Method for treating fracturing flow-back fluid of oil and gas field by adopting PolyCera series membrane

Abstract

The invention discloses a method for treating oil and gas field fracturing flow-back fluid by adopting a PolyCra series membrane, and belongs to the technical field of water treatment. The method comprises the following steps: S1, homogenizing the oil and gas field fracturing flow-back fluid, adding an inorganic coagulant and an organic flocculant, stirring, settling, oxidizing, and carrying out solid-liquid separation; s2, adding an impurity removal reagent into the feed liquid obtained in the S1, stirring, settling, and carrying out solid-liquid separation; and S3, enabling the feed liquid obtained in the step S2 to pass through a PolyCra series membrane, and completing treatment. Part of colloids, suspended solids, petroleum and the like in raw water are removed through pretreatment, and the stability of the raw water is destroyed; removing easy-to-scale components and part of suspended matters in the raw water through an impurity removal unit; finally, a PolyCra series membrane is adopted for fine filtration, suspended solids, petroleum and the like in water are further removed, the treatment effect on easily-scaled components, suspended solids and petroleum in the fracturing flow-back fluid of the oil and gas field is improved, and the effluent quality is stable.

Description

Technical Field

[0001] The invention relates to the technical field of water treatment, and in particular to a method for treating oil and gas field fracturing flowback fluid by using a PolyCera series membrane. Background Art

[0002] Hydraulic fracturing is the core technology currently used in the development of unconventional oil and gas fields. The hydraulic fracturing operation process consumes a large amount of water resources in a short period of time. The number of wells required for mining is large and the water demand for each well is large. Some of the injected hydraulic fracturing fluid will remain in the formation, but a part of the injected water will return to the ground after the fracturing fluid pressure is released. These refluxed liquids usually contain: proppant, chemical residues, formation water, rock cuttings, sand and gravel and other substances.

[0003] The differences in geological structure and groundwater environment of oil and gas fields in different regions of my country lead to differences in the water quality of fracturing flowback fluid in different regions. In addition, during the fracturing process, it is usually necessary to configure fracturing fluids with different components in combination with different geological structures, which further leads to the complex composition of fracturing flowback fluid pollutants. In addition, fracturing flowback fluid also has the characteristics of stable system and difficult treatment.

[0004] The main destinations of the treated fracturing flowback fluid in the industry are: secondary fluid preparation, enterprise reuse, etc. At present, the existing treatment methods for fracturing flowback fluid are mostly pretreatment + sand filtration / multi-media filtration / walnut shell filtration and other treatment processes. The disadvantages of the existing processes are mainly in two aspects: on the one hand, the filter device needs regular air washing and water washing during operation; on the other hand, the filter device has poor oil removal stability, which leads to large fluctuations in the content of suspended matter and petroleum in the effluent. If you want to ensure the stability of the effluent water quality through pretreatment + sand filtration / multi-media filtration / walnut shell filtration + ultrafiltration device, once oil, colloids and other pollutants enter the ultrafiltration device, it is very easy to cause blockage of the ultrafiltration membrane. It is urgent to develop a fracturing flowback fluid treatment method that can efficiently remove suspended matter, colloids, petroleum and other substances in the fracturing flowback fluid to solve the problems of low treatment efficiency, poor treatment effect and poor treatment stability of the existing treatment methods. Summary of the invention

[0005] In order to solve the above technical problems, the purpose of the present invention is to provide a method for treating oil and gas field fracturing flowback fluid using PolyCera series membranes, so as to solve the problems of low treatment efficiency, poor treatment effect and poor treatment stability existing in the existing treatment methods of fracturing flowback fluid.

[0006] The technical solution of the present invention to solve the above technical problems is as follows:

[0007] A method for treating oil and gas field fracturing flowback fluid using a PolyCera series membrane, characterized by comprising the following steps:

[0008] S1: After homogenizing the oil and gas field fracturing flowback fluid, add inorganic coagulants and organic flocculants, stir, settle, oxidize, and perform solid-liquid separation;

[0009] S2: adding impurity removal reagent to the liquid obtained in S1, stirring, settling, and performing solid-liquid separation again;

[0010] S3: The liquid obtained in S2 is passed through the PolyCera series membrane to complete the treatment.

[0011] Furthermore, the inorganic coagulant in S1 includes at least one of polyaluminium chloride, polyferric sulfate and polyferric chloride.

