A method of treating oilfield produced water

Abstract

The application provides an oilfield produced water treatment method. The method comprises the following steps: adding a polymeric aluminum ferric silicate solution into oilfield produced water to be treated, and stirring for a period of time at a first rotating speed; increasing the first rotating speed to a second rotating speed, adding a polyacrylamide solution, stirring for a period of time at the second rotating speed after the addition is completed, and then standing for a period of time; and filtering to obtain treated oilfield produced water. The method has the advantages of simplicity, high efficiency, low cost, easy operation, remarkable treatment effect and the like.

Description

Technical Field

[0001] This invention relates to a method for treating produced water from oil fields, belonging to the field of wastewater treatment technology. Background Technology

[0002] Produced water from oilfields is extracted from the formation along with crude oil. After oil-water separation, it forms a multiphase system containing suspended solids, oil, and dissolved substances. For environmental protection and resource conservation reasons, how to economically and effectively treat oilfield produced water and achieve its resource utilization has become a research hotspot in oilfield wastewater treatment.

[0003] CN112607839A discloses an aluminum-iron silicate flocculant and its preparation method. This method uses polydimethyldiallyl ammonium chloride emulsion as raw material. Although the oil removal rate of this aluminum-iron silicate flocculant reaches 90%, this method is suitable for treated produced water with low oil content; it may not be applicable to produced water with high oil content.

[0004] CN102276030A describes a composite flocculant of cationic polyacrylamide with a molecular weight of 4 million and polyaluminum chloride, which is simple to use. However, the oil removal efficiency of this composite flocculant is only average, with an oil removal rate of only 88%.

[0005] CN101781624A discloses an aerobic bacterial strain enriched, screened, and cultured from activated sludge and oily soil, which can efficiently degrade crude oil and organic matter in produced water with high salinity in low-permeability oilfields. The drawback of this method is its long processing time, which affects efficiency.

[0006] CN111825265A describes a method for treating produced water from oilfields using a gravity settling device, an electric field oil removal device, and a filtration device. Although this method can effectively reduce the oil content in produced water, it is cumbersome to operate, the equipment is expensive, and the treatment cost is high.

[0007] CN105217761A discloses a treatment agent for oilfield produced water, formulated from 10 parts polyurethane, 20 parts industrial wastewater-specific coagulant (containing 26%-30% aluminum oxide), and 70 parts water. This agent exhibits significant oil removal efficiency, but its main drawback is the relatively large dosage required.

[0008] Therefore, developing a method for treating produced water from oil fields remains one of the urgent problems to be solved in this field. Summary of the Invention

[0009] To address the aforementioned technical problems, the present invention aims to provide a method for treating produced water from oilfields. This method offers advantages such as high efficiency, low cost, and ease of operation.

[0010] To achieve the above objectives, the present invention provides a method for treating oilfield produced water, comprising the following steps:

[0011] (1) Add polyaluminum ferric silicate solution to the produced water of the oilfield to be treated and stir at the first speed for a period of time;

[0012] (2) Increase the first rotation speed to the second rotation speed, add polyacrylamide solution, stir at the second rotation speed for a period of time after the addition is complete, let stand for a period of time, filter, and obtain the treated oilfield produced water.

[0013] According to a specific embodiment of the present invention, preferably, the oil content in the produced water from the oilfield to be treated is 100-1000 mg / L.

[0014] According to a specific embodiment of the present invention, preferably, the produced water from the oilfield to be treated is produced water from a binary flooding oilfield with a polymer concentration of 150-300 mg / L. The polymer is a polymer commonly used in polymer / surfactant binary flooding, and the present invention does not specifically limit it.

[0015] According to a specific embodiment of the present invention, preferably, in step (1), the concentration of polyaluminum ferric silicate in the produced water after adding the polyaluminum ferric silicate solution is 15-400 mg / L. It should be noted that the concentration of the polyaluminum ferric silicate solution can be conventionally adjusted by those skilled in the art based on the concentration of polyaluminum ferric silicate in the produced water after adding the polyaluminum ferric silicate solution.

