General contracting of the integrated Gas control through the directional boreholes in Longfeng coal mine
1. Introduction
Longfeng coal mine is under construction and is expected to be put into production in June 2020. The first mining district of the mine is located in the middle of the mine field, with 2 coal seams, the average thickness of coal seam 9 is 2.8m, the average thickness of coal seam 7 is 0.5m, the interval between layers is 5.65m, and the lithology between layers is mainly sandstone. The structural complexity of the coal mine is medium, and the f values of coal seams 7 and 9 are 1.40 and 1.94 respectively, which are suitable for directional drilling. For this reason, Longfeng coal mine is based on the advanced gas extraction and efficient control to ensure that the first mining working face of the mine is put into production on time. In combination with CCTEG Xi'an Research Institute Co., Ltd., the research on the high-efficiency gas extraction technology of directional long boreholes in the first mining working face was carried out, and the technical measures suitable for the advanced and efficient control of the mine water were explored.
2. Treatment solution
Due to the small distance between No.7 and No.9 coal seams in the first mining face, the gas in No.7 coal seam will diffuse to the mining space during the mining process, threatening the safe production of the mine, so it is necessary to comprehensively consider the gas control of the two coal seams. According to the mine development conditions, the first circulation was designed with 2 drilling fields, each drilling field was designed with 10 boreholes. Two rows of boreholes were arranged and the upper row of boreholes was designed for No.7 coal seam gas drainage, and the lower row of boreholes was designed for No.9 coal seam gas drainage. The designed depth of the boreholes was 300m. The horizontal spacing of the drilling face was 6m, covering about 15m around the transportation chute of the working face 1903. The drilling adopted three-stage design, included the first stage casing, second stage and third stage open hole. The opening diameter of the first stage was 133mm, and the casing was put in to seal the hole. The opening diameter of the second stage was 133mm, and the opening diameter of the third stage was 98mm
Drilling layout plan
Borehole layout section
3. Work situation
In the working face 1903 of Longfeng coal mine, 20 directional boreholes holes were drilled in two directional drilling fields of track 1 joint and return air inclined shaft, with a cumulative footage of 7225 m, including 14 directional boreholes in coal seam 9, with a cumulative footage of 5686m, a footage of 4466m in coal seam section, and a footage of 1220m in rock section, covering about 15m around the transportation chute of the working face1903. There were 6 directional boreholes in coal seam 7, with a total footage of 1539m; the maximum single hole depth was 360m, and the longest drilling distance along the coal seam was 318m.
Physical drawing of directional drilling rig
Drilling construction plan of No.9 coal seam of return inclined shaft
Drilling construction plan of No.9 coal seam of track 1 joint
4. Achieved accomplishment
In Longfeng coal mine, the breakthrough of drilling 318m along the coal seam by hydraulic directional drilling was realized. By using the technology of opening and closing drill bit and big hole spiral drill pipe, the test of downward directional drilling was carried out, with the depth of 350～360m (hole depth 360m).
According to the data of main pipe drainage in the drilling fields, the gas drainage amount of 213 days and the residual extraction of 195 days was 260.21 ~ 14764.03m3/d, average 2695.18m3/d, extraction concentration 13% ~ 77.3%, average 55.12% and total amount of gas drainage 574100 m3. During 161 days of combined extraction, the residual gas content of No.9 coal seam was measured by sampling, ranging from 7.14 to 14.84m3/t, with an average of 13.05m3/t and a decrease of 5.89m3/t.
Gas drainage curves of the directional boreholes in the air return inclined shaft
141 days of pumping and 91 days of combineds pumping were accumulated in the directional drilling field of track 1, the extraction volume was 709.00 ~ 5397.93m3/d, with an average of 3005.24m3/d. The concentration of gas extraction was 8.8% ~ 89.70%, with an average of 51.74%. The total amount of gas extraction was 423700 m3. In 89 days of the combined extraction, the measured residual gas content of No.9 coal seam was 3.92 ~ 16.62m3/t, and the average maximum and minimum gas content of coal seam was 12.91m3/t (affected by the uncovering coal borehole) and 5.67m3/t respectively.
Gas drainage curve of No.1 combined directional boreholes
5. FAQ
(1) What is the significance of the successful implementation of the project? What is the inspiration or promotion for the concept and technology of regional gas control.
The implementation of the project has important reference significance for the gas control in the area of long directional boreholes in the southwest and even in the mine with complex geological conditions in the country. For the mine without the construction conditions of the bottom drainage roadway or the construction of the bottom drainage roadway lags behind, the technology can be used for strip gas pre -drainage and tunnel excavation. In the mine with better conditions, directional long borehole can be directly used instead of bottom drainage tunnel through layer borehole for strip gas pre -drainage.
(2) What are the applicable conditions and technical advantages of gas control in the long directional drilling area.
The directional long drilling has the technical advantages of wide coverage, large drilling depth, accurate and controllable drilling track, etc. Therefore, as long as the proper layer is selected, the construction can be carried out. For the coal mine with poor coal seam conditions, the roof or floor can be selected as the target layer to drill the directional boreholes, and then the downward or upward branch holes can enter the coal seam for gas drainage. In order to fully reflect the technical advantages of gas extraction of the directional long boreholes, try to ensure a longer extraction time.
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