Old goaf exploration method based on directional drilling hydraulic fracturing in coal seam

Abstract

The invention discloses an old goaf exploration method based on directional drilling hydraulic fracturing in a coal seam. The method is specifically implemented according to the following steps that 1, a coal seam hydraulic fracturing test is conducted to determine the hydraulic fracturing radius; 2, the directional drilling arrangement distance is determined according to the hydraulic fracturing radius; 3, directional drilling is constructed according to the directional drilling arrangement interval determined in the step 2, segmented hydraulic fracturing is carried out, and data monitoring is carried out in the hydraulic fracturing process; 4, judging the development condition of the old goaf according to the hydrofracture monitoring data; and 5, a subsequent drilling construction scheme is determined according to the communication condition of the directional drilling hydraulic fracturing fracture and the old goaf. The problem that in the prior art, the position of goaf water can only be detected and cleared by increasing the density of the drill holes is solved.

Description

Technical Field

[0001] The invention belongs to the technical field of water hazard prevention and control methods for old coal mines, and relates to an old coal mine exploration method based on directional drilling hydraulic fracturing in coal seams. Background Art

[0002] Water hazards in old empty areas are one of the most threatening types of water hazards in the mining process. Once they occur, they often cause huge losses of life and property. At present, the prevention and control methods for water hazards in old empty areas are mainly to explore the location of water accumulation through drilling work, and eliminate the threat of water hazards through active drainage. A relatively mature four-step working method of "full investigation, clear exploration, clean drainage, and accurate verification" has also been formed. The exploration of old empty areas is the prerequisite for the drainage of old empty water, and it is also the key to the prevention and control of water hazards in old empty areas. The current main exploration method is a combination of geophysical exploration and drilling. Drilling includes conventional drilling and directional long-distance drilling. Because geophysical exploration results often have multiple solutions, the location of old empty water can only be accurately explored by increasing the drilling density, but this will greatly increase the project cost and seriously affect the mining succession of the mine. Especially in areas with thick coal seams, such as Figure 1 As shown, the old void area is not only unevenly distributed in the plane, but its vertical position in the coal seam is also difficult to predict. Whether it is conventional drilling or directional long-distance drilling, the drilling density must be increased to clearly explore the location of the old void water. Summary of the invention

[0003] The purpose of the present invention is to provide a method for exploring old empty areas in coal seams based on directional drilling and hydraulic fracturing, which solves the problem in the prior art that the location of the old empty areas can only be explored by increasing the drilling density.

[0004] The technical solution adopted by the present invention is a method for detecting old empty areas in coal seams based on directional drilling and hydraulic fracturing, which is specifically implemented according to the following steps:

[0005] Step 1, conducting a coal seam hydraulic fracturing test to determine the hydraulic fracturing radius;

[0006] Step 2, determining the spacing of directional drilling holes according to the hydraulic fracturing radius;

[0007] Step 3, constructing directional drilling holes and performing segmented hydraulic fracturing according to the directional drilling hole arrangement spacing determined in step 2, and performing data monitoring during the hydraulic fracturing process;

[0008] Step 4, judging the development of old empty areas according to hydraulic fracturing monitoring data;

[0009] Step 5: Determine the subsequent drilling construction plan based on the communication between the directional drilling hydraulic fracturing cracks and the old empty area.

[0010] The present invention is also characterized in that:

[0011] Step 1 is as follows:

[0012] A complete section of the coal seam was selected for directional drilling, and then a hydraulic fracturing test was carried out to verify the hydraulic fracturing radius of the coal seam under different pressures and different fracturing times.

[0013] The method for determining the hydraulic fracturing radius in step 1 is to conduct construction verification drilling or construction exploration to determine the change in the water content of the coal seam or the development of coal seam cracks. The water content of the coal seam increases and the cracks develop within the hydraulic fracturing radius. Finally, it is determined that the hydraulic fracturing radius of the coal seam corresponding to the pressure and fracturing time is not less than the coal seam thickness and the hydraulic fracturing radius is not greater than 50m.

[0014] The spacing of directional drilling holes in step 2 must ensure that the hydraulic fracturing range of two adjacent directional holes covers the entire coal seam thickness.

