Method for treating high-salinity produced water in gas field

Abstract

The invention belongs to the technical field of industrial / mine wastewater treatment processes, and relates to a method for treating high-salinity produced water in a gas field. Carrying out oil-water separation on the gas field water, adding a certain amount of water treatment agent and heavy metal ion trapping agent, and precipitating to obtain pretreated gas field water. Adjusting the pH value of the pretreated gas field water to 2-3, reacting for at least 2 hours, degrading COD (Chemical Oxygen Demand) and heavy metal ions in the gas field water by utilizing iron-carbon catalytic oxidation, adjusting the pH value to 3-4, and adding a reagent to form the Fenton reagent system gas field water. The Fenton's reagent system gas field water is subjected to dual-alkali process hardness removal, multi-stage filtration and evaporation, and distilled water is obtained. And carrying out hydrolytic acidification and aeration oxidation on the distilled water to obtain biochemical water. And carrying out secondary adsorption on the biochemical water to obtain purified water. The mercury-containing wastewater treatment agent can be effectively used for treating mercury-containing wastewater with complex components and high stability, the COD removal rate reaches 99% or above, the total mercury removal rate reaches 99.99% or above, the total salt removal rate reaches 98% or above, and treated effluent meets the farmland irrigation water quality requirement.

Description

Technical Field

[0001] The invention belongs to the technical field of industrial / mine wastewater treatment technology and relates to a method for treating high-mineralization produced water from a gas field. Background Art

[0002] Due to the long-term coexistence with underground gas reservoirs, the produced water of natural gas fields has dissolved or mixed with a large amount of petroleum, soluble salts, suspended matter, organic matter and other components. In addition, in the process of natural gas extraction and gathering and transportation, it is usually necessary to add chemical additives such as foaming agents, corrosion inhibitors, and scale inhibitors, making the composition of produced water in natural gas fields more complex, often showing characteristics such as high petroleum content, high suspended matter content, high organic matter content and high mineralization content. For mercury-containing natural gas fields, the produced water also contains toxic substances such as mercury ions, elemental mercury, and organic mercury, which are high-concentration mercury-containing and salt-containing wastewater that is difficult to degrade.

[0003] Currently, produced water from exploited mercury-containing gas fields is mainly treated by reinjection into the formation. Therefore, there are few reports on the research and application of treatment technologies for the discharge or recycling of produced water from mercury-containing gas fields. Most of the existing public reports focus on the removal of mercury from produced water from mercury-containing gas fields. The technologies used mainly include coagulation and sedimentation, electrochemical method, etc., which are mainly suitable for situations where the chloride and organic matter content of gas field produced water is relatively low. The membrane method and ion exchange method are technically feasible and economically reasonable.

[0004] Mercury is a highly toxic heavy metal element that has serious harm to the environment and human health. In recent years, the consumption of mercury has increased year by year, and mercury pollution is very serious. Mercury-containing wastewater is also one of the most serious industrial wastewaters that pollute the environment. At present, the common methods for treating mercury-containing wastewater include reduction, sulfidation, adsorption, ion exchange, flocculation and sedimentation, etc.

[0005] Research on mercury-containing gas field produced water focuses on the pretreatment of total mercury in the wastewater, but the treatment effect is still at the secondary standard of comprehensive sewage discharge, that is, the total mercury content in the water is less than 0.05 mg / L, and research and application of mercury removal from gas field water reaching the level of 0.001 mg / L has not been reported.

[0006] The ion exchange method is often used for deep treatment of mercury-containing wastewater. It is to load several resin columns to form a wastewater purification series. After the mercury-containing wastewater passes through several exchange columns, the mercury in the effluent is below the detection limit.

