A water-reinjection coal mining technology and optimization method for open-pit mines

Abstract

The present invention discloses a water-saving coal mining technology and optimization method for open-pit mine drainage and reinjection. First, detailed regional hydrogeological data and mine water resource call conditions are mastered; the maximum amount of mine water that can be used for reinjection is determined based on a drainage management optimization model; a three-dimensional mine drainage model is established, and the location and amount of reinjection wells are designed in combination with a water-blocking curtain; the water level recovery and the change in drainage volume are predicted, and the reinjection plan is evaluated and determined. This method can change the flow direction of groundwater outside the curtain, effectively restore the regional groundwater level, reduce the drainage volume of the open-pit mine, and contribute to water resource protection and ecological environment restoration during open-pit mining.

Description

Technical Field

[0001] The invention relates to the field of mine water gushing control and mining area ecological restoration, and in particular to an open-pit mine drainage and water conservation coal mining technology and an optimization method. Background Art

[0002] my country's Xinjiang and Inner Mongolia regions are rich in coal resources, accounting for 50% of the country's total, of which open-pit mining accounts for 90% of the country's open-pit mining. These regions themselves have fragile ecological environments and scarce water resources, and are the areas with the most serious soil erosion in my country. Coal mining in open-pit mining areas further drains a large amount of groundwater, causing the regional groundwater level to drop and water resources to be lost, further deteriorating the ecological environment. The drainage water of northern open-pit mines mainly comes from the Quaternary System. Recharging the drainage water to the Quaternary aquifer can not only realize the recycling of water resources and reduce the amount of external drainage, but also effectively replenish groundwater resources, maintain the stability of the groundwater level, and protect the regional ecological environment.

[0003] The existing open-pit mine water conservation method mainly builds reservoirs on the surface, pit bottom, and side walls. However, the construction and maintenance costs of large-scale surface and pit bottom reservoirs are high, it is difficult to continue to maintain the properties of groundwater resources, and they are easily polluted. Only some coal mines will build water-cutting curtains outside the mine to reduce the amount of drainage, trying to keep the groundwater in the original aquifer as much as possible. However, there is a phenomenon of curtain disturbance, the direction of regional groundwater flow has not changed, and the water level outside the curtain will still gradually decrease over time. Therefore, it is urgent to develop a new water-saving coal mining technology that can both restore the groundwater level and reduce mine water. Summary of the invention

[0004] In view of the above-mentioned technical deficiencies, the purpose of the present invention is to provide an open-pit mine drainage and reinjection water-preservation coal mining technology and optimization method, which can change the flow direction of groundwater outside the curtain, effectively restore the regional groundwater level, and reduce the amount of drainage.

[0005] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0006] The present invention provides an open-pit mine drainage and water-reinjection coal mining technology and optimization method, comprising the following steps:

[0007] S1: Investigate key hydrogeological parameters in the open-pit mine area, including the range of the bottom ecological water level of the Quaternary aquifer groundwater, groundwater loss, water level drop, the shape of the drop funnel formed by mining in the mining area, and the permeability parameters of the aquifer;

[0008] S2: Investigate water resources and utilization in open-pit mines and find out the water demand for drainage and drainage, and understand the water quality, water quantity and dynamic change relationship of drainage and quaternary drainage;

[0009] S3: Determine the amount of reinjection; establish a drainage management optimization model, construct the objective function and constraints, and use a non-dominated genetic algorithm and a local search algorithm to solve it;

[0010] S4: Construct a three-dimensional mine drainage model; construct a detailed three-dimensional mine hydrogeological model based on drilling data; generalize the mine boundary to the drainage boundary, generalize the mine waterproof curtain to the weak permeability surface, establish the mine drainage mathematical control equation, and simulate the mine drainage, curtain water blocking and reinjection;

[0011] S5: Design and optimize the same-layer reinjection plan outside the curtain; determine whether to directly reinject through water quality testing; design the location and amount of the reinjection well, and evaluate based on water level rise, drainage volume, and water quality changes to determine the most appropriate plan.

[0012] Preferably, in step S4, according to the three-dimensional mine drainage model established in step S3, three parts of simulation and prediction are performed in step S4:

[0013] (1) Simulate the regional groundwater level drop caused by drainage in open-pit mines, and analyze and evaluate the environmental and ecological effects caused by drainage in mining areas;

[0014] (2) Simulate the reduction of drainage and the rise of regional groundwater after the curtain is built to evaluate the water-stopping effect of the mine curtain;

[0015] (3) The simulation prediction is no greater than the injection volume Q after optimization in step S3 r The resulting groundwater recovery and drainage volume changes outside the pit are used to evaluate the effectiveness of the reinjection plan and optimize it.

