Great breakthroughs have been recently made in exploring oil and gas in the Middle Permian Qixia Formation, the southwestern Sichuan Basin, China. These discoveries in dolomitic reservoirs revealed abundant hydrocarbon reserves, agreeing on traditional predictions associated with dolomite prospect, which also left the controversy about the nature of dolomitization. Therefore, it is particularly important to research dolomite reservoirs characteristics and their genesis. In this study, comprehensive analyses, including pore-casted thin-section observation, scanning electron microscopy, physical property analysis, mercury injection measurement, fluid inclusion test, and isotopic measurement, are carried out to characterize Qixia Formation dolomites that are sampled from five outcrop sections and nine wells, followed by an investigation into controlling factors of these characteristics and establishment of pore evolution models. Granular dolomites, especially fine-grained and coarser dolomites, are demonstrated to be the best reservoir rocks, with their reservoir capacity positively related to dolomite grain sizes. There are mainly four types of pore-throat structures, namely large pores with wide throats, medium pores with medium throats, small pores with narrow throats, and fracture pore-throat structure. Dolomite reservoirs in the study area have experienced complex diagenetic changes, including the meteoric water dissolution in the penecontemporaneous stage, dolomitization in the shallow-burial stage, and hydrothermal- and formation water-related dissolution during the middle-deep burial stage. High-quality reservoirs are mainly distributed in the shoal facies deposits, especially where both dolomitization and multi-stage dissolution have occurred.

近期，四川盆地西南部中二叠统栖霞组油气勘探取得重大突破。白云岩储层的这些发现揭示了丰富的油气储量，与白云岩远景相关的传统预测一致，这也留下了关于白云岩化性质的争议。因此，研究白云岩储层特征及其成因显得尤为重要。本研究通过铸孔薄片观察、扫描电镜、物性分析、压汞测量、流体包裹体试验、同位素测量等综合分析，对5个露头的栖霞组白云岩进行了表征。部分和九口井，随后研究了这些特征的控制因素并建立了孔隙演化模型。粒状白云岩，特别是细粒和粗粒白云岩，被证明是最好的储集岩，其储集能力与白云石粒度呈正相关。孔喉构造主要有大孔宽喉、中孔中喉、小孔窄喉和裂缝孔喉结构四种。研究区白云岩储层经历了复杂的成岩变化，包括准同生阶段的大气水溶蚀、浅埋藏阶段的白云石化作用以及中深埋藏阶段的热液及地层水溶蚀作用。