废弃矿井煤层气运移通道空间分布及抽采靶区优选

Spatial distribution of coalbed methane migration channel and optimization of extraction target area in abandoned mines

  • 摘要: 【目的和方法】 有效运移通道的空间分布及其长期演变特征不仅决定了废弃矿井遗留煤层气的运移路径,同时也是煤层气抽采钻孔靶区优选和抽采效益最大化的重要依据。以重庆松藻煤矿一水平一采区为研究对象,采用理论分析、数值模拟与物理相似试验相结合的方法,系统研究了倾斜多煤层条件下废弃矿井煤层气有效运移通道的分布规律,并提出了抽采靶区优选方案。【结果和结论】 (1)理论计算、数值模拟和物理相似试验获得的K2b、K1、K3b煤层重复开采裂隙带最大高度分别为72.89 m、76.4 m和77.3 m,结果高度一致;(2)覆岩应力场演化呈现“拱形卸压-非对称转移-动态平衡”三阶段特征,最终形成“顶板卸压穹窿-侧向应力壳”三维非对称结构;(3)覆岩裂隙发育遵循“采动主导-空间分异-时序累积”的协同演化规律,初始阶段上覆岩层受采动影响快速运移形成基础裂隙网络,中期在重复开采影响下,裂隙叠加扩展,后期受长达10余年的固结恢复,最终形成三维“O”形裂隙圈闭体,进入相对稳定阶段,为煤层气提供了有效运移通道,并在上方厚硬石灰岩阻隔下形成富集区;(4)长期压实后裂隙高度降至67.97 m,呈现走向对称梯形与倾向斜梯形的分异格局,结合煤层气运移规律,建议抽采靶区优选在K3b采空区底板上方6.41-36.70 m范围内的上隅角区域。

     

    Abstract: Objective and Methods The spatial distribution of effective migration channels and their long-term evolution characteristics not only determine the migration path of coalbed methane (CBM) left behind in abandoned mines but also serve as an important basis for the selection of CBM pumping drilling target areas and the maximization of pumping efficiency. Taking the first level and first mining panel of Chongqing Songzao Coal Mine as the research object, this research systematically investigates the distribution patterns of effective CBM migration channels in abandoned mines under inclined multi-seam conditions through an integrated approach combining theoretical analysis, numerical simulation, and physical similarity experiments. A methodology for optimizing extraction target zones is proposed. Results and conclusions (1) The maximum heights of the repetitively mined fracture zones in the K2b, K1 and K3b coal seams obtained from theoretical calculations, numerical simulations and physical similarity tests are 72.89 m, 76.4 m and 77.3 m, respectively, and the results are highly consistent. (2) The evolution of the overburden stress field shows three-stage characteristics of ".arch-shaped pressure relief-asymmetric transfer - dynamic balance.", and eventually forms a three-dimensional asymmetric structure of " roof pressure relief dome - lateral stress shell ". (3) The development of overburden fractures follows the co-evolution law of "mining-dominated-spatial differentiation-time series accumulation." In the initial stage, the overlying strata migrate rapidly under the influence of mining to form a basic fracture network. In the middle stage, the superimposition and expansion of repeated mining impacts occur. In the later stage, after more than 10 years of consolidation and recovery, a three-dimensional "O"-shaped fracture trap is finally formed, which enters a relatively stable stage, provides an effective migration channel for CBM, and forms an enrichment area under the barrier of thick and hard limestone above. (4) After long-term compaction, the fracture height decreases to 67.97 m, showing a differentiation pattern of symmetrical trapezoid and inclined trapezoid. Combined with the migration law of CBM, it is suggested that the extraction target area should be preferably located in the upper corner area within the range of 6.41-36.70 m above the floor of K3b goaf.

     

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