A high-efficiency purification treatment method for oilfield high-temperature high-salt reinjection water

Abstract

The application discloses a kind of efficient purification treatment methods of oilfield high temperature high salt reinjection water.The method of the application comprises the following steps: adjusting pH value of oilfield high temperature high salt produced water, effluent is added with oxidizing agent and modified magnetic loading agent in turn and stirred to carry out oxidation reaction; effluent after oxidation reaction is added with coagulant to carry out coagulation reaction; effluent after coagulation reaction is added with flocculating agent, and loose floc is formed; effluent is adsorbed and salvaged magnetic floc, and the effluent enters subsequent filtration treatment or is injected into formation; magnetic floc is sequentially subjected to magnetic floc deflocculation and recovery operation, and magnetic powder is recycled to oxidation reaction for recycling; modified magnetic loading agent is regenerated from reaction sludge, and is recycled to oxidation reaction, and supernatant is discharged to waste liquid treatment system; residual sludge discharged from the bottom of reaction tank is transported out for disposal after sludge dewatering; filter press liquid produced in the dewatering process is returned to the main treatment system for treatment.The application can efficiently purify and treat oilfield high temperature high salt reinjection water.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of oilfield produced water treatment, and relates to a high-efficiency purification treatment method for oilfield high-temperature and high-salt reinjection water. BACKGROUND

[0002] Offshore oil production is the most potential oil exploitation method in the 21st century, and is an important measure to maintain national energy security and maritime rights and interests, which is of great strategic significance. Due to the short service life and high risk of offshore oil platforms, the reinjection water development method is generally adopted in advance.

[0003] Reinjection after produced water treatment is an important way to ensure the sustainable development of oilfields and reduce environmental pollution. Due to the limitations of offshore operation conditions, the treatment process of oilfield produced water is mainly focused on the removal of suspended solids and oil. The existing oilfield reinjection water treatment is aimed at separate water injection, and the main purpose is to remove oil, suspended solids, SRB bacteria, and oxygen, and there is no targeted treatment for incompatible mixed water injection. The traditional treatment process is generally: hydrocyclone reactor-inclined plate settling tank-sand filter-fine filter-sterilization-oxygen removal-reinjection. The traditional oilfield reinjection water treatment process has the following problems: 1) long process flow and low efficiency; 2) large amount of chemical agents such as oil removal agent, flocculant, and coagulant, high treatment cost; 3) unstable treatment effect, and unable to adapt to the fine water treatment demand of offshore low-permeability oilfields. The current magnetic coagulation and magnetic separation technology is mainly applied to river channel management, settlement of coal-containing wastewater containing ultra-fine coal powder, and other fields, and has not been applied to high-temperature and high-salt oilfield wastewater. The existing magnetic coagulation and magnetic separation technology process is as follows: the water enters the three-way box reactor for coagulation reaction, PAC, magnetic powder, and PAM agents are added respectively in the reactor to make the magnetic powder fully combined with the reaction floc, and then enters the magnetic separator to recover the floc under the action of the magnetic field. The treated clear water is discharged, and the recovered floc enters the floc breaking unit to separate the floc from the magnetic powder under the action of water flow and reaction time, the magnetic powder is recycled into the reactor, and the floc is discharged in the form of sludge. The existing magnetic separation device has the following disadvantages in dealing with high-temperature and high-salt oilfield reinjection water treatment: ①The composition of the magnetic powder is Fe3O4, which is easy to agglomerate under the action of magnetism. The specific surface area of the agglomerated magnetic powder decreases, the gravity increases, and it is difficult to disperse in water and combine with the floc, and it is also difficult to be recovered by the magnetic separator. ②The reinjection water contains a large amount of salt, and part of the scale-forming factors is in the metastable zone under high temperature conditions. After adding magnetic powder, part of the salt will form heterogeneous crystallization on the surface of the magnetic powder particles, resulting in an increase in the particle size of the magnetic powder particles, which cannot be recovered, and the treatment efficiency is reduced. ③The surface crystallization of the magnetic powder cannot be effectively broken up by the floc breaking device, resulting in a significant reduction in the recovery rate. ④A large amount of unrecoverable magnetic powder accumulates at the bottom of the reactor, and is carried into the subsequent process under the condition of water fluctuation, thereby blocking the subsequent equipment.

