Multi-well joint control mining method for brine mining area

Abstract

The application provides a multi-well joint control mining method for a brine mining area, and belongs to the field of hydrogeology and groundwater dynamics. Based on a multi-well joint control pattern of "central pumping-fourth surrounding water injection", a plurality of directional transverse seepage means are forced to form to effectively displace high-salinity brine in a weak permeable layer and release the brine to a mining well in a directional manner, so that the brine yield and mining efficiency are significantly improved, and the brine yield increasing effect is obvious. The method comprises the following steps: arranging a well group in a target brine mining area, wherein the well group comprises a mining well and water injection wells arranged around the mining well; pumping underground brine through the mining well, and injecting the pumped brine into the underground through the water injection wells after treatment, to form a closed loop of "pumping-treatment-water injection-displacement"; and using the injection pressure of the water injection wells and the suction negative pressure of the mining well to form a directional hydraulic gradient pointing to the mining well, to drive the injected fluid to forcibly flow transversely through the weak permeable layer and displace the high-salinity brine in the weak permeable layer to the mining well.

Description

Technical Field

[0001] This application relates to the fields of hydrogeology and groundwater dynamics, and specifically proposes a method for increasing production in brine mining areas by improving the release efficiency of brine in weakly permeable layers through multi-well joint control and pumping-injection circulation to enhance lateral seepage. Background Technology

[0002] The underground brine areas distributed along my country's coast are important salt resource producing areas, rich in useful components such as sodium chloride, potassium chloride, and bromine, serving as raw material sources for industries such as salt chemical industry and bromine extraction. For a long time, coastal brine extraction has mainly employed single-well extraction methods, directly drawing brine from aquifers through boreholes. However, with the continuous development of coastal brine resources, existing extraction methods are facing the following increasingly prominent problems.

[0003] Firstly, coastal brine deposits typically consist of alternating layers of highly permeable aquifers and low-permeability, weakly permeable layers. Under long-term, large-scale mining, the recoverable brine in the aquifers is gradually depleted, increasing pressure on resource supply. Exploration data shows that although the weakly permeable layers have poor permeability, they contain large amounts of high-salinity brine in their pores, with pore water salinity reaching 2-3 times that of adjacent aquifers, making them a potential and important source of salt. However, in traditional single-well extraction, the water flow is mainly radial, preferentially converging along the high-permeability aquifers into the wellbore, with extremely limited displacement effect on the weakly permeable layers. This results in the large amount of high-salinity brine contained in the weakly permeable layers being difficult to effectively extract, forming de facto "dead reserves" and causing resource waste.

[0004] Secondly, coastal areas have complex geological conditions, with the weakly permeable layer mainly consisting of clay layers, whose permeability coefficient is typically below 0.1 m / d. Current technologies lack methods to enhance lateral seepage in weakly permeable layers, making it impossible to actively drive the forced release of salt from low-permeability strata, thus hindering the full utilization of this important salt reservoir.

[0005] Furthermore, long-term extraction from a single well can easily lead to a decrease in formation pressure, causing geological and environmental problems such as land subsidence and seawater intrusion, further exacerbating the ecological and environmental pressures on coastal areas. At the same time, production declines significantly in the later stages of extraction, reducing the economic benefits of mining, and traditional methods are no longer sufficient to meet the current needs of sustainable development of coastal brine resources.

[0006] Therefore, there is an urgent need to develop a brine production enhancement method that can be tailored to the characteristics of coastal brine mining areas, strengthen brine release from weakly permeable layers, increase recovery rates, and maintain formation pressure. Summary of the Invention

[0007] In view of this, the purpose of this application is to provide a multi-well joint control mining technology solution for brine mining areas. Based on the multi-well joint control pattern of "central pumping and surrounding water injection", the high-salt brine in the weak permeable layer is effectively driven to be released into the mining well by forcibly forming lateral seepage in multiple directions, thereby significantly improving brine production and mining efficiency, and the brine production increase effect is obvious.