[0007] The application number is CN201610789519.1, and the patent name is an invention patent for a method for treating mercury-containing gas field water. It discloses: a method for treating mercury-containing gas field water, which aims to solve the problem that the mercury-containing wastewater has complex components and strong stability, and the existing methods are difficult to meet the needs of mercury-containing gas field water treatment. The method includes the following steps: demulsification and oil removal, destabilization reduction, flocculation precipitation, multiphase electrocatalysis, and adsorption. The present invention can be effectively used for the treatment of mercury-containing wastewater, especially mercury-containing wastewater with complex components and strong stability, and the SS removal rate reaches 80-90%, the petroleum removal rate reaches 95-99%, the COD removal rate reaches 85-95%, and the total mercury removal rate reaches 95-98%, which is a significant improvement. It has been determined that the total mercury and alkyl mercury in the effluent water quality treated by the present invention meet the discharge standards of the "Comprehensive Sewage Discharge Standard" (GB8978-1996).

[0008] The invention patent with the publication number CN111573921A and the patent name is a method for treating mercury-containing gas field water. The method for treating mercury-containing gas field water is disclosed. The produced water from the gas field is introduced into an electrocoagulation reactor, with an aluminum plate as an anode and a graphite plate as a cathode. After electrolyte flocculation and precipitation treatment, primary electrolytic wastewater is obtained; the primary electrolytic wastewater is introduced into an electrocatalytic reactor, with Ti / RuO2-IrO2-SnO2 as an anode and a stainless steel plate as a cathode. After electrolytic oxidation-reduction reaction, secondary electrolytic wastewater is obtained; the secondary electrolytic wastewater is sent to an activated carbon adsorption tower for adsorption treatment to obtain discharge water that meets the standards.

[0009] That is, the flocculation-adsorption method is a combination of flocculation and adsorption technologies for the treatment of mercury-containing gas field water. The experiment used the flocculation-adsorption method to treat the mercury-containing wastewater from the KL gas field. The results showed that the raw water was pretreated: the pH value of the raw water was appropriately adjusted, 90 mg / L of flocculant polyaluminium chloride (PAC) was added, and then 2 mg / L of coagulant aid polyacrylamide (PAM) was added. The wastewater was then deeply treated by adsorption on silver-loaded activated carbon. The mercury content in the purified water can be lower than 50 μg / L, which meets the discharge standards for mercury-containing wastewater from gas fields in my country. The flocculation-adsorption method is feasible for treating mercury-containing wastewater from gas fields, but the flocculation-adsorption method still has a certain amount of discharge in treating mercury-containing wastewater from gas fields. The long-term discharge of large amounts of mercury-containing wastewater will still cause mercury pollution. Summary of the invention

[0010] In order to overcome the shortcomings of the above-mentioned prior art, the purpose of the present invention is to provide a method for treating high-mineralization produced water from a gas field. The present invention can be effectively used for the treatment of mercury-containing wastewater with complex components and strong stability. The COD removal rate is more than 99%, the total mercury removal rate is more than 99.99%, and the total salt removal rate is more than 98%. The effluent after treatment meets the water quality requirements for farmland irrigation.

[0011] In order to achieve the above object, the present invention adopts the following technical solutions:

[0012] The invention discloses a method for treating high-mineralization produced water from a gas field, comprising the following steps:

[0013] Adding a quantitative water treatment agent and a heavy metal ion trapping agent to the gas field water after oil-water separation to form alum floccules, precipitate, and obtain pretreated gas field water;

[0014] The pH value of the pretreated gas field water is adjusted to 2-3, reacted for at least 2 hours, COD and heavy metal ions in the gas field water are degraded by iron-carbon catalytic oxidation, the pH is adjusted to 3-4, and reagents are added to form Fenton reagent system gas field water;

[0015] The Fenton reagent system gas field water is subjected to double alkali method de-hardening and multi-stage filtration to obtain de-hardened gas field water;

[0016] Evaporating the de-hardened gas field water to obtain distilled water;

[0017] The distilled water is hydrolyzed, acidified and aerated to obtain biochemical water;

[0018] The biochemical water is subjected to secondary adsorption to obtain purified water.