[0004] For the oilfield produced water has the characteristics of high temperature, high salt, etc., when the produced water containing sulfur and the groundwater containing ferrous ions are mixed for injection, a large amount of black ferrous sulfide and other suspended impurities will be formed during the mixing process, thereby blocking the formation and causing the injection water to fail to meet the design requirements. In order to effectively solve the problems of incompatibility of clean and contaminated injection in the development of oilfield injection water, long process, low efficiency and difficult operation and maintenance of deep treatment of injection water, it is urgent to develop a high-efficiency clarification treatment process to solve the problem of injection water treatment in overseas oilfields and offshore oilfields, and to provide technical support for the development of clean and contaminated injection oilfields and low-permeability oilfields. SUMMARY

[0005] The purpose of the present application is to provide a high-efficiency purification treatment method for high-temperature and high-salt injection water in oilfields

[0006] The present application adopts loading oxidation technology, magnetic separation technology, magnetic carrier deflocculation and circulation technology, magnetic carrier regeneration and modification, etc., to shorten the treatment process, shorten the reaction and purification time, improve the stability of oxidation and flocculation reaction in high-temperature and high-salt environment, reduce the influence of salt effect and precipitation effect, and improve the recovery rate of magnetic powder; thereby supporting the development of offshore clean and contaminated injection oilfields and low-permeability oilfields.

[0007] The present application provides a high-efficiency purification treatment method for high-temperature and high-salt injection water in oilfields, comprising the following steps: 1) pumping the high-temperature and high-salt produced water in oilfields into a pH adjusting tank, adding acid / base adjusting agent to adjust the pH value;

[0008] 2) The effluent of the pH adjusting tank enters a high-temperature oxidation reaction tank and a high-temperature magnetic loading reaction tank in sequence, and oxidation reaction is carried out by adding an oxidizing agent and a modified magnetic loading agent respectively and stirring;

[0009] 3) The effluent of the high-temperature oxidation reaction tank and the magnetic loading reaction tank enters a high-temperature coagulation reaction tank, and coagulation reaction is carried out by adding a coagulant;

[0010] 4) The effluent of the high-temperature coagulation reaction tank enters a high-temperature flocculation reaction tank, and a flocculant is added to form loose flocs;

[0011] 5) The effluent of the high-temperature flocculation reaction tank enters the flow channel of a magnetic separation system, and the magnetic flocs in the sewage are salvaged by magnetic adsorption, and the effluent of the magnetic separation system enters subsequent filtration treatment or is injected into the formation as oilfield exploitation injection water;

[0012] 6) The magnetic flocs enter a magnetic carrier recovery tank, and deflocculation and recovery operations are carried out in sequence, and the magnetic powder is recycled to the high-temperature magnetic loading oxidation reaction tank for recycling;

[0013] 7) the sludge density instrument is arranged in the high-temperature oxidation reaction tank and the high-temperature coagulation reaction tank, when the value difference of the two is less than a preset value, the reaction tank bottom sludge discharge valve of the high-temperature oxidation reaction system, the magnetic loading reaction system, the high-temperature coagulation reaction tank and the high-temperature flocculation reaction tank is opened, the sedimentary crystal is discharged to the magnetic carrier regeneration reactor, and citric acid is added;

[0014] 8) the sedimentary crystal in the magnetic carrier regeneration reactor is modified by citric acid, and a modified magnetic loading agent is regenerated, which is recovered to the high-temperature magnetic loading oxidation reaction tank by a water jet, and the supernatant is discharged to a waste liquid treatment system;

[0015] 9) the residual sludge discharged from the reaction tank bottom in step 7) is transported out for disposal after sludge dewatering, and the filter pressing liquid produced in the dewatering process is returned to the main treatment system for treatment, so that the closed-loop treatment of wastewater is realized.

[0016] In the above method, in step 1), the pH value is adjusted to 7-10.