[0016] Preferably, in step S3, the economic objective function f in the drainage management optimization model is s (x), social objective function f e (x), ecological environment objective function f k (x) are:

[0017] F = opt [ρ s f s (x) +ρ e f e (x) +ρ k f k (x)] (17)

[0018]

[0019] Where: s , e , k Respectively represent the weight coefficients of the objective function; is the unit water extraction cost of water source i; represents the unit cost of delivering water from source i to distribution agency j; is the unit treatment cost of water source i; x ij represents the amount of water allocated from water source i to department j; μ j is the weight coefficient of department j; x j and D j are the actual water supply and the minimum demand respectively; p i represents the pollution intensity of water source i; x i represents the amount of water taken from water source i; economic benefits, social benefits and ecological and environmental benefits are represented by water supply cost, water supply income and total amount of pollutants respectively;

[0020] Establish constraints, including water supply capacity constraints, demand satisfaction constraints, water quality requirements constraints, water supply structure constraints, and non-negativity constraints:

[0021]

[0022] Where: S i The maximum water supply capacity of water source i; D j is the minimum water demand of department j; q i is the water quality index of water source i; Q j is the water quality requirement of department j; and They represent the minimum and maximum proportions of water obtained by department j from water source i respectively; the NSGA-II algorithm is used to solve various water source utilization models to obtain the Pareto frontier solution set; simulated annealing is used to locally optimize the Pareto frontier solution set to obtain the amount of reinjection outside the curtain Q under the premise of meeting various water demands in the mining area r .

[0023] Preferably, in step S4, in order to finely depict the mine drainage boundary, curtain and reinjection well, a quadtree grid is used for modeling;

[0024] Because the vertical velocity of the phreatic water around the curtain and the pit is relatively large, a regional scale phreatic water unsteady flow mathematical model without considering the Dupuit hypothesis is adopted:

[0025]

[0026] Given a hydraulic head boundary:

[0027] H(x,y,z,t)| t＝0 =H0 x,y,z∈Ω,t≥0 (27)

[0028] Waterproof border:

[0029]

[0030] Given a flow boundary:

[0031]

[0032] Where: μ s is the water supply degree of the phreatic aquifer; H is the hydraulic head; K is the permeability tensor of the aquifer, obtained through hydrogeological data or field experiments; ε is the source and sink term per unit time, including rainfall infiltration, river recharge, mine drainage, and reinjection outside the curtain; for a certain grid (i, j, k) of the model:

[0033] ε i,j,k =(Q p | i,j,k +Q h | i,j,k -Q r | i,j,k -Q d | i,j,k ) / △V i,j,k (30)

[0034] Where: Q p | i,j,k Recharged by rainfall infiltration; Q h | i,j,k is the water exchange at a given head boundary; Q r | i,j,k The amount of water used for reinjection after optimization of mine water allocation; Q d | i,j,k is the drainage volume at the mine boundary; ΔV i,j,k is the grid unit volume;

[0035] The pit boundary is the drainage boundary, and the drainage volume of the model grid to the boundary is:

[0036]

[0037] Where: K d is the equivalent hydraulic conductivity; H i,j,k is the hydraulic head of the model grid; d b | i,j,k is the bottom elevation of the mine drainage boundary;

[0038] PEST is used to calibrate the model parameters; the minimum value of the objective function is solved based on the Levenberg-Marquardt algorithm. The objective function is the weighted variance between the calculated value of the model parameter and the actual observed value:

[0039]

[0040] Where: w i is the weight coefficient; To observe the water head; To simulate the water head.

[0041] Preferably, in step S5, the designed reinjection method is non-pressure or micro-pressure constant flow reinjection; the reinjection well is at a straight-line distance d outside the curtain, and the well spacing is d r , the single well reinjection volume is Q i , the number of wells is N, and the total amount of reinjection is The following conditions are met:

[0042] (1) the total amount of reinjection does not exceed the amount available for reinjection or the maximum reinjection potential of the aquifer,

[0043] (2) The water level rise caused by reinjection reaches the expected level and is conducive to ecological recovery.

[0044] (3) The increase in drainage volume caused by curtain overflow and curtain bypass does not exceed expectations, △Q d <△Q d,0 ;

[0045] (4) The groundwater quality caused by reinjection meets the Class III water standard,

[0046] If the above expected effects are not met, the reinjection water quality, well spacing and reinjection water volume will be further optimized.

