A method for classifying and processing oil and gas field waste liquid in stages

Abstract

The application provides an oil and gas field waste liquid classification gradient treatment method. The method comprises the following steps: performing electro-oxidation treatment on produced water to obtain electro-oxidation treated produced water; performing adsorption treatment on part of the electro-oxidation treated produced water by using an adsorption material to capture active chlorine, so as to obtain the adsorption material for capturing active chlorine and the adsorption treated produced water; performing biological treatment on the adsorption treated produced water to obtain treated produced water; mixing the other part of the electro-oxidation treated produced water with operation waste liquid, adding the adsorption material for capturing active chlorine, and obtaining gel breaking and de-stabilizing treated operation waste liquid; and performing coagulation and flocculation separation and ion control on the gel breaking and de-stabilizing treated operation waste liquid to obtain treated operation waste liquid. The method is suitable for large platform production mode of oil and gas field development, and can perform classification gradient treatment on produced water and operation waste liquid produced and discharged from platforms in the same region or adjacent regions, so that the treatment cost is reduced.

Description

TECHNICAL FIELD

[0001] The application relates to a classification and gradient treatment method for oil and gas field waste liquid and belongs to the technical field of oil and gas field exploitation. BACKGROUND

[0002] With the development of the oil and gas industry, the production of oil and gas field sewage is correspondingly increased. There are mainly two types of wastewater, one is produced water, which accounts for more than 90% of all oil and gas field produced and discharged wastewater; the other is operation waste liquid, which involves drilling wastewater, fracturing backflow liquid, well washing waste liquid, etc. The produced water is large in quantity, and the reinjection capacity and the remaining reinjection space are insufficient in some blocks. In a specific area, standard discharge will become the main outlet for produced water. However, due to the limited regional environmental capacity, the emission indicators of pollutants such as organic matter and ammonia nitrogen are increasingly strict, and the existing treatment process needs to be extended to meet the discharge requirements, and the treatment cost is increased. At the same time, the pollution composition of operation waste liquid is more complex, the existing treatment process has a large amount of reagent addition, high cost, and causes a large amount of solid waste and secondary pollution. Therefore, based on the existing large platform development mode, the treatment efficiency and cost of produced water and operation waste liquid need to be considered comprehensively on the same regional platform, and a collaborative control process for efficient wastewater treatment and solid waste reduction is developed.

[0003] When treating salt-containing wastewater by electro-oxidation technology, chlorine, hypochlorite and other oxidants are easily produced, which can promote the removal of pollutants, especially ammonia nitrogen, and are commonly used for treating nitrogen-containing and salt-containing wastewater such as landfill leachate. Some researchers have used "electrocoagulation + electro-oxidation process" to treat coalbed methane produced water (Hu Zehua, Coalbed Methane Produced Water Electrocoagulation + Electro-oxidation Treatment Cathode Fouling Mitigation Technology Research, Master Thesis, 2021). On the other hand, due to the accumulation of residual chlorine, the electro-oxidation effluent has color and odor. When treating landfill membrane filtration concentrate, the electro-oxidation effluent is yellow-green and emits a pungent odor (Hu Yulong, Influence of Residual Chlorine in Electro-oxidation Process Effluent on COD and Countermeasures Research, Master Thesis, 2022). CN209161700U discloses a combined electrocoagulation wastewater treatment device for strengthening the electro-oxidation process, and a dechlorination secondary sedimentation tank is specially provided to reduce the influence of active chlorine generated in the electro-oxidation process.

[0004] In addition to produced water, oil and gas field operation waste liquid also faces great challenges. Due to the multiphase effect of pollutants such as high molecular substances, surfactants, oils, and particulate matter, the flowback liquid system is very stable. Gel breaking and destabilization is the key to breaking the flowback liquid stable system, and gel breaker is the most commonly used chemical method. At present, due to low mass transfer efficiency, the dosage of gel breaker is large, and the cost is high. Sodium hypochlorite, as a strong oxidizing agent, has a low mineralization degree of organic matter, but can react with certain specific functional groups, leading to chain breaking of long-chain organic matter, reducing the viscosity of the system, and is a relatively effective gel breaker. According to the literature (Peng Jie et al., Optimization of produced water treatment process containing fracturing flowback liquid, Industrial Water Treatment, 2022), increasing sodium hypochlorite treatment can reduce the pollution load of produced water mixed with fracturing flowback liquid.

[0005] In summary, both electro-oxidation technology and sodium hypochlorite oxidizing agent are commonly used technologies or reagents, but there is no report on the comprehensive treatment or application of different types of waste liquids based on large platforms. Therefore, developing an oil and gas field waste liquid classification and gradient treatment method has become one of the problems to be solved in the field. SUMMARY

[0006] To solve the above technical problems, the purpose of the present application is to provide an oil and gas field waste liquid classification and gradient treatment method. The method of the present application can classify and gradient treat different types of waste water such as produced water, operation waste liquid and the like produced and discharged from the same regional platform or adjacent regional platform of the large platform production mode of oil and gas field development, can realize collaborative control, and can reduce the treatment cost.