[0017] In the above method, the temperature of the oilfield high-temperature high-salt produced water can be 65-90℃, and the chloride ion content can be 1000mg / l-190000mg / l.

[0018] In the above method, in step 2), the oxidizing agent is a conventional type, and is specifically selected from sodium hypochlorite or hydrogen peroxide; and the addition amount of the oxidizing agent can be 200-600mg / l.

[0019] The modified magnetic loading agent is composed of the following components in mass percentage: modified ferroferric oxide 60%; ferrous oxide 20%; copper sulfate 10%; and anhydrous ferrous sulfate 10%; wherein the modified ferroferric oxide is citric acid adsorbed on the surface of ferroferric oxide particles, and forms carboxylic acid iron by coordination, and the mass ratio of the citric acid to the ferroferric oxide is 0.1-0.2:1.

[0020] The particle size of the modified magnetic loading agent is 50-70 microns.

[0021] In the present application, the preparation method of the modified ferroferric oxide comprises the following steps:

[0022] The ferroferric oxide is added into a sodium citrate solution to obtain a suspension, the mixing mass ratio is 1:80-100, heated to 80-100℃ for 1-2h of vigorous stirring, the formed precipitate is centrifuged, the precipitate is washed with ultrapure water and then centrifuged again, the process is repeated for 2-3 times, and finally the precipitate is vacuum dried to obtain the modified ferroferric oxide.

[0023] In the above method, the coagulant is polyaluminum chloride (PAC for short) or polyferric sulfate (PFS for short), and the dosage can be 50 mg / l; after the medicament is added, stirring and reaction are carried out for 5-20 min, so that the water sample with extremely high salt content is fully mixed and flocs are formed;

[0024] The flocculant is high-temperature-resistant polyacrylamide (PAM for short), and the dosage can be 1-5 mg / l, and specifically can be 2 mg / l, so as to fully adhere to the magnetic powder and overcome the influence of ionic atmosphere; after the medicament is added, stirring and reaction are carried out for 5-20 min.

[0025] In the above method, in step 7), the initial preset value of the sludge density instrument can be 500 mg / L, which is adjusted according to the water quality characteristics; according to the test results, when the density difference before and after is less than 500 mg / L, the magnetic loading agent can well adsorb the flocs, the effluent suspended solids meet the standard, and the recovery rate is normal.

[0026] In the above method, in step 8), the citric acid dosage concentration can be 10%-15%, and the modified magnetic loading agent regeneration reaction time can be 30-120 min, and the reaction temperature can be 70-90 DEG C.

[0027] The oilfield high-temperature high-salt reinjection water efficient purification treatment method has the following beneficial effects:

[0028] The oilfield high-temperature high-salt reinjection water efficient purification treatment method can directly treat the oil reinjection water in the high-temperature (65-90 DEG C) and high-salt (chloride ion content 1000 mg / l-190000 mg / l) range, and the five-connected oxidation flocculation reaction is used for the incompatible problem of reinjection water scaling, which is different from the traditional process; meanwhile, the existing magnetic loading agent is regenerated and modified online, the dispersity and chemical stability of the magnetic loading agent are improved, the combination efficiency of the magnetic loading agent and the flocs and the recovery rate of the magnetic loading agent are improved, and the application scene of the high-temperature high-salt wastewater treatment is more suitable. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 The flow chart of the offshore oilfield high-temperature high-salt produced water efficient purification treatment method is shown. DETAILED DESCRIPTION

[0030] In the following examples, the experimental methods used are conventional methods unless otherwise specified.

[0031] In the following examples, the materials, reagents, etc. used are commercially available unless otherwise specified.

