四川盆地东南地区龙马溪组页岩气有效保存区综合评价

Comprehensive evaluation of effective preservation zone of Longmaxi Formation shale gas in the Southeast Sichuan Basin

受差异构造边界的制约,四川盆地东南地区(简称川东南)中新生代发生差异构造变形,使得保存条件成为控制该区下古生界页岩气富集的主要因素。为此,从制约保存条件的直接原因——构造作用出发,对该区页岩气保存条件进行了综合评价。首先以构造研究为先导,立足于中新生代差异构造变形方式和强度,将评价区划分为7个构造形变带,并对各构造形变带的断裂规模、断裂密度、顶底板岩性和厚度、目的层埋深、构造形态和裂缝间距指数等影响因素进行系统揭示,确立页岩气有效保存区的评价指标和标准,建立页岩气保存条件综合评价体系。在此基础上,依据该区页岩气保存条件最优评价参数标准,对7个构造形变带下志留统龙马溪组页岩气的保存条件进行了宏观评价。结果表明:齐岳山断裂以西地区的保存条件整体上好于东侧;齐岳山断裂以东地区,以武隆断褶带的保存条件为最好,其次为彭水断褶带和黔江断褶带,道真叠加断褶带、务川叠加断褶带和沿河叠加断褶带相对较差。

Under the differential tectonic boundary constraints,the differential structural deformation occurred in Meso-Cenozoic strata in the southeastern part of the Sichuan Basin,and the complex preservation conditions became a major factor that controls the accumulation of shale gas within the Lower Paleozoic strata.Thus,based on tectonism which is considered a direct factor restricting the preservation condition,this paper provides an integrated evaluation of preservation conditions of shale gas in this area.First,the evaluation zone,led by structure,was divided into seven tectonic deformation belts,based on the mode and intensity of Meso-Cenozoic differential tectonic deformation.The influencing factors for each tectonic deformation belt,such as fracture scale,fracture density,roof and bottom lithology and thickness,buried depth of target layer,structural feature and fracture spacing index,were systematically revealed.The criterion and standard for evaluating the effective preservation zone of shale gas were determined to construct an integrated evaluation system of shale gas preservation condition.Then,the preservation condition of the Lower Silurian Longmaxi Formation shale gas were evaluated macroscopically concerning the seven tectonic deformation belts on the basis of the optimal evaluation parameter standard for the preservation condition of shale gas in this area.The result suggests that,the preservation condition appears to be better in the region to the west of the Qiyueshan Fault than to the east;and in the region to the east,the Wulong Fault-fold Belt has the best preservation condition,followed by the Pengshui and Qianjiang Fault-fold Belts,while the Daozhen,Wuchuan and Yanhe superimposed fault-fold belts have relatively worse conditions.