A method for protecting and utilizing water resources under mining variations in different double-aquifer structures

Abstract

The present invention provides a method for protecting and utilizing water resources under mining-induced variations in different double-aquifer structures, belonging to the field of mining engineering technology. First, based on the formation conditions and parameters obtained on-site, combined with the spatial position relationship between the main key layer and the aquifer, three types of double-aquifer structures are proposed, namely, upper main key layer-lower group vulnerable type, middle main key layer-upper and lower unidirectional type, and lower main key layer-upper group protective type. Secondly, based on the different variation characteristics of the double-aquifer structure caused by mining activities, the height h of the water guide channel after mining, the distance D3 from the main key layer to the coal seam, the thickness d3 of the main key layer, the thickness d1 and d2 of the upper and lower protective layers, and the distance D1 and D2 of the double aquifer from the coal seam are compared, and five water resource protection and utilization methods are proposed, namely, upper storage-lower storage, upper resistance-lower storage, upper protection-lower storage, upper resistance-lower resistance, and upper resistance-lower protection, thereby achieving the coordinated development of coal resource development and comprehensive protection and utilization of water resources in the mining area.

Description

Technical Field

[0001] The present invention relates to the technical field of mining engineering, and in particular to a method for protecting and utilizing water resources under mining variations of different double-aquifer structures. Background Art

[0002] During the coal resource recovery process, mining activities cause overburden damage, reduced roof stability, and rock fragmentation, which in turn creates water channels, causes changes in the aquifer structure, leads to the loss of groundwater resources, and a drop in groundwater levels, which further causes vegetation that relies on groundwater to die due to lack of water, resulting in a sharp decline in biodiversity, soil erosion, and land desertification.

[0003] During the development of the Huanglong Jurassic Coalfield, it was discovered that two aquifers, each buried at different depths, existed above the coalface. These were the Jurassic Zhiluo Formation and the Cretaceous Luohe Formation. This geological feature has long posed a threat to safe coal mining and has imposed high costs on the company in terms of water resource conservation.

[0004] The Chinese invention patent with patent publication number CN103513281A discloses a method for predicting the development height of the water-conducting fracture zone in the overburden during solid filling coal mining. The invented method for predicting the development height of the water-conducting fracture zone in the overburden during solid filling coal mining is based on engineering geological condition information and rock mechanics experiments. It adopts a method combining numerical simulation with multiple regression analysis to obtain the relationship expression between the filling rate, mining height and the development height of the water-conducting fracture zone. Then, based on the actual engineering parameters of the filling coal mining, that is, the designed filling rate and the actual mining height, the development height of the water-conducting fracture zone in the overburden is calculated.

[0005] Chinese invention patent publication number CN118705007A discloses a method and device for protecting groundwater in coal mining areas. Based on the groundwater's velocity and recovery time, the invention determines a transfer storage area within the target stratum. This ensures that, during the recovery period, mine water does not flow into the mine, causing flooding and thus impacting mine production.

[0006] The above-mentioned prior art has the following problems:

[0007] First, the impact of other factors on the aquifer besides water-conducting fractures was not considered;

[0008] Second, only consider filling the goaf to protect the aquifer, but this general protection method often results in a waste of funds;

[0009] 3. Failure to utilize the mined-out areas created by mining as storage space for aquifers;

[0010] Fourth, the two aquifers are only protected as a whole, and no classified protection measures are taken for aquifers at different burial depths. Summary of the Invention

[0011] The purpose of the present invention is to provide a method for protecting and utilizing water resources under mining variations of different double-aquifer structures, thereby achieving the coordinated development of coal resource development and comprehensive protection and utilization of water resources in mining areas.

[0012] To achieve the above-mentioned object, the present invention provides a method for protecting and utilizing water resources under different double-aquifer structure mining variations, comprising the following steps:

[0013] Step S1: Based on the geological characteristics of two aquifers, the Jurassic Zhiluo Formation and the Cretaceous Luohe Formation, above the longwall mining face during the development of the Huanglong Jurassic Coalfield, the mining height M of the coal mining face, the distance D1 between the upper aquifer and the coal seam, and the distance D2 between the lower aquifer and the coal seam are obtained. In the double aquifers, the aquifer with the smaller distance from the ground surface is defined as the upper aquifer, and the aquifer with the larger distance from the ground surface is defined as the lower aquifer. Physical parameters of the coal body and each rock layer are obtained using rock mechanics tests, and the in situ rock stress σ of the rock is measured using hydraulic fracturing methods.

