四川盆地中二叠统层序地层格架下岩相古地理特征

Lithofacies Paleographic Characteristic of Middle Permian under Sequence Stratigraphic Framework in Sichuan Basin

摘要: 随着对四川盆地碳酸盐岩储层的重视和大力勘探，中二叠统发育的滩相储层也构成了盆内有利的含气层位之一。本文根据岩心观察、野外剖面实测、镜下岩石薄片鉴定分析和其它测试资料，结合岩石学、古生物、沉积构造等沉积相标志的综合研究，认为研究区中二叠世主要发育浅水型碳酸盐岩台地沉积，细分为碳酸盐岩台地和台地前缘斜坡相及若干亚相和微相。以经典层序地层学理论为指导，通过以岩性–岩相转换界面为主的层序界面识别，确定中二叠统发育5个II型三级层序，每个层序划分出TST和HST两个沉积体系域。在沉积相和层序地层学分析的基础上，以各层序体系域作为编图单元和“单因素分析综合作图法”为技术方法，编制了各体系域的岩相古地理图并对其演化特征进行了分析。结合各相带储集物性特征，认为台缘滩和台内滩为最有利储集相带，尤以SQ2-HST和SQ4-HST沉积期形成的滩相颗粒灰岩经过白云石化作用改造后更具储集意义。

Abstract: With the recognition and vigorous exploration of carbonate reservoirs in Sichuan Basin, bank facies reservoir developed in middle Permian Maokou and Qixia Formation also constitute beneficial layer of the basin where new gas source can be discovered. According to core observation, field profile measurement, microscopically rock thin section identification, and other testing data, combining the research of sedimentary facies signs such as petrology, paleontology, sedimentary structure, etc., the area develops sedimentary model as shallow-water carbonate platform in middle Permian, further classifies as the sedimentary facies of carbonate platform, platform margin slope and several subfacies and microfacies. We apply Vail’s classical sequence stratigraphy theory as guidance and identify stratigraphic sequence boundaries as lithology-lithofacies convert interface, so determine that Middle Permian develops five Ⅱ-type third degree sequence, and each sequence is divided into two depositional system tracts as TST and HST. Base on sedimentary facies and sequence stratigraphy analysis, we take each sequence systems tract as the mapping unit and the “single-factor analysis and comprehensive mapping method” as the technical methods and compose lithofacies paleogeography map of each sequence system tract and describe its evolution character. Associated with reservoir physical property character of each phase belt, the platform edge shoals and inner platform shoals that are considered the most beneficial reservoir facies, especially shoal facies grain limestone in SQ2 HST and SQ4 HST which was dolomitisated has more reservoir significance.