[0012] Furthermore, the organic flocculant in S1 includes at least one of anionic polyacrylamide, nonionic polyacrylamide and natural polymer flocculant.

[0013] Furthermore, the amount of inorganic coagulant added in S1 is 300-350 mg / L; the amount of organic flocculant added is 1-3 mg / L.

[0014] The beneficial effects of adopting the above-mentioned further technical scheme are as follows: the present invention combines an inorganic coagulant and an organic flocculant, adsorbs impurities through the electrical neutralization effect of the inorganic coagulant, and combines with the bridging effect of the organic flocculant to form a larger floc structure, thereby significantly improving the efficiency of flocculation and sedimentation. At the same time, the addition of the organic flocculant can make up for the defects of the short molecular chain and insufficient sweeping particles of the inorganic coagulant, enhance the stability and sedimentation effect of the floc, and significantly improve the removal rate of suspended matter, petroleum and heavy metals in sewage.

[0015] Furthermore, the homogenization time in S1 is 10-30 hours.

[0016] Furthermore, the stirring speed in S1 is 300-1000 rpm, the time is 10-30 h, and the sedimentation time is 10-30 h.

[0017] Further, the impurity removal agent in S2 includes alkaline substances, metal salts, inorganic coagulants and organic flocculants;

[0018] The alkaline substance includes at least one of sodium hydroxide and slaked lime;

[0019] The metal salt includes at least one of sodium carbonate, potassium carbonate, sodium sulfate and potassium sulfate;

[0020] The inorganic coagulant includes at least one of polyaluminium chloride, polyferric sulfate and polyferric chloride;

[0021] The organic flocculant includes at least one of anionic polyacrylamide, nonionic polyacrylamide and natural polymer flocculant.

[0022] Furthermore, an alkaline substance is added until the pH of the liquid is 9.0-11.0.

[0023] Furthermore, the addition amount of the metal salt is: 17500-23000 mg / L; the addition amount of the inorganic coagulant is 300-350 mg / L; and the addition amount of the organic flocculant is 1-3 mg / L.

[0024] The beneficial effect of adopting the above further technical scheme is: the present invention combines alkaline substances, salt substances and anionic polyacrylamide to carry out impurity removal process. On the one hand, sodium hydroxide, slaked lime, sodium carbonate, sodium sulfate and potassium sulfate as alkaline substances and salt substances can effectively remove metal ions in sewage. On the other hand, by adjusting the pH, the adsorption and impurity removal efficiency of anionic polyacrylamide is effectively improved.

[0025] Furthermore, the stirring speed in S2 is 30-100 rpm, the time is 10-30 min, and the sedimentation time is 1.0-1.5 h.

[0026] Furthermore, the membrane operating pressure of the PolyCera series membrane in S3 is 0.2-0.4MPa, and the membrane operating flux is 20-40L / m 2 / h, influent suspended matter concentration <100mg / L, influent petroleum content <100mg / L.

[0027] The present invention has the following beneficial effects:

[0028] The present invention provides a method for treating oil and gas field fracturing flowback fluid by using PolyCera series membranes. The method mainly adopts the method of "pretreatment + impurity removal + membrane separation". The method first removes some colloids, suspended matter, petroleum and other substances in the raw water through pretreatment to destroy the stability of the raw water; secondly, the scale-forming components and some suspended matter in the raw water are removed through the impurity removal unit; finally, the PolyCera series membranes are used for fine filtration to further remove suspended matter, petroleum, colloid and other components in the water. The treated fracturing flowback fluid can be used for: secondary liquid preparation, enterprise reuse, etc. The main purpose of the present invention is to improve the reuse rate of water resources and save water resources. At the same time, it also relies on a short processing flow to achieve energy conservation and emission reduction for enterprises and reduce the workload of personnel. During the operation, the system's operating stability is maintained by not adding drugs or adding less drugs. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 The present invention is a process flow chart of using the PolyCera series membrane to treat oil and gas field fracturing flowback fluid. DETAILED DESCRIPTION

[0030] The principles and features of the present invention are described below in conjunction with the accompanying drawings. The examples are only used to explain the present invention and are not intended to limit the scope of the present invention. If specific conditions are not specified in the examples, they are carried out according to conventional conditions or conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments is not specified, they are all conventional products that can be purchased commercially.

