AU2015299588B2

AU2015299588B2 - Freezing cross-cut coal cutting method based on hydraulic seam-cutting

Info

Publication number: AU2015299588B2
Application number: AU2015299588A
Authority: AU
Inventors: Quangui LI; Baiquan LIN; Guanhua NI; Shen Peng; Zongqing TANG; Shiliang WU; Xianwei XIANG; Jizhao XU; Yanming XU; Wei Yang; Xu Yu; Cheng ZHAI; Chao Zhong
Original assignee: China University of Mining and Technology CUMT; China University of Mining and Technology Beijing CUMTB
Current assignee: China University of Mining and Technology Beijing CUMTB
Priority date: 2014-08-07
Filing date: 2015-07-31
Publication date: 2018-08-02
Anticipated expiration: 2035-07-31
Also published as: CN104213921A; AU2015299588A1; CN104213921B; WO2016019826A1

Abstract

A freezing cross-cut coal cutting method based on hydraulic seam-cutting, comprising: constructing a plurality of water injection holes (5) on a coal cutting working surface (2) at a position where the minimum normal distance between the coal cutting working surface (2) and a coal layer (1) is greater than or equal to 7 m; employing a conventional hydraulic seam-cutting technique to perform hydraulic seam cutting on the water injection holes (5); after finishing the seam cutting, connecting the water injection holes (5) to a gas extraction pipe network and performing gas extraction; when the gas content of the coal layer is less than 8 m

Description

Freezing Cross-Cut Coal Cutting Method Based on Hydraulic Seam-Cutting

Field of the Invention

The present invention relates to a gas extraction method, particularly to a freezing cross-cut coal cutting method based on hydraulic seam-cutting, which is applicable to gas outburst control for coal seams with high gas concentration and low air permeability.

Background Art Discussion

Coal and gas outburst is one of the major disasters that threaten safe production in coal mines; especially, coal and gas outburst is at the highest outburst intensity and is the most dangerous during cross-cut coal seam cutting. The stress state of the coal rock in front of the coal cutting working face may change suddenly, and high-intensity gas outburst may happen owing to the elastic latent energy of the rock and the coal seam and the vehement release of gas energy.

The average gas outburst intensity during cross-cut coal cutting is 6 times or higher of the gas outburst intensity in other various roadways, and 80% or more extra serious gas outbursts happen in cross-cut coal cutting processes. Owing to the particularities of the cross-cut coal cutting technology, an outburst risk exists in the entire cross-cut coal cutting process; furthermore, continuous outburst, delayed outburst, and self-uncovering outburst may happen, and the difficulty in control of these outbursts is higher than that in control of ordinary outbursts.

At present, measures in two aspects (namely, pressure relief and reinforcement) are mainly taken in cross-cut coal cutting methods for coal seams with a high gas outburst risk; in the coal seam pressure relief and air permeability improvement aspect, the measures mainly include hydraulic flushing, loose blasting, and hydraulic seam-cutting, etc.; in the coal mass reinforcement aspect, the measures mainly include metal skeleton reinforcement and grout injection reinforcement, etc. Those measures have attained some effects in the outburst control work that utilizes cross-cut coal cutting, but have severe limitations.

The hydraulic seam-cutting measure can effectively relieve ground stress and gas pressure, but damages the integrality of the coal mass, and thereby result in decreased coal mass strength in the coal cutting area; grout injection reinforcement can effectively improve the coal mass strength, but the cement mortar can only infiltrate and diffuse in fissures; owing to the small fissure opening in the coal mass, the diffusion radius of the cement mortar is limited, and the coal mass strength can be improved only in a small range in the cross-cut coal cutting area; therefore, regional reinforcement can't be realized.

Hence, there is an urgent need for a cross-cut coal cutting method, which can meet the requirement for pressure relief and air permeability improvement for efficient gas extraction from a coal mass, and can increase the coal mass strength in the coal cutting region at the same time, and achieve safe and rapid coal cutting.

Summary of the Invention

Technical problem: In order to solve the problems in the prior art, the present invention provides a freezing cross-cut coal cutting method based on hydraulic seam-cutting, which is simple, highly safe, and attains a good coal cutting effect.

