Device and method for treating gas-bearing oilfield produced water on the basis of vertical shallow air flotation

Abstract

Provided by the present application are a device and method for treating gas-bearing oilfield produced water on the basis of vertical shallow air flotation. The treatment device provided by the present application comprises a pressure stabilizing buffer tank, a dosing system, a primary tubular dissolved air releaser, a high-pressure vertical cyclone floating device, a secondary tubular dissolved air releaser, a low-pressure vertical shallow air flotation device, a slop oil tank, and a sludge tank. In the present application, tubular dissolved microbubble generation technology, air flotation separation technology, cyclone separation technology, shallow sedimentation strengthening separation technology and the like are organically combined, a large amount of dissolved air resources contained in produced water is effectively utilized, high-quality microbubble sources are provided for the high-pressure vertical cyclone flotation device and the low-pressure vertical shallow air flotation device by means of a pressure step release mode, efficient treatment of gas-bearing oilfield produced water is implemented, the treatment process of the gas-bearing oilfield produced water is greatly simplified, and treatment costs are reduced.

Description

A gas-bearing oilfield produced water treatment device and method based on vertical shallow flotation Technical Field

[0001] The invention relates to a gas-bearing oilfield produced water treatment device and method based on vertical shallow-layer air flotation, belonging to the technical field of gas-bearing oilfield produced water treatment. Background Art

[0002] Produced water from a gas-bearing oilfield refers to water containing large amounts of dissolved gas, oil, suspended solids (SS), salts, and organic matter. During conventional crude oil extraction and processing, the produced fluid undergoes decompression and sedimentation in high- and low-pressure three-phase separators to separate the oil, gas, and water phases. During this process, most of the dissolved gas is released and collected for gas purification. The crude oil, after sedimentation and separation, enters subsequent crude oil processing or export processes. The remaining produced water enters subsequent water treatment processes, undergoing gravity sedimentation, flotation separation, filtration, and membrane separation before meeting discharge standards or reinjection.

[0003] The above existing process mainly has the following three problems: (1) After the high-pressure and low-pressure three-phase separators have reduced pressure and dissipated energy, most of the dissolved gas in the produced liquid has completed the reduced pressure release process, and the gas content in the produced liquid is very low. Therefore, when the subsequent produced water is subjected to flotation treatment, it needs to be re-injected with gas to generate enough fine bubbles to ensure the flotation separation efficiency, which causes a waste of resources. At the same time, the operation and maintenance costs of the gas injection system are high; (2) After the three-phase separator has reduced pressure and dissipated energy, the subsequent water treatment process of the produced water needs to be equipped with a booster pump to increase the pressure of the produced water to meet the operation requirements of the subsequent water treatment equipment. This depressurization-boosting process causes a large amount of energy consumption; (3) The flotation equipment in the existing water treatment process generally has problems such as long hydraulic retention time, large footprint, and high energy consumption. At the same time, the supporting bubble generating device also has problems such as large footprint, poor bubble generation quality, and high operation and maintenance costs.

[0004] As the water content of oil well produced fluids continues to increase, some of the existing oilfield water treatment processes are operating at full load and overload, and it is difficult to meet the increasingly stringent discharge or reinjection standards. Therefore, there is an urgent need to improve and innovate the treatment process of existing gas-bearing oilfield produced water.

[0005] In Chinese patent CN213895275U, published on August 6, 2021, Wang Yufang et al. proposed a self-gas circulation flotation solid-liquid and liquid-liquid separation device for oilfield produced water treatment. The process mainly includes a flotation separation tank, a dissolved air pump, a dissolved air tank, and a recovery tank. The process uses a dissolved air pump to form a gas circulation system to achieve gas recycling, which not only meets the requirements of oil removal but also reduces the loss of gas source. However, the process requires a dissolved air pump and a gas reflux system, which has problems such as complex process, high energy consumption, and high operation and maintenance costs. In Chinese patent CN215592663U, published on January 21, 2022, Jiang Chuansheng et al. proposed a self-gas circulation multi-stage pressure-type dissolved air flotation system. The system mainly includes a first-stage flotation separation tank, a second-stage flotation separation tank, an oil and gas recovery tank, and a dissolved air pipe. The process fully recycles the dissolved gas released by the incoming liquid, which not only meets the requirements of efficient oil removal but also reduces the cost of generating a microbubble gas source. However, this process still has problems such as insufficient gas source, the need for additional gas supply, and the gas collecting tank taking up too much space, resulting in the overall process structure being not compact enough and the operation and maintenance costs being relatively high. SUMMARY OF THE INVENTION

[0006] The present invention aims to provide a gas-bearing oilfield produced water treatment device and method based on vertical shallow flotation technology. The device has the advantages of a small footprint and low operating and maintenance costs. The method for treating gas-bearing oilfield produced water using the device has the advantages of a simple process flow and high separation efficiency.