[0031] Embodiment 1:

[0032] A method for treating oil and gas field fracturing flowback fluid using PolyCera series membranes (process flow chart as shown in FIG. Figure 1 As shown), comprising the following steps:

[0033] S1: The oil and gas field fracturing flowback fluid to be treated is stored in a homogenizing tank, subjected to 24-hour homogenization treatment, and the water quality is adjusted to obtain a homogenized feed liquid;

[0034] S2: The feed liquid homogenized by S1 is passed into the pretreatment unit, 320 mg / L of polyferric sulfate and 2 mg / L of anionic polyacrylamide are first added, stirred at 60 rpm for 20 min, then stopped stirring, allowed to stand for 30 min, and finally the scum and settled sludge are removed to obtain the pretreated feed liquid;

[0035] S3: The pretreated liquid of S2 is passed into the impurity removal unit, and slaked lime and sodium hydroxide are first added to adjust the pH of the liquid to about 11, and then 17500 mg / L of sodium carbonate and 320 mg / L of polyferric sulfate are added, followed by 2 mg / L of anionic polyacrylamide, and stirred at 50 rpm for 20 min, then the stirring is stopped, and the mixture is allowed to stand for 60 min, and finally the settled sludge is removed to obtain the impurity-removed liquid;

[0036] S4: The impurity-free liquid from S3 is connected to the separation membrane device, which includes 12 3-core pressure vessels. Each pressure vessel is equipped with 3 filter membrane structures. The filter membrane structure is a PolyCera series TITAN-UF-70-OFFSHORE-40 membrane element. The area of ​​a single membrane is 23.5m 2 , membrane flux is 30L / m 2 / h, the membrane operating pressure is 0.3MPa, the operating temperature is 25℃, and the PolyCera series membranes are used to further intercept the remaining suspended matter, petroleum and some colloids in the water. The filtered water is directly introduced into the product water pool, and the intercepted concentrated water is returned to the pretreatment unit.

[0037] Embodiment 2:

[0038] A method for treating oil and gas field fracturing flowback fluid using a PolyCera series membrane comprises the following steps:

[0039] S1: The oil and gas field fracturing flowback fluid to be treated is stored in a homogenizing tank, subjected to 24-hour homogenization treatment, and the water quality is adjusted to obtain a homogenized feed liquid;

[0040] S2: The feed liquid after homogenization treatment in S1 is passed into the pretreatment unit, 320 mg / L of polyferric chloride and 2 mg / L of anionic polyacrylamide are first added, stirred at 60 rpm for 30 min, allowed to stand for separation for 30 min, and finally the scum and settled sludge are removed to obtain the pretreated feed liquid;

[0041] S3: The pretreated feed liquid of S2 is passed into the impurity removal unit, and sodium hydroxide is first added to adjust the pH of the feed liquid to about 11, and then 13000 mg / L of sodium sulfate, 7500 mg / L of sodium carbonate and 320 mg / L of polyferric chloride are added, followed by 2 mg / L of anionic polyacrylamide, and stirred at 50 rpm for 20 min, then the stirring is stopped, and the mixture is allowed to stand for 60 min, and finally the settled sludge is removed to obtain the impurity-removed feed liquid;

[0042] S4: The impurity-free liquid from S3 is connected to the separation membrane device, which includes 12 3-core pressure vessels. Each pressure vessel is equipped with 3 filter membrane structures. The filter membrane structure is a PolyCera series TITAN-UF-70-OFFSHORE-40 membrane element. The area of ​​a single membrane is 23.5m 2 , membrane flux is 30L / m 2 / h, the membrane operating pressure is 0.3MPa, the operating temperature is 25℃, and the PolyCera series membranes are used to further intercept the remaining suspended matter, petroleum and some colloids in the water. The filtered water is directly introduced into the product water pool, and the intercepted concentrated water is returned to the pretreatment unit.

