雪峰隆起西南缘寒武系牛蹄塘组地质特征及页岩气选区评价

    Geological characteristics and shale gas site selection evaluation of the Cambrian Niutitang Formation in the southwestern margin of Xuefeng Uplift

    • 摘要: 黔南坳陷位于扬子地块西南缘与雪峰隆起的过渡带,多期构造挤压与抬升剥蚀叠加改造导致该地区寒武系页岩气保存条件差异显著。以雪峰隆起西南缘寒武系牛蹄塘组为研究对象,综合区域构造解释和钻井资料,结合岩心与薄片观察、有机地球化学、矿物学与孔隙结构特征,系统刻画牛蹄塘组沉积-地球化学-储层-含气性特征。结果表明: 研究区牛蹄塘组以深水陆棚相黑色碳质页岩为主,区域厚度为35~158 m; 研究区牛蹄塘组总有机碳(total organic carbon, TOC)含量和热演化程度较高,含气性良好,干酪根类型以Ⅰ型为主; 储层整体表现为特低孔-低渗,孔隙类型以无机孔为主。根据研究区牛蹄塘组物质基础、热演化程度和保存条件,综合储层含气性与可改造性,提出页岩气有利区分级评价标准,可为黔南坳陷及邻区寒武系页岩气调查井部署与区带优选提供依据。

       

      Abstract: The southern Guizhou Depression is situated in the transition zone between the southwestern margin of the Yangtze Block and the Xuefeng Uplift. The superimposed reworking of multi-stage tectonic compression, uplift and denudation has resulted in significant variations in the preservation conditions of the Cambrian shale gas. Taking the Cambrian Niutitang Formation in the southwestern margin of Xuefeng Uplift as the research object, the authors in this study systematically characterized the sedimentary, geochemical, reservoir and gas-bearing properties of Niutitang Formation by integrating regional structural interpretation, data from wells, core and thin-section observation, organic geochemistry, mineralogy and pore structure characterization. The results showed that Niutitang Formation in the study area was dominated by black carbonaceous shales of deep-water shelf facies, with a regional thickness ranging from 35 to 158 m. Niutitang Formation in the study area exhibited high total organic carbon (TOC) content and high thermal maturity, favorable gas-bearing properties, and the kerogen type was predominantly Type Ⅰ. The reservoir was characterized by ultra-low porosity and low permeability as a whole, with reservoir spaces dominated by inorganic pores. Based on the material basis, thermal evolution degree and preservation conditions of Niutitang Formation in the study area, as well as the comprehensive analysis of gas-bearing properties and reformability of the reservoir, the authors proposed a grading evaluation criteria for the shale gas favorable area, providing basis for the deployment of the Cambrian shale gas survey wells and optimal play fairway selection in the southern Guizhou Depression and its adjacent areas.

       

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