Oilfield produced water treatment system and method

Abstract

The present application relates to a kind of oilfield produced water treatment system and method, the system includes the gas floatation pond connected in turn, coagulation sedimentation device, oxidation pond, high concentration membrane device and forced evaporation device, gas floatation pond is equipped with two stages, the float oil water outlet of primary gas floatation pond is connected secondary gas floatation pond, clear liquid production water outlet is connected coagulation sedimentation device;Coagulation sedimentation device includes tubular membrane system and solid-liquid separation device, the liquid inlet of tubular membrane system is connected primary gas floatation pond, contains mud water outlet and connects solid-liquid separation device, and the permeate water production water outlet is connected oxidation pond;Oxidation pond is equipped with two stages, and the outlet of secondary oxidation pond is connected high concentration membrane device;High concentration membrane device includes tubular reverse osmosis membrane and tubular nanofiltration membrane, the inlet of tubular reverse osmosis membrane is connected secondary oxidation pond, and concentrated water outlet is connected tubular nanofiltration membrane, and the outlet of tubular nanofiltration membrane is connected forced evaporation device;The present application couples high-level oxidation and tubular membrane process, can effectively handle oilfield produced water, meet reuse.

Description

[TECHNICAL FIELD]

[0001] The present application relates to the technical field of oilfield produced water treatment, in particular to an oilfield produced water treatment system and method. [BACKGROUND]

[0002] Oilfield produced water is the formation water discharged in the process of oil exploitation, which has the characteristics of large water volume, high salt content, high hardness, high organic matter concentration and complex composition. It also contains surfactant compounds added in the process of oil exploitation. Direct discharge of this kind of wastewater will seriously pollute the environment and destroy the ecology. In addition, due to the influence of region and resource endowment, the composition of produced water in different regions often differs greatly, and even for the same oilfield, as the exploitation proceeds, the produced water volume and composition will change greatly. The above problems further increase the difficulty of treating this kind of wastewater. A single treatment method cannot effectively solve this problem, and the water produced by a single treatment technology is difficult to meet the requirements of discharge and reinjection, so multiple processes need to be coupled to achieve efficient desalination, efficient organic matter removal, and large operation flexibility to adapt to produced water in different regions and different periods.

[0003] Patent with publication number CN115403181A discloses an oilfield produced water treatment system to adjust the pool combined with decolorization, gel breaking and flocculation sedimentation tank for treatment. Patent with publication number CN114920385A discloses an oilfield produced water treatment process, including decolorization, gel breaking, flocculation sedimentation and filtration. Among them, multi-medium filtration or quartz sand filtration is adopted, and the water quality and treatment efficiency are difficult to control. In addition, patent with publication number CN113816457A discloses an integrated treatment process system for oilfield acidic produced water, which is treated by taking air flotation as the core, but the process is relatively simple and may have certain limitations in operation flexibility.

[0004] The "oil removal + biochemical + filtration" process and the "sedimentation oil removal + biochemical + filtration" process are common produced water treatment technologies, in which the filtration device adopts a roll-type reverse osmosis membrane element. However, due to the complexity of organic matter in the composition of produced water, the operation flexibility of biochemical treatment is small, the parameter adjustment is difficult, and the effluent often fails to meet the standards. In addition, the roll-type reverse osmosis membrane element has low water recovery rate, and due to the complexity of the composition of produced water, the membrane element is prone to membrane pollution and blockage, which needs to be cleaned frequently, seriously affecting the treatment efficiency. Therefore, a technology for efficiently treating organic matter in produced water is needed, which can adjust the treatment parameters in real time according to the changes in the water inflow, and can also filter the produced water without being prone to pollution and blockage, achieve efficient high-concentration, and produce water with high quality to meet the requirements of reuse. [SUMMARY]

[0005] The present application aims to solve the above problems and provide an oilfield produced water treatment system and method, which couples advanced oxidation and tubular membrane process, can effectively treat oilfield produced water and meet the reuse requirements.

