(1. Chongqing Branch of Coal Science Research Institute; 2. Shanxi Yamei Daning Energy Co., Ltd.
This paper introduces the hole-forming test of a thousand-meter dendritic borehole along the bedding in Daning Coal Mine. The longest VLD directional borehole reaches 1005 m (depth). This paper studies the technology of gas drainage with a kilometer long branch borehole and the corresponding drainage effect, and obtains good results. After 1.5 years of pre-drainage in the first mining face of Daning Mine, the pre-drainage rate is about 49%, and the mine gas drainage rate is 70.35%.
Underground gas drainage; Directional kilometer drilling rig; Pre-drainage rate of long-branch borehole along bedding; Kilometer drilling parameters; Drainage effect
A new technology for extracting coalbed methane by long-distance tree-shaped borehole along coal seam underground
Du Zizi 1, Liu Zilong 2
(1. Chongqing Branch of Coal Science Research Institute; 2. Shanxi Yamei Daning Energy Co., Ltd.
Abstract: This paper introduces the construction experience of long-distance tree-shaped drilling in Daning Coal Mine. The longest directional VLD well reaches1005m. In this case, the drilling technology with a depth of 1,000 meters and the gas drainage effect are studied. Practice has proved that the drainage effect of long-distance tree-shaped borehole in Daning Coal Mine is satisfactory. After one and a half years of mining in the first mining area, the gas extraction rate reached about 49% and the gas recovery rate reached 70.35%.
Keywords: underground mining of coal mine gas; Kilometer directional drilling device; Long-distance tree drilling along the coal seam; Pre-extraction rate; Drilling parameters; Extraction effect
order
According to statistics, from 200/kloc-0 to the end of February 2005, there were 28 accidents with more than 30 deaths in coal mines nationwide, with 1689 deaths. Among them, there were 24 gas accidents and deaths 1558, and the number of gas accidents and deaths accounted for 85.7438+0% and 92.2% of the total respectively. Mine gas disaster has become a major problem in coal mine safety production in China, and the situation of mine safety production needs to be changed urgently.
Judging from the national industrial policy of "pumping before mining" and the technical level of gas control, the root of controlling mine gas disaster lies in mine gas drainage. Mine gas drainage has a series of comprehensive benefits, such as promoting coal mine safety production, making full use of clean resources and protecting atmospheric environment. On the one hand, gas is the most harmful gas in coal mines, and strengthening underground gas drainage can fundamentally reduce gas emission in coal mines, which is conducive to ensuring mine safety and liberating mine productivity; On the other hand, the exploitation and utilization of natural gas can significantly increase the supply of clean resources and improve and optimize the energy structure; In addition, gas is a strong greenhouse gas, and gas extraction and utilization reduces the amount of gas discharged into the atmosphere during coal mining and protects the atmospheric environment.
However, in the past, gas drainage in many mines in China has been restricted by drilling equipment, long drilling and gas drainage technology. On the one hand, although the existing drilling rig in China has realized the drilling construction with a length of 800m, the drilling orientation and inclination measurement technology is still not perfect, and the bottom-hole motorized drilling technology has not been adopted. At present, there is no real directional drilling rig in China, and the long drilling construction lacks corresponding equipment. On the other hand, China's coal seam conditions are complex, and the long drilling technology is difficult. At present, domestic drilling rigs are used to drill along the bed, and 250m drilling has been realized in coal and gas outburst mines, and the successful drilling depth can reach 500m in Sihe Mine in Jincheng with good coal seam conditions (f = 1 ~ 2). But in general, the implementation of large-scale pre-pumping measures to prevent and control mine gas is still greatly limited.
Therefore, the national "Tenth Five-Year Plan" scientific and technological research project "Study on the application of complete sets of technology for underground development of coalbed methane" has carried out technical research by introducing foreign thousand-meter drilling rigs and independently developing the deep-hole gas extraction technology of thousand-meter drilling rigs. The longest directional drilling in Jincheng mining area has been realized, reaching 1005m, and the length of test drilling holes is mostly over 800m m. On this basis, the research on gas drainage technology with 1000-meter long branch drilling holes and the corresponding investigation on drainage effect have been carried out.