[0019] Further, a quantitative water treatment agent and a heavy metal ion trapping agent are added to the gas field water after oil-water separation to form alum floccules, which are precipitated to obtain pretreated gas field water, as follows:

[0020] The gas field water is separated into oil and water, and the pH value of the separated gas field water is adjusted to 7-8. A quantitative water treatment agent and a heavy metal ion capture agent are added to form alum flocs, which are then settled in a gravity sedimentation tank for 3.5 hours to remove organic matter, heavy metals and other impurities in the water.

[0021] Furthermore, the oil-water separation of gas field water is as follows:

[0022] The gas field water is first separated from the oil and water in the oil separator, and then a demulsifier is added. The water is fully stirred and floated to further separate the emulsified oil in the water from the gas field water.

[0023] Further, the pH value of the pretreated gas field water is adjusted to 2-3, and the reaction is performed for at least 2 hours, and the COD and heavy metal ions in the gas field water are degraded by iron-carbon catalytic oxidation, as follows:

[0024] Sulfuric acid is added to the gas field water after coagulation and sedimentation pretreatment, the pH value is adjusted to 2-3, the gas field water is allowed to react for at least 2 hours, and the COD and heavy metal ions in the gas field water are degraded by iron-carbon catalytic oxidation.

[0025] Further, the pH is adjusted to 3-4, and reagents are added to form Fenton reagent system gas field water, as follows:

[0026] Sulfuric acid or caustic soda solution is added to the gas field water after iron-carbon catalytic oxidation degradation to maintain the pH at 3-4, and then reagents are added to form a Fenton reagent system to degrade COD and heavy metal ions in the gas field water.

[0027] Furthermore, the Fenton reagent system gas field water is subjected to double alkali method de-hardening and multi-stage filtration as follows:

[0028] Add lye and soda ash to the Fenton reagent system gas field water to precipitate;

[0029] The pH value of the precipitated gas field water is adjusted to 7-8, and filtered using a multi-media filter and a precision filter to obtain de-hardened gas field water.

[0030] Furthermore, the distilled water is hydrolyzed, acidified and aerated to obtain biochemical water, as follows:

[0031] After the distilled water is hydrolyzed, acidified and aerated, it is separated into mud and water through the MBR membrane to obtain biochemical water.

[0032] Furthermore, the biochemical water is subjected to secondary adsorption to obtain purified water as follows:

[0033] The biochemical water is adsorbed by activated carbon adsorbent and ion exchange resin respectively to obtain purified water.

[0034] Furthermore, the activated carbon adsorbent is silver-loaded activated carbon.

[0035] Furthermore, the ion exchange resin is a special mercury removal ion exchange resin.

[0036] Compared with the prior art, the present invention has the following beneficial effects:

[0037] The invention adds a quantitative water treatment agent and a heavy metal ion trapping agent to the gas field water after oil-water separation to form alum floccules, precipitate, obtain pretreated gas field water, and preliminarily remove impurities such as organic matter and heavy metals in the water. The pH value of the pretreated gas field water is adjusted to 2-3, reacted for at least 2 hours, and COD and heavy metal ions in the gas field water are degraded by iron-carbon catalytic oxidation. The pH is adjusted to 3-4, and a reagent is added to form Fenton reagent system gas field water. The Fenton reagent system is added to form a Fenton reagent system for degrading COD and heavy metals in the gas field water. The Fenton reagent system gas field water is subjected to double alkali de-hardening and multi-stage filtration to obtain de-hardened gas field water. The de-hardened gas field water is evaporated to obtain distilled water. The distilled water is hydrolyzed, acidified and aerated oxidized to obtain biochemical water. Under the action of a microbial composite flora, pollutants such as COD and ammonia nitrogen in the water are reduced to achieve the purpose of water purification. The biochemical water is subjected to secondary adsorption to obtain purified water. The present invention can be effectively used for treating mercury-containing wastewater with complex components and strong stability, with a COD removal rate of more than 99%, a total mercury removal rate of more than 99.99%, and a total salt removal rate of more than 98%. The effluent after treatment meets the water quality requirements for farmland irrigation. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 is a flow chart of the method of the present invention;