[0007] To achieve the above object, the present invention provides the following technical solutions:

[0008] A device for treating produced water from a gas-bearing oil field, comprising a pressure-stabilizing buffer tank, a first-stage tubular dissolved air releaser, a high-pressure vertical cyclone floatation device, a second-stage tubular dissolved air releaser, and a low-pressure vertical shallow-layer floatation device connected in sequence;

[0009] The liquid phase inlet of the pressure stabilizing buffer tank is connected to the water inlet pipeline of the gas-bearing oil field produced water;

[0010] A dosing system is provided between the pressure stabilizing buffer tank and the first-level tubular dissolved air releaser;

[0011] The dirty oil outlet of the pressure stabilizing buffer tank, the oil outlet of the high-pressure vertical cyclone flotation device, and the oil outlet of the low-pressure vertical shallow air flotation device are respectively connected to the dirty oil tank;

[0012] The slag discharge port of the high-pressure vertical cyclone flotation device and the slag discharge port of the low-pressure vertical shallow flotation device are respectively connected to the sludge tank;

[0013] The air outlet of the high-pressure vertical cyclone flotation device and the air outlet of the low-pressure vertical shallow air flotation device are respectively connected to the gas pipeline;

[0014] The liquid outlet of the high-pressure vertical cyclone flotation device and the liquid outlet of the low-pressure vertical shallow air flotation device are both connected to the water outlet pipeline.

[0015] Furthermore, a vertical partition with a grid structure on the upper part is vertically arranged at the bottom of the pressure stabilizing buffer tank, dividing the middle and lower space in the tank into an oblique partition area and a horizontal partition area;

[0016] The microporous inclined partition, small-pore inclined partition and large-pore inclined partition are arranged in parallel from bottom to top in the inclined partition area;

[0017] The upper portion of the diaphragm area is provided with a small-hole diaphragm for outflow, and the lower portion is provided with a large-hole diaphragm for outflow;

[0018] An oil separator is horizontally provided at the upper end of the vertical separator, intersecting the vertical separator vertically and connected to the side wall of the tank body;

[0019] A gas phase inlet and a gas phase outlet are provided on the top of the pressure stabilizing buffer tank;

[0020] A liquid phase inlet is provided at the lower portion of the side wall of the inclined partition area;

[0021] A liquid phase outlet is provided at the lower portion of the side wall of the diaphragm zone;

[0022] A dirty oil outlet is provided on the upper portion of the side wall of the transverse partition area, and the top end of the dirty oil outlet is tangentially connected to the bottom end of the oil separator.

[0023] Furthermore, the diameter of the pressure stabilizing buffer tank is D1;

[0024] The distance between the vertical partition and the vertical axis of the pressure stabilizing buffer tank is D1 / 6, and the plate length L is 5D1 / 4;

[0025] The aperture d1 of the microporous inclined partition is 10 mm; the aperture d2 of the small-pore inclined partition is 30 mm; the aperture d3 of the large-pore inclined partition is 60 mm; the angle between a single inclined partition and the horizontal is 60°, and the spacing between the inclined partitions is D1 / 6;

[0026] The aperture d4 of the outflow small hole transverse partition is 30 mm, and the aperture d5 of the outflow large hole transverse partition is 30 mm; the distance between the outflow small hole transverse partition and the outflow large hole transverse partition is D1 / 4.

[0027] Furthermore, the first-stage tubular dissolved air releaser and the second-stage tubular dissolved air releaser both adopt a tubular multi-stage Venturi series structure; the number of the Venturi tube series stages is controlled to be 2 to 5.

[0028] Furthermore, the high-pressure vertical cyclone flotation device includes a main separation tank with a tank diameter of D2;

[0029] The main separation tank is provided with an oil overflow cover, an oil collecting cylinder, and a uniformly distributed swirl inlet from top to bottom; the uniformly distributed swirl inlet extends to the outside of the main separation tank and is connected to the water inlet pipeline;

[0030] An oil outlet is provided on the upper portion of the side wall of the main separation tank, and the bottom of the oil outlet is tangentially connected to the bottom surface of the oil overflow cover;

[0031] The top of the main separation tank is provided with an air outlet;

[0032] A slag discharge port is provided at the bottom axis of the main separation tank;

[0033] A liquid outlet is provided at a position D2 / 8 from the axis line on the bottom of the main separation tank.

