Treatment method and system for oil field fracturing flow-back fluid

Abstract

The invention belongs to the technical field of fracturing flow-back fluid treatment, and particularly relates to a treatment method and system for oil field fracturing flow-back fluid. The method comprises a pretreatment step and a wind energy carrier band evaporation step. The pretreatment step is used for providing qualified inlet water for the wind energy carrier band evaporation step by reducing SS (suspended solids), total hardness, COD (chemical oxygen demand), petroleum and viscosity of flow-back liquid and adjusting the pH value of the flow-back liquid; in the wind energy carrier band evaporation step, the inlet water is evaporated through a wind energy carrier band, and volatile COD (Chemical Oxygen Demand) is removed through a gas-liquid mass transfer effect. According to the pretreatment step, SS, petroleum, total hardness and COD can be effectively removed; tDS (total dissolved solids) and volatile COD (chemical oxygen demand) can be effectively removed in the wind energy carrier band evaporation step. Meanwhile, according to the wind energy carrier band evaporation step, a gas-liquid contact interface is constructed through a carrier with the high specific surface area, mass transfer is accelerated with wind energy as core power, and the energy consumption and the operation cost are greatly reduced.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of fracturing flowback fluid treatment, and particularly relates to a treatment method and system for oilfield fracturing flowback fluid. BACKGROUND

[0002] For the development of low-permeability oil and gas resources, fracturing reconstruction has become a core technology for enhancing recovery. However, the flowback fluid generated by fracturing operations has the characteristics of "four high and two complex" (high suspended solids, high hardness, high salinity, high COD, complex composition, and complex water quality fluctuations), which has become a key bottleneck restricting the green development of oilfields. Traditional treatment technologies generally have high energy consumption, high operating costs, and incomplete salt separation.

[0003] For example, Yulin Oilfield is located in the northeastern part of Ordos Basin, with proven oil and gas reserves exceeding 2 billion tons. The main reservoir is a low-permeability to ultra-low-permeability rock formation, with a porosity generally less than 15% and a permeability of only 0.1-10 mD. According to data from 2023, the oilfield has a fracturing operation volume of 12,000 wells per year, with a single well fracturing fluid consumption of 1,000-5,000 m³, a flowback rate of 30%-60%, and an annual production of fracturing flowback fluid of 1.8-3.6 million m³, with a growing trend. The fracturing flowback fluid in this region is mainly based on guanidine gum water-based fracturing fluid, which forms a complex system after mixing with reservoir fluid. Monitoring data from five typical treatment stations in Jingbian and Dingbian shows that the SS concentration of the flowback fluid is 256-1430 mg / L, the COD is 1600-4100 mg / L, the TDS is 20000-60000 mg / L, the total hardness (in terms of CaCO3) is 6000-22000 mg / L, and the oil content is 0-1500 mg / L. The pollutant concentration in the early stage (1-3 days) is significantly higher than that in the middle and late stages. The surrounding area of Yulin Oilfield is the ecologically fragile area of the edge of the Mu Us Desert, and if such wastewater is discharged without treatment, it will cause soil salinization and groundwater pollution; if it is directly reused, it will exacerbate reservoir damage and pipeline blockage, and the treatment demand is urgent.

[0004] Current fracturing flowback fluid treatment technologies can be divided into three categories, but all have obvious limitations: physical and chemical methods (coagulation, flotation, etc.) can only remove suspended solids and oil, and the TDS removal rate is less than 5%; biological treatment methods have a COD removal rate of less than 30% when TDS > 15000 mg / L due to high salt inhibition; and evaporation concentration methods (MVR, multi-effect evaporation) can achieve salt separation, but the unit energy consumption of MVR is 80-120 kWh / ton of water, the treatment cost is 40-60 yuan / ton of water, and it is prone to fouling and blockage, with a continuous operation cycle of only 45 days. SUMMARY

[0005] The present application aims to at least solve one of the problems in the prior art or related art, that is, in the treatment process of fracturing flowback fluid, the COD removal rate is low, the energy consumption is high, the operation cost is high, and the salt separation is not complete.