[0014] Among them, the physical parameters of coal body and each rock layer include rock density ρ, shear modulus G, bulk modulus K and compressive strength σ c ;

[0015] Step S2: Based on the data obtained in step S1, a three-dimensional numerical simulation model is established in 3DEC numerical simulation software to obtain the height h of the water channel generated from bottom to top in the overlying rock strata of the working face; using the protective layer thickness calculation formula in the "Specifications for Coal Pillar Retention and Coal Compressed Mining of Buildings, Water Bodies, Railways and Main Wells and Lanes", the protective layer thickness d1 of the upper aquifer and the protective layer thickness d2 of the lower aquifer are calculated;

[0016] Step S3: Based on the physical parameters of the coal body and each rock layer obtained in step S1, the distance D3 between the main key layer and the coal seam is obtained by using the key layer identification software KSPB, and the thickness d3 of the main key layer is obtained by using the stratigraphic histogram;

[0017] Comparing D1, D2, and D3, we can determine the positional relationship between the main key layer structure and the upper and lower aquifers, which include the following three types:

[0018] When D1<D3, it is an upper main key layer-lower group vulnerable double aquifer structure, that is, the main key layer is located above the upper aquifer and has no protective effect on the double aquifer;

[0019] When D1>D3>D2, it is a median main key layer-upper and lower unidirectional double aquifer structure, that is, the main key layer is located between the upper and lower aquifers, and plays a unidirectional protective role for the upper aquifer, but has no protective effect on the lower aquifer.

[0020] When D3<D2, it is a lower main key layer-upper group protective double aquifer structure, that is, the main key layer is located below the lower aquifer and has a protective effect on both aquifers;

[0021] Step S4: Based on the spatial relationship between the aquifer and the main key layer and the different protection methods, the following five water resource protection and utilization methods are designed:

[0022] Upper-lower storage method: The upper and lower aquifers are connected by a water channel, and artificial dams and coal pillar dams are built to block the goaf, turning the goaf into an underground reservoir. The water channel is then used to divert water flow to the underground reservoir for storage.

[0023] Upper-blocking-lower-storage method: The water diversion channel penetrates the lower aquifer without affecting the upper aquifer. The water-blocking property of the protective layer of the upper aquifer is used to block the loss of water in the upper aquifer. At the same time, the water diversion channel is used to divert water from the lower aquifer to the underground reservoir for storage.

[0024] Upper protection and lower storage method: The water diversion channel is developed into the protective layer of the upper aquifer, and the mined-out area is filled with waste rock. This protects the upper aquifer by lowering the water diversion channel, while at the same time using the water diversion channel to divert water from the lower aquifer to the underground reservoir for storage;

[0025] Upper-blocking-lower-protection method: The water channel is developed into the protective layer of the lower aquifer, without affecting the upper aquifer. The water-blocking property of the protective layer of the upper aquifer is used to block water loss in the upper aquifer. At the same time, waste rock is used to fill the mined-out area, thereby protecting the lower aquifer by lowering the water channel.

[0026] Upper-lower blocking method: The water channel does not affect the stability of the upper and lower aquifers, and the water-blocking properties of the upper and lower protective layers are used to prevent water loss;

[0027] Step S5: Determine a specific protection method based on the main key layer structure type, the water channel height h, and the thicknesses d1 and d2 of the upper and lower protective layers;

[0028] In the case of a double aquifer structure with an upper key layer and a lower vulnerable layer, the protection method is determined as follows:

[0029] When D1 < h, the water channel caused by mining activities develops above the upper aquifer, that is, the upper and lower aquifers are connected, and the upper storage-lower storage method is adopted;

[0030] When D1>h>D1-d1, the water channel caused by mining activities develops into the protective layer of the upper aquifer and affects the protective layer of the upper aquifer, and the upper protection-lower storage method is adopted;

[0031] When D2<h<D1-d1, the water channel caused by mining activities develops between the lower aquifer and the upper aquifer protection layer, and the upper blockage-lower storage method is adopted;