1 test mine
Shanxi Yamei Daning Energy Co., Ltd. (hereinafter referred to as "Daning Mine"), the original Daning No.1 Mine in Jincheng, is the only underground coal mine jointly produced by China and foreign countries in China. The designed production capacity of the mine is 4 million tons. The mined coal measures strata belong to Permian Shanxi Formation, Carboniferous Taiyuan Formation and benxi formation. Total thickness of coal measures strata 15 1m, * * * coal-bearing strata 10 ~ 22, of which 3 layers are recoverable and partially recoverable. The 3 # coal seam mainly mined in the mine belongs to anthracite with moderate metamorphic degree, which is nearly horizontal, with a thickness of 2.2 1 ~ 6.97 m and an average of 4.45m The coal firmness coefficient f is 1 ~ 2, and the coal seam is rich in gas with a gas content of1.1.
The mine was completed and put into operation in July 2005, and the gas drainage capacity of the mine was increased from 18.28m3/min in 2002 to 184.8m3/min at present. The concentration of mine gas drainage is above 55%, and the gas drainage rate is as high as 70%. Gas pumping has achieved remarkable results.
Hole-forming test of 2 km drilling rig and underground 1 km long dendritic drilling
2. 1 VLD- 1000 directional drilling rig
In the experiment, VLD- 1000 downhole motor directional drilling rig produced in Australia was selected, as shown in figure 1. The drilling rig consists of walking mechanism, power system, drilling system, electrical control system and inclinometer orientation system.
The drilling rig uses a bottom hole motor to drill holes without rotating the drill pipe. The bottom hole motor is driven by high-pressure water, the feed speed is 0 ~ 5m per minute, and the speed of recovering drill pipe can reach 0 ~ 20m per minute. The bottom hole motor drilling reduces the friction resistance between the drill pipe and the borehole, so the drilling capacity of the drilling rig is above 1000m, and the power loss is small.
The main technical parameters of the drilling rig are:
Figure 1 VLD- 1000 Directional Drilling Rig
Drilling length:1000m; ;
The motor power is 90kW( 1 140V, 50hz);
Measurement accuracy of inclinometer orientation system: up-and-down deviation 0.2 degrees, horizontal deviation 0.5 degrees;
Total weight of drilling rig: 8500kg；;
Overall dimensions: 4000mm (length) ×2000mm (width) × 1600mm (height).
2.2 Underground bedding kilometer-long dendritic drilling hole-forming test.
VLD directional drilling rig was put into operation in April 2003 in Shanxi Yamei Daning Energy Co., Ltd. As shown in Figure 2, from the start of operation to the end of April 2004, the total footage of the whole year was 78,484 meters, setting a world record for directional drilling with a VLD single directional drilling rig. By the end of September, the VLD drilling rig had completed directional drilling 160, and the total footage reached 1 127 16m. The longest VLD directional drilling in Shanxi Yamei Daning Energy Co., Ltd. has reached 1005m (depth), and most of the drilling holes are over 800m (depth).
Since 2005, underground drilling with kilometer drilling rig has become a routine work in Daning Coal Mine.
In the test, the directional and inclined drilling in the longitudinal section of bedding is emphatically tested. Fig. 3 shows the actual drilling trajectory (longitudinal section) measured by V-P2 T22-20 borehole.
As shown in Figure 2, in the experiment, branch drilling was also carried out along the bedding plane, that is, in the drilling process of 1 hole, the multi-branch bedding long drilling of 1 hole was realized by using the inclination adjustment function of the kilometer drill.
Completion drawing of dendritic long drilling with bedding kilometer drilling rig in Daning Coal Mine.
Fig. 3 Trajectory of actual longitudinal section of borehole V-P2T22-20
Experiment on gas drainage by bedding kilometer-long dendritic borehole
3. 1 test work
At the same time, the drilling technology of long drilling hole with kilometer drilling rig is studied, and the drainage effect of drilling holes with different depths is studied in the field. As shown in Table 1, the gas drainage of boreholes with different depths is mainly investigated ("borehole depth" refers to the length from the borehole opening point to the borehole end point, and "total borehole length" refers to all borehole inclinations (plane and profile) and the total borehole length of branch boreholes from the borehole opening point to the borehole end point).
The drilling depth of this group with a drilling depth of 800m is 80 1 ~ 852 m, the total drilling length is 849 ~ 1548 m, and the survey time is 371~ 833 d.
The drilling depth of this group is 600 meters, the drilling depth is 5 13 ~ 7 14m, the total drilling length is 720 ~1062m, and the survey time is 379 ~ 836 days.
The drilling depth of this group with a drilling depth of 400m is 363 ~ 426 m, the total drilling length is 597 ~ 966 m, and the survey time is 413 ~ 598 d.
