Dual-purpose well with double screen pipes for improving efficiency of fresh water underground storage and recovery

Abstract

The application discloses a dual-purpose well with double screen pipes for improving fresh water underground storage and recovery efficiency, which comprises a well hole drilled into a pressure-bearing water-bearing stratum, a water injection screen pipe and a water pumping screen pipe arranged in the well hole, gravel filtering fillers filled between the two screen pipes and between the screen pipes and the well hole wall, a grouting sealing layer corresponding to the well hole wall of the upper soil and the water-resisting roof, and a packer arranged at the top of the screen pipes. The screen hole density of the water injection screen pipe linearly increases with the depth, while the screen hole density of the water pumping screen pipe linearly decreases with the depth. The screen hole density distribution correspondingly generates different well flow rates with the depth distribution during water injection and water pumping, so that the interface between the injected fresh water and the in-situ underground salt water is kept approximately vertical, the time node of the salt water invading the dual-purpose well and polluting the pumped water is delayed, and the negative influence of the density difference between the injected water and the in-situ underground water on the fresh water underground storage and recovery is offset.

Description

Technical Field

[0001] This invention relates to a dual-purpose well with a double-screen tube for improving the efficiency of freshwater underground storage and recovery, belonging to the field of water resource regulation and storage technology. Background Technology

[0002] Freshwater, as a vital natural resource, is a crucial pillar of national economic development and plays a prominent role in sustainable social development and ecological civilization construction. In recent years, with global population growth, climate change, and water waste, water security pressures have become increasingly severe in most parts of the world. Water scarcity has become a global water crisis, posing challenges to human development and social progress.

[0003] my country faces challenges due to the uneven spatial and temporal distribution of water resources, dense population, and immense urban water pressure. Over-extraction of groundwater in some areas has led to natural disasters such as declining groundwater levels, land subsidence, and seawater intrusion. Utilizing water storage projects for water resource regulation is a crucial technical means to achieve "spatial balance" within the water management policy of "prioritizing water conservation, spatial balance, systematic governance, and dual-pronged approach." It is also an important way to enhance the nation's water security capabilities and address water crises.

[0004] The key technology for constructing underground reservoirs is to use dual-purpose wells (both pumping and injection wells) to periodically inject freshwater into and extract it from underground aquifers. This allows for the regulation of water resources throughout the year and long-term interannual storage, ultimately achieving a healthy regional water balance. Compared with traditional surface water storage technologies (such as surface reservoirs and ponds), using dual-purpose wells to construct underground reservoirs has advantages such as low construction cost, no land occupation, low evaporation loss, large water storage capacity, low risk of water pollution from human activities, and the ability to mitigate various ecological problems caused by groundwater over-extraction.

[0005] However, due to the inherent concentration and density differences between in-situ groundwater and injected freshwater (generally, in-situ groundwater is denser than injected freshwater, especially in coastal and arid / semi-arid regions), the density difference, driven by gravity and buoyancy, causes tilting and deformation at the interface between the two water bodies. Specifically, injected freshwater rises to the shallow layers of the reservoir and flows horizontally away, while in-situ groundwater accumulates in the deeper layers of the reservoir near the well. This phenomenon means that during freshwater extraction, premature extraction of in-situ groundwater from the deeper layers of the reservoir affects the quality of the extracted water, leading to premature termination of extraction and significantly impacting the efficiency of freshwater recovery and utilization.

[0006] In order to solve the above-mentioned technical problems of freshwater storage, those skilled in the art urgently need to design a new freshwater storage structure. Summary of the Invention

[0007] The purpose of this invention is to overcome the shortcomings of the existing technology and provide a dual-screen pipe well that improves the efficiency of freshwater underground storage and recovery. By setting two screen pipes with different screen hole density distributions in the same drilled well, different well flow distributions are achieved during the injection and recovery stages to offset the negative impact of density differences on freshwater recovery efficiency. It also has the advantages of simple structure and low cost.

[0008] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: a dual-screen well for improving the efficiency of freshwater underground storage and recovery, including a wellbore drilled into a confined aquifer.

[0009] The injection screen and the pumping screen are placed inside the wellbore. Gravel filter media are filled in the space between the two screens and between the two screens and the wellbore wall. Packers are installed at the top of the two screens. The injection pump passes through the packers and is installed inside the injection screen, and the pumping pump passes through the packers and is installed inside the pumping screen. The pore density of the injection screen increases with depth, and the pore density of the pumping screen decreases with depth.

[0010] As a preferred embodiment, the sieve aperture density of the water injection screen increases linearly with depth, while the sieve aperture density of the water pumping screen decreases linearly with depth, with the degree of linear change being η.