[0008] To achieve the aforementioned objectives, the multi-well coordinated mining method for brine extraction areas involves setting up a well group in the target brine extraction area. The well group includes a single extraction well and several injection wells arranged around the extraction well. Utilizing the combined effect of the injection pressure from the injection wells and the suction negative pressure from the extraction wells, a directional lateral seepage flow is forcibly formed between the extraction well and the injection wells, directed towards the extraction well. This actively displaces the high-salinity brine from the pore water of the low-permeability, weakly permeable layer, continuously releasing it into the extraction well. Step S1, Well Group Layout; Core analysis or well logging methods were used to confirm that the pore water salinity of the target weakly permeable layer was higher than that of the adjacent aquifer; several injection wells were evenly arranged around the production well as the center. Step S2: Reinjection water treatment; While extracting underground brine through mining wells, the extracted brine undergoes desalination treatment. The results of desalination treatment and mineralization control are as follows: Assuming the original formation brine mineralization is... The target reinjected water salinity is Then the desalination ratio coefficient Desalination ratio coefficient The value range is 0.20 to 0.80; the treated low-mineralization water is temporarily stored in a reservoir in preparation for reinjection; Regarding the desalination ratio coefficient A dynamic adjustment mechanism is adopted to dynamically adjust the salt release effect based on the weak permeability layer. When the salinity of the water produced from the extraction well is monitored Continue to rise, When the increase is greater than 1 g / L·d, it indicates that the salt release flux of the weak permeable layer is sufficient, the concentration gradient drive is still effective, and the salinity of the reinjected water is increased, thus maintaining the production increase effect while reducing desalination energy consumption. When detected The trend is towards stabilization or decline. When this occurs, it indicates that the driving force of the concentration gradient weakens, reducing the salinity of the reinjected water; Desalination ratio coefficient The adjustment step size does not exceed 0.05 at a time, and after adjustment, one hydraulic response cycle is completed. , Well spacing The effect will be evaluated after the seepage rate is determined. Step S3: Cyclic injection; The treated low-mineral water is simultaneously injected underground through all the injection wells; Step S4: Lateral seepage displacement; Under the combined action of the injection pressure in the injection well and the suction negative pressure in the production well, a directional hydraulic gradient is formed in the formation pointing towards the production well. Driven by this hydraulic gradient, the injected low-mineralized water is forced to seep laterally, penetrating the weakly permeable layer with low permeability. This drives the salt in the weakly permeable layer to change from a molecular diffusion mode to a convection-diffusion mode. Step S5: Parameter adjustment and optimization; Based on the dynamic feedback of various monitoring indicators, parameters such as injection flow rate, injection pressure, reinjection water salinity, and well spacing are dynamically adjusted.

[0009] A mining well is set up in the center of the well group in the target brine mining area, and the mining wells are arranged symmetrically and equidistantly.

[0010] The extraction wells are constructed by modifying existing extraction wells or abandoned wells in the brine extraction area. The extracted brine is treated and then recycled back into several injection wells.

[0011] In step S1, the distance between the injection well and the production well is determined comprehensively based on factors such as formation permeability, thickness of the weak permeable layer and injection pressure. It can be optimized through numerical simulation or on-site injection test, and the distance range is 30m to 100m.

[0012] Step S2 includes membrane separation, using nanofiltration or reverse osmosis membrane modules, with the operating pressure controlled between 0.8 and 2.5 MPa, and the salinity of the product water side... With influent salinity satisfy: in, For desalination rate, reverse osmosis membrane Typical values ​​are 90%–98%; Online turbidity meters and conductivity sensors monitor the quality of the produced water in real time. A PLC control system automatically adjusts the opening of the blending valves based on conductivity feedback. Keep the value within ±5% of the target value; install a security filter before the membrane module and perform regular chemical cleaning to prevent fouling and clogging of the membrane surface.

[0013] Step S2 includes a thermal evaporation method, employing a multi-effect evaporation or multi-stage flash evaporation device. The brine is sequentially evaporated and concentrated in each effect evaporator. After the steam is condensed, low-mineralization condensate is formed. By adjusting the mixing ratio of the condensate and the original liquid, the mineralization of the reinjected water is controlled at the target value. Within the range.

[0014] Step S2 includes a chemical precipitation method, in which Ca(OH)2 is added to the brine at a dosage of 1.0-2.0 g / L and soda ash Na2CO3 at a dosage of 0.5-1.0 g / L, which precipitate CaCO3 and Mg(OH)2 respectively. After the sedimentation tank is in a settling tank for a period of ≥2 hours, the supernatant is filtered through quartz sand at a rate of 5-8 m / h and then discharged.

[0015] Step S3 includes adjusting the water injection pressure; Water injection pressure The unit is MPa, and the following constraints must be met: in, The minimum injection pressure required to maintain the lowest lateral seepage velocity, Formation fracture pressure, in MPa; formation fracture pressure Obtain the pressure through on-site water injection testing or estimate it using the following formula: in, Poisson's ratio of the strata, The effective stress of the overlying strata is expressed in MPa. Formation tensile strength, in MPa; minimum water injection pressure. Based on the expected minimum lateral seepage velocity and permeability coefficient of weakly permeable layer Its unit is m / d: in, For the first The distance between the injection well and the production well, in meters. Pick N / m³; Implementation steps: Each injection well is equipped with a digital pressure transmitter, and the upper limit of the injection pressure is set by the PLC system. The pressure is gradually increased in increments of 0.05 MPa, with each pressure increase stabilizing for at least 30 minutes. At the same time, the formation pressure response is monitored. If the wellhead pressure of a certain direction well has reached the upper limit but the seepage velocity is still insufficient, the hydraulic gradient is supplemented by increasing the power of the pump. Calculation and control of water injection volume distribution in each injection well; The total water injection volume of the injection wells and the water pumping volume of the production wells are kept in dynamic balance in order to maintain stable formation pressure. The injection volume of each injection well is determined based on the equivalent permeability coefficient of the weak permeable layer in each direction and the well spacing. More injection volume is allocated to the direction with higher permeability and closer well spacing. Assume the pumping rate of the well is The unit is m³ / d, representing the total water injection volume of all injection wells. Water volume allocated to each injection well Determine by the following formula: Weight Taking into account both well spacing and formation heterogeneity: in, For the first The equivalent permeability coefficient of the weakly permeable layer along the path between the injection well and the production well, expressed in m / d, is obtained through pumping tests or formation testing. This corresponds to the well spacing, in meters (m). When the actual total water injection volume deviates from the pumping volume by more than 5%, the PLC system automatically adjusts the output frequency of each water injection pump inverter proportionally to restore the total water injection volume to balance.

