煤层水力压裂过程“三场”演化规律特征

Regularity of three fields evolution of hydraulic fracturing process in coal seam

  • 摘要: 根据固液耦合方程与Mohr-Coulomb准则,对煤层水力压裂过程进行了数值模拟,研究了煤层裂纹扩展过程中渗流场、应力场和裂隙场(“三场”)的演化过程,结果表明,水力压裂过程中“三场”连续动态变化,水压力是裂隙扩展的动力,裂隙的扩展引起裂隙损伤增加、渗流场以裂隙为中心逐渐扩大、应力场逐渐分化出高应力与低应力区域,最终在主裂隙的垂直方向上形成低应力-高渗透性区域,达到卸压增透效果。

     

    Abstract: Numerical simulation was conducted for hydraulic fracturing process in coal seam according to solid-liquid coupling equations and Mohr-Coulomb principle. The evolution of seepage field, stress field and fracture field (three fields) during process of crack propagation in coal seam was analyzed respectively. The results show that the three fields are changing dynamically during the process of hydraulic fracturing. The fracture is motivated to expand by pore water pressure, as a result of which, crack damage increases, seepage field centering to the fracture expands gradually, and high stress area and low stress area are developed from original stress field, and two regimes of low stress and high permeability field in a vertical direction of main fracture are ultimately formed. All of the above contribute to an effect of pressure relief and permeability improvement.

     

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