Water-preserved coal mining method for sandstone strong runoff area

Abstract

A water-preserved coal mining method for a sandstone strong runoff area comprises the steps that a natural gamma-ray logging contour map is drawn through an interpolation method, and the position of a large-diameter drainage drill hole is selected to be within the minimum interval of the natural gamma-ray logging result contour map; then, after the water discharge amount of the sandstone strong runoff area, the permeability coefficient of the area where the large-diameter drainage drill holes are located, the limit water discharge amount of a single large-diameter drainage drill hole, the number of the large-diameter drainage drill holes and the hole diameter of final water pumping holes are determined, large-diameter drainage drill holes are implemented, and small-diameter communication drill holes are implemented around the large-diameter drainage drill holes; and finally, the large-aperture drainage drill hole is adopted for continuously pumping water at the maximum pumping amount, a coal pillar is reserved for the large-aperture drainage drill hole, and coal mining is carried out after water exploration and drainage are carried out on the sandstone aquifer. According to the method, the influence of non-uniformity can be effectively reduced, and the drilling drainage effect is good; the method is not easily influenced by geological conditions and is wide in application range; drained water resources can be prevented from being polluted; the implementation is simple and easy.

Description

Technical Field

[0001] The present invention relates to a water - retaining coal mining method in a strong sandstone runoff area, belonging to the technical field of safe coal mining. Background Art

[0002] With the westward shift of the coal - mining strategy, the ecological environment in the western region is fragile and water resources are scarce, and the contradiction between coal mining and water - resource protection has become increasingly prominent. As the main means to solve this contradiction, the water - retaining coal mining method mainly protects the roof sandstone aquifer, which is currently the most common water - filling source. The local water - rich property in the roof sandstone aquifer is strong, forming a strong sandstone runoff zone. For this type of water body, mines often use methods such as drainage, underground strong drainage, and grouting curtains for water - resource protection and utilization. However, the traditional methods have the following problems:

[0003] (1) Small - diameter drainage and water - release often result in poor borehole drainage effects due to the heterogeneity of the sandstone aquifer when implemented in water - free areas, and it is impossible to protect the main sandstone aquifer in advance.

[0004] (2) The grouting curtain can solve the problem to a large extent, but a large amount of grouting works are required for sealing. Due to the difficult construction of water - driven grouting sealing in the strong sandstone runoff zone, and it may flow into the mining space from other hidden channels after sealing, the construction effect cannot be guaranteed.

[0005] (3) The freezing method can be implemented for groundwater with poor hydrodynamic conditions, but it is difficult to complete freezing under the conditions of a strong runoff zone.

[0006] (4) Underground strong drainage will cause pollution to the water resources after they enter the mine, which is not environmentally friendly. Moreover, underground strong drainage requires a strong drainage system, resulting in an excessive system burden and potential safety hazards. Summary of the Invention

[0007] The object of the present invention is to provide a water - retaining coal mining method in a strong sandstone runoff area, which can effectively reduce the influence of heterogeneity, has good borehole drainage effect, is not easily affected by geological conditions, has a wide application range, can avoid pollution of the drained water resources, and is simple and easy to implement.

[0008] To achieve the above object, the present invention provides a water - retaining coal mining method in a strong sandstone runoff area, including the following steps:

[0009] S1. Select the position of large - diameter drainage boreholes: Draw an isogram of natural gamma logging by the interpolation method, and select the position of large - diameter drainage boreholes in the smallest interval of the isogram of natural gamma logging results.

[0010] S2. Determine the water volume Qz to be discharged in the strong sandstone runoff area.

[0011] S3. Determine the permeability coefficient K of the area where the large - diameter drainage borehole is located.