[0039] Figure 2 It is a process flow chart of the present invention. DETAILED DESCRIPTION

[0040] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0041] It should be noted that the terms "first", "second", etc. in the specification and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchanged where appropriate, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units that are clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0042] The present invention is further described in detail below in conjunction with the accompanying drawings:

[0043] See also Figure 1 The present invention discloses a method for treating high-mineralization produced water from a gas field, comprising the following steps:

[0044] S1. Adding a quantitative water treatment agent and a heavy metal ion trapping agent to the gas field water after oil-water separation to form alum floccules, precipitate, and obtain pretreated gas field water;

[0045] S2. The pH value of the pretreated gas field water is adjusted to 2-3, reacted for at least 2 hours, COD and heavy metal ions in the gas field water are degraded by iron-carbon catalytic oxidation, the pH is adjusted to 3-4, and a reagent is added to form a Fenton reagent system gas field water;

[0046] S3. The Fenton reagent system gas field water is subjected to double alkali method de-hardening and multi-stage filtration to obtain de-hardened gas field water;

[0047] S4. Evaporating the de-hardened gas field water to obtain distilled water;

[0048] S5. hydrolyzing, acidifying and aerating the distilled water to obtain biochemical water;

[0049] S6. Perform secondary adsorption on the biochemical water to obtain purified water.

[0050] See also Figure 1 In another feasible embodiment of the present invention, the following is adaptively modified according to the situation. Add a quantitative water treatment agent and a heavy metal ion trapping agent to the gas field water after oil-water separation to form alum floccules, precipitate, obtain pretreated gas field water, and preliminarily remove organic matter, heavy metals and other impurities in the water. Adjust the pH value of the pretreated gas field water to 2-3, react for at least 2 hours, use iron-carbon catalytic oxidation to degrade COD and heavy metal ions in the gas field water, adjust the pH to 3-4, add reagents to form Fenton reagent system gas field water, add reagents to form Fenton reagent system for degrading COD and heavy metals in gas field water. Perform double alkali de-hardening and multi-stage filtration on the Fenton reagent system gas field water to obtain de-hardened gas field water. Evaporate the de-hardened gas field water to obtain distilled water. Hydrolyze and acidify the distilled water and aerate and oxidize it to obtain biochemical water. Under the action of the microbial composite flora, pollutants such as COD and ammonia nitrogen in the water are reduced to achieve the purpose of water purification. Perform secondary adsorption on the biochemical water to obtain purified water. The present invention can be effectively used for the treatment of mercury-containing wastewater with complex components and strong stability, with a COD removal rate of more than 99%, a total mercury removal rate of more than 99.99%, and a total salt removal rate of more than 98%. The treated effluent meets the water quality requirements for farmland irrigation. The present invention has the characteristics of stable technology and low cost for the comprehensive utilization of high-salinity, high-COD mercury-containing gas field water, has high application value and broad application prospects, and is worthy of large-scale promotion and application.

[0051] Embodiment 1:

[0052] See also Figure 1 and Figure 2 This embodiment discloses a method for treating high-mineralization produced water from a gas field, comprising the following steps:

[0053] S1. Add a quantitative water treatment agent and a heavy metal ion trapping agent to the gas field water after oil-water separation to form alum floccules, precipitate, and obtain pretreated gas field water, as follows:

[0054] The gas field water is separated into oil and water, and the pH value of the separated gas field water is adjusted to 7-8. A quantitative water treatment agent and a heavy metal ion capture agent are added to form alum flocs, which are then settled in a gravity sedimentation tank for 3.5 hours to remove organic matter, heavy metals and other impurities in the water.

[0055] The details of oil-water separation of gas field water are as follows:

[0056] The gas field water is first separated from the oil and water in the oil separator, and then a demulsifier is added. The water is fully stirred and floated to further separate the emulsified oil in the water from the gas field water.