[0047] The beneficial effects of the present invention are:

[0048] (1) The present invention proposes a water-saving coal mining technology for reinjecting drainage water in the same layer of open-pit coal mines, which is helpful for protecting water resources in open-pit coal mines. This technology replenishes the micro-treated drainage water to the original shallow Quaternary aquifer, reduces the enterprise's mine water treatment costs, realizes the recycling of water resources, is of great significance to maintaining the balance of regional water resources, and provides a new method for restoring the ecological environment in mining areas;

[0049] (2) Based on the water quality testing and monitoring plan, ensure that the reinjection water meets environmental protection requirements. Through drainage and Quaternary aquifer groundwater quality testing, a suitable mine water treatment process is formulated to ensure that the quality of reinjection water is better than that of primary water. At the same time, water level and water quality monitoring wells are set up near the reinjection wells to monitor the water quality in real time to ensure the smooth implementation of the coal mining water conservation plan.

[0050] (3) Through the drainage resource management optimization model, the reinjection volume is determined under the premise of ensuring the water demand for production, life and agricultural irrigation in the mining area. Through the detailed hydrogeological structure model of the mining area, the water level rise and drainage volume change after reinjection are predicted, and the reinjection plan design is finally determined. It can not only achieve the regional groundwater level rise, but also maximize the drainage volume increase within the allowable range, or even reduce the drainage volume. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0052] Figure 1 A schematic flow chart of a water-reinjection and water-preservation coal mining technology and an optimization method for an open-pit mine provided by the present invention;

[0053] Figure 2 A schematic diagram of the recharging provided by the present invention;

[0054] Figure 3 Constructing a map for a three-dimensional geological model of water levels in the mining area;

[0055] Figure 4 a is the model unstructured grid and initial seepage vector diagram;

[0056] Figure 4 b is the design of reinjection and monitoring points outside the curtain and the seepage vector diagram after reinjection;

[0057] Figure 5 The water level rise prediction results caused by the two reinjection schemes are shown in the figure;

[0058] Figure 6 This is the prediction result diagram when the drainage volume is stable under different single well reinjection volume conditions;

[0059] Figure 7 This is the prediction result of water level rise near the curtain under different single well reinjection conditions. DETAILED DESCRIPTION

[0060] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0061] like Figure 1-Figure 2 As shown, this embodiment provides an open-pit mine drainage and water-reinjection coal mining technology and optimization method, including the following steps:

[0062] S1: Investigate key hydrogeological parameters in the open-pit mine area, including the range of the bottom ecological water level of the Quaternary aquifer groundwater, groundwater loss, water level drop, the shape of the drop funnel formed by mining in the mining area, and the permeability parameters of the aquifer;

[0063] S2: Investigate water resources and utilization in open-pit mines and find out the water demand for drainage and drainage, and understand the water quality, water quantity and dynamic change relationship of drainage and quaternary drainage;

[0064] S3: Determine the amount of reinjection; establish a drainage management optimization model, construct the objective function and constraints, and use a non-dominated genetic algorithm and a local search algorithm to solve it;

[0065] S4: Construct a three-dimensional mine drainage model; construct a detailed three-dimensional mine hydrogeological model based on drilling data; generalize the mine boundary to the drainage boundary, generalize the mine waterproof curtain to the weak permeability surface, establish the mine drainage mathematical control equation, and simulate the mine drainage, curtain water blocking and reinjection;

[0066] S5: Design and optimize the same-layer reinjection plan outside the curtain; determine whether to directly reinject through water quality testing; design the location and amount of the reinjection well, and evaluate based on water level rise, drainage volume, and water quality changes to determine the most appropriate plan.

[0067] In one example, the survey data showed that the total amount of drainage water after the curtain water cutoff in an open-pit mine was 3081.2×10 4 m 3 / a, 2705.8×10 4 m 3 / a is used for other purposes (such as agricultural irrigation, ecological water use, power plant water intake, etc.), of which ecological water use is 1311.8×10 4 m 3 / a. Remaining 375.4×10 4 m 3 / a can be used for production, life and shallow reinjection in the mine. x1, x2, x3 represent the amount of water used for production, life and reinjection in the mine area (unit ×10 4 m 3 / a), then x1+x2+x3≤375.4. Economic objective function f s (x) is the water use cost and social benefit f e (x) is the water efficiency coefficient, and the constraints are the minimum water demand and treatment capacity.

