Full-effect resourceful treatment method and device for high-salinity oil and gas field produced water

Abstract

The invention belongs to the field of oil and gas field produced water purification, and relates to a full-effect resourceful treatment method and device for high-salinity oil and gas field produced water. By removing oil, mercury and suspended solids in the oil and gas field produced water with high salinity, the pretreated produced water is obtained, and subsequent further purification treatment is facilitated. The pretreated produced water is desalted to obtain desalted water and a gas field water concentrated solution, the desalted water can be used for desertification recharge, ecological agriculture development and carbon sink forest planting, meanwhile, water electrolysis hydrogen production can be carried out, treatment of high-salinity oil and gas field produced water is achieved, and the treatment method is simple and efficient. CO2 is added into the gas field water concentrated solution, calcium ions and magnesium ions in the gas field water concentrated solution are removed, after the calcium ions and the magnesium ions are removed, sulfuric acid is added to adsorb lithium ions in the gas field water concentrated solution, a lithium sulfate solution and a tail solution are obtained, and the removed calcium ions and the magnesium ions and the obtained lithium sulfate solution can be further recycled.

Description

Technical Field

[0001] This invention belongs to the field of produced water purification and treatment in oil and gas fields, and relates to a method and apparatus for the comprehensive resource utilization treatment of produced water with high mineralization in oil and gas fields. Background Technology

[0002] With the in-depth development of the main gas reservoirs in the oilfield, water has been commonly found in the gas reservoirs. In order to ensure the continuous and stable production of the gas field and improve the gas reservoir recovery rate, a series of gas reservoir drainage measures have been carried out. At present, the main method to solve the problem of produced water in the gas field is reinjection. However, with the continuous increase in the efforts to control water in the gas reservoir, there is a serious shortage of reinjection wells, and the contradiction between injection and production is becoming increasingly prominent. It is difficult and expensive to build new reinjection wells, and the cost of treating the water to meet the standards for reinjection is high. Moreover, as the reinjection volume increases, the reinjection pressure gradually rises, making it difficult to continuously solve the problem of produced water treatment.

[0003] Produced water contains abundant valuable elements such as lithium, bromine, rubidium, iodine, and cesium. If this produced water can be utilized as a resource, turning waste into treasure, it can not only solve the produced water treatment problem but also generate significant economic benefits. However, the chloride ionization (CL) in produced water... - The water has extremely high total mineralization and contains high levels of salt, COD, and suspended solids. Treatment is extremely difficult and inefficient, and the cost of treating and discharging high-mineralized oil and gas field produced water to meet standards is exorbitant, generally exceeding 260 yuan / m³. 3 Improper treatment of produced water from highly salinized oil and gas fields can also cause significant environmental damage. Therefore, there is an urgent need for a simple, efficient, and economical method for the comprehensive resource utilization of produced water from oil and gas fields. Summary of the Invention

[0004] In order to overcome the shortcomings of the prior art, the purpose of this invention is to provide a method and apparatus for the comprehensive resource utilization of produced water from high-mineralization oil and gas fields. This invention can realize the treatment of produced water from high-mineralization oil and gas fields, and the treatment method is simple and efficient, while realizing the comprehensive resource utilization of produced water.

[0005] To achieve the above objectives, the present invention employs the following technical solution:

[0006] This invention discloses a method for the comprehensive resource utilization of produced water from high-salinity oil and gas fields, comprising the following steps:

[0007] Oil, mercury, and suspended solids are removed from produced water from high-salinity oil and gas fields to obtain pretreated produced water;

[0008] The pretreated produced water is desalinated to obtain desalinated water and gas field water concentrate;

[0009] CO2 is added to the gas field water concentrate to remove calcium and magnesium ions. After the calcium and magnesium ions in the gas field water concentrate are removed, lithium ions are adsorbed in a lithium ion adsorption tower and then subjected to sulfuric acid to obtain lithium sulfate solution and tail liquid.

[0010] Furthermore, oil is removed from produced water from high-salinity oil and gas fields, specifically as follows:

[0011] Oil is removed from produced water with high salinity in oil and gas fields using an air flotation device. After oil removal, the produced water with high salinity in oil and gas fields enters a mercury removal device for mercury removal.