[0032] The offshore oilfield high-temperature high-salt produced water efficient purification treatment method provided in the present application comprises the following steps:

[0033] S10: The high-temperature and high-salt produced water is pumped into a PH adjusting system, and an acid / base adjusting agent is added to adjust the PH value of the produced water to 7-10;

[0034] S20: The water from the PH adjusting tank is pumped into a high-temperature oxidation reaction system and a high-temperature magnetic loading reaction system, and a modified magnetic loading agent (magnetic powder) and an oxidizing agent are added and stirred uniformly to cause the incompatible scale-forming factors to form micro colloids and be adsorbed on the surface of the magnetic powder through oxidation reaction in a high-temperature environment; wherein the oxidizing agent is sodium hypochlorite or hydrogen peroxide, and the added mass is 200-600 mg / l;

[0035] S30: The water from the high-temperature oxidation reaction and magnetic loading reaction system is pumped into a high-temperature coagulation reaction system, a coagulant is added and stirred uniformly, the coagulant is allowed to react with the pollutants separated out by oxidation in the previous step to form fine magnetic flocs with the magnetic powder particles as the core;

[0036] The modified magnetic loading agent is composed of the following components in mass percentage: modified ferroferric oxide 60%; ferrous oxide 20%; copper sulfate 10%; anhydrous ferrous sulfate 10%; and magnetic powder particle size 50-70 microns;

[0037] S40: The water from the high-temperature coagulation reaction system is pumped into a high-temperature flocculation reaction system, a flocculant is added and stirred uniformly; and the flocculant is allowed to form loose flocs through adsorption and bridging;

[0038] S50: The water from the high-temperature flocculation system is pumped into the flow channel of a magnetic separation system, and after slow release and energy dissipation, the wastewater enters a special separation flow channel, and the wastewater flows through the magnetic adsorption cylinder in the magnetic separation system uniformly and evenly, the magnetic adsorption cylinder is provided with a high-temperature-resistant magnetic source group, which can provide a strong magnetic field on the surface of the magnetic adsorption cylinder, thereby adsorbing and salvaging the magnetic flocs in the wastewater, realizing rapid separation of the magnetic flocs from the water; the magnetic flocs adsorbed on the surface of the magnetic adsorption cylinder are scraped off and enter the magnetic carrier recovery system with the rotation of the cylinder; the water from the magnetic separation host enters subsequent filtration treatment or is directly reinjected; wherein the surface magnetic field strength of the adsorption area of the magnetic separation host is ≥5000Gs, the flow channel angle of the adsorption area is ≥150°, and all flow parts are designed and coated with high-temperature-resistant and high-salt-resistant materials;

[0039] S60: The magnetic flocs (sludge) entering the magnetic carrier recovery system are sequentially subjected to magnetic floc deflocculation and recovery operations, and the magnetic powder is recovered to the high-temperature magnetic loading oxidation reaction tank;

[0040] S70: A sludge density instrument is arranged in the high-temperature oxidation reaction system and the high-temperature coagulation reaction system, and when the numerical difference between the two is less than a preset value, the sludge discharge valves kv1, kv2, kv3 and kv4 at the bottom of the reaction tank are opened to discharge the precipitated crystals to the magnetic carrier regeneration reactor, and citric acid is added to the tank, and a stirrer is arranged in the tank to mix; the reaction tank has two functions: ① the acid is used to dissolve the precipitated crystals to regenerate the magnetic powder and restore the magnetism; ② the carboxyl group of the citric acid is combined with the coordination bond of the iron on the surface of the magnetic powder to modify the magnetic powder, and the modified magnetic powder has enhanced interaction with water and increased dispersibility to avoid agglomeration; the initial numerical difference of the sludge density instrument is specifically set to 500 mg / L, which can be adjusted according to the water quality characteristics;

[0041] S80: The magnetic powder in the magnetic carrier regeneration reactor is settled after being regenerated by the citric acid, and the supernatant is discharged, and the magnetic powder at the bottom is recovered by a water jet to the high-temperature loading oxidation reaction tank; the concentration of the citric acid is 10% to 15%, the modification reaction time of the magnetic carrier regeneration is 30 to 50 minutes, and the reaction temperature is 70 to 90°C;

[0042] S90: The residual sludge discharged from the bottom of the sludge distribution tank is dehydrated and then transported for disposal; the filter press liquor produced in the dehydration process is returned to the main treatment system for treatment to realize closed-loop treatment of the wastewater.

