环开江——梁平海槽长兴组生物礁类型及储层特征

Types and characteristics of reefs of Permian Changxing Formation around Kaijiang-Liangping trough,eastern Sichuan Basin

环开江—梁平海槽发育的台地边缘礁、滩相地层为川东地区长兴组最重要的油气勘探层段,储层岩性主要为礁、滩相的结晶白云岩,具有分布面积广、厚度较大和物性较好等特点。通过露头、岩心观察和薄片鉴定,对研究区台地边缘生物礁内部结构及发育特征进行了研究,结果表明生物礁在海槽周缘不同部位的发育特征及储层特征差别较大,按其发育规模可分为丘礁和点礁。礁的生长发育受控于古地貌和海平面的变化,具有不同的生长演化阶段和储层特征。相对而言,点礁生长持续时间较短、储层厚度较小、储集性能较差,丘礁生长持续时间较长、储层厚度较大、储集性能较好。研究区台缘生物礁储层总体表现为低孔、低渗特征,其中台缘丘礁的孔、渗性明显好于台缘点礁,而台缘点礁中长二时期的点礁其孔、渗性又明显好于长一时期的点礁。

Platform-edge reef flat facies is the most important oil and gas exploration layer of Changxing Formation around Kaijiang-Liangping trough, eastern Sichuan Basin. The lithology of the reservoir is mainly reef flat facies crystal dolomites, and it has the characteristics of broad distribution areas, great thickness and fine physical properties. Through the observation of outcrop, core and thin section, this paper studied the internal structures and development characteristics of platform-edge reefs in the study area. The result shows that the platform-edge reefs have very different sedimentary characteristics in different places near the trough, and could be divided into patch reefs and mound reefs according to the development scales. Because of the different palaeogeomorphology and sea-level change,the patch reefs and mound reefs possess different evolution stages and reservoir characteristics. The patch reefs developed with the characteristics of shorter formation time, thinner reservoir thickness and poor properties, while the mound reefs mainly developed with the characteristics of larger formation time, thicker reservoir thickness and fine properties. Platform-edge reefs reservoir belongs to low porosity and low permeability reservoir. As a kind of the platform edge reefs, the mound reefs reservoir is better than that of patch reefs, and the patch reefs reservoir developed in the second period of Changxing Formation is better than patch reefs reservoir developed in the first period of Changxing Formation.