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旋卷压扭构造作用控制下煤层气富集地质控制模式以河西走廊带东部魏家地煤矿为例

Geological controlling mode of coalbed methane enrichment controlled by vortex compression-torsion tectonic:Taking the Weijiadi Coal Mine in the eastern part of the Hexi Corridor belt as an example

  • 摘要: 我国西北地区河西走廊带东部广泛发育的小型断陷含煤盆地,煤层厚度大且变化快,受中新生代陇西旋卷构造叠加影响,煤层气含量分布不均一,治理难度大。以靖远煤田魏家地煤矿为研究区,以煤层气钻井、录井、测井数据及勘探与生产期间获得的构造和水文资料为基础,系统分析研究区煤层气富集特征及其构造控制作用,取得如下主要认识:受“旋卷挤出效应”和“断层阻挡效应”控制,研究区形成高角度逆断层间夹东西雁列状排列的背−向斜。以F3断层为界,分为西南部压性构造区、东北部压扭构造区,各构造分区煤层含气量整体偏低,且差异明显。旋卷压扭构造作用控制下的断层面泥岩涂抹封闭、顶板有效封盖、构造煤吸附性能强且封闭性强是煤层气富集关键控因。本次构建了3种煤层气富集模式:旋扭构造过渡段裂隙闭合区煤层气富集模式、逆断层下盘构造高点煤层气富集模式和向斜核部煤层气富集模式,其中靠近断层位置地层偏转明显,中间位置存在一个旋扭的过渡段,旋卷压扭构造区内过渡段现今水平最大主应力方向与裂隙方向垂直煤层裂隙闭合程度高,煤层气富集。以上认识可以为河西走廊带东部旋卷压扭断陷盆地瓦斯治理和煤层气开发提供理论支撑。

     

    Abstract: The small faulted coal basins are extensively developed in the eastern part of the Hexi Corridor belt in the northwest region of China, and the coal seams exhibit large thicknesses and rapid variations. Affected by the superimposition of the Longxi vortex tectonic activity in the Mesozoic and Cenozoic eras, the coalbed methane (CBM) distribution is uneven and difficult to manage. This research takes the Weijiadi Coal Mine in the Jingyuan Coalfield as the research area, based on drilling and logging data of CBM, as well as tectonical and hydrological data obtained during exploration and production, to systematically analyze the occurrence characteristics of CBM and the tectonic control effect of it in the research area. The following main understandings are obtained: Controlled by the “vortex extrusion effect” and “fault blocking effect”, the study area forms high-angle reverse faults and anticline-syncline axes with east-west echel arrangement between them. Divided by the F3 fault, the study area consists of two sets of tectonic systems: the southwestern compressive tectonic area and the northeastern compressive-torsion tectonic area. The CBM content in all areas is gerenally low, with significant variations among them. The enrichment of CBM is mainly controlled by the positive factors such as the mudstone smearing and sealing of the fault plane, the effective sealing of the roof, the strong adsorption and sealing properties of the tectonically deformed coal with strong deformation. Three CBM enrichment models have been constructed: the CBM enrichment mode in the closed fracture zone of the transition section of the vortex tectonic, the CBM enrichment model in the high position of the reverse fault’s footwall, and the CBM enrichment model in the core of the syncline. Among them, the strata near the fault location show significant deviation, and there is a transitional section of twisting in the middle position, the direction of the current maximum horizontal principal stress is perpendicular to the fracture within the vortex tectonic structure, determines the high degree of fracture closure in the torsion transition section, resulting in the enrichment of CBM. The understandings obtained in this study provide theoretical support for gas control and CBM development in the vortex compressive-torsional faulted basins in the eastern part of the Hexi Corridor belt.

     

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