[0012] S4. Determine the ultimate drainage volume Q of a single large-diameter drainage borehole 1 ;

[0013] S5. Determine the number of large-diameter drainage boreholes and the final hole diameter for pumping

[0014] S6. According to the positions, numbers, and final hole diameters of the large-diameter drainage boreholes determined in S1 to S5, implement large-diameter drainage boreholes. Drill the boreholes 2 - 5 meters below the bottom plate of the sandstone formation. Leave permeable perforated pipes in the sandstone formation area and leave water-blocking casing pipes in other areas

[0015] S7. Implement small-diameter connecting boreholes around the positions of the large-diameter drainage boreholes, where the periphery is within a distance less than the set value R from the large-diameter drainage boreholes

[0016] S8. Continuously pump water at the maximum pump volume using large-diameter drainage boreholes, leave coal pillars L for the large-diameter drainage boreholes, and conduct coal mining after exploring and draining water from the sandstone aquifer

[0017] Further, the smallest interval of the natural gamma logging curve contour map in S1 refers to the 20% area with the smallest natural gamma logging values among all exploration boreholes in the coal mining area

[0018] Further, in S2, the water volume Qz to be discharged in the strong sandstone runoff area is calculated according to the following formula

[0019]

[0020] where Q 0 is the water inflow already mined in the strong sandstone runoff area, obtained through underground observations; F 0 is the mined area already in the strong sandstone runoff area, obtained from the coal mining design drawing; Fz is the total future mined area in the strong sandstone runoff area, obtained from the coal mining design drawing; A is the average value of the natural gamma logging results in the already mined area, obtained from the drawn natural gamma logging contour map; B is the average value of the natural gamma logging results in the future mined area, obtained from the drawn natural gamma logging contour map

[0021] Further, the method for determining the permeability coefficient K of the area where the large-diameter drainage borehole is located in S3 is as follows: Collect rock samples from the strong sandstone runoff area where the large-diameter drainage borehole is located, make thin sections of the rock samples, use IPP software to measure the average sand grain diameter d, and calculate the permeability coefficient K through the following formula

[0022]

[0023] where γ Sρ is the average specific gravity of sand grains in sandstone, obtained through testing; n is the reduction coefficient, taking values from 0.0001 to 0.001; γ is the specific gravity of water, taking 1000 kg / m³; d is the average grain size of sand grains, obtained through thin section testing; h is the depth of ancient river water, generally taking values from 0.1 to 5 m, obtained through the isogram of natural gamma logging; I is the natural gradient of the bottom plate of the sandstone formation, obtained through calculation of the drilling columnar section.

[0024] Further, the ultimate drainage volume Q of a single large-diameter drainage borehole in S4 1 is calculated by the following formula:

[0025]

[0026] where K is the permeability coefficient; M is the thickness of the sandstone aquifer, obtained through the drilling columnar section; S is the height of the water head of the sandstone aquifer from the bottom plate of the sandstone formation, obtained through hydrological observation.

[0027] Further, the determination method of the number of large-diameter drainage boreholes and the final hole diameter of pumping in S5 is as follows: when f ≤ 1, the number of large-diameter drainage boreholes is 1, and the final hole diameter ≥ 1000 mm; when f > 1, the number of large-diameter drainage boreholes is the integer obtained by rounding up the f value, and the final hole diameter ≥ 1000 mm; f is calculated according to the following formula:

[0028]

[0029] where Qz is the water volume to be discharged in the strong runoff area of the sandstone; Q 1 is the ultimate drainage volume of a single large-diameter drainage borehole.

[0030] Further, the periphery of the position in S7 is at a distance less than the set value R from the large-diameter drainage borehole, and R is calculated according to the following formula:

[0031]

[0032] where S is the height of the water head of the sandstone aquifer from the bottom plate of the sandstone formation, obtained through hydrological observation; K is the permeability coefficient;

[0033] The small-diameter connection borehole penetrates all the strata within the height H of the water-conducting fracture zone of coal mining, and all permeable perforated pipes are left. The height H of the water-conducting fracture zone of coal mining is calculated by the following formula:

[0034]

[0035] In the formula, m is the coal mining thickness, obtained through the mining design drawing.

[0036] Further, the calculation of the coal pillar L left by the large-diameter drainage borehole in S8 is carried out according to the following formula:

[0037]

[0038] Among them, C is the safety factor, taking a value of 3 to 5; m is the coal mining thickness, obtained from the mining design drawing; p is the hydrostatic pressure, p = ρgS, where ρ is the water density and S is the height of the water head of the sandstone aquifer from the bottom of the sandstone formation, obtained through hydrogeological observation; v is the underground water flow velocity, v = K×I, where K is the permeability coefficient; I is the natural slope of the bottom of the sandstone formation, calculated from the borehole columnar section; K p is the tensile strength of the coal body, obtained through sampling tests.