[0043] Embodiment 3:

[0044] A method for treating oil and gas field fracturing flowback fluid using a PolyCera series membrane comprises the following steps:

[0045] S1: The oil and gas field fracturing flowback fluid to be treated is stored in a homogenizing tank, subjected to 24-hour homogenization treatment, and the water quality is adjusted to obtain a homogenized feed liquid;

[0046] S2: The feed liquid after homogenization treatment in S1 is passed into the pretreatment unit, 350 mg / L of polyaluminium chloride and 2 mg / L of anionic polyacrylamide are first added, stirred at 60 rpm for 30 min, allowed to stand for separation for 30 min, and finally the scum and settled sludge are removed to obtain the pretreated feed liquid;

[0047] S3: The pretreated feed liquid of S2 is passed into the impurity removal unit, and sodium hydroxide is first added to adjust the pH of the feed liquid to about 11, and then 13000 mg / L of sodium sulfate, 7500 mg / L of sodium carbonate and 350 mg / L of polyaluminium chloride are added, followed by 2 mg / L of anionic polyacrylamide, and stirred at 50 rpm for 20 min, then the stirring is stopped, and the mixture is allowed to stand for 60 min, and finally the settled sludge is removed to obtain the impurity-removed feed liquid;

[0048] S4: The impurity-free liquid from S3 is connected to the separation membrane device, which includes 12 3-core pressure vessels. Each pressure vessel is equipped with 3 filter membrane structures. The filter membrane structure is a PolyCera series TITAN-UF-70-OFFSHORE-40 membrane element. The area of ​​a single membrane is 23.5m 2 , membrane flux is 30L / m 2 / h, the membrane operating pressure is 0.3MPa, the operating temperature is 25℃, and the PolyCera series membranes are used to further intercept the remaining suspended matter, petroleum and some colloids in the water. The filtered water is directly introduced into the product water pool, and the intercepted concentrated water is returned to the pretreatment unit.

[0049] Embodiment 4:

[0050] A method for treating oil and gas field fracturing flowback fluid using a PolyCera series membrane comprises the following steps:

[0051] S1: The oil and gas field fracturing flowback fluid to be treated is stored in a homogenizing tank, subjected to 24-hour homogenization treatment, and the water quality is adjusted to obtain a homogenized feed liquid;

[0052] S2: The feed liquid after homogenization treatment in S1 is passed into the pretreatment unit, 350 mg / L of polyaluminium chloride and 2 mg / L of anionic polyacrylamide are first added, stirred at 60 rpm for 30 min, allowed to stand for separation for 30 min, and finally the scum and settled sludge are removed to obtain the pretreated feed liquid;

[0053] S3: The pretreated feed liquid of S2 is passed into the impurity removal unit, and sodium hydroxide is first added to adjust the pH of the feed liquid to about 11, and then 17500 mg / L of sodium carbonate and 350 mg / L of polyaluminium chloride are added, followed by 2 mg / L of anionic polyacrylamide, and stirred at 50 rpm for 20 min, then the stirring is stopped, and the mixture is allowed to stand for 60 min, and finally the settled sludge is removed to obtain the impurity-removed feed liquid;

[0054] S4: The impurity-free liquid from S3 is connected to the separation membrane device, which includes 12 3-core pressure vessels. Each pressure vessel is equipped with 3 filter membrane structures. The filter membrane structure is a PolyCera series TITAN-UF-70-OFFSHORE-40 membrane element. The area of ​​a single membrane is 23.5m 2 , membrane flux is 30L / m 2 / h, the membrane operating pressure is 0.3MPa, the operating temperature is 25℃, and the PolyCera series membranes are used to further intercept the remaining suspended matter, petroleum and some colloids in the water. The filtered water is directly introduced into the product water pool, and the intercepted concentrated water is returned to the pretreatment unit.

[0055] Comparative Example 1:

[0056] A method for treating oil and gas field fracturing flowback fluid using a PolyCera series membrane comprises the following steps:

[0057] S1: The oil and gas field fracturing flowback fluid to be treated is stored in a homogenizing tank, subjected to 24-hour homogenization treatment, and the water quality is adjusted to obtain a homogenized feed liquid;

[0058] S2: The feed liquid homogenized by S1 is passed into the pretreatment unit, 320 mg / L of polyferric sulfate and 2 mg / L of anionic polyacrylamide are first added, stirred at 60 rpm for 20 min, then stopped stirring, allowed to stand for 30 min, and finally the scum and settled sludge are removed to obtain the pretreated feed liquid;

[0059] S3: The pretreated feed liquid of S2 is passed into the impurity removal unit, sodium hydroxide is first added to adjust the pH of the feed liquid to about 11, then 320 mg / L of polyferric sulfate is added, followed by 2 mg / L of anionic polyacrylamide, stirred at 50 rpm for 20 min, then stopped stirring, allowed to stand for 60 min, and finally the settled sludge was removed to obtain the impurity-removed feed liquid;