[0016] Step S5 includes establishing the following multi-parameter linkage control model: (1) Status monitoring indicator system; Define real-time monitoring indicators, including the salinity of water produced from production wells. Hydraulic gradients in all directions The ratio of injection pressure to formation fracturing pressure in each injection well Concentration gradient of weakly permeable layer And as a regulatory input; (2) Multi-parameter linkage control matrix; The monitoring indicators are combined with adjustable parameters, including injection flow rate. Water injection pressure Reinjected water salinity Well spacing The response relationship between them is integrated into the following control matrix M: Among them, each element of matrix M Indicates the first The monitoring deviation affects the first Adjustment weights for each adjustable parameter; (3) Regulation logic and priority: The PLC system periodically collects all monitoring indicators and performs control measures according to priority. (4) Parameter adjustment boundary conditions: The following boundary constraints must be met when adjusting each parameter: , , , When the matrix calculation result exceeds the above boundary, the boundary value is taken and executed, and an early warning is issued to the operator.

[0017] The priorities for implementing regulation include: First priority: If any injection well Immediately reduce the injection pressure of the well, while increasing the power of the pump to compensate for hydraulic gradient loss and prevent formation fracturing. Second priority: If If the decrease is greater than 2 g / L·d, proceed with the reduction sequentially. Increase the pumping volume of the well. ,improve ; Third priority: Periodic evaluation The cumulative trend; if the average over 30 consecutive days If the decrease exceeds 20%, a well spacing optimization assessment will be initiated, and the well spacing will be re-optimized through numerical simulation. When conditions permit, construction should be carried out to increase the density or spacing of wells.

[0018] In summary, the beneficial effects and advantages of this application compared with the prior art include: 1. This application, through a well cluster pattern of "one extraction and four injections," transforms the radial flow method used in existing technologies into a directional transverse seepage method. Therefore, it can force the injected fluid to penetrate the weakly permeable layer, forcibly replace and activate the high-salt brine contained in the weakly permeable layer, thereby increasing the production of non-traditional brine-producing layers and achieving high economic benefits.

[0019] 2. This application creates a concentration gradient between the reinjected low-mineralized water and the high-concentration brine in the pores of the weakly permeable layer, thereby driving the salt to change from molecular diffusion to convection-diffusion. At the same time, the pressure difference between the injection well and the pumping well will form a stable hydraulic gradient. Under this dual effect, the salt dissolution efficiency can be significantly improved, which is an extremely important and stable promoting factor for brine production.

[0020] 3. This application effectively maintains formation pressure by controlling the dynamic balance of injection and extraction flow rates, thereby avoiding ground subsidence caused by long-term extraction, extending the production life of brine wells, and correspondingly reducing production costs.

[0021] 4. This application can utilize existing mining wells or abandoned wells for renovation, which can not only reduce engineering construction costs, but also achieve water resource recycling after the extracted brine is treated and reinjected, thus having social benefits of zero discharge and environmental protection. Attached Figure Description

[0022] The accompanying drawings, which are included to provide a further understanding of this application and form part of this application, illustrate exemplary embodiments and are used to explain this application, but do not constitute an undue limitation of this application. Some specific embodiments of this application will be described in detail below with reference to the accompanying drawings in an exemplary and non-limiting manner. The same reference numerals in the drawings designate the same or similar parts or components. It should be understood by those skilled in the art that these drawings are not necessarily drawn to scale.

[0023] Figure 1 This is a top view schematic diagram of the well group arrangement in the embodiment; Figure 2 This is a schematic cross-sectional view of the transverse seepage displacing of salt in the weakly permeable layer in the embodiment. Figure 3 This is a flowchart of the multi-well joint control mining method for brine mining areas described in this application; In the above-mentioned attached diagram, there is a mining well 1, a first water injection well 2, a second water injection well 3, a third water injection well 4, a fourth water injection well 5, and a brine mining area 6. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0025] Example 1, as Figures 1 to 3 As shown, in response to the problem of low single-well mining efficiency in existing brine mining areas, this application innovatively proposes a multi-well joint control mining method, which is applicable to coastal brine mining area 6. The geological conditions of this mining area are multi-layered, consisting of a cover layer, an aquifer, and a weakly permeable layer from top to bottom. Although the weakly permeable layer has low permeability, its pores generally contain high-salt brine, which has the potential to increase production.