[0012] Furthermore, mercury is removed from produced water from high-salinity oil and gas fields, specifically as follows:

[0013] After oil removal, produced water with high salinity from oil and gas fields enters a mercury removal unit for mercury removal.

[0014] Furthermore, suspended solids are removed from produced water from high-salinity oil and gas fields, specifically as follows:

[0015] Oil and gas field produced water, after being de-oiled and de-mercurized, undergoes catalytic oxidation and sedimentation filtration to remove COD and high suspended solids, resulting in pretreated produced water.

[0016] Furthermore, the pretreated produced water is desalinated, as detailed below:

[0017] Desalination of produced water is achieved by pretreatment using a multi-stage evaporation desalination device;

[0018] The pretreated produced water is used to circulate and cool the primary evaporation desalination unit.

[0019] Furthermore, a multi-stage evaporation desalination device is used to pre-treat the produced water for desalination. During the desalination process, solar and wind energy are used to provide energy for the multi-stage evaporation desalination device, and production is flexibly adjusted according to the output of solar and wind energy.

[0020] Furthermore, a multi-stage evaporation desalination device is used to pre-treat the produced water for desalination. During the desalination process, an alkaline descaling agent is added to the multi-stage evaporation device.

[0021] Furthermore, during the desalination process, an alkaline descaling agent is added to the multi-stage evaporation unit, as detailed below:

[0022] At night or during periods of low production load, a 50% alkaline descaling agent is injected into the multi-stage evaporation desalination unit to remove the scale generated during daytime desalination.

[0023] Furthermore, the tail liquid enters the evaporation device to evaporate and crystallize, producing crude salt.

[0024] Based on the above method, the present invention also discloses a high-mineralization oil and gas field produced water full-efficiency resource utilization system, including an oil and gas field produced water temporary storage tank, which is connected in sequence to an air flotation device, a mercury removal device, a filtration device, a multi-stage evaporation desalination device and a lithium extraction device.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] 1. The method of this invention removes oil, mercury, and suspended solids from produced water from high-mineralization oil and gas fields to obtain pretreated produced water, which facilitates further purification. The pretreated produced water is then desalinated to obtain desalinated water and gas field water concentrate. The desalinated water can be used for desertification recharge, ecological agriculture, and carbon sink forest planting. It can also be used for hydrogen production through water electrolysis, achieving the purification and utilization of high-mineralization oil and gas field produced water. The treatment method is simple and efficient.

[0027] 2. The method of the present invention removes calcium and magnesium ions from the gas field water concentrate by adding CO2. After the removal of calcium and magnesium ions from the gas field water concentrate, lithium ions are adsorbed in a lithium ion adsorption tower and obtained as lithium sulfate solution and tail liquid under the action of sulfuric acid. The removed calcium and magnesium ions and the obtained lithium sulfate solution can be further recycled and reused, thus realizing the extraction of valuable elements.

[0028] 3. This invention system includes an oil and gas field produced water storage tank, a flotation device, a mercury removal device, a filtration device, a multi-stage evaporation desalination device, a valuable element extraction device, and a lithium extraction device. The oil and gas field produced water storage tank is mainly used for the temporary storage of produced water and production wastewater, providing produced water and cooling water for the solar desalination device, acting as an intermediate medium. The flotation device is used for oil removal from produced water from high-salinity oil and gas fields. The mercury removal device is used for mercury removal from produced water from high-salinity oil and gas fields. The filtration device is used for filtering suspended solids from produced water from high-salinity oil and gas fields. The multi-stage evaporation desalination device is used for pre-treatment and evaporation purification of produced water, obtaining desalinated water and gas field water concentrate. The gas field water concentrate is then used for lithium extraction by the lithium extraction device. This system achieves the treatment of high-salinity oil and gas field produced water in a simple and efficient manner, while simultaneously realizing the full resource utilization of the produced water. Attached Figure Description

[0029] Figure 1 This is a flowchart of the method of the present invention;

[0030] Figure 2 This is a flowchart of the high-salinity oil and gas field produced water treatment process of the present invention;

[0031] Figure 3 This is a flowchart of one embodiment of the present invention;

[0032] Figure 4This is a system connection diagram of the present invention.