[0032] When D2>h>D2-d2, the water channel caused by mining activities affects the protective layer of the lower aquifer, and the upper blockage-lower protection method is adopted;

[0033] When h<D2-d2, the water channel caused by mining activities develops below the protective layer of the lower aquifer, and the upper blockage-lower blockage protection method is adopted;

[0034] In the case of a median main key layer - upper and lower unidirectional double aquifer structure, the protection method is determined as follows:

[0035] When D3+d3<h, the water channel caused by mining activities penetrates the main key layer, and the main key layer cannot serve as a bearing structure, which plays a protective role for the upper aquifer. The upper storage-lower storage method is adopted;

[0036] When D3+d3>h>D1-d1, the water channel caused by mining activities develops into the protective layer of the upper aquifer, and the main key layer is not broken and still has a bearing function, so the upper protection and lower storage method is adopted;

[0037] When D2<h<D1-d1, the water channel develops between the protective layer of the upper aquifer and the lower aquifer. The upper aquifer uses the protective layer to block the water channel and the aquifer, and the lower aquifer uses the underground reservoir to store water, adopting the upper blocking-lower storage method.

[0038] When D2>h>D2-d2, the water channel develops into the protective layer of the lower aquifer, and the upper blockage-lower protection method is adopted;

[0039] When h<D2-d2, the water channel develops below the protective layer of the lower aquifer, and the upper resistance-lower resistance method is adopted;

[0040] In the case of a lower main key layer-upper protective double aquifer structure, the protection method is determined as follows:

[0041] When h>D3+d3, the water channel caused by mining activities penetrates the main key layer, and the main key layer cannot serve as a bearing structure, so the upper storage-lower storage method is adopted;

[0042] When D2-d2<h<D3+d3, the water channel develops into the protective layer of the lower aquifer, and the main key layer is not broken and still has a bearing function, so the upper blocking-lower protection method is adopted;

[0043] When D2-d2>h, the water channel develops below the protective layer of the lower aquifer, and the protective layer is used to block water loss to achieve groundwater protection, adopting the upper-lower-blocking method.

[0044] Therefore, the present invention adopts the above-mentioned method for protecting and utilizing water resources under mining variation of different double-aquifer structures, and the beneficial technical effects are as follows:

[0045] (1) Adopting precise classification protection methods for double aquifers based on the distance between the aquifer and the ground surface, making the protection of underground aquifers more precise, more scientific and less costly;

[0046] (2) Utilizing the goaf formed by coal mining can reduce the damage caused by spontaneous combustion of coal in the goaf to the working face and reduce the cost of fire prevention and fire fighting;

[0047] (3) The original criterion of considering only water-conducting cracks has been expanded to include multiple criteria such as the thickness of the protective layer, making the protection method more refined and the protection effect more reliable and safe. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 A schematic flow chart of a method for protecting and utilizing water resources under different double-aquifer structure mining variations according to the present invention;

[0049] Figure 2 The stratigraphic cross section is for the upper main key layer;

[0050] Figure 3 The stratigraphic cross section is for the median main key layer;

[0051] Figure 4 The stratigraphic cross section for the lower main key layer;

[0052] Reference numerals

[0053] 1. Upper aquifer; 2. Main key layer; 3. Lower aquifer; 4. Water conduit; 5. Goaf; 6. Coal seam. DETAILED DESCRIPTION

[0054] The technical solution of the present invention is further described below with reference to the accompanying drawings and embodiments.

[0055] Unless otherwise defined, technical or scientific terms used in the present invention shall have the same meaning as commonly understood by one of ordinary skill in the art to which the present invention belongs.

[0056] like Figure 1As shown, in response to the geological characteristics of the presence of two aquifers, the Jurassic Zhiluo Formation and the Cretaceous Luohe Formation, above the longwall mining face during the development of the Huanglong Jurassic Coalfield, and the water resource loss and ecological environmental problems caused by improper groundwater protection methods in this area, the present invention proposes a method for protecting and utilizing water resources under mining variations of different dual aquifer structures. The method includes the following steps:

[0057] Step S1: First, obtain the mining height M of the coal mining face, the distance D1 between the upper aquifer and the coal seam, and the distance D2 between the lower aquifer and the coal seam. In the double aquifer in the formation, the aquifer with a smaller distance from the ground surface is defined as the upper aquifer, and the aquifer with a larger distance from the ground surface is defined as the lower aquifer;

[0058] Secondly, the physical parameters of the coal body and each rock layer are obtained by rock mechanics test, including rock density ρ, shear modulus G, bulk modulus K and compressive strength σ c , and the in situ rock stress σ of the rock was measured using the hydraulic fracturing method.

