METHOD OF PERFORMING COMBINED DRILLING, FLUSHING, AND CUTTING OPERATIONS ON COAL SEAM HAVING HIGH GAS CONTENT AND PRONE TO BURSTS TO RELIEVE PRESSURE AND INCREASE PERMEABILITY

Abstract

The present invention relates to a “drilling-flushing-slotting” coupled pressure relief and permeability increasing method for a high gas outburst coal seam, which is more particularly suitable for the pressure relief and permeability increasing when gas of a roadway band of the high gas outburst coal seam is pre-extracted through crossing boreholes. On the basis of the crossing borehole pre-extraction measures for the coal seam gas, the hydraulic flushing and the hydraulic slotting are reasonably combined, and a “drilling-flushing-slotting” dedicated device is utilized to implement the coupled operation of “low pressure drilling-medium pressure flushing-high pressure slotting” in a borehole, so that the coal in the pre-extraction area is deformed and moved to form network cracks, passages are provided to the desorption flow of the gas, and the gas is easier to extract. The method can enlarge the single-hole pressure relief influence range, increase the gas permeability of the coal seam, improve the gas extraction efficiency, reduce the number of pre-extraction boreholes, shorten the pre-extraction time and have good applicability to the coal seams in different occurrence states. The present invention can reduce the number of the crossing boreholes by 32.5% and can reduce the length of each crossing borehole by 42.9%, is remarkable in coal roadway regional outburst eliminating effect, and obviously increases the tunneling speed.

Claims

1. A “drilling-flushing-slotting” coupled pressure relief and permeability increasing method for a high gas outburst coal seam, comprising adjusting a water inlet pressure of a water jet at different stages according to different positions where a borehole construction is carried out, wherein when in drilling, the water jet is controlled to respectively perform a low pressure water flow drilling and a medium pressure water flow flushing; when a drill bit is withdrawn, a high pressure water flow slotting is performed; and the water inlet pressure is gradually released level by level according to the low pressure water flow, the medium pressure water flow and the high pressure water flow, thereby implementing the “drilling-flushing-slotting” coupled pressure relief and permeability increasing integrated method inside a crossing borehole (3); and the method comprising the following steps: a. arranging multiple crossing boreholes (3) to a pre-extraction area of a coal seam (2) from a floor rock roadway (1); b. constructing the multiple crossing boreholes (3) arranged in the pre-extraction area one by one by utilizing a pressure control integrated drill bit (7), wherein when the pressure control integrated drill bit (7) does not drill to reach the coal seam (2), a low-pressure water jet of 3 to 5 MPa is utilized to assist the drilling and the slagging, so that while the drilling speed is increased, a dust-fall effect is achieved; c. increasing the pressure of the water jet to 8 to 12 MPa when the pressure control integrated drill bit (7) drills to reach a coal seam floor (5) and enters the coal seam (2), and flushing the borehole by utilizing a medium-pressure water jet at the coal seam (2), wherein since a front portion of the pressure control integrated drill bit (7) is pressed in the drilling process, a side spray nozzle of the pressure control integrated drill bit (7) is closed under the pressure, the water jet flushes the front coal only through a front spray nozzle, as the broken coal is discharged, a pressure relief hole (9) is formed in the coal seam (2), and the internal energy of the coal is primarily released; d. observing a coal output situation at a drilling opening, determining an occurrence condition of the coal seam (2), and stopping the drilling when the borehole (3) runs through the coal seam (2); e. withdrawing the drill bit, further increasing the water pressure of the water jet in the withdrawing process, and adopting a high-pressure water jet of 15 to 25 MPa to cut the coal, wherein since the front portion of the pressure control integrated drill bit (7) is not pressed, the front spray nozzle is closed, the side spray nozzle is opened, the water jet is sprayed out only from the side spray nozzle, and a lot of hydraulic cutting slots (10) are formed in the coal seam (2) in the withdrawing process, so that the homogeneous pressure relief of the coal is realized; and f. forming a crossing extraction borehole (11) of a particular shape after the hydraulic slotting is completed in the coal seam (2), stopping conveying high-pressure water to the pressure control integrated drill bit (7), and withdrawing the pressure control integrated drill bit (7) and a drill stem (8) from the borehole (3) while keeping rotating.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] FIG. 1 is a layout schematic diagram illustrating a crossing borehole according to the present invention.