Table 1 Summary of Investigation on Drainage Effect of Long Boreholes in Bedding Kilometers Branch
sequential
Note: The "drilling depth" in the table refers to the length from the drilling opening point to the drilling end point; "Total drilling length" refers to the total drilling length of all drilling inclination angles (plane and section) and long-branch drilling between the opening point of drilling and the final hole point of drilling; In the table, the displacement per 100 m borehole is calculated according to the total borehole length.
3.2 Gas Drainage Effect Investigation
3. 2. 1 800m drilling drainage.
As mentioned above, the drilling depth of the group with drilling depth of 800m ranges from 80 1 ~ 852 m, the total drilling length is 849 ~ 1548 m, and the survey time is 371~ 833 d.
Fig. 4 p5t 22- 1 1 Inspection diagram of borehole drainage effect.
During the test, the drainage process of five 800-meter-deep boreholes listed in table 1 was monitored. Now the drilling situation of P5 T22- 1 1 is detailed as follows.
P5T22- 1 1 The inclination of drilling opening is 2.46, the drilling completion time is August 5, 2003, the drilling diameter is 94mm, the depth is 80 1m, and the total drilling length is10/4 m.. The investigation time is June 5438+065438+1October 65438+May, 2005. See Figure 4 for gas concentration and borehole drainage.
As shown in Figure 4, from the beginning of drilling P5T22- 1 1, the drainage capacity of 100m was 0.55 m3/min·hm, and the gas concentration reached about 97%. Later, with the extension of the drainage time, the drainage concentration and the drainage amount gradually decreased with the drainage time in a negative exponential law, until the drainage amount of the last 100 m borehole was 0.02 m3/min·hm, and the drainage concentration was about 20%. The negative pressure of borehole drainage is about 10 ~ 13 kPa. 100m borehole drainage and drainage time relationship is as follows.
q=0.5459e-0.0045t ( 1)
Where: q-100m borehole drainage capacity, m3/min hm; T-extraction time, d
According to the investigation on the drainage effect of other boreholes in this group, as shown in Table 1, the average drainage situation of boreholes with a borehole depth of 800m is: borehole depth 82 1.4m, total borehole length1/37m, drainage time 643.8d, and average borehole drainage1.
3.2.2 When the drilling depth is 600 meters, drill holes in groups for drainage.
The drilling depth of this group is 600 meters, the drilling depth is 5 13 ~ 7 14m, the total drilling length is 720 ~1062m, and the survey time is 379 ~ 836 days.
During the test, the drainage process of five 600-meter-deep boreholes listed in table 1 was monitored. Now the drilling situation of P2 T22- 12 is detailed as follows.
P2T22- 12 borehole opening inclination is 2.63, and the drilling completion time is August 8, 2003. The borehole diameter is 94 mm, the depth is 640 m, and the total borehole length is 790 m. The investigation time is July, 2005 1 day, and the gas concentration and borehole drainage amount are shown in Figure 5.
Fig. 5 p2t 22- 12 Survey of Borehole Drainage Effect
As shown in Figure 5, from the beginning of drilling P2T22- 12, the pumping capacity of 100m borehole was 0.42 m3/min·hm, and the pumping concentration reached about 95%. Later, with the extension of the drainage time, the drainage concentration and the drainage amount gradually decreased with the drainage time in a negative exponential law, until the drainage amount of the last 100 m borehole was 0.03 m3/min·hm, and the drainage concentration was about 22%. The negative pressure of borehole drainage is about 10 ~ 13 kPa. 100m borehole drainage and drainage time relationship is as follows.
q=0.5924e-0.0049t (2)
According to the investigation on the drainage effect of other boreholes in this group, as shown in Table 1, the average drainage situation of boreholes with a drilling depth of 600m is: the drilling depth is 6 18.60m, the total drilling length is 91.00 m, the drainage time is 662.20d, and the average drainage of boreholes is/.
3.2.3 When the drilling depth is 400 meters, drill holes in groups for drainage.
As mentioned above, the drilling depth of the group with drilling depth of 400m ranges from 363 to 426 m, the total drilling length is 597 to 966 m, and the survey time is 413 to 598 d.
In the experiment, the whole process of monitoring the drainage of five groups with drilling depth of 400m listed in table 1 was carried out. Now the drilling situation of W 12 S27-5 is detailed as follows.
