Differences in preservation conditions of deep shale gas in high-steep complex tectonic belt: taking Qijiang high-steep complex tectonic belt in southeast Sichuan as an example
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摘要: 川东南地区是中国页岩气勘探的重点目标之一,现阶段的勘探领域正逐步迈入深层、超深层,但由于受钻井与地震等多种因素的制约,对该地区的构造特征及页岩气保存条件的研究还不够深入。为了查明川东南地区綦江高陡复杂构造带构造变形特征及其对深层页岩气富集规律的影响,为后续勘探部署提供依据,选取典型三维地震剖面,从构造变形特征剖析入手,结合实钻数据分析,建立高陡构造模型,在此基础上开展保存条件差异的主控因素定量评价。结果表明,綦江高陡构造具备“上陡下缓+膏岩主控+前锋变陡”的分层变形特征;綦江地区发育一套大范围的寒武系膏盐层,其塑性形变对上覆构造的隆起起到控制作用;区内影响页岩气保存条件的因素包含主动变形强度、断裂体系、断面正应力、构造与地应力夹角、顶板滑脱层等,各因素相互作用,导致研究区内部保存条件差异明显。据此,建立了綦江高陡构造保存条件评价标准,明确隆盛—桃子荡构造带构造应力单一,主动变形强度低,构造封闭性强,是下一步勘探的主要有利目标。Abstract: The southeastern Sichuan Basin is one of the key targets for shale gas exploration in China. Currently, the exploration has gradually been delved into deep and ultra-deep formation fields. However, due to various constraint factors such as drilling and earthquakes, research on the tectonic characteristics and shale gas preservation conditions in this area is inadequate. In order to find out the tectonic deformation characteristics of Qijiang high-steep complex tectonic belt in southeast Sichuan and its impact on the enrichment law of deep shale gas, and to provide a basis for subsequent exploration deployment, a high-steep structural model is established based on the analysis of tectonic deformation characteristics and practice drilling data, and the quantitative evaluation of the main controlling factors of differences in preservation conditions is carried out on the basis of the model. The research results show that: (1) Qijiang high-steep structure has the layered deformation feature of "steep upper part and flat lower part + dominated by gypsolyte + steep front"; (2)There is a widely developed Cambrian gypsum salt layer in the Qijiang area, whose plastic deformation controls the uplift of the overlying structure; (3) The factors affecting the preservation conditions of shale gas in the study area include active deformation strength, fracture system, normal stress of fault plane, angle between structure and geostress, roof detachment layer and other factors. The interaction of multiple factors leads to obvious differences in the preservation conditions in the study area. According to the analysis results, the evaluation criteria for the preservation conditions of Qijiang high-steep structures are established, and it is defined that the Longsheng-Taozidang tectonic belt has single tectonic stress, low active deformation intensity and well-closed structure, which is the main favorable target for the next exploration.
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表 1 川东南綦江高陡构造带膏岩与上覆构造隆升幅度统计
Table 1. Uplift amplitude of gypsolyte and overlying structure in Qijiang high-steep tectonic belt in southeast Sichuan
石龙峡 中梁山 铁厂沟 石油沟 隆盛 桃子荡 膏盐层变形幅度/ms 290 265 270 310 390 400 上覆构造隆升幅度/ms 530 650 510 630 645 680 总变形幅度/ms 820 915 780 940 1 035 1 280 变化趋势 表 2 川东南地区主控顶板滑脱层对页岩气目的层保存条件影响能力统计
Table 2. Statistics of influence of main roof detachment layer on preservation conditions of shale gas target stratum in southeast Sichuan
XY1 SY1 FB1 HC1 断层滑移量/km 1.32 1.02 1.12 1.22 距目的层垂直距离/km 0.305 0.192 0.215 0.209 含气量/(m3/t) 6.17 1.88 1.04 0.84 表 3 川东南綦江高陡构造埋深5 km以浅有利目标评价
Table 3. Evaluation of favorable targets of Qijiang high-steep structure with buried depth less than 5 km, southeast Sichuan
构造名称 构造变形强度 构造封闭性 滑脱层距目
的层距离/km有利面积/km2 资源量/108 m3 优选排队 主要断裂体系 主动变形强度/km 断面正应力/MPa 构造与地应力
夹角/(°)桃子荡 走滑断裂、逆冲断裂 0.03 125.0 75.0 0.35 52.2 443.7 1 370.2 一类 隆盛 逆冲断裂、转换断裂 0.11 120.0 80.0 0.30 109.0 926.5 石油沟 逆冲断裂、转换断裂 0.17 108.0 78.0 0.26 80.0 680.0 725.0 二类 铁厂沟 逆冲断裂、转换断裂 0.20 92.0 25.0 0.25 5.3 45.0 中梁山 先存基底断裂、走滑断裂、转换断裂 0.26 80.0 10.0 0.21 18.3 155.6 399.6 三类 石龙峡 先存基底断裂、走滑断裂、转换断裂 0.24 75.0 5.0 0.19 28.7 244.0 合计 293.5 2 494.8 -
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