Patent Application
20210040822
The present disclosure relates to a method for precisely extracting coal-mine gas, which is particularly applicable to precise and efficient extraction of gas in a gas-bearing coal seam of a coal mine, including accurate borehole positioning of a bottom hole point and accurate quantization of a gas extraction amount and residual gas content, so that gas extraction blanking zones caused by inappropriate extraction borehole design can be avoided.
Borehole gas extraction is the major measure of gas control. Coal seams in China have relatively poor gas permeability, and ground drilling has a small influence range and a poor drainage effect. Therefore, small-diameter boreholes are usually constructed in coal mines to perform extraction. The construction of such boreholes is simple, and a quantity of the boreholes is relatively large. However, currently, an unsatisfactory extraction effect is achieved. One major cause is that coal seams are softer than other relatively hard rocks and have short distances. As a result, it is very difficult to control construction trajectories of boreholes. Both an actual coal length and a bottom hole point of a borehole are unclear. However, most of the existing designs are based on the assumption that a borehole is a straight-line borehole constructed from a drilling point, and an end point location of a borehole is not accurately positioned. Moreover, the trajectory of a borehole is not completely in a straight-line form. As a result, an amount of gas that can be extracted from each borehole is misjudged. In addition, coal seams in China have unstable occurrence and have greatly varying thicknesses. Previous designs are all based on the assumption that a coal seam has stable occurrence and even thickness and unvarying strike and dip angles. As a result, significantly different amounts of gas may be extracted from boreholes having the same design parameters. The foregoing causes lead to inaccurate calculation of an amount of gas extracted from each borehole, and gas extraction blanking zones are formed. During late-stage coal drift excavation, a gas overrun problem occurs easily, resulting in potential safety hazards and putting miners' lives at risk.
Embodiments of the present invention provide a method for precisely extracting coal-mine gas to resolve the problem of uneven time and space in gas extraction in coal seams and extraction blanking zones caused by unprecise design and construction of gas extraction boreholes in coal mines. By using methods of precisely positioning coal seam occurrence and precisely design gas boreholes, precise extraction of coal-mine gas is implemented, and the target precision of gas control is improved.
In accordance with an embodiment of the invention, a method for precisely extracting coal-mine gas includes:
(f) performing construction in the coal seam by using the drill, tracking trajectories of a group of boreholes having various construction parameters, and recording borehole drilling point construction parameters and actual coal-point coordinates and hole-bottom coordinates;
A stratum profiler is used to scan the stratum profile in step (a) in a roadway excavation direction with a construction location being a coal seam floor roadway.
The stratum probe boreholes in step (b) should be constructed to penetrate a coal bearing member, until cinder is no longer discharged.
For a method for drawing the change trend graph of coal-seam strike, coal-seam dip, and coal-seam thickness in the to-be-extracted area in step (c), a comprehensive determination method combining scan with a stratum profiler and borehole coordinate correction is used: first determining strike trend of a coal-bearing stratum by using the stratum profiler, and then delimiting an accurate boundary of the coal seam by using borehole coordinates.
For actual coal-seam floor coal-point coordinates and actual coal-seam roof coal-point coordinates in step (f), the endoscopic camera is used to record trajectory points respectively corresponding to borehole floor coal points and borehole roof coal end points, and specific coordinate values are then correspondingly determined from borehole trajectory points recorded by the gyroscope.
A method for adjusting the borehole construction parameters in step (g) is: first adjusting an azimuth angle, so that horizontal projections of a roof coal point of an actual borehole-trajectory and a designed roof coal point have the same length in a direction perpendicular to a roadway, and then adjusting a drilling location in a direction opposite to an offset direction according to an offset amount of a borehole in a roadway direction.
Beneficial effect: Because the foregoing technical solution is used, in some embodiments of the present invention, the method for precisely extracting coal-mine gas is implemented. Therefore, in one aspect, occurrence conditions of a coal seam and gas may be accurately obtained, and a gas extraction solution is precisely designed according to actual occurrence conditions of the coal seam and gas. In another aspect, construction parameters may be adjusted according to borehole trajectory features to accurately reach predesigned borehole locations, so as to avoid the problem of extraction blanking zones caused by inappropriate design of coal-mine gas extraction projects because engineers and technicians lack precise knowledge of occurrence variations of coal seams and gas. Moreover, actual borehole trajectories are tracked and positioned to avoid the problem of difficulty in positioning actual borehole trajectories and coal point locations, thereby implementing accurate assessment of gas extraction amounts and further determine residual gas content of a coal seam to provide a reference for gas control in later-stage mining or excavation in the coal seam.
