Coagulation-ultrafiltration combined low-permeability oilfield reinjection water treatment method

Abstract

The invention discloses a coagulation-ultrafiltration combined low-permeability oilfield reinjection water treatment method. The method comprises the following steps: 1) performing online coagulation on wastewater by using a flocculant, and feeding the wastewater into a laminated filter to remove impurities including heavy metal ions and suspended solids so as to obtain wastewater subjected to coagulation pretreatment; and 2) performing permeable membrane treatment on the wastewater subjected to coagulation pretreatment to obtain the treated low-permeability oilfield reinjection water. The method has the characteristics of wide treatment range, remarkable treatment effect and low treatment cost.

Description

Technical Field

[0001] The invention belongs to the field of water treatment and relates to a coagulation-ultrafiltration combined low-permeability oilfield reinjection water treatment method. Background Art

[0002] Water injection exploitation of low-permeability and ultra-low-permeability oil reservoirs not only consumes a large amount of water resources, but also produces a huge amount of produced wastewater. Oilfield produced wastewater has high suspended matter (50-700 mg / L), high oil content (20-300 mg / L, complex oil composition (both suspended oil and dispersed oil, emulsified oil), complex organic composition, and difficulty in degradation (in addition to crude oil, it also contains fatty acids, surfactants, oil displacement agents, demulsifiers, viscosity reducers, corrosion inhibitors, organic sulfur, etc.). High oil content, complex water quality components, poor biodegradability, difficulty in treatment, and high treatment cost are the important characteristics of this type of wastewater.

[0003] Coagulation technology uses the physical and chemical effects of flocculants to absorb suspended pollutants. Ceramic membranes are not easily deformed, can withstand high temperature and high pressure, and have strong resistance to chemical agents. They can effectively remove oil and suspended matter in wastewater, provide good water quality for fine filters, and avoid pollution and clogging of fine filters.

[0004] In view of the difficulties of existing technologies in fine treatment of reinjection water in low permeability oil fields, such as great difficulty, low efficiency, large investment and high cost, it is urgent to provide an innovative fine treatment process for reinjection water in low permeability oil fields. Summary of the invention

[0005] The purpose of the present invention is to provide a coagulation-ultrafiltration combined low-permeability oilfield reinjection water treatment method.

[0006] The present invention provides a method for treating low-permeability oilfield reinjection water by combining coagulation and ultrafiltration, comprising the following steps:

[0007] 1) The wastewater is coagulated online using a flocculant and filtered through a laminated filter to obtain wastewater after coagulation pretreatment;

[0008] 2) The wastewater after the coagulation pretreatment is subjected to membrane treatment to obtain treated low-permeability oilfield reinjection water.

[0009] In the above method, the flocculant is selected from at least one of polyaluminum sulfate, ferrous sulfate, polyferric sulfate, polyvinyl alcohol and polyacrylamide.

[0010] In the above method, the amount of the flocculant added to the wastewater may be 5 to 1000 mg / L, specifically 5 mg / L, 500 mg / L, or 1000 mg / L;

[0011] The wastewater may be coagulated for 10 to 50 minutes, specifically 10, 15, 20, 25, 30 minutes or 10 to 30 minutes.

[0012] In the above method, the membrane treatment is performed using a ceramic membrane separation device.

[0013] In the above method, the permeable membrane used in the permeable membrane treatment is a ceramic membrane;

[0014] The material of the ceramic membrane is selected from at least one of aluminum oxide, titanium oxide, zirconium oxide, silicon nitride and silicon dioxide.

[0015] In the above method, the pore size of the ceramic membrane may be 0.01 μm to 5 μm, specifically 0.01 μm, 0.05 μm, 0.5 μm, 5 μm;

[0016] During the transmembrane treatment, the pressure difference on both sides of the transmembrane may be 0.5-4 bar, specifically 0.5 bar, 0.8 bar, 1 bar, 2 bar, 4 bar.

[0017] In the above method, the laminated filter removes impurities including heavy metal ions and suspended matter;

[0018] The suspended matter includes mud, sand, fibers or oil droplets.

[0019] The present invention has the following beneficial effects:

[0020] 1. It has a wide range of treatment and can be applied to the treatment of many types of industrial wastewater, and has universal requirements on the source and composition of wastewater;

[0021] 2. Excellent treatment effect. Through multi-stage treatment, pollutants such as organic matter, heavy metal ions, suspended solids in wastewater can be effectively removed, and the treatment effect is remarkable;

[0022] 3. The pretreatment part is mainly used to remove large particle impurities, suspended matter and sediments. The main steps are coagulation / flocculation pretreatment and membrane separation. It does not require a buffer tank and occupies a small area, which is particularly suitable for occasions with small space.