[0007] To achieve the above purpose, the present application provides an oil and gas field waste liquid classification and gradient treatment method, which comprises the following steps:

[0008] (1) electro-oxidation treatment of produced water to produce chlorine in situ while denitrifying and decarbonizing and retain active chlorine to obtain electro-oxidation treated produced water;

[0009] (2) adsorption treatment of a part of the electro-oxidation treated produced water with an adsorption material to capture active chlorine to obtain an adsorption material for capturing active chlorine and adsorption treated produced water;

[0010] (3) at least biological treatment of the adsorption treated produced water to obtain treated produced water for discharge;

[0011] (4) mixing another part of the electro-oxidation treated produced water with operation waste liquid, and adding the adsorption material for capturing active chlorine as catalytic and oxidative gel breaking material to carry out gel breaking and destabilization treatment to obtain gel breaking and destabilization treated operation waste liquid;

[0012] (5) The operation waste liquid after the gel breaking and destabilization treatment is subjected to coagulation and flocculation separation, and then, after the influence ion control, a treated operation waste liquid is obtained.

[0013] In the oil and gas field waste liquid classification and step-by-step treatment method, preferably, the produced water and the operation waste liquid can be waste liquid produced and discharged by the same oil and gas field development platform, or can be waste liquid produced and discharged by a nearby platform.

[0014] In the oil and gas field waste liquid classification and step-by-step treatment method, preferably, before the electric oxidation treatment of the produced water, the step (1) further comprises a pretreatment of the produced water, the pretreatment comprising coagulation treatment and / or sedimentation treatment, etc., to remove impurities and / or oil, etc., from the produced water, thereby improving the efficiency of the electric oxidation treatment. In the coagulation treatment of the pretreatment, the treatment agent can comprise one or a combination of inorganic coagulants, organic flocculants, and microbial flocculants, etc. More specifically, the treatment agent used in the coagulation treatment of the pretreatment comprises one or a combination of inorganic coagulants such as polyaluminum chloride and / or aluminum salt, iron salt inorganic composite coagulant (such as polyaluminum ferric sulfate), etc.; organic flocculants such as organic quaternary ammonium salt and polyacrylamide; microbial flocculants such as microbial secretions, etc. Preferably, the dosage of the treatment agent used in the coagulation treatment of the pretreatment can be 50-1000 mg / L, i.e., 50-1000 mg of the treatment agent is added per L of the produced water. The sedimentation treatment in the pretreatment can be performed in a conventional manner in the art, which is not particularly limited in the present application. Preferably, the time of the pretreatment can be 30-120 min.

[0015] In the oil and gas field waste liquid classification and step-by-step treatment method, preferably, in the step (1), the anode of the electrode material used in the electric oxidation treatment comprises Ti, Pt, PbO2, SnO2, DSA, or BDD, etc., and the cathode comprises titanium, stainless steel, or graphite, etc. More preferably, the distance between the anode and the cathode in the electric oxidation treatment is 1.5-4.5 cm, the current density is 5-60 mA / cm 2 , and the time of the electric oxidation treatment is 10-180 min. After the selective pretreatment of the produced water, the present application performs the electric oxidation treatment for denitrification and decarburization and in-situ production of chlorine, thereby reducing the pollutant load of organic matter, ammonia nitrogen, and total nitrogen in the produced water, improving the biodegradability of the produced water, facilitating the subsequent treatment and discharge, and retaining active chlorine during the electric oxidation process. In the electric oxidation treatment, the efficiency of denitrification, decarburization, and in-situ production of chlorine can be investigated by using indicators such as COD, ammonia nitrogen, and total nitrogen, the chlorine production efficiency can be directly monitored by using a residual chlorine detector, a colorimetric method, etc., or indirectly measured by determining the concentration of chloride ions.

[0016] In the oil and gas field waste liquid classification and step-by-step treatment method, preferably, in step (1), the active chlorine concentration in the produced water after the electro-oxidation treatment is ≥2 mg / L.

[0017] In the oil and gas field waste liquid classification and step-by-step treatment method, preferably, in step (1), the COD content in the produced water after the electro-oxidation treatment is ≤300 mg / L, the ammonia nitrogen content is ≤30 mg / L, and the TN (total nitrogen) content is ≤60 mg / L.

[0018] In the oil and gas field waste liquid classification and step-by-step treatment method, preferably, in step (2), the adsorption material includes one or a combination of several of activated carbon, modified activated carbon, and fibers. The adsorption material used in the present application is a material capable of adsorbing active chlorine. Those skilled in the art can select activated carbon, modified activated carbon, and fibers existing in the prior art, and the present application does not specially limit the specific modification method of the modified activated carbon and the specific type of the fibers. More preferably, the dosage of the adsorption material is 1-20 g / L, that is, 1-20 g of adsorption material is added per L of the part of the produced water after the electro-oxidation treatment. More preferably, the adsorption treatment time can be 20-240 min.