[0043] In the following examples, the preparation method of the modified ferroferric oxide includes the following steps: ferroferric oxide is added to a sodium citrate solution to obtain a suspension, the mixing mass ratio is 1:100, heating to 100°C for 2h of vigorous stirring, centrifugation of the formed precipitate, washing of the precipitate with ultrapure water and then centrifugation again, repeating 3 times, and finally vacuum drying of the precipitate to obtain the modified ferroferric oxide.

[0044] Example 1,

[0045] An oilfield in the Middle East treats reinjection water, and the reinjection water source is oilfield produced water with high salinity. The produced water has a temperature of 85°C, a salt content of 135000 mg / l, a pH value of 5.0, and a suspended solids content of about 3000 mg / l. The water contains Ca 2+ ions 17000 mg / L, Mg 2+ ions 3800 mg / L, SO4 2+ ions 2400 mg / L, Sr 2+ ions 300 mg / L, S 2- ions 50 mg / L, and suspended solids content 3000 mg / L. The sulfur ions and suspended solids need to be removed to meet the reinjection water standard and then reinjected into the formation. According to the process shown in FIG. Figure 1 , the process specifically includes the following steps:

[0046] S10: The high-temperature and high-salt oilfield produced water is a produced water from an oilfield in a certain Middle East region. The produced water has a temperature of 85°C, a salinity of 135000 mg / l, a pH value of 5.0, and a suspended solids content of about 3000 mg / l;

[0047] The high-temperature and high-salt offshore oilfield produced water is pumped into a pH adjusting tank, and NaOH is added to adjust the pH to 7.5;

[0048] S20: The water from the pH adjusting tank is pumped into a high-temperature oxidation reaction tank, and sodium hypochlorite is added with a dosage of 400 mg / l. The mixture is stirred uniformly and reacted for 20 minutes in a high-temperature environment of 85°C for oxidation reaction;

[0049] S30: The water from the high-temperature oxidation tank is pumped into a high-temperature magnetic loading tank, and modified magnetic loading agent (magnetic powder) is added. The mixture is stirred uniformly to allow the oxidation reaction products to fully combine with the magnetic powder;

[0050] The modified magnetic loading agent is composed of the following components in mass percentage: modified ferroferric oxide 60%; ferrous oxide 20%; copper sulfate 10%; anhydrous ferrous sulfate 10%; and magnetic powder with a particle size of 50-70 microns;

[0051] S40: The water from the high-temperature magnetic loading reaction tank is pumped into a high-temperature coagulation reaction tank, and coagulant PAC is added with a dosage of 50 mg / l, and stirred for 5 minutes. The coagulant reacts with the pollutants precipitated by the oxidation in the previous step to form fine magnetic flocs with the modified magnetic loading agent as the core;

[0052] S50: The water from the high-temperature coagulation reaction tank is pumped into a high-temperature flocculation reaction tank, and flocculant is added and stirred uniformly. The flocculant combines the fine magnetic flocs in the wastewater into large magnetic flocs through adsorption and bridging;

[0053] S60: The water from the high-temperature flocculation tank is pumped into the flow channel of the high-temperature and high-salt magnetic separation main machine, and after slow release and energy dissipation, the wastewater enters the special separation flow channel. The wastewater flows evenly through the magnetic adsorption cylinder in the magnetic separation main machine, which is equipped with a high-temperature-resistant magnetic source group that can provide a strong magnetic field on the surface of the magnetic adsorption cylinder, thereby adsorbing and salvaging the magnetic flocs in the wastewater, achieving rapid separation of the magnetic flocs from the water. The magnetic flocs adsorbed on the surface of the magnetic adsorption cylinder are separated from the water surface and enter the unloading area as the cylinder rotates. Under the action of the unloading scraper, they fall into the magnetic carrier deflocculation recycler. The water discharged from the magnetic separation main machine is subjected to subsequent filtration treatment or directly reinjected;

[0054] S70: The magnetic flocs enter the magnetic carrier deflocculation recycler, and are subjected to magnetic floc deflocculation and magnetic loading agent recovery in sequence. The magnetic loading agent in the magnetic flocs is recovered to the high-temperature magnetic loading reaction tank. The deflocculated sludge is discharged to a sludge treatment system for dewatering and external transport;