[0034] Furthermore, the low-pressure vertical shallow flotation device includes a main separation tank with a tank diameter of D3;

[0035] The main separation tank is provided with an oil overflow cover, an oil collecting inclined plate and a hollow frustum from top to bottom in sequence;

[0036] The oil collecting inclined plate is composed of a plurality of hollow frustum-shaped inclined plates stacked up and down. The inclination angle of a single inclined plate is optimally set at an angle of 60° to 65° to the horizontal. The diameter of the large end of the inclined plate is 0.7 to 0.9 times the inner diameter D3 of the tank of the low-pressure vertical shallow air flotation device, and the diameter of the small end of the inclined plate is 0.3 to 0.5 times the inner diameter D3 of the tank of the low-pressure vertical shallow air flotation device. The vertical spacing of the inclined plates is controlled at 40 mm to 100 mm, and the number of inclined plates is set at about 6 to 10.

[0037] A uniformly distributed outlet is provided above the interior of the hollow frustum, and a flow balancing plate is provided below;

[0038] A slag discharge port is provided at the bottom axis of the hollow frustum and extends to the outside of the bottom of the main separation tank;

[0039] An air outlet is provided at the top center of the main separation tank;

[0040] An oil outlet is provided on the upper portion of the side wall of the main separation tank, and the bottom of the oil outlet is connected to the ground section of the oil overflow cover;

[0041] A liquid inlet is provided at the lower portion of the side wall of the main separation tank, which is horizontally connected to the uniformly distributed outlet;

[0042] A liquid outlet is provided at the bottom end of the main separation tank.

[0043] The present invention also provides a method for treating produced water from a gas-bearing oil field using the treatment device, comprising the following steps:

[0044] S1, the produced water from the gas-bearing oil field is subjected to pressure stabilization in the pressure stabilization buffer tank, and after the pressure stabilization treatment, a reagent is added thereto and the produced water enters the first-level tubular dissolved air releaser;

[0045] S2, the dissolved gas in the produced water of the gas-bearing oil field is released under reduced pressure in the first-stage tubular dissolved gas releaser to form fine bubbles, and then the produced water rich in fine bubbles enters the high-pressure vertical cyclone flotation device and generates cyclonic flow through the uniformly distributed outlet;

[0046] During the flow process, fine bubbles, oil droplets and solid suspensions form "oil droplet-bubble adhesion bodies" and "solid suspension-bubble adhesion bodies", which move centripetally under the action of the swirling centrifugal force and float up to be discharged into the waste oil tank through the oil outlet; the gas phase is discharged into the gas pipeline through the gas outlet; the solid phase settles and is discharged from the slag discharge port; the separated produced water enters the two-stage tubular dissolved air releaser.

[0047] S3, the produced water obtained in step S2 is decompressed and released in the two-stage tubular dissolved air releaser to generate micro bubble groups for the second time. The produced water rich in micro bubble groups enters the low-pressure vertical shallow flotation device and flows evenly under the action of the flow equalizing plate;

[0048] During the flow process, the fine bubble groups collide and adhere to the oil droplets and solid suspensions to form "oil droplet-bubble adhesion bodies" and "solid suspension-bubble adhesion bodies". Under the action of shallow sedimentation, the oil droplets are aggregated, coalesced and separated. The treated enriched oil phase is discharged to the waste oil tank through the oil outlet, and the gas phase is discharged into the gas pipeline through the gas outlet. The solid phase settles and is discharged from the slag discharge port; the treated produced water flows out from the liquid outlet and into the water outlet pipeline.

[0049] In step S1, the hydraulic retention time in the pressure stabilizing buffer tank is controlled to be above 30 minutes, and the water pressure is 0.50-0.6 MPa; the agent is one of polyaluminum chloride PAC, polyacrylamide PAM and a water purifier.

[0050] In step S2, the water pressure of the outlet pipe section of the first-stage tubular dissolved air releaser is controlled between 0.30 and 0.35 MPa.

[0051] In step S3, the water pressure of the outlet pipe section of the two-stage tubular dissolved air releaser is controlled between 0.10 and 0.15 MPa. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] FIG1 is a process flow chart of a treatment device and method for producing water from a gas-bearing oil field based on vertical shallow flotation technology provided by the present invention.

[0053] FIG2 is a schematic structural diagram of the pressure-stabilizing buffer tank 2 in the processing device provided by the present invention.

[0054] FIG3 is a schematic structural diagram of the high-pressure vertical cyclone floatation tank 8 in the treatment device provided by the present invention.

[0055] FIG4 is a schematic structural diagram of a low-pressure vertical shallow air flotation tank 13 in the treatment device provided by the present invention.

[0056] Figure numerals: 1-high-pressure transport pipeline; 2-pressure-stabilizing buffer tank; 3-dosing system; 4-high-pressure treatment pipeline; 5-first-stage tubular dissolved air releaser; 6-slag discharge pipeline; 7-waste oil transport pipeline; 8-high-pressure vertical cyclone flotation device; 9-second-stage tubular dissolved air releaser; 10-waste oil tank; 11-low-pressure treatment pipeline; 12-gas transmission pipeline; 13-low-pressure vertical shallow flotation device; 14-water outlet pipeline; 15-sludge tank.