[0060] S4: The impurity-free liquid from S3 is connected to the separation membrane device, which includes 12 3-core pressure vessels. Each pressure vessel is equipped with 3 filter membrane structures. The filter membrane structure is a PolyCera series TITAN-UF-70-OFFSHORE-40 membrane element. The area of ​​a single membrane is 23.5m 2 , membrane flux is 30L / m 2 / h, the membrane operating pressure is 0.3MPa, the operating temperature is 25℃, and the PolyCera series membranes are used to further intercept the remaining suspended matter, petroleum and some colloids in the water. The filtered water is directly introduced into the product water pool, and the intercepted concentrated water is returned to the pretreatment unit.

[0061] Comparative Example 2:

[0062] A method for treating oil and gas field fracturing flowback fluid using a PolyCera series membrane comprises the following steps:

[0063] S1: The oil and gas field fracturing flowback fluid to be treated is stored in a homogenizing tank, subjected to 24-hour homogenization treatment, and the water quality is adjusted to obtain a homogenized feed liquid;

[0064] S2: The feed liquid after homogenization treatment in S1 is passed into the pretreatment unit, 320 mg / L of polyferric chloride and 2 mg / L of anionic polyacrylamide are first added, stirred at 60 rpm for 30 min, allowed to stand for separation for 30 min, and finally the scum and settled sludge are removed to obtain the pretreated feed liquid;

[0065] S3: The pretreated liquid of S2 is passed into the impurity removal unit, and 17500 mg / L of sodium carbonate and 320 mg / L of polyferric chloride are first added, followed by 2 mg / L of anionic polyacrylamide, and stirred at 50 rpm for 20 min, then the stirring is stopped, and the liquid is allowed to stand for 60 min, and finally the settled sludge is removed to obtain the impurity-removed liquid;

[0066] S4: The impurity-free liquid from S3 is connected to the separation membrane device, which includes 12 3-core pressure vessels. Each pressure vessel is equipped with 3 filter membrane structures. The filter membrane structure is a PolyCera series TITAN-UF-70-OFFSHORE-40 membrane element. The area of ​​a single membrane is 23.5m 2 , membrane flux is 25L / m 2 / h, the membrane operating pressure is 0.3MPa, the operating temperature is 25℃, and the PolyCera series membranes are used to further intercept the remaining suspended matter, petroleum and some colloids in the water. The filtered water is directly introduced into the product water pool, and the intercepted concentrated water is returned to the pretreatment unit.

[0067] Comparative Example 3:

[0068] A method for treating oil and gas field fracturing flowback fluid comprises the following steps:

[0069] S1: The oil and gas field fracturing flowback fluid to be treated is stored in a homogenizing tank, subjected to 24-hour homogenization treatment, and the water quality is adjusted to obtain a homogenized feed liquid;

[0070] S2: The feed liquid after homogenization treatment in S1 is passed into the pretreatment unit, 320 mg / L of polyaluminium chloride and 2 mg / L of anionic polyacrylamide are first added, stirred at 60 rpm for 30 min, allowed to stand for separation for 30 min, and finally the scum and settled sludge are removed to obtain the pretreated feed liquid;

[0071] S3: The pretreated liquid of S2 is passed into the impurity removal unit, 320 mg / L of polyaluminium chloride is first added, and then 2 mg / L of anionic polyacrylamide is added, and the mixture is stirred at 50 rpm for 20 min, and then the stirring is stopped, and the mixture is allowed to stand for 60 min, and finally the settled sludge is removed to obtain the impurity-removed liquid;

[0072] S4: The impurity-free liquid from S3 is connected to the separation membrane device, which includes 12 3-core pressure vessels. Each pressure vessel is equipped with 3 filter membrane structures. The filter membrane structure is a PolyCera series TITAN-UF-70-OFFSHORE-40 membrane element. The area of ​​a single membrane is 23.5m 2 , membrane flux is 30L / m 2 / h, the membrane operating pressure is 0.3MPa, the operating temperature is 25℃, and the PolyCera series membranes are used to further intercept the remaining suspended matter, petroleum and some colloids in the water. The filtered water is directly introduced into the product water pool, and the intercepted concentrated water is returned to the pretreatment unit.