[0068]

[0069] The result of water resource management optimization is that the production water is 170.2×10 4 m 3 / a, domestic water consumption 50.8×10 4 m 3 / a, reinjection water volume 154.4×10 4 m 3 / a. Two reinjection volume plans were initially determined: (1) The total reinjection volume determined by the drainage management optimization model is approximately 4230.1m 3 / d; (2) 1 / 3 of the ecological water used in the mining area is used for reinjection, so the total reinjection volume is about 11979.9m 3 / d.

[0070] According to the water level geological survey data, after the mine curtain was built, the inner water level was 450m, the outer water level elevation was H0=461m, and the ground elevation outside the curtain was Z=474m, so the water level burial depth outside the curtain was determined to be s=13m. In order to avoid curtain overflow caused by reinjection, the water level rose by ΔH<13m after reinjection. Other hydrogeological data are shown in Table 2.

[0071] Table 2 Statistics of basic parameters of the model

[0072]

[0073]

[0074] Based on the detailed geological drilling data of 230 mining areas, a fine three-dimensional hydrogeological structure of the mining area was constructed, in which the mine section of the model is shown in Figure 3 .

[0075] Determine the boundary and initial conditions of the regional surface model, simulate the initial flow field and the flow field after the curtain is built, see Figure 4 ,in, Figure 4 a is the model unstructured grid and initial seepage vector diagram; Figure 4 b is the design of reinjection and monitoring points outside the curtain and the seepage vector diagram after reinjection.

[0076] The designed reinjection well is located 130m to the right outside the curtain. A total of 5 injection wells are designed with a spacing of 115m. The reinjection depth is a complete well of the Quaternary phreatic aquifer, and the reinjection duration is two years.

[0077] The water level rise in the curtain, between the curtain and the reinjection well, and at 300m and 1000m to the right of the reinjection well under different reinjection schemes is statistically analyzed. Figure 5 Among them, the second option can make the water level rise by more than 1m within a range of 1km, and it is finally determined that the second option can better meet the needs.

[0078] Originally, groundwater seeped into the mine in the form of a descending funnel. After reinjection, groundwater seeped in the opposite direction outside the curtain, thus changing the direction of regional groundwater flow. Since the reinjection water itself comes from the mine water, the amount of water used for reinjection is subtracted from the drainage volume every day during the simulation and prediction process. The changes in the total drainage water volume under different reinjection conditions are shown in Figure 6 . It is proved that the drainage volume is continuously reduced while the reinjection restores the ecological water level.

[0079] Option 2 is limited by drainage volume. When the water supply is sufficient, the reinjection volume is further increased, and the water level outside the curtain is constrained to rise no more than 13m. Simulation prediction results show that the maximum single well injection volume is about 8000m under the condition of simultaneous reinjection of 5 wells. 3 / d( Figure 7 ).

[0080] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A water-reinjection coal mining technology and optimization method for open-pit mines, characterized in that: The following steps are involved: S1: Investigate key hydrogeological parameters in the open-pit mine area, including the range of the bottom ecological water level of the Quaternary aquifer groundwater, groundwater loss, water level drop, the shape of the drop funnel formed by mining in the mining area, and the permeability parameters of the aquifer; S2: Investigate water resources and utilization in open-pit mines and find out the water demand for drainage and drainage, and understand the water quality, water quantity and dynamic change relationship of drainage and quaternary drainage; S3: Determine the amount of reinjection; establish a drainage management optimization model, construct the objective function and constraints, and use a non-dominated genetic algorithm and a local search algorithm to solve it; S4: Construct a three-dimensional mine drainage model; construct a detailed three-dimensional mine hydrogeological model based on drilling data; generalize the mine boundary to the drainage boundary, generalize the mine waterproof curtain to the weak permeability surface, establish the mine drainage mathematical control equation, simulate the mine drainage, curtain water blocking and reinjection, specifically: According to the model established in step S3, three parts of simulation and prediction are performed, including: (1) Simulate the regional groundwater level drop caused by drainage in open-pit mines, and analyze and evaluate the environmental and ecological effects caused by drainage in mining areas; (2) Simulate the reduction of drainage and the rise of regional groundwater after the curtain is built to evaluate the water-stopping effect of the mine curtain; (3) The simulation prediction is no greater than the reinjection amount Q in step S3 r The resulting groundwater recovery and drainage volume changes outside the pit are used to evaluate the effect of the reinjection plan and optimize the plan; S5: Design and optimize the same-layer reinjection plan outside the curtain; determine whether to directly reinject through water quality testing; design the location and amount of the reinjection well, and evaluate based on water level rise, drainage volume, and water quality changes to determine the most appropriate plan.