[0057] 21-Liquid phase inlet; 22-Microporous inclined baffle; 23-Small hole inclined baffle; 24-Large hole inclined baffle; 25-Vertical baffle; 26-Oil separator; 27-Gas phase inlet; 28-Gas phase outlet; 29-Dirty oil outlet; 210-Outflow of small hole transverse baffle; 211-Outflow of large hole transverse baffle; 212-Liquid phase outlet.

[0058] 81- oil overflow cover; 82- oil outlet; 83- oil collecting cylinder; 84- uniform swirl inlet; 85- liquid inlet; 86- slag discharge port; 87- liquid outlet; 88- air outlet.

[0059] 131- oil overflow cover; 132- oil outlet; 133- oil collecting inclined plate; 134- uniform outlet; 135- hollow cone; 136- flow equalizing plate; 137- liquid inlet; 138- slag discharge port; 139- liquid outlet; 1310- air outlet. Best Mode for Carrying Out the Invention

[0060] To make the objectives, technical solutions, and advantages of the present invention more clear, the technical solutions of the present invention are described in detail below. Obviously, the embodiments described are only some of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other implementation methods obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0061] Referring to Figures 1 to 4, a gas-bearing oilfield produced water treatment device based on vertical shallow flotation technology includes the following equipment units:

[0062] Pressure stabilizing buffer tank 2, dosing system 3, first-stage tubular dissolved air releaser 5, high-pressure vertical cyclone floatation device 8, second-stage tubular dissolved air releaser 9, waste oil tank 10, low-pressure vertical shallow flotation device 13 and sludge tank 15;

[0063] in:

[0064] The liquid phase inlet 21 of the pressure-stabilizing buffer tank 2 is connected to the water inlet pipeline; the liquid phase outlet 212 of the pressure-stabilizing buffer tank 2 is connected in sequence to the first-stage tubular dissolved air releaser 5 and the liquid inlet 85 of the high-pressure vertical cyclone flotation device 8 through the high-pressure treatment pipeline 4; the liquid outlet 87 of the high-pressure vertical cyclone flotation device 8 is connected in sequence to the second-stage tubular dissolved air releaser 9 and the liquid inlet 137 of the low-pressure vertical shallow air flotation device 13 through the low-pressure treatment pipeline 11; the liquid outlet 139 of the low-pressure vertical shallow air flotation device 13 is connected to the water outlet pipeline 14;

[0065] An injection port of the dosing system 3 is provided in the middle of the high-pressure treatment pipeline 4 between the pressure stabilizing buffer tank 2 and the first-level tubular dissolved air releaser 5;

[0066] The waste oil outlet 29 of the pressure stabilizing buffer tank 2, the oil outlet 82 of the high-pressure vertical cyclone flotation device 8, and the oil outlet 132 of the low-pressure vertical shallow air flotation device 13 are respectively connected to the oil inlet of the waste oil tank 10 through the waste oil transportation pipeline 7;

[0067] The slag discharge port 86 of the high-pressure vertical cyclone flotation device 8 and the slag discharge port 138 of the low-pressure vertical shallow air flotation device 13 are respectively connected to the inlet of the sludge tank 15 through the slag discharge pipeline 6;

[0068] The air outlet 88 of the high-pressure vertical cyclone floatation device 8 and the air outlet 1310 of the low-pressure vertical shallow air floatation device 13 are respectively connected to the gas transmission pipeline 12.

[0069] Furthermore, the pressure stabilizing buffer tank 2 adopts a horizontal or vertical gravity sedimentation tank. Taking the vertical gravity sedimentation tank as an example, as shown in Figure 2, the diameter of the vertical gravity sedimentation tank is D1, and the height H of the tank is 3D1 / 2; a vertical partition 25 is vertically set at the bottom of the tank, the thickness δ2 is 20mm, and the length L is 5D1 / 4; the distance between the vertical partition and the vertical axis of the tank is D1 / 6, dividing the middle and lower part of the tank into an inclined partition area and a transverse partition area; the upper part of the vertical partition is a grid structure to ensure that the produced water in the inclined partition area can flow to the transverse partition area; the microporous inclined partition 22, the small hole inclined partition 23, the large hole inclined partition 24 are arranged in the inclined partition area from bottom to top. 24; the aperture of the microporous inclined baffle 22 is d1 = 10mm, the aperture of the small-pore inclined baffle 23 is d2 = 30mm, and the aperture of the large-pore inclined baffle 24 is d3 = 60mm; the inclined baffles are arranged in parallel and at an angle of 60° to the horizontal, and the spacing between the inclined baffles is D1 / 6; the outflow small-pore transverse baffle 210 and the outflow large-pore transverse baffle 211 are arranged in sequence from top to bottom in the transverse baffle area; the aperture of the outflow small-pore transverse baffle 210 is d4 = 30mm, and the aperture of the outflow large-pore transverse baffle 211 is d5 = 30mm. The two transverse baffles are arranged in parallel and are spaced apart by D1 / 4. An oil separator 26 is horizontally arranged at the upper end of the vertical baffle 25, which intersects the vertical baffle 25 at right angles and is connected to the side wall of the tank. A gas phase inlet 27 and a gas phase outlet 28 are provided at the top of the vertical gravity sedimentation tank; a liquid phase inlet 21 is provided at the lower part of the tank side wall in the inclined partition area; a liquid phase outlet 212 is provided at the lower part of the tank side wall in the transverse partition area; a dirty oil outlet 29 is provided at the upper part of the tank side wall in the transverse partition area, and the top end of the dirty oil outlet 29 is tangentially connected to the bottom end of the oil separator 26.