Technical solution: The freezing cross-cut coal cutting method based on hydraulic seam-cutting provided in the present invention comprises the following steps: a. constructing a plurality of water injection holes at an interval towards a coal seam direction through protective rock pillars at a position where the minimum normal distance of the coal cutting working face from the coal seam is greater than or equal to 7m; b. performing hydraulic seam-cutting for each water injection hole sequentially with a conventional hydraulic seam-cutting technique, injecting grout into the water injection hole to seal the hole after hydraulic seam-cutting; c. connecting all of the water injection holes with a gas extraction pipe network for gas extraction, and stopping the gas extraction when the gas content in the coal seam is lower than 8m3/t; d. constructing a freezing hole at two sides of each water injection hole respectively at 0.2 to 0.5m distance from the hole orifice of the water injection hole, with the final distance from the water injection hole at 5 to 10m, and then constructing a temperature measuring hole between the freezing hole and the water injection hole respectively; e. feeding a temperature sensor into the temperature measuring hole, sealing the temperature measuring hole by grout injection, running a freezing pipe into the freezing hole to a depth not smaller than 80% of the depth of the freezing hole; f. connecting a high-pressure water injection pipe to the water injection hole, injecting high-pressure water into the water injection hole by a high-pressure water-injection pump through the high-pressure water injection pipe at 3 to 15MPa of water injection pressure, and stopping the water injection when a water seepage phenomenon occurs on the coal wall around the water injection hole, or the water injection pressure decreases suddenly, or continuously injecting water until the water injection pressure has no change persistently; g. connecting the freezing pipe in the freezing hole to an underground freezing system, and freezing the coal seam through the freezing pipe; in the freezing process, transmitting a coal seam temperature signal to a digital temperature display device through a data wire by the temperature sensor in the temperature measuring hole, so as to monitor the coal seam temperature in the temperature measuring hole in real time with the digital temperature display device; judging the coal seam in the cross-cut coal cutting area has been frozen when the coal seam temperature in all of the temperature measuring holes reaches -3 °C; h. cutting the coal seam with a conventional coal cutting method.

Beneficial effects: With the above-mentioned technical solution, the method provided in the present invention utilizes a hydraulic seam-cutting technique to cut the coal mass around the drilled holes with high-pressure water jet generated by a high-pressure pump station, so as to relieve the pressure in a target coal seam and improve air permeability of the coal mass in the cross-cut coal cutting area, and thereby form a complex fissure network in the coal mass to increase gas flow channels in the coal seam and improve the gas extraction effect; Meanwhile, the method utilizes the phase transition effect of water and combines a water injection and freezing technique for the coal seam, so as to freeze the cross-cut coal cutting area by the phase transition of water and further eliminate the risk of gas outburst in the cross-cut coal cutting process.

The high-pressure water jet formed with the hydraulic seam-cutting technique cuts the coal mass around the borehole, forms flat slots in certain thickness and height, and thereby increase gas flow channels in the coal seam, changes the mechanical properties of the coal mass, improves air permeability in the high gas-containing coal seam, and improves the flow state of the gas in the coal seam.

The influence radius on gas extraction from the borehole is as high as 10 to 40m. Compared with ordinary extraction boreholes, the effective radius of influence on gas extraction from a single hole is enlarged by 5 to 20 times, the number of gas extraction borehole can be reduced by 20% to 60%, the gas content in the coal seam can be decreased efficiently, and thereby the outburst risk in the cross-cut coal cutting process is decreased.

Meanwhile, utilizing water injection technique and coal seam freezing technique in combination, the coal mass around the cross-cut coal cutting area is frozen, the strength and impact resistance of the target coal mass are improved, and the outburst risk in the cross-cut coal cutting area is further decreased.

Brief Description of the Drawings

Fig. lisa schematic diagram of the freezing cross-cut coal cutting based on hydraulic seam-cutting at a coal cutting working face according to the present invention;

Fig. 2 is a schematic layout diagram of a freezing unit at the coal cutting working face along A-A of Fig. 1;

Fig. 3 is a schematic diagram illustrating the connection between a water injection hole and a water injection system according to the present invention;

Fig. 4 is a schematic diagram illustrating the connection between a temperature measuring hole and a temperature measuring system according to the present invention;

Fig. 5 is a schematic diagram illustrating the connection between a freezing hole and a freezing system according to the present invention.

In the figures: 1 - coal seam; 2 - coal cutting working face; 3 - rock roadway; 4 -protective rock pillar; 5 - water injection hole; 6 - temperature measuring hole; 7 - freezing hole; 8 - high-pressure water-injection pump; 9 - high-pressure water injection pipe; 10 - stop valve; 11 - extraction pipe; 12 - capsule hole sealer; 13 -digital temperature display device; 14 - data wire; 15 - borehole sealing section; 16 -temperature sensor; 17 - freezing pipe; 18 - freezing system; 19 - drilling machine; 20 - drill stem.

Detailed Description of the Drawings

Hereunder the present invention will be detailed in an embodiment with reference to the accompanying drawings.