[0039] The present invention draws a natural gamma logging isogram by the interpolation method, and selects the position of the large-diameter drainage borehole in the smallest interval of the natural gamma logging result isogram; then, after determining the water volume to be discharged in the strong sandstone runoff area, the permeability coefficient of the area where the large-diameter drainage borehole is located, the ultimate drainage volume of a single large-diameter drainage borehole, the number of large-diameter drainage boreholes, and the final hole diameter of the pumping, the large-diameter drainage borehole is implemented, and small-diameter connecting boreholes are implemented around the position of the large-diameter drainage borehole. Finally, the large-diameter drainage borehole is pumped with the maximum pump volume continuously, a coal pillar is left for the large-diameter drainage borehole, and the sandstone aquifer is explored and drained before coal mining. The present invention does not require a large-scale curtain grouting project, only needs to implement drainage boreholes, and estimates the underground water flow velocity through sedimentology and hydraulics principles, does not require many exploration holes, and is simple and easy to implement; compared with small-diameter boreholes, large-diameter boreholes can effectively reduce the influence of heterogeneity, avoid local aquitards, and have better water drainage and release effects; the drained water resources do not pass through the mining and excavation system, avoiding pollutants such as oil stains, and are more environmentally friendly; fundamentally, water drainage and release reduce the water filling source and have better safety; it is not affected by various complex geological conditions, such as the richness of the aquifer and the water flow velocity, and has a wider application range. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 is a flow block diagram of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0041] The present invention will be further described below with reference to the accompanying drawings.

[0042] As Figure 1 shown, a water-preserving coal mining method in a strong sandstone runoff area includes the following steps:

[0043] S1. Select the position of the large-diameter drainage borehole: Draw a natural gamma logging isogram by the interpolation method, and select the position of the large-diameter drainage borehole in the smallest interval of the natural gamma logging result isogram;

[0044] S2. Determine the water volume Qz to be discharged in the strong sandstone runoff area;

[0045] S3. Determine the permeability coefficient K of the area where the large-diameter drainage borehole is located;

[0046] S4. Determine the ultimate drainage volume Q of a single large-diameter drainage borehole 1 ;

[0047] S5. Determine the number of large-diameter drainage boreholes and the final hole diameter for pumping;

[0048] S6. According to the location, number, and final hole diameter of the large-diameter drainage boreholes determined in S1 to S5, implement the large-diameter drainage boreholes. Drill the boreholes 2 - 5 meters below the bottom plate of the sandstone formation. Leave a permeable slotted pipe in the sandstone formation area and leave a water-proof casing in other areas;

[0049] S7. Implement small-diameter connecting boreholes around the location of the large-diameter drainage borehole, where the periphery of the location is less than the set value R from the large-diameter drainage borehole;

[0050] S8. Continuously pump water at the maximum pump volume using the large-diameter drainage borehole, leave a coal pillar L for the large-diameter drainage borehole, and conduct water exploration and coal mining on the sandstone aquifer after water exploration.

[0051] Example: The Yushenfu mining area is a major coal mining base in China. A large amount of coal resources have been mined here, but there have been multiple water inrush accidents in the strong runoff zone of the roof sandstone. Existing explorations have shown that there is an ancient river here. In the past, grouting curtains were used for plugging and strong underground drainage, resulting in huge underground drainage costs and difficulties in grouting curtain projects. Applying the method of this invention for water-preserved coal mining, the specific steps are as follows:

[0052] Step 1: Select the location of the large-diameter drainage borehole: The location is selected in the smallest interval (12 - 16 API) of the isogram of the natural gamma logging results. The smallest interval of the isogram of the natural gamma logging curve refers to the area with the smallest 20% of the natural gamma logging values among all exploration boreholes in the coal mining area (the total is 12 - 80 API), and the isogram of the natural gamma logging is drawn by the interpolation method;

[0053] Step 2: Determine the water volume Q to be discharged in the strong runoff area of the sandstone z , calculated according to the following formula:

[0054]

[0055] In the formula, Q 0 is the water inrush volume that has been mined in the strong runoff area of the sandstone, obtained through underground observation as 222 m 3 / h; F 0 is the area that has been mined in the strong runoff area of the sandstone, obtained through coal mining design, which is 0.3 km 2 ; Fz is the total area to be mined in the future strong runoff area of the sandstone, obtained through coal mining design, which is 11.2 km2 ; A is the average value of the natural gamma logging results in the already mined area, obtained through Step 1, which is 30 API; B is the average value of the natural gamma logging results in the future mining area, obtained through Step 1, which is 14 API;