[0006] In view of this, the first aspect of the present application provides a treatment method for oilfield fracturing flowback fluid, by which the SS removal rate is 99.7%, the petroleum removal rate is 99.9%, the total hardness removal rate is 99.2%, the TDS removal rate is 95.0%, and the COD removal rate is 74.3%; at the same time, the wind energy carrier technology is introduced into the treatment of fracturing flowback fluid, the gas-liquid contact interface is constructed by a high specific surface area carrier, and the mass transfer is accelerated by wind energy as the core power, thereby greatly reducing the energy consumption and operation cost.

[0007] The second aspect of the present application provides a treatment system for oilfield fracturing flowback fluid, which is used for treating the oilfield fracturing flowback fluid by the above treatment method.

[0008] Specifically, the following technical solutions are included: According to the first aspect of the present application, a treatment method for oilfield fracturing flowback fluid is provided, which includes a pretreatment step and a wind energy carrier evaporation step; the pretreatment step reduces the SS, total hardness, COD, petroleum, and viscosity of the flowback fluid, and adjusts the pH value of the flowback fluid, so as to provide qualified feed water for the wind energy carrier evaporation step; the wind energy carrier evaporation step evaporates the feed water by wind energy carrier, and removes volatile COD through gas-liquid mass transfer.

[0009] Further, the pretreatment step includes: S1: pre-settling adjustment: through stirring and standing, large particle suspensions in the liquid are precipitated and removed, so that SS≤426mg / L; S2: gel breaking: ammonium persulfate is added to the liquid to destroy the colloidal structure in the liquid and release the wrapped suspensions and oil, so that the viscosity of the liquid is <1.5mPa·s, and COD≤2600mg / L; S3: hardness removal: lime is added to the liquid to make magnesium ions in the liquid generate Mg(OH)2 precipitate, and soda ash is added to the liquid to make calcium ions in the liquid generate CaCO3 precipitate, so that the hardness of the liquid is ≤200mg / L; S4: high-density precipitation: PAC and PAM are added to the liquid, so that the micro-suspended particles and colloidal substances in the liquid are coagulated and precipitated, so that SS≤5mg / L; S5: air flotation: air is introduced into the liquid, so that the suspensions and oil in the liquid which are light in density and not easy to settle are attached to micro-bubbles to quickly float and be scraped off, so that the concentration of petroleum is ≤0.8mg / L.

[0010] Preferably, in the S1 step, the frequency of the stirring is 90r / min-100r / min; and the standing time is 4h-5h.

[0011] Preferably, in the S2 step, the ammonium persulfate is added in an amount of 0.8 g / L to 0.9 g / L, the reaction temperature is 50°C to 60°C, and the reaction time is 2 h to 3 h.

[0012] Preferably, in the S3 step, the step of adding lime to the liquid brings the pH value of the liquid to 10.5 to 11; and the sodium carbonate is added in an amount of 1.2 to 1.3 times the theoretical requirement.

[0013] Preferably, in the S4 step, the PAC is added in an amount of 100 mg / L to 110 mg / L, the PAM is added in an amount of 3 mg / L to 4 mg / L, and the precipitation time is 60 min to 70 min.

[0014] Preferably, in the S5 step, the pressure of the dissolved gas is 0.3 MPa to 0.4 MPa, and the water reflux ratio of the dissolved gas is 30% to 35%.

[0015] According to a second aspect of the embodiments of the present application, a treatment system for oilfield fracturing flowback fluid is provided, which is used for treating oilfield fracturing flowback fluid by the method according to any one of the above technical solutions, and comprises a pretreatment system and a wind energy carrier evaporation unit in communication; the pretreatment system comprises a pre-sedimentation adjustment unit, a gel breaking unit, a hardness removal unit, a high-density sedimentation unit, and a gas flotation unit in sequence; the wind energy carrier evaporation unit comprises a plurality of water distribution pipes and a plurality of evaporation curtains; the water distribution pipes are in communication with a water storage pool storing the flowback fluid, and the plurality of water distribution pipes are arranged in parallel on the same horizontal plane; a vertical evaporation curtain is arranged in parallel at the bottom of each water distribution pipe; a plurality of water injection holes are formed in the water distribution pipe, and the injection direction of the water injection holes is towards the surface of the evaporation curtain.