[0015] The calculation formula for the directional drilling arrangement spacing L is as follows:

[0016]

[0017] Where: L is the spacing between directional holes / m; M is the thickness of the coal seam / m; G is the fracturing control range / m;

[0018] The directional drilling construction requirements in step 3 are: after the construction reaches the designed hole depth, determine whether the old void area is exposed according to the empty push, water leakage and water leakage during the directional drilling construction process. If there is empty push, leakage or water leakage, it means that the directional hole exposes the old void area. Otherwise, the old void area is not exposed. Then, the area where the old void area is not found is subjected to segmented hydraulic fracturing. The segment length is not more than 60m. Backward fracturing is adopted. The fracturing pressure and fracturing time are determined according to the fracturing pressure and fracturing time determined by the hydraulic fracturing test in step 1. The pressure and pump volume change data are recorded during the fracturing process.

[0019] The segment length is equal to the spacing L of the directional drilling arrangement.

[0020] Step 4 is specifically as follows: if the pressure drops and the pump volume increases during the fracturing process, it is judged that the fracturing cracks are connected to the old empty area, otherwise the fracturing is continued until the fracturing time determined by the fracturing test and then the fracturing is stopped.

[0021] Step 5 is as follows:

[0022] If no communication with the old empty area is found during the hydraulic fracturing of the entire directional hole, the branch hole will be grouting to seal the fracturing cracks. The grouting material is cement-water-glass double liquid slurry, and then the next directional hole will be constructed;

[0023] If it is found that there is communication with the old void area, the outer fracturing radius range of this section will be regarded as the old void area development area. Conventional drilling exploration will be carried out before the tunnel construction reaches this area. If water comes out of the borehole, the water will be continuously drained until the water volume is stable or there is no water. If there is no water in the borehole, cement-water-glass double-liquid slurry will be used to seal the hole and continue to construct the next directional hole.

[0024] The beneficial effects of the present invention are:

[0025] The present invention utilizes long-distance directional drilling underground to carry out coal seam hydraulic fracturing, so that the hydraulic fracturing fissures connect the directional drilling and the old goaf area, and reflect the monitoring data of the hydraulic fracturing process, which lays a foundation for the threat level evaluation and water drainage of the goaf area. At the same time, after the hydraulic fracturing fissures guide the old goaf water, the water can be drained through directional drilling, which improves the old goaf water exploration effect without increasing a large amount of drilling engineering, and can provide technical support for the old goaf water exploration.

[0026] The method of the present invention does not require a large increase in drilling work or the use of in-hole geophysical exploration technology. The old void development area in the exploration area can be explored and the accumulated water can be drained, thereby achieving the purpose of preventing water damage in the old void. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a cross-sectional diagram of the control of goaf or tunnel by directional drilling in coal seam;

[0028] Figure 2 It is a flow chart of the old empty area exploration method based on directional drilling hydraulic fracturing in the coal seam of the present invention;

[0029] Figure 3 It is a schematic diagram of verification of hydraulic fracturing radius in the old empty area exploration method based on directional drilling hydraulic fracturing in the coal seam of the present invention;

[0030] Figure 4 is a plan view of a directional drilling arrangement scheme in Example 6 of the present invention;

[0031] Figure 5 It is a schematic cross-sectional diagram of controlling an old empty area by directional drilling hydraulic fracturing in Example 6 of the present invention.

[0032] In the figure: A. Coal seam, B. Directional drilling, C. Abandoned tunnel, D. Verification borehole, E. Exploration tunnel, F. Fracturing fracture, G. Fracturing control range, H. Fracturing section, I. Tunnel. DETAILED DESCRIPTION

[0033] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0034] Example 1

[0035] The old empty area exploration method based on directional drilling hydraulic fracturing in the coal seam of the present invention has the following process: Figure 2 As shown, the specific steps are as follows:

[0036] Step 1: Conduct a coal seam hydraulic fracturing test to determine the hydraulic fracturing radius:

[0037] Select a complete section of the coal seam, construct directional drilling, and then carry out hydraulic fracturing tests to verify the hydraulic fracturing radius of the coal seam under different pressures and different fracturing times;

[0038] Step 2: Determine the spacing of directional drilling holes according to the hydraulic fracturing radius. The spacing of directional drilling holes should ensure that the hydraulic fracturing range of two adjacent directional holes covers the entire coal seam thickness.

[0039] Step 3, constructing directional drilling holes and performing segmented hydraulic fracturing according to the directional drilling hole arrangement spacing determined in step 2, and performing data monitoring during the hydraulic fracturing process;

[0040] Step 4, judging the development of the old empty area according to the hydraulic fracturing monitoring data, specifically: if the pressure drops and the pump volume increases during the fracturing process, it is judged that the fracturing cracks are connected to the old empty area, otherwise the fracturing is continued until the fracturing time determined by the fracturing test and then the fracturing is stopped.

