Green short-process treatment process for oilfield produced water

Abstract

The invention discloses a green short-flow treatment process for oilfield produced water, and belongs to the field of wastewater treatment. The process comprises the following steps: lifting oilfield produced water from a raw water regulating reservoir to an air flotation unit, and removing suspended oil under the action of micro-nano bubbles; the raw water treated by the air floatation unit is lifted to a PEK membrane unit to be treated; feeding the concentrated water of the PEK membrane unit into a sludge tank, carrying out desliming treatment, and returning desliming produced water to the air flotation unit; and conveying the water produced by the PEK membrane unit to a clear liquid buffer tank. The final produced water meets the first-level requirements of Technical Requirements and Analytical Methods for Water Quality Index of Injection Of Clastic Rock Oil Reservoir SY / T 5329-2022, that is, the solid content of suspended solids is less than or equal to 8mg / L, the median diameter of suspended solid particles is less than or equal to 3mu m, the oil content is less than or equal to 5mg / L, and the average corrosion rate is less than or equal to 0.076 mm / a.

Description

Technical Field

[0001] The invention relates to the field of wastewater treatment, and in particular to a green short-process treatment technology for oilfield produced water. Background Art

[0002] During the crude oil extraction process, the water in the oil reservoir will be extracted together with the crude oil. The water after the crude oil is dehydrated is called oilfield produced water (commonly known as: oily wastewater). The reservoirs in the Ordos Basin are mainly low-permeability and ultra-low-permeability oil reservoirs. The most common oily wastewater treatment processes in this area are oil separators or oil separators, flotation, flocculation sedimentation and two-stage filtration. Among them, there are quartz sand, walnut shells, fiber balls, diatomaceous earth, PE sintered tubes, ceramic membranes, high-flux membranes, bag filters and other filtering devices in the filtration link, which are widely used in this area. With the release and implementation of new clastic rock water quality industry standards and the annual improvement of environmental protection requirements, higher and more stringent requirements have been put forward for oilfield wastewater treatment. Under the heavy pressure of sustainable development and safety and environmental protection, oil companies have put forward higher requirements for safety and environmental protection, energy saving and consumption reduction, controllability, oil resistance, corrosion resistance and cost-effectiveness of fine filtration devices for oily wastewater treatment.

[0003] Defects and shortcomings of existing technologies: Traditional filtering devices such as quartz sand, walnut shells, fiber balls, etc. are large in size, inconvenient to replace filter media, have low filtration accuracy, easily compacted filter media, short replacement cycle, and produce a lot of hazardous waste. The backwashing operation is complicated and the price has certain advantages. Diatomaceous earth, PE sintered tubes, ceramic membranes, and large flux membranes have high filtration accuracy but slow flux recovery and complex recovery process. They must be used in conjunction with pre-treatment and coarse filtration in the treatment process. They have certain requirements for water quality before entering the equipment, and have poor oil resistance and corrosion resistance. Repair and maintenance are cumbersome and costly. Portable filtering devices such as bag filters have high filter element replacement frequency, unstable effluent water quality, fast loss of accuracy, and poor filtration stability, and are temporary devices. Summary of the invention

[0004] In view of the deficiencies of the prior art, the present invention proposes a green short-process treatment process for oilfield produced water.

[0005] The purpose of the present invention can be achieved through the following technical solutions:

[0006] A first aspect of the present invention relates to a green treatment process for oilfield produced water, comprising the following steps:

[0007] The produced water from the oil field is lifted from the raw water regulating tank to the flotation unit, where the suspended oil is removed under the action of micro-nano bubbles;

[0008] The raw water treated by the air flotation unit is lifted to the PEK membrane unit for treatment;

[0009] The concentrated water of the PEK membrane unit is sent to the sludge tank for desludge treatment, and the desludged water is returned to the flotation unit;

[0010] The produced water of the PEK membrane unit is transported to the clear liquid buffer tank.

[0011] Furthermore, the air flotation unit is a vertical structure, and the rising velocity of the water flow of the air flotation unit does not exceed 20 mm / s.