[0059] Step S2: Based on the working face mining height M, the distances D1 and D2 between the two aquifers and the coal seam, and the physical and mechanical parameters of the coal and rock mass obtained in step S1, a three-dimensional numerical simulation model is established in the 3DEC numerical simulation software to obtain the water-conducting channel generated from bottom to top in the overlying rock formation on the working face, and its height is recorded as h; at the same time, in order to determine the penetration distance of water in the pores of the rock formation, the protective layer thickness calculation formula in the "Specifications for the Installation of Coal Pillars and Compressed Coal Mining in Buildings, Water Bodies, Railways and Main Wells and Tunnels" is used to calculate the protective layer thickness d1 of the upper aquifer and the protective layer thickness d2 of the lower aquifer, that is, the penetration distance of water in the upper aquifer is d1, and the penetration distance of water in the lower aquifer is d2.

[0060] Step S3: Based on the physical parameters of the coal body and each rock layer obtained in step S1, and with the help of the key layer identification software KSPB, the distance D3 between the main key layer and the coal seam is obtained, and the thickness d3 of the main key layer is obtained using the stratigraphic histogram. At the same time, by comparing D1, D2, and D3 obtained in step S1, the positional relationships between the following three main key layer structures and the upper and lower aquifers can be obtained:

[0061] When D1<D3, it is called the upper main key layer-lower group vulnerable double aquifer structure, that is, the main key layer is located above the upper aquifer and has no protective effect on the double aquifer;

[0062] When D1>D3>D2, it is called a median main key layer-upper and lower unidirectional double aquifer structure, that is, the main key layer is located between the upper and lower aquifers, and plays a unidirectional protective role for the upper aquifer, but has no protective effect on the lower aquifer.

[0063] When D3<D2, it is called the lower main key layer-upper group protective double aquifer structure, that is, the main key layer is located below the lower aquifer and has a protective effect on both aquifers.

[0064] Step S4: Based on the spatial relationship between the aquifer and the main key layer and the different protection methods, five specific protection methods are designed: ① upper storage-lower storage method, ② upper blocking-lower storage method, ③ upper protection-lower storage method, ④ upper blocking-lower protection method, and ⑤ upper blocking-lower blocking method.

[0065] The upper-lower storage method involves connecting both upper and lower aquifers through water channels, making it impossible to utilize the impermeability of the protective layer to prevent water loss. First, the parameters of the underground reservoir are designed based on the characteristics of the overburden rock. Then, an artificial dam and a coal pillar dam are constructed to seal the mined-out area. This allows water to flow through the water channels and be stored in the underground reservoir, achieving the goal of lower storage and protection of both upper and lower aquifers.

[0066] The upper blocking and lower storage method means that the water diversion channel penetrates the lower aquifer, making it impossible to use the protective layer of the lower aquifer to prevent water loss. However, the upper aquifer is not affected by the water diversion channel, and its protective layer can be used to prevent water loss. The upper aquifer uses the water-isolating properties of its protective layer to block the loss of water in the upper aquifer, thereby achieving the purpose of upper blocking protection for the upper aquifer. At the same time, the parameters of the underground reservoir are designed for the lower aquifer based on the characteristics of the overlying rock. Then, an artificial dam and a coal pillar dam are constructed to seal the goaf, allowing the water flow to be diverted through the water diversion channel to the underground reservoir for storage, thereby achieving the purpose of lower storage for the lower aquifer.

[0067] The upper protection and lower storage method involves developing a water channel within the protective layer of the upper aquifer, penetrating the lower aquifer and affecting its protective layer. The protective layer thickness calculation formula for the upper aquifer is first calculated using the "Specifications for Coal Pillar Retention and Compressed Coal Mining in Buildings, Water Bodies, Railways, and Major Shafts and Tunnelings." This calculation also deduces the water channel height threshold. 3DEC numerical simulation software is then used to simulate the water channel height at different filling rates. The water channel height threshold and the water channel height at different filling rates are compared to determine the critical filling rate. Finally, under the critical filling rate, the mined-out area is backfilled with waste rock, achieving the upper protection of the upper aquifer. Simultaneously, the parameters of the groundwater reservoir for the lower aquifer are designed based on the characteristics of the overburden. Then, an artificial dam and a coal pillar dam are constructed to seal the mined-out area, diverting water through the water channel to the groundwater reservoir for storage, achieving the lower protection of the lower aquifer.