[0026] Specifically, based on a multi-well joint control and simultaneous pumping and injection exploitation method, a directional lateral seepage is forcibly formed between the production wells and the injection wells. This actively displaces the high-salinity brine in the pore water of low-permeability, weakly permeable layers, continuously releasing it into the production well area. This effectively addresses the shortcomings of existing technologies in enhancing lateral seepage in weakly permeable layers, thereby achieving increased production from non-traditional brine-producing layers; including... A well group is set up in the target brine mining area. The strata in the target brine mining area have an alternating structure of aquifer and weakly permeable layer. The weakly permeable layer is a stratum unit in the brine mining system with lower permeability than aquifer, but containing high-salt brine. The well group includes a production well and injection wells arranged around the production well; The brine is extracted from the ground through mining wells, and after being treated, it is reinjected back into the ground through injection wells, forming a closed-loop cycle of "pumping-treatment-injection-displacement". By utilizing the injection pressure of the injection well and the suction negative pressure of the production well, a directional hydraulic gradient is formed pointing towards the production well, driving the injected fluid to force transverse seepage through the weak permeable layer, displacing the high-salt brine in the weak permeable layer and transporting it towards the production well.

[0027] In this embodiment, a mining well 1 is set at the center of the well group in the target brine mining area. Several injection wells are set symmetrically and equidistantly around the mining well 1, such as the first injection well 2, the second injection well 3, the third injection well 4 and the fourth injection well 5 set in this embodiment. Through the combined effect of the fluid pressure injected synchronously by several injection wells and the negative pressure of the extraction well, the injected fluid is driven to seep laterally through the weak permeable layer, and the high-salt brine in the weak permeable layer is displaced and transported to the mining well area. The extraction well 1 can be an existing extraction well or an abandoned well. The extracted brine is treated and then recycled back into several injection wells.

[0028] The multi-well coordinated mining method in the brine extraction area has the following implementation process: Step S1, Well Group Layout; At the beginning of the operation, core analysis or well logging methods are used to confirm that the pore water salinity of the target weakly permeable layer is higher than that of the adjacent aquifer, so as to identify the target brine mining area with the conditions for increased production. For a defined brine extraction area, an existing extraction well is selected as the extraction well, and several injection wells are evenly distributed around it, with the injection wells arranged symmetrically and equidistant from the extraction well. Figure 1 As shown, the four water injection wells are distributed in a square or rhombus shape; The spacing between injection wells and production wells is determined comprehensively based on factors such as formation permeability, thickness of the aquifer, and injection pressure, with a selectable range of 30m to 100m. The specific values ​​are determined as follows: First, the well spacing range is initially estimated based on the permeability coefficient of the aquifer in the target production area and the expected radius of lateral seepage influence; second, a hydrogeological numerical model of the production area is established to simulate the lateral seepage field distribution and salt displacement effect under different well spacing conditions; finally, with the goal of maximizing the salt release efficiency of the aquifer, the optimal well spacing is selected within the range of 30m to 100m. When conditions permit, the numerical simulation results can be verified and corrected by combining the results of on-site water injection tests. Step S2: Reinjection water treatment; While extracting underground brine through mining wells, the extracted brine is desalinated to reduce its mineralization to 20%-80% of the original formation brine in order to achieve a concentration gradient between the injected water and the pore water in the weakly permeable layer. The desalination process employs one or more of the following methods: membrane separation, thermal evaporation, or chemical precipitation.

[0029] Desalination treatment primarily utilizes membrane separation (reverse osmosis), which is suitable for scenarios with large treatment volumes and high requirements for effluent quality. In scenarios where waste heat resources are available, thermal evaporation methods, such as multi-effect evaporation or multi-stage flash evaporation, can be used as an alternative. In scenarios where the main objective is to prevent scaling, chemical precipitation methods, such as adding lime or soda ash to remove calcium and magnesium ions, can be used as an alternative. The above three methods can also be combined depending on site conditions.

[0030] The results of desalination treatment and mineralization control are as follows: assuming the original formation brine mineralization is... (g / L), target reinjected water salinity is Then the desalination ratio coefficient Desalination ratio coefficient The value range is 0.20 to 0.80; the treated low-mineralization water is temporarily stored in a reservoir in preparation for reinjection; (1) Membrane separation method; Nanofiltration (NF) or reverse osmosis (RO) membrane modules are used. Taking reverse osmosis as an example, the operating pressure is controlled between 0.8 and 2.5 MPa, and the salinity of the product water is... With influent salinity satisfy: in, For desalination rate, reverse osmosis membrane Typical values ​​are 90%–98%; Online turbidity meters and conductivity sensors monitor the quality of the produced water in real time. A programmable logic controller (PLC) system automatically adjusts the opening of the blending valves based on conductivity feedback. Keep the value within ±5% of the target value. Install a security filter (5μm accuracy) before the membrane module and perform regular chemical cleaning to prevent fouling and clogging of the membrane surface.

