Coastal underground reservoir residual saline water restoration method based on underground water exploitation

Abstract

According to the coastal underground reservoir residual saline water restoration method based on underground water exploitation, an exploitation well optimization technology capable of ensuring safe exploitation of underground fresh water and restoring residual saline water pollution is established by utilizing a ubiquitous underground water exploitation well and optimizing the form, the distribution and the capacity of the exploitation well; and the dual purposes of utilizing and protecting fresh water resources of the coastal underground reservoir are achieved. In order to solve the problem of underground reservoir residual salt water pollution, an exploitation well optimization technology capable of ensuring safe exploitation of underground fresh water and repairing residual salt water pollution is established by optimizing the form, the distribution and the capacity of an exploitation well by utilizing a ubiquitous underground water exploitation well.

Description

Technical Field

[0001] The present invention relates to the technical field of coastal saltwater restoration, and in particular to a method for restoring residual saltwater in a coastal underground reservoir based on groundwater exploitation. Background Art

[0002] In the late 1980s, due to years of drought, groundwater exploitation increased significantly, and many areas experienced large-scale groundwater drop funnels and seawater intrusion and other environmental geological problems. A new way of groundwater development and utilization, "underground reservoirs", began to be applied in the Shandong Peninsula. A water conservancy hub built using natural underground water storage space that has the functions of intercepting, regulating and utilizing groundwater flow has incomparable advantages over surface engineering. The development of underground reservoirs not only effectively increased the supply of water resources, but also basically eliminated the increasingly serious threat of seawater intrusion in the region, and has important application and promotion value for the development, utilization and protection of groundwater resources.

[0003] When building underground reservoirs in coastal areas, it is often necessary to take into account the dual needs of regulating water resources and preventing seawater intrusion. Basically, underground seepage dams need to be built to prevent the landward intrusion of downstream seawater. The commonly used construction materials for underground seepage dams are concrete, cement slurry, bentonite, etc. The bottom of the dam body is embedded in the aquifer waterproof bottom plate. The height of the dam body is generally close to the ground or the 0 m contour line, thus forming a full-section physical blockade of salt water advancing to the land, basically isolating the hydraulic connection between the underground reservoir and the downstream. According to geological conditions, common construction techniques include in-situ mixing method, steel sheet pile method, high-pressure jet grouting method, underground continuous wall method, etc. After the project is implemented, the residual salt water in the dam will inevitably be retained in the underground reservoir. Due to the isolated hydraulic connection, it cannot be removed by seaward discharge.

[0004] The retained residual salt water continues to move inland, polluting the groundwater and becoming a source of pollution that cannot be ignored in the groundwater reservoir. The practice of the Qingdao Dagu River Groundwater Reservoir Project shows that 20 years after the construction of the cut-off dam, the residual salt water pollution area increased to 15.17 km 2 The construction of underground reservoirs is to better utilize and protect freshwater resources, but the residual saltwater pollution caused by them goes against the original intention of the project. It is urgent to develop low-cost and effective in-situ remediation technology to remove residual saltwater and achieve the goal of protecting freshwater resources in underground reservoirs.

[0005] After the construction of coastal underground reservoirs, the residual salt water in the underground seepage dams is inevitably retained in the underground reservoirs due to the hydraulic connection with the downstream, and cannot be removed by discharge to the sea. The retained residual salt water continues to move inland, polluting the underground fresh water, and becoming a non-negligible pollution source for underground reservoirs. Existing technical solutions are either not universal or are theoretical and divorced from actual working conditions, and cannot solve the pollution problem of existing underground reservoirs.