[0068] The upper-blocking-lower-protection method involves developing a water channel between the protective layer of the upper aquifer and the lower aquifer, penetrating the lower aquifer while leaving the upper aquifer unaffected. The upper aquifer utilizes the water-repellent properties of the protective layer to block water loss from the upper aquifer, thereby achieving upper-blocking protection for the upper aquifer. Simultaneously, the protective layer thickness of the lower aquifer is calculated using the formula for calculating protective layer thickness in the "Specifications for Coal Pillar Retention and Pressure Coal Mining in Buildings, Water Bodies, Railways, and Major Shafts and Tunnelings." This calculation also deduces the water channel height threshold. 3DEC numerical simulation software is then used to simulate the water channel height at different filling rates. The water channel height threshold and the water channel height at different filling rates are compared to determine the critical filling rate. Finally, under the critical filling rate, the goaf is backfilled with waste rock, thereby achieving lower-protection protection for the lower aquifer.

[0069] The upper-blocking-lower-blocking method means that the development of the water-conducting channel does not affect the stability of the upper and lower aquifers. Therefore, the upper and lower aquifers both use the water-isolating properties of the corresponding protective layers to prevent water loss, thereby achieving the upper-blocking-lower-blocking protection purpose of the upper and lower aquifers.

[0070] Step S5: In a dual-aquifer structure with an upper primary key layer and a lower vulnerable layer, that is, the primary key layer is above the upper aquifer. As a load-bearing structure, the primary key layer cannot protect the dual aquifer. The appropriate protection method is determined by comparing the distances D1 and D2 from the dual aquifer to the coal seam, the height h of the water channel, and the thicknesses d1 and d2 of the protective layers.

[0071] When D1 < h, the water channel caused by mining activities develops above the upper aquifer, that is, the upper and lower aquifers are connected, and the upper storage-lower storage protection method is adopted;

[0072] When D1>h>D1-d, the water channel caused by mining activities develops into the protective layer of the upper aquifer and affects the protective layer of the upper aquifer, and the protection method of upper protection and lower storage is adopted;

[0073] When D2<h<D1-d1, the water channel caused by mining activities develops between the lower aquifer and the upper aquifer protection layer, and the upper blockage-lower storage protection method is adopted;

[0074] When D2>h>D2-d2, the water channel caused by mining activities affects the protective layer of the lower aquifer, and the upper blocking-lower protection method is adopted;

[0075] When h<D2-d2, the water channel caused by mining activities develops below the protective layer of the lower aquifer, and the upper resistance-lower resistance protection method is adopted.

[0076] In the case of a dual-aquifer structure with a central key layer and upper and lower unidirectional aquifers, the main key layer is located between the upper and lower aquifers. In this case, the key layer, as a load-bearing structure, can maintain the stability of the upper aquifer. At this time, the thicknesses of the protective layers d1 and d2, the height of the water channel h, the distance D3 from the main key layer to the coal seam, and the thickness d3 of the main key layer are compared to determine whether the water channel will penetrate the aquifer and determine the corresponding protection method.

[0077] When D3+d3<h, the water channel caused by mining activities penetrates the main key layer, and the main key layer cannot serve as a bearing structure, which plays a protective role for the upper aquifer. The upper storage-lower storage protection method is adopted;

[0078] When D3+d3>h>D1-d1, the water channel caused by mining activities develops into the protective layer of the upper aquifer, and the main key layer is not broken and still has a bearing function. The upper protection and lower storage protection method is adopted;

[0079] When D2<h<D1-d1, the water channel develops between the protective layer of the upper aquifer and the lower aquifer. The upper aquifer uses the protective layer to block the water channel and the aquifer, and the lower aquifer uses the underground reservoir to store water, adopting the upper blocking-lower storage protection method.