[0041] Step 5: Determine the subsequent drilling construction plan based on the communication between the directional drilling hydraulic fracturing cracks and the old empty area.

[0042] Example 2

[0043] On the basis of Example 1, the method for determining the hydraulic fracturing radius in step 1 is to conduct construction verification drilling or construction exploration to determine the change in the water content of the coal seam or the development of coal seam cracks. The water content of the coal seam increases and the cracks develop within the hydraulic fracturing radius. Finally, it is determined that the hydraulic fracturing radius of the coal seam corresponding to the pressure and fracturing time is not less than the coal seam thickness and the hydraulic fracturing radius is not greater than 50m.

[0044] Example 3

[0045] On the basis of Example 2, step 2 is specifically as follows: determining the directional drilling arrangement spacing according to the hydraulic fracturing radius, the directional drilling arrangement spacing must ensure that the hydraulic fracturing range of two adjacent directional holes covers the entire coal seam thickness, wherein the directional drilling arrangement spacing L is calculated by the following formula:

[0046]

[0047] Where: L is the spacing between directional holes / m; M is the thickness of the coal seam / m; G is the fracturing control range / m;

[0048] Example 4

[0049] On the basis of Example 3, the old empty area exploration method based on directional drilling hydraulic fracturing in the coal seam of the present invention has the following process: Figure 2 As shown, the specific steps are as follows:

[0050] Step 1: Conduct a coal seam hydraulic fracturing test to determine the hydraulic fracturing radius:

[0051] Select a complete section of the coal seam, construct directional drilling, and then carry out hydraulic fracturing tests to verify the hydraulic fracturing radius of the coal seam under different pressures and different fracturing times;

[0052] Step 2: Determine the spacing of directional drilling holes according to the hydraulic fracturing radius. The spacing of directional drilling holes should ensure that the hydraulic fracturing range of two adjacent directional holes covers the entire coal seam thickness.

[0053] Step 3, construct directional drilling and perform segmented hydraulic fracturing according to the directional drilling arrangement spacing determined in step 2, and perform data monitoring during the hydraulic fracturing process; wherein, the directional drilling construction requirements are: after the construction reaches the designed hole depth position, determine whether the old empty area is exposed according to the empty push situation, water output, and leakage situation during the directional drilling construction process. If there is empty push or leakage or water output, it means that the directional hole exposes the old empty area, otherwise the old empty area is not exposed, and then the area where the old empty area is not found is subjected to segmented hydraulic fracturing, the segment length is not more than 60m, and backward fracturing is adopted. The fracturing pressure and fracturing time are determined according to the fracturing pressure and fracturing time determined by the hydraulic fracturing test in step 1, and the pressure and pump volume change data are recorded during the fracturing process; wherein, the segment length is equal to the directional drilling arrangement spacing L;

[0054] Step 4, judging the development of the old empty area according to the hydraulic fracturing monitoring data, specifically: if the pressure drops and the pump volume increases during the fracturing process, it is judged that the fracturing cracks are connected to the old empty area, otherwise the fracturing is continued until the fracturing time determined by the fracturing test and then the fracturing is stopped.

[0055] Step 5: Determine the subsequent drilling construction plan based on the communication between the directional drilling hydraulic fracturing cracks and the old empty area.

[0056] Example 5

[0057] On the basis of Example 2, the present invention provides a method for detecting old empty areas in coal seams based on directional drilling hydraulic fracturing, the process of which is as follows: Figure 2 As shown, the specific steps are as follows:

[0058] Step 1: Conduct a coal seam hydraulic fracturing test to determine the hydraulic fracturing radius:

[0059] Select a complete section of the coal seam, construct directional drilling, and then carry out hydraulic fracturing tests to verify the hydraulic fracturing radius of the coal seam under different pressures and different fracturing times;

[0060] Step 2: Determine the spacing of directional drilling holes according to the hydraulic fracturing radius. The spacing of directional drilling holes should ensure that the hydraulic fracturing range of two adjacent directional holes covers the entire coal seam thickness.