The freezing cross-cut coal cutting method based on hydraulic seam-cutting provided in the present invention comprises the following steps: a. constructing a plurality of water injection holes 5 at an interval towards a coal seam 1 direction through protective rock pillars 4 at a position where the minimum normal distance of a coal cutting working face 2 in rock roadway 3 from the coal seam 1 is greater than or equal to 7m, till the hole penetrates the target coal seam 1 completely and the diameter of the hole is 75-13 0mm; b. driving a drill stem 20 with a high-pressure sealed through-hole by a drilling machine 19 to a preset position of the hole 5 to be seam-cut, starting the drilling machine 19 and a high-pressure water-injection pump 8 at the same time, cutting the coal mass around the borehole with the drill stem 20 with a high-pressure sealed through-hole by injecting a high-pressure water stream at certain pressure and flow rate in the hole 5, while withdrawing the drill stem 20, to form flat slots in certain height and width, wherein, the water injection pressure is 25 to 30Mpa, the flow rate is 40 to 80L/min., the flat slots formed around the borehole has a radius of 400 to 700mm and a width of 20 to 30mm; performing hydraulic seam-cutting for each water injection hole 5 through a conventional hydraulic seam-cutting technique, and sealing the water injection hole 5 by grout injection after hydraulic seam-cutting, and sealing the water injection hole 5 with a capsule hole sealer 12 in the prior art; c. connecting all of the water injection holes 5 with a gas extraction pipe network after hydraulic seam cutting, performing gas extraction in the area influenced by hydraulic seam cutting with a conventional technique, and stopping the gas extraction when the gas content in the coal seam is lower than 8m3/t; d. performing phase-transition fracturing sequentially in groups from a cross-cut roadway to the target coal seam 1 through the protective rock pillars, constructing a freezing hole 7 at two sides of each water injection hole 5 at 0.2 to 0.5m distance from the hole orifice of the water injection hole 5, with final distance from the water injection hole 5 at 5 to 10m, and then constructing a temperature measuring hole 6 between the freezing hole 7 and the water injection hole 5 respectively; e. feeding a temperature sensor 16 into the temperature measuring hole 6, sealing the temperature measuring hole 6 by grout injection in a hole sealing section in length not smaller than 5m, and running a freezing pipe 17 into the freezing hole 7 to a depth not smaller than 80% of the depth of the freezing hole 7; f. connecting a high-pressure water injection pipe 9 to a gas extraction pipe 11 in the water injection hole 5, injecting high-pressure water into the water injection hole 5 by a high-pressure water-injection pump 8 through the high-pressure water injection pipe 9 at 3 to 15MPa of water injection pressure, and stopping the water injection when a water seepage phenomenon occurs on the coal wall of the water injection hole 5, or the water injection pressure decreases suddenly, or continuously injecting water until the water injection pressure has no change persistently, and closing a check valve 10 at the hole orifice of the water injection hole 5; g. connecting the freezing pipe 17 in the freezing hole 7 to an underground freezing system 18, and freezing the coal seam 1 through the freezing pipe 17; in the freezing process, transmitting a temperature signal in coal seam 1 to a digital temperature display device 13 through a data wire 14 by the temperature sensor 16 in the temperature measuring hole 6, so as to monitor the coal seam temperature in the temperature measuring hole 6 in real time with the digital temperature display device 13; judging the coal seam 1 in the cross-cut coal cutting area has been frozen when the coal seam temperature in all of the temperature measuring holes 6 reaches -3°C; h. cutting the coal seam with a conventional coal cutting method.

Claims

CLAIMS:
1. A freezing cross-cut coal cutting method based on hydraulic seam-cutting, wherein said method comprises the following steps: a. constructing a plurality of water injection holes (5) at an interval towards a coal seam (1) direction through protective rock pillars (4) at a position where a minimum normal distance of a coal cutting working face (2) from the coal seam (1) is greater than or equal to 7m; b. performing hydraulic seam-cutting for each water injection hole (5) sequentially with a conventional hydraulic seam-cutting technique, injecting grout into the water injection hole (5) to seal the hole after hydraulic seam-cutting; c. connecting all of the water injection holes (5) with a gas extraction pipe network for gas extraction, and stopping the gas extraction when the gas content in the coal seam is lower than 8m7t; d. constructing a freezing hole (7) at two sides of each water injection hole (5) respectively at 0.2 to 0.5m distance from a hole orifice of the water injection hole (5), with a final distance between an end of the freezing hole (7) and an end of the water injection hole (5) at 5 to 10m, and then constructing a temperature measuring hole (6) between the freezing hole (7) and the water injection hole (5) respectively; e. feeding a temperature sensor (16) into the temperature measuring hole (6), sealing the temperature measuring hole (6) by grout injection, running a freezing pipe (17) into the freezing hole (7) to a depth not smaller than 80% of the depth of the freezing hole (7); f. connecting a high-pressure water injection pipe (9) to the water injection hole (5), injecting high-pressure water into the water injection hole (5) by a high-pressure water-injection pump (8) through the high-pressure water injection pipe (9) at 3 to 15MPa of water injection pressure, and stopping the water injection when a water seepage phenomenon occurs on a coal wall of the water injection hole (5), or the water injection pressure decreases suddenly, or continuously injecting water until there is no change in water injection pressure for a period of time; g. connecting the freezing pipe (17) in the freezing hole (7) to an underground freezing system (18), and freezing the coal seam (1) through the freezing pipe (17); in a freezing process, transmitting a temperature signal in coal seam 1 to a digital temperature display device (13) through a data wire (14) by the temperature sensor (16) in the temperature measuring hole (6), so as to monitor the coal seam temperature in the temperature measuring hole (6) in real time with the digital temperature display device (13); and h. cutting the coal seam with a conventional coal cutting method when the coal seam (1) in the cross-cut coal cutting area has been frozen when the coal seam temperature in all of the temperature measuring holes (6) reaches -3C°.