特厚煤层地面L型水平井分段压裂技术应用研究

Research on the application of stage fracturing technology of L-shaped horizontal well in extra-thick coal seam

特厚煤层开采过程中,煤层上方坚硬顶板强度高、破断步距大、难垮落,特别是开采扰动范围广,大面积坚硬顶板岩层破断失稳,造成采场冲击动力显现更加强烈;井下大孔径卸压、煤层爆破卸压以及井下长钻孔水力压裂技术仅限于局部卸压和小范围顶板弱化,不能有效对煤层上方高位大面积坚硬岩层进行弱化改性。提出了地面L型水平井分段压裂技术,通过对岩层破断方向进行理论分析并综合岩层特性给出了压裂关键层位范围,结合井上下微震一体化联合监测技术,形成了地面水平井分段压裂控制技术体系,并进行了地面压裂工程实践。井下微震-地音联合监测表明:压裂期间微震监测总能量达到16.93×10^(4)J,地音监测总能量达到1.36×10^(8)J,压裂过程可对井下围岩的宏观破裂具有明显的诱发作用;地面压裂裂缝扩展范围广,2口压裂井裂缝扩展长度分别达到790、851 m,裂缝宽度最大达到380~390 m,裂缝高程达到375~450、390~410 m,裂缝扩展均可覆盖工作面及两巷道,并穿透目标层位。井下采场矿压监测表明:工作面周期来压期间,支架阻力降低32%,煤壁片帮率降低34%,工作面超前支护范围无底鼓、帮部收敛等现象,微震监测总频次及总能量均降低达到90%以上。因此,地面水平井分段压裂可有效减小采场上覆岩层的强矿压,进而降低工作面回采期间的冲击地压灾害。

In the process of extra-thick coal seam mining,the strength of hard roof above the coal seam is high,the breaking step distance is large,and it is dificult to collapse,especially the mining disturbance range is wide,and the rock strata of large area of hard roof is broken and unstable,which causes the impact force of the stope to appear more intense.The research shows that the hydraulic fracturing technology of downhole large aperture pressure relief,coal seam blasting pressure relief and downhole long drlling is limited to local pressure relief and weakening of small roof,it is not effective to weaken and modify the high large area of hard rock above the coal seam;we propose the staged fracturing technology of L-shaped horizontal wells on the surface based on the theoretical analysis of the fracture direction of the rock layer and the comprehensive characteristics of the rock layer,the range of key fracturing horizons is given.Combined with the integrated micro-seismic monitoring technology up and down the well,the control technology system of horizontal horizontal wells under the stage fracturing is formed,and the ground fracturing engineering practice is carried out.The joint monitoring analysis of underground micro-seismic and ground sound shows that:the total energy of micro-seismic monitoring during fracturing reaches 16.93×10^(4) J and the total energy of ground sound monitoring reaches 1.36×10^(8) J.The fracturing process can induce the macroscopic fracture of underground surrounding rock obviously;the surface fracturing has a wide fracture propagation range.The fracture propagation length of the two fracturing wells reaches 790 m and 851 m respectively,the maximum fracture width reaches 380-390 m,and the fracture elevation reaches 375-450 m and 390-410 m.The fracture propagation can cover the working face and two grooving,and penetrate the target horizon.The mine pressure monitoring in underground stope shows that during the periodic pressure period of working face,the support resistance is reduced by 32%,the coal wall slab rate is reduced by 34%,and there is no floor heave and wall convergence in the advanced support range of working face.The total frequency and energy of micro-seismic monitoring decreased by more than 90%.Therefore,segmented fracturing of horizontal wells can effectively reduce the strong rock pressure in the overlying strata of the stope,and then reduce the rock burst disaster during the working face mining.