[0011] As a preferred embodiment, the formula for calculating the degree of linear change η is as follows:

[0012]

[0013] Where, n max n represents the maximum sieve aperture density (the maximum number of apertures per unit length). min This represents the minimum sieve aperture density (the minimum number of apertures per unit length).

[0014] As a preferred embodiment, the height of the water injection screen and the water pumping screen is the same as the height of the water storage area of ​​the confined aquifer.

[0015] As a preferred embodiment, the diameters of the injection screen and the pumping screen are less than half the diameter of the wellbore, taking into account the thickness of the gravel filter packing.

[0016] As a preferred embodiment, the wellbore diameter is greater than or equal to 500 mm.

[0017] As a preferred embodiment, the sieve holes are circular.

[0018] As a preferred option, a water-proof top plate is provided around the top of the well, and an upper layer of soil is provided above the water-proof top plate. A grouting sealing layer is provided between the inner wall of the water-proof top plate and the upper layer of soil and the inner wall of the well.

[0019] Beneficial effects:

[0020] The working principle of this invention is as follows: The pore density of the injection screen increases linearly with depth, and the injection flow rate also increases linearly with depth, offsetting the deformation and tilting of the brackish water interface caused by density differences. The pore density of the pumping screen decreases linearly with depth, causing the pumping flow rate to decrease linearly with depth, extracting more fresh water from shallow layers and minimizing the extraction of brackish water. These two effects keep the interface between the injected fresh water and the in-situ groundwater as vertical as possible, thereby delaying the time when in-situ groundwater intrudes into the dual-purpose well and contaminates the pumped-back water, ultimately improving the recovery rate (RE).

[0021] This invention, by employing the above technical solutions, offers the following advantages compared to existing technologies: The invention provides a dual-screen well for improving the efficiency of underground freshwater storage and recovery. By separately installing injection screens and pumping screens with completely opposite mesh densities with depth within the same wellbore, different well flow distributions are achieved during the injection and pumping stages, minimizing the negative impact of density differences and thus significantly improving the efficiency of underground freshwater storage and recovery. Furthermore, this invention has a simple structure, eliminates the need for drilling multiple wellbores, and has low construction costs. Attached Figure Description

[0022] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

[0023] Figure 1 This is a schematic diagram of the structure of the present invention.

[0024] Figure 2 This is a schematic diagram of the conceptual model used in the numerical simulation of this invention.

[0025] Figure 3 This is a graph showing the variation of recovery rate with sieve mesh density ratio for different water storage areas with varying permeability coefficients and relative density differences.

[0026] The components are: 1. Wellbore; 2. Injection screen; 3. Pumping screen; 4. Injection pump; 5. Pumping pump; 6. Gravel filter packing; 7. Top cover soil; 8. Waterproof roof; 9. Grouting sealing layer; 10. Packer; 11. Water storage area. Detailed Implementation

[0027] To better understand the above-mentioned objects, features, and advantages of the present invention, the following description is provided in conjunction with... Figures 1 to 3 A specific description of a dual-purpose well with a double-screen tube for improving the efficiency of freshwater underground storage and recovery, according to an embodiment of the present invention, will be provided.

[0028] like Figure 1As shown, the present invention proposes a dual-purpose well with two screens to improve the efficiency of freshwater underground storage and recovery. It includes a wellbore 1 drilled into a confined aquifer, a water injection screen 2 and a water pumping screen 3 placed in the wellbore 1, a water injection pump 4 and a water pump 5 respectively installed in the two screens, gravel filter filler 6 filling the space between the two screens and between the screens and the wellbore wall, a grouting sealing layer 9 corresponding to the upper overburden 7 and the waterproof top plate 8, and a packer 10 installed on the top of the screens.

[0029] The drilled wellbore 1 should be drilled to the bottom plate of the confined aquifer. The diameter of the wellbore should not be too small and should be at least 500 mm.

[0030] The well section corresponding to the upper soil cover 7 and the water-proof top plate 8 is grouted with concrete, bentonite, or cement mortar to form a grouting sealing layer 9.

[0031] A water injection screen 2 and a water pumping screen 3 are vertically installed in the well section corresponding to the water storage zone 11 of the confined aquifer. The height of both screens is the same as the height of the water storage zone, and their outer diameter should be less than half the diameter of the well 1 considering the thickness of the gravel filter packing.

[0032] Gravel filter media 6 is used to fill the space between the injection screen pipe 2 and the pumping screen pipe 3, as well as between them and the well wall, to filter fine particles. Packers 10 are installed at the top of the two screen pipes to restrict water injection and pumping to the well section corresponding to the water storage area.

