坚硬厚层状顶板垂直预裂缝定向压裂技术基础研究

Caving of hard thick stratified roof in coal mine can produced strong impact pressure, which will be the great threaten of the coal safety; Meanwhile it can lead to great difficult in coal recovery process and roadway support and it can also cause great loss of coal in coal recovery. In order to eliminate the adverse effect, the vertical roof pre-splitting crack directional fracturing technology is put forward. By using such technology, the strata in the specified direction and position can be caved timely and fully, impact pressure can be eliminated, mining pressure can be reduced. So this research has important theoretical significance and practical application value.In this project, the following studies will be processed: Study the horizontal stress evolution law in roof strata at working face end and 50 m in advance affected by mining, the relationship between maximum and minimum horizontal principal stress and the direction of the working face advancing, and its influence law of vertical roof directional fracturing.Research the influence of fracturing parameters such as included angle of direction of maximum horizontal principal stress and pre-splitting crack, different horizontal stress ratio, and different way of fracturing, fracturing pressure and displacement on the crack, expansion and extension law of fracturing fracture and on the critical length of crack before direction change ;Study the relationship of fracturing fracture surface fractal dimension with mechanical properties such as shear strength and internal friction Angle;Through the in-situ fracturing test, a study of fracturing fracture extension, steering characteristics and regularity of spatial distribution, as well as the roof caving characteristic and the rule of stope and pillar mining pressure weakening law will be researched. The results will provide new technical and theoretical guidance to reduce the size of separate pillar and high reliability control of stope pressure.

煤矿坚硬厚层状顶板垮落产生巨大的冲击压力，威胁着安全生产，并给回采、巷道支护和资源回收带来重大影响，由此提出顶板垂直预裂缝定向压裂技术，使岩层在指定方向和位置及时充分垮落，消除冲击，减小采动压力，具有重要的理论意义和实际应用价值。本项目主要研究采动作用下工作面端头区域及超前50m内顶板岩层水平应力演化规律，最大、最小水平主应力与工作面推进方向的相关关系，以及对顶板垂直定向压裂的影响规律；研究最大水平主应力与预裂缝方向不同夹角、不同水平应力比、以及不同压裂方式、压力与排量等参数下，压裂裂缝起裂、扩展、延伸的规律及裂缝转向的临界长度；研究压裂裂缝面的分形维数与抗剪强度、内摩擦角等力学特性的相关关系；通过现场压裂试验，研究压裂裂缝扩展、延伸、转向空间分布的特征与规律，以及顶板垮落特征、采场与煤柱矿压显现弱化的规律。为减小工作面隔离煤柱、高可靠性控制采场矿压提供新的技术原理和理论指导。

针对坚硬顶板悬顶威胁着矿井的安全生产，给回采、巷道支护和资源回收都带来了重大影响。提出了沿钻孔壁垂直预裂缝定向压裂切顶技术，目的是产生定向裂缝，使煤矿开采顶板能够按照一定的方向和位置断裂，实现充分垮落之目的。研究了回采对顶板应力偏转规律，水平应力差、预制裂缝角、注液速率、黏度和滤失对预制裂缝的起裂与扩展规律，得出如下结论：. （1）随着回采工作面推进，煤层顶板最大主应力变化分量向工作面宽度方向偏转的越多，对沿巷道长轴方向水力压裂定向切顶影响越大，顶板压裂应在工作面支承压力超前段进行。. （2）预制裂缝起裂压力随着预制裂缝角的增大而增大，水平应力差的增大而减小，注液速率的增大而增大，黏度的增大而增大，滤失的增大而减小。. （3）预制裂缝角为0°时，容易起裂和扩展，裂缝角为90°时，最不利于起裂与扩展。当预制裂缝角大于0°而小于90°时，在相同偏转角下的裂缝扩展长度随着预制裂缝角的增大，裂缝扩展长度先减小后增大，在45°为达到最小值，随着应力差、滤失的增大而减小，注液速率、压裂液黏度和断裂韧度的增大而增大。. （4）能够提供定向起裂的临界预制裂缝角随着水平应力差的增大而减小，压裂液黏度的增大而增大，滤失的增大而减小。. （5）建立了基于黏聚型裂纹的水力压裂模型，提出了采用含裂隙流水压的黏聚型裂纹模型来描述水力压裂裂纹尖端断裂处理区并确立裂纹起裂准则。提出了求解水力压裂黏聚型裂纹的方法，即在传统黏聚型裂纹中引入新的自由度来离散裂隙水压。