煤矿井下水力压裂钻孔封孔力学模型及试验研究

Mechanical model and test study of sealed drilling for hydraulic fracturing in underground coal mines

针对目前煤矿井下水力压裂钻孔封孔理论缺乏,封孔材料密封效果差、成本高,封孔长度不合理等问题,建立了水力压裂钻孔封孔力学模型,得出封孔材料能够承受的最大水压与封孔材料性质、封孔长度等参数之间的关系。综合分析了密封条件、抽采条件以及施工条件下压裂孔的合理封孔长度,并进行现场试验验证。结果表明:封孔材料性质和封孔长度是影响封孔材料能够承受最大水压的主要因素,封孔材料能够承受的最大水压随封孔材料强度、弹性模量以及封孔长度的增大而增大;当封孔长度达到某一定值后,封孔材料能够承受的最大水压随封孔长度的增大而趋于定值。以重庆松藻矿区为例,确定出穿层压裂孔的合理封孔长度为10 m,本煤层压裂孔的合理封孔长度为13 m,现场试验结果与理论分析基本一致。

Considering the problems of lacking sealing theory, poor effect and high cost of sealing material and unreasonable sealing length for hydraulic fracturing drilling sealing in mine, mechanical models of sealed drilling for hydraulic fracturing were established. Relationships between the maximum bearing capacity of sealing material and sealing material property, sealing length were obtained. The reasonable sealing lengths of hydraulic fracturing under the sealed conditions, drainage conditions and constructional conditions were analyzed;and the field experiments were conducted. The results show that sealing material property and sealing length are the main factors influencing the maximum bearing capacity of sealing material. The maximum bearing capacity of sealing material increases with the increase of the strength of sealing material, the elasticity modulus and the sealing length. However, when the sealing length reaches a certain value, the maximum bearing capacity of sealing material verges to a constant value along with the increase of the sealing length. Taking Chongqing Songzao mine area as an example, the reasonable sealing length of crossing boreholes for hydraulic fracturing is considered to be 10 m;and the reasonable sealing length of coal seam boreholes for hydraulic fracturing is considered to be 13 m. The results of field experiment and the theoretical analysis are virtually consistent.