[0057] S2. The pH value of the pretreated gas field water is adjusted to 2-3, reacted for at least 2 hours, COD and heavy metal ions in the gas field water are degraded by iron-carbon catalytic oxidation, the pH is adjusted to 3-4, and a reagent is added to form a Fenton reagent system gas field water;

[0058] The pH value of the pretreated gas field water is adjusted to 2-3, and the reaction is carried out for at least 2 hours. The COD and heavy metal ions in the gas field water are degraded by iron-carbon catalytic oxidation as follows:

[0059] Sulfuric acid is added to the gas field water after coagulation and sedimentation pretreatment, the pH value is adjusted to 2-3, the gas field water is allowed to react for at least 2 hours, and the COD and heavy metal ions in the gas field water are degraded by iron-carbon catalytic oxidation.

[0060] Adjust the pH to 3-4 and add reagents to form Fenton reagent system gas field water, as follows:

[0061] Sulfuric acid or caustic soda solution is added to the gas field water after iron-carbon catalytic oxidation degradation to maintain the pH at 3-4, and then reagents are added to form a Fenton reagent system to degrade COD and heavy metal ions in the gas field water.

[0062] S3. The Fenton reagent system gas field water is subjected to double alkali method de-hardening and multi-stage filtration to obtain de-hardened gas field water;

[0063] The details are as follows:

[0064] Add lye and soda ash to the Fenton reagent system gas field water to precipitate;

[0065] The pH value of the precipitated gas field water is adjusted to 7-8, and filtered using a multi-media filter and a precision filter to obtain de-hardened gas field water.

[0066] S4. Evaporating the de-hardened gas field water to obtain distilled water;

[0067] The details are as follows:

[0068] After the distilled water is hydrolyzed, acidified and aerated, it is separated into mud and water through the MBR membrane to obtain biochemical water.

[0069] S5. hydrolyzing, acidifying and aerating the distilled water to obtain biochemical water;

[0070] S6. Perform secondary adsorption on the biochemical water to obtain purified water;

[0071] The details are as follows:

[0072] The biochemical water is adsorbed by activated carbon adsorbent and ion exchange resin respectively to obtain purified water.

[0073] The activated carbon adsorbent is silver-loaded activated carbon.

[0074] The ion exchange resin is a special ion exchange resin for mercury removal.

[0075] Embodiment 2:

[0076] See also Figure 1 and Figure 2 This embodiment discloses a method for treating high-mineralization produced water from a gas field, comprising the following steps:

[0077] S1. Demulsification, air flotation and coagulation coupling:

[0078] The gas field water is first separated from the oil and water in the oil separator, and then enters the demulsifier tank. The demulsifier is manually adjusted by the metering pump, and the emulsified oil in the water is fully stirred and floated to further separate the emulsified oil from the gas field water. After that, the gas field water enters the coagulation tank, and the pH is manually adjusted to 7-8. Then, a quantitative water treatment agent and heavy metal ion trap are added to form alum flocs, which are then settled in the gravity sedimentation tank for 3.5 hours to remove organic matter, heavy metals and other impurities in the water.

[0079] S2, Micro-electrolysis Strong Oxidation Fenton Coupling:

[0080] Sulfuric acid is added to the gas field water after coagulation and sedimentation pretreatment, and the pH value is adjusted to 2-3. The gas field water is allowed to react in the facility for 2 hours, and the COD and heavy metal ions in the gas field water are degraded by iron-carbon catalytic oxidation. After that, it enters the Fenton oxidation system, and the pH is maintained at 3-4 by adding sulfuric acid or caustic soda solution, and then reagents are added to form a Fenton reagent system to degrade COD and heavy metal ions in the gas field water. The sludge generated in the process is filtered through a plate filter press, and the filtrate is discharged back into the coagulation tank.

