扩散主控型煤层定义、特征及瓦斯促抽路径分析

Definition, characteristics and analysis of gas extraction improvement method in diffusion-dominated coal seams

  • 摘要: 随着我国煤炭资源生产重心向中西部转移、开采水平向深部延伸,煤层结构呈现多元化、差异化特征,导致瓦斯储运规律发生变化,构建适用于多煤体结构类型的差异化瓦斯抽采方案是发展趋势。当前,关于煤粒或煤体的瓦斯解吸特征演化过程仍缺乏数学性系统分析,对解吸曲线是裂隙(渗流)主控还是孔隙(扩散)主控仍存在争议。基于扩散与渗流的相互竞争制约关系,对瓦斯解吸曲线形态进行了综述性总结和归纳,并分析了其内在控制机制;对扩散主控型煤层进行了定义,探讨了低瓦斯厚煤层以及高瓦斯构造煤层瓦斯抽采的有效途径及隐含机制,并给出了扩散主控型煤层瓦斯治理的适配性方法;提出了未来扩散主控型煤层瓦斯储运规律的研究重点。研究表明:中西部低压厚煤层普遍瓦斯含量低、运移动力不足,可称为直接扩散体;深部构造煤层等效扩散距离长、运移难度大,可称为等效扩散体。扩散主控型煤层具有低压敏感性、应变敏感性、时间敏感性和压力差异化响应等特点,使得瓦斯治理时要着重考虑增能增扩和减距增扩,形成驱替、微生物降解基质、表面活性剂等基质面改性技术,以及水力冲孔造穴、保护层开采等基质体改性技术2类强化抽采措施。未来仍需在扩散力学模型及响应机理、扩散系数正向测试方法、扩散主控体瓦斯抽采评价指标等着重研究。研究结果可为煤层瓦斯差异化治理体系建立提供参考。

     

    Abstract: As China’s coal production center shifts to the central and western regions and mining levels extend deeper, coal seam structures exhibit diversified and differentiated characteristics, leading to changes in gas storage and transportation patterns. It is a development trend to construct differentiated gas extraction schemes that are applicable to multiple coal seams. Currently, there is a lack of mathematical systematic analysis on the evolution process of gas desorption characteristics in coal particles/coal bodies, and there is still controversy over whether desorption curves are dominated by fractures (seepage) or pores (diffusion). Based on the competitive relationship between diffusion and seepage, the shapes of gas desorption curves presented in the literature were summarized, and their internal control mechanisms were analyzed. Furthermore, diffusion-dominated coal seams were defined, effective approaches and underlying mechanisms for gas extraction in low-gas thick coal seams and high-gas structural coal seams were discussed, and adaptive methods for gas control in diffusion-dominated coal seams were proposed. Finally, research priorities for future gas storage and transportation in diffusion-dominated coal seam were put forward. The study found that low-pressure thick coal seams in the central and western regions generally have low gas content and insufficient migration power, which can be referred to as direct diffusion bodies. Deep structural coal seams have long equivalent diffusion distances and difficult migration, which can be referred to as equivalent diffusion bodies. Diffusion-dominated coal seams have characteristics such as low-pressure sensitivity, strain sensitivity, time sensitivity, and pressure-differentiated response, which make it important to consider, increasing diffusion source power or reducing equivalent diffusion distances, forming displacement, microbial degradation matrix, surfactant surface modification techniques, and matrix body modification techniques such as hydraulic punching and protective layer mining when managing gas. In the future, it is still necessary to focus on research on diffusion mechanics models and response mechanisms, forward testing methods for diffusion coefficients, and evaluation indicators for gas extraction in diffusion-dominated coal seams. The results of this study can provide a reference for establishing a differentiated gas management system for coal seams.

     

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