[0019] In the oil and gas field waste liquid classification and step-by-step treatment method, preferably, in step (3), the microorganism used in the biological treatment includes one or a combination of several of Proteobacteria, Firmicutes, Acidobacteria, and Cyanobacteria. More preferably, the bacterial species used in the biological treatment includes a combination of Bacillus subtilis and Brucella at a volume ratio of 1:1-5:1, and the dosage of the combination of Bacillus subtilis and Brucella is 2-5% (v / v) based on the total volume of the produced water after the adsorption treatment for biological treatment. More preferably, the biological treatment time can be 10-24 h. More specifically, the biological treatment can be carried out using an SBR system or a CAST system, etc. The biological treatment of the present application can reduce carbon and nitrogen, effectively reducing the COD in the produced water.

[0020] In the oil and gas field waste liquid classification and step-by-step treatment method, preferably, step (3) further includes a depth treatment after the biological treatment, and the depth treatment includes ozone and / or ultraviolet deep degradation or activated carbon adsorption. More preferably, when the COD content in the effluent of the biological treatment is 60 mg / L or more, the depth treatment is carried out to obtain the treated produced water with COD ≤60 mg / L, which meets the discharge standard.

[0021] Preferably, in step (3), the COD content of the treated produced water for discharge is less than or equal to 60 mg / L, the ammonia nitrogen content is less than or equal to 8 mg / L, and the TN content is less than or equal to 40 mg / L.

[0022] After the produced water is subjected to electro-oxidation treatment, a part of the produced water is subjected to adsorption treatment by using an adsorption material to capture active chlorine, the produced water after adsorption treatment is subjected to biological treatment, and is selectively subjected to deep treatment, so that the treated produced water can reach the discharge standard.

[0023] In the oil and gas field waste liquid classification and step-by-step treatment method, preferably, in step (4), the mixing ratio of the other part of the electro-oxidation treated produced water and the operation waste liquid is such that the active chlorine concentration in the mixed waste liquid is greater than or equal to 1.0 mg / L.

[0024] In the oil and gas field waste liquid classification and step-by-step treatment method, preferably, in step (4), the dosage of the adsorption material for capturing active chlorine is 0.1-10 g / L, that is, 0.1-10 g of the adsorption material for capturing active chlorine is added to each L of the mixed waste liquid of the other part of the electro-oxidation treated produced water and the operation waste liquid.

[0025] In the oil and gas field waste liquid classification and step-by-step treatment method, preferably, in step (4), a gel breaker is added during the gel breaking and destabilization treatment. More preferably, the gel breaker includes persulfate and / or Fenton reagent, etc. Further preferably, the dosage of the gel breaker is 10-1000 mg / L, that is, 10-1000 mg of the gel breaker is added to each L of the mixed waste liquid of the other part of the electro-oxidation treated produced water and the operation waste liquid.

[0026] In the oil and gas field waste liquid classification and step-by-step treatment method, preferably, in step (4), an oxygen releasing agent is added during the gel breaking and destabilization treatment. More preferably, the oxygen releasing agent includes percarbonate and / or peroxide, etc. Further preferably, the dosage of the oxygen releasing agent is 50-1000 mg / L, that is, 50-1000 mg of the oxygen releasing agent is added to each L of the mixed waste liquid of the other part of the electro-oxidation treated produced water and the operation waste liquid.

[0027] In the oil and gas field waste liquid classification and step-by-step treatment method, preferably, in step (4), the degree of turbulence is increased by rapid stirring and / or pipeline jetting, etc. during the gel breaking and destabilization treatment.

[0028] In the oil and gas field waste liquid classification and step-by-step treatment method, preferably, in step (4), the gel breaking and destabilization treatment is performed for 10-60 min.

[0029] In step (4) of the present application, another part of the produced water after electro-oxidation treatment is mixed with the working waste liquid, the treatment efficiency of the working waste liquid is improved by the gel-breaking and destabilization of the active chlorine retained therein and the dilution effect, while the gel-breaking agent dosage is reduced and the treatment cost is lowered. The active chlorine concentration in the produced water after electro-oxidation treatment is ≥2 mg / L, the higher the active chlorine concentration, the better the gel-breaking effect on the working waste liquid, and the adsorption material for capturing active chlorine is added to the mixed waste liquid as a catalytic and oxidizing gel-breaking material. The organic matter in the waste liquid is broken and destabilized at the interface of active chlorine, adsorbent, etc., and the material loaded on the surface of the adsorbent plays a catalytic role. The oxygen-releasing agent can also be added at the same time as the gel-breaking agent to increase the dissolved oxygen concentration of the waste liquid and improve the gel-breaking efficiency. The working waste liquid is left to stand for 10-60 min for gel-breaking and destabilization treatment, and the working waste liquid after gel-breaking and destabilization treatment is obtained. During the gel-breaking and destabilization treatment, the gel-breaking effect can be improved and the dosage of the gel-breaking agent can be reduced by increasing the degree of turbulence and supplementing the oxygen-releasing agent. The present application effectively solves the problem of gel-breaking and destabilization of the working waste liquid.