[0070] Furthermore, the first-stage tubular dissolved air releaser 5 adopts a tubular multi-stage Venturi series structure, and the number of Venturi tube series stages is controlled at 2 to 5; the second-stage tubular dissolved air releaser 9 has the same structure as the first-stage tubular dissolved air releaser 5.

[0071] The high-pressure vertical cyclone flotation device 8 includes a main separation tank; as shown in Figure 3, the tank body has a diameter of D2, an oil overflow cover 81 is provided at the upper part of the main separation tank, and an oil collecting cylinder 83 is provided below the oil overflow cover 81; a uniformly distributed cyclone inlet 84 is provided below the oil collecting cylinder 83, which extends to the outside of the main separation tank and is connected to the high-pressure treatment pipeline 4; an oil outlet 82 is provided on the upper part of the side wall of the main separation tank, and the bottom of the oil outlet 82 is tangentially connected to the bottom surface of the oil overflow cover 81; an air outlet 88 is provided on the top of the main separation tank; a slag discharge port 86 is provided at the axis of the bottom of the main separation tank; and a liquid outlet 87 is provided at the bottom of the main separation tank at a distance D2 / 8 from the axis.

[0072] Furthermore, the low-pressure vertical shallow flotation device 13 includes a main separation tank; the tank body has a diameter of D3, and the main separation tank is provided with an oil overflow cover 131, an oil collecting inclined plate 133, and a hollow frustum 135 in sequence from top to bottom; the oil collecting inclined plate 133 is composed of a plurality of hollow frustum-shaped inclined plates stacked up and down, and the inclination angle of a single inclined plate is optimally set to an angle of 60°~65° with the horizontal, the diameter of the large end of the inclined plate is 0.7~0.9 times the inner diameter D3 of the low-pressure vertical shallow flotation device tank, the diameter of the small end of the inclined plate is 0.3~0.5 times the inner diameter D3 of the low-pressure vertical shallow flotation device tank, the vertical spacing of the inclined plates is controlled at 40mm~100mm, and the number of inclined plates is set at about 6~10 pieces. A uniformly distributed outlet 134 is provided at the upper part of the interior of the hollow frustum 135, and a flow equalizing plate 136 is provided at the lower part of the interior; a slag discharge port 138 is provided at the bottom center of the hollow frustum 135 and extends to the outside of the bottom of the main separation tank; an air outlet 1310 is provided at the top center of the main separation tank; an oil outlet 132 is provided at the upper part of the side wall of the main separation tank, and the bottom of the oil outlet 132 is connected to the ground section of the oil overflow cover 131; a liquid inlet 137 is provided at the lower part of the side wall of the main separation tank, which is horizontally connected to the uniformly distributed outlet 134; a liquid outlet 139 is provided at the bottom end of the main separation tank, and the distance between it and the vertical axis of the tank body is D3 / 8.

[0073] When using the treatment device provided by the present invention to treat produced water from a gas-bearing oil field, the following steps can be followed:

[0074] (1) The produced water from the gas-bearing oil field is stabilized by the pressure stabilizing buffer tank 2, the hydraulic retention time is controlled at more than 30 minutes, and the internal water pressure should be maintained between 0.50 and 0.6 MPa; the produced water after pressure stabilization flows into the high-pressure treatment pipeline 4 and is injected with reagents through the dosing system 3; the pressure of the produced water in the high-pressure treatment pipeline 4 is about 0.5 MPa; the reagents are PAC, PAM, water purifier and other reagents, which can be adjusted according to the requirements of the oil field site to meet the requirements of the subsequent treatment process;

