川南下志留统龙马溪组页岩岩相表征

页岩岩相表征是页岩气地质评价和选层、选区的基础性研究工作。本文以露头和钻井资料为基础，依据岩矿、薄片、地化和测井资料，建立了海相页岩岩相划分方法，对川南上奥陶统五峰组下志留统龙马溪组主要岩相进行了精细表征，并形成4点认识：(1)应用岩石矿物三端员法+沉积微相划分页岩岩相类型及其组合，是开展海相页岩岩相表征的有效方法；(2)川南五峰组龙马溪组页岩发育6种岩相类型和3种典型岩相组合，其中硅质页岩和钙质硅质混合页岩是(半)深水环境的特有岩相，黏土质页岩和黏土质钙质混合页岩是半深水浅水环境的主要岩相，黏土质硅质混合页岩是浅水深水环境下的共有岩相；(3)随着水体由深变浅和水动力条件逐渐增强以及陆源物质输入量增大，不同成因岩相组合的页岩矿物成分、基质组构、古生物和有机质富集程度、测井响应等基本特征均发生重大变化；(4)受海平面变化控制，主力产层为深水陆棚沉积的硅质页岩、钙质硅质混合页岩和黏土质硅质混合页岩组合，产层顶板为半深水浅水陆棚沉积的黏土质页岩、黏土质硅质混合页岩和黏土质钙质混合页岩组合；前者因富含硅质和有机质，具有良好的脆性和物性，是形成页岩气产层的优质岩相；后者因富含黏土和贫有机质，脆性和渗透性差，是形成页岩气藏区域封盖层的优质岩相；两者自下而上构成良好的自封自储型储盖组合。

Lithofacies characterization of Longmaxi Formation of the Lower Silurian,southern Sichuan

Lithofacies characterization is fundamental to the geologic evaluation and favorable layers and plays selection in shale gas exploration. Based on the outcrops and drilling data, a lithofacies classification method for marine shale was developed to finely characterize the lithofacies of the Upper Ordovician Wufeng Lower Silurian Longmaxi shale through analysis of mineral composition, thin section, geochemical and logging data. Four preliminary conclusions were obtained: (1) Ternary diagram combined with sedimentary microfacies is an effective method in the classification of lithofacies types and their association for marine shale. (2) Six types of lithofacies were developed in the Wufeng Longmaxi shale in the Southern Sichuan Basin and they can be further classified into three types of lithofacies association, among which siliceous and calcareous siliceous mixed shales are typical in (semi) deep water environment, argillaceous and argillaceous calcareous mixed shales are dominant in semi deep to shallow water environment, and argillaceous siliceous mixed shale is developed in both shallow and deep water environment. (3) The basic features of each lithofacies association with different genesis, including mineral composition, matrix fabric, palaeontology, organic matter richness and log response, vary greatly with the decrease of water depth, stronger hydrodynamic force, and the increase of terrestrial input. (4) With the control of sea level change, the lithofacies associations deposited in deep water shelf, including siliceous, calcareous siliceous shale and argillaceous siliceous mixed shale are principal producing pay, while the lithofacies associations deposited in semi deep to shallow water shelf, including argillaceous, argillaceous siliceous shale and argillaceous calcareous mixed shale, are the caprock of the producing pay. They form a self sealed and self stored reservoir cap association vertically, and the former, which is rich in siliceous and organic matter, is favorable lithofacies to serve as producing pay, and the latter, which is rich in clay and deficient in organic matter, is favorable lithofacies to serve as capping bed.