[0030] In the above-mentioned oil and gas field waste liquid classification and step-by-step treatment method, preferably, in step (5), coagulation and flocculation separation is carried out, which includes adding a coagulant and / or a flocculant for coagulation and flocculation treatment, and then separating by sedimentation to obtain the working waste liquid after coagulation and flocculation separation. More preferably, the coagulant includes inorganic coagulants; and the flocculant includes organic flocculants and / or microbial flocculants. More specifically, the coagulant includes polyaluminum chloride and / or aluminum salt, iron salt inorganic composite coagulant (such as polyaluminum ferric sulfate), etc.; and the flocculant includes one or a combination of several of organic quaternary ammonium salt, organic flocculants such as polyacrylamide, microbial flocculants such as microbial secretions, etc. The dosage of the coagulant can be 100-1000 mg / L, i.e., 100-1000 mg of coagulant is added per L of working waste liquid after gel-breaking and destabilization treatment. The dosage of the flocculant is 1-10 mg / L, i.e., 1-10 mg of flocculant is added per L of working waste liquid after gel-breaking and destabilization treatment. More preferably, the coagulation and flocculation treatment time is 10-45 min; and the sedimentation separation time is 30-120 min. The sedimentation separation can be carried out in a conventional manner in the art, which is not particularly limited in the present application.

[0031] In the oil and gas field waste liquid classification and step-by-step treatment method, preferably, in step (5), the ion control includes: adding one or a combination of several of chemical precipitants, metal ion chelating agents, and metal ion adsorbents to the operation waste liquid after the coagulation and flocculation separation to remove most of the metal ions that have an impact, such as calcium ions, magnesium ions, etc., and adding a polyhydroxy organic masking agent to treat the metal ions that cannot be removed, such as boron ions, etc. More preferably, the chemical precipitants include sodium carbonate and / or calcium hydroxide, etc. The metal ion chelating agents include amine-based organic compounds and / or carboxyl-based organic compounds, etc. The metal ion adsorbents include one or a combination of several of activated carbon, modified activated carbon, zeolite, and modified zeolite, etc. Those skilled in the art can select the existing activated carbon, modified activated carbon, zeolite, and modified zeolite in the prior art, and the present application does not specifically limit the specific modification method of the modified activated carbon and the modified zeolite. The dosage of one or a combination of several of the chemical precipitants, the metal ion chelating agents, and the metal ion adsorbents can be 50-5000 mg / L. The polyhydroxy organic masking agent includes polyhydroxy amine and / or chitosan, etc. The dosage of the polyhydroxy organic masking agent can be 10-600 mg / L.

[0032] In the oil and gas field waste liquid classification and step-by-step treatment method, preferably, in step (5), the viscosity of the treated operation waste liquid is ≤1.5 mpa·s, the suspended matter content is ≤50 mg / L, the hardness ion concentration is ≤500 mg / L, and the oil content is ≤50 mg / L.

[0033] In the oil and gas field waste liquid classification and step-by-step treatment method, preferably, step (5) further includes: recycling the treated operation waste liquid. The recycling can include reinjection and / or back blending.

[0034] Oil and gas field development produces large amount of waste liquid, various types, high processing cost, and needs to improve the processing efficiency and resource utilization rate. The technical scheme of the present application is around the large platform production mode of oil and gas field development, aiming at different types of wastewater such as produced water and operation waste liquid produced and discharged in the same regional platform or adjacent regional platform, fully considering the cascade effect between wastewater types and treatment process, realizing the collaborative control of pollutants, reducing the treatment cost, and improving the resource utilization efficiency of wastewater. Specifically, the method of the present application carries out electro-oxidation treatment on the produced water, can degrade the nitrogen-containing and carbon-containing organic matter in the produced water, improve the biodegradability of the produced water, and in-situ produce active chlorine; a part of the produced water carrying active chlorine is mixed with the operation waste liquid, the active chlorine in the produced water is used for gel breaking and de-stabilization, and the dilution effect is used to improve the treatment efficiency of the operation waste liquid, reduce the discharge treatment amount of the produced water, and increase the reuse amount of the operation waste liquid; the remaining produced water after electro-oxidation treatment is used to capture active chlorine by adsorption material, the de-chlorinated produced water is biologically treated, and can be further deep treated, and then discharged according to the standard; and the adsorption material for capturing active chlorine is further used to treat the mixed operation waste liquid, and the catalytic degradation effect of active chlorine and adsorption material is used to carry out gel breaking and de-stabilization treatment on the operation waste liquid; then, the operation waste liquid after gel breaking and de-stabilization treatment is controlled in terms of influencing ions, and the treated operation waste liquid can be reused.