[0075] (2) The produced water after the addition of the drug enters the first-stage tubular dissolved air releaser 5, where the dissolved gas in the produced water of the gas-bearing oil field is released under reduced pressure in the form of fine bubbles and fully mixed and dispersed with the drug, thereby obtaining produced water rich in fine bubbles; the water pressure of the outlet pipe section of the first-stage tubular dissolved air releaser is controlled at 0.30~0.35MPa, which is the water pressure of the water inlet of the high-pressure vertical cyclone flotation device;

[0076] (3) After the produced water rich in micro-bubbles flows into the high-pressure vertical cyclone flotation device 8, it generates a strong cyclonic flow through the uniformly distributed cyclone inlet 84. The micro-bubbles with lower density collide and adhere with oil droplets and solid suspended matter due to turbulence, forming "oil droplet-bubble adhesion bodies" and "solid suspended matter-bubble adhesion bodies". Under the action of the centrifugal force of the cyclone, they tend to move centripetally. At the same time, they rely on buoyancy to float upward through the oil collecting cylinder 83 to the vicinity of the upper liquid surface in the tank, and finally overflow from the oil overflow cover 81 and discharge into the waste oil tank 10 through the oil outlet 82; the gas phase released from the upper liquid surface in the tank is discharged into the gas pipeline 12 through the gas outlet 88; the solid impurities with larger mass settle to the bottom of the tank under the action of gravity and are discharged regularly from the slag discharge port 86;

[0077] The separated produced water flows out from the liquid outlet 87 of the high-pressure vertical cyclone flotation device 8 and enters the secondary tubular dissolved air releaser 9 through the low-pressure treatment pipeline 11;

[0078] (4) The produced water obtained in step (3) is treated by a two-stage tubular dissolved air releaser 9, where it is decompressed and released, generating a secondary micro bubble group. The water pressure is reduced to 0.10-0.15 MPa, which is the water pressure of the water inlet 137 of the low-pressure vertical shallow air flotation device 13.

[0079] (5) The produced water rich in fine bubble groups enters the low-pressure vertical shallow flotation device 13 and flows evenly under the action of the flow equalizer 136. During the flow, the fine bubble groups collide and adhere with the oil droplets and solid suspended matter to form "oil droplet-bubble adhesion bodies" and "solid suspended matter-bubble adhesion bodies". Under the action of shallow sedimentation, the oil droplet aggregation and separation process is enhanced, thus achieving secondary efficient treatment of the produced water.

[0080] The produced water obtained after treatment flows out from the liquid outlet 139; the treated enriched oil phase eventually overflows through the oil overflow cover 131 and is discharged to the waste oil transportation pipeline 7 through the oil outlet 132; the continuous gas phase released in the upper part of the tank is discharged into the gas pipeline 12 through the gas outlet 1310; the solid impurities with larger mass settle to the bottom of the tank under the action of gravity and are discharged regularly, finally completing the efficient separation of oil, gas, water and solid suspended matter.

[0081] In this embodiment, a high-pressure vertical cyclone flotation device 8 is combined with a low-pressure vertical shallow flotation device 13 to carry out flotation pretreatment of produced water from gas-bearing oil fields; cyclone flotation technology is used to efficiently remove oil droplets with larger particle sizes and remove a portion of the gas, and then a vertical shallow flotation device with an additional shallow settling inclined plate is used to further enhance the removal process of dispersed oil and part of the emulsified oil.

[0082] In this embodiment, the fine bubbles used in the flotation separation process of the high-pressure vertical cyclonic flotation device 8 and the low-pressure vertical shallow flotation device 13 are derived from the natural gas dissolved and released from the produced water of the gas-bearing oil field. Compared to using external sources such as nitrogen injection, the fine bubbles formed by natural gas are more likely to collide and adhere to oil droplets, resulting in higher flotation separation efficiency. This also significantly simplifies the process flow, reduces the system footprint, and achieves efficient resource utilization. Furthermore, the overall high-pressure, sealed operation reduces harmful gas emissions, eliminates secondary pollution, and ensures safety and stability at the production site.

[0083] Of course, the gas-bearing oilfield produced water treatment device based on vertical shallow flotation technology provided by the present invention is not limited to single-stage operation of the pressure-stabilizing buffer tank 2, the high-pressure vertical cyclone flotation device 8, the low-pressure vertical shallow flotation device 13, etc. According to actual needs, a two-stage or even multi-stage series operation mode can be adopted, but the liquid inlet, oil outlet, slag discharge port, gas outlet, etc. of each stage of the pressure-stabilizing buffer tank 2, the high-pressure vertical cyclone flotation device 8, and the low-pressure vertical shallow flotation device 13 need to be connected to the supporting processing pipeline or device.

[0084] Although the present invention has been described in detail above using general descriptions and specific embodiments, it will be apparent to those skilled in the art that modifications and improvements may be made based on the present invention. Therefore, such modifications and improvements, which do not depart from the spirit of the present invention, are intended to be within the scope of protection claimed herein.