[0016] Preferably, the distance between two adjacent evaporation curtains is 50 mm to 60 mm.

[0017] Preferably, the evaporation curtain comprises a silicon-based evaporation curtain.

[0018] Compared with the prior art, the present application has at least the following beneficial effects: The present application has the following beneficial effects: The removal rates of SS, petroleum, and total hardness are 99.7%, 99.9%, and 99.2%, respectively, through the pretreatment step, effectively solving the problems of clogging and fouling of the evaporation system, and degrading part of the organic polymers to achieve a COD removal rate of 36.2%; in the wind energy carrier evaporation step, the TDS removal rate reaches 95.0% through wind energy carrier evaporation, and 38.1% of the volatile COD is removed through gas-liquid mass transfer. At the same time, the wind energy carrier evaporation step of the present application constructs a gas-liquid contact interface through a high specific surface area carrier, and accelerates mass transfer with wind energy as the core power, greatly reducing energy consumption and operating costs. Attached Figure Description

[0019] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the scope of this application. In the drawings: Figure 1 This is a flowchart illustrating an embodiment of this application; Figure 2 This is a schematic diagram of the processing system according to an embodiment of this application; Figure 3 This is a schematic diagram of the structure of the wind power carrier evaporation unit in an embodiment of this application; Figure 4 This is a comparison table of the embodiments of this application and the prior art.

[0020] The attached figures are labeled as follows: 1-Water distribution pipe; 2-Evaporation curtain. Detailed Implementation

[0021] To better understand the above technical solutions, the technical solutions of the embodiments of this application will be described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the embodiments of this application and the specific features in the embodiments are detailed descriptions of the technical solutions of the embodiments of this application, rather than limitations on the technical solutions of this application. In the absence of conflict, the embodiments of this application and the technical features in the embodiments can be combined with each other.

[0022] In view of this, according to a first aspect of the embodiments of this application, a method for treating oilfield fracturing flowback fluid is provided, such as... Figure 1 As shown, the method includes a pretreatment step and a wind power carrier evaporation step; the pretreatment step provides qualified feed water for the wind power carrier evaporation step by reducing the SS, total hardness, COD, petroleum hydrocarbons, and viscosity of the return liquid, and adjusting the pH value of the return liquid; the wind power carrier evaporation step evaporates the feed water through the wind power carrier and removes volatile COD through gas-liquid mass transfer.

[0023] Specifically, the core objective of the pretreatment step is to control SS to be below 5 mg / L, total hardness to be below 200 mg / L, and viscosity to be ≤1.5 mPa·s, so as to provide qualified water for the wind energy carrier evaporation unit and avoid the evaporation curtain from being blocked and scaled. The wind energy carrier evaporation in the wind energy carrier evaporation step is the core unit of the treatment method, and has the advantages of low carbon, high efficiency, and anti-pollution. The wind energy carrier evaporation technology is based on Dalton's evaporation law, and constructs a gas-liquid contact interface through a high specific surface area carrier, accelerates mass transfer by taking wind energy as the core power, that is, increases the contact area of the liquid and air as much as possible, so that the liquid can evaporate as soon as possible under the action of wind energy. At the same time, part of the COD with volatility is also removed in the wind energy carrier evaporation step, and the removal amount reaches 38.1% to 38.3%. In addition, experiments show that the evaporation rate of the liquid is significantly positively correlated with the temperature, and is significantly negatively correlated with the relative humidity, and there is an obvious interaction between the two. That is, under the condition of the same humidity, when the temperature rises from 5°C to 30°C, the evaporation rate increases by 317%, and the increase in temperature not only increases the kinetic energy of water molecules, accelerates their escape from the liquid film surface, but also increases the saturated water vapor pressure difference of air, providing a greater driving force for mass transfer; under the condition of the same temperature, when the relative humidity rises from 40% to 70%, the evaporation rate decreases by 38.5%, and when the relative humidity exceeds 80%, the air is close to saturation, the mass transfer driving force is sharply weakened, and the evaporation rate is less than 1 kg / (m²·h). Therefore, when the nature is in the low-temperature and high-humidity performance valley, the evaporation rate can be increased to more than 1.2 kg / (m²·h) by using solar energy to assist heating (increasing the water temperature by 5-8°C) in addition to wind energy, so as to ensure the efficiency of the wind energy carrier evaporation step.