[0035] In summary, the method of the present application is used for the large platform production mode of oil and gas field development, and different types of wastewater such as produced water and operation waste liquid produced and discharged in the same regional platform or adjacent regional platform are classified and cascade treated; the high-efficiency treatment effect of electro-oxidation is fully utilized, the discharge treatment process and discharge treatment amount of the produced water are shortened, and the treatment cost is reduced; the produced water and the operation waste liquid are mixed and treated, the reuse amount of the operation waste liquid is increased, and the water resource utilization rate is reduced; the active chlorine produced in-situ by electro-oxidation is mixed by the produced water and added by the active chlorine adsorption material, the gel breaker addition amount is reduced, and the reagent cost is reduced. The oil and gas field wastewater classification cascade treatment method of the present application realizes the collaborative control of pollutants, reduces the treatment cost, and improves the resource utilization efficiency of wastewater. BRIEF DESCRIPTION OF DRAWINGS

[0036] Figure 1 The process flow chart of the oil and gas field wastewater classification cascade treatment method is provided for the specific embodiment of the present application. DETAILED DESCRIPTION

[0037] In order to have a clearer understanding of the technical features, objects and beneficial effects of the present application, the technical scheme of the present application is described in detail as follows, but cannot be understood as limiting the implementable scope of the present application.

[0038] EMBODIMENT

[0039] The embodiment provides a kind of oil and gas field waste liquid classification cascade processing method.The method is handled to produced water and operation waste liquid of certain oilfield development platform.The oilfield development platform has 20 wells, part of well carries out drilling, fracturing operation, part of well has carried out oil production operation, and produces produced water.

[0040] As Figure 1 Indicated, the method comprises the following steps:

[0041] (1) the pretreatment of produced water, the pretreatment includes coagulation treatment and sedimentation treatment, to carry out impurity removal and oil removal etc. to produced water;The coagulation treatment in the pretreatment adopts the treating agent, including the combined agent of polyaluminum chloride, bacillus microbial flocculant and polyacrylamide, the mass ratio of polyaluminum chloride, bacillus microbial flocculant and polyacrylamide is 100:10:1, the dosing amount of the treating agent is 800mg / L, and the time of the pretreatment is 60min;

[0042] Then carry out electro-oxidation treatment, in-situ production of chlorine and retention of active chlorine while denitrification and decarbonization, to obtain the produced water after electro-oxidation treatment;The anode of the electrode material used in the electro-oxidation treatment is Ti, Pt, PbO2, SnO2, DSA or BDD, and the cathode is graphite, the distance between anode and cathode in the electro-oxidation treatment is 3cm, and the current density is 5-60mA / cm 2 , the time of the electro-oxidation treatment is 10-120min;The COD removal rate, TN removal rate and active chlorine concentration of the produced water after electro-oxidation treatment obtained by different anodes, current densities and electro-oxidation treatment times are shown in table 1;

[0043] Table 1

[0044]

[0045]

[0046] It can be seen that the different anodes of the embodiment can degrade the COD and TN of produced water under certain reaction time and current density, the longer the reaction time and the greater the current density, the higher the COD and TN removal rate, and the residual active chlorine concentration in wastewater is ≥4.0mg / L after 60min of reaction at lower current density;

[0047] The active chlorine concentration in the produced water after electro-oxidation treatment is ≥2mg / L;The average COD content in the produced water after electro-oxidation treatment is 250mg / L, the average ammonia nitrogen content is 28mg / L, and the average TN content is 54mg / L;

[0048] (2) using an adsorption material to adsorb a part of the produced water treated by electro-oxidation to capture active chlorine, to obtain the adsorption material capturing active chlorine and the produced water after adsorption treatment; the adsorption material is alkali modified activated carbon, the dosage of the adsorption material is 10 g / L, and the adsorption treatment time is 60 min;

[0049] (3) using the produced water after adsorption treatment to carry out biological treatment, using SBR system or CAST system, the bacteria used in the biological treatment include a combination of Bacillus subtilis and Brucella at a volume ratio of 1:1 to 5:1, and the dosage of the combination of Bacillus subtilis and Brucella is 2-5% (v / v) based on the total volume of the produced water after adsorption treatment, which is 100%; the biological treatment time is 12 h; the COD removal rates of the produced water after biological treatment obtained by different volume ratios of Bacillus subtilis and Brucella and different dosages of the combination of Bacillus subtilis and Brucella are shown in Table 2;

[0050] Table 2

[0051]

[0052]

[0053] In Table 2, the sterile agent dosage is used as a comparison, and it can be seen that, using the combination of Bacillus subtilis and Brucella in the present embodiment, especially under the condition that the volume ratio of Bacillus subtilis and Brucella is 3:1 and the dosage is 2%, the COD content in the effluent of biological treatment can be reduced to 43.075 mg / L, and no subsequent advanced treatment is needed to reach the discharge standard;

[0054] When the COD content in the effluent of biological treatment is 60 mg / L or more, further advanced treatment is carried out, the advanced treatment includes ozone and / or ultraviolet advanced degradation, to obtain the produced water after treatment, the COD content in the produced water after treatment is <60 mg / L, the ammonia nitrogen content is <8 mg / L, and the TN content is <40 mg / L, reaching the discharge standard;