[0006] To achieve the above-mentioned purposes, an oilfield produced water treatment system is designed, which comprises a gas floatation tank, a coagulation and sedimentation device, an oxidation tank, a high-concentration membrane device and a forced evaporation device connected in sequence, wherein,

[0007] The gas floatation tank comprises a primary gas floatation tank and a secondary gas floatation tank, the float oil water outlet of the primary gas floatation tank is connected to the inlet of the secondary gas floatation tank through a pipeline, a backflow port is arranged on the secondary gas floatation tank, the backflow port is connected to the primary gas floatation tank through a pipeline, and the clear liquid of the secondary gas floatation tank is backflowed to the primary gas floatation tank, and the clear liquid production water outlet of the primary gas floatation tank is connected to the coagulation and sedimentation device through a pipeline;

[0008] The coagulation and sedimentation device comprises a tubular membrane system and a solid-liquid separation device, the solid-liquid separation device is a filter press, the liquid inlet of the tubular membrane system is connected to the clear liquid production water outlet of the primary gas floatation tank through a pipeline, a coagulant inlet is arranged on the tubular membrane system, the muddy water outlet of the tubular membrane system is connected to the inlet of the solid-liquid separation device through a pipeline, a backflow port two is arranged on the solid-liquid separation device, and the clear liquid is backflowed to the tubular membrane system through the backflow port two, and the permeate water production water outlet of the tubular membrane system is connected to the oxidation tank through a pipeline;

[0009] The oxidation tank comprises a primary oxidation tank and a secondary oxidation tank, the permeate water production water outlet of the tubular membrane system is connected to the primary oxidation tank and the secondary oxidation tank through a pipeline respectively, the primary oxidation tank and the secondary oxidation tank are arranged in parallel, an oxidizing agent inlet is arranged on the primary oxidation tank, the outlet of the primary oxidation tank is connected to the inlet of the secondary oxidation tank through a pipeline, and the outlet of the secondary oxidation tank is connected to the high-concentration membrane device through a pipeline;

[0010] The high-concentration membrane device comprises a tubular reverse osmosis membrane and a tubular nanofiltration membrane, the inlet of the tubular reverse osmosis membrane is connected to the secondary oxidation tank through a pipeline, the concentrated water outlet of the tubular reverse osmosis membrane is connected to the inlet of the tubular nanofiltration membrane, the water production of the tubular nanofiltration membrane is backflowed to the tubular reverse osmosis membrane through a pipeline, a fresh water outlet is arranged on the tubular reverse osmosis membrane, and the outlet of the tubular nanofiltration membrane is connected to the forced evaporation device through a pipeline;

[0011] The forced evaporation device is a multi-effect evaporation or mechanical compression evaporation MVR.

[0012] Further, the forced evaporation device is provided with a fixed salt outlet and a fresh water outlet, solid salt product is obtained through the fixed salt outlet, fresh water is obtained through the fresh water outlet, and the fresh water is mixed with the fresh water production of the tubular reverse osmosis membrane as system production water.

[0013] Further, the upper part of the first and second oxidation tanks is provided with a gas collection device connected to the first air floatation tank, which is used to deliver the unreacted ozone to the bubble generator in the first air floatation tank, so as to use the unreacted ozone in the oxidation process as the added gas in the air floatation process.

[0014] Further, the second oxidation tank is provided with an adsorption resin between the second oxidation tank and the tube type reverse osmosis membrane, so that the produced water after the second oxidation tank is removed of boron, calcium and magnesium impurity ions by the adsorption resin before entering the tube type reverse osmosis membrane, thereby selectively connecting the adsorption resin to remove boron, calcium and magnesium impurity ions according to the concentration of boron, calcium and magnesium ions in the solution, so as to reduce the pollution of the subsequent membrane system.

[0015] Further, the second air floatation tank contains a coalescence resin with oil-water separation function, and the clear liquid after the second air floatation is pumped into the coalescence resin in the air floatation tank, the oil produced by the coalescence resin is discharged, and the clear liquid produced by the coalescence resin is returned to the first air floatation tank as the second air floatation clear liquid.

[0016] The application also provides an oilfield produced water treatment method, which comprises the following steps:

[0017] 1) inputting the oilfield produced water into the first air floatation tank, taking the water containing floating oil in the first air floatation tank as the feed of the second air floatation tank, and providing a reflux component to return the clear liquid of the second air floatation tank to the first air floatation tank, so as to take the first air floatation clear liquid as the produced water;

[0018] 2) adding a coagulant to the first air floatation clear liquid, and then concentrating the coagulant by a tube type membrane, so that the concentrated muddy water enters a filter press to obtain a solid filter cake, i.e., oil sludge, and the clear liquid is returned to the tube type membrane system for secondary treatment, and the permeated water of the tube type membrane is taken as the produced water to enter the next stage of treatment;

