坚硬煤层水力致裂机理及应用研究

发布时间：2018-10-05 09:14

【摘要】：“高产高效,绿色安全”是煤炭企业的追求目标。西部大煤田的开发以及采煤深度的递增,所发现的坚硬煤层也越来越多,而开采坚硬煤层存在截齿消耗大、割煤效率低、块煤含量低、煤尘浓度大等问题,严重制约着煤炭企业的高产高效与生产安全。基于此,本文利用水力致裂技术预先对坚硬煤层块裂改造,通过发挥支承压力的碎裂作用实现坚硬煤层的弱化。(1)对煤岩体水力裂缝的开裂及扩展行为进行分析。基于弹性力学孔口围岩应力解,得出完整孔壁的开裂压力及方向,利用复变函数保角变换,将圆形孔边对称裂纹映射在数学平面的单位圆内部,以远场地应力及内部水压为边界条件,得出了裂纹尖端应力强度因子表达式。采用断裂力学K判据,推导裂缝尖端扩展压力。结合流体力学Navier-Stokes方程导出水在裂缝内的压降方程,推导了孔底水压力与起裂长度之间的关系表达式;(2)水力裂缝在坚硬煤层中的开裂及扩展行为,是水力裂缝改造坚硬煤层的前提条件。采用定向切槽只是降低起裂压力、控制开裂方向的一项措施,旨在对坚硬煤层的块裂改造。水在坚硬煤层钻孔及裂缝面边界上的渗透过程,只起到辅助软化作用。而经过块裂改造和渗透软化的煤层,为发挥支承压力的碎裂作用创造了条件。基于抗压强度的尺寸效应和宽高比,得出了发生碎裂作用的水力钻孔间距公式;(3)随着采面的推进,支承压力的遍历促使坚硬煤层碎裂。弱化后的坚硬煤层,削弱了截齿与煤体的研磨作用,实现坚硬煤层快速回采的同时,对提高块煤率、降低截齿消耗、降低煤尘浓度均起到一定的作用。以柠条塔煤矿南翼2-2煤S1201综采工作面为背景,设计了水力致裂施工方案。
[Abstract]:"High yield and high efficiency, green safety" is the goal of coal enterprises. With the development of large coal fields in the west and the increasing mining depth, more and more hard coal seams have been found. However, there are some problems in mining hard coal seams, such as high cutting consumption, low cutting efficiency, low mass coal content and high dust concentration. Seriously restricts the coal enterprise high production efficiency and the production safety. Based on this, this paper uses hydraulic fracturing technology to pre-transform the hard coal seam, and realizes the weakening of hard coal seam by giving full play to the fragmentation of supporting pressure. (1) the cracking and spreading behavior of hydraulic crack in coal and rock mass are analyzed. Based on the stress solution of surrounding rock at the orifice of elastic mechanics, the crack pressure and direction of the intact hole wall are obtained. Using the conformal transformation of complex variable function, the symmetric crack of circular hole edge is mapped in the unit circle of mathematical plane. The expression of stress intensity factor at crack tip is obtained by taking the far field ground stress and internal water pressure as boundary conditions. The crack tip propagation pressure is derived by using K criterion of fracture mechanics. Combined with the Navier-Stokes equation of fluid mechanics, the pressure drop equation of water in fracture is derived, and the relation between the pressure of hole bottom water and the initiation length of crack is derived. (2) the cracking and spreading behavior of hydraulic crack in hard coal seam. It is a precondition for hydraulic crack to transform hard coal seam. The adoption of directional cutting is only a measure to reduce the initiation pressure and control the crack direction in order to reform the block crack of hard coal seam. The permeation process of water in hard coal seam drilling and fracture surface boundary only plays an auxiliary softening role. The coal seams with block cracking and permeability softening create conditions for the fragmentation of bearing pressure. Based on the dimension effect of compressive strength and the ratio of width to height, a formula for the spacing of hydraulic boreholes is obtained. (3) with the advance of mining face, the traversal of bearing pressure causes the hard coal seam to break. After weakening the hard coal seam, it weakens the grinding action of cutting teeth and coal body, and realizes the quick mining of hard coal seam, at the same time, it plays a certain role in raising block coal rate, reducing tooth cutting consumption and reducing coal dust concentration. Based on the fully mechanized coal face S1201 of 2-2 coal in the south wing of Caragana Tower Coal Mine, the hydraulic fracturing construction scheme is designed.
【学位授予单位】：西安科技大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：TD821

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