[0031] (2) Thermal evaporation method: Multi-effect evaporation (MEE) or multi-stage flash evaporation (MSF) devices are used; taking multi-effect evaporation as an example, the brine is evaporated and concentrated in each effect evaporator in turn, and the steam is condensed to form low-mineralized condensate; (3) Chemical precipitation method: Lime slurry (Ca(OH)2, 1.0–2.0 g / L) and soda ash (Na2CO3, 0.5–1.0 g / L) are added to the brine, causing Ca²⁺ and Mg²⁺ to precipitate as CaCO3 and Mg(OH)2, respectively. After gravity settling in a sedimentation tank for ≥2 hours, the supernatant is filtered through quartz sand at a rate of 5–8 m / h before being discharged. The main purpose of this method is to soften and reduce hardness, but the reduction in mineralization is limited, typically 5%–15%. Further reductions in mineralization to... The target range requires combination with membrane separation. Furthermore, regarding the desalination ratio coefficient A dynamic adjustment mechanism is adopted, that is, the adjustment is made dynamically according to the salt release effect of the weakly permeable layer. The adjustment logic is as follows: When the salinity of the water produced from the extraction well is monitored Continue to rise, when When the increase is >1 g / L·d, it indicates that the salt release flux of the weakly permeable layer is sufficient, the concentration gradient driving is still effective, and the concentration gradient can be appropriately increased. That is, to increase the salinity of the reinjected water, thereby reducing desalination energy consumption while maintaining increased production; When detected tending to stabilize or decline, when When this occurs, it indicates that the driving force of the concentration gradient is weakening, and the concentration should be reduced. That is, to further reduce the salinity of the reinjected water in order to restore the concentration gradient between the weakly permeable layer and the injected water and maintain the salt release flux; Desalination ratio coefficient The adjustment step size is no more than 0.05 at a time, and after adjustment, one hydraulic response cycle is elapsed. , Well spacing The effect should be evaluated after the seepage rate is adjusted to prevent over-adjustment from causing system oscillation. Step S3: Cyclic injection; The treated low-mineral water is simultaneously injected underground through all the injection wells; The water injection pressure is adjusted according to the formation fracturing pressure and water injection capacity. The engineering range of water injection pressure is 0.3 to 1.5 MPa, with the actual limit being [missing value]. The smaller of 1.5 MPa; The water injection volume of each injection well is allocated according to factors such as well spacing and formation heterogeneity. The total water injection volume of the four wells and the water pumping volume of the production well are kept in dynamic balance to maintain formation pressure stability and avoid large fluctuations in formation pressure.

[0032] (1) Regulation of water injection pressure; Water injection pressure The unit is MPa, and the following constraints must be met: in, The minimum injection pressure required to maintain the lowest lateral seepage velocity, Formation fracture pressure, in MPa; formation fracture pressure Obtained through on-site water injection pressure testing, or estimated using the following formula: in, The Poisson's ratio of the strata (typical value for clay layers: 0.35–0.45). The effective stress of the overlying strata is expressed in MPa and is equal to the unit weight of the overlying strata multiplied by the burial depth. The tensile strength of the stratum is expressed in MPa, with a typical value of 0.1–0.3 MPa for clay layers. Minimum water injection pressure Based on the expected minimum lateral seepage velocity The value can be 0.01 m / d and the permeability coefficient of the weakly permeable layer. The unit is m / d. Let's calculate backwards: in, For the first The distance between the injection well and the production well, in meters. Pick N / m³ brine; Implementation steps: Each injection well is equipped with a digital pressure transmitter at its wellhead, with a range of 0–2 MPa and an accuracy of ±0.25%FS. The upper limit of the injection pressure is set by the PLC system. (A 10% safety margin can be left), gradually increase the pressure in increments of 0.05 MPa, with each step of pressure increase stabilization time not less than 30 minutes, while monitoring the formation pressure response (judged by changes in water level in each well). If the wellhead pressure of a well in a certain direction has reached the upper limit but the seepage velocity is still insufficient, prioritize increasing the power of the pump to supplement the hydraulic gradient. (2) Calculation and control of water injection volume distribution in each injection well; The total water injection volume of the injection wells and the water pumping volume of the production wells are kept in dynamic balance in order to maintain stable formation pressure. The injection volume of each injection well is determined based on the equivalent permeability coefficient of the weak permeable layer in each direction and the well spacing. More injection volume is allocated to the direction with higher permeability and closer well spacing. Assume the pumping rate of the well is The unit is m³ / d, the total water injection volume of the four injection wells. Water volume allocated to each injection well Determine by the following formula: Weight Taking into account both well spacing and formation heterogeneity: in, For the first The equivalent permeability coefficient of the weakly permeable layer along the path between the injection well and the production well, expressed in m / d. Obtained through pumping tests or formation tests; The corresponding well spacing is in meters (m).