[0006] Existing technical solutions 1) Application Publication No. CN114319404A: The present invention provides an underground curtain for preventing and controlling seawater intrusion and purifying residual salt water and a construction method thereof. According to the hydrogeological conditions of the coastal area, relevant areas such as seawater intrusion and underground aquifers are determined; the combined underground curtain includes two walls and is distributed front and back along the direction of groundwater flow, including an upper hanging wall located on one side of the inland underground aquifer and a sunken wall located on the side close to the seawater; the sunken wall is arranged at the bottom of the aquifer, and the lower part is embedded in the impermeable bedrock; the upper opening of the wall is located between the local sea level and the 10% seawater salinity contour line of the saltwater wedge; the upper hanging wall is arranged at the upper part of the aquifer, and is constructed from the surface, leaving an opening at the bottom of the aquifer, and the bottom end of the upper hanging wall needs to be lower than the top end of the sunken wall; the distance between the upper hanging wall and the sunken wall is 1 / 5 to 4 / 5 of the height of the sunken wall; through the technical scheme of the present invention, seawater intrusion can be effectively prevented and controlled, and residual salt water in the upstream groundwater source can be removed after the underground curtain is established.

[0007] 2) Academic paper "Study on the desalination process of residual salt water behind dam in unconfined aquifer under non-isothermal conditions" (Journal of Ocean University of China (Natural Science Edition), 2024, 54 (05): 115-124): This paper uses a site-scale two-dimensional groundwater-salt-heat coupled numerical model to study the impact of freshwater and saltwater temperature difference on the residual salt water retreat (desalination) process, and quantitatively evaluates the dynamic changes of residual salt water wedge length and total residual salt after dam construction. The paper assumes that there is a hydraulic connection between the groundwater reservoir and the downstream. By reducing the height of the underground seepage dam (to 53% of the aquifer thickness), the fresh water and residual salt water in the groundwater reservoir are allowed to bypass the dam top and discharge to the sea. Driven by the freshwater hydraulic gradient, the residual salt water gradually retreats, achieving the goal of removing residual salt water. This study provides a scientific reference for future groundwater reservoir construction and seepage dam height design.

[0008] 3) Academic paper "Utilization of pit lake on the cleaning process of residual saltwater in unconfined coastal aquifers" (Science of the Total Environment, 2021, 770: 144670): In the Dagu River underground reservoir in Qingdao, sand mining has formed an artificial sand pit with a depth of 8-26 m. The groundwater in the underground reservoir flows into the sand pit through lateral recharge, forming a surface pit lake with an area of ​​nearly 94 hectares. This paper proposes to use artificial pit lakes to accelerate the discharge of residual salt water, thereby gradually removing the residual salt water in the groundwater reservoir, and predicts the efficiency of artificial pit lakes in draining and repairing residual salt water through site monitoring and numerical simulation technology. It was found that when the pit lake discharge rate increased to 1.6×105 m 3 / d, the repair efficiency increased by 17 times and the repair time was shortened from 20 years to 5 years.

[0009] Both existing technologies (1) and (2) assume that there is a hydraulic connection between the underground reservoir and the downstream. By lowering the height of the underground seepage dam, the fresh water and residual salt water in the underground reservoir are allowed to bypass the dam top and discharge to the sea. Driven by the hydraulic gradient of fresh water, the residual salt water gradually retreats, achieving the goal of removing the residual salt water. In particular, in the existing technology (1), a suspended seepage dam with a diversion function is installed upstream of the underground physical dam to guide the groundwater flow into the residual salt water area and accelerate the purification of the residual salt water. These methods provide scientific references for the future construction of underground reservoirs and the height design of seepage dams, but they are not applicable to the currently built underground reservoirs. The reason is that the currently built underground physical dams often penetrate the aquifer, and their height is greater than the thickness of the aquifer, thereby completely isolating the hydraulic connection between the underground reservoir and the downstream, and the residual salt water cannot be discharged to the sea at all.