[0056] Step 3: Determine the permeability coefficient K of the area where Step 1 is located. Obtain the rock samples from the strong runoff area of sandstone in the area where Step 1 is located, and make thin sections of the rock samples. Use IPP software to measure the average grain size d of sand grains = 0.0003 m;

[0057]

[0058] In the formula, γ S is the average specific gravity of sand grains in sandstone, obtained through testing; γ is the specific gravity of water, taken as 1000 kg / m³; d is the average grain size of sand grains, obtained through thin section testing, taken as 17000 kg / m³; h is the depth of ancient river water, taken as 0.1 m; I is the natural slope of the bottom plate of the sandstone formation, calculated through the drilling columnar section, which is 0.1;

[0059] Step 4: Determine the ultimate drainage volume Q of a single large-diameter drainage borehole 1 , and the calculation formula is as follows:

[0060]

[0061] In the formula, K is the permeability coefficient, obtained through Step 4, which is 21.4 m / d; M is the thickness of the sandstone aquifer, obtained through the drilling columnar section, which is 10 m; S is the height of the water head of the sandstone aquifer from the bottom plate of the sandstone formation, obtained through hydrographic observation, which is 32 m;

[0062] Step 5: Determine the number of large-diameter drainage boreholes and the final hole diameter for pumping. Since f ≤ 1, the number of large-diameter drainage boreholes is 1, and the final hole diameter is 1000 mm and above.

[0063]

[0064] Step 6: Implement large-diameter drainage boreholes according to the quantity, final hole diameter, and location determined in the above steps. Drill the boreholes 5 m below the bottom plate of the sandstone formation, and leave permeable slotted pipes in the sandstone formation area and impermeable casing pipes in other areas.

[0065] Step 7: Implement small-diameter connecting boreholes around the location of the large-diameter drainage borehole. The "around the location" means within a distance less than m from the large-diameter drainage borehole, and set a circle at 500 m. The depth of the small-diameter connecting boreholes connects all the strata within the height H of the coal mining water-conducting fracture zone, and all leave permeable slotted pipes. The height H of the coal mining water-conducting fracture zone is calculated using the following formula:

[0066] meter;

[0067] In the formula, m is the coal mining thickness, which is obtained through mining design.

[0068] Step Eight: Continuously pump water at the maximum pump capacity using large-diameter drainage boreholes, leave a coal pillar L = 20 meters for the large-diameter drainage boreholes, and then conduct coal mining after exploring and draining water from the sandstone aquifer;

[0069] Therefore, 20 meters is taken.

[0070] Finally, the water inflow during coal mining is within the controllable range of the mine drainage system, remaining within 2000 m 3 / d, achieving safe coal resource mining.

Claims

1. A water-retaining coal mining method in a sandstone strong runoff area, characterized in that: The steps include: S1. Select the location of the large-diameter drainage borehole: draw the natural gamma logging contour map by interpolation method, and the location of the large-diameter drainage borehole is selected in the minimum interval of the natural gamma logging result contour map; S2. Determine the amount of water Qz that should be discharged in the sandstone strong runoff area; S3. Determine the permeability coefficient K of the area where the large-diameter drainage borehole is located; S4. Determine the maximum drainage capacity Q1 of a single large-diameter drainage borehole; S5. Determine the number of large-diameter drainage boreholes and the final borehole diameter for pumping water; S6. Based on the location, number and final hole diameter of the large-diameter drainage boreholes determined in S1 to S5, large-diameter drainage boreholes are drilled to 2 to 5 meters below the bottom of the sandstone formation, and permeable flower pipes are left in the sandstone formation area, and waterproof casings are left in other areas; S7, implement small-diameter interconnecting drilling around the location of the large-diameter drainage drilling hole, where the location is smaller than a set value R from the large-diameter drainage drilling hole; S8. Use large-aperture drainage boreholes to continuously pump water at the maximum pumping capacity, leave a coal pillar L in the large-aperture drainage boreholes, and conduct coal mining after exploring and draining water from the sandstone aquifer.