[0033] Figure 5 This is a flowchart of an embodiment of the present invention.

[0034] The components include: 1. Oil and gas field produced water storage pond; 2. Mercury removal device; 3. Filtration device; 4. Multi-stage evaporation and desalination device; 5. Lithium extraction device; and 6. Air flotation device. Detailed Implementation

[0035] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0036] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover a non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0037] The present invention will now be described in further detail with reference to the accompanying drawings:

[0038] See Figure 1 This invention discloses a method for the comprehensive resource utilization of produced water from high-salinity oil and gas fields, comprising the following steps:

[0039] S1. Remove oil, mercury, and suspended solids from produced water with high salinity in oil and gas fields to obtain pretreated produced water;

[0040] Preferably, oil is removed from produced water from high-salinity oil and gas fields, specifically as follows:

[0041] Oil is removed from produced water with high salinity in oil and gas fields through an air flotation device. After oil removal, the produced water with high salinity in oil and gas fields enters a mercury removal device for mercury removal.

[0042] Preferably, the method for removing mercury from produced water in high-salinity oil and gas fields is as follows:

[0043] High-salinity produced water from oil and gas fields, after oil removal, enters a mercury removal device for mercury removal.

[0044] Preferably, the removal of suspended solids from produced water in high-salinity oil and gas fields is carried out as follows:

[0045] Oil and gas field produced water, after being de-oiled and de-mercurized, undergoes catalytic oxidation and sedimentation filtration to remove COD and high suspended solids, resulting in pretreated produced water.

[0046] S2. Desalinate the pretreated produced water to obtain desalinated water and gas field water concentrate;

[0047] Preferably, the pretreated produced water is desalinated, as follows:

[0048] Desalination of produced water is achieved by pretreatment using a multi-stage evaporation desalination device;

[0049] The pretreated produced water is used to circulate and cool the primary evaporation desalination unit.

[0050] Preferably, a multi-stage evaporation desalination device is used to pre-treat the produced water for desalination. During the desalination process, solar and wind energy are used to provide energy for the multi-stage evaporation desalination device, and production is flexibly adjusted according to the output of solar and wind energy.

[0051] Preferably, a multi-stage evaporation desalination device is used for pretreatment of the produced water. During the desalination process, an alkaline descaling agent is added to the multi-stage evaporation device, as follows:

[0052] At night or during periods of low production load, a 50% alkaline descaling agent is injected into the multi-stage evaporation desalination unit to remove the scale generated during daytime desalination.

[0053] S3. Add CO2 to the gas field water concentrate to remove calcium and magnesium ions. After the calcium and magnesium ions in the gas field water concentrate are removed, lithium ions are adsorbed in the lithium ion adsorption tower and lithium sulfate solution and tail liquid are obtained under the action of sulfuric acid.

[0054] Preferably, the tailings enter an evaporation unit for evaporation and crystallization to produce crude salt. The crude salt can be used as drilling mud material in oil fields, or it can be used to produce industrial salt in the local salt chemical industry.

[0055] See Figure 1In another feasible embodiment of the present invention, the following modifications are made as appropriate. Oil, mercury, and suspended solids are removed from the produced water of high-mineralization oil and gas fields to obtain pretreated produced water, which facilitates further purification. The pretreated produced water is desalinated to obtain desalinated water and gas field water concentrate. The desalinated water can be used for desertification recharge, ecological agriculture, and carbon sink forest planting. It can also be used for hydrogen production through water electrolysis, realizing the treatment and utilization of high-mineralization oil and gas field produced water. CO2 is added to the gas field water concentrate to remove calcium and magnesium ions. After the removal of calcium and magnesium ions, lithium ions are adsorbed in a lithium ion adsorption tower, and lithium sulfate solution and tailings are obtained under the action of sulfuric acid. The removed calcium and magnesium ions and the obtained lithium sulfate solution can be further recycled. The present invention can treat high-mineralization oil and gas field produced water in a simple and efficient manner, while achieving full resource utilization of the produced water.