[0081] S3, double alkali de-hardening and multi-stage filtration:

[0082] Alkali and soda ash are added to the gas field water to combine calcium ions and magnesium ions from the environment with chloride ions as the main anion to form calcium carbonate and magnesium hydroxide precipitation, so as to achieve the effect of removing calcium and magnesium ions from the gas field water. After the hardness is removed, the gas field water enters the clean water area, and sulfuric acid solution is added to adjust the pH value to 7-8. The water is then pumped into the multi-media filter and precision filter through a high-pressure pump to further remove impurities in the water. The sludge generated in the process is filtered through a plate filter press, and the filtrate is discharged back into the coagulation tank.

[0083] S4. Evaporation:

[0084] The gas field water after pretreatment enters the second-effect evaporator, where most of the salt in the water is concentrated. The evaporated distilled water is collected in the secondary intermediate water tank through condensation. The evaporated concentrated bottom liquid is a high-concentration nearly saturated liquid. After passing through the nano-interception purification equipment, the separated oil is recovered and disposed of by a third-party qualified enterprise, and the purified water is transported to the reinjection system. The nano-interception purification equipment is a nano-oil-blocking equipment.

[0085] S5. Biochemistry:

[0086] The treatment process of this method is that the gas field water undergoes hydrolysis, acidification and aeration oxidation, and under the action of the microbial complex, pollutants such as COD and ammonia nitrogen in the water are reduced to achieve the purpose of water purification. The effluent is separated from the mud by the MBR membrane to further remove impurities such as suspended matter in the effluent.

[0087] S6, Secondary adsorption:

[0088] Silver-loaded activated carbon is selected as the activated carbon adsorbent, and special mercury removal ion exchange resin is selected as the ion exchange resin. Silver-loaded activated carbon and ion-specific mercury removal ion exchange resin are combined in the order of front and back loading and in different loading amounts. This secondary adsorption process combination of activated carbon + ion exchange resin can be used as a deep mercury removal security measure to ensure that the mercury content in the effluent is fully controllable and the mercury content in the gas field water is reduced to below 1μg / L.

[0089] The water sample treated in this embodiment is actual produced water from a natural gas field. The COD and mercury contents of the raw water after each step of treatment are shown in Table 1.

[0090] Table 1, data statistics of the experimental example of treatment of high-salinity and high-COD mercury-containing gas field water:

[0091] Serial number Processing Unit Outlet COD Mercury in water 1 Regulating pool 7639.26 1.0326 2 Demulsification, air flotation and coagulation coupling 3625.14 0.0352 3 Micro-electrolysis strong oxidation Fenton 826.33 0.0352 4 Double alkali de-hardening + multi-medium 826.33 0.0352 5 evaporation 537.64 0.0114 6 Biochemistry 383.57 0.0114 7 Secondary adsorption 24.53 0.0002

[0092] The experimental research results show that the present invention can effectively solve the problem of standard treatment and comprehensive utilization of high-salinity, high-COD and mercury-containing gas field water. Relying on the superimposed concentration membrane technology, the treated clean water can meet the water quality requirements for farmland irrigation, and the high-concentration salt water can meet the gas field water formation injection index requirements. The concentration process of this method adopts FRO superimposed concentration membrane technology, which is stable and reliable.

[0093] The present invention aims to provide an economical and applicable method for treating mercury-containing gas field water, aiming at the problem that the existing methods are difficult to meet the treatment needs of mercury-containing gas field water, which has complex components and strong stability. The present invention can be effectively used for the treatment of mercury-containing wastewater with complex components and strong stability, with a COD removal rate of more than 99%, a total mercury removal rate of more than 99.99%, and a total salt removal rate of more than 98%. The effluent after treatment meets the water quality requirements for farmland irrigation. The invention has significant technical innovation, practical value and environmental benefits. The present invention has the characteristics of stable technology and low cost for the comprehensive utilization of high-salt, high-COD mercury-containing gas field water, has high application value and broad application prospects, and is worthy of large-scale promotion and application.

[0094] The above contents are only for explaining the technical idea of ​​the present invention and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution in accordance with the technical idea proposed by the present invention shall fall within the protection scope of the claims of the present invention.