[0061] Step 3, construct directional drilling and perform segmented hydraulic fracturing according to the directional drilling arrangement spacing determined in step 2, and perform data monitoring during the hydraulic fracturing process; wherein, the directional drilling construction requirements are: after the construction reaches the designed hole depth position, determine whether the old empty area is exposed according to the empty push situation, water output, and leakage situation during the directional drilling construction process. If there is empty push or leakage or water output, it means that the directional hole exposes the old empty area, otherwise the old empty area is not exposed, and then the area where the old empty area is not found is subjected to segmented hydraulic fracturing, the segment length is not more than 60m, and backward fracturing is adopted. The fracturing pressure and fracturing time are determined according to the fracturing pressure and fracturing time determined by the hydraulic fracturing test in step 1, and the pressure and pump volume change data are recorded during the fracturing process; wherein, the segment length is equal to the directional drilling arrangement spacing L;

[0062] Step 4, judging the development of the old empty area according to the hydraulic fracturing monitoring data, specifically: if the pressure drops and the pump volume increases during the fracturing process, it is judged that the fracturing cracks are connected to the old empty area, otherwise the fracturing is continued until the fracturing time determined by the fracturing test and then the fracturing is stopped.

[0063] Step 5: Determine the subsequent drilling construction plan based on the communication between the directional drilling hydraulic fracturing cracks and the old empty area, specifically:

[0064] If no communication with the old empty area is found during the hydraulic fracturing of the entire directional hole, the branch hole will be grouting to seal the fracturing cracks. The grouting material is cement-water-glass double liquid slurry, and then the next directional hole will be constructed;

[0065] If it is found that there is communication with the old void area, the outer fracturing radius range of this section will be regarded as the old void area development area. Conventional drilling exploration will be carried out before the tunnel construction reaches this area. If water comes out of the borehole, the water will be continuously drained until the water volume is stable or there is no water. If there is no water in the borehole, cement-water-glass double-liquid slurry will be used to seal the hole and continue to construct the next directional hole.

[0066] Example 6

[0067] On the basis of Example 5, the thickness of the coal seam in the study area is 10m. According to the historical mining data of the area, there may be old empty areas. Therefore, the exploration of old empty areas is carried out in the study area. The specific steps are as follows:

[0068] 1. Conduct coal seam hydraulic fracturing test to determine the hydraulic fracturing radius

[0069] like Figure 3As shown, a complete section of coal seam A was selected, and directional drilling B was constructed. Then, hydraulic fracturing tests were carried out to verify the hydraulic fracturing radius of the coal seam under different pressures and different fracturing times. The method for determining the hydraulic fracturing radius was to construct exploration tunnel E and verification drilling hole D, and judge the change of water content in the coal seam and the development of fracturing fissures F in the coal seam. The water content of the coal seam increased and the fracturing fissures developed within the hydraulic fracturing radius. Finally, the hydraulic fracturing pressure was determined to be 25MPa, the fracturing time was 4h, and the fracturing radius was 40m.

[0070] 2. Determine the spacing of directional drilling holes according to the hydraulic fracturing radius

[0071] like Figure 4 As shown, it is planned to construct two directional boreholes B in the coal seam A to explore the potential abandoned tunnel C in the coal seam. The borehole spacing L of the directional boreholes should make the fracturing control range G of the two adjacent directional boreholes cover the entire coal seam thickness M. The calculation formula for the borehole spacing is as follows:

[0072]

[0073] In the formula: L is the spacing between directional holes / m; M is the thickness of the coal seam / m, which is 10m; G is the fracturing control range / m, which is 40m. After calculation, L=55.7m, that is, the drilling spacing is 55.7m.

[0074] 3. Directional drilling and staged hydraulic fracturing

[0075] like Figure 5 As shown, according to the data, it is speculated that there may be an abandoned tunnel C in front of the constructed tunnel I in the coal seam A. Directional borehole B is constructed at the head of the tunnel. The spacing between directional boreholes is 55.7m. No empty push, water outflow or leakage is found during the directional drilling construction to the designed hole depth. It is judged that the old empty area is not exposed. Then the directional borehole is hydraulically fractured in sections with a section length of 60m. It is divided into three fracturing sections H. Backward fracturing is adopted. The fracturing pressure and fracturing time are determined by the fracturing test. The pressure and pump volume change data are recorded during the fracturing process.

[0076] 4. Determine the situation of old empty areas based on hydraulic fracturing monitoring data

[0077] There was a pressure drop and an increase in pump volume during the fracturing process in the first and second fracturing stages, which indicated that the fracturing cracks were connected to the old empty area. There was an old empty area within 40m outside the directional branch hole. There was no pressure drop and increase in pump volume in the third fracturing stage, which indicated that there was no old empty area in this area.