[0013] FIG. 2(a) is a structural schematic diagram illustrating low pressure drilling according to the present invention.

[0014] FIG. 2(b) is a structural schematic diagram illustrating medium pressure flushing according to the present invention.

[0015] FIG. 2(c) is a structural schematic diagram illustrating high pressure slotting according to the present invention.

[0016] In the drawings: 1—floor rock roadway; 2—coal seam; 3—crossing borehole; 4—coal roadway; 5—coal seam floor; 6—coal seam roof; 7—pressure control integrated drill bit; 8—drill stem; 9—pressure relief hole; 10—pressure relief slot; 11—crossing extraction borehole of particular shape.

DETAILED DESCRIPTION

[0017] The present invention is further described below in combination with embodiments in the drawings:

[0018] A “drilling-flushing-slotting” coupled pressure relief and permeability increasing method for a high gas outburst coal seam of the present invention adjusts the water inlet pressure of a water jet at different stages according to different positions where the borehole construction is carried out; when drilling, the water jet is controlled to respectively perform the low pressure water flow drilling and the medium pressure water flow flushing; when a drill bit is withdrawn, high pressure water flow slotting is performed; and the pressure is gradually released level by level according to the low pressure water flow, the medium pressure water flow and the high pressure water flow, thereby implementing the “drilling-flushing-slotting” coupled pressure relief and permeability increasing integrated operation inside a crossing borehole 3. The method includes specific steps as follows: [0019] a. arranging multiple crossing boreholes 3 to a pre-extraction area of a coal seam 2 from a floor rock roadway 1; [0020] b. constructing multiple crossing boreholes 3 arranged in the pre-extraction area one by one by utilizing a pressure control integrated drill bit 7, where when the pressure control integrated drill bit 7 does not drill to reach the coal seam 2, a low-pressure water jet of 3 to 5 MPa is utilized to assist the drilling and the slagging, so that while the drilling speed is increased, a dust-fall effect is achieved; [0021] c. increasing the pressure of the water jet to 8 to 12 MPa when the pressure control integrated drill bit 7 drills to reach a coal seam floor 5 and enters the coal seam 2, and flushing the borehole by utilizing a medium pressure water jet at the coal seam 2, where since a front portion of the pressure control integrated drill bit 7 is pressed in the drilling process, a side spray nozzle of the pressure control integrated drill bit 7 is closed under the pressure, the water jet flushes the front coal only through a front spray nozzle, as the broken coal is discharged, a pressure relief hole 9 is formed in the coal seam 2, and the internal energy of the coal is primarily released; [0022] d. observing a coal output situation at a drilling opening, determining an occurrence condition of the coal seam 2, and stopping the drilling when the borehole 3 runs through the coal seam 2; [0023] e. withdrawing the drill bit, further increasing the water pressure of the water jet in the withdrawing process, and adopting a high-pressure water jet of 15 to 25 MPa to cut the coal, where since the front portion of the pressure control integrated drill bit 7 is not pressed, the front spray nozzle is closed, the side spray nozzle is opened, the water jet is sprayed out only from the side spray nozzle, and many hydraulic cutting slots 10 are formed in the coal seam 2 in the withdrawing process, so that the homogeneous pressure relief of the coal is realized; and [0024] f. forming a crossing extraction borehole 11 of a particular shape after the hydraulic slotting is completed in the coal seam 2, stopping conveying high-pressure water to the pressure control integrated drill bit 7, and withdrawing the pressure control integrated drill bit 7 and a drill stem 8 from the borehole 3 while keeping rotating.