W 12S27-5 borehole opening is 1.38, and the drilling completion time is July 8, 2004. The diameter of the borehole is 94 mm, the depth is 363 m, and the total length of the borehole is 660 m ... The investigation time is from June, 2005 10 to October, 2, 20051day. See Figure 6 for the gas concentration and gas extraction amount from the borehole.
Figure 6 w 12s 27-5 Survey of Borehole Drainage Effect
As shown in Figure 6, when water is pumped from the W 12S27-5 borehole, the pumping capacity of the 100m borehole is 0.60 m3/min·hm, and the pumping concentration reaches about 99%. Later, with the extension of drainage time, the drainage concentration and the drainage amount gradually decreased with the drainage time in a negative exponential law, until the drainage amount of the last 100m borehole was 0.65438+100 m3/min hm, and the drainage concentration was about 40%. The negative pressure of borehole drainage is about 10 ~ 13 kPa. 100m borehole drainage and drainage time relationship is as follows.
q=0.6998e-0.0053t (3)
According to the investigation on the drainage effect of other boreholes in this group, as shown in Table 1, the average drainage situation of boreholes with a drilling depth of 400m is: the drilling depth is 389.80m, the total length of boreholes is 720.6m, the drainage time is 535.40d, and the average drainage of boreholes is 1.90m3/min.
Evaluation and analysis of drainage effect of 4 km long dendritic borehole along bedding
4. 1 Drainage Effect of Boreholes with Different Length
The drainage methods of typical boreholes with drilling depths of 800m, 600m and 400m are analyzed. The extraction effects of different drilling lengths are shown in Table 2. From the data analysis in the table, it can be seen that the total drilling length of the group with drilling depth of 800 meters is 153% of that of the group with drilling depth of 400 meters, and the cumulative drainage amount of 1 year, the second year and the 800th day is133% ~139% of that of the group with drilling depth of 400 meters. The total drilling length of the group with drilling depth of 600 meters is 120% of that of the group with drilling depth of 400 meters, and the cumulative drainage on the first 1 year, the second year and the 800th day is 106% ~ 120% of that of the group with drilling depth of 400 meters. It can be seen that with the increase of drilling depth,
Table 2 Analysis Table of Drainage Effect of Branch Long Boreholes with Different Kilometers Length
By analyzing the data in Table 2, since all the test boreholes are located in the first mining area of Daning Mine, the drainage characteristics (the relationship between the drainage of boreholes with the same length and time) should be basically the same under the condition that the branches are basically the same, that is, it can be considered that the drainage characteristics of boreholes with the length less than 660m conform to the characteristics of 400m group, and the drainage characteristics of boreholes with the length of 660 ~ 790 m conform to the characteristics of 600m group. The drainage characteristics of boreholes from 790 to 10 14m meet the characteristics of 800m group, so the drainage of each borehole section (1 drainage year) is shown in Table 3.
Table 3 Analysis Table of Gas Drainage Volume in Various Sections of Bedding Kilometers of Dendritic Boreholes (Drainage Year 1)
As can be seen from Table 3, the unit length of the 660 ~ 790 m long branch borehole is 33.2 1% of the length of 0 ~ 660 m, and 790 ~10/4m is 79.86% of the length of 0 ~ 660 m. This shows that with the increase of the length of the drainage borehole, the drainage amount of the unit borehole length is increased. But the reduction is not significant (the length of 790 ~ 10 14m is only reduced by 20% compared with the length of 0 ~ 660m), which also proves that the longer the drilling length is, the more gas is extracted under the experimental conditions.
4.2 Drainage effect of drilling holes with different drainage time
The drainage modes of typical drilling holes with drilling depths of 800m, 600m and 400m are analyzed. The drainage effects of different drainage times are shown in Table 4. From the data analysis in the table, it can be concluded that at the end of the second year, the cumulative total drainage ratio of boreholes increased by 1 4% ~ 29%, while the cumulative total drainage at the end of 800 d only increased by about 1% compared with the end of the second year. It can be concluded that the reasonable drainage time of drilling is 2 years.
Table 4 Analysis Table of Drainage Effect of Kilometers Long Boreholes with Different Drainage Time
4.3 Reasonable Spacing of Bedding Kilometers of Dendritic Boreholes
4.3. 1 Pre-drainage rate of bedding borehole
Pre-drainage rate of bedding borehole refers to the proportion of gas extracted by borehole to the total gas reserves of coal seam within the extraction range, and the pre-drainage rate of bedding borehole is calculated according to the following formula:
η = QPumping/QTotal (4)
Where: η-pre-drainage rate,%; Q Drainage —— the total amount of gas pumped by drilling holes, m3; QTotal-the total natural gas reserves within the drilling control range, m3, QTotal = L * D * M * R * W; L—— drilling depth, m; D—— drilling spacing, m; M-coal seam thickness, m, Daning mine is 4.45 m; R-unit weight of coal seam, t/m3; W-coal seam gas content, m3/t, Daning mine proving ground is14.00m3/t.