[0085] This application claims priority to Chinese patent application No. 202310635482.7, entitled "A device and method for treating produced water from a gas-bearing oil field based on vertical shallow flotation," filed by applicants CNOOC (China) Limited and CNOOC (China) Limited Beijing Research Center on June 1, 2023. The entire contents of the application are incorporated herein by reference. Industrial Applicability

[0086] This application has the following beneficial technical effects:

[0087] The present invention makes full use of the dissolved gas resources rich in produced water from gas-bearing oil fields, and through coupling the synergistic dissolution and release of fine bubble generation technology, flotation technology, cyclone separation technology, shallow sedimentation technology, etc., effectively controls the release process of dissolved gas in produced water through a pressure step release method, provides a high-quality fine bubble source for the high-pressure vertical cyclone flotation device and the low-pressure vertical shallow flotation device, and realizes efficient oil removal, suspension removal and degassing of produced water from gas-bearing oil fields.

[0088] The entire treatment process has the advantages of high separation efficiency, simple process, compact structure and small footprint. It can effectively solve the problems or shortcomings of the current gas-bearing oil field produced water treatment process, such as high energy consumption and purification efficiency, and help promote the development goals of energy conservation, consumption reduction, quality improvement and efficiency enhancement in oil fields.

Claims

1. A treatment device for produced water from a gas-bearing oil field, characterized in that: It includes a pressure stabilizing buffer tank, a first-stage tubular dissolved air releaser, a high-pressure vertical cyclone flotation device, a second-stage tubular dissolved air releaser, and a low-pressure vertical shallow-layer flotation device connected in sequence; The liquid phase inlet of the pressure stabilizing buffer tank is connected to the water inlet pipeline; A dosing system is provided between the pressure stabilizing buffer tank and the first-stage tubular dissolved air releaser; The dirty oil outlet of the pressure-stabilizing buffer tank, the oil outlet of the high-pressure vertical cyclone flotation device, and the oil outlet of the low-pressure vertical shallow air flotation device are respectively connected to the dirty oil tank; The slag discharge port of the high-pressure vertical cyclone flotation device and the slag discharge port of the low-pressure vertical shallow air flotation device are respectively connected to the sludge tank; The air outlet of the high-pressure vertical cyclone flotation device and the air outlet of the low-pressure vertical shallow air flotation device are respectively connected to the gas pipeline; The liquid outlet of the high-pressure vertical cyclone flotation device and the liquid outlet of the low-pressure vertical shallow air flotation device are both connected to the water outlet pipeline.

2. The processing device according to claim 1, characterized in that: A vertical partition with a grid structure on the upper part is vertically arranged at the bottom of the pressure stabilizing buffer tank, dividing the middle and lower space in the tank into an oblique partition area and a horizontal partition area; In the inclined partition area, a microporous inclined partition, a small-pore inclined partition, and a large-pore inclined partition are arranged in parallel from bottom to top; The upper part of the diaphragm area is provided with a small-hole diaphragm for outflow, and the lower part is provided with a large-hole diaphragm for outflow; An oil separator is horizontally arranged at the upper end of the vertical separator, which intersects the vertical separator vertically and is connected to the side wall of the tank body; A gas phase inlet and a gas phase outlet are arranged on the top of the pressure stabilizing buffer tank; A liquid phase inlet is arranged at the lower part of the side wall of the inclined partition area; A liquid phase outlet is provided at the lower portion of the side wall of the diaphragm zone; A dirty oil outlet is arranged on the upper part of the side wall of the transverse partition area, and the top end of the dirty oil outlet is tangentially connected to the bottom end of the oil separator.

3. The processing device according to claim 2, characterized in that: The tank body diameter of the pressure stabilizing buffer tank is D1; The distance between the vertical partition and the vertical axis of the pressure stabilizing buffer tank is D1 / 6, and the plate length L is 5D1 / 4; The aperture d1 of the microporous inclined partition is 10 mm; the aperture d2 of the small-pore inclined partition is 30 mm; the aperture d3 of the large-pore inclined partition is 60 mm; the angle between a single inclined partition and the horizontal is 60°, and the spacing between the inclined partitions is D1 / 6; The aperture d4 of the outflow small hole baffle is 30 mm, and the aperture d5 of the outflow large hole baffle is 30 mm; the distance between the outflow small hole baffle and the outflow large hole baffle is D1 / 4.

4. The processing device according to claim 1, characterized in that: The first-stage tubular dissolved air releaser and the second-stage tubular dissolved air releaser both adopt a tubular multi-stage Venturi series structure; the number of series-connected Venturi tubes is controlled to be 2 to 5.