[0056] Example 1:

[0057] See Figure 1 , Figure 2 and Figure 3 This embodiment discloses a method for the comprehensive resource utilization of produced water from high-salinity oil and gas fields, including the following steps:

[0058] S1. Produced water from high-mineralization oil and gas fields contains high levels of salt, mercury, COD, and suspended solids, requiring pretreatment. Liquid from the temporary storage tank is pumped into an air flotation unit for oil removal, with an efficiency ≥85%. The oil-removed produced water then enters a mercury removal unit, achieving a mercury content ≤0.001 mg / L. After mercury removal, the produced water undergoes catalytic oxidation and sedimentation filtration to remove COD and suspended solids, resulting in pretreated produced water. This invention employs a multi-stage evaporation desalination process, which has relatively relaxed water quality requirements; therefore, simple removal of COD and suspended solids is sufficient. This pretreated produced water serves as both the circulating cooling water for the multi-stage desalination unit and as the raw material for desalination.

[0059] S2. During desalination, green energy sources such as solar and wind power are used to provide energy for the multi-stage evaporation desalination unit, and production is flexibly adjusted according to the output of solar and wind power.

[0060] Desalinating highly mineralized produced water can lead to scaling in multi-stage evaporation desalination units. This scaling significantly reduces desalination efficiency and causes pipeline corrosion. Since this solution utilizes flexible solar and wind power generation, a 50% alkaline descaling agent is injected into the multi-stage evaporation desalination units at night or during low-load production periods. This alkaline descaling agent prevents corrosion of the multi-stage evaporation units and pipelines, removes scale generated during daytime desalination, and thus achieves synergy between produced water desalination and new energy sources. The desalinated water is primarily used for desertification control and photovoltaic water electrolysis for hydrogen production.

[0061] S3. Gas field water concentrate enters the feed liquid pretreatment unit, see Figure 2 CO2 is added to remove calcium and magnesium ions. The feed solution, after removing calcium and magnesium ions, enters a lithium-ion adsorption tower. Under the combined action of sulfuric acid, lithium ions in the pretreated solution are adsorbed, with an adsorption rate exceeding 90%, forming a lithium sulfate solution and tailings. The lithium sulfate solution is then concentrated in a lithium sulfate concentration unit. Electrodialysis of the concentrated lithium sulfate yields a lithium hydroxide solution and sulfuric acid, which is recycled. The lithium hydroxide solution is concentrated to crystallize, yielding a 99.9% pure lithium hydroxide product. The lithium extraction tailings enter an evaporation crystallization unit, utilizing new energy sources such as solar and wind power for evaporation and crystallization to produce crude salt. This crude salt can be used as drilling mud material in oil fields or, relying on the local salt chemical industry, can be used to produce industrial salt, thus achieving full-efficiency resource utilization of produced water from oil and gas fields. (See also...) Figure 3 .

[0062] See Figure 4 Based on the above method, this invention also discloses a comprehensive resource utilization system for produced water from high-mineralization oil and gas fields, including a produced water storage tank 1. The produced water storage tank 1 is sequentially connected to a flotation device 6, a mercury removal device 2, a filtration device 3, a multi-stage evaporation desalination device 4, and a lithium extraction device 5. The produced water storage tank 1 is mainly used for the temporary storage of produced water and production wastewater, providing produced water and cooling water for the solar desalination device, acting as an intermediate medium. The flotation device 6 is used for oil removal from the produced water from high-mineralization oil and gas fields. The mercury removal device 2 is used for mercury removal from the produced water from high-mineralization oil and gas fields. The filtration device 3 is used for filtering suspended solids from the produced water from high-mineralization oil and gas fields. The multi-stage evaporation desalination device 4 is used for pre-treatment and evaporation purification of the produced water, obtaining desalinated water and gas field water concentrate. The gas field water concentrate is then processed by the lithium extraction device 5 to extract valuable elements and lithium. This invention enables the treatment of produced water from oil and gas fields with high mineralization. The treatment method is simple and efficient, and at the same time, it realizes the full resource utilization of produced water.

[0063] Preferred, see Figure 4 The lithium extraction unit 5 is connected to an evaporation and crystallization unit, which is used to evaporate and crystallize the tailings liquid to produce crude salt. The crude salt can be used as drilling mud material in oil fields, or it can be used to produce industrial salt in the local salt chemical industry.

