定向水力压裂控制煤矿坚硬难垮顶板试验

TEST ON HARD AND STABLE ROOF CONTROL BY MEANS OF DIRECTIONAL HYDRAULIC FRACTURING IN COAL MINE

针对煤矿坚硬难垮顶板控制的研究现状及存在的问题,进行定向水力压裂控制煤矿坚硬难垮顶板井下试验。通过在压裂孔两侧布置监测孔和在压裂过程中实时监测泵压变化,深入分析煤矿坚硬难垮顶板水力压裂特点。试验结果表明:(1)KZ54型切槽钻头能够在坚硬岩层中预制横向切槽,可有效降低裂缝破裂所需压力;(2)采用跨式膨胀型封隔器可对岩层坚硬段分段逐次压裂,压裂过程中可在顶板中产生多条裂缝,从而有效弱化顶板;(3)随着压裂处与孔口距离的增大,裂缝破裂和扩展所需的压力也相应增大,裂缝的扩展半径最大可达20 m;(4)在压裂过程中,由于岩层均匀性、渗透性、地应力场、岩层结构面等影响因素的变化,压力–时间曲线呈现出多种形态;(5)岩石抗拉强度与地应力值较为接近时,岩石强度对水力压裂有较大影响。

In view of the research situation and existing problems involved with the hard and stable roof control in coal mine,the test of directional hydraulic fracturing employed for the roof control is presented;the characteristics of hydraulic fracturing in the roof are obtained via the monitoring boreholes decorated on both sides of the fracturing borehole and the pressure record during hydraulic fracturing.The test results show that：（1） The transverse notch is introduced successfully in the roof by means of KZ54 drill and is capable of reducing the pressure required for crack breakdown during the directional hydraulic fracturing.（2） The inflatable straddle packer adopted for hole sealing ensures the stepwise fracturing in the hard strata,the stepwise fracturing can create multiple cracks in the roof,which ultimately weakens the hard strata.（3） The breakdown pressure and propagation pressure change in proportion to the depth of fracturing location;the crack can propagate to a large scope radius of 20 m approximately.（4） The pressure versus time curve is recorded and presents a variety of forms potentially related to the rock uniformity,permeability,geostress field and rock structure surface.（5） The rock strength is the main factor that controls the fracturing process when the values of geostress and rock tensile strength are nearly identical.