[0010] Existing technology (3) uses groundwater to drain into artificial pit lakes to accelerate the purification of residual salt water, achieving good restoration results. However, this method has its own particularity. There is a relatively deep artificial pit lake just above the residual salt water area of ​​the Dagu River underground reservoir, allowing groundwater to drain into surface water. However, this does not mean that all groundwater reservoirs in Binhai have such artificial pit lakes. Therefore, this method is not universal and is not suitable for all groundwater reservoirs in Binhai.

[0011] In addition to underground seepage dams, underground reservoir systems also include groundwater extraction projects, which mainly refer to various extraction wells, water collection corridors and ancillary structures used to extract groundwater. The purpose of building underground reservoirs is to better use water, and water extraction projects play an important role in the performance of underground reservoirs. Summary of the invention

[0012] In order to make up for the shortcomings of the prior art, the present invention provides a method for repairing residual saltwater in coastal underground reservoirs based on groundwater exploitation. The present invention utilizes the ubiquitous groundwater exploitation wells, and by optimizing the form, distribution and capacity of the exploitation wells, establishes an exploitation well optimization technology that can not only ensure the safe exploitation of underground fresh water, but also repair residual saltwater pollution, thereby achieving the dual goals of utilizing and protecting freshwater resources in coastal underground reservoirs. In response to the problem of residual saltwater pollution in groundwater reservoirs, the present invention utilizes the ubiquitous groundwater exploitation wells, and by optimizing the form, distribution and capacity of the exploitation wells, establishes an exploitation well optimization technology that can not only ensure the safe exploitation of underground fresh water, but also repair residual saltwater pollution.

[0013] The present invention is realized by the following technical scheme: a method for repairing residual salt water in a coastal underground reservoir based on groundwater exploitation, characterized in that it specifically comprises the following steps: Step S1: Conduct hydrogeological survey and monitoring of the coastal aquifer to determine the average sea level position, ground surface, unsaturated zone, water table, and aquifer insulation bottom plate. Seawater intrusion will form a saltwater intrusion zone at the bottom of the coastal aquifer. By building an impermeable underground physical dam in the saltwater intrusion zone, the invading seawater is intercepted, and the upstream of the underground physical dam is the underground reservoir. Due to the isolation effect of the underground physical dam body, part of the saltwater is retained in the underground reservoir to form an initial residual saltwater zone, which can be further divided into an initial high-concentration residual saltwater zone and an initial low-concentration residual saltwater zone. Step S2: In the underground reservoir, the density of residual salt water is higher than that of the surrounding underground fresh water. Driven by the density difference between salt and fresh water, the residual salt water continues to invade inland. The instantaneous residual salt water area surrounded by the chloride ion 0.25 g / L isoconcentration line is the polluted area; the scope of the polluted area gradually increases with time, and the area surrounded by the chloride ion 17.5 g / L isoconcentration line is the instantaneous high-concentration residual salt water area, and the area surrounded by the chloride ion 17.5 g / L isoconcentration line and the chloride ion 0.25 g / L isoconcentration line is the instantaneous low-concentration residual salt water area; the instantaneous high-concentration residual salt water area transports salt to the instantaneous low-concentration residual salt water area, causing the instantaneous high-concentration residual salt water area to gradually decrease in scope over time until it disappears. At this time, the entire instantaneous residual salt water area is composed of the instantaneous low-concentration residual salt water area; Step S3: a mining well is vertically set on the underground reservoir. Fresh water in the underground reservoir is extracted through the mining well. If the chloride ion concentration of the well water exceeds 0.25 g / L during the pumping process, it means that the extracted water has been contaminated by residual salt water. Pumping is stopped and the mining well is invalid. Step S4: The mining well includes continuous pumping and intermittent pumping, and the mining well adopts continuous pumping; Step S5: The repair effect of continuous pumping on residual salt water is measured by the total salt content inside the instantaneous residual salt water area. SM t Change to measure; repair efficiency DSE Defined as: (1) In the formula, SM 0 is the total salt content inside the initial residual salt water area.