[0073] Comparative Example 4:

[0074] A method for treating oil and gas field fracturing flowback fluid comprises the following steps:

[0075] S1: The oil and gas field fracturing flowback fluid to be treated is stored in a homogenizing tank, subjected to 24-hour homogenization treatment, and the water quality is adjusted to obtain a homogenized feed liquid;

[0076] S2: The feed liquid after homogenization treatment in S1 is passed into the pretreatment unit, 350 mg / L of polyaluminium chloride and 2 mg / L of anionic polyacrylamide are first added, stirred at 60 rpm for 30 min, allowed to stand for separation for 30 min, and finally the scum and settled sludge are removed to obtain the pretreated feed liquid;

[0077] S3: The pretreated feed liquid of S2 is passed into the impurity removal unit, sodium hydroxide is added to adjust the pH of the feed liquid to about 11, and 17500 mg / L of sodium carbonate and 350 mg / L of polyaluminium chloride are added, and 2 mg / L of anionic polyacrylamide is added, and the mixture is stirred at 60 rpm for 20 min, and then the stirring is stopped, and the mixture is allowed to stand for 60 min, and finally the settled sludge is removed to obtain the impurity-removed feed liquid;

[0078] S4: The impurity-free liquid from S3 is connected to a separation membrane device. The separation membrane device includes 12 3-core pressure vessels. Each pressure vessel is equipped with 3 filter membrane structures. The filter membrane structure is a commercially available polyvinyl chloride ultrafiltration membrane. The area of ​​a single membrane is 23.5m 2 , membrane flux is 30L / m 2 / h, the membrane operating pressure is 0.3MPa, the operating temperature is 25℃, and the remaining suspended matter, petroleum and some colloids in the water are further intercepted by the polyvinyl chloride ultrafiltration membrane. The filtered water is directly introduced into the product water pool, and the intercepted concentrated water is returned to the pretreatment unit.

[0079] Test example:

[0080] The methods of Examples 1-4 and Comparative Examples 1-4 were used to treat the fracturing flowback fluid of the oil and gas field. The system influent water quality indicators of the fracturing flowback fluid are shown in Table 1.

[0081] Table 1 Water quality indicators of fracturing flowback fluid treatment system

[0082] index unit Numeric Total hardness mg / L ～16000 Suspended matter mg / L ～500 Petroleum mg / L ～300 pH - 6-7 COD mg / L ～5000

[0083] The above 6 methods were used to treat the fracturing flowback fluid, and the relevant water quality indicators of the effluent after one week of operation were tested. The test results are shown in Table 2:

[0084] Table 2 Water quality indicators of fracturing flowback fluid treatment system

[0085] index Total hardness Suspended matter Petroleum COD Example 1 284.3 0.037 0.17 4683 Example 2 292.7 0.044 0.20 4510 Example 3 287.1 0.041 0.19 4600 Example 4 286.5 0.040 0.18 4590 Comparative Example 1 12587 0.084 0.31 4625 Comparative Example 2 4156 0.096 0.47 4760 Comparative Example 3 16440 0.081 0.52 4560 Comparative Example 4 287.2 0.18 0.86 4695

[0086] As shown in Table 2, the present invention adopts a combination of inorganic iron coagulants, inorganic aluminum coagulants and organic flocculants to pretreat the fracturing return fluid. Through the combination of organic and inorganic, on the one hand, impurities are adsorbed by electrical neutralization, and on the other hand, the bridging effect of the organic flocculant and the inorganic coagulant are combined to form larger flocs, thereby improving the efficiency of flocculation and sedimentation; and further impurities are removed by combining alkaline substances, salt substances and anionic polyacrylamide. On the one hand, the addition of alkaline substances can more effectively remove residual metal ions in the feed liquid, and on the other hand, the addition of alkaline substances to adjust the pH improves the efficiency of the anionic polyacrylamide, thereby achieving further improvement in the sedimentation effect; the addition of salt substances can simultaneously and synergistically remove the hardness in the water; finally, the PolyCera series membrane is used for filtration, which effectively removes most of the divalent metal ions such as calcium and magnesium in the fracturing return fluid, and removes suspended matter, petroleum and some colloids. Compared with Comparative Example 1 in which no metal salt was added, Comparative Example 2 in which no alkaline substance was added, Comparative Example 3 in which no metal salt and alkaline substance were added, and Comparative Example 4 using a traditional polyvinyl chloride ultrafiltration membrane, the total hardness, suspended matter, and petroleum content of the effluent after treatment by the method of the present invention are significantly lower, and the method of the present invention has a better fracturing flowback fluid treatment effect.