[0023] Therefore, compared with the prior art, the present application has made significant progress in many aspects such as treatment scope, treatment effect, and treatment cost, and provides a new method for the fine treatment of low-permeability oilfield reinjection water. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a flow chart of the method provided in this application. DETAILED DESCRIPTION

[0025] Unless otherwise specified, the experimental methods used in the following examples are conventional methods.

[0026] Unless otherwise specified, the materials and reagents used in the following examples can be obtained from commercial sources.

[0027] The present invention is further described in detail below through specific implementation modes.

[0028] In the following examples, the main components and contents of oilfield produced water are as follows: median particle size is 3.09 μm, suspended solids is 56.1 mg / L, and COD is 269 mg / L.

[0029] Example 1

[0030] This embodiment provides a method for fine treatment of low-permeability oilfield reinjection water, comprising the following steps:

[0031] (1) Coagulation pretreatment: The produced water from the oil field is pretreated. The pretreatment methods include online dosing and coagulation, followed by filtration in a laminated filter. The online dosing is connected to the inlet through a pipeline, and the pipeline flows through the coagulation time for 20 minutes. The coagulant and heavy metal ions produce colloids, thereby removing heavy metal ions and the like in the wastewater. In this embodiment, the coagulant is polyaluminum sulfate, and the addition amount is 5 mg / L. Then it enters the laminated filter for filtration.

[0032] (2) Membrane separation: The wastewater after coagulation pretreatment is treated by membrane separation device to pass water through the membrane. The membrane separation device is used to separate the remaining organic macromolecules. The particle size of organic molecules is generally greater than 1 μm, so water can pass through, but organic molecules with larger particle sizes are difficult to pass through. The membrane separation membrane can be made of alumina, titanium oxide, zirconium oxide, silicon nitride and silicon dioxide ceramic membranes, and the pore size is preferably controlled at 0.01 μm to 2 μm. In this embodiment, the selected membrane is an alumina ceramic membrane with a pore size of 0.01 μm and a pressure difference of 4 bar.

[0033] Example 2

[0034] This embodiment provides a method for treating industrial wastewater, comprising the following steps:

[0035] (1) Coagulation pretreatment: pre-treat the produced water from the oil field. The pre-treatment methods include online dosing and coagulation, and then entering the laminated filter for filtration. The online dosing adopts the pipeline access method at the entrance, and the pipeline flows through the coagulation time for 15 minutes. The coagulant mainly produces colloids to remove heavy metal ions in the wastewater. The coagulant / flocculant can be any one of polyaluminum sulfate, ferrous sulfate, polyferric sulfate, polyvinyl alcohol, and polyacrylamide, and the addition amount is 10 to 500 mg / L. In this embodiment, the coagulant is polyaluminum sulfate, and the addition amount is 500 mg / L. Then enter the laminated filter for filtration.

[0036] (2) Membrane separation: The wastewater after coagulation pretreatment is treated by membrane separation device to pass water through the membrane. The membrane separation device is used to separate the remaining organic macromolecules. The particle size of organic molecules is generally greater than 1 μm, so water can pass through, but organic molecules with larger particle sizes are difficult to pass through. In this embodiment, the permeable membrane selected is a titanium oxide ceramic membrane with a pore size of 0.05 μm and a pressure difference of 2 bar.

[0037] Example 3

[0038] This embodiment provides a method for treating industrial wastewater, comprising the following steps:

[0039] (1) Coagulation pretreatment: The produced water from the oil field is pretreated, and the pretreatment methods include online dosing and coagulation, and then entering the laminated filter for filtration. The online dosing adopts the pipeline access method at the entrance, and the pipeline flows through the coagulation time for 25 minutes. The coagulant mainly produces colloids, thereby removing heavy metal ions and the like in the wastewater. In this embodiment, the coagulant is polyaluminum sulfate, and the addition amount is 1000 mg / L. Then it enters the laminated filter for filtration.