[0014] Step S6: The potential location of the production well is divided into an effective pumping area and a failure area by the failure boundary. The vertical distance between the failure boundary and the initial residual salt water area is about 10 m. In the effective pumping area, the closer the production well is to the failure boundary, the higher its repair efficiency. The repair efficiency of residual salt water by continuous pumping is DSEImproved by more than 20%; the vertical distance of 50 m from the initial residual salt water area of ​​10-1 is the target line for improving the repair efficiency by 20%; the area surrounded by the target line for improving the repair efficiency by 20% and the failure boundary is the target area for improving the repair efficiency of the mining well by more than 20%; Step S7: The capacity of the mining well affects the effect of continuous pumping on the remediation of residual salt water; the remediation efficiency is improved by 20%, the target line moves inland, and the pumping flow rate increases by 0.5 m 3 / d / m, the target line for the 20% improvement in remediation efficiency moves 10 m inland, and the target area for the 20% improvement in remediation efficiency of the production well increases by 20%; Step S8: The production wells are continuously pumped, and their distribution, i.e., location and capacity, i.e., pumping flow rate, are selected within the target area where the restoration efficiency is increased by more than 20%.

[0015] As a preferred option, water is pumped intermittently in the form of a production well.

[0016] The present invention provides a new technology for repairing residual salt water in underground reservoirs. By using continuous exploitation wells located in the optimized target area, it can not only ensure the safe exploitation of underground fresh water, but also reduce the area of ​​residual salt water pollution, remove residual salt, and achieve the goal of repairing residual salt water pollution.

[0017] Although the optimized target areas and restoration efficiencies of mining wells in different coastal groundwater reservoirs may not be consistent, the design ideas for the form, distribution and capacity of mining wells provided by the present invention can help designers solve the problem of residual salt water pollution in groundwater reservoirs.

[0018] Due to the adoption of the above technical solution, the present invention has the following beneficial effects compared with the prior art: 1. The present invention provides a new idea for the remediation of residual saltwater pollution based on groundwater exploitation. The exploitation wells located in the optimized target area can not only ensure the safe exploitation of groundwater freshwater through continuous pumping, but also reduce the area of ​​residual saltwater pollution, remove residual salt, and achieve the goal of residual saltwater pollution remediation.

[0019] 2. Universality. The purpose of building underground reservoirs is to better use water, and mining wells are very common in the operation and management of underground reservoirs. The use of such commonly used water-taking facilities to repair residual saltwater pollution makes the present invention universal.

[0020] Additional aspects and advantages of the present invention will become apparent from the following description or may be learned by practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The above and / or additional aspects and advantages of the present invention will become apparent and easily understood from the description of the embodiments in conjunction with the following drawings, in which: Figure 1Schematic diagram of residual salt water remediation technology in coastal groundwater reservoirs based on groundwater exploitation. Figure 2 This is the residual salt water landward pollution process diagram. Figure 3 To suppress the landward pollution process of residual salt water for continuous pumping; Figure 4 The groundwater flow field distribution of the underground reservoir under continuous pumping; Figure 5 The efficiency of remediating residual saline water in production wells at different pumping rates; Figure 6 is the instantaneous change of residual saltwater area and invasion distance; Figure 7 It is the instantaneous change of salt content in the residual salt water area. DETAILED DESCRIPTION

[0022] In order to more clearly understand the above-mentioned purpose, features and advantages of the present invention, the present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be noted that the embodiments of the present application and the features in the embodiments can be combined with each other without conflict.

[0023] In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention may also be implemented in other ways different from those described herein. Therefore, the protection scope of the present invention is not limited to the specific embodiments disclosed below.

[0024] Combine the following Figures 1 to 3 The method for repairing residual salt water in a coastal underground reservoir based on groundwater exploitation according to an embodiment of the present invention is specifically described.