[0064] Example 2:

[0065] See Figure 4 and Figure 5 This embodiment discloses a high-mineralization oil and gas field produced water full-efficiency resource treatment system, including an oil and gas field produced water temporary storage tank 1, an air flotation device 6, a mercury removal device 2, a filtration device 3, a multi-stage evaporation desalination device 4, a lithium extraction device 5, an evaporation crystallization device, and an electrolysis water hydrogen production device.

[0066] In this embodiment, the multi-stage evaporation desalination device 4 is a solar desalination device, and the lithium extraction device 5 is specifically a lithium-ion adsorption tower.

[0067] The oil and gas field produced water storage pond 1 is mainly used for the temporary storage of produced water, production wastewater, etc., and provides produced water and cooling water for the solar desalination device, playing the role of an intermediate medium.

[0068] The gas field water solar desalination device desalinates and concentrates the gas field water to obtain desalinated water and gas field water concentrate. The desalinated water can be used for desertification control and for electrolysis of water to produce hydrogen. The gas field water concentrate is further processed to remove calcium, magnesium and other ions under the action of CO2.

[0069] The lithium-ion adsorption tower adsorbs lithium ions in the pretreatment liquid under the combined action of sulfuric acid, forming a lithium sulfate solution and tail liquid. The tail liquid is then reintroduced into the gas field water solar evaporation device. The lithium sulfate solution is then concentrated in a lithium sulfate concentration device. The concentrated lithium sulfate is electrodialyzed to obtain a lithium hydroxide solution and sulfuric acid, which is then reused. The lithium hydroxide solution is then concentrated to form crystals, yielding the lithium hydroxide product.

[0070] This invention desalinates and concentrates produced water. The desalinated water is used for desertification control, ecological agriculture, and carbon sink forest planting. It can also be used for hydrogen production through water electrolysis. The hydrogen is used for hydrogen-blended combustion in heating devices, external hydrogen transmission, and as a power source for microgrid construction. The concentrated produced water enters a lithium and other valuable element extraction device. The tailings generated during the extraction process are sent to an oil and gas field produced water storage pond for further desalination, thereby achieving near-zero discharge and comprehensive utilization of produced water.

[0071] See Figure 3 This is a schematic diagram of the process for the comprehensive energy utilization of produced water from high-mineralization oil and gas fields. It mainly includes a produced water storage tank, a solar desalination unit, a water electrolysis hydrogen production unit, and a valuable element extraction unit. Gas field water enters the solar desalination unit for desalination and concentration. The concentrated solution enters the feed liquid pretreatment unit, where calcium and magnesium ions are removed under CO2. The resulting lithium-containing solution, after calcium and magnesium ion removal, enters a lithium-ion adsorption tower, where lithium ions in the pretreatment solution are adsorbed under the action of sulfuric acid, forming a lithium sulfate solution and tailings. The tailings are returned to the produced water storage tank. The lithium sulfate solution enters the lithium sulfate concentration unit for concentration. The concentrated lithium sulfate is then electrodialyzed to obtain a lithium hydroxide solution and sulfuric acid, which is reused. The lithium hydroxide solution is concentrated to form crystals, yielding lithium hydroxide product. The freshwater produced from desalination is used for desertification recharge, ecological agriculture, and carbon sink forest planting. It can also be used for water electrolysis hydrogen production. This invention not only solves the problem of produced water treatment, but also turns produced water from waste into treasure, realizing a new approach to the full-efficiency energy utilization of produced water from high-mineralization oil and gas fields.

[0072] Compared with the prior art, the present invention has the following beneficial effects:

[0073] 1. The method of this invention changes the way gas field water is reinjected or treated to meet standards for discharge, and provides a new mode of resource utilization of produced water in oil and gas fields. By carrying out solar desalination and extraction of valuable elements in a coordinated manner, it realizes the resource utilization of gas field water and the development of associated resources, achieving the goal of win-win for both economic benefits and environmental protection.

