四川盆地中二叠统栖霞组层序——岩相古地理

Sequence-lithofacies palaeogeography of the Middle Permian Qixia Formation in Sichuan Basin

随着对四川盆地碳酸盐岩储集层的重视和大力勘探,中二叠统栖霞组发育的滩相储集层成为盆地内寻找新气源的有利层位之一。文中根据岩心观察、野外剖面实测和室内镜下岩石薄片鉴定分析,并结合各种沉积相标志研究,确定研究区栖霞组主要发育浅水型碳酸盐岩台地沉积,其可进一步划分为碳酸盐岩台地相及若干亚相和微相。以Vail的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,确定栖霞组发育2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,以层序格架内体系域为编图单元,用"单因素分析多因素综合作图法"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滩相颗粒灰岩经过白云岩化改造后更具储集意义。

With the recognition and vigorous exploration of carbonate reservoirs in the Sichuan Basin,bank facies reservoir developed in the Middle Permian Qixia Formation constitute beneficial layer of the basin where new gas source can be discovered.According to core observation,the actual measurement of field section,the identification and analysis of microscope thin sections ,combined with the research of sedimentary facies marks,it indicates that mainly shallow-water carbonate platform was developed in the Middle Permian in the study area. It can be classified as carbonate platform,platform margin slope facies and several subfacies and microfacies.We apply Vail＇s classical sequence stratigraphy theory and propose that stratigraphic sequence boundaries are mainly lithology-lithofacies converting interfaces,and determine that the Qixia Formation develops two Ⅱ-type third-order sequences,and each sequence can be divided into two depositional systems tracts as TST and HST.Based on sedimentary facies and sequence stratigraphic analysis, each sequence systems tract is taken as a mapping unit and the ＂single-factor analysis and comprehensive mapping method＂ as a technical method, and the lithofacies palaeogeography map of each sequence systems tract have been compiled. The authors also described its evolution character,combined with reservoir physical property characters of each facies belt. The results indicate that platform margin bank facies and inner platform bank facies are the most beneficial reservoir facies,especially the bank facies grain limestones in HST of SQ2 which experienced dolomitization are more favorable reservoirs.