[0025] like Figure 1 As shown, the present invention proposes a method for repairing residual salt water in a coastal groundwater reservoir based on groundwater exploitation, which specifically includes the following steps: Step S1: The residual salt water restoration technology of coastal underground reservoir based on groundwater exploitation according to the present invention has a composition diagram as shown in FIG. Figure 1 As shown, a hydrogeological survey and monitoring is conducted on the coastal aquifer 1 to determine the average sea level position 2, the ground 3, the unsaturated zone 4, the water table 5, and the aquifer insulation bottom plate 6. Seawater intrusion will form a saltwater intrusion zone 7 at the bottom of the coastal aquifer 1; an impermeable underground physical dam 8 is built in the saltwater intrusion zone 7 to intercept the invading seawater, thereby achieving the purpose of preventing and controlling seawater intrusion. The underground reservoir 9 is located upstream of the underground physical dam 8; due to the isolation effect of the dam body of the underground physical dam 8, part of the saltwater is retained in the underground reservoir 9, forming an initial residual saltwater zone 10-1, which can be further divided into an initial high-concentration residual saltwater zone 11-1 and an initial low-concentration residual saltwater zone 12-1; Step S2: In the underground reservoir 9, the density of the residual salt water is higher than that of the surrounding underground fresh water. Driven by the density difference between salt water and fresh water, the residual salt water continues to invade inland. Figure 2 , the instantaneous residual salt water area 10-2 surrounded by the chloride ion 0.25 g / L isoconcentration line 13 is the polluted area; the scope of the polluted area gradually increases over time, becoming a serious threat to the freshwater quality in the groundwater reservoir. The area surrounded by the chloride ion 17.5 g / L isoconcentration line 14 is the instantaneous high-concentration residual salt water area 11-2, and the area surrounded by the chloride ion 17.5 g / L isoconcentration line 14 and the chloride ion 0.25 g / L isoconcentration line 13 is the instantaneous low-concentration residual salt water area 12-2; the instantaneous high-concentration residual salt water area 11-2 transports salt to the instantaneous low-concentration residual salt water area 12-2, causing the scope of the instantaneous high-concentration residual salt water area 11-2 to gradually decrease over time until it disappears. At this time, the entire instantaneous residual salt water area 10-2 is composed of the instantaneous low-concentration residual salt water area 12-2; Step S3: The purpose of building an underground reservoir is to better use water. The water extraction project plays an important role in the performance of the underground reservoir. A mining well 15 is vertically set on the underground reservoir 9. Fresh water in the underground reservoir 9 is extracted through the mining well 15, which is the main way of groundwater discharge. If the chloride ion concentration of the well water exceeds 0.25 g / L during the pumping process, it means that the extracted water has been contaminated by residual salt water, and the pumping is stopped, and the mining well is invalid; Step S4: The form, distribution and capacity of the extraction wells 15 affect the landward contamination process of residual salt water. The extraction wells 15 include continuous pumping and intermittent pumping. Intermittent pumping will increase the area of ​​residual salt water contamination and more easily lead to failure of the extraction wells. Continuous pumping will inhibit the landward intrusion of residual salt water. Figure 3 , reducing the area of ​​residual salt water pollution. Therefore, continuous pumping has a positive environmental effect on the problem of residual salt water pollution. The form of mining well 15 adopts continuous pumping; Step S5: The repair effect of continuous pumping on residual salt water is measured by the total salt content inside the instantaneous residual salt water area 10-2. SM t Change to measure; repair efficiency DSE Defined as: (1) In the formula, SM 0 is the total salt content inside the initial residual salt water area 10-1.