[0012] Furthermore, the desludging process includes: plate and frame filter pressing, filter cloth, flushing, filtered water recovery, pressing equipment and compressed air purging.

[0013] The second aspect of the present invention relates to a green treatment system for oilfield produced water, characterized in that it comprises:

[0014] A raw water regulating tank for receiving produced water from oil fields;

[0015] Air flotation unit, used to remove suspended oil under the action of micro-nano bubbles;

[0016] PEK membrane unit, used to filter and treat the raw water after being treated by the flotation unit;

[0017] A desludging device, used for desludging the concentrated water of the PEK membrane unit and returning the desludging produced water to the air flotation unit;

[0018] And, a clear liquid buffer tank is used to receive the water produced by the PEK membrane unit.

[0019] A third aspect of the present invention relates to the application of the above-mentioned green treatment process for oilfield produced water or the above-mentioned green treatment system for oilfield produced water in treating oilfield produced wastewater.

[0020] Furthermore, the final water quality reaches: suspended solid content ≤ 1 mg / L, median diameter of suspended particles ≤ 1 μm, and oil content ≤ 1 mg / L.

[0021] Furthermore, the air flotation device is a vertical structure, the water flow rate does not exceed 20 mm / s, and the hydraulic retention time is not less than 30 min.

[0022] Furthermore, the PEK membrane device is a PEK (polyetherketone) material separation membrane with a membrane pore size of 5nm to 0.2μm. It uses the screening principle of the membrane and the hydrophilic and oleophobic properties of the PEK material to intercept suspended matter and impurities such as petroleum and bacteria without pre-membrane pretreatment.

[0023] Furthermore, the entire treatment process including flotation, membrane filtration and desludging does not require the addition of any chemical agents, thus achieving green production.

[0024] Furthermore, the water resource recovery rate is greater than 99%, and only a small amount of water is taken away by the sludge.

[0025] Beneficial effects of the present invention:

[0026] 1. The characteristics of the present invention are simple processing flow, no need to add chemical agents, small equipment footprint, low investment cost, stable water output, and full automatic control;

[0027] 2. The present invention is particularly suitable for treating wastewater with high oil content, high suspended matter content and high salt content;

[0028] 3. The PEK membrane device used in the present invention has the characteristics of acid and alkali resistance, COD resistance, oil resistance, good hydrophilicity, large flux, no need for backwashing, etc. The retention pore size is 5nm~0.2μm, and it has outstanding advantages as a mud-water separation with high suspended matter concentration and high organic matter;

[0029] 4. The process of the present invention adopts the treatment process of air flotation + PEK membrane filtration + sludge dehydration. The water quality of the process is stable, the operating cost is low, the equipment is integrated and the service life is long. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The present invention will be further described below in conjunction with the accompanying drawings.

[0031] Figure 1 The present invention discloses a flow chart of a green short-process treatment process for oilfield produced water. DETAILED DESCRIPTION

[0032] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0033] In some embodiments of the present invention, a green short-process treatment process for oilfield produced water is disclosed, such as Figure 1 As shown, the process of the present invention is carried out according to the following steps:

[0034] Step 1: The wastewater is pumped from the raw water regulating tank to the flotation device, where the suspended oil is removed by the action of micro-nano bubbles;

[0035] Step 2: The raw water obtained in step 1 is lifted to the PEK membrane device to remove impurities such as emulsified oil, dissolved oil, bacteria and suspended matter;

[0036] Step 3: Send the PEK membrane concentrated water obtained in step 2 to the sludge pool. The dehydrated sludge is entrusted to a qualified unit for harmless treatment, and the desludge water is returned to the system;

[0037] Step 4: Transfer the PEK membrane produced water obtained in step 2 to the clear liquid buffer tank and inject it back when it meets the standards.

[0038] More specifically, the air flotation device in the above embodiment is a vertical structure, the water flow rate does not exceed 20 mm / s, and the hydraulic retention time is not less than 30 min.