[0024] Further, in one embodiment, as shown in FIG. 1, Figure 1 The pretreatment step includes: S1: pre-settling adjustment: through stirring and standing, large particle suspensions in the liquid are precipitated and removed, so that SS≤426 mg / L; S2: gel breaking: ammonium persulfate is added to the liquid to destroy the colloidal structure in the liquid and release the wrapped suspended solids and oil, so that the viscosity of the liquid is <1.5 mPa·s, and COD≤2600 mg / L; S3: hardness removal: lime is added to the liquid to make magnesium ions in the liquid generate Mg(OH)2precipitate, and soda ash is added to the liquid to make calcium ions in the liquid generate CaCO3precipitate, so that the hardness of the liquid is ≤200 mg / L; S4: high-density precipitation: PAC and PAM are added to the liquid to make the small suspended particles and colloidal substances in the liquid coagulate and precipitate, so that SS≤5 mg / L; and S5: air flotation: air is introduced into the liquid, so that the suspended solids and oil in the liquid which are light in density and not easy to settle are attached to micro-bubbles to quickly float and be scraped off, so that the petroleum concentration is ≤0.8 mg / L.

[0025] Preferably, in specific embodiments, in the S1 step, the frequency of stirring is 90 r / min to 100 r / min; and the length of time for standing is 4 h to 5 h.

[0026] Specifically, taking the water sample with SS of 1430 mg / L as an example: when the residence time is extended from 2 h to 4 h, the SS removal rate jumps from 42.3% to 68.5%, and the effluent SS decreases from 826 mg / L to 446 mg / L, because the large-particle suspended solids (such as proppant debris, rock particles) are fully settled; when the residence time is more than 4 h, the removal rate growth tends to be flat, and the removal rates at 6 h and 8 h only differ by 0.3%, and the effluent SS is stable at about 426 mg / L. Considering the treatment efficiency and equipment footprint, the optimal residence time for pre-sedimentation adjustment is determined to be 4 h, which can remove about 70% of the large-particle suspended solids, creating favorable conditions for subsequent S2 and S3 steps.

[0027] Preferably, in specific embodiments, in the S2 step, the ammonium persulfate dosage is 0.8 g / L to 0.9 g / L, the reaction temperature is 50°C to 60°C, and the reaction time is 2 h to 3 h.

[0028] Specifically, the unbroken guanidine gel polymer in the fracturing flowback fluid is the main reason for the increase in liquid viscosity, which will affect the uniformity of water distribution and evaporation efficiency in the wind energy carrying evaporation step, so the viscosity needs to be reduced to below 1.5 mPa·s through gel breaking treatment. Experiments show that the influence of various factors on the viscosity removal rate in the gel breaking process is in the order of gel breaker dosage > reaction temperature > reaction time, so the gel breaker dosage is the core influencing factor. When the gel breaker dosage is insufficient, the guanidine gel molecular chain is not broken enough, and the viscosity decreases slowly; while too high gel breaker dosage will increase the COD content, and experiments show that when the gel breaker dosage is 1.0 g / L, the COD content increases by 5% compared with the gel breaker dosage of 0.8 g / L, and causes reagent waste. Considering the viscosity removal rate and economy, the optimal gel breaking process parameters are determined to be: ammonium persulfate dosage 0.8 g / L, reaction temperature 50°C, and reaction time 2 h, under which the effluent viscosity is reduced to 1.2 mPa·s, the viscosity removal rate is 83.3%, and the COD is controlled at about 2600 mg / L, which meets the requirements of subsequent processes and avoids the cost problem caused by excessive reagents.

[0029] Preferably, in specific embodiments, in the S3 step, the step of adding lime to the liquid makes the pH value of the liquid 10.5 to 11; and the soda ash dosage is 1.2 to 1.3 times the theoretical requirement.