[0033] When the actual total water injection volume deviates from the pumping volume by more than 5%, the PLC system automatically adjusts the output frequency of each water injection pump inverter proportionally to restore the total water injection volume to balance within 2 minutes. Step S4: Lateral seepage displacement; Under the combined action of the injection pressure (push) of the injection well and the suction negative pressure (pull) of the production well, a directional hydraulic gradient is formed in the formation pointing towards the production well; Driven by the hydraulic gradient, the injected low-mineralized water is forced to seep laterally, penetrating the weakly permeable layer with low permeability. At the same time, a concentration gradient is formed between the injected water and the high-concentration brine in the pores of the weakly permeable layer, driving the salt in the weakly permeable layer to change from molecular diffusion mode to convection-diffusion combined release mode, accelerating the dissolution of salt. like Figure 2 As shown, with the continuous circulation and injection, the high-salinity brine in the weakly permeable layer is constantly displaced and replaced, migrating towards the production well, and eventually extracted by the production well; the entire circulation process flow diagram is as follows. Figure 3 As shown; (1) Calculation and implementation of directional hydraulic gradient: Water injection well (number) =1-4) and the directional hydraulic gradient formed between the well and the production well Determined by the following formula: = / ; in, For the first The head difference (m) between the pressure head at the wellhead of the injection well and the dynamic water level in the production well. For the first The straight-line distance between the injection well and the production well, in meters; The calculation method is as follows: =( - ) / ( )+( - ); in, For the first Injection pressure at the wellhead of the injection well (Pa). The negative pressure (Pa, negative value during pumping) is the pressure at which the well is pumped. The density of groundwater is (kg / m³, for brine it is 1050-1200 kg / m³). The acceleration due to gravity is 9.81 m / s². and The elevations (m) of the injection well and the pumping well are respectively. (2) Establishment and quantification of concentration gradient: Concentration gradient between injected water and pore water in the weakly permeable layer (g / L·m) is determined by the following formula: ; in, The original pore water salinity (g / L) of the weakly permeable layer. The salinity of the reinjected water (g / L, i.e., the output of step S2) = ), Thickness of the permeable layer (m); The convection-diffusion flux F_s (g / m²·d) of salt driven by the concentration gradient is described by the following equation: ; in The effective porosity of the weakly permeable layer (typical value 0.30-0.45). The pore flow velocity is (m / d). The effective diffusion coefficient of the weakly permeable layer (m² / d, typical value 0.005-0.02m² / d). During implementation, a pressure transmitter (range 0–2 MPa, accuracy ±0.25%FS) was installed at the wellhead of each injection well, and a water level gauge (accuracy ±1 cm) and a salinity sensor were installed in the production wells. Monitoring wells were also installed in the weakly permeable layer to periodically collect pore water samples for monitoring. The dynamic changes; the hydraulic gradient in each direction is calculated in real time by the PLC control system. Value, when (It is recommended that the minimum gradient threshold be set to 0.01) When this is the case, the injection pressure of the corresponding injection well will be automatically increased to ensure the lateral seepage velocity within the weakly permeable layer. m / d; simultaneously monitor concentration gradient changes, when rate of descent When the concentration is below the threshold (recommended value is 0.5 g / L·d), the desalination ratio coefficient in step S2 will be adjusted accordingly. A dynamic adjustment mechanism reduces the salinity of reinjected water to restore the concentration gradient driving force. Step S5: Parameter adjustment and optimization; To achieve coordinated dynamic optimization of multiple parameters such as injection flow rate, injection pressure, reinjection water salinity, and well spacing, the following multi-parameter linkage control model is established; (1) Status monitoring indicator system; The following four real-time monitoring indicators are defined as control inputs: : Mineralization of well water produced, expressed in g / L, reflects the salt release effect of the weakly permeable layer; Hydraulic gradient in each direction, in m / m, reflects the driving force of injection-production pressure difference; The ratio of injection pressure to formation fracturing pressure in each injection well. This reflects the safety margin of formation pressure; Concentration gradient of the weakly permeable layer, in g / L·m, reflects the strength of the diffusion driving force.

[0034] (2) Multi-parameter linkage control matrix; The above four monitoring indicators are combined with four adjustable parameters, including injection flow rate. Water injection pressure Reinjected water salinity Well spacing The response relationships between them are integrated into the following control matrix. : Among them, matrix Each element Indicates the first The monitoring deviation affects the first The adjustment weights of the adjustable parameters are shown in the table below: Explanation of matrix element symbols: Positive values ​​indicate that when the deviation of the monitoring indicator increases, the corresponding control parameter should increase in the same direction; negative values ​​indicate that it should be adjusted in the opposite direction; 0 indicates that the monitoring indicator has no direct impact on the control parameter. The larger the absolute value of the weight, the more sensitive the control response.

