High efficient gas extraction method of long drill hole directional segmental fracturing in soft and low permeability coal seam

Abstract

The invention discloses a high efficient gas extraction method of long drill hole directional segmental fracturing in a soft and low permeability coal seam. The method comprises the following steps that firstly, a kilometer drilling rig passes through the coal seam from a coal seam floor rock tunnel to a roof rock seam to drill a horizontal fracturing hole, the horizontal fracturing hole is controlled to be in a rock stratum with a distance of 0.5 to 1 meter from the top boundary of the coal seam; then, the sectional downward directional perforating is carried out in the horizontal fracturinghole section to communicate with the lower target coal seam, and the target coal seam is subjected to step-by-step fracturing by adopting a hydraulic jet sectional fracturing technology; after fracturing of the horizontal fracturing hole is completed, a drainage gas production hole is drilled in the target coal seam again in the liquid discharging process, a full-sleeve pipe protection hole technology is adopted, and a sleeve pipe is arranged to protect the holes while drilling ; and finally, hole sealing and drainage are conducted on the horizontal fracturing hole and the drainage gas production hole, and after the liquid level is reduced, the drainage gas production hole is used as a extraction hole to draw gas. The method can effectively overcome the problems of gas extraction in the soft and low-permeability coal seam, such as the difficulty of hole formation, the poor effect of fracturing and permeability increasing and the fracture blocking by fracturing fluid, and realize the high efficient gas extraction in the soft and low permeability coal seam.

Description

technical field [0001] The invention belongs to the technical field of underground gas drainage in coal mines, in particular to a high-efficiency gas drainage method for directional and segmented fracturing with long boreholes in soft and low-permeability coal seams. Background technique [0002] In coal mining, mine gas disaster has always been one of the main disasters that threaten the safety of coal mine production. Gas drainage in soft and low-permeability coal seams is the main factor that restricts the safety and high-efficiency production of coal mines in my country, and is also the main factor that restricts the efficient exploitation of coalbed methane in my country. my country's coal seams generally have poor geological conditions, low hardness, high gas content, and low gas permeability. The characteristics will be more significant, which will lead to great challenges in gas control and safe and efficient production in deep soft low-permeability coal seams. The ...

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Problems solved by technology

However, it is difficult to drill holes in soft and low-permeability coal seams, and the drilling depth will be greatly limited, and problems such as drill sticking, borehole collapse and blockage, and difficulty in running casing are prone to occur, and the construction risk is high

In view of the above problems, the current better solution is to arrange horizontal long boreholes in the coal seam roof rock, and then conduct directional hydraulic fracturing to increase the permeability of the coal seam and efficiently extract coal seam gas, but this method faces difficulties in fracturing fluid discharge The problem is that the fracturing fluid is difficult to effectively discharge from the coal seam after fracturing the coal seam, resulting in the fracturing fluid remaining in the coal seam cracks, so that the gas in the coal seam cannot smoothly enter the gas drainage borehole from the cracks, which results in the The soft and low permeability coal seam has been enhanced by hydraulic fracturing, but because the fracturing fluid cannot be effectively discharged to block the cracks, the permeability enhancement effect of the coal seam and the gas drainage efficiency have been greatly reduced

Therefore, in view of the current difficulties in gas drainage of soft and low-permeability coal seams, such as the difficulty of drilling holes, the poor effect of fracturing and increasing permeability, the ineffective discharge of fracturing fluid, and the low efficiency of gas drainage, a reliable and effective soft and low-permeability coal seam is developed. High-efficiency gas drainage methods for directional and segmented fracturing with long boreholes are urgently needed

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