塔里木盆地克拉苏油气区是我国“西气东输”的重要气源地,也是我国已建成的最大超深油气田。该区主要目的层组白垩系巴什基奇克组为一套中厚层细-中砂岩夹薄层泥岩建造,埋深主要介于6 000~8 000 m,储层基质孔隙度普遍低于10%,孔喉结构复杂,构造裂缝普遍发育,且有效裂缝网络对该类气藏高产稳产至关重要。同时,深埋高温压条件下,成岩流体沿裂缝快速活动,对储层裂缝有效性产生了差异影响。本文针对井下大量岩心构造裂缝开展CT扫描、主体薄片、阴极发光、激光共聚焦、扫描电镜等实验分析,系统研究了成岩流体在微裂缝尺度、岩心裂缝尺度、圈闭尺度、油气田尺度上对构造裂缝的成岩类型、配置关系、裂缝有效开度及影响分布范围。认为成岩流体对克拉苏油气田白垩系巴什基奇克组构造裂缝有效性的影响主要表现为裂缝面本身及周围储层孔喉的胶结充填及溶蚀作用,主体裂缝(超60%)胶结充填率不足5%,有效开度介于0.2~2 mm,成岩流体沿微裂缝胶结沉淀或溶蚀改造,但仅影响裂缝周围约4 mm~20 m范围,在岩石的差异矿物之间(一般为石英颗粒及长石颗粒)更易发生溶蚀;成岩流体垂向上沿背斜储层中上部50~150 m内的裂缝网络发生胶结、溶蚀作用,整体充填率约为60%~80%,在底水层中裂缝胶结充填率达60%~90%;平面上,成岩流体沿先期沉积水系迹线、顺构造裂缝活动,南北向影响距离为20~40 km,主要为方解石充填与胶结。由于高效沟通的裂缝网络位于目的层中-上部,应考虑在中部或中上部地层中钻完井,避开顶部的“基底式胶结”层,在北部区块针对裂缝中的方解石充填物大开度裂缝实施酸化压裂措施,提升储层整体渗流能力。

The Kelasu oil and gas area in the Tarim Basin serves as a significant gas source for the “West East Gas Transmission” project in China and stands as the largest ultra-deep oil and gas field developed in the country. The primary reservoir formation targeted in this region is the Cretaceous Bashjiqike Formation, characterized by medium-thick fine to medium sandstone interbedded with thin mudstone layers. Burial depths typically range between 6000 m and 8000 m, and the reservoir matrix’s porosity generally remains below 10%. The pore-throat structure is intricate, with widespread development of structural fractures. The presence of an effective fracture network is essential for achieving high and consistent gas production from this type of reservoir. In the context of deep burial, high temperatures, and pressures, the rapid activity of diagenetic fluids along fractures significantly influences the effectiveness of reservoir fractures. This article conducts microscopic experimental analyses, including CT scanning, main thin section analysis, cathodoluminescence, laser confocal scanning, and scanning electron microscopy on numerous underground rock core structural fractures. The study systematically investigates the diagenetic types of fluids, their configuration relationships, effective fracture openings, and impact distribution range at various scales—from micro-fracture to core fracture, trap, and oil and gas field scales. The impact of diagenetic fluids on the effectiveness of structural fractures within the Cretaceous Bashjiqike Formation of the Kelasu oil and gas field primarily manifests in the cementation, filling, and dissolution of the fracture surfaces themselves and the surrounding reservoir pores. The cementation filling rate of the main fractures, exceeding 60%, typically remains below 5%, with effective openings ranging from 0.2 mm to 2 mm. Diagenetic fluids precipitate or dissolve along microcracks, affecting an approximate range of 4mm to 20 mm around the fractures. Dissolution tends to occur between different minerals in the rocks, particularly quartz and feldspar particles. Vertically, diagenetic fluids follow the fracture network within the upper and middle parts of the anticlinal reservoir, where both cementation and dissolution processes take place. The overall filling rate ranges from 60% to 80%, with the cementation filling rate of fractures in the lower water layer reaching 60% to 90%. Horizontally, diagenetic fluids migrate along the paths of previous sedimentary water systems and structural fractures, with a north-south influence distance spanning 20 km to 40 km, predominantly filled and cemented with calcite. Given the efficient communication of the fracture network in the middle to upper part of the target layer, drilling and completion operations are recommended in these sections to avoid the “basal cementation” layer at the top. In the northern block, acid fracturing techniques are employed to enhance the overall permeability of the reservoir by targeting the large opening fractures filled with calcite material.