[0030] Specifically, the high concentration of Ca² + and Mg² +is the main inducement of evaporation system scaling, using lime-soda composite hardness removal process, through lime to adjust pH value to make Mg² + Generate Mg(OH)2 precipitate, and then through soda to make Ca² + Generate CaCO3 precipitate, and realize hardness removal. Because the solubility product (Ksp=1.8×10 - ¹¹) of Mg(OH)2 is low, Mg² + ² can be fully precipitated only when pH value is ≥10.5, and too high pH value will lead to reverse movement of CaCO3 precipitate dissolution equilibrium, which is not conducive to hardness removal. Taking water sample with total hardness of 18000 mg / L as an example, the experimental results show that when pH value increases from 9.5 to 10.5, total hardness removal rate increases from 72.3% to 93.8%, and effluent hardness decreases from 5040 mg / L to 1116 mg / L; when pH value exceeds 10.5, removal rate increases slowly, and when pH=11.0, removal rate is 94.2% and effluent hardness is 1044 mg / L. Therefore, the optimal pH value is determined to be 10.5. Under the condition of pH=10.5, the experimental results show that when soda dosage increases from 1.0 times to 1.2 times of the theoretical value, Ca² + Removal rate increases from 88.5% to 99.2%, and effluent Ca² + Concentration decreases from 1480 mg / L to 120 mg / L; when soda dosage exceeds 1.2 times of the theoretical value, removal rate is basically stable; when soda dosage reaches 1.5 times of the theoretical value, removal rate only increases by 0.3%, but the cost of medicament increases by 25%. Therefore, the optimal dosage of soda is determined to be 1.2 times of the theoretical requirement. In summary, total hardness of effluent of S3 step decreases to 180 mg / L, and removal rate reaches 98.9%, which fully meets the requirement of wind energy belt evaporation system on inlet water hardness (≤200 mg / L), and effectively avoids the problem of evaporation curtain surface scaling.

[0031] Preferably, in specific embodiments, in the S4 step, the dosage of PAC is 100 mg / L-110 mg / L, the dosage of PAM is 3 mg / L-4 mg / L, and the sedimentation time is 60 min-70 min.

[0032] Specifically, after S3 step, the flowback fluid still contains a small amount of fine precipitate and petroleum, which needs to be further purified through S4 step and S5 step. In S4 step, by adding coagulant (PAC) and flocculant (PAM), the small suspended particles and colloidal substances in water are coagulated into large and dense alunite flowers, which quickly settle in the sedimentation tank, so as to further remove SS. The experimental results show that when PAC dosage is 100 mg / L, PAM dosage is 3 mg / L, and sedimentation time is 60 min, SS removal rate reaches 99.2%, and effluent SS decreases to less than 5 mg / L.

[0033] Preferably, in specific embodiments, in the S5 step, the pressure of the dissolved gas is 0.3-0.4 MPa, and the water reflux ratio of the dissolved gas is 30%-35%.

[0034] Specifically, in the S5 step, micro-bubbles are generated by introducing the dissolved gas into the liquid. The suspended matter and oil in the liquid, which are lighter in density and not easy to settle, will adhere to the micro-bubbles and quickly float to the water surface and be scraped off, thereby reducing the concentration of petroleum. Experiments show that when the dissolved gas pressure is 0.3 MPa and the dissolved gas water reflux ratio is 30%, the petroleum removal rate reaches 99.0%, and the petroleum concentration in the effluent is ≤0.8 mg / L.

[0035] In summary, taking the water sample with SS of 1430 mg / L, total hardness of 18000 mg / L, COD of 4100 mg / L, and petroleum of 1500 mg / L as an example, after the pretreatment step, the effluent water quality indicators are: pH of 7.8, SS of 3.2 mg / L, total hardness of 180 mg / L, COD of 2400 mg / L, petroleum of 0.6 mg / L, and viscosity of 1.2 mPa·s, which fully meets the water inlet requirements of the wind energy carrier evaporation system and lays a solid foundation for subsequent evaporation enhancement treatment.