[0078] 5. Determine the subsequent drilling construction plan based on the communication between the directional drilling hydraulic fracturing cracks and the old empty area

[0079] It was found that the first directional drilling hole was connected to the old empty area, and the 40m radius of the outer fracturing section was regarded as the old empty area development area. Conventional drilling exploration was carried out before the tunnel construction reached this area. However, there was no water in the hole, so cement-water-glass double liquid slurry was used to seal the hole and continue to construct the next directional hole.

Claims

1. A method for detecting old empty areas in coal seams based on directional drilling and hydraulic fracturing, characterized in that: The specific steps are as follows: Step 1, conducting a coal seam hydraulic fracturing test to determine the hydraulic fracturing radius; Step 2, determining the spacing of directional drilling holes according to the hydraulic fracturing radius; Step 3, constructing directional drilling holes and performing segmented hydraulic fracturing according to the directional drilling hole arrangement spacing determined in step 2, and performing data monitoring during the hydraulic fracturing process; Step 4, judging the development of old empty areas according to hydraulic fracturing monitoring data; Step 5: Determine the subsequent drilling construction plan based on the communication between the directional drilling hydraulic fracturing cracks and the old empty area.

2. The method for detecting old empty areas in coal seams based on directional drilling hydraulic fracturing according to claim 1 is characterized in that: The step 1 is specifically as follows: A complete section of the coal seam was selected for directional drilling, and then a hydraulic fracturing test was carried out to verify the hydraulic fracturing radius of the coal seam under different pressures and different fracturing times.

3. The method for detecting old empty areas in coal seams based on directional drilling hydraulic fracturing according to claim 2 is characterized in that: The method for determining the hydraulic fracturing radius in step 1 is to conduct construction verification drilling or construction exploration to determine the change in the water content of the coal seam or the development of coal seam fissures. The water content of the coal seam increases and the fissures develop within the hydraulic fracturing radius. Finally, it is determined that the hydraulic fracturing radius of the coal seam corresponding to the pressure and fracturing time is not less than the coal seam thickness and the hydraulic fracturing radius is not greater than 50m.

4. The method for detecting old empty areas in coal seams based on directional drilling hydraulic fracturing according to claim 3 is characterized in that: The spacing of the directional drilling holes in step 2 should ensure that the hydraulic fracturing range of two adjacent directional holes covers the entire coal seam thickness.

5. The method for detecting old empty areas in coal seams based on directional drilling hydraulic fracturing according to claim 4 is characterized in that: The calculation formula for the directional drilling arrangement spacing L is as follows: Where: L is the spacing between directional holes / m; M is the thickness of the coal seam / m; G is the fracturing control range / m.

6. The method for detecting old empty areas in coal seams based on directional drilling hydraulic fracturing according to claim 5, characterized in that: The directional drilling construction requirements in step 3 are as follows: after the construction reaches the designed hole depth, determine whether the old empty area is exposed according to the empty push, water leakage and water leakage during the directional drilling construction process. If there is empty push, leakage or water leakage, it means that the directional hole exposes the old empty area. Otherwise, the old empty area is not exposed. Then, the area where the old empty area is not found is subjected to segmented hydraulic fracturing. The segment length is not more than 60m. Backward fracturing is adopted. The fracturing pressure and fracturing time are determined according to the fracturing pressure and fracturing time determined by the hydraulic fracturing test in step 1. The pressure and pump volume change data are recorded during the fracturing process.

7. The method for detecting old empty areas in coal seams based on directional drilling hydraulic fracturing according to claim 6, characterized in that: The segment length is equal to the spacing L between the directional drilling holes.

8. The method for detecting old empty areas in coal seams based on directional drilling hydraulic fracturing according to claim 7, characterized in that: The step 4 is specifically as follows: if the pressure drops and the pump volume increases during the fracturing process, it is judged that the fracturing cracks are connected to the old empty area; otherwise, the fracturing is continued until the fracturing time determined by the fracturing test and then the fracturing is stopped.

9. The method for detecting old empty areas in coal seams based on directional drilling hydraulic fracturing according to claim 7, characterized in that: The step 5 is specifically as follows: If no communication with the old empty area is found during the hydraulic fracturing of the entire directional hole, the branch hole will be grouting to seal the fracturing cracks. The grouting material is cement-water-glass double liquid slurry, and then the next directional hole will be constructed; If it is found that there is communication with the old void area, the outer fracturing radius range of this section will be regarded as the old void area development area. Conventional drilling exploration will be carried out before the tunnel construction reaches this area. If water comes out of the borehole, the water will be continuously drained until the water volume is stable or there is no water. If there is no water in the borehole, cement-water-glass double-liquid slurry will be used to seal the hole and continue to construct the next directional hole.

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