[0016] According to a specific embodiment of the present invention, preferably, in step (1), when the produced water to be treated is produced water with an oil content of 100-1000 mg / L and no polymer, the concentration of polyaluminum silicate iron in the produced water after adding the polyaluminum silicate iron solution is 15-20 mg / L.

[0017] According to a specific embodiment of the present invention, preferably, in step (1), when the produced water to be treated is produced water from a binary flooding oilfield with a polymer concentration of 150-300 mg / L, the concentration of the polymeric aluminum ferric silicate in the produced water after adding the polymeric aluminum ferric silicate solution is 300-400 mg / L.

[0018] According to a specific embodiment of the present invention, preferably, in step (1), the first rotation speed is 90-110 r / min, and the stirring time at the first rotation speed is 1-10 min.

[0019] According to a specific embodiment of the present invention, preferably, step (1) is carried out at a temperature of 30-60°C, more preferably at a temperature of 40-55°C.

[0020] According to a specific embodiment of the present invention, preferably, in step (2), the polyacrylamide used is cationic polyacrylamide with a molecular weight of 8 million to 13 million and an ionic degree of 30 to 80. More preferably, the polyacrylamide used is cationic polyacrylamide with a molecular weight of 9 million to 12 million and an ionic degree of 40 to 70.

[0021] According to a specific embodiment of the present invention, preferably, in step (2), the concentration of polyacrylamide in the produced water after adding the polyacrylamide solution is 1-2 mg / L. It should be noted that the concentration of the polyacrylamide solution can be conventionally adjusted by those skilled in the art based on the concentration of polyacrylamide in the produced water after adding the polyacrylamide solution.

[0022] According to a specific embodiment of the present invention, preferably, in step (2), the second rotational speed is 140-200 r / min.

[0023] According to a specific embodiment of the present invention, preferably, in step (2), the polyacrylamide solution is added by gradually and cumulatively dripping it in batches. More preferably, the polyacrylamide solution is added 3-5 times per liter of produced water from the oilfield, at a dripping rate of 10-15 mL per second, until the concentration of polyacrylamide in the produced water is 1-2 mg / L. Further preferably, after each addition of the polyacrylamide solution, the mixture is stirred at the second rotation speed for 2-5 minutes.

[0024] According to a specific embodiment of the present invention, preferably, in step (2), the stirring time at the second rotation speed after the addition is completed is 6-10 minutes.

[0025] According to a specific embodiment of the present invention, preferably, in step (2), the settling time is 1-4 hours.

[0026] According to a specific embodiment of the present invention, preferably, step (2) is carried out at a temperature of 30-60°C, more preferably at a temperature of 40-55°C.

[0027] According to a specific embodiment of the present invention, preferably, the oil content in the treated oilfield produced water is below 50 mg / L.

[0028] According to a specific embodiment of the present invention, preferably, the oil removal rate of the oilfield produced water to be treated by the treatment method is above 93%.

[0029] According to a specific embodiment of the present invention, preferably, the polymer concentration in the treated oilfield produced water is 50-100 mg / L.

[0030] According to a specific embodiment of the present invention, preferably, the treatment method removes polymers from the produced water of the oilfield to be treated at a rate of 50% or more, more preferably 50%-75%.

[0031] This invention provides a method for treating produced water from oilfields. The method first adds a polyaluminum ferric silicate solution to the produced water to be treated, stirs it at a first rotation speed for a period of time, then increases the rotation speed to a second speed, and then adds a polyacrylamide solution. Stirring continues at the second speed for a period of time, followed by a period of settling. After filtration, the oil content in the treated produced water is reduced to below 50 mg / L, achieving an oil removal rate of over 93%. This method treats produced water by first adding a polyaluminum ferric silicate solution and then adding a polyacrylamide solution for flocculation and sedimentation. Furthermore, by using a combination of polyaluminum ferric silicate solution and polyacrylamide solution, and by controlling the polyacrylamide used to be cationic polyacrylamide with a specific molecular weight and ionic degree, this method is particularly suitable for treating produced water from binary flooding with high polymer content. It can efficiently remove polymers from the produced water while achieving an oil removal rate of over 93%. This method can also remove suspended solids from produced water. Meanwhile, the method of this invention, by gradually and cumulatively adding a poorly soluble polyacrylamide solution in batches, and stirring for a period of time after each addition, ensures thorough mixing of the poorly soluble polyacrylamide and the produced water from the oilfield, further enhancing flocculation performance. The reagents used in this invention are widely available, inexpensive, and easy to obtain, resulting in larger flocs with rapid settling rates. This method promotes the application of polyacrylamide and polyaluminum ferric silicate in the treatment of produced water from oilfields. Compared to existing technologies, it offers advantages such as simplicity, high efficiency, low cost, ease of operation, and significant treatment effects. It is suitable for produced water from oilfields with high oil content and high polymer content, and is suitable for large-scale industrial application and promotion. Attached Figure Description