2. The water-retaining coal mining method in sandstone strong runoff area according to claim 1 is characterized in that: The minimum interval of the natural gamma logging curve contour map in S1 refers to the 20% area with the smallest natural gamma logging values ​​in all exploration boreholes in the coal mining area.

3. The water-retaining coal mining method in sandstone strong runoff area according to claim 1 is characterized in that: In S2, the amount of water Qz to be discharged from the sandstone strong runoff area is calculated according to the following formula: Among them, Q0 is the water inflow that has been mined in the sandstone strong runoff area, which is obtained through underground observation; F0 is the area that has been mined in the sandstone strong runoff area, which is obtained through the coal mining design map; Fz is the total area of ​​sandstone strong runoff area to be mined in the future, which is obtained through the coal mining design map; A is the average value of the natural gamma logging results in the mined area, which is obtained by drawing the natural gamma logging contour map; B is the average value of the natural gamma logging results in the future mining area, which is obtained by drawing the natural gamma logging contour map.

4. The water-retaining coal mining method in sandstone strong runoff area according to claim 1 is characterized in that: The method for determining the permeability coefficient K of the area where the large-diameter drainage borehole is located in S3 is as follows: by collecting rock samples from the sandstone strong runoff area in the area where the large-diameter drainage borehole is located, and making rock sample slices, the average particle size d of the sand particles is determined by IPP software, and the permeability coefficient K is calculated by the following formula: Among them, γ S is the average specific gravity of sand particles in sandstone, obtained through testing; n is the reduction coefficient, which is taken as 0.0001~0.001; γ is the specific gravity of water, which is taken as 1000 kg / cubic meter; d is the average particle size of sand particles, obtained through thin section testing; h is the depth of ancient river water, generally taken as 0.1~5 meters, obtained through natural gamma logging contour map; I is the natural gradient of the bottom plate of sandstone formation, which is calculated through drilling column chart.

5. The water-retaining coal mining method in sandstone strong runoff area according to claim 1 is characterized in that: The maximum drainage volume Q1 of a single large-diameter drainage borehole in S4 is calculated by the following formula: Among them, K is the permeability coefficient; M is the thickness of the sandstone aquifer, which is obtained through the borehole column chart; S is the height of the sandstone aquifer head from the bottom of the sandstone formation, which is obtained through hydrological observation.

6. The water-retaining coal mining method in sandstone strong runoff area according to claim 1 is characterized in that: The method for determining the number of large-diameter drainage boreholes and the final hole diameter for pumping water in S5 is as follows: when f≤1, the number of large-diameter drainage boreholes is 1, and the final hole diameter is ≥1000mm; when f>1, the number of large-diameter drainage boreholes is the integer of f value rounded up, and the final hole diameter is ≥1000mm; f is calculated according to the following formula: Among them, Qz is the amount of water that should be discharged in the sandstone strong runoff area; Q1 is the maximum discharge capacity of a single large-diameter drainage borehole.

7. The water-retaining coal mining method in sandstone strong runoff area according to claim 1 is characterized in that: The position in S7 is located at a distance from the large-diameter drainage borehole less than a set value R, and R is calculated according to the following formula: Where S is the height of the water head of the sandstone aquifer from the bottom of the sandstone formation, obtained through hydrological observation; K is the permeability coefficient; The small-diameter interconnected boreholes are connected to all strata within the height H of the coal mining water-conducting fracture zone, and all of them are provided with permeable flower pipes. The height H of the coal mining water-conducting fracture zone is calculated using the following formula: In the formula, m is the coal mining thickness, which is obtained through the mining design drawing.

8. The water-retaining coal mining method in sandstone strong runoff area according to claim 1 is characterized in that: The calculation of the coal pillar L for the large-diameter drainage borehole in S8 is based on the following formula: Among them, C is the safety factor, which is 3 to 5; m is the mining thickness, which is obtained from the mining design drawing; p is the hydrostatic pressure, p = ρgS, ρ is the water density, S is the height of the water head of the sandstone aquifer from the bottom of the sandstone formation, which is obtained through hydrological observation; v is the groundwater flow rate, v = K × I, K is the permeability coefficient; I is the natural gradient of the bottom of the sandstone formation, which is obtained by calculating the borehole column chart; K p It is the tensile strength of coal body, obtained through sampling test.

Images