Embodiment 1: As Shown in FIG. 1

[0025] The coal seam 2 is a high gas outburst coal seam, a coal roadway 4 is high in outburst danger when in tunneling. In order to eliminate the outburst danger, the coal seam gas of a roadway band is pre-extracted, the upward crossing borehole 3 is constructed to the coal seam 2 in the floor rock roadway 1 at the lower portion of the coal seam 2 to pre-extract the gas of the coal seam 2 so as to protect the tunneling of the coal roadway 4; multiple crossing boreholes 3 are arranged to a pre-extraction area of the coal seam 2 from the floor rock roadway 1; the multiple crossing boreholes 3 arranged in the pre-extraction area are gradually constructed one by one by utilizing a pressure control integrated drill bit 7, when the pressure control integrated drill bit 7 does not drill to reach the coal seam 2, as shown in FIG. 2(a), a low-pressure water jet of 3 to 5 MPa is utilized to assist the drilling and the slagging, so that while the drilling speed is increased, the dust is effectively settled; when the pressure control integrated drill bit 7 enters the coal seam 2 from the coal seam floor 5, as shown in FIG. 2(b), the water pressure is increased to 8 to 12 MPa, the medium-pressure water jet is utilized to flush the borehole, since the front portion of the pressure control integrated drill bit 7 is pressed, a side spray nozzle of the pressure control integrated drill bit 7 is closed under the pressure, the water jet flushes the front coal only through a front spray nozzle, as the broken coal is discharged, a pressure relief hole 9 is formed in the coal seam 2, and the internal energy of the coal is primarily released, so that the peripheral coal is deformed and moved towards the pressure relief area, and the elastic energy of the coal and the internal energy of the gas are primarily released. For the coal seam 2 with relatively high stress or having soft coal, the primary pressure relief can avoid the collapse of the borehole 3 and the closing of the pressure relief slots 10, so that the long-term pressure relief effect is ensured; by observing the coal output situation at a drilling opening, the formation condition of the coal seam 2 is determined, and the drilling is stopped after the borehole 3 runs through the coal seam 2; the drill bit is withdrawn, the water pressure is further increased in the withdrawing process, a high-pressure water jet of 15 to 25 MPa is utilized to cut the coal, since the front portion of the pressure control integrated drill bit 7 is not pressed, the front spray nozzle is closed, the side spray nozzle is opened, the water jet is sprayed out from the side spray nozzle, the slots 10 are formed in the coal seam 2, as shown in FIG. 2(c), the peripheral coal is subjected to strong disturbance in different directions, the homogeneous pressure relief is realized through the borehole 3, the influence range of the borehole is increased, the gas permeability of the coal is improved, and the gas is easier to extract.

[0026] For the coal seam 2 having a hard sublayer or a parting, homogeneous coal output is difficult to implement through a single borehole, and the pressure relief effect is difficult to ensure; however, the pressure is further released by means of the slotting, the influence area of the borehole 3 is increased, the coal is homogeneous in pressure relief, and the extraction effect is better; and after the slotting is completed in the coal seam 2, the crossing extraction borehole 11 of a particular shape is formed, the high-pressure water is stopped being conveyed to the pressure control integrated drill bit 7, and the pressure control integrated drill bit 7 and a drill stem 8 are withdrawn from the borehole 3 while keeping rotating.

[0027] By virtue of the superposed effect of the water jet in different directions, the range of a plastic zone surrounding the borehole 3 is increased, a great number of secondary cracks are developed, expanded and penetrated, and the number of gas flowing passages is rapidly increased, so that the gas permeability of the coal is remarkably increased. Thus it can be seen that after the crossing borehole 3 adopts the “drilling-flushing-slotting” coupled pressure relief technology, the single-hole pressure relief influence range is enlarged, the gas permeability of the coal seam 2 is increased, gas extraction efficiency is improved, the number of the pre-extraction boreholes 3 is further reduced, the pre-extraction time is shortened, and the technology has good applicability to the coal seams 2 in different formation states.