[0055] The high-temperature magnetic carrier deflocculation recovery device is composed of a magnetic floc deflocculation device and a magnetic loading agent recovery and adding device; the magnetic floc deflocculation device realizes the separation of the magnetic loading agent and the sludge by high-speed mechanical shearing / stirring to disperse the magnetic floc; the magnetic loading agent recovery and adding device recovers the magnetic loading agent in the dispersed sludge by a strong magnetic field and adds the magnetic loading agent to the reaction tank again; the surface magnetic field strength of the magnetic loading agent recovery and adding device is greater than or equal to 5000Gs;

[0056] S80: A sludge density instrument is arranged in the high-temperature oxidation reaction tank and the high-temperature coagulation reaction tank, and when the difference between the two values is less than a preset value 500 mg / L, the automatic sludge discharge valves kv1, kv2, kv3 and kv4 at the bottom of the reaction tanks are opened to discharge the sedimentary crystals to the magnetic carrier regeneration reactor, citric acid is added to the tank, the concentration of the added citric acid is 10%, and the modified reaction is carried out by stirring and mixing, the modified reaction time is 40 min, the reaction temperature is 80 DEG C (the temperature of the treated water itself), the magnetic carrier is regenerated and modified, the dispersion of the modified magnetic carrier is enhanced, and the agglomeration phenomenon is avoided;

[0057] S90: After the regeneration and modification reaction of the magnetic carrier is completed, the supernatant is discharged, and the magnetic carrier at the bottom is recovered into the high-temperature magnetic carrier reaction tank by pressurization of a water jet, and the supernatant is discharged to a waste liquid treatment system.

[0058] Example 2,

[0059] A high-temperature and high-salt produced water efficient purification treatment method for offshore oilfields, according to the process shown in Figure 1 , the specific steps are the same as those of the embodiment 1 of the present application, and the difference is that:

[0060] The sludge density of the reinjection water high-temperature oxidation reaction tank of a certain Middle East oilfield is 20000 mg / l, and the sludge density of the high-temperature flocculation reaction tank is 30000 mg / l, and the difference between the two is more than a preset value 5000 mg / l;

[0061] The PLC control system sends a command to control the sludge discharge valves kv1 and kv4 to be opened, and the magnetic sludge deposited at the bottom of the reaction tank is discharged to the magnetic carrier regeneration reactor;

[0062] The citric acid with a mass concentration of 15% is added to the magnetic carrier regeneration reactor, and the addition amount is 200 mg / l;

[0063] The citric acid and the magnetic sludge react in the reactor, the reaction time is 45 min, the reaction temperature is controlled at 80 DEG C, the scale on the surface of the magnetic sludge is removed by reaction, the magnetic carrier cluster is dispersed and opened, and the regenerated magnetic carrier is obtained;

[0064] The wastewater generated by the reactor is discharged into a regeneration liquid treatment system for treatment; and the regenerated magnetic sludge obtained by the reactor is injected into clean water, stirred uniformly, and then sent to the high-temperature magnetic loading reaction tank.

[0065] In the implementation of the embodiment, the magnetic floc collected in the magnetic carrier regeneration reactor is weakened in loading reaction capacity due to surface fouling, agglomeration, etc., and under the action of citric acid, the surface scale of the magnetic floc is dissolved and disappears, and under the action of high temperature, stirring and acid bubbles, the floc is dispersed, and the regeneration of the magnetic carrier is realized; the regenerated magnetic carrier has good loading effect, the super-magnetic separation device can effectively adsorb and remove the magnetic carrier, the water outlet effect is good, and the loss of the magnetic carrier is small; the regenerated magnetic carrier flows back to the high-temperature loading reaction tank, reduces the dosage of the reagent, and improves the recovery rate of the magnetic carrier.

[0066] Obviously, the above embodiments of the present application are only examples for clearly illustrating the present application, and are not intended to limit the implementation modes of the present application. Based on the above description, other different forms of changes or variations can be made by those skilled in the art. Here, it is not necessary and impossible to enumerate all the implementation modes. Any modification, equivalent replacement and improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the claims of the present application.

