塔里木盆地肖尔布拉克剖面走滑断裂带内部结构及控储模式

Internal architecture of strike-slip fault zone and its control over reservoirs in the Xiaoerbulake section， Tarim Basin

马庆佑 曾联波 徐旭辉 曹自成 蒋华山 王海学

Qingyou Ma Lianbo Zeng Xuhui Xu Zicheng Cao Huashan Jiang Haixue Wang

选取塔里木盆地西北缘肖尔布拉克剖面出露的走滑断裂带为研究对象，通过详细观察描述、取样鉴定、地化分析等研究，刻画出肖尔布拉克剖面走滑断裂带的内部结构，建立了该断裂带的控储模式，为塔里木盆地断溶体目标研究提供了地质模型。结果表明：肖尔布拉克剖面走滑断裂带近垂直切穿中寒武统沙依里克组与阿瓦塔格组，根据两盘地层对接关系判断其为右行走滑。断裂带内部发育由断层核与破碎带组成的“二元结构”，其中断层核主要由断层角砾岩带与方解石充填脉组成，角砾岩性与围岩一致，呈棱角-次棱角状，反映近源破碎、垮塌堆积形成。断层角砾岩被方解石胶结充填，方解石晶粒尺寸大小不等，越靠近角砾壁的方解石晶粒越细小，反映多期流体活动与改造形成。断层核内的方解石胶结物δC值在-8 ‰～-2 ‰，Sr/Sr值普遍高于同沉积海水，稀土元素具有Ce明显负异常等特征，反映受到后期大气淡水改造。断层破碎带内裂缝较发育，大部分裂缝半开启或全开启，局部沿裂缝溶蚀形成扩大孔洞，少部分裂缝被方解石胶结充填。基于上述研究，初步建立了该断裂带内部结构的成因演化及控储模式：走滑断裂带初始剪切活动，引起中寒武统碳酸盐岩地层脆性剪切破裂，长期摩擦滑动后形成了无内聚力的角砾岩带及裂缝带，为高孔渗性储集层；大气淡水携带矿物质垂向运移至断裂带深部，在温度、压力改变后发生水-岩相互作用，形成大量方解石脉胶结充填，降低了断裂带早期的孔渗性能，最终形成多期改造后的溶洞-胶结型断裂带结构。

The fault zone outcropping the Xiaoerbulake section in the northwest margin of Tarim Basin is selected to conduct detailed field investigation and description， sampling identification， geochemical analyses and other studies with the aim of establishing an architecture-reservoir model for a better geological description of fractured-vuggy reservoir bodies in the basin. The results show that the fault zone comprises right-lateral strike-slip faults （according to the juxtaposition relationship between the fault walls） and vertically cuts through the Middle Cambrian Shayilike and Awatage Formations. A dual structure of fault core and damage zone can be observed within the zone. The fault core is mainly composed of fault breccia with calcite veins. The angular and sub-angular shaped breccia is consistent with surrounding rocks in terms of lithology， indicating a possible damage-collapse-accumulation genesis of near-source material. The calcite particles in veins vary in size but tend to be finer toward the wall of breccia， indicating a multi-stage activities and reformation of fluids. With δC values ranging from -8‰ to -2‰， Sr/Sr values generally higher than those of synsedimentary seawater， and significant negative Ce anomalies in REE （rare earth elements） analyses， the calcite veins truthfully record the visit of a later atmospheric fresh water. Fractures are well developed in the damage zone， most fractures are half or fully open with enlarged caverns from dissolution occurring locally along the fractures， and some fractures are filled by calcite cement. Based on the above research， a model is set up to describe the genetic evolution of the internal architecture and its control over the reservoirs in the fault zone. It suggests that the initial shear activity of strike-slip fault zone led to a brittle shear fracturing of the Middle Cambrian carbonate stratum， which then experienced long-term friction and slide to form noncohesive breccia and fracture zone with highly porous and permeable reservoirs. However， this strike-slip fault zone with high-quality reservoirs was later degraded into a vug-cemented fault zone as a result of multi-stage activities of calcite cementation jointly triggered by materials brought by atmospheric fresh water migrated vertically from surface to the deep along the zone and changes in temperature and pressure.

10.11743/ogg20220106