[0019] 3) dividing the permeated water of the tube type membrane into two parts to enter the first and second oxidation tanks, and using micro-nano ozone bubbles to oxidize in the two oxidation tanks in cooperation with an oxidizing agent, so as to remove organic matters by the two-stage parallel connection of the oxidizing agent, and to adjust the oxidation effect by combining the treatment of the divided raw water;

[0020] 4) taking the produced water of the second oxidation tank into a tube type reverse osmosis membrane, taking the concentrated water of the tube type reverse osmosis membrane into a tube type nanofiltration membrane, returning the produced water of the tube type nanofiltration membrane to the tube type reverse osmosis membrane, and taking the produced water of the tube type reverse osmosis membrane as the produced water of the system;

[0021] 5) connecting a forced evaporation device to the outlet of the tube type nanofiltration membrane, obtaining a solid salt as the product of the system, and mixing the obtained fresh water with the produced water of the tube type reverse osmosis membrane as the produced water of the system.

[0022] Further, the influent of the primary and secondary oxidation tanks is split, wherein 5-50% of the permeate of the tubular membrane system is split to the secondary oxidation tank, and the oxidation process is controlled by the split amount, the water after primary oxidation enters the secondary oxidation, and then the unoxidized tubular membrane permeate is split and added, so that the oxidant is effectively used, and the oxidation effect can be accurately adjusted by split adjustment.

[0023] Further, the oxidant added in the primary oxidation tank is a mixed solution of hydrogen peroxide and iron salt, wherein the mass content of hydrogen peroxide is controlled to be 0.1-5%, and the concentration of trivalent iron ions in the iron salt is 0.01-0.5%.

[0024] Further, the concentration of the concentrated water of the tubular membrane system is 1-30% before entering the solid-liquid separation device.

[0025] Further, the water containing floating oil in the primary flotation tank enters the secondary flotation tank, and the content of floating oil is controlled to be 0.01-5%.

[0026] Compared with the prior art, the present application has the following advantages:

[0027] (1) The present application is an oilfield produced water treatment system coupled with advanced oxidation and tubular reverse osmosis process, which combines multi-stage flotation and multi-stage split oxidation to treat produced water, is simple to operate, improves treatment efficiency, and introduces reflux in the membrane system part to realize high-efficiency concentration filtration;

[0028] (2) The present application uses ozone oxidation combined with oxidant for deep oxidation on the basis of flotation and coagulation sedimentation, has high efficiency in removing organic matter, has large operation flexibility, is less affected by water quality, and has negligible scale-up effect;

[0029] (3) The present application uses tubular reverse osmosis membrane module for concentration filtration after oxidation treatment, has high automation degree, high water recovery rate, and can reach more than 80%;

[0030] (4) The present application has high concentration multiple, and the concentrated water amount is greatly reduced, the membrane process is stable, the pollution resistance is good, and the cleaning frequency is low. The water produced by the process is stable, the water amount is easy to adjust, and the water quality is high, so that the water can be used for life and industry, and can also be injected into the oilfield;

[0031] In summary, the present application provides an oilfield produced water treatment system coupled with advanced oxidation and tubular membrane process, which can effectively treat oilfield produced water and meet the reuse requirements. [DETAILED DESCRIPTION]

[0032] Figure 1 is a brief process schematic diagram of the present application;

[0033] Figure 2 is a flow schematic diagram of the present application. [DETAILED DESCRIPTION]

[0034] As shown in the drawings, the present application provides an oilfield produced water treatment system, comprising a floatation tank, a coagulation and sedimentation device, an oxidation tank, a high concentration membrane device and a forced evaporation device connected in sequence, wherein,

[0035] The floatation tank comprises a primary floatation tank and a secondary floatation tank, the float oil water outlet of the primary floatation tank is connected to the inlet of the secondary floatation tank through a pipeline, a backflow port is arranged on the secondary floatation tank, the backflow port is connected to the primary floatation tank through a pipeline, and the clear liquid of the secondary floatation tank is backflowed to the primary floatation tank, and the clear liquid production water outlet of the primary floatation tank is connected to the coagulation and sedimentation device through a pipeline;

[0036] The coagulation and sedimentation device comprises a tubular membrane system and a solid-liquid separation device, the solid-liquid separation device is a filter press, the liquid inlet of the tubular membrane system is connected to the clear liquid production water outlet of the primary floatation tank through a pipeline, a coagulant inlet is arranged on the tubular membrane system, the muddy water outlet of the tubular membrane system is connected to the inlet of the solid-liquid separation device through a pipeline, a backflow port two is arranged on the solid-liquid separation device, and the clear liquid is backflowed to the tubular membrane system through the backflow port two, and the permeate water production water outlet of the tubular membrane system is connected to the oxidation tank through a pipeline;