In the drawings: 1-floor roadway; 2-coal-bearing stratum; 3-coal seam; 4-stratum probe borehole; 5-actual borehole floor coal point; 6-actual borehole roof coal end point; 7-coal-seam floor; 8-coal-seam roof; 901˜907-actual construction borehole; 10-designed borehole; 11-designed borehole floor coal point; 12-designed borehole roof coal end point; 13-actual borehole azimuth angle; 14-rectified borehole azimuth angle; 15-designed borehole azimuth angle; 16-actual borehole trajectory horizontal projection; 17-designed borehole trajectory horizontal projection; and 18-rectified borehole trajectory horizontal projection.
As shown in
Aspects of the present invention are further described below with reference to the illustrated embodiments in the accompanying drawings.
The gas content in a coal seam of a coal mine is 12 m3/t. A geographically explored coal-seam thickness is 4 m. A floor roadway is constructed below a coal seam. The floor roadway has a length of 1 km. A perpendicular distance of the floor roadway from the coal seam is 10 m. A cross borehole is constructed in the floor roadway to pre-extract coal-seam gas to reduce the gas content in a pre-extraction area to be less than 8 m3/t. The length and the width of the pre-extraction area are required to be 30 m and 4 m respectively. The coal density is 1.2 t/m3. In this case, the coal reserve that can be effectively control has a total of 576 tons. Seven boreholes are first designed originally. 2304 m3 of gas can be extracted through pre-extraction for six months, so that the residual gas content can be less than 8 m3/t.
As shown in
Next, a drill is disposed in the floor roadway 1. After construction is completed, a group of actual construction boreholes 901 to 907 are formed, as shown in
Boreholes are rectified according to the data in Table 1. The borehole 907 is used as an example. An actual borehole azimuth angle 13 is first adjusted to a rectified borehole azimuth angle 14, so that an actual trajectory obtained after azimuth angle adjustment is consistent with a horizontal coordinate X of a designed borehole 10. When only an azimuth angle is adjusted, a trajectory shape of a borehole does not change. Therefore, the length L of a rectified borehole trajectory horizontal projection 18 is the same as the length of an actual borehole trajectory horizontal projection 16. That is, an X coordinate value of an actual roof coal end point of the borehole 907 in Table 1 is 18.4 m/cos 336°=20.1 m. Therefore, the arccosine value of a ratio of an X-axis length LX of a designed borehole trajectory horizontal projection 17 to the length L of the rectified borehole trajectory horizontal projection 18 is arcos(LX/L)=41.7°. The X coordinate of the designed roof coal end point of the borehole 907 in Table 1 is 15 m. Therefore, the rectified borehole azimuth angle 14 is 360°−41.7°=318.3°.
Lp of the borehole obtained after azimuth angle adjustment is then adjusted in a direction opposite to a Y-axis offset direction. Lp is equal to the projection length Lj of the post-azimuth-angle-rectification borehole trajectory horizontal projection 18 of the actual construction borehole 907 on the Y axis minus a projection length Ly of the designed borehole 10 on the Y axis. The Y coordinate value of the designed roof coal end point of the borehole numbered 907 in Table 1 is 1.3 m, where LJ=L×sin(arcos(LX/L))=12.2 m. In this case, Lp=Lj−Ly=10.9 m, so as to obtain the designed parameters after rectification: the azimuth angle is 318.3°, the tilt angle is 42°, the X coordinate of the drilling hole is 0 m, the Y coordinate of the drilling hole is −10.9 m, and the Z coordinate of the drilling hole is 0 m.
Eventually, the rectified and reconstructed boreholes 901 to 907 are connected to a gas extraction pipeline, and an accumulated gas extraction amount per meter of each borehole in six months is measured respectively and filled in Table 2. It can be known according to an actual hole length and an actual single-meter gas drainage amount that an accumulated extraction amount of gas in six months may be 2816.8 m3. In this case, in the controlled area, the gas content may be actually reduced to 5.6 m3/t, and the residual gas content may be 6.4 m3/t, so that requirements are satisfied.
Boreholes are constructed in groups in a roadway direction. Each group of boreholes have the same design and construction parameters. Therefore, other groups of boreholes are constructed according to the foregoing rectified borehole design parameters, so as to achieve expected design effects of the group of boreholes, thereby improving the accuracy of design and construction.
In general, in the following claims, the terms used should not be construed to limit the claims to the specific embodiments disclosed in the specification and the claims, but should be construed to include all possible embodiments along with the full scope of equivalents to which such claims are entitled.
| Number | Date | Country | Kind |
|---|---|---|---|
| 201710301504.0 | May 2017 | CN | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/CN2017/114363 | 12/4/2017 | WO | 00 |
