A method of low-temperature fracturing and caving of hard roof in coal mine goaf

Abstract

The invention discloses a low-temperature fracturing and caving method for a hard roof in a goaf of a coal mine, which is applicable to the technical field of enhanced fracturing of the roof in a goaf of a coal seam. Using digital thermometers, temperature sensors, water injection pipes, cryogenic fluid freezing pipes, capsule hole sealers, high-pressure water injection systems and cryogenic fluid tankers, multiple fracturing boreholes and an empty hole are sequentially constructed on the hard roof of the goaf Connect the spiral low-temperature fluid pipe, water injection pipe and capsule hole sealer into multiple fracturing boreholes, use the capsule hole sealer to seal the holes at high pressure, and freeze the cylindrical reaming section of the fracturing borehole, A self-sealing hole structure is formed, and then multiple fracturing boreholes are frozen, and the coal seam roof is cracked by using the phase change of water and ice. When the temperature sensors all rise above 3°C, the freezing is repeated, forming a cycle of frost heaving-thawing-frost heaving and cracking. The method is simple, easy to operate, low in cost, simple in operation and good in cracking effect by using low-temperature fluid to undergo water-ice phase transition to produce an expansion rate of 9.1% to crack the hard roof of the coal seam.

Description

technical field [0001] The invention relates to a method for low-temperature fracturing and caving of hard roofs in goafs of coal mines, and is especially suitable for the roofs of goafs in coal seams that are dense and hard, difficult to collapse naturally, and must be artificially strengthened for fracturing. Background technique [0002] With the continuous advancement of the coal mining face in the coal mine, the length of the left roof and the area of ​​the overhanging roof in the goaf are getting larger and larger, and the strength of the coal pillars used to support the roof of the goaf is getting smaller and smaller, and it is easy to form stress concentration, which will last for a long time It is easy to cause accidents such as roof collapse, injury and mine impact accidents. For high-gas mines, it is easy to form local accumulation of gas at the roof of the goaf, causing gas accidents. Therefore, it is necessary to pre-crack the roof of the goaf, artificially col...

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Problems solved by technology

[0003] However, the traditional fracturing method has certain defects. For example, the deep hole blasting method requires a large amount of high explosives. The stress wave during the blasting process produces strong stress disturbances on the original rock, changing the stress distribution of the original rock, and easily inducing rock burst accidents. In addition, when explosives explode, a large amount of smoke is produced, which pollutes the underground environment; in addition, gas is easy to accumulate in goafs in underground coal mines, and it is easy to induce gas explosions by using explosives to blast and crack.

High-pressure hydraulic fracturing equipment is bulky and poorly adaptable to small underground spaces. Due to relatively high water pressure, drilling and sealing are difficult and the probability of failure is high

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