[0055] (4) mixing another part of the produced water treated by electro-oxidation with the working waste liquid, the mixing ratio is to make the active chlorine concentration in the mixed waste liquid ≥1.0 mg / L, and adding the adsorption material capturing active chlorine as catalytic and oxidative breaker material, the dosage of the adsorption material capturing active chlorine is 1-3 g / L, and adding breaker and oxygen releasing agent, the breaker is Fenton reagent with a dosage of 800 mg / L, and the oxygen releasing agent is sodium percarbonate with a dosage of 600 mg / L, to carry out breaker de-stabilization treatment, the time is 10-60 min, to obtain the working waste liquid after breaker de-stabilization treatment;

[0056] (5) adding coagulant and flocculant to the working waste liquid after the gel breaking and destabilization treatment to perform coagulation and flocculation treatment, and then performing sedimentation separation to obtain working waste liquid after coagulation and flocculation separation; the coagulant used includes polyaluminum ferric sulfate, and the dosage is 600 mg / L; the flocculant includes polyacrylamide, and the dosage is 5 mg / L; the coagulation and flocculation treatment time is 25 min, and the sedimentation separation time is 40 min;

[0057] adding citric acid modified activated carbon to the working waste liquid after coagulation and flocculation separation, and the dosage is 400 mg / L, to remove most of the metal ions having influence, and adding polyhydroxy amine, and the dosage is 200 mg / L, to treat the metal ions that cannot be removed, and then performing influence ion control to obtain treated working waste liquid, the viscosity of the treated working waste liquid is ≤1.35 mPa·s, the suspended matter content therein is ≤45 mg / L, the hardness ion concentration is ≤450 mg / L, and the oil content is ≤40 mg / L, which can meet the reinjection or back blending standard.

[0058] Test Example 1

[0059] In this test example, the produced water after electro-oxidation treatment with an active chlorine concentration of 10 mg / L and the working waste liquid with a viscosity of 10.1 mPa·s are mixed in different proportions, different dosages of adsorption materials (specifically, alkali modified activated carbon) are added, and the gel breaking and destabilization treatment is performed for different residence times, and the viscosity of the working waste liquid after gel breaking and destabilization treatment is analyzed. The test conditions and results are shown in Table 3.

[0060] Table 3

[0061]

[0062]

[0063] It can be seen that the higher the mixing ratio of the produced water after electro-oxidation treatment and the working waste liquid, the larger the dosage of adsorption material, and the longer the residence time, the lower the viscosity of the effluent, which can be reduced to below 1.5 mPa·s.

[0064] Test Example 2

[0065] In this test example, different dosages of oxygen releasing agent (specifically, sodium percarbonate) and gel breaker (specifically, Fenton reagent) are added to the working waste liquid with a viscosity of 4.5 mPa·s, and the gel breaking and destabilization treatment is performed for 10 min, and the viscosity of the working waste liquid after gel breaking and destabilization treatment is analyzed. The test conditions and results are shown in Table 4.

[0066] Table 4

[0067]

[0068] It can be seen that the breaking effect can be improved and the adding amount of the breaking agent can be reduced by adding the oxygen releasing agent.

[0069] Comparative Example 1

[0070] The comparative example provides an oil and gas field waste liquid treatment method. The method is basically the same as the embodiment, and the difference is that the produced water is not mixed with the operation waste liquid, but is pretreated, electro-oxidized, adsorbed, biologically treated, and deeply treated to obtain treated produced water, which is discharged up to standard; the operation waste liquid is mixed with the adsorption material for capturing active chlorine, the breaking agent and the oxygen releasing agent for breaking and destabilizing treatment, and then coagulation and flocculation treatment, and then precipitation separation, and then ion control to obtain treated operation waste liquid, which can meet the standard of reinjection or back blending. In the case that the content of each pollutant in the treated produced water and the treated operation waste liquid reaches the standard of the above embodiment, it is found that the treatment amount and cost of the produced water increase by more than 30% compared with the embodiment, and the total cost of each treatment agent in the treatment process of the operation waste liquid increases by more than 20%.

[0071] Comparative Example 2

[0072] The comparative example provides an oil and gas field waste liquid treatment method. The method is basically the same as the embodiment, and the difference is that the adsorption material for capturing active chlorine is not added in step (4). In the case that the content of each pollutant in the treated operation waste liquid reaches the standard of the above embodiment, it is found that the total cost of each treatment agent in the treatment process of the operation waste liquid increases by more than 10%, and the subsequent treatment cost of the adsorption material for capturing active chlorine is also increased.

[0073] Comparative Example 3

[0074] The comparative example provides an oil and gas field produced water treatment method. The method is to pretreat, biologically treat and electro-oxidize the produced water to obtain treated produced water; the specific conditions of pretreatment, biological treatment and electro-oxidation treatment are the same as those of the embodiment, wherein the ratio of the bacterial agent is 3:1 and the adding amount is 2%. The results compared with the effluent of the biological treatment in the embodiment (bacterial agent ratio 3:1, adding amount 2%) are shown in Table 5.