[0040] (2) Membrane separation: The wastewater after coagulation pretreatment is treated by membrane separation device to pass water through the membrane. The membrane separation device is used to separate the remaining organic macromolecules. The particle size of organic molecules is generally greater than 1 μm, so water can pass through, but organic molecules with larger particle sizes are difficult to pass through. In this embodiment, the selected membrane is a silicon dioxide ceramic membrane with a pore size of 0.5 μm and a pressure difference of 0.8 bar.

[0041] Example 4

[0042] This embodiment provides a method for treating industrial wastewater, comprising the following steps:

[0043] (1) Coagulation pretreatment: The produced water from the oil field is pretreated. The pretreatment methods include online dosing and coagulation, and then entering the laminated filter for filtration. The online dosing adopts the pipeline access method at the entrance, and the pipeline flows through the coagulation time for 10 minutes. The coagulant mainly produces colloids, thereby removing heavy metal ions and the like in the wastewater. In this embodiment, the coagulant is polyaluminum sulfate, and the addition amount is 2500 mg / L. Then it enters the laminated filter for filtration.

[0044] (2) Membrane separation: The wastewater after coagulation pretreatment is treated by membrane separation device to pass water through the membrane. The membrane separation device is used to separate the remaining organic macromolecules. The particle size of organic molecules is generally greater than 1 μm, so water can pass through, but organic molecules with larger particle sizes are difficult to pass through. In this embodiment, the selected membrane is a silicon dioxide ceramic membrane with a pore size of 2 μm and a pressure difference of 0.5 bar.

[0045] Example 5

[0046] The wastewater treated by the scheme of Example 2 of the present invention has a median particle size of 0.031 μm, suspended matter of 0.89 mg / L, and COD of 29.59 mg / L. The median particle size decreased from 3.09 μm to 0.031 μm, a decrease of about 98.8%, which may be due to the fact that the treatment steps such as coagulation pretreatment and membrane separation can effectively remove large particles and suspended matter in the wastewater; the suspended matter decreased from 56.1 mg / L to 0.89 mg / L, a decrease of about 98.4%, which is similar to the reason for the decrease in particulate matter. The pretreatment step and the membrane separation device both play a role in the removal of suspended matter; COD decreased from 269 mg / L to 29.59 mg / L, a decrease of about 89.9%, which is due to the contribution of coagulation pretreatment to the reduction of COD. Coagulation pretreatment can remove heavy metal ions and organic matter in wastewater. At the same time, the membrane separation device also has a certain removal effect on COD.

[0047] In summary, the pollutant components in the wastewater have been effectively removed through coagulation pretreatment, membrane separation and other steps. At the same time, the synergistic cooperation of coagulants and ceramic membranes is also the key to achieving efficient wastewater treatment.

[0048] This specific embodiment is merely an explanation of the present application and is not a limitation of the present application. After reading this specification, those skilled in the art may make modifications to the present embodiment without any creative contribution as needed, but such modifications are protected by the patent law as long as they are within the scope of the claims of the present application.

Claims

1. A method for treating low-permeability oilfield reinjection water by combining coagulation and ultrafiltration, characterized in that: The steps include: 1) The wastewater is coagulated online using a flocculant and filtered through a laminated filter to obtain wastewater after coagulation pretreatment; 2) The wastewater after the coagulation pretreatment is subjected to membrane treatment to obtain treated low-permeability oilfield reinjection water.

2. The method according to claim 1, characterized in that The flocculants are selected from at least one of polyaluminum sulfate, ferrous sulfate, polyferric sulfate, polyvinyl alcohol and polyacrylamide.

3. The method according to claim 1 or 2, characterized in that: In the wastewater, the flocculant is added in an amount of 5 to 1000 mg / L. The wastewater has a coagulation time of 10 to 50 minutes in the channel.

4. The method according to any one of claims 1 to 3, characterized in that The membrane treatment is carried out using a ceramic membrane separation device.

5. The method according to any one of claims 1 to 4, characterized in that The permeable membrane used in the permeable membrane treatment is a ceramic membrane; The material of the ceramic membrane is selected from at least one of aluminum oxide, titanium oxide, zirconium oxide, silicon nitride and silicon dioxide.

6. The method according to claim 5, characterized in that The pore size of the ceramic membrane is 0.01 μm to 5 μm.

7. The method according to any one of claims 1 to 6, characterized in that During the membrane treatment, the pressure difference on both sides of the membrane is 0.5-4 bar.

8. The method according to any one of claims 1 to 7, characterized in that The laminated filter removes impurities including heavy metal ions and suspended matter; The suspended matter includes mud, sand, fibers or oil droplets.

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