Crack initiation method adopting crack prefabricating and orientated hydraulic fracturing

Abstract

The invention belongs to a hard roof control range, and particularly discloses a crack initiation method adopting crack prefabricating and orientated hydraulic fracturing. The crack initiation methodadopting crack prefabricating and orientated hydraulic fracturing comprises the steps that firstly the magnitude and direction of the maximum horizontal stress of a hard rock stratum are measured, andthen vertically upward or obliquely upward drilling holes are constructed from one side of an open-off cut coal pillar of a working face or a conveying gate road or one side of a return wind gate road channel or the above three positions to the hard rock stratum, after the drilling construction is completed, cracks are symmetrically prefabricated on both sides of hard rock stratum sections in thedrilling holes in the axial direction, after the prefabrication of the cracks is completed, the drilling holes are rinsed with clean water, then waterproofing agents are applied in the drilling holes, and after the waterproofing agents solidify, the drilling holes are sealed and fractured. The crack initiation method adopting crack prefabricating and orientated hydraulic fracturing overcomes thedisadvantages that when rock permeability is good and the prefabricated cracks and the maximum horizontal stress have a certain included angle, the prefabricated cracks cannot provide the crack initiation position due to the fluid loss of fracturing fluid by rock, so that the crack initiation position and the direction of hydraulic crack propagation are effectively controlled, the spacing of the fractured drilling holes is increased, and the cost of the drilling holes and labor intensity are reduced.

Description

technical field [0001] The invention belongs to a stope and roadway surrounding rock control technology, in particular to a method suitable for directional cutting of a hard roof, in particular to a prefabricated crack directional hydraulic fracturing initiation method. Background technique [0002] In the process of coal mining, if there is a hard and difficult roof in the overlying strata of the coal seam within a certain height, there will be safety problems in the following three aspects: First, it is easy to form a large area of ​​suspended roof behind the working face. The collapse produces a strong impact load, causing a hurricane, and at the same time squeezes out a large amount of gas in the goaf, causing a major mine accident. Second, for gob-side retention and gob-side excavation without coal pillars, it is easy to form a suspended roof in the side gob of the side goaf, which leads to an increase in the load of the sideways support, large deformation of the roadwa...

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Problems solved by technology

[0002] In the process of coal mining, if there is a hard and difficult roof in the overlying strata of the coal seam within a certain height, there will be safety problems in the following three aspects: First, it is easy to form a large area of ​​suspended roof behind the working face. Collapse, produce strong impact load, cause hurricane, squeeze out a large amount of gas in the goaf at the same time, cause major mine accidents

Second, for gob-side retaining and gob-side excavation for mining without coal pillars, it is easy to form a suspended roof in the side gob of the roadside support, which will increase the load of the roadside support, cause large deformation of the roadway retention, and make it difficult to maintain

Third, for the coal pillar roadway protection, the hard suspended roof at the goaf increases the width of the coal pillar, resulting in a serious decline in the recovery rate.

[0003] The traditional hard roof treatment methods include: pre-splitting blasting (energy-concentrated blasting), forced caving, directional hydraulic fracturing and other methods have achieved certain success, but there are certain shortcomings: such as energy-concentrated blasting has a large charge, blasting Pollution of underground air, and poor safety for high-gas mine blasting

In engineering practice, there is often a certain angle between the direction of the long axis of the cutting eye on the working face or the direction of the long axis of the transport chute or the return air chute and the direction of the maximum horizontal stress. , there are the following problems: First, because the hard roof of the coal mine is mostly sandstone, glutenite and limestone, with well-developed voids and good permeability, the fracturing fluid leakage on the drilling wall and fracture surface is serious during fracturing, resulting in poor fracturing fractures. The crack starts along the end of the prefabricated crack, but along the direction of the maximum principal stress of the borehole wall. At this time, the slot does not play any positioning role

Second, even if the fracture starts along the tip of the prefabricated fracture, if the orientation of the slot and the orientation of the maximum horizontal stress are too large, the fracturing fracture will quickly deflect to the direction of the maximum horizontal stress due to the leakage of the borehole wall and fracture surface. Hole fracturing fractures are connected to each other, and unlimited infill drilling is necessary. Unlimited infill drilling is impossible in engineering and economically unreasonable

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