[0037] The oxidation tank comprises a primary oxidation tank and a secondary oxidation tank, the permeate water production water outlet of the tubular membrane system is connected to the primary oxidation tank and the secondary oxidation tank through a pipeline respectively, the primary oxidation tank and the secondary oxidation tank are arranged in parallel, the primary oxidation tank is provided with an oxidizing agent inlet, the outlet of the primary oxidation tank is connected to the inlet of the secondary oxidation tank through a pipeline, and the outlet of the secondary oxidation tank is connected to the high concentration membrane device through a pipeline;

[0038] The high concentration membrane device comprises a tubular reverse osmosis membrane and a tubular nanofiltration membrane, the inlet of the tubular reverse osmosis membrane is connected to the secondary oxidation tank through a pipeline, the concentrated water outlet of the tubular reverse osmosis membrane is connected to the inlet of the tubular nanofiltration membrane, the water production of the tubular nanofiltration membrane is backflowed to the tubular reverse osmosis membrane through a pipeline, the tubular reverse osmosis membrane is provided with a fresh water outlet, and the outlet of the tubular nanofiltration membrane is connected to the forced evaporation device through a pipeline;

[0039] The forced evaporation device is a multiple-effect evaporation or mechanical compression evaporation MVR.

[0040] The forced evaporation device is provided with a fixed salt outlet and a fresh water outlet, and solid salt product is obtained through the fixed salt outlet, the solid salt product is a system product, and fresh water is obtained through the fresh water outlet, which is mixed with fresh water produced by the tube type reverse osmosis membrane to serve as system water.

[0041] The gas collecting device is connected with the primary air flotation tank, and is used to deliver the unreacted ozone to the bubble generating device in the primary air flotation tank, so that the unreacted ozone in the oxidation process is used as the added gas in the air flotation process, the ozone is fully utilized, and the oxidation treatment is performed in the air flotation part.

[0042] The application further provides an oilfield produced water treatment method, which comprises the following steps.

[0043] 1) The oilfield produced water is input into the primary air flotation tank, the secondary air flotation tank takes the water containing floating oil in the primary air flotation tank as feed, and is provided with a reflux component, the clear liquid in the secondary air flotation tank is refluxed to the primary air flotation tank, and the primary air flotation clear liquid is used as water production;

[0044] 2) After the primary air flotation clear liquid water production is added with a coagulant and then concentrated by the tubular membrane, the concentrated muddy water is input into a filter press, solid filter cake, i.e., oil sludge, is obtained, and the clear liquid is refluxed to the tubular membrane system for secondary treatment, the part takes the permeate water of the tubular membrane as water production and enters the next stage of treatment;

[0045] 3) The permeate water of the tubular membrane is divided into two parts and input into the primary oxidation tank and the secondary oxidation tank, the two-stage oxidation tank is oxidized by micro-nano ozone bubbles and cooperates with an oxidizing agent, the oxidizing agent is used to remove organic matters through parallel connection of the two stages, and the oxidation effect is regulated and controlled in combination with the split flow of the raw water;

[0046] 4) The water production of the secondary oxidation tank is input into the tube type reverse osmosis membrane, the concentrated water of the tube type reverse osmosis membrane is input into the tube type nanofiltration membrane, the water production of the tube type nanofiltration membrane is refluxed to the tube type reverse osmosis membrane, and the fresh water production of the tube type reverse osmosis membrane is used as system water production;

[0047] 5) The outlet of the tubular nanofiltration membrane is connected to a forced evaporation device, and solid salt is obtained as the product of the system, and the fresh water obtained is mixed with the water produced by the tubular reverse osmosis membrane to obtain the product water of the system.

[0048] The water inlet of the primary oxidation tank and the secondary oxidation tank is split, 5%-50% of the water produced by the tubular membrane system is split to the secondary oxidation tank, and the split flow is used to adjust and control the oxidation process, the water after the primary oxidation enters the secondary oxidation, and then the water produced by the tubular membrane is split and added to perform the oxidation, the oxidant is effectively used, and the oxidation effect can be accurately adjusted by the split flow.

[0049] The oxidant added to the primary oxidation tank is a mixed solution of hydrogen peroxide and iron salt, the mass content of the hydrogen peroxide is controlