Abstract
Hydraulic punching technology has recently developed into an effective pressure relief measure and permeability enhancement method for soft and low permeability coalbeds. Different coal outputs directly affect the shape and size of boreholes as well as the effective extraction radius. Taking the Zhongmacun mine as an example, the influence of different coal outputs and different extraction periods on effective extraction radius was analyzed and studied through field tests and numerical simulation. The results show that the increase in coal outputs from hydraulic punching can improve the effective extraction radius of the boreholes. For example, when the gas extraction reaches 90 days, with a coal output of 0.5 t/m, 1.0 t/m, and 1.5 t/m, the effective extraction radius is 3.08 m, 3.46 m, and 3.83 m, respectively. The difference in gas extraction effect of different coal output boreholes increases significantly with the extension of the extraction time, but the speed of growth gradually decreases, which is consistent with the conclusions obtained on-site. This result has important practical significance for optimizing the technical parameters of hydraulic punching, guiding the accurate layout of extraction and drilling, and enhancing the effect of gas control in mines.
Highlights
Coalbed methane (CBM) is one of the main factors restricting the safe production of coal in underground coal mines, but it is a form of high-quality energy that can be used in many fields such as power generation, heating, and chemical industries. erefore, extracting gas safely and efficiently can reduce the gas content substantially, thereby reducing the probability of dynamic gas disasters during coal production, but it can be used as a lowpollution energy source [1,2,3]
In order to increase the gas extraction rate, shorten the preextraction time, and reduce the number of boreholes, measures must be taken to increase the gas permeability of the coal seam [8]. erefore, scholars have proposed a variety of drilling pressure relief and permeability enhancement technologies, such as deep-hole blasting, hydraulic fracturing, hydraulic punching, and hydraulic slotting [9,10,11,12,13], which have improved the efficiency of gas extraction in China to a certain extent
Hydraulic slotting is to cut the coal by high-pressure water jets to form slots around the borehole, thereby broadening the scope of influence of the borehole, improving gas flow, and increasing coal seam permeability
Summary
Coalbed methane (CBM) is one of the main factors restricting the safe production of coal in underground coal mines, but it is a form of high-quality energy that can be used in many fields such as power generation, heating, and chemical industries. erefore, extracting gas safely and efficiently can reduce the gas content substantially, thereby reducing the probability of dynamic gas disasters during coal production, but it can be used as a lowpollution energy source [1,2,3]. Hydraulic slotting is to cut the coal by high-pressure water jets to form slots around the borehole, thereby broadening the scope of influence of the borehole, improving gas flow, and increasing coal seam permeability. It has poor continuity in soft coal seams. In the process of hydraulic punching, a large amount of gas and a certain amount of coal are flushed out, so an area of pressure relief and gas discharge is formed in the coal mass In this safe area, the basic conditions required for the occurrence of outbursts are removed and effective gas outburst prevention is achieved. Since the borehole radius is very small when compared with the extraction radius, we omit the second-order infinitesimal and obtain
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