑断裂体系成因与控藏机制,并总结了研究取得的新进展与新认识。研究表明:(1)塔里木盆地北部走滑断裂体系是盆地中部大型逆冲带向北推挤时形成的伴生调节构造,具有“非共轴挤压、调节区域变形”动力学成因机制;(2)随着走滑断裂滑移距增大,核部角砾岩类型由裂隙角砾岩、破碎角砾岩演变为杂乱角砾岩和碎裂岩,高阶演化程度的角砾岩可降低断层核部渗透性;(3)强压扭背景下形成的走滑压脊构造具有“上张下压”纵向应力分布特征,断控储集体主要沿断裂带在深部发育;(4)走滑断裂相关盐构造耦合-解耦变形特征对油气垂向输导具有重要控制作用;(5)分层变形是小滑移距走滑断裂在深埋条件下的变形特征,可控制油气沿走滑断裂垂向输导后在多个层系分层聚集。

In recent years,strike-slip fault system over large areas has been identified in multiple cratonic basins in China,representing a significant structural style in interior cratonic basins.With the strike-slip fault system in the northern Tarim Basin in mind,we apply techniques like seismic-geological analysis of the faulted structure,discrete element numerical simulation of the fault dynamic evolution,finite element numerical simulation of off-fault deformations,and structural analysis of the fault cores and associated damage zones(also referred to as the fault coredamage zone architectures)to study.In combination with well production data,new understandings on the origin of the strike-slip fault system and its control on hydrocarbon accumulation are proposed.The results are as follows.(1)The strike-slip fault system in the northern Tarim Basin is formed as a result of northward thrusting of large thrust belts to accommodate regional shortening under the non-coaxial extrusion in the central Tarim Basin,featuring a dynamic genetic mechanism of non-coaxial extrusion and accommodation of regional deformations.(2)With increasing strikeslip fault displacement,the crackle and mosaic breccias in the fault cores gradually evolve into chaotic breccias and cataclasites.The resulted breccias of high evolutionary degree can reduce the fault core-damage zone permeability.(3)The pressure-ridge structures along the strike-slip faults formed under intense strike-slip transpressional stress,is characterized by extension in the upper part and compression in the lower part,resulting in the fault-controlled reservoirs in large scale primarily occurring at depths.(4)The decoupling of the gypsum-salt layer with the overlying strata related to the strike-slip faulting plays an important role in controlling the vertical hydrocarbon migration.(5)Layered deformation,as an inherent characteristic of the strike-slip faults with small displacement at great deeps,governs the vertical migration and accumulation of hydrocarbons in multiple layers along the strike-slip faults.