本文以海石湾煤矿6125-1工作面为工程背景，采用理论分析、数值模拟及现场试验相结合的方法对厚硬顶板分段水力压裂裂缝扩展规律及卸压控制技术进行了系统研究。着重分析了分段水力压裂卸压机理、缝间扰动规律及裂缝性地层水力裂缝扩展规律，并在工作面运输顺槽开展了工业性试验。主要结论如下：

（1）钻孔方位和地应力状态改变导致裂缝扩展形态产生多样变化，当钻孔布置方向与三向主应力方向一致时，水力裂缝主要有垂直钻孔轴向的径向裂缝和平行于钻孔轴向的轴向裂缝两种类型，其中径向裂缝有利于裂缝网络的形成，因此布置钻孔最优方案是沿着最小水平主应力方向布置，可在所有地应力状态下都产生径向裂缝。

（2）水力裂缝扩展时会在其周围产生诱导应力，在裂缝尖端产生拉应力集中区，使水平主应力值减小，在裂缝两侧产生压应力集中区，使水平主应力值增大，总体上诱导应力值随着距裂缝距离的增加而趋向于原始应力值，停泵卸压后，诱导应力值随时间推移逐渐减小。多缝扩展时由于诱导应力场的存在裂缝间相互干扰，不同地层力学参数和施工参数影响下缝间扰动效应强弱不同，对于地层力学参数而言，具体排序为水平主应力差>弹性模量>泊松比，对于施工参数而言，具体排序为分段间距>注水排量>压裂顺序。

（3）试验工作面地质条件下，水力裂缝与天然裂缝间共发生穿透扩展、偏转扩展及沿天然裂缝扩展三种相互作用模式。水力裂缝在高逼近角与高应力差条件下扩展时接触天然裂缝容易发生穿透行为，在低逼近角条件下接触天然裂缝容易发生沿天然裂缝扩展的行为。在裂缝性地层中，较高的水平主应力差和注水排量以及较低的天然裂缝处岩石抗拉强度有利于激活天然裂缝，促使地层中形成压裂裂缝网络。

（4）采用分段顺序压裂分层垮落技术对运输顺槽上方厚硬顶板进行了预裂处理，提出了包括压裂设备选型、压裂钻孔布置及施工流程设计在内的成套厚硬顶板卸压控制技术方法，试验结果表明分段压裂过程中产生了较丰富的径向裂缝，取得了较好的效果。

Based on the engineering background of 6125-1 working face in Haishiwan Coal Mine, this paper has been systematically studied the fracture propagation law and pressure relief control technology of sectional hydraulic fracturing in thick and hard roof by means of theoretical analysis, numerical simulation and field test. The pressure relief mechanism of sectional hydraulic fracturing, the law of mutual interference between fractures and the law of hydraulic fracture propagation in fractured strata are emphatically analyzed, and the industrial test is carried out in the working face transportation roadway. The main conclusions are as follows:

(1)The change of borehole orientation and in-situ stress state leads to various changes in fracture propagation morphology. When the borehole arrangement direction is consistent with the direction of three-dimensional principal stress, there are two types of hydraulic fractures: radial fractures perpendicular to the axial direction of the borehole and axial fractures parallel to the axial direction of the borehole. The radial fractures are beneficial to the formation of fracture network. Therefore, the optimal scheme for arranging boreholes is to arrange along the direction of the minimum horizontal principal stress, which can produce radial fractures in all in-situ stress states.

(2)When the hydraulic fracture propagation, the induced stress will be generated around it. The tensile stress concentration zone will be generated at the fracture tip, which will reduce the horizontal principal stress value. The compressive stress concentration zone will be generated on both sides of the fracture, which will increase the horizontal principal stress value. In general, the induced stress value tends to the original stress value with the increase of the distance from the fracture. After the pump is stopped to relieve pressure, the induced stress value gradually decreases with time. Due to the interference between fractures in the induced stress field during multi-fracture propagation, the strength of the disturbance effect between fractures is different under the influence of different strata mechanical parameters and construction parameters. For the strata mechanical parameters, the specific order is horizontal differential principal stress > elastic modulus > Poisson 's ratio. For the construction parameters, the specific order is sectional spacing > water injection displacement > fracturing sequence.

(3)Under the geological conditions of the test working face, there are three interaction modes between the hydraulic fracture and the natural fracture, including penetration propagation, deflection propagation and propagation along the natural fracture. When the hydraulic fracture propagates under the conditions of high approach angle and high stress difference, the contact natural fracture is prone to penetration behavior. Under the condition of low approach angle, the contact natural fracture is prone to propagation along the natural fracture. In fractured strata, higher horizontal differential principal stress and water injection displacement and lower rock tensile strength at natural fractures are conducive to activating natural fractures and promoting the formation of fracturing fracture networks in the strata.

(4)The pre-splitting treatment of the thick and hard roof above the transport roadway was carried out by using the sectional sequential fracturing and layered falling technology. A complete set of pressure relief control technology methods for thick and hard roof, including fracturing equipment selection, fracturing borehole layout and construction process design was proposed. The test results show that abundant radial fractures are generated during the sectional fracturing process, and the good results were obtained.

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