川西南宝兴地区二叠系栖霞组一段白云岩储层充填序列及流体指示

川西南中二叠统栖霞组白云岩受多期成岩作用改造明显，优质储层成因复杂。结合野外勘察、宏观—微观岩石学特征、阴极发光及流体包裹体测温等对研究区白云岩储层充填特征展开分析。研究结果表明： ①川西南宝兴地区中二叠统栖霞组一段白云岩由半自形中—粗晶白云石组成，斑马构造及构造角砾白云岩发育，储集空间类型以残余晶间孔、残余晶间溶孔及溶蚀缝为主，其次为扩溶缝及晶洞，孔隙度多为1%～4%。②研究区白云岩储层以中—粗晶鞍状白云石及亮晶方解石充填为主，其次为少量石英充填，局部见中—粗晶白云石呈带状与方解石共同分布于裂缝中，总体上白云岩的分布受断层控制明显，缝洞较发育且表现为粗晶鞍状白云石→石英→方解石的充填序列。③研究区在中—晚三叠纪，深盆富镁热卤水沿断裂进入地层并交代原岩形成热液白云岩，热液冷却效应对早期储层进行溶蚀改造，并伴随压力降低导致粗晶鞍状白云石及少量方解石沉淀；侏罗纪末期受燕山运动影响，深盆富硅热液进入储层，部分交代早期鞍状白云石并见少量石英充填孔洞；燕山期晚期，高温-低盐度富二氧化碳流体因构造抬升过饱和析出晚期方解石，大幅度降低了储集空间。④多期流体对白云岩复合改造后，区内储层致密化明显，部分孔洞缝连通的晶粒白云岩可形成渗透性储层。

Sequence filling succession and fluid indication of dolomite reservoirs of the first member of Permian Qixia Formation in Baoxing area,southwestern Sichuan Basin

Dolomites of Qixia Formation of Middle Permian in Baoxing area of southwestern Sichuan Basin display a complex diagenetic alteration and complex genesis of high-quality reservoirs. The filling characteristics of dolomite reservoirs in the study area were analyzed based on field investigation, macroscopic and microscopic petrological characteristics, cathodoluminescence and fluid inclusion measurement. The results show that:(1) The dolomites of the first member of Qixia Formation of Middle Permian are composed of subhedral medium to coarse-grained dolomites, with zebra texture and tectonic breccia developed. The reservoir spaces are mainly residual intercrystalline pores, residual intercrystalline dissolved pores and dissolved fractures, followed by expanding dissolved fractures and geodes, with porosity of 1%-4%.(2) The dolomite reservoirs in the study area are mainly filled with medium to coarse-grained saddle dolomites and bright crystal calcites, followed by a small amount of quartzs. Locally, medium to coarse-grained dolomites are distributed in the fractures together with calcites in a belt shape. In general, the distribution of dolomites is obviously controlled by faults, and the fractures and caves are relatively developed, and the filling sequence is coarse-grained saddle dolomite-quartz-calcite.(3) During the Middle-Late Triassic period, the Mg-rich thermal brine in deep basin entered the formation along faults and replaced original rock to form hydrothermal dolomites. The hydrothermal cooling effect carried out the dissolution transformation of the early reservoirs, and accompanied by the pressure reduction, led to the precipitation of coarse-grained saddle dolomite and a small amount of calcite. Under the influence of Yanshan movement at the end of Jurassic, the silicon-rich hydrothermal solution in deep basin entered the reservoir and replaced some saddle dolomites and a small amount of quartzs filled holes. In the late Yanshanian period, the carbon dioxide rich fluids with high-temperature and low salinity were supersaturated due to tectonic uplift and precipitated late calcites, which greatly reduced the reservoir space.(4) The reservoirs are intense densification after episodic fluid alteration, and part of the residual vugs or fracture networks are relative porous for hydrocarbon accumulation and migration.