[0075] Table 5

[0076]

[0077] It can be seen that the biodegradability of the produced water treated by electro-oxidation in the embodiment of the application is improved, which is beneficial to subsequent biological treatment. In the comparative example, the pretreated produced water is directly biologically treated, the biodegradability is low, the biochemical efficiency is low, and then electro-oxidation treatment is performed, and the pollutant content of the effluent is also much higher than that of the embodiment.

Claims

1. A method for classified and tiered treatment of oil and gas field wastewater, comprising the following steps: (1) The produced water is subjected to electro-oxidation treatment to produce chlorine in situ while removing nitrogen and carbon and retaining active chlorine, thus obtaining the produced water after electro-oxidation treatment; (2) Adsorption material is used to adsorb a portion of the produced water after electro-oxidation treatment to capture active chlorine, thereby obtaining the adsorption material for capturing active chlorine and the produced water after adsorption treatment. (3) The adsorption-treated produced water shall be subjected to at least biological treatment to obtain treated produced water that meets the standards for discharge. (4) Mix another part of the produced water after electro-oxidation treatment with the work waste liquid, and add the adsorbent material that captures active chlorine as a catalyst and oxidative de-gelling material to carry out de-gelling and destabilization treatment to obtain the work waste liquid after de-gelling and destabilization treatment. (5) The work waste liquid after the de-gelling and destabilization treatment is subjected to coagulation and flocculation separation, and then subjected to ion control to obtain the treated work waste liquid.

2. The method for classified and tiered treatment of oil and gas field wastewater according to claim 1, wherein, The produced water and the waste liquid from the operation are either waste liquid produced and discharged from the same oil and gas field development platform or waste liquid produced and discharged from a platform in a neighboring area.

3. The method for classified and tiered treatment of oil and gas field wastewater according to claim 1, wherein, Step (1) further includes pre-treating the produced water before electro-oxidation treatment, the pre-treatment including coagulation treatment and / or sedimentation treatment.

4. The method for classified and tiered treatment of oil and gas field wastewater according to claim 3, wherein, The coagulation treatment used in the pretreatment includes one or a combination of inorganic coagulants, organic flocculants, and microbial flocculants.

5. The method for classified and tiered treatment of oil and gas field wastewater according to claim 4, wherein, The dosage of the coagulation agent used in the pretreatment is 50~1000mg / L.

6. The method for classified and tiered treatment of oil and gas field wastewater according to claim 3, wherein, The pretreatment time is 30~120 min.

7. The method for classified and tiered treatment of oil and gas field wastewater according to claim 1, wherein, In step (1), the anode of the electrode material used in the electro-oxidation treatment includes Ti, Pt, PbO2, SnO2, DSA or BDD, and the cathode includes titanium, stainless steel or graphite.

8. The method for classified and tiered treatment of oil and gas field wastewater according to claim 1, wherein, In step (1), the distance between the anode and cathode in the electro-oxidation treatment is 1.5~4.5cm, and the current density is 5~60mA / cm. 2 The electro-oxidation treatment time is 10~180 min.

9. The method for classified and tiered treatment of oil and gas field wastewater according to claim 1, wherein, In step (1), the concentration of active chlorine in the extracted water after the electro-oxidation treatment is ≥2 mg / L.

10. The method for classified and tiered treatment of oil and gas field wastewater according to claim 1, wherein, In step (1), the COD content, ammonia nitrogen content, and TN content in the extracted water after electro-oxidation treatment are ≤300mg / L, ≤30mg / L, and ≤60mg / L, respectively.

11. The method for classified and tiered treatment of oil and gas field wastewater according to claim 1, wherein, In step (2), the adsorption material includes one or a combination of activated carbon, modified activated carbon and fibers.

12. The method for classified and tiered treatment of oil and gas field wastewater according to claim 11, wherein, In step (2), the amount of adsorbent added is 1~20g / L.

13. The method for classified and tiered treatment of oil and gas field wastewater according to claim 1, wherein, In step (2), the adsorption treatment time is 20~240 min.

14. The method for classified and tiered treatment of oil and gas field wastewater according to claim 1, wherein, In step (3), the microorganisms used in the biological treatment include one or a combination of several of the following: Proteobacteria, Firmicutes, Acidobacteria, and Cyanobacteria.

15. The method for classified and tiered treatment of oil and gas field wastewater according to claim 14, wherein, In step (3), the bacterial strains used in the biological treatment include a combination of Bacillus subtilis and Brucella in a volume ratio of 1:1 to 5:

1. Based on the total volume of the extracted water after the adsorption treatment of the biological treatment being 100%, the dosage of the combination of Bacillus subtilis and Brucella is 2 to 5%.

16. The method for classified and tiered treatment of oil and gas field wastewater according to claim 1, wherein, In step (3), the biological treatment time is 10-24 hours.