[0032] Figure 1 This is an optical image of an oilfield produced water sample before treatment in Example 1.

[0033] Figure 2 This is an optical image of an oilfield produced water sample after processing in Example 1. Detailed Implementation

[0034] In order to provide a clearer understanding of the technical features, objectives and beneficial effects of the present invention, the technical solution of the present invention will now be described in detail below, but it should not be construed as limiting the scope of implementation of the present invention.

[0035] Example 1

[0036] This embodiment provides a method for treating produced water from an oilfield, which includes the following steps:

[0037] Weigh 1g of polyaluminum ferric silicate powder and prepare a polyaluminum ferric silicate solution of appropriate concentration; weigh 0.1g of cationic polyacrylamide powder with a molecular weight of 9 million and an ionic degree of 60 and prepare a polyacrylamide solution of appropriate concentration; take 500mL of oilfield produced water with an oil content of 702mg / L, and add the polyaluminum ferric silicate solution to the oilfield produced water at a water bath temperature of 45℃ until the concentration of polyaluminum ferric silicate in the produced water is 20mg / L, and stir at 100r / min for 1min; then stir... The rotation speed was increased to 140 r / min, and the polyacrylamide solution was added in batches, gradually and cumulatively. The polyacrylamide solution was added in two separate additions at a rate of 10 mL per second. After each addition, the mixture was stirred at 140 r / min for 3 minutes. The concentration of polyacrylamide in the produced water was increased to 2 mg / L. After the addition was complete, the mixture was stirred at 140 r / min for 6 minutes, allowed to stand for 90 minutes, and then filtered to obtain the treated oilfield produced water. The oil content of the treated oilfield produced water was measured to be 41.3 mg / L, and the oil removal rate was 94.11%. Optical images of the oilfield produced water samples before and after treatment in this embodiment are shown below. Figure 1 and Figure 2 As shown.

[0038] Comparative Example 1

[0039] This comparative example provides a method for treating produced water in oil fields. In this comparative example, polyacrylamide solution is added all at once, instead of adding it gradually in batches.

[0040] The method includes the following steps:

[0041] 1g of polyaluminum ferric silicate powder was weighed and prepared into a polyaluminum ferric silicate solution of appropriate concentration. 0.1g of cationic polyacrylamide powder with a molecular weight of 9 million and an ionic degree of 60 was weighed and prepared into a polyacrylamide solution of appropriate concentration. 500mL of oilfield produced water with an oil content of 702mg / L was taken. Under a water bath temperature of 45℃, the polyaluminum ferric silicate solution was added to the produced water until the concentration of polyaluminum ferric silicate in the produced water reached 20mg / L, and the mixture was stirred at 100r / min for 1min. Then, the stirring speed was increased to 140r / min, and the polyacrylamide solution was added all at once until the concentration of polyacrylamide in the produced water reached 2mg / L. After the addition was complete, the mixture was stirred at 140r / min for 6min, allowed to stand for 90min, and then filtered to obtain the treated oilfield produced water. The oil content of the treated oilfield produced water was measured to be 212.16mg / L, and the oil removal rate was 69.78%.

