李作泉,屈争辉,王勃,等. 煤层脆性与地应力耦合条件下瓦斯抽采方案探讨[J]. 石油钻采工艺,2025,47(2):235-244. DOI: 10.13639/j.odpt.202411043
引用本文: 李作泉,屈争辉,王勃,等. 煤层脆性与地应力耦合条件下瓦斯抽采方案探讨[J]. 石油钻采工艺,2025,47(2):235-244. DOI: 10.13639/j.odpt.202411043
LI Zuoquan, QU Zhenghui, WANG Bo, et al. Discussion on gas extraction schemes under the coupling conditions of coal seam brittleness and in-situ stress[J]. Oil Drilling & Production Technology, 2025, 47(2): 235-244. DOI: 10.13639/j.odpt.202411043
Citation: LI Zuoquan, QU Zhenghui, WANG Bo, et al. Discussion on gas extraction schemes under the coupling conditions of coal seam brittleness and in-situ stress[J]. Oil Drilling & Production Technology, 2025, 47(2): 235-244. DOI: 10.13639/j.odpt.202411043

煤层脆性与地应力耦合条件下瓦斯抽采方案探讨

Discussion on gas extraction schemes under the coupling conditions of coal seam brittleness and in-situ stress

  • 摘要: 魏家地煤矿地质构造复杂,煤储层脆性差异大,现今地应力场空间分布不均一性强,造成煤层瓦斯抽采效果差异的地质控制机理不明确。以魏家地煤矿地质资料为基础,采用Petrel三维建模软件,开展了煤层弹性参数空间分布和地应力场模拟。基于煤层弹性模量、泊松比分区叠合,划分了3个脆性区。基于研究区水平最大主应力(σH)远大于水平最小主应力(σh)和垂向应力(σv),根据σhσv的相对大小,划分了2类应力模式区。研究表明煤层脆性为压裂裂缝扩展的主控因素。脆性相对较高的煤层有利于裂缝扩展,表现为瓦斯抽采效果好;反之,不利于裂缝扩展,表现为瓦斯抽采效果较差。脆性较低的煤层,更适合采用L型井进行瓦斯抽采以达到煤层气降压解吸目的。脆性相对较高的煤层,则根据σvσh的相对大小选择合适井型:当σvσh时,裂隙不易在煤层中延展,建议采用L型井进行瓦斯抽采;当σhσv时,裂隙容易在煤层水平方向发生延展,有利于煤层气降压解吸,该条件下可考虑采用直井或L型井,采用两种井型进行煤层瓦斯抽采效果均较好。结合工程实例分析,L型井在压裂过程中需要同时考虑顶板岩层含水性。顶板为含水层时,L型井应选择煤层作为水平段来实施较小规模的压裂;顶板为非含水层时,则根据煤层脆性选择水平段层位。结合煤矿采动卸压区L型井成功案例,原位瓦斯抽采L型井在设计时应考虑“一井两用”工程部署。

     

    Abstract: Weijiadi Coal Mine is characterized by complex geological structures, significant heterogeneity in the spatial distribution of coal reservoir brittleness and current in-situ stress field, and an unclear geological control mechanism on the variability of gas extraction efficiency. In light of this, based on the geological data from Weijiadi Coal Mine, Petrel 3D modeling software was employed to conduct modeling of the spatial distribution of coal seam elastic properties and simulation of the in-situ stress field. The results indicate that, through the superposition of zoning based on the elastic modulus and Poisson’s ratio of the coal seam, three brittleness zones were delineated. In the study area, the maximum horizontal principal stress (σH) significantly exceeds both the minimum horizontal principal stress (σh) and the vertical stress (σv). Based on the relative magnitudes of σh and σv, two types of stress regime zones were classified. Research indicates that coal seam brittleness is the primary controlling factor governing the propagation of hydraulic fracturing fractures. coal seams with relatively high brittleness is conducives to fracture propagation, demonstrating good gas drainage performance. Conversely, coal seams that are not in this condition are unfavorable for fracture propagation, resulting in poor gas drainage effects. Therefore, for coal seams with low brittleness, L-shaped wells are more suitable for gas drainage to achieve the goal of coalbed methane (CBM) pressure reduction and desorption. For coal seams with relatively high brittleness, appropriate well types should be selected based on the relative magnitudes of σv and σh. When σvσh, fractures are less likely to extend within the coal seam, and it is recommended to adopt L-shaped wells to achieve gas drainage objectives. When σhσv, fractures are more prone to propagate in the horizontal direction of the coal seam, which is beneficial for CBM pressure reduction and desorption. In this case, both vertical and L-shaped wells can be considered, and both types of wells can achieve relatively good gas drainage effects. Based on engineering case analyses, it is considered that during the fracturing process of either vertical or horizontal wells, the water-bearing property of the roof strata must be taken into account simultaneously. When the roof is a water-bearing layer, L-shaped wells should select the coal seam as the horizontal section and implement small-scale fracturing. When the roof is a non-water-bearing layer, the horizontal section stratum should be chosen according to the coal seam's brittleness. Drawing from successful cases of L-shaped wells in mining-induced stress relief zones, it is suggested that "one well for dual purposes" engineering layouts should be considered in the design of in-situ gas extraction L-shaped wells.

     

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