Claims

1. Treatment methods for high-mineralization produced water from gas fields, It is characterized in that The following steps are involved: Adding a quantitative water treatment agent and a heavy metal ion trapping agent to the gas field water after oil-water separation to form alum floccules, precipitate, and obtain pretreated gas field water; The pH value of the pretreated gas field water is adjusted to 2-3, reacted for at least 2 hours, COD and heavy metal ions in the gas field water are degraded by iron-carbon catalytic oxidation, the pH is adjusted to 3-4, and reagents are added to form Fenton reagent system gas field water; The Fenton reagent system gas field water is subjected to double alkali method de-hardening and multi-stage filtration to obtain de-hardened gas field water; Evaporating the de-hardened gas field water to obtain distilled water; The distilled water is hydrolyzed, acidified and aerated to obtain biochemical water; The biochemical water is subjected to secondary adsorption to obtain purified water.

2. The method for treating high-mineralization produced water from a gas field according to claim 1, It is characterized in that The method of adding a quantitative water treatment agent and a heavy metal ion trapping agent to the gas field water after oil-water separation to form alum floccules and precipitate to obtain pretreated gas field water is as follows: The gas field water is separated into oil and water, and the pH value of the separated gas field water is adjusted to 7-8. A quantitative water treatment agent and a heavy metal ion capture agent are added to form alum flocs, which are then settled in a gravity sedimentation tank for 3.5 hours to remove organic matter, heavy metals and other impurities in the water.

3. The method for treating high-mineralization produced water from a gas field as claimed in claim 2, It is characterized in that The specific method of separating gas field water from oil is as follows: The gas field water is first separated from the oil and water in the oil separator, and then a demulsifier is added. The water is fully stirred and floated to further separate the emulsified oil in the water from the gas field water.

4. The method for treating high-mineralization produced water from a gas field according to claim 1, It is characterized in that The pH value of the pretreated gas field water is adjusted to 2-3, and the reaction is performed for at least 2 hours, and the COD and heavy metal ions in the gas field water are degraded by iron-carbon catalytic oxidation, as follows: Sulfuric acid is added to the gas field water after coagulation and sedimentation pretreatment, the pH value is adjusted to 2-3, the gas field water is allowed to react for at least 2 hours, and the COD and heavy metal ions in the gas field water are degraded by iron-carbon catalytic oxidation.

5. The method for treating high-mineralization produced water from a gas field according to claim 1, It is characterized in that The pH is adjusted to 3-4, and reagents are added to form Fenton reagent system gas field water, specifically as follows: Sulfuric acid or caustic soda solution is added to the gas field water after iron-carbon catalytic oxidation degradation to maintain the pH at 3-4, and then reagents are added to form a Fenton reagent system to degrade COD and heavy metal ions in the gas field water.

6. The method for treating high-mineralization produced water from a gas field according to claim 1, It is characterized in that The double alkali method for de-hardening and multi-stage filtration of Fenton reagent system gas field water is specifically as follows: Add lye and soda ash to the Fenton reagent system gas field water to precipitate; The pH value of the precipitated gas field water is adjusted to 7-8, and filtered using a multi-media filter and a precision filter to obtain de-hardened gas field water.

7. The method for treating high-mineralization produced water from a gas field according to claim 1, It is characterized in that The distilled water is hydrolyzed, acidified and aerated to obtain biochemical water, as follows: After the distilled water is hydrolyzed, acidified and aerated, it is separated into mud and water through the MBR membrane to obtain biochemical water.

8. The method for treating high-mineralization produced water from a gas field according to claim 1, It is characterized in that The method of performing secondary adsorption on biochemical water to obtain purified water is specifically as follows: The biochemical water is adsorbed by activated carbon adsorbent and ion exchange resin respectively to obtain purified water.

9. The method for treating high-mineralization produced water from a gas field according to claim 8, It is characterized in that The activated carbon adsorbent is silver-loaded activated carbon.

10. The method for treating high-mineralization produced water from a gas field according to claim 8, It is characterized in that The ion exchange resin is a special mercury removal ion exchange resin.

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