AU2013330947A1

AU2013330947A1 - High-pressure pneumatic blasting pressure relieving and transmission increasing method

Info

Publication number: AU2013330947A1
Application number: AU2013330947A
Authority: AU
Inventors: Baiquan LIN; Wei Yang; Chunshan ZHENG
Original assignee: China University of Mining and Technology CUMT
Current assignee: China University of Mining and Technology CUMT
Priority date: 2012-10-17
Filing date: 2013-04-19
Publication date: 2015-02-05
Anticipated expiration: 2033-04-19
Also published as: ZA201407507B; AU2013330947B2; CN102852506B; RU2014138190A; CN102852506A; WO2014059777A1

Abstract

A high-pressure pneumatic blasting pressure relieving and transmission increasing method comprises constructing a blasting drill hole in a coal layer, and carrying out high-pressure water jet seam cutting operation in the blasting drill hole at intervals, so that a lead seam groove is formed in a coal body around the blasting drill hole; feeding a blasting steel pipe with plugged top part into the blasting drill hole, forming a plurality of air vents at the front part of the blasting steel pipe, and sealing a section inside a hole opening of the blasting drill hole by 8-10 m, so as to form a cement plug; and connecting the blasting steel pipe with a high-pressure air station through a pipeline at the exposed end of the blasting steel pipe, and opening a valve arranged on the pipeline to inject high-pressure gas, so that the high-pressure gas is jetted by the blasting steel pipe from the air vents. On the basis of forming cracks and fractures formed in the fractures and cutting grooves of the original coal body, the high-pressure gas instantly impacts the blasting effect, so that the cracks and the fractures can be continuously expanded, and a lot of new fractures can be generated. Finally, a mutually communicated large fracture screen is formed in the coal body by using the blasting drill hole as a center, so that the purpose of pressure relief and transmission increase of the coal body can be realized. Furthermore, the method has the advantages of simple operation, easiness of realization and obvious effect.