17. The method for classified and tiered treatment of oil and gas field wastewater according to claim 1, wherein, Step (3) further includes a deep treatment following the biological treatment, which includes ozone and / or ultraviolet deep degradation or activated carbon adsorption.

18. The method for classified and tiered treatment of oil and gas field wastewater according to claim 17, wherein, When the COD content in the effluent from the biological treatment is above 60 mg / L, the advanced treatment is carried out to obtain treated produced water.

19. The method for classified and tiered treatment of oil and gas field wastewater according to claim 1, wherein, In step (3), the COD content of the treated effluent discharged in compliance with the standards is ≤60mg / L, the ammonia nitrogen content is ≤8mg / L, and the TN content is ≤40mg / L.

20. The method for classified and tiered treatment of oil and gas field wastewater according to claim 1, wherein, In step (4), the mixing ratio of the other part of the electro-oxidized produced water to the operation waste liquid is such that the active chlorine concentration in the mixed waste liquid is ≥1.0 mg / L.

21. The method for classified and tiered treatment of oil and gas field wastewater according to claim 1, wherein, In step (4), the amount of adsorbent material for capturing active chlorine added is 0.1~10 g / L.

22. The method for classified and tiered treatment of oil and gas field wastewater according to claim 1, wherein, In step (4), a de-destabilizing agent is added during the de-de-destabilizing process.

23. The method for classified and tiered treatment of oil and gas field wastewater according to claim 22, wherein, In step (4), the de-icing agent includes persulfate and / or Fenton's reagent.

24. The method for classified and tiered treatment of oil and gas field wastewater according to claim 23, wherein, In step (4), the dosage of the de-gelling agent is 100~1000 mg / L.

25. The method for classified and tiered treatment of oil and gas field wastewater according to claim 1 or 22, wherein, In step (4), an oxygen-releasing agent is added during the destabilization process.

26. The method for classified and tiered treatment of oil and gas field wastewater according to claim 25, wherein, In step (4), the oxygen-releasing agent includes percarbonate and / or peroxide.

27. The method for classified and tiered treatment of oil and gas field wastewater according to claim 26, wherein, In step (4), the amount of oxygen-releasing agent added is 50~1000 mg / L.

28. The method for classified and tiered treatment of oil and gas field wastewater according to claim 1, wherein, In step (4), the destabilization treatment time is 10~60 min.

29. The method for classified and tiered treatment of oil and gas field wastewater according to claim 1, wherein, In step (5), coagulation and flocculation separation includes: adding coagulant and / or flocculant for coagulation and flocculation treatment, followed by sedimentation and separation to obtain the coagulated and flocculated waste liquid.

30. The method for classified and tiered treatment of oil and gas field wastewater according to claim 29, wherein, In step (5), the coagulant includes inorganic coagulants; the flocculant includes organic flocculants and / or microbial flocculants.

31. The method for classified and tiered treatment of oil and gas field wastewater according to claim 30, wherein, In step (5), the dosage of the coagulant is 100~1000 mg / L; the dosage of the flocculant is 1~10 mg / L.

32. The method for classified and tiered treatment of oil and gas field waste liquid according to claim 29, wherein, In step (5), the coagulation and flocculation treatment time is 10~45 min; the sedimentation and separation time is 30~120 min.

33. The method for classified and tiered treatment of oil and gas field wastewater according to claim 29, wherein, In step (5), the control of influencing ions includes: adding one or more of the following to the waste liquid after coagulation and flocculation separation: chemical precipitant, metal ion chelating agent and metal ion adsorbent to remove most of the influencing metal ions; and adding a polyhydroxy organic masking agent to treat the metal ions that cannot be removed.

34. The method for classified and tiered treatment of oil and gas field wastewater according to claim 33, wherein, In step (5), the chemical precipitant includes sodium carbonate and / or calcium hydroxide; the metal ion chelating agent includes amine organics and / or carboxyl organics; and the metal ion adsorbent includes one or a combination of activated carbon, modified activated carbon, zeolite and modified zeolite.

35. The method for classified and tiered treatment of oil and gas field wastewater according to claim 33, wherein, In step (5), the dosage of one or more of the chemical precipitant, metal ion chelating agent and metal ion adsorbent is 50~5000 mg / L.

36. The method for classified and tiered treatment of oil and gas field wastewater according to claim 33, wherein, In step (5), the polyhydroxy organic masking agent includes polyhydroxyamines and / or chitosan.

37. The method for classified and tiered treatment of oil and gas field wastewater according to claim 33, wherein, In step (5), the dosage of the polyhydroxy organic masking agent is 10~600 mg / L.

38. The method for classified and tiered treatment of oil and gas field waste liquid according to claim 1, wherein, In step (5), the viscosity of the treated waste liquid is ≤1.5 mpa·s, the suspended solids content is ≤50 mg / L, the hardness ion concentration is ≤500 mg / L, and the oil content is ≤50 mg / L.

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