[0026] Step S6: The distribution of production wells affects the effect of continuous pumping on the repair of residual salt water; the location of the production wells close to the initial residual salt water area 10-1 is likely to cause well failure. Figure 1The middle area 16 is the failure area of ​​the production well. The potential location of the production well is divided into the effective pumping area 18 and the failure area 16 by the failure boundary 17. The vertical distance between the failure boundary 17 and the initial residual salt water area 10-1 is about 10 m. In the effective pumping area 18, the closer the production well 15 is to the failure boundary 17, the darker the color of its repair efficiency is. Without pumping, residual salt water invades inland, increasing the instantaneous residual salt water area by 10-2. During this process, the salt in the instantaneous residual salt water area migrates to the surrounding fresh water area through convection diffusion, thereby achieving the desalination effect. Taking the restoration efficiency in this natural scenario as a reference, the design of the present invention requires continuous pumping to restore the residual salt water. DSE Increase by more than 20%; Figure 1 The middle line 19 is the target line for 20% improvement in restoration efficiency, and the vertical distance of 50 m from the initial residual salt water area 10-1 is the target line 19 for 20% improvement in restoration efficiency; the area enclosed by the target line 19 for 20% improvement in restoration efficiency and the failure boundary 17 is the target area 20 for more than 20% improvement in the restoration efficiency of the mining well; the mining well 15 in the target area 20 can not only ensure the safe exploitation of underground fresh water through continuous pumping, but also reduce the residual salt water pollution area, remove residual salt, and achieve the goal of residual salt water pollution restoration.

[0027] Under the continuous pumping action of the mining wells in the target area 20, the groundwater flow field distribution of the underground reservoir is as follows: Figure 4 As shown. The salt water in the instantaneous high-concentration residual salt water area 11-2 migrates to the instantaneous low-concentration residual salt water area 12-2, while the groundwater in the fresh water area on the left side of the chloride ion 0.25 g / L isoconcentration line 13 flows toward the instantaneous low-concentration residual salt water area 12-2, thereby inhibiting the inland pollution process of the instantaneous low-concentration residual salt water area 12-2. At the same time, the groundwater in the salt water area on the right side of the chloride ion 0.25 g / L isoconcentration line 13 flows toward the mining well, gradually transferring the salt transferred from the high-salt area to the mining well, and taking it away from the groundwater reservoir by pumping, achieving the goal of residual salt water pollution remediation. During the whole process, the chloride ion concentration of the well water was lower than 0.25 g / L, and the mining well did not fail.

[0028] Step S7: The capacity of the mining well affects the effect of continuous pumping on the remediation of residual salt water; Figure 5 The efficiency of remediation of residual salt water in production wells under different pumping flow rates is shown. With the increase of pumping flow rate, the efficiency of remediation of production wells gradually increases. The target line 19 moves inland with a 20% increase in pumping flow rate by 0.5 m 3 / d / m, the restoration efficiency is increased by 20%. The target line 19 moves 10 m inland, and the target area 20 where the restoration efficiency of the production well is increased by more than 20% is enlarged. When the pumping flow is very small, for example, 0.2 m 3 / d / m, the well repair efficiency does not meet the target requirements, and the target area 20 where the well repair efficiency is improved by more than 20% does not exist.

[0029] Step S8: The production well adopts continuous pumping mode, and its distribution, i.e. location and capacity, i.e. pumping flow rate, is Figure 5 The provided restoration efficiency is increased by more than 20% within the target area, and the requirements for safe extraction of groundwater and restoration of residual saltwater pollution can be met.

[0030] Different coastal underground reservoirs have different aquifer boundary conditions, hydrogeological parameters, and underground physical dam locations, and the residual saltwater pollution ranges formed are also different. Therefore, for different engineering sites, the optimized target area for the restoration of residual saltwater in mining wells may deviate from that provided by the present invention, and readers can make fine adjustments according to actual engineering conditions. Example

[0031] The variable density model of residual saltwater migration in coastal groundwater reservoirs was established using the professional groundwater numerical simulation software FEFLOW. The groundwater flow and solute migration process were controlled by the Richard equation coupled with the convection-diffusion equation. The length of the entire aquifer is 300 m and the thickness is 30 m. The average permeability, porosity, longitudinal dispersion, lateral dispersion, and molecular diffusion coefficient of the aquifer are 6×10 -4 m / s, 0.4, 1 m, 0.1 m, 1×10 -9 m 2 The sea level at the ocean boundary is 28.5 m, and the groundwater level at the inland freshwater boundary is 29.6 m. The hydraulic gradient between the two is 0.37%, which is a common hydraulic gradient in coastal aquifers.