Description

HIGH-PRESSURE PNEUMATIC BLASTING PRESSURE RELIEVING AND TRANSMISSION INCREASING METHOD DESCRIPTION Field of the Invention The present invention relates to a method for pressure relief and permeability increase by high-pressure pneumatic blasting, which is especially suitable for pressure relief and permeability increase of coal body in gas control in the area of underground coal mine. Background of the Invention The gas geological conditions in coal mines in China are complex. In those coal mines, high gas coal seams account for 50%-70%, and low-permeability coal seams account for about 70% in the high gas coal seams. Therefore, the gas control should be of uppermost priority in the safety control work in the coal mines. However, for low-permeability coal seams, effective pressure relief and permeability increase of the coal body shall be regarded as the primary task, in order to attain an optimal gas control result. Presently, there are many methods for pressure relief and permeability increase of coal body, such as mining protective seam, directional hydraulic fracturing, deep-hole loose blasting and hydraulic flushing, etc. The mining protective coal seam is proven as an effective method, but may not always be applicable to all coal seams since it has rigorous requirements for the coal seam occurrence conditions; though the directional hydraulic fracturing method is also effective, the experience of the former Soviet Union shows that the gas extraction rate can be as high as approx. 60%, but an area of stress concentration will be created around the induced fractures, resulting in a potential safety hazard, in addition, the method has high requirements for the sealing of the borehole so that a phenomenon that the high-pressure water injected into the coal body seeps out through the upper part of the porthole occurs 1 frequently in the directional hydraulic fracturing work in coal mines; the hydraulic flushing method attains an excellent effect in soft coal seams where the in situ stress is high, the gas pressure is high, and the coal whose quality is soft and loose and has a tendency of efflorescence and rheology and has flowing capacity, but it is difficult to use widely because it results in high water consumption and the process is complex. Summary of the Invention Technical problem In view of the drawbacks in the prior art, the object of the present invention is to provide a method for pressure relief and permeability increase of coal body, which is easy to implement and operate, and attains an outstanding effect. Technical scheme The method for pressure relief and permeability increase by high-pressure pneumatic blasting in the present invention comprises: drilling blasting boreholes in a coal seam, and operating the high-pressure water jetting cutting seam at an appropriate interval in the blasting boreholes to form guide slits in the coal body around the blasting boreholes; inserting a blasting steel tube with a sealed top into the blasting boreholes, and several pores are provided on the fore part of blasting steel tube, and sealing 8-10m inward from the opening of each blasting borehole to form a cement plug; connecting the exposed end of each blasting steel tube to a high-pressure gas station through a pipeline, and opening a valve provided on the pipeline to inject high-pressure gas, so that the high-pressure gas is jetted out from the pores via blasting steel tube, and thereby the coal body is blasted pneumatically under high pressure. The pressure of the injected high pressure gas is 25Mpa. Beneficial effects Especially for the gasses flowing at a high speed, the gasses are compressible fluids and usually have a high compressibility, the isothermal compressibility of air f,=10-'m 2 N at one atmosphere pressure , while the isothermal compressibility of water is 5-10-m2 N under the same conditions, which means the compressibility of air is higher than that of water by five orders of magnitude, and therefore a 2 high-pressure gas will produce huge energy when it is released instantaneously. Hence, inthe present invention, using high-pressure gas to carry out high-pressure pneumatic blasting for coal body and supplementing hydraulic cutting seam measures. That method is an effective method for implementing pressure relief and permeability increase of coal body. In the present invention, after blasting boreholes are formed, hydraulic cutting seam operation is carried out first, and to form guide slits and fractures for guiding a high-pressure gas, so as to attain a better fracture generation and communication effect after high-pressure pneumatic blasting; then, after the opening section of each blasting borehole is sealed, a valve is opened suddenly, so that the high-pressure gas is jetted from the pores via blasting steel tubes quickly and acts on the coal body around the pores. As the high-pressure gas rushes in and inflates instantaneously, the original slits and fractures are enlarged continuously and new fractures are created; subsequently, the high-pressure gas entering into the network of fractures creates small local pneumatic blasting in the fractures, and thereby the fractures in the coal body are enlarged continuously and communicated; consequently, the fractures become larger and larger, and more and more new fractures are created. That process continues on. Finally, a network of big fractures communicating with each other is formed in the coal body, centering on the blasting boreholes. In that way, the object of pressure relief and permeability increase of coal body is attained, the gas extraction rate is improved, and the technical problem of low permeability and poor gas extraction effect in high gas-containing and low-permeability coal seams is solved. In addition, the method is easy to operate and implement and can attain an outstanding effect. Description of the Drawings Fig. 1 is a vertical sectional view of the high-pressure pneumatic blasting method provided in the present invention. In the figure: 1 - high-pressure gas station; 2 - valve; 3 - blasting steel tube; 4 - cement plug; 5 - blasting borehole; 6 - pore; 7 - coal seam; 8 - guide slit Detailed Description of the Embodiments Hereunder the present invention will be described in detailed with reference to the 3 embodiments of accompanying drawings: With the method for pressure relief and permeability increase by high-pressure pneumatic blasting in the present invention, firstly, blasting boreholes 5 in depth of 25-30m are drilled out in a coal seam 7 in a conventional way; then, after the blasting boreholes 5 are formed, high-pressure water jet cutting seam is carried out in the blasting boreholes 5 from interior to exterior at an appropriate interval, to form guide slits 8 in the coal body around the interior of blasting boreholes 5 at an equal interval; on one hand, the cutting seam operation causes more fractures in the coal body, on the other hand, the slits and fractures attain a guiding and control effect, so that the high-pressure gas impacts centrally in several directions, thus, the slit generation and inter-communication effect is better, and the blasting effect is improved; a blasting steel tube 3 is inserted into blasting borehole 5 and sealed in the top part , several pores 6 are arranged on the wall of the forepart seal end of the blasting steel tube 3, and the opening section of the blasting borehole 5 is sealed with a sealing material that can withstand high strength pneumatic impact through an appropriate process, to form a 8-10m cement plug 4; alternatively, a "strong-weak-strong" sealing method can be used to seal the opening section of the blasting borehole 5, wherein, the two ends of the opening seal section of the "strong-weak-strong" sealing are sealed with a sealing material with higher strength, while the middle section of the opening seal section is sealed with a sealing material with higher plasticity; the high strength sealing material at the two ends can effectively resist the blast wave of the high-pressure gas, while the sealing material with higher plasticity in the middle section can effectively absorb the blast wave. Thus, effectively sealing is achieved, and a good blasting effect is ensured. The open end of the blasting steel tube 3 is connected to a high-pressure gas station 1 via a valve 2. The valve 2 is a quick-action switch, with which the high-pressure gas can be released instantaneously. In addition, the valve 2 can be provided as a remote control switch, and the operation can be controlled with a sensor, to meet safety requirements. The high-pressure gas is injected when the valve 2 on the pipeline is opened. The pressure of the high-pressure gas is 25Mpa. The high-pressure gas is jetted out from the pores 6 via blasting steel 4 tube 3 and acts on the coal body around the borehole to form new slits. On the basis of the original fractures and cutting seam slits and fractures exists, the high-pressure gas with high cutting power acts on the coal body continuously; meanwhile, the high-pressure gas rushes into the coal body instantaneously and enlarges the original fractures continuously; hence, the number and size of the fractures are significantly increased; subsequently, more high-pressure gas enters into more and enlarged fractures in the coal body. Since the compressibility of the high-pressure gas is very high, the high-pressure gas in the fractures contains huge inflation energy. As the gas volume inflates continuously, local pneumatic blasts are created in the fractures; consequently, the fractures in the coal body become more and the size become bigger, and join and communicate with each other continually; thus, even more high-pressure gas will enter into the fractures in the coal body. That process accumulate and overlay constantly, and cycle repeatedly. Finally, a network of big fractures communicating with each other is formed in the coal body, centering on the blasting boreholes. Hence, the object of pressure relief and permeability increase of coal body is attained, and the coal body is blasted pneumatically under high pressure. 5

Claims

1. A method for pressure relief and permeability increase by high-pressure pneumatic blasting, comprising: drilling blasting boreholes (5) in a coal seam (7), wherein, operating the high-pressure water jetting cutting seam at an appropriate interval in the blasting boreholes (5) to form guide slits (8) in the coal body around the blasting boreholes (5); a blasting steel tube (3) with a sealed top is sent into the blasting boreholes (5), and several pores (6) are provided on the fore part of the blasting steel tube (3), and a 8-10m section is sealed inward from the opening of each blasting borehole (5) to form a cement plug (4); the exposed end of each blasting steel tube (3) is connected to a high-pressure gas station (1) through a pipeline, and a valve (2) provided on the pipeline is opened to inject high-pressure gas, so that the high-pressure gas is jetted out from the pores (6) via the blasting steel tube (3) and thereby the coal body is blasted pneumatically under high pressure.

2. The method for pressure relief and permeability increase by high-pressure pneumatic blasting according to claim 1, wherein, the pressure of the injected high-pressure gas is 25Mpa. 6