[0035] (3) Regulation logic and priority: The PLC system collects all monitoring indicators every hour and performs control according to the following priorities: First priority (safety constraint): If any injection well... Immediately reduce the injection pressure of the well, while increasing the power of the pump to compensate for hydraulic gradient loss and prevent formation fracturing. Second priority (production increase target): If If the decrease is greater than 2 g / L·d, perform the following steps in sequence: ① Reduce (Adjust step size not exceeding 0.05) → ② Increase (Step size 5% of rated flow) → ③ Increase (Step size 0.05MPa); Third priority (long-term optimization): Evaluate every 30 days. The cumulative trend; if the average over 30 days If the decrease exceeds 20%, a well spacing optimization assessment will be initiated, and the well spacing will be re-optimized through numerical simulation. When conditions permit, construction should be carried out to increase the density or spacing of wells.

[0036] (4) Parameter adjustment boundary conditions: The following constraints must always be met when adjusting each parameter: When the matrix calculation result exceeds the above boundary, the boundary value is taken and executed, and an early warning is issued to the operator, who then judges whether the system operation mode needs to be adjusted.

[0037] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A multi-well coordinated mining method for brine extraction areas, characterized in that: A well cluster is established in the target brine extraction area. The well cluster includes a single extraction well and several injection wells arranged around the extraction well. Utilizing the combined injection pressure of the injection wells and the suction negative pressure of the extraction wells, a directional lateral seepage flow is forcibly formed between the extraction well and the injection wells, directed towards the extraction well. This actively displaces the high-salinity brine from the pore water of the low-permeability, weakly permeable layer, continuously releasing it into the extraction well. Step S1, Well Group Layout; Core analysis or well logging methods were used to confirm that the pore water salinity of the target weakly permeable layer was higher than that of the adjacent aquifer; several injection wells were evenly arranged around the production well as the center. Step S2: Reinjection water treatment; While extracting underground brine through mining wells, the extracted brine undergoes desalination treatment. The results of desalination treatment and mineralization control are as follows: Assuming the original formation brine mineralization is... The target reinjected water salinity is Then the desalination ratio coefficient Desalination ratio coefficient The value range is 0.20 to 0.80; the treated low-mineralization water is temporarily stored in a reservoir in preparation for reinjection; Regarding the desalination ratio coefficient A dynamic adjustment mechanism is adopted to dynamically adjust the salt release effect based on the weak permeability layer. When the salinity of the water produced from the extraction well is monitored Continue to rise, When the increase is greater than 1 g / L·d, it indicates that the salt release flux of the weak permeable layer is sufficient, the concentration gradient drive is still effective, and the salinity of the reinjected water is increased, thus maintaining the production increase effect while reducing desalination energy consumption. When detected The trend is towards stabilization or decline. When this occurs, it indicates that the driving force of the concentration gradient weakens, reducing the salinity of the reinjected water; Desalination ratio coefficient The adjustment step size does not exceed 0.05 at a time, and after adjustment, one hydraulic response cycle is completed. , Well spacing The effect will be evaluated after the seepage rate is determined. Step S3: Cyclic injection; The treated low-mineral water is simultaneously injected underground through all the injection wells; Step S4: Lateral seepage displacement; Under the combined action of the injection pressure in the injection well and the suction negative pressure in the production well, a directional hydraulic gradient is formed in the formation pointing towards the production well. Driven by this hydraulic gradient, the injected low-mineralized water is forced to seep laterally, penetrating the weakly permeable layer with low permeability. This drives the salt in the weakly permeable layer to change from a molecular diffusion mode to a convection-diffusion mode. Step S5: Parameter adjustment and optimization; Based on the dynamic feedback of various monitoring indicators, the parameters of injection flow rate, injection pressure, reinjection water salinity, and well spacing are dynamically adjusted.

2. The multi-well coordinated mining method for brine extraction areas according to claim 1, characterized in that: A mining well is set up in the center of the well group in the target brine mining area, and the mining wells are arranged symmetrically and equidistantly.

3. The multi-well coordinated mining method for brine extraction areas according to claim 2, characterized in that: The extraction wells are constructed by modifying existing extraction wells or abandoned wells in the brine extraction area. The extracted brine is treated and then recycled back into several injection wells.

4. The multi-well coordinated mining method for brine extraction areas according to claim 1, characterized in that: In step S1, the distance between the injection well and the production well is determined comprehensively based on factors such as formation permeability, thickness of the weak permeable layer, and injection pressure. It can be optimized through numerical simulation or on-site injection tests, and the distance range is 30m to 100m.

5. The multi-well coordinated mining method for brine extraction areas according to claim 1, characterized in that: Step S2 includes membrane separation, using nanofiltration or reverse osmosis membrane modules, with the operating pressure controlled between 0.8 and 2.5 MPa, and the salinity of the product water side... With influent salinity satisfy: in, For desalination rate, reverse osmosis membrane Typical values ​​are 90%–98%; Online turbidity meters and conductivity sensors monitor the quality of the produced water in real time. A PLC control system automatically adjusts the opening of the blending valves based on conductivity feedback. Keep the value within ±5% of the target value; install a security filter before the membrane module and perform regular chemical cleaning to prevent fouling and clogging of the membrane surface.