[0036] According to a second aspect of the embodiments of the present application, a treatment system for oilfield fracturing flowback fluid is provided for treating the oilfield fracturing flowback fluid by the method according to any of the above technical solutions, as shown in Figure 2 The pretreatment system includes a pre-sedimentation adjustment unit, a gel breaking unit, a hardness removal unit, a high-density sedimentation unit, and a flotation unit connected in sequence. As shown in Figure 3 The wind energy carrier evaporation unit includes a plurality of water distribution pipes 1 and a plurality of evaporation curtains 2. The water distribution pipes 1 are connected to a water storage pool storing the flowback fluid, and a plurality of the water distribution pipes 1 are arranged in parallel on the same horizontal plane. A vertical evaporation curtain 2 is arranged in parallel at the bottom of each water distribution pipe 1. A plurality of water injection holes are formed in the water distribution pipe 1, and the injection direction of the water injection holes is toward the surface of the evaporation curtain 2.

[0037] Specifically, in the wind energy carrier evaporation unit, the water injection holes uniformly inject liquid onto the evaporation curtain 2, and a large number of evaporation curtains 2 enable the liquid to be in contact with air to the greatest extent, thereby improving the evaporation efficiency.

[0038] Preferably, in specific embodiments, the distance between two adjacent evaporation curtains 2 is 50-60 mm.

[0039] Specifically, the performance of the wind energy carrier with the evaporation unit directly determines the efficiency, energy consumption and cost of the entire treatment system, and the distance between the two adjacent evaporation curtains 2 determines the uniformity of airflow distribution and the contact time of gas and liquid. Experiments show that when the distance between the evaporation curtains 2 is too small (≤ 30 mm), the resistance of airflow passing through the evaporation curtains 2 increases, resulting in uneven airflow distribution, airflow dead angle in some areas, and the liquid film cannot be updated in time, limiting the evaporation rate; when the distance between the evaporation curtains 2 is too large (≥ 70 mm), the gas-liquid contact time is shortened, and water molecules cannot fully diffuse into the airflow, resulting in a decrease in mass transfer efficiency. Therefore, the optimal distance between the two adjacent evaporation curtains 2 is determined to be 50 mm.

[0040] Preferably, in specific embodiments, the evaporation curtain 2 comprises a silicon-based evaporation curtain.

[0041] Specifically, the evaporation curtain 2 serves as the core carrier for gas-liquid mass transfer, and its hydrophilicity, corrosion resistance, specific surface area and cost directly affect the evaporation efficiency and system life. The silicon-based evaporation curtain has the following comprehensive performance: first, excellent hydrophilicity, which can quickly adsorb pretreated water and form a uniform liquid film, avoiding local dry areas or liquid accumulation; second, strong corrosion resistance, after soaking in high-salinity wastewater with TDS = 38000 mg / L for 30 days, no corrosion or aging, and the service life is expected to reach 18 months, which is much higher than other materials; third, the specific surface area reaches 850 m² / m³, providing sufficient interface for gas-liquid mass transfer; and fourth, the cost is appropriate, with significant economic advantages.

[0042] In summary, as shown in Figure 4 The nursing method and system of the present application have the following significant comprehensive advantages over the prior art: first, the treatment efficiency is close to MVR and multi-effect evaporation, the TDS removal rate reaches 95.2%, and the effluent meets the discharge and reinjection requirements; second, the energy consumption and cost advantage is outstanding, the unit energy consumption is reduced by 78.6% compared with MVR, and the treatment cost is only 30.3% of MVR; third, the running stability and land occupation advantage are obvious, the continuous running period is twice that of MVR, and the land occupation area is only 5% of natural evaporation. Among them, although natural evaporation has the lowest energy consumption, its efficiency is extremely low (evaporation rate is only 0.033 kg / (m²·h)), and the land occupation area is huge, which cannot meet the large-scale treatment demand of oilfields.

[0043] In the description of the present specification, the description of the terms "one embodiment", "some embodiments", "a specific embodiment" and the like means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In the present specification, the illustrative description of the above terms does not necessarily refer to the same embodiment or example. Moreover, the described specific features, structures, materials or characteristics can be combined in any one or more embodiments or examples in a suitable manner.