[0087] The fracturing flowback fluid treatment method of Example 4 and Comparative Example 4 was used to continuously treat the fracturing flowback fluid for 3 months, and the treatment effect was measured every week. The results are shown in Table 3.

[0088] Table 3 Treatment stability test results

[0089] Example 4 Total hardness Suspended matter Petroleum COD Week 1 284.3 0.037 0.17 4600 First Month 285.1 0.037 0.17 4610 Second month 285.4 0.038 0.18 4660 Third month 286.2 0.040 0.19 4590 Comparative Example 4 Total hardness Suspended matter Petroleum COD Week 1 290.5 0.18 0.82 4560 First Month 288.6 0.21 0.94 4580 Second month 289.6 0.27 1.16 4650 Third month 291.4 0.39 1.48 4570

[0090] According to the data in the above table, compared with Comparative Example 4, Example 4 of the present invention adopts the PolyCera series membrane to treat fracturing return fluid, which has more sustained stability, and the indicators of the effluent have almost no obvious changes within three months. However, in Comparative Example 4 using the traditional polyvinyl chloride ultrafiltration membrane, the oil resistance of the polyvinyl chloride ultrafiltration membrane is poor after the oil substances enter the ultrafiltration membrane, which can easily cause the ultrafiltration membrane to be blocked, resulting in the inability to effectively maintain stability during the subsequent fracturing return fluid treatment, requiring frequent cleaning, and the subsequent treatment effect is significantly deteriorated, requiring further cleaning and maintenance.

[0091] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for treating oil and gas field fracturing flowback fluid using a PolyCera series membrane, characterized in that: The following steps are involved: S1: After homogenizing the oil and gas field fracturing flowback fluid, add inorganic coagulants and organic flocculants, stir, settle, oxidize, and perform solid-liquid separation; S2: adding impurity removal reagent to the liquid obtained in S1, stirring, settling, and performing solid-liquid separation again; S3: The liquid obtained in S2 is passed through the PolyCera series membrane to complete the treatment.

2. The method for treating oil and gas field fracturing flowback fluid using a PolyCera series membrane according to claim 1, characterized in that: The inorganic coagulant in S1 includes at least one of polyaluminium chloride, polyferric sulfate and polyferric chloride.

3. The method for treating oil and gas field fracturing flowback fluid using the PolyCera series membrane according to claim 1, wherein the organic flocculant in S1 comprises at least one of anionic polyacrylamide, nonionic polyacrylamide and natural polymer flocculant.

4. The method for treating oil and gas field fracturing flowback fluid using a PolyCera series membrane according to claim 1, characterized in that: The amount of inorganic coagulant added in S1 is 300-350 mg / L; the amount of organic flocculant added is 1-3 mg / L.

5. The method for treating oil and gas field fracturing flowback fluid using a PolyCera series membrane according to claim 1, characterized in that: The impurity removal agent in S2 includes alkaline substances, metal salts, inorganic coagulants and organic flocculants; The alkaline substance includes at least one of sodium hydroxide and slaked lime; The metal salt includes at least one of sodium carbonate, potassium carbonate, sodium sulfate and potassium sulfate; The inorganic coagulant includes at least one of polyaluminium chloride, polyferric sulfate and polyferric chloride; The organic flocculant includes at least one of anionic polyacrylamide, nonionic polyacrylamide and natural polymer flocculant.

6. The method for treating oil and gas field fracturing flowback fluid using the PolyCera series membrane according to claim 5, characterized in that: Add alkaline substances until the pH of the liquid is 9.0-11.

0.

7. The method for treating oil and gas field fracturing flowback fluid using a PolyCera series membrane according to claim 5, characterized in that: The addition amount of metal salt is: 17500-23000 mg / L; the addition amount of inorganic coagulant is 300-350 mg / L; the addition amount of organic flocculant is 1-3 mg / L.

8. The method for treating oil and gas field fracturing flowback fluid using a PolyCera series membrane according to claim 1, characterized in that: The membrane operating pressure of the PolyCera series membrane in S3 is 0.2-0.4MPa, and the membrane operating flux is 20-40L / m 2 / h, influent suspended matter concentration <100mg / L, influent petroleum content <100mg / L.

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