[0080] When D2>h>D2-d2, the water channel develops into the protective layer of the lower aquifer, and the upper blocking-lower protection method is adopted;

[0081] When h<D2-d2, the water channel develops below the protective layer of the lower aquifer, and the upper resistance-lower resistance protection method is adopted.

[0082] When the lower main key layer and upper protective double aquifer structure are formed, that is, the main key layer is located below the lower aquifer. As a bearing structure, the main key layer controls the stability of the upper and lower aquifers and the development height of the water channel. At this time, the protection method is determined by comparing the water channel height h, the distance D3 from the main key layer to the coal seam, and the thickness d3 of the main key layer.

[0083] When h>D3+d3, the water channel caused by mining activities penetrates the main key layer, and the main key layer cannot serve as a bearing structure. The upper storage-lower storage protection method is adopted;

[0084] When D2-d2<h<D3+d3, the water channel develops into the protective layer of the lower aquifer, and the main key layer is not broken and still has a bearing function, so the upper blocking-lower protection method is adopted;

[0085] When D2-d2>h, the water channel develops below the protective layer of the lower aquifer, and the protective layer is used to block water loss to achieve groundwater protection, adopting the upper-blocking-lower-blocking protection method.

[0086] Example 1

[0087] The stratigraphic cross-section structure of the mining area in this embodiment is as follows: Figure 2 The upper main key layer shown is a stratigraphic cross-section, which, from top to bottom, is: main key layer 2, upper aquifer 1, lower aquifer 3, water channel 4, goaf 5, and coal seam 6.

[0088] like Figure 3 The middle main key layer shown is a stratigraphic cross-section, which, from top to bottom, is: upper aquifer 1, main key layer 2, lower aquifer 3, water channel 4, goaf 5, and coal seam 6.

[0089] like Figure 4 The lower main key layer shown is a stratigraphic cross-section, which, from top to bottom, is: upper aquifer 1, lower aquifer 3, main key layer 2, water channel 4, goaf 5, and coal seam 6.

[0090] Step S1: Obtain the mining height of the working face M = 4m, the original rock stress σ = 11Mpa, the distance between the upper aquifer and the coal seam D1 = 54.2m, and the distance between the lower aquifer and the coal seam D2 = 20m.

[0091] Collect coal rock samples from the mining area and use rock mechanics experiments to test the bulk modulus K, shear modulus G, and compressive strength σ of the coal rock samples to be tested c , and rock density ρ, as shown in Table 1, the physical parameters of the coal body and each rock layer.

[0092] Table 1 Physical parameters of coal body and rock layers

[0093]

[0094] Step S2: Based on the working face mining height M = 4m obtained in step S1 and the physical parameters of the coal body and each rock layer in Table 1, and with the help of 3DEC numerical simulation software, a numerical simulation model of the water guide channel development is established, and the height of the water guide channel generated from bottom to top in the overlying rock layer of the working face is obtained to be h = 47m; the protective layer thickness calculation formula in the "Specifications for Coal Pillar Retention and Coal Compressed Mining of Buildings, Water Bodies, Railways and Main Wells and Lanes" is used to calculate the protective layer thickness. Among them, the rock layer below the upper aquifer in Table 1 is a medium-hard rock layer, and the thickness of the clay layer at the bottom of the loose layer is greater than the mining height M = 4m. Therefore, d = 3M is used to calculate the protective layer thickness, and the seepage distance d1 = 12m of water in the upper aquifer is obtained; the rock layer below the lower aquifer is a medium-hard rock layer, and the thickness of the clay layer at the bottom of the loose layer is less than the mining height M = 4m. Therefore, d = 4M is used to calculate the protective layer thickness, and the seepage distance d2 = 16m of water in the lower aquifer is obtained.

[0095] Step S3: Based on the physical parameters of the coal body and various rock formations in Table 1, and using the key layer identification software KSPB, the distance D3 from the main key layer to the coal seam is 35.6 m, and the thickness of the main key layer is d3 = 10.5 m. The distance D3 from the main key layer to the coal seam is compared with the distances D1 and D2 from the upper and lower aquifers to the coal seam, where D1 = 54.2 m, D2 = 20 m, and D3 = 25.3 m. The distance D3 from the main key layer to the coal seam is greater than the distance D2 from the upper aquifer to the coal seam, but less than the distance D1 from the upper aquifer to the coal seam, that is, D2 < D3 < D1. This determines that the main key layer and the dual aquifer structure are a median main key layer-upper and lower unidirectional dual aquifer structure.

