再论岩相古地理可作为页岩气地质调查之指南

Recomment on the Study of Lithofacies Palaeogeography as a Guide for Geology Survey of Shale Gas

在页岩气的区域地质调查阶段,主要通过有机质含量(TOC)与类型、有机质热演化程度、含气页岩厚度、矿物组分类型与含量以及储集层特征等基本地质条件参数,对页岩气有利区进行评价,而以上页岩气基本地质因素均受沉积相的控制。以详细的沉积相研究为基础,通过岩相古地理编图,可以明确富有机质页岩的展布特征,所以岩相古地理控制了页岩气的发育特征。通过利用主要基本地质条件参数,对川南及邻区志留系龙马溪组黑色岩系页岩气有利区进行初步评价,认为川南及邻区志留系龙马溪组,只要已进入中成岩阶段的浅海陆棚相黑色岩系,就能形成页岩气储层。在前人研究的基础上,进一步实例论证并提出沉积相或岩相古地理研究应为页岩气地质调查和选区评价的关键和基础。

The basic geological parameters,including total organic carbon conten(TOC)and type,thermal evolution of organic matter(R o)thickness of hydrocarbon source rocks,mineral composition and content,reservoir characteristics,which all controlled by sedimentary facies,are the main elements to evaluate the enrichment of shale gas in regional geology survey stage.On the basis of the detailed study of sedimentary facies,by mapping the lithofacies palaeogeography,distribution of the fine-grained sedimentary rocks which are rich in organic matter can be figured out.So,the lithofacies paleogeography controls the developmental characteristics of the shale gas.Using the basic geological parameters,the shale gas favorable areas in southern Sichuan Basin and its peripheral region were preliminarily evaluated.The black rocks of shallow shelf facies in Longmaxi Formation of Silurian,as long as being up into middle diagenetic stage,would be able to be shale gas reservoirs in southern Sichuan Basin and its periphery.On the basis of our previous study,through analyzing the shale gas geologic feature of Longmaxi Formation in southern Sichuan Basin and its periphery,the point of view is further demonstrated,that the study of sedimentary facies or lithofacies palaeogeography is the key and foundation of shale gas geology survey and evaluation.