川东及周缘地区五峰组—龙马溪组海相页岩气保存条件评价

Evaluation of the preservation conditions of marine shale gas in Wufeng-Longmaxi formations in eastern Sichuan Basin and peripheral areas

保存条件是影响中国南方海相页岩气富集高产的关键因素。本文以川东及周缘下古生界奥陶系五峰组—志留系龙马溪组海相页岩为研究对象,论述了构造作用、封盖条件、流体特征等3方面对页岩气保存的影响,并结合勘探开发实践建立了川东及周缘地区海相页岩气保存评价的指标体系。研究表明:构造运动是页岩气破坏与散失的根本原因,主要体现在构造变形强度、断层规模与断裂发育程度、地层隆升剥蚀程度等3个方面;封盖条件是页岩气藏富集的基础保障,厚度大、展布稳定、岩性致密的顶底板条件以及厚层页岩自身封闭性是有利于页岩气保存的宏观地质条件;地层压力系数与页岩气含气量呈对数正相关关系,是页岩气保存评价的重要判别指标。

Preservation conditions are the key factors affecting the enrichment and high yield of marine shale gas in southern China.Taking the marine shales of the Lower Paleozoic Ordovician Wufeng Formation-Silurian Longmaxi Formation in eastern Sichuan Basin and its periphery as the research object,this paper discusses the influence on the preservation of shale gas from three aspects:tectonic,capping conditions and fluid characteristics,and establishes an index system for evaluating the preservation of marine shale gas in eastern Sichuan Basin and its periphery in combination with the practice of exploration and development.The study concluded that tectonic movement is the root cause of shale gas destruction and dispersion,which is mainly reflected in the intensity of tectonic deformation,the scale of faults and the degree of fracture development,and the degree of uplift and denudation of strata;the capping conditions are the basic guarantee for the enrichment of shale gas reservoirs,and the conditions of top and bottom plates with large thickness,stable spreading,and dense petrography,as well as the closure of thick shale rocks,are the macroscopic geological conditions conducive to the preservation of shale gas.The pressure coefficient has a logarithmic positive correlation with the gas content of shale gas,which is an important index for shale gas preservation evaluation.