6. The multi-well coordinated mining method for brine extraction areas according to claim 1, characterized in that: Step S2 includes a thermal evaporation method, employing a multi-effect evaporation or multi-stage flash evaporation device. The brine is sequentially evaporated and concentrated in each effect evaporator. After the steam is condensed, low-mineralization condensate is formed. By adjusting the mixing ratio of the condensate and the original liquid, the mineralization of the reinjected water is controlled at the target value. Within the range.

7. The multi-well coordinated mining method for brine extraction areas according to claim 1, characterized in that: Step S2 includes a chemical precipitation method, in which Ca(OH)2 is added to the brine at a dosage of 1.0-2.0 g / L and soda ash Na2CO3 at a dosage of 0.5-1.0 g / L, which precipitate CaCO3 and Mg(OH)2 respectively. After the sedimentation tank is in a settling tank for a period of ≥2 hours, the supernatant is filtered through quartz sand at a rate of 5-8 m / h and then discharged.

8. The multi-well coordinated mining method for brine extraction areas according to claim 1, characterized in that: Step S3 includes adjusting the water injection pressure; Water injection pressure The unit is MPa, and the following constraints must be met: in, The minimum injection pressure required to maintain the lowest lateral seepage velocity, Formation fracture pressure, in MPa; formation fracture pressure Obtain the pressure through on-site water injection testing or estimate it using the following formula: in, Poisson's ratio of the strata, The effective stress of the overlying strata is expressed in MPa. Tensile strength of the formation, in MPa; Minimum water injection pressure Based on the expected minimum lateral seepage velocity and permeability coefficient of weakly permeable layer Its unit is m / d: in, For the first The distance between the injection well and the production well, in meters. Pick N / m³; Implementation steps: Each injection well is equipped with a digital pressure transmitter, and the upper limit of the injection pressure is set by the PLC system. The pressure is gradually increased in increments of 0.05 MPa, with each pressure increase stabilizing for at least 30 minutes. At the same time, the formation pressure response is monitored. If the wellhead pressure of a certain direction well has reached the upper limit but the seepage velocity is still insufficient, the hydraulic gradient is supplemented by increasing the power of the pump. Calculation and control of water injection volume distribution in each injection well; The total water injection volume of the injection wells and the water pumping volume of the production wells are kept in dynamic balance in order to maintain stable formation pressure. The injection volume of each injection well is determined based on the equivalent permeability coefficient of the weak permeable layer in each direction and the well spacing. More injection volume is allocated to the direction with higher permeability and closer well spacing. Assume the pumping rate of the well is The unit is m³ / d, representing the total water injection volume of all injection wells. Water volume allocated to each injection well Determine by the following formula: Weight Taking into account both well spacing and formation heterogeneity: in, For the first The equivalent permeability coefficient of the weakly permeable layer along the path between the injection well and the production well, expressed in m / d, is given. Obtained through pumping tests or formation tests. This corresponds to the well spacing, in meters (m). When the actual total water injection volume deviates from the pumping volume by more than 5%, the PLC system automatically adjusts the output frequency of each water injection pump inverter proportionally to restore the total water injection volume to balance.

9. The multi-well coordinated mining method for brine extraction areas according to claim 1, characterized in that: Step S5 includes establishing the following multi-parameter linkage control model: (1) Status monitoring indicator system; Define real-time monitoring indicators, including the salinity of water produced from production wells. Hydraulic gradients in all directions The ratio of injection pressure to formation fracturing pressure in each injection well Concentration gradient of weakly permeable layer And as a regulatory input; (2) Multi-parameter linkage control matrix; The monitoring indicators are combined with adjustable parameters, including injection flow rate. Water injection pressure Reinjected water salinity Well spacing The response relationship between them is integrated into the following control matrix M: Among them, each element of matrix M Indicates the first The monitoring deviation affects the first Adjustment weights for each adjustable parameter; (3) Regulation logic and priority: The PLC system periodically collects all monitoring indicators and performs control measures according to priority. (4) Parameter adjustment boundary conditions: The following boundary constraints must be met when adjusting each parameter: , , , When the matrix calculation result exceeds the above boundary, the boundary value is taken and executed, and an early warning is issued to the operator.

10. The multi-well joint control mining method for brine mining areas according to claim 9, characterized in that: The priorities for implementing regulation include: First priority: If any injection well Immediately reduce the injection pressure of the well, while increasing the power of the pump to compensate for hydraulic gradient loss and prevent formation fracturing. Second priority: If If the decrease is greater than 2 g / L·d, proceed with the reduction sequentially. Increase the pumping volume of the well. ,improve ; Third priority: Periodic evaluation The cumulative trend; If the average over 30 consecutive days If the decrease exceeds 20%, a well spacing optimization assessment will be initiated, and the well spacing will be re-optimized through numerical simulation. When conditions permit, construction should be carried out to increase the density or spacing of wells.

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