[0033] A water injection pump is installed in the injection screen pipe 2 to inject freshwater into the storage area when surface water is abundant (during the high-water season). The screen aperture density of the injection screen pipe 2 increases linearly with depth, causing the water flow rate to increase linearly with depth, thus offsetting the deformation and tilting of the brackish water interface caused by density differences. A water pump is installed in the pumping screen pipe 3 to pump back the freshwater from the storage area for utilization when the demand for freshwater is high (during the low-water season). The screen aperture density of the pumping screen pipe 3 decreases linearly with depth, causing the pumping flow rate to decrease linearly with depth, allowing more freshwater to be extracted from the shallow layer and avoiding premature pumping back into brackish water.

[0034] To facilitate a quantitative description of the change in sieve aperture density, this invention sets the maximum number of apertures per unit length of sieve tube as n. max The minimum value is n min The sieve aperture density of the water injection screen pipe 2 with built-in water injection pump 4 is from the top n min n increases linearly to the bottom max The situation is the opposite for the pumping screen pipe 3 with built-in pump 5; the screen aperture density increases from n at the top. max linearly decreasing to the bottom n min The pumping and injection flow rates change linearly based on the variation of the density of the two sieve openings with depth. The sieve opening density ratio η is used to quantify the degree of change of the sieve openings with depth. η is defined as:

[0035]

[0036] The larger the value of η, the greater the degree of change in sieve aperture density with depth.

[0037] Example 1

[0038] Wellbore 1 has a diameter of 600 mm, and the outer diameter of both screens is 200 mm. The water-bearing aquifer has a water-retaining zone height of 50 m, and the screens have the same height of 50 m. The porosity of the water-bearing zone is 0.3, and the water-retaining coefficient is 1×10⁻⁶. -4 / m, longitudinal diffusion 0.1m, lateral diffusion 0.01m, and molecular diffusion coefficient 1×10 -9 m 2 The values ​​for parameters such as / s are all adopted from the values ​​reported in relevant literature.

[0039] Based on such Figure 2 The conceptual model shown uses the open-source software SEAWAT-2000 to simulate saturated variable density groundwater flow and solute transport in this embodiment for numerical simulation. This allows for a comparison and explanation of the effects of freshwater underground storage and recovery, while also determining the optimal sieve density distribution.

[0040] Numerical simulations were performed on a complete "injection-storage-extraction" cycle spanning one year (365 days), including 100 days of freshwater injection, 165 days of static storage, and 100 days of freshwater recovery. The total pumping and injection flow rates of the dual-purpose well were both set to 500 m³ / s. 3 / d. In the numerical simulation, the concentration of freshwater is 0, and the density is 1000 kg / m³. 3 .

[0041] This invention uses recovery rate (RE) to evaluate the efficiency of freshwater underground storage and recovery, and the effectiveness of freshwater recovery. RE is defined as:

[0042]

[0043] In the formula, V inj V is the volume of water injected. rec This refers to the volume of extracted water that meets water quality standards (salt concentration not exceeding the maximum TDS limit, set at 0.5 g / L in this embodiment). A higher RE value indicates better freshwater underground storage and recovery.

[0044] To facilitate the quantification and comparison of the effectiveness of dual-screen pipe wells in improving the efficiency of freshwater underground storage and recovery, this invention further employs the recovery improvement rate (I... RE Evaluate the effectiveness of the invention. RE The definition of is:

[0045]

[0046] In the formula, RE s This is the recovery rate under traditional single-screen tube conditions, RE d This is the recovery rate under dual-screen tube conditions. RE The larger the value, the more significant the effect of the dual-screen pipe dual-purpose well on improving the recovery rate.

[0047] In the simulation, the permeability coefficient of the confined aquifer reservoir was set to K = 1 m / d, and the relative density difference between the injected freshwater and the in-situ groundwater was set to δ = 1% (i.e., the density of the in-situ groundwater was 10¹⁰ kg / m³). 3 The corresponding in-situ groundwater concentration is ); η represents the recovery improvement rate I when 0 (screen aperture density does not change with depth, equivalent to a traditional single-screen dual-purpose well), 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, and 1 (screen aperture density is minimum 0, corresponding to the maximum degree of screen aperture density change). RE See Figure 3 .