[0032] Seawater intrusion occurs under the drive of density difference. When it reaches stability, the seawater intrusion distance is 100 m. An underground physical dam with a height of 30 m is built 50 m away from the ocean boundary to control seawater intrusion. Inside the underground physical dam, that is, in the underground reservoir, the initial residual saltwater area 10-1 is 510 m 2 Two cases are defined, one without pumping and one with continuous pumping. The case without pumping is used as a control to observe the landward pollution process of residual salt water under natural conditions. In the case with continuous pumping, the pumping flow rate of the production well is 1.0 m 3 / d / m, within the target area 20 where the recovery efficiency of the recovery well is improved by more than 20%, a location (200 m, 12.5 m) is selected to install a recovery well, and the continuous pumping recovery process of residual saltwater pollution is observed.

[0033] The area and invasion distance of the instantaneous residual salt water area 10-2, i.e., the polluted area, and the internal high-salinity area 11-2 are calculated. The results are as follows: Figure 6As shown. For the pumping and non-pumping examples, the area and invasion distance of the instantaneous high-concentration residual saltwater zone 11-2 change with time in basically the same way, indicating that pumping has little effect on the instantaneous high-concentration residual saltwater zone 11-2. Without pumping, the area and invasion distance of the instantaneous residual saltwater zone surrounded by the 0.25 g / L chloride ion isoconcentration line gradually increase with time, the invasion distance is up to 100% (invasion to the inland boundary), and the pollution area reaches 20% (occupying the underground reservoir area) in 20,000 days. Under continuous pumping, the area and invasion distance of the instantaneous residual saltwater zone surrounded by the 0.25 g / L chloride ion isoconcentration line first increase and then decrease with time, and the pollution area is reduced to 4% in 20,000 days, showing the inhibitory effect of continuous pumping on residual saltwater pollution.

[0034] Figure 7 The changes of the total salt content of the instantaneous residual saline water area 10-2 (greater than 0.25 g / L), the salt content of the instantaneous high-concentration residual saline water area 11-2 (greater than 17.5 g / L), and the salt content of the instantaneous low-concentration residual saline water area 12-2 (0.25-17.5 g / L) over time are shown. The salt content of the high-concentration residual saline water area is consistent with that of the non-pumping case, indicating that the pumping has little effect on the high-concentration area. The salt content of the high-concentration residual saline water area decreased to 0 in 2000 days, and the entire instantaneous residual saline water area became a low-concentration residual saline water area. The total salt content of the instantaneous residual saline water area 10-2 gradually decreased over time, but the rate of reduction of the residual salt content was significantly accelerated under the action of continuous pumping, and the restoration efficiency was as high as 95% in 20,000 days, which was 28% higher than the natural restoration efficiency without pumping.

