煤层钻孔水压致裂的裂缝扩展规律研究

Study on the Propagation Mechanism of the Crack for the Borehole Hydraulic Fracturing in Coal Seam

煤层钻孔水压致裂是提高地面煤层气抽采效果的有效方法之一,借助于数值模拟方法对煤层钻孔水压致裂的裂缝扩展规律进行了分析.研究表明:当两个方向水平地应力值相等时,煤层钻孔围岩裂缝起裂角和扩展方向呈随机性,而当两个方向水平地应力值不相等时,则裂缝起裂角和扩展垂直于数值较大的水平地应力方向;钻孔围岩主裂缝的扩展长度随水平应力系数和注水压力的增大而增大;地面煤层气井的合理布置方式宜为菱形,且菱形对角线应平行于最大和最小水平地应力方向.

Hydraulic fracturing for coal seam through boreholes is one effective method to increase extraction efficiency on the ground.In this paper,propagation mechanism of hydraulic fracturing cracks in coal seam was analyzed by using numerical stimulation.Research results indicate that 1） starting-crack angle and propagation direction of cracks in surrounding rock behave randomly when horizontal ground stresses in two direction are equal,but they will plumb the direction of the horizontal ground stress with a bigger value when ground stress have different value;2） propagation length of main crack in surrounding rock increases with the growth of horizontal stress coefficient and injection pressure;3）the reasonable borehole pattern for methane wells on the ground is rhombus,whose diagonals should parallel the directions of the maximum and minimum horizontal ground stress.