2. The open-pit mine drainage and water-reinjection coal mining technology and optimization method according to claim 1, characterized in that: In step S3, the economic objective function f in the drainage management optimization model is s (x), social objective function f e (x), ecological environment objective function f k (x) are: F=opt[ρ s f s (x)+p e f e (x)+p k f k (x)](1) Where: s , e , k Respectively represent the weight coefficients of the objective function; c i source is the unit water extraction cost of water source i; c ij transport represents the unit cost of transporting water from source i to water distribution department j; c i treatment is the unit treatment cost of water source i; x ij represents the amount of water allocated from water source i to department j; μ j is the weight coefficient of department j; x j and D j are the actual water supply and the minimum demand respectively; p i represents the pollution intensity of water source i; x i represents the amount of water taken from water source i; economic benefits, social benefits and ecological and environmental benefits are represented by water supply cost, water supply income and total amount of pollutants respectively; Establish constraints, including water supply capacity constraints, demand satisfaction constraints, water quality requirements constraints, water supply structure constraints, and non-negativity constraints: Where: S i The maximum water supply capacity of water source i; D j is the minimum water demand of department j; q i is the water quality index of water source i; Q j is the water quality requirement of department j; α j i and β j i They represent the minimum and maximum proportion of water obtained by department j from source i; The NSGA-II algorithm is used to solve various water source utilization models and obtain the Pareto frontier solution set. Simulated annealing is used to locally optimize the Pareto frontier solution set and obtain the amount of reinjection outside the curtain Q under the premise of meeting various water demands in the mining area. r .

3. The open-pit mine drainage and water-reinjection coal mining technology and optimization method according to claim 1, characterized in that: In step S4, in order to finely characterize the mine drainage boundary, curtain and reinjection well, a quadtree grid is used for modeling; Because the vertical velocity of the phreatic water around the curtain and the pit is relatively large, a regional scale phreatic water unsteady flow mathematical model without considering the Dupuit hypothesis is adopted: Given a hydraulic head boundary: H(x,y,z,t) t＝0 =H0 x,y,z∈Ω,t≥0(11) Waterproof border: Given a flow boundary: Where: μ s is the water supply degree of the phreatic aquifer; H is the hydraulic head; K is the permeability tensor of the aquifer, obtained through hydrogeological data or field experiments; ε is the source and sink term per unit time, including rainfall infiltration, river recharge, mine drainage, and reinjection outside the curtain; for a certain grid (i, j, k) of the model: ε i,j,k =(Q p | i,j,k +Q h | i,j,k -Q r | i,j,k -Q d | i,j,k ) / ΔV i,j,k (14) Where: Q p | i,j,k Recharged by rainfall infiltration; Q h | i,j,k is the water exchange at a given head boundary; Q r | i,j,k The amount of water used for reinjection after optimization of mine water allocation; Q d | i,j,k is the drainage volume at the mine boundary; ΔV i,j,k is the grid unit volume; The boundary of the mine pit is the drainage boundary, and the drainage volume of the model grid to the boundary is: Where: K d is the equivalent hydraulic conductivity; H i,j,k is the hydraulic head of the model grid; d b | i,j,k is the bottom elevation of the mine drainage boundary; PEST is used to calibrate the model parameters. The objective function is solved for the minimum value based on the Levenberg-Marquardt algorithm. The objective function is the weighted variance between the calculated value of the model parameter and the actual observed value: Where: w i is the weight coefficient; H i obs H is the observed water head; i sim To simulate the water head.

4. The open-pit mine drainage and water-reinjection coal mining technology and optimization method according to claim 1, characterized in that: In step S5, the designed reinjection method is no-pressure or micro-pressure constant flow reinjection; the straight-line distance between the reinjection wells outside the curtain is d, and the distance between the wells is d r , the single well reinjection volume is Q i , the number of wells is N, and the total amount of reinjection is The following conditions are met: (1) the total amount of reinjection does not exceed the amount available for reinjection or the maximum reinjection potential of the aquifer, (2) The water level rise caused by reinjection reaches the expected level and is conducive to ecological recovery. (3) The increase in drainage volume caused by curtain overflow and curtain bypass does not exceed expectations, ΔQ d <ΔQ d,0 ; (4) The groundwater quality caused by reinjection meets the Class III water standard, If the above conditions are not met, the reinjection water quality, well spacing and reinjection water volume are further optimized.

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