[0044] The above only is the preferred embodiment of the present application, and is not used to limit the present application, for those skilled in the art, the present application can have various changes and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method of treating oilfield fracturing flowback fluid, characterized in that, The method comprises a pretreatment step and a wind energy carrier evaporation step; The pretreatment step reduces the SS, total hardness, COD, oil, and viscosity of the flowback fluid, and adjusts the pH value of the flowback fluid, so as to provide qualified water for the wind energy carrier evaporation step; The wind energy carrier evaporation step evaporates the water by wind energy carrier, and removes volatile COD through gas-liquid mass transfer.

2. The method of treating oilfield fracturing flowback fluid according to claim 1, characterized in that, The pretreatment step comprises: S1: pre-sedimentation adjustment: through stirring and standing, large particle suspensions in the liquid are precipitated and removed, so that SS≤426 mg / L; S2: gel breaking: ammonium persulfate is added to the liquid to destroy the colloidal structure in the liquid and release the wrapped suspensions and oil, so that the viscosity of the liquid is <1.5 mPa·s, and COD≤2600 mg / L; S3: hardness removal: lime is added to the liquid to generate Mg(OH)2 precipitate from magnesium ions in the liquid, and soda ash is added to the liquid to generate CaCO3 precipitate from calcium ions in the liquid, so that the hardness of the liquid is ≤200 mg / L; S4: high-density precipitation: PAC and PAM are added to the liquid to agglomerate and precipitate the small suspended particles and colloidal substances in the liquid, so that SS≤5 mg / L; S5: air flotation: air is introduced into the liquid, so that the suspensions and oil with low density and poor sedimentation in the liquid adhere to the micro-bubbles to quickly float and be scraped off, so that the oil concentration is ≤0.8 mg / L.

3. The method of treating oilfield fracturing flowback fluid according to claim 2, characterized in that, In the S1 step, the stirring frequency is 90 r / min-100 r / min, and the standing time is 4 h-5 h.

4. The method of treating oilfield fracturing flowback fluid of claim 2, wherein, In the S2 step, the ammonium persulfate dosage is 0.8 g / L-0.9 g / L, the reaction temperature is 50°C-60°C, and the reaction time is 2 h-3 h.

5. The method of treating oilfield fracturing flowback fluid of claim 2, wherein, In the S3 step, The step of adding lime to the liquid adjusts the pH value of the liquid to 10.5-11; The soda ash dosage is 1.2-1.3 times the theoretical requirement.

6. The method of treating oilfield fracturing flowback fluid according to claim 2, characterized in that, In the S4 step, the PAC dosage is 100 mg / L-110 mg / L, the PAM dosage is 3 mg / L-4 mg / L, and the precipitation time is 60 min-70 min.

7. The method of treating oilfield fracturing flowback fluid of claim 2, wherein, In the S5 step, the air pressure is 0.3 MPa-0.4 MPa, and the air-water reflux ratio is 30%-35%.

8. A treatment system for oilfield fracturing flowback fluid for treating oilfield fracturing flowback fluid by the method of any one of claims 1-7, characterized in that, The method comprises a pretreatment system and a wind energy carrier evaporation unit in communication; The pretreatment system comprises a pre-sedimentation adjustment unit, a gel breaking unit, a hardness removal unit, a high-density precipitation unit, and an air flotation unit in sequence; The wind energy carrier evaporation unit comprises a plurality of water distribution pipes (1) and a plurality of evaporation curtains (2); The water distribution pipes (1) are in communication with a water storage pool storing flowback fluid, and a plurality of the water distribution pipes (1) are arranged in parallel on the same horizontal plane; A vertical evaporation curtain (2) is arranged in parallel at the bottom of each water distribution pipe (1); A plurality of water injection holes are formed in the water distribution pipe (1), and the injection direction of the water injection holes is towards the surface of the evaporation curtain (2).

9. The treatment system for oilfield fracturing flowback fluid of claim 8, wherein, The distance between adjacent two evaporation curtains (2) is 50 mm-60 mm.

10. The treatment system for oilfield fracturing flowback fluid of claim 8, wherein, The evaporation curtain (2) comprises a silicon-based evaporation curtain. The evaporation curtain (2) comprises a silicon-based evaporation curtain.

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