4.3.2 Total amount of gas extracted by drilling holes at different times
By analyzing the pre-drainage effect of the test borehole, it can be found that the pre-drainage characteristics of the borehole are shown in formulas (1), (2) and (3).
According to formulas (1), (2) and (3), the total amount of gas extracted by drilling holes at different times is as follows:
800m group: Q draw =1399250.88 (1-e-0.0045t) m3 (5)
Group 600m: Q-draw =114195.59 (1-e-0.0049t) m3 (6).
Group 400m: q-draw = 690187.65 (1-e-0.0053t) m3 (7).
4.3.3 Pre-drainage rate with different drainage time and different borehole spacing
Pre-drainage rate of different borehole drainage time and different borehole spacing is determined by formula (4). The pre-drainage time is 0.5 years, 1, 2 years and 3 years. See Table 5 for the pre-drainage rate of borehole spacing 15, 20 and 30m.
Table 5 Pre-drainage rate of long branch holes with different drainage time and different hole spacing
Note: The original gas content of coal seam is 14.0m3/t, the residual gas content is 4.2m3/t, and the final pre-drainage rate of coal seam is 70%. According to the requirement that the gas content in coal seam before mining is lower than 8m3/t, the pre-drainage rate is above 42.86%. "-"in the table indicates that the pre-drainage rate is outside the range of 42.86% ~ 70%.
4.3.4 Drilling spacing under the conditions of different pre-pumping time and different drilling length in Daning Coal Mine ensures safety in production.
According to relevant research, the original gas content in the first fully mechanized top-coal caving face is 14.0m3/t, and the pre-drainage rate to ensure the safe production in the first fully mechanized top-coal caving face should be 45%. Analysis of Table 5 shows that:
If the pre-pumping time of fully mechanized top-coal caving face is 0.5 years, the drilling spacing should be 15m when 800m or 600m drilling groups are selected, and 20m when 400m drilling groups are selected.
If the pre-pumping time of fully mechanized top-coal caving face is 1 year, the drilling spacing should be 20m when the 800m or 600m group is selected, and 30m when the 400m group is selected.
If the pre-pumping time of fully mechanized top-coal caving face is 2 years, when selecting 800m, 600m or 400m groups, the drilling spacing should be 30 m.
Actual drainage effect of 4.4 km long dendritic borehole in Daning Coal Mine
4.4. 1 Pre-drainage effect of the first mining face
As shown in figure 1, the first mining face in Daning Coal Mine is 500 meters long and 320 meters wide. In 2003, we began to drill a long dendritic hole of about 20 ~ 30m, with a drilling depth of about 600m m. The pre-pumping time is about 1.5 years.
The original gas content of the first mining face is 14.0m3/t, and the coal seam gas content measured by the direct method of the first mining face before mining is 7.2m3/t, so the pre-drainage rate of the first mining face is 48.57%.
4.4.2 Mine gas drainage rate
In 2005, the gas emission in Daning Mine was 184.8m3/min, of which the drainage amount was 130m3/min, and the gas drainage rate reached 70.35%.
5 conclusion
Through research and test, the underground bedding 1000 meter long dendritic drilling has achieved success in gas drainage in Daning coal mine, and achieved good results, which has obtained beneficial experience and reference for large-scale pre-drainage of coal seam gas.
(1) The VLD- 1000 downhole motor directional drilling rig made in Australia is selected. Under the condition of coal seam in Daning coal mine, the long dendritic drilling along the bed can achieve about 1000 meters.
(2) The research shows that with the increase of borehole length, the gas drainage amount of bedding 1000 long dendritic borehole in Daning Coal Mine also increases, which shows that gas drainage is effective under experimental conditions.
(3) Through research, the reasonable borehole spacing at different drainage times with a pre-drainage rate of 45% was determined under experimental conditions.
(4) In Daning Coal Mine, gas is extracted by underground bedding long dendritic drilling. After 1.5 years of pre-drainage, the pre-drainage rate reached nearly 49%, and the mine gas drainage rate reached 70.35%.