[0042] Example 2

[0043] This embodiment provides a method for treating produced water from an oilfield, which includes the following steps:

[0044] Weigh 1g of polyaluminum ferric silicate powder and prepare a polyaluminum ferric silicate solution of appropriate concentration; weigh 0.1g of cationic polyacrylamide powder with a molecular weight of 10 million and an ionic degree of 60 and prepare a polyacrylamide solution of appropriate concentration; take 500mL of oilfield produced water with an oil content of 610mg / L, and add the polyaluminum ferric silicate solution to the oilfield produced water at a water bath temperature of 45℃ until the concentration of polyaluminum ferric silicate in the produced water is 20mg / L, and stir at 100r / min for 1min; then stir... The rotation speed was increased to 140 r / min, and the polyacrylamide solution was added in batches, gradually and cumulatively. The polyacrylamide solution was added in two separate additions at a rate of 10 mL per second. After each addition, the mixture was stirred at 140 r / min for 3 minutes. The polyacrylamide concentration in the produced water was increased to 1 mg / L. After the addition was complete, the mixture was stirred at 140 r / min for 10 minutes, allowed to stand for 90 minutes, and then filtered to obtain the treated oilfield produced water. The oil content of the treated oilfield produced water was measured to be 39.30 mg / L, and the oil removal rate was 93.55%.

[0045] Comparative Example 2

[0046] This comparative example provides a method for treating produced water in oilfields. The comparative example uses commonly used produced water treatment agents from the Liuzan Joint Station in the Jidong Oilfield onshore operation area.

[0047] The method includes the following steps:

[0048] Weigh 0.1g of the produced water treatment agent and prepare a solution of appropriate concentration. Take 500mL of produced water from an oilfield with an oil content of 610mg / L. Under a water bath temperature of 45℃, add the agent solution to the produced water in batches, gradually and cumulatively. The agent solution is added in two batches at a drip rate of 10mL per second. After each addition, stir at 140r / min for 3min. Add the agent solution until the concentration in the produced water reaches 33mg / L. After the addition is complete, stir at 140r / min for 10min, let stand for 90min, and then filter to obtain the treated produced water. The oil content of the treated produced water is measured to be 38.4mg / L, and the oil removal rate is 93.70%. While achieving similar results, the cost of using this agent to treat produced water is higher than the cost of this invention.

[0049] Example 3

[0050] This embodiment provides a method for treating produced water from an oilfield, which includes the following steps:

[0051] Weigh 1g of polyaluminum ferric silicate powder and prepare a polyaluminum ferric silicate solution of appropriate concentration; weigh 0.1g of cationic polyacrylamide powder with a molecular weight of 12 million and an ionic degree of 40 and prepare a polyacrylamide solution of appropriate concentration; take 500mL of oilfield produced water with an oil content of 610mg / L, and add the polyaluminum ferric silicate solution to the oilfield produced water at a water bath temperature of 45℃ until the concentration of polyaluminum ferric silicate in the produced water is 20mg / L, and stir at 100r / min for 1min; then stir... The rotation speed was increased to 140 r / min, and the polyacrylamide solution was added in batches, gradually and cumulatively. The polyacrylamide solution was added in two separate additions at a rate of 10 mL per second. After each addition, the mixture was stirred at 140 r / min for 3 minutes. The concentration of polyacrylamide in the produced water was increased to 1.5 mg / L. After the addition was complete, the mixture was stirred at 140 r / min for 6 minutes, allowed to stand for 90 minutes, and then filtered to obtain the treated oilfield produced water. The oil content of the treated oilfield produced water was measured to be 29.68 mg / L, and the oil removal rate was 95.13%.

[0052] Comparative Example 3

[0053] This comparative example provides a method for treating produced water in oil fields. In this comparative example, polyacrylamide solution is added first, followed by polyaluminum ferric silicate solution.

