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沁水盆地武乡南区块煤层气富集区的构造与沉积控制

Structural and sedimentary control of coalbed methane enrichment areas in south exploration block of Wuxiang County, Qinshui Basin

  • 摘要: 山西沁水盆地武乡南勘探区块是我国重要的煤层气资源富集区之一,然而其复杂的地质构造特征,尤其是褶皱与断裂的交错分布,极大地限制了煤层气的高效开发。为此,结合区域地质动力学背景,系统分析了该区块的褶皱和断裂构造特征,在对三维地震、测井和钻井资料精细解释的基础上,构建了研究区块的断层和煤层三维模型,并重点分析了该区块内沉积和构造特征与煤厚及煤层气含量变化的相关性。研究成果主要体现在以下3方面:一是依据构造组成与产状特征划分了4个不同的分布区域,并论述了各区域主要构造的性质、要素和分布特点,为区域地质构造的系统分类提供了科学依据;二是依据构造几何学与动力学分类方法,将区块控煤构造样式划分为3种构造类型(伸展、挤压、走滑断层)和9个亚类型,进一步细化了构造对煤层气富集的影响机制;三是通过对山西组与太原组砂泥比值、沉积、顶底板岩性及地质构造特征分析,概要论述了沉积环境、顶底板岩性与煤层厚度及含气量变化的相关性,揭示了沉积环境对煤层厚度具有直接控制作用,且煤层厚度进而影响含气量的分布,并进一步研究了构造对含气量丰度的控制作用。在此基础上,分别划出了3号和15号煤储层各3个煤层气富集区域, 并绘制了煤层气富集区分布特征图。该研究成果可为该区块煤层气高效开发的科学选区提供判识依据。

     

    Abstract: The south exploration block of Wuxiang County in Qinshui Basin of Shanxi Province is one of the important coalbed methane resource rich areas in China. However, its complex geological structure features, especially the alternating distribution of folds and faults, greatly restrict the efficient development of CBM. Therefore, combined with the regional geodynamic background, the structural characteristics of folds and faults in this block are systematically analyzed, on the basis of detailed interpretation of 3D seismic, logging and drilling data, a 3D model of fault and coal seam in the study block is constructed, and the correlation of sedimentary and structural characteristics with the variation of coal thickness and CBM content in this block is analyzed emphatically. From the researched results, it can be concluded that: Firstly, according to the structural composition and occurrence characteristics, four different distribution regions are divided, and the nature, elements and distribution characteristics of the main structures in each region are discussed, which provides a scientific basis for the systematic classification of regional geological structures; Secondly, according to the structural geometry and dynamic classification method, the block coal-controlling structural styles are divided into 3 structural types (extension, extrusion, strike-slip fault) and 9 subtypes, and the influence mechanism of structure on CBM enrichment is further refined. Thirdly, through the analysis of sand-mud ratio, sediment, lithology and geological structure characteristics of Shanxi Formation and Taiyuan Formation, the correlation between sedimentary environment, lithology of top and floor and changes of coal seam thickness and gas content is briefly discussed, revealing that sedimentary environment has a direct control effect on the thickness of coal seam, and the thickness of coal seam further affects the distribution of gas content. The controlling effect of structure on gas abundance is further studied. On this basis, three CBM enrichment areas in No. 3 and No. 15 coal reservoirs are delineated respectively, and the distribution characteristics of CBM enrichment areas are drawn. The research results can provide a basis for the scientific selection of efficient CBM development in this block.

     

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