[0096] Step S4: Based on the physical parameters of the coal body and each rock layer in Table 1, the height of the water channel is compared with the distance between the upper aquifer and the coal seam, the distance between the main key layer and the coal seam, and the thickness parameters of the main key layer, where h=47m, D1=54.2m, D2=20m, D3=35.6m, d3=15.5m, and d1=12m. It is found that the height of the water channel is greater than the distance between the main key layer and the coal seam and greater than the distance between the lower aquifer and the coal seam, and less than the distance between the upper aquifer and the coal seam, that is, D3+d3>h>D1-d1, and then it is determined to adopt the upper protection-lower storage protection method.

[0097] The water channel threshold h1 is obtained by subtracting the distance D1 between the upper aquifer and the coal seam and the thickness d1 of the protective layer of the upper aquifer, that is, h1=D1-d1=42.2m.

[0098] Based on the mining height M = 4 m and the physical parameters of the rock formation in Table 1, and with the help of 3DEC numerical simulation software, a model of the development of water-conducting channels in the overburden under different filling rates was established, and the development heights of the water-conducting channels under different filling rates were obtained, as shown in Table 2.

[0099] Table 2 Development height of water-conducting channels at different filling rates

[0100]

[0101] Based on the water channel height at different filling rates in Table 2, the linear relationship between filling rate and water channel height is y = 0.8744 - 0.00673x, where y is the filling rate and x is the water channel threshold h. Substituting the water channel threshold h1 = 42.2 into y = 0.8744 - 0.00673x, the optimal filling rate is 59%.

[0102] Therefore, the present invention adopts the above-mentioned method for protecting and utilizing water resources under mining variations of different double-aquifer structures, thereby achieving the coordinated development of coal resource development and comprehensive protection and utilization of water resources in the mining area.