[0048] Example 2

[0049] In addition to setting the permeability coefficient K = 1 m / d for the confined aquifer reservoir during the simulation, the relative density difference δ between the injected freshwater and the in-situ groundwater was set to 2% (i.e., the density of the in-situ groundwater was 10¹⁰ kg / m³). 3 The corresponding in-situ groundwater concentration is ); η represents the recovery improvement rate I when 0 (screen aperture density does not change with depth, equivalent to a traditional single-screen dual-purpose well), 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, and 1 (screen aperture density is minimum 0, corresponding to the maximum screen aperture density change). RE See Figure 3 Apart from that, the other conditions are the same as in Example 1.

[0050] Example 3

[0051] In addition to setting the permeability coefficient K = 2 m / d for the confined aquifer reservoir during the simulation, the relative density difference δ between the injected freshwater and the in-situ groundwater was set to 0.5% (i.e., the density of the in-situ groundwater was 1005 kg / m³). 3 The corresponding in-situ groundwater concentration is ); η represents the recovery improvement rate I when 0 (screen aperture density does not change with depth, equivalent to a traditional single-screen dual-purpose well), 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, and 1 (screen aperture density is minimum 0, corresponding to the maximum screen aperture density change). RE See Figure 3 Apart from that, the other conditions are the same as in Example 1.

[0052] Example 4

[0053] In addition to setting the permeability coefficient K = 2 m / d for the confined aquifer reservoir during the simulation, the relative density difference δ between the injected freshwater and the in-situ groundwater was set to 1% (i.e., the density of the in-situ groundwater was 10¹⁰ kg / m³). 3 The corresponding in-situ groundwater concentration is ); η represents the recovery improvement rate I when 0 (screen aperture density does not change with depth, equivalent to a traditional single-screen dual-purpose well), 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, and 1 (screen aperture density is minimum 0, corresponding to the maximum screen aperture density change). RE See Figure 3 Apart from that, the other conditions are the same as in Example 1.

[0054] like Figure 3 As shown, after adopting a dual-screen well (corresponding to the case where η>0), under different combinations of permeability coefficient K and relative density difference δ, the recovery improvement rate I... RE All results show a range greater than zero, and in the four embodiments, the recovery rate can be increased by at least 20%. Although the numerical model is highly generalized, the above results strongly demonstrate that the dual-screen pipe dual-purpose well proposed in this invention can effectively improve the efficiency of freshwater underground storage and recovery.

[0055] Depend on Figure 3 It can be seen that as the permeability coefficient K or the relative density difference δ increases, I RE The range >0 also increases, to the point that it can cover the entire range of η = 0 to 1. With K = 1 m / d and δ = 2%, when the sieve aperture density ratio η = 0.85, the recovery improvement rate I... RE The maximum improvement can exceed 120%. The above results further illustrate that the present invention is particularly suitable for situations where the permeability coefficient of the water storage area is high or the relative density difference between the injected water and the in-situ groundwater is large, in which case it can achieve a huge improvement in the freshwater regulation and storage effect.

[0056] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A dual screen dual purpose well for improving fresh water underground storage and recovery efficiency, characterized in that: The wellbore drilled into the confined aquifer; The injection screen and the pumping screen are arranged in the wellbore, the gravel filter pack is filled in the space between the two screens and between the two screens and the wellbore wall, the packer is arranged at the top of the two screens, the injection pump is arranged in the injection screen through the packer, the pumping pump is arranged in the pumping screen through the packer, the screen density of the injection screen increases with the depth, and the screen density of the pumping screen decreases with the depth.

2. The dual screen well for improving the efficiency of fresh water underground storage and recovery according to claim 1, characterized in that: The screen hole density of the water injection screen pipe linearly increases with depth, the screen hole density of the water pumping screen pipe linearly decreases with depth, and the linear change degree is η .

3. The dual screen well of claim 2, wherein: the degree of linear change η The calculation formula is as follows: ； wherein n max is the maximum value of the mesh density, n min is the minimum value of the mesh density.

4. The dual screen well of any one of claims 1-3, wherein: The height of the injection screen and the pumping screen is the same as the height of the water storage area of the confined aquifer.

5. The dual screen well of any one of claims 1-3, wherein: The diameter of the injection screen and the pumping screen is less than half of the diameter of the wellbore considering the thickness of the gravel filter pack.

6. The dual screen well of any one of claims 1-3, wherein: The diameter of the wellbore is greater than or equal to 500 mm.

7. The dual screen well of any one of claims 1-3, wherein: The screen hole adopts a circular structure.

8. The dual screen well of any one of claims 1-3, wherein: There is a water-resisting roof around the top of the wellbore, and an upper layer of soil above the water-resisting roof, and a grouting sealing layer is arranged between the water-resisting roof and the upper layer of soil and the inner wall of the wellbore.

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