5. The processing device according to claim 1, characterized in that: The high-pressure vertical cyclone flotation device comprises a main separation tank, the diameter of which is D2; The main separation tank is provided with an oil overflow cover, an oil collecting cylinder, and a uniformly distributed swirl inlet from top to bottom; the uniformly distributed swirl inlet extends to the outside of the main separation tank and is connected to a water inlet pipeline; An oil outlet is arranged on the upper part of the side wall of the main separation tank, and the bottom of the pipe opening of the oil outlet is tangentially connected to the bottom surface of the oil overflow cover; The top of the main separation tank is provided with an air outlet; A slag discharge port is arranged at the bottom axis of the main separation tank; A liquid outlet is arranged at a position D2 / 8 from the axis line at the bottom of the main separation tank.

6. The processing device according to claim 1, characterized in that: The low-pressure vertical shallow air flotation device comprises a main separation tank, the diameter of which is D3; The main separation tank is provided with an oil overflow cover, an oil collecting inclined plate, and a hollow frustum from top to bottom in sequence; The oil collecting inclined plate is composed of a plurality of hollow frustum-shaped inclined plates stacked up and down, the inclination angle of a single inclined plate is optimally set at 60°~65° with respect to the horizontal angle, the diameter of the large end of the inclined plate is 0.7~0.9 times the inner diameter D3 of the tank body of the low-pressure vertical shallow air flotation device, the diameter of the small end of the inclined plate is 0.3~0.5 times the inner diameter D3 of the tank body of the low-pressure vertical shallow air flotation device, the vertical spacing of the inclined plates is controlled at 40mm~100mm, and the number of inclined plates is set at 6~10 pieces; A uniformly distributed outlet is arranged above the interior of the hollow frustum, and a flow balancing plate is arranged below; A slag discharge port is arranged at the bottom axis of the hollow frustum and extends to the outside of the bottom of the main separation tank; An air outlet is arranged at the top center of the main separation tank; An oil outlet is arranged on the upper part of the side wall of the main separation tank, and the bottom of the oil outlet is connected to the ground section of the oil overflow cover; A liquid inlet is provided at the lower part of the side wall of the main separation tank, and is horizontally connected to the uniformly distributed outlet; A liquid outlet is arranged at the bottom end of the main separation tank.

7. A method for treating produced water from a gas-bearing oil field using the treatment device according to any one of claims 1 to 6, characterized in that: The steps include: S1, the produced water from the gas-bearing oil field is subjected to pressure stabilization in the pressure stabilization buffer tank, and after the pressure stabilization treatment, a reagent is added thereto and the produced water enters the first-level tubular dissolved air releaser; S2, the dissolved gas in the produced water of the gas-bearing oil field is decompressed and released in the first-stage tubular dissolved gas releaser to form fine bubbles, and then the produced water rich in fine bubbles enters the high-pressure vertical cyclone flotation device and generates cyclonic flow through the uniformly distributed outlets; During the flow process, fine bubbles, oil droplets and solid suspensions form "oil droplet-bubble adhesion bodies" and "solid suspension-bubble adhesion bodies", which move centripetally under the action of the cyclonic centrifugal force and float upward and are discharged to the waste oil tank through the oil outlet; the gas phase is discharged into the gas pipeline through the gas outlet; the solid phase settles and is discharged from the slag outlet; the separated produced water enters the two-stage tubular dissolved gas releaser; S3, the produced water obtained by the treatment in step S2 is released under reduced pressure in the two-stage tubular dissolved air releaser to generate micro bubble groups for the second time, and the produced water rich in micro bubble groups enters the low-pressure vertical shallow air flotation device and flows evenly under the action of the flow equalizing plate; During the flow process, the fine bubble groups collide and adhere with the oil droplets and the solid suspension to form "oil droplet-bubble adhesion bodies" and "solid suspension-bubble adhesion bodies", and the oil droplets are aggregated, coalesced and separated under the action of shallow sedimentation; the treated enriched oil phase is discharged to the waste oil tank through the oil outlet, the gas phase is discharged to the gas pipeline through the gas outlet, and the solid phase settles and is discharged from the slag outlet; The treated produced water flows out from the liquid outlet and enters the water outlet pipeline.

8. The method according to claim 7, characterized in that: In step S1, the hydraulic retention time in the pressure stabilizing buffer tank is controlled to be more than 30 minutes, and the water pressure is 0.50-0.6 MPa; The agent is one of PAC, PAM and water purifier.

9. The method according to claim 7, characterized in that: In step S2, the water pressure of the outlet pipe section of the first-stage tubular dissolved air releaser is controlled between 0.30 and 0.35 MPa.

10. The method according to claim 7, characterized in that: In step S3, the water pressure of the outlet pipe section of the two-stage tubular dissolved air releaser is controlled between 0.10 and 0.15 MPa.

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