[0103] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the same. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solutions of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for protecting and utilizing water resources under mining variations in different double aquifer structures, characterized in that: The following steps are involved: Step S1: Based on the geological characteristics of two aquifers, the Jurassic Zhiluo Formation and the Cretaceous Luohe Formation, above the longwall mining face during the development of the Huanglong Jurassic Coalfield, the mining height M of the coal mining face, the distance D1 between the upper aquifer and the coal seam, and the distance D2 between the lower aquifer and the coal seam are obtained. In the double aquifers, the aquifer with the smaller distance from the ground surface is defined as the upper aquifer, and the aquifer with the larger distance from the ground surface is defined as the lower aquifer. Physical parameters of the coal body and each rock layer are obtained using rock mechanics tests, and the in situ rock stress σ of the rock is measured using hydraulic fracturing methods. Among them, the physical parameters of coal body and each rock layer include rock density ρ, shear modulus G, bulk modulus K and compressive strength σ c ; Step S2: Based on the data obtained in step S1, a three-dimensional numerical simulation model is established in 3DEC numerical simulation software to obtain the height h of the water channel generated from bottom to top in the overlying rock strata of the working face; using the protective layer thickness calculation formula in the "Specifications for Coal Pillar Retention and Coal Compressed Mining of Buildings, Water Bodies, Railways and Main Wells and Lanes", the protective layer thickness d1 of the upper aquifer and the protective layer thickness d2 of the lower aquifer are calculated; Step S3: Based on the physical parameters of the coal body and each rock layer obtained in step S1, the distance D3 between the main key layer and the coal seam is obtained by using the key layer identification software KSPB, and the thickness d3 of the main key layer is obtained by using the stratigraphic histogram; Comparing D1, D2, and D3, we can determine the positional relationship between the main key layer structure and the upper and lower aquifers, which include the following three types: When D1<D3, it is a double aquifer structure of upper main key layer and lower vulnerable layer, that is, the main key layer is located above the upper aquifer and has no protective effect on the double aquifer; When D1>D3>D2, it is a median main key layer-upper and lower unidirectional double aquifer structure, that is, the main key layer is located between the upper and lower aquifers, and plays a unidirectional protective role for the upper aquifer, but has no protective effect on the lower aquifer. When D3<D2, it is a lower main key layer-upper group protective double aquifer structure, that is, the main key layer is located below the lower aquifer and has a protective effect on both aquifers; Step S4: Based on the spatial relationship between the aquifer and the main key layer and the different protection methods, the following five water resource protection and utilization methods are designed: Upper-lower storage method: The upper and lower aquifers are connected by a water channel, and artificial dams and coal pillar dams are built to block the goaf, turning the goaf into an underground reservoir. The water channel is then used to divert water flow to the underground reservoir for storage. Upper-blocking-lower-storage method: The water diversion channel penetrates the lower aquifer without affecting the upper aquifer. The water-blocking property of the protective layer of the upper aquifer is used to block the loss of water in the upper aquifer. At the same time, the water diversion channel is used to divert water from the lower aquifer to the underground reservoir for storage. Upper protection and lower storage method: The water diversion channel is developed into the protective layer of the upper aquifer, and the mined-out area is filled with waste rock. This protects the upper aquifer by lowering the water diversion channel, while at the same time using the water diversion channel to divert water from the lower aquifer to the underground reservoir for storage; Upper-blocking-lower-protection method: The water channel is developed into the protective layer of the lower aquifer, without affecting the upper aquifer. The water-blocking property of the protective layer of the upper aquifer is used to block water loss in the upper aquifer. At the same time, waste rock is used to fill the mined-out area, thereby protecting the lower aquifer by lowering the water channel. Upper-lower blocking method: The water channel does not affect the stability of the upper and lower aquifers, and the water-blocking properties of the upper and lower protective layers are used to prevent water loss; Step S5: Determine a specific protection method based on the main key layer structure type, the water channel height h, and the thicknesses d1 and d2 of the upper and lower protective layers; In the case of a double aquifer structure with an upper key layer and a lower vulnerable layer, the protection method is determined as follows: When D1 < h, the water channel caused by mining activities develops above the upper aquifer, that is, the upper and lower aquifers are connected, and the upper storage-lower storage method is adopted; When D1>h>D1-d1, the water channel caused by mining activities develops into the protective layer of the upper aquifer and affects the protective layer of the upper aquifer, and the upper protection-lower storage method is adopted; When D2<h<D1-d1, the water channel caused by mining activities develops between the lower aquifer and the upper aquifer protection layer, and the upper blockage-lower storage method is adopted; When D2>h>D2-d2, the water channel caused by mining activities affects the protective layer of the lower aquifer, and the upper blockage-lower protection method is adopted; When h<D2-d2, the water channel caused by mining activities develops below the protective layer of the lower aquifer, and the upper blockage-lower blockage protection method is adopted; In the case of a median main key layer - upper and lower unidirectional double aquifer structure, the protection method is determined as follows: When D3+d3<h, the water channel caused by mining activities penetrates the main key layer, and the main key layer cannot serve as a bearing structure, which plays a protective role for the upper aquifer. The upper storage-lower storage method is adopted; When D3+d3>h>D1-d1, the water channel caused by mining activities develops into the protective layer of the upper aquifer, and the main key layer is not broken and still has a bearing function, so the upper protection and lower storage method is adopted; When D2<h<D1-d1, the water channel develops between the protective layer of the upper aquifer and the lower aquifer. The upper aquifer uses the protective layer to block the water channel and the aquifer, and the lower aquifer uses the underground reservoir to store water, adopting the upper blocking-lower storage method. When D2>h>D2-d2, the water channel develops into the protective layer of the lower aquifer, and the upper blockage-lower protection method is adopted; When h<D2-d2, the water channel develops below the protective layer of the lower aquifer, and the upper resistance-lower resistance method is adopted; In the case of a lower main key layer-upper protective double aquifer structure, the protection method is determined as follows: When h>D3+d3, the water channel caused by mining activities penetrates the main key layer, and the main key layer cannot serve as a bearing structure, so the upper storage-lower storage method is adopted; When D2-d2<h<D3+d3, the water channel develops into the protective layer of the lower aquifer, and the main key layer is not broken and still has a bearing function, so the upper blocking-lower protection method is adopted; When D2-d2>h, the water channel develops below the protective layer of the lower aquifer, and the protective layer is used to block water loss to achieve groundwater protection, adopting the upper-lower-blocking method.

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