穿层梳状分支孔煤层段精准水力压裂工程试验
Accurate hydraulic fracturing engineering test in coal seam section with comb-shaped branch holes through layers
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摘要: 为解决穿层梳状分支孔整体水力压裂及分段水力压裂技术存在压裂作业对象偏差大和作业效果不高的问题，开展了穿层梳状分支孔煤层段精准水力压裂试验，试验采用“后退式边施工边压裂”工艺流程完成了1个主孔及4个分支孔的钻进及其煤层段的精准压裂，总压裂长度248.3 m，总注液量5 730 m3，各孔煤层段起裂压力介于10.6～11.8 MPa，最大泵注压力介于14.9～16.8 MPa。试验结果表明：压裂期间煤层破裂过程表现为“局部结构弱面打开阶段-初始起裂阶段-周期性锯齿微破裂累计阶段-明显破裂阶段”，且随着压裂持续，发生明显破裂时的水体压力在不断的升高，锯齿微破裂累计周期也在不断的加长；相比于压裂前，压裂后煤层平均透气性系数提高至原来14.08倍，钻孔平均流量衰减系数降低至原来0.56倍；相比于前期该巷道同水平控制范围相当的穿层梳状钻孔整体水力压裂试验，此次穿层梳状分支孔煤层段精准水力压裂试验单孔瓦斯抽采体积分数提高了2.7倍，瓦斯抽采纯量提高了11.8倍。Abstract: In order to solve the problems of large deviation of fracturing objects and low efficiency in the integral hydraulic fracturing and segmented hydraulic fracturing techniques of combing branch holes through layers, the precise hydraulic fracturing test of coal seam section with comb branch holes through the layer was carried out, and the drilling of 1 main hole and 4 branch holes and the precise fracturing of coal seam section were completed by adopting the technological process of “backward construction and fracturing at the same time”. The total fracturing length was 248.3 m, the total fluid injection volume was 5 730 m3, and the initiation pressure of coal seam section with each hole ranged from 10.6 MPa to 11.8 MPa. The maximum pumping pressure is 14.9-16.8 MPa. The test results show that during the fracturing process, the coal seam rupture process appears as “local structure weak surface opening stage - initial crack initiation stage - periodic sawtooth micro-fracture accumulation stage - obvious fracture stage”, as the fracturing continues, the water pressure when obvious fracture occurs is increasing, and the cumulative period of sawtooth micro-fracture is also lengthening. Compared with non-fracturing, the average permeability coefficient of coal seam after fracturing increases to 14.08 times of the original, and the average attenuation coefficient of drilling flow decreases to 0.56 times of the original. Compared with the previous overall hydraulic fracturing test of combing borehole in the same horizontal control range of this tunnel, the volume fraction of gas extraction from single hole in the precision hydraulic fracturing test of coal seam section with combing branching hole in this tunnel has increased by 2.7 times and the pure gas extraction has increased by 11.8 times.
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