[0039] The PEK membrane device in the above embodiment is a PEK (polyetherketone) material separation membrane with a pore size of 5nm to 0.2μm. It uses the screening principle of the membrane and the hydrophilicity and oleophobicity of the PEK material to intercept suspended matter, petroleum, bacteria and other impurities without pre-membrane pretreatment.

[0040] The sludge dehydration described in this embodiment is achieved by a plate and frame filter press system, which specifically includes a plate and frame filter press, filter cloth, flushing, filtered water recovery, pressing equipment, compressed air purging and other sub-equipment. The final produced water obtained in step 4 is tested and the final produced water quality reaches: suspended solid content ≤1mg / L, median diameter of suspended particles ≤1μm, oil content ≤1mg / L, produced water recovery rate greater than 99%, and no chemical agents are added in the whole process.

[0041] In some more specific examples of the present invention, the produced wastewater of a certain oil production plant joint station is taken as the research object, according to the above embodiments and Figure 1 The process shown in the experiment was used, and the wastewater regulating tank was sampled. The final water produced met the first-level requirements of "Technical Requirements and Analysis Methods for Water Quality Indicators in Clastic Reservoirs SY / T 5329-2022", with suspended solid content ≤1000mg / L and oil content ≤100mg / L. After treatment, the suspended solid content was ≤0.15mg / L, the median diameter of suspended particles was ≤1μm, and the oil content was ≤0.3mg / L.

[0042] In the description of this specification, the description with reference to the terms "one embodiment", "example", "specific example", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0043] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments, and the above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, and these changes and improvements all fall within the scope of the present invention to be protected.

Claims

1. A green treatment process for oilfield produced water, characterized in that: The following steps are involved: The produced water from the oil field is lifted from the raw water regulating tank to the flotation unit, where the suspended oil is removed under the action of micro-nano bubbles; The raw water treated by the air flotation unit is lifted to the PEK membrane unit for treatment; The concentrated water of the PEK membrane unit is sent to the sludge tank for desludge treatment, and the desludged water is returned to the flotation unit; The produced water of the PEK membrane unit is transported to the clear liquid buffer tank.

2. The green treatment process for oilfield produced water according to claim 1, characterized in that: The PEK membrane in the PEK membrane unit is a separation membrane made of polyetherketone, and the membrane pore size is 5nm to 0.2μm.

3. The green treatment process for oilfield produced water according to claim 1, characterized in that: The air flotation unit is a vertical structure, and the rising flow rate of the water flow in the air flotation unit does not exceed 20 mm / s.

4. The green treatment process for oilfield produced water according to claim 1, characterized in that: The desludging process includes: plate and frame filter pressing, filter cloth, flushing, filtered water recovery, pressing equipment and compressed air purging.

5. A green treatment system for oilfield produced water, characterized in that: include: A raw water regulating tank for receiving produced water from oil fields; Air flotation unit, used to remove suspended oil under the action of micro-nano bubbles; PEK membrane unit, used to filter and treat the raw water after being treated by the flotation unit; A desludging device, used for desludging the concentrated water of the PEK membrane unit and returning the desludging produced water to the air flotation unit; And, a clear liquid buffer tank is used to receive the water produced by the PEK membrane unit.

6. The green treatment system for oilfield produced water according to claim 5, characterized in that: The PEK membrane in the PEK membrane unit is a separation membrane made of polyetherketone, and the membrane pore size is 5nm to 0.2μm.

7. The green treatment system for oilfield produced water according to claim 5, characterized in that: The air flotation unit is a vertical structure, and the rising flow rate of the water flow in the air flotation unit does not exceed 20 mm / s.

8. The green treatment system for oilfield produced water according to claim 5, characterized in that: The desludging process includes: plate and frame filter pressing, filter cloth, flushing, filtered water recovery, pressing equipment and compressed air purging.

9. Use of the green treatment process for oilfield produced water according to any one of claims 1 to 4 or the green treatment system for oilfield produced water according to any one of claims 5 to 8 in treating oilfield produced wastewater.

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