[0035] In the description of the present invention, the term "plurality" refers to two or more than two. Unless otherwise clearly defined, the orientation or positional relationship indicated by the terms "upper" and "lower" is based on the orientation or positional relationship shown in the drawings. It is only for the convenience of describing the present invention and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, it cannot be understood as a limitation of the present invention; the terms "connection", "installation", "fixation", etc. should be understood in a broad sense. For example, "connection" can be a fixed connection, a detachable connection, or an integral connection; it can be directly connected or indirectly connected through an intermediate medium. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0036] In the description of this specification, the description of the terms "one embodiment", "some embodiments", "specific embodiments", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0037] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for repairing residual salt water in coastal underground reservoirs based on groundwater exploitation, characterized in that , specifically including the following steps: Step S1: Conduct hydrogeological survey and monitoring of the coastal aquifer (1) to determine the average sea level position (2), the ground (3), the unsaturated zone (4), the water table (5), and the aquifer insulation bottom plate (6). Seawater intrusion will form a saltwater intrusion zone (7) at the bottom of the coastal aquifer (1); an impermeable underground physical dam (8) is built in the saltwater intrusion zone (7) to intercept the invading seawater, and the upstream of the underground physical dam (8) is the underground reservoir (9); due to the isolation effect of the underground physical dam (8), part of the saltwater is retained in the underground reservoir (9), forming an initial residual saltwater zone (10-1), which can be further divided into an initial high-concentration residual saltwater zone (11-1) and an initial low-concentration residual saltwater zone (12-1); Step S2: In the underground reservoir (9), the density of residual salt water is higher than that of the surrounding underground fresh water. Driven by the density difference between salt water and fresh water, the residual salt water continues to invade inland. The instantaneous residual salt water area (10-2) surrounded by the chloride ion 0.25 g / L isoconcentration line (13) is the polluted area. The scope of the polluted area gradually increases with time. The area surrounded by the chloride ion 17.5 g / L isoconcentration line (14) is the instantaneous high-concentration residual salt water area (11-2). The area surrounded by the g / L isoconcentration line (13) is the instantaneous low-concentration residual saltwater area (12-2); the instantaneous high-concentration residual saltwater area (11-2) transports salt to the instantaneous low-concentration residual saltwater area (12-2), causing the instantaneous high-concentration residual saltwater area (11-2) to gradually decrease over time until it disappears. At this time, the entire instantaneous residual saltwater area (10-2) is composed of the instantaneous low-concentration residual saltwater area (12-2); Step S3: a mining well (15) is vertically arranged on the underground reservoir (9), and fresh water in the underground reservoir (9) is extracted through the mining well (15). During the pumping process, if the chloride ion concentration of the well water exceeds 0.25 g / L, it means that the extracted water has been contaminated by residual salt water, and the pumping is stopped, and the mining well is invalid; Step S4: The form of the mining well (15) includes continuous pumping and intermittent pumping, and the form of the mining well (15) adopts continuous pumping; Step S5: The effect of continuous pumping on the restoration of residual salt water is measured by the total salt content inside the instantaneous residual salt water area (10-2) SM t Change to measure; repair efficiency DSE Defined as: （1） In the formula, SM 0 is the total salt content inside the initial residual saltwater zone (10-1); Step S6: The potential location of the production well is divided into an effective pumping area (18) and a failure area (16) by the failure boundary (17). The vertical distance between the failure boundary (17) and the initial residual salt water area (10-1) is about 10 m. In the effective pumping area (18), the closer the production well (15) is to the failure boundary (17), the higher its repair efficiency. The repair efficiency of the residual salt water by continuous pumping is DSE The vertical distance of 50 m from the initial residual salt water area of ​​10-1 is the target line (19) for improving the repair efficiency by 20%. The area enclosed by the target line (19) for improving the repair efficiency by 20% and the failure boundary (17) is the target area (20) for improving the repair efficiency of the mining well by more than 20%. Step S7: The capacity of the mining well affects the effect of continuous pumping on the remediation of residual salt water; the remediation efficiency is improved by 20%. The target line (19) moves inland, and the pumping flow rate increases by 0.5 m 3 / d / m, the target line (19) for improving the restoration efficiency by 20% moves 10 m inland, and the target area 20 for improving the restoration efficiency of the production well by more than 20% increases; Step S8: The production wells are continuously pumped, and their distribution, i.e., location and capacity, i.e., pumping flow rate, are selected within the target area where the restoration efficiency is increased by more than 20%.

2. A method for repairing residual salt water in a coastal underground reservoir based on groundwater exploitation according to claim 1, characterized in that , the extraction well (15) is pumped water intermittently.

Images