[0074] 2. The method of this invention adopts a multi-technology synergistic approach, has low requirements for wastewater quality, and has a wide range of applications. It is not only suitable for the full-efficiency resource utilization of produced water from high-mineralization oil and gas fields, but also for domestic wastewater and industrial wastewater. Through solar desalination devices, the desalinated water can be used for desertification recharge, ecological agriculture, carbon sequestration forestry, etc., and can also be used for hydrogen production. This method not only solves the problem of produced water treatment, but also turns produced water into a valuable resource, realizing an economical and industrialized full-chain water treatment process.

[0075] The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solution based on the technical concept proposed in this invention shall fall within the scope of protection of the claims of this invention.

Claims

1. A method for the comprehensive resource utilization of produced water from high-salinity oil and gas fields, characterized in that, Includes the following steps: Oil, mercury, and suspended solids are removed from produced water from high-salinity oil and gas fields to obtain pretreated produced water; The pretreated produced water is desalinated to obtain desalinated water and gas field water concentrate; CO2 is added to the gas field water concentrate to remove calcium and magnesium ions. After the calcium and magnesium ions in the gas field water concentrate are removed, lithium ions are adsorbed in a lithium ion adsorption tower and then subjected to sulfuric acid to obtain lithium sulfate solution and tail liquid.

2. The method for the comprehensive resource utilization of produced water from high-salinity oil and gas fields according to claim 1, characterized in that, The removal of oil from produced water in high-salinity oil and gas fields is specifically as follows: Oil is removed from produced water with high salinity in oil and gas fields using an air flotation device. After oil removal, the produced water with high salinity in oil and gas fields enters a mercury removal device for mercury removal.

3. The method for the comprehensive resource utilization of produced water from high-salinity oil and gas fields according to claim 1, characterized in that, The removal of mercury from produced water in high-salinity oil and gas fields is specifically as follows: After oil removal, produced water with high salinity from oil and gas fields enters a mercury removal unit for mercury removal.

4. The method for the comprehensive resource utilization of produced water from high-salinity oil and gas fields according to claim 1, characterized in that, The removal of suspended solids from produced water with high salinity in oil and gas fields is specifically as follows: Oil and gas field produced water, after being de-oiled and de-mercurized, undergoes catalytic oxidation and sedimentation filtration to remove COD and high suspended solids, resulting in pretreated produced water.

5. The method for the comprehensive resource utilization of produced water from high-salinity oil and gas fields according to claim 1, characterized in that, The desalination of the pretreated produced water is specifically as follows: Desalination of produced water is achieved by pretreatment using a multi-stage evaporation desalination device; The pretreated produced water is used to circulate and cool the primary evaporation desalination unit.

6. The method for the comprehensive resource utilization of produced water from high-salinity oil and gas fields according to claim 5, characterized in that, The desalination of the extracted water is pretreated using a multi-stage evaporation desalination device. During the desalination process, solar and wind energy are used to provide energy for the multi-stage evaporation desalination device, and production is flexibly adjusted according to the output of solar and wind energy.

7. The method for the comprehensive resource utilization of produced water from high-salinity oil and gas fields according to claim 6, characterized in that, The desalination of the extracted water is pretreated using a multi-stage evaporation desalination device. During the desalination process, an alkaline descaling agent is added to the multi-stage evaporation device.

8. The method for the comprehensive resource utilization of produced water from high-salinity oil and gas fields according to claim 7, characterized in that, During the desalination process, an alkaline descaling agent is added to the multi-stage evaporation unit, as detailed below: At night or during periods of low production load, a 50% alkaline descaling agent is injected into the multi-stage evaporation desalination unit to remove the scale generated during daytime desalination.

9. The method for comprehensive resource utilization of produced water from high-salinity oil and gas fields according to claim 8, characterized in that, The tail liquid enters an evaporation device for evaporation and crystallization to produce crude salt.

10. A comprehensive resource utilization system for produced water from high-salinity oil and gas fields using the method described in any one of claims 1 to 9, characterized in that, It includes an oil and gas field produced water storage tank (1), which is connected in sequence to an air flotation device (6), a mercury removal device (2), a filtration device (3), a multi-stage evaporation desalination device (4), and a lithium extraction device (5).

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