Claims

1. A highly efficient purification method for high-temperature, high-salinity oilfield reinjection water, comprising the following steps: 1) pumping the high-temperature, high-salinity oilfield produced water into a pH adjustment tank, adding an acid / base regulator to adjust the pH value; 2) The effluent from the pH adjustment tank enters the high-temperature oxidation reaction tank and the high-temperature magnetic loading reaction tank in sequence, and the oxidant and the modified magnetic loading agent are added respectively and stirred to carry out oxidation reaction; 3) The effluent from the high-temperature oxidation reaction tank and the magnetic loading reaction tank enters the high-temperature coagulation reaction tank, where coagulant is added to perform a coagulation reaction; 4) The effluent from the high-temperature coagulation reaction tank enters the high-temperature flocculation reaction tank, where flocculants are added to form loose flocs; 5) The effluent from the high-temperature flocculation reaction tank enters the flow channel of the magnetic separation system, where the magnetic flocs in the sewage are salvaged through magnetic adsorption. The effluent from the magnetic separation system enters subsequent filtration treatment or is reinjected into the formation; 6) The magnetic flocs enter the magnetic carrier recovery pool, undergo magnetic flocculent deflocculation and recovery operations in sequence, and the magnetic powder is recovered to the high-temperature magnetic loading oxidation reaction pool for recycling; 7) A sludge density meter is installed in the high-temperature oxidation reaction tank and the high-temperature coagulation reaction tank. When the difference between the two values ​​is less than a preset value, the sludge discharge valves at the bottom of the high-temperature oxidation reaction tank, the magnetic loading reaction tank, the high-temperature coagulation reaction tank, and the high-temperature flocculation reaction tank are opened to discharge the deposited crystals into the magnetic carrier regeneration reactor, and citric acid is added; 8) The deposited crystals in the magnetic carrier regeneration reactor are modified with citric acid to obtain a modified magnetic loading agent, which is recovered to the high-temperature magnetic loading oxidation reaction tank via a water ejector, and the supernatant is discharged to a waste liquid treatment system; 9) The excess sludge discharged from the bottom of the reaction tank in step 7) is dehydrated and then transported for disposal. The filtrate produced during the dehydration process is returned to the main treatment system for treatment, achieving closed-loop wastewater treatment. The modified magnetic loading agent is composed of the following components calculated by mass percentage: Modified ferrosoferric oxide 60%; ferric oxide 20%; copper sulfate 10%; Anhydrous ferrous sulfate 10%; wherein, the modified ferrosoferric oxide is citric acid adsorbed on the surface of ferrosoferric oxide particles to form iron carboxylate, and the mass ratio of the citric acid to the ferrosoferric oxide is 0.1-0.2:

1.

2. The method according to claim 1, characterized in that In step 1), the pH value is adjusted to 7-10.

3. The method according to claim 1 or 2, characterized in that The temperature of the high-temperature and high-salt produced water from the oil field is 65-90° C., and the chloride ion content is 1000 mg / l-190000 mg / l.

4. The method according to claim 1 or 2, characterized in that In step 2), the added mass of the oxidant is 200-600 mg / l; The particle size of the modified magnetic loading agent is 50 to 70 microns.

5. The method according to claim 1 or 2, characterized in that The coagulant is polyaluminium chloride or polyferric sulfate, and the dosage is 50mg / l; after the agent is added, the mixture is stirred for 5-20 minutes; The flocculant is polyacrylamide, and the dosage is 1-5 mg / l. After the agent is added, the reaction is stirred for 5-20 minutes.

6. The method according to claim 1 or 2, characterized in that In step 7), the initial preset value of the sludge density meter is set to 500 mg / L.

7. The method according to claim 1 or 2, characterized in that In step 8), the citric acid is added at a concentration of 10% to 15%, the modified magnetic loading agent regeneration reaction time is 30 to 120 minutes, and the reaction temperature is 70 to 90°C.

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