[0054] The method includes the following steps:

[0055] Weigh 1g of polyaluminum ferric silicate powder and prepare a polyaluminum ferric silicate solution of appropriate concentration; weigh 0.1g of cationic polyacrylamide powder with a molecular weight of 12 million and an ionic degree of 40 and prepare a polyacrylamide solution of appropriate concentration; take 500mL of oilfield produced water with an oil content of 610mg / L, and add the polyacrylamide solution to the oilfield produced water in batches and gradually, cumulatively, under the condition of a water bath temperature of 45℃. The polyacrylamide solution is added in two batches at a dripping rate of 10mL per second. After adding the polyacrylamide solution, stir at 140 rpm for 3 minutes. Continue adding polyacrylamide solution until the concentration in the produced water is 1.5 mg / L. After the addition is complete, stir at 140 rpm for 6 minutes. Then, reduce the stirring speed to 100 rpm and add polyaluminum ferric silicate solution until the concentration in the produced water is 20 mg / L. Stir at 100 rpm for 1 minute, let stand for 90 minutes, and then filter to obtain the treated oilfield produced water. The oil content of the treated oilfield produced water was measured to be 127.6 mg / L, and the oil removal rate was 79.08%.

[0056] Example 4

[0057] This embodiment provides a method for treating produced water from an oilfield, which includes the following steps:

[0058] Weigh 0.75g of polyaluminum ferric silicate powder and prepare a polyaluminum ferric silicate solution of appropriate concentration; weigh 0.1g of cationic polyacrylamide powder with a molecular weight of 10 million and an ionic degree of 60 and prepare a polyacrylamide solution of appropriate concentration; take 500mL of oilfield produced water with an oil content of 495mg / L, and add the polyaluminum ferric silicate solution to the oilfield produced water at a water bath temperature of 45℃ until the concentration of polyaluminum ferric silicate in the produced water is 15mg / L, and stir at 100r / min for 1min; then... The stirring speed was increased to 140 r / min, and the polyacrylamide solution was added in batches, gradually and cumulatively. The polyacrylamide solution was added in two separate additions at a rate of 10 mL per second. After each addition, the mixture was stirred at 140 r / min for 3 minutes. The polyacrylamide concentration in the produced water was increased to 1 mg / L. After the addition was complete, the mixture was stirred at 140 r / min for 6 minutes, allowed to stand for 90 minutes, and then filtered to obtain the treated oilfield produced water. The oil content of the treated oilfield produced water was measured to be 21.29 mg / L, and the oil removal rate was 95.72%.

[0059] Example 5

[0060] This embodiment provides a method for treating produced water from an oilfield, which includes the following steps:

[0061] Weigh 1g of polyaluminum ferric silicate powder and prepare a polyaluminum ferric silicate solution of appropriate concentration; weigh 0.1g of cationic polyacrylamide powder with a molecular weight of 9 million and an ionic degree of 60 and prepare a polyacrylamide solution of appropriate concentration; take 500mL of oilfield produced water with an oil content of 850mg / L, and add the polyaluminum ferric silicate solution to the oilfield produced water at a water bath temperature of 45℃ until the concentration of polyaluminum ferric silicate in the produced water is 20mg / L, and stir at 100r / min for 1min; then turn the stirring speed... The flow rate was increased to 140 r / min, and the polyacrylamide solution was added in batches, gradually and cumulatively. The polyacrylamide solution was added in two separate additions at a rate of 10 mL per second. After each addition, the mixture was stirred at 140 r / min for 3 minutes. The concentration of polyacrylamide in the produced water was increased to 1.5 mg / L. After the addition was complete, the mixture was stirred at 140 r / min for 6 minutes, allowed to stand for 90 minutes, and then filtered to obtain the treated oilfield produced water. The oil content of the treated oilfield produced water was measured to be 46.13 mg / L, and the oil removal rate was 94.57%.

[0062] Example 6

[0063] This embodiment provides a method for treating produced water from an oilfield, which includes the following steps:

[0064] Weigh 1g of polyaluminum ferric silicate powder and prepare a polyaluminum ferric silicate solution of appropriate concentration; weigh 0.1g of cationic polyacrylamide powder with a molecular weight of 12 million and an ionic degree of 40 and prepare a polyacrylamide solution of appropriate concentration; take 500mL of produced water from a binary flooding oilfield with an oil content of 220mg / L and a polymer concentration of 210mg / L, and add the polyaluminum ferric silicate solution to the produced water at a water bath temperature of 45℃ until the concentration of polyaluminum ferric silicate in the produced water is 300mg / L, and stir at a speed of 100r / min for 1 minute. 0 min; then the stirring speed was increased to 140 r / min, and the polyacrylamide solution was added in batches, gradually and cumulatively. The polyacrylamide solution was added in two batches at a dropping rate of 10 mL per second. After each addition of the polyacrylamide solution, the stirring speed was increased to 140 r / min for 3 min. The polyacrylamide solution was added until the concentration of polyacrylamide in the produced water was 2 mg / L. After the addition was completed, the stirring speed was increased to 140 r / min for 6 min, and the mixture was allowed to stand for 240 min. Then it was filtered to obtain the treated oilfield produced water. The oil content of the treated oilfield produced water was measured to be 15.2 mg / L, with an oil removal rate of 93.1%; the polymer concentration in the treated oilfield produced water was 61.5 mg / L, with a polymer removal rate of 70.7%.

[0065] Comparative Example 4

[0066] This comparative example provides a method for treating produced water in oil fields. The comparative example uses cationic polyacrylamide with a molecular weight of 6 million and an ionicity of 30.

[0067] Weigh 1g of polyaluminum ferric silicate powder and prepare a polyaluminum ferric silicate solution of appropriate concentration; weigh 0.1g of cationic polyacrylamide powder with a molecular weight of 6 million and an ionic degree of 30 and prepare a polyacrylamide solution of appropriate concentration; take 500mL of produced water from a binary flooding oilfield with an oil content of 220mg / L and a polymer concentration of 210mg / L, and add the polyaluminum ferric silicate solution to the produced water at a water bath temperature of 45℃ until the concentration of polyaluminum ferric silicate in the produced water is 300mg / L, and stir at a speed of 100r / min for 10 minutes. The stirring speed was then increased to 140 r / min, and the polyacrylamide solution was added in batches, gradually and cumulatively. The polyacrylamide solution was added in two separate additions at a rate of 10 mL per second. After each addition, the mixture was stirred at 140 r / min for 3 minutes. The polyacrylamide solution was added until the concentration in the produced water reached 2 mg / L. After the addition was complete, the mixture was stirred at 140 r / min for 6 minutes, allowed to stand for 240 minutes, and then filtered to obtain the treated oilfield produced water. The oil content of the treated oilfield produced water was measured to be 81.2 mg / L, with an oil removal rate of 63.1%. The polymer concentration in the treated oilfield produced water was 92.1 mg / L, with a polymer removal rate of 56.1%.

[0068] Example 7

[0069] This embodiment provides a method for treating produced water from an oilfield, which includes the following steps:

[0070] Weigh 1g of polyaluminum ferric silicate powder and prepare a polyaluminum ferric silicate solution of appropriate concentration; weigh 0.1g of cationic polyacrylamide powder with a molecular weight of 10 million and an ionic degree of 60 and prepare a polyacrylamide solution of appropriate concentration; take 500mL of produced water from a binary flooding oilfield with an oil content of 220mg / L and a polymer concentration of 210mg / L, and add the polyaluminum ferric silicate solution to the produced water at a water bath temperature of 45℃ until the concentration of polyaluminum ferric silicate in the produced water is 400mg / L, and stir at a speed of 100r / min for 1 minute. 0 min; then the stirring speed was increased to 200 r / min, and the polyacrylamide solution was added in batches, gradually and cumulatively. The polyacrylamide solution was added in two batches at a dropping rate of 10 mL per second. After each addition of the polyacrylamide solution, the stirring speed was increased to 200 r / min for 3 min. The polyacrylamide solution was added until the concentration of polyacrylamide in the produced water was 2 mg / L. After the addition was completed, the stirring speed was increased to 200 r / min for 10 min, and the mixture was allowed to stand for 240 min. Then it was filtered to obtain the treated oilfield produced water. The oil content of the treated oilfield produced water was measured to be 12.1 mg / L, with an oil removal rate of 94.5%; the polymer concentration in the treated oilfield produced water was 57.4 mg / L, with a polymer removal rate of 72.6%.

[0071] Comparative Example 5

[0072] This comparative example provides a method for treating produced water in oil fields. The comparative example uses anionic polyacrylamide with a molecular weight of 10 million and an ionicity of 50.

[0073] Weigh 1g of polyaluminum ferric silicate powder and prepare a polyaluminum ferric silicate solution of appropriate concentration; weigh 0.1g of anionic polyacrylamide powder with a molecular weight of 10 million and an ionic degree of 50 and prepare a polyacrylamide solution of appropriate concentration; take 500mL of produced water from a binary flooding oilfield with an oil content of 220mg / L and a polymer concentration of 210mg / L, and add the polyaluminum ferric silicate solution to the produced water at a water bath temperature of 45℃ until the concentration of polyaluminum ferric silicate in the produced water is 400mg / L, and stir at a speed of 100r / min for 10 minutes. The stirring speed was then increased to 200 rpm, and the polyacrylamide solution was added in batches, gradually and cumulatively. The polyacrylamide solution was added in two separate additions at a rate of 10 mL per second. After each addition, the mixture was stirred at 200 rpm for 3 minutes. The polyacrylamide solution was added until the concentration in the produced water reached 2 mg / L. After the addition was complete, the mixture was stirred at 200 rpm for 10 minutes, allowed to stand for 240 minutes, and then filtered to obtain the treated oilfield produced water. The oil content of the treated oilfield produced water was measured to be 93.0 mg / L, with an oil removal rate of 57.72%. The polymer concentration in the treated oilfield produced water was 142.7 mg / L, with a polymer removal rate of 32.04%.

[0074] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. For those skilled in the art, other variations or modifications can be made based on the above description. It is impossible to exhaustively list all the implementation methods here. All obvious variations or modifications derived from the technical solutions of the present invention are still within the protection scope of the present invention.

Claims

1. A method for treating produced water from an oilfield, comprising the following steps: (1) Add a polymeric aluminum ferric silicate solution to the produced water of the oilfield to be treated and stir at the first speed for a period of time; wherein, the produced water of the oilfield to be treated is produced water of a binary flooding oilfield with an oil content of 100-1000 mg / L and a polymer concentration of 150-300 mg / L, and the concentration of polymeric aluminum ferric silicate in the produced water of the oilfield after adding the polymeric aluminum ferric silicate solution is 300-400 mg / L; (2) Increase the first rotation speed to the second rotation speed, add polyacrylamide solution, stir at the second rotation speed for a period of time after the addition is complete, let stand for a period of time, filter to obtain the treated oilfield produced water; wherein, the polyacrylamide solution is added 3-5 times per liter of oilfield produced water, at a dropping rate of 10-15 mL per second until the concentration of polyacrylamide in the oilfield produced water is 1-2 mg / L, and after each addition of the polyacrylamide solution, stir at the second rotation speed for 2-5 min; the polyacrylamide used is cationic polyacrylamide, with a molecular weight of 8 million-13 million and an ionic degree of 30-80; The oil content in the treated produced water is below 50 mg / L. The treatment method achieves an oil removal rate of over 93% for the produced water from the oilfield to be treated. The polymer concentration in the treated oilfield produced water is 50-100 mg / L; The treatment method achieves a polymer removal rate of over 50% in the produced water from the oilfield to be treated.

2. The oilfield produced water treatment method according to claim 1, wherein, In step (1), the first rotation speed is 90-110 r / min, and the stirring time at the first rotation speed is 1-10 min.

3. The oilfield produced water treatment method according to claim 1, wherein, In step (1), step (1) is carried out at a temperature of 30-60°C.

4. The oilfield produced water treatment method according to claim 1, wherein, In step (2), the polyacrylamide used is cationic polyacrylamide with a molecular weight of 9 million to 12 million and an ionic degree of 40 to 70.

5. The oilfield produced water treatment method according to claim 1, wherein, In step (2), the second rotational speed is 140-200 r / min.

6. The oilfield produced water treatment method according to claim 1, wherein, In step (2), after the addition is complete, the stirring time at the second speed is 6-10 minutes.

7. The oilfield produced water treatment method according to claim 1, wherein, In step (2), the settling time is 1-4 hours.

8. The method for treating produced water from oilfields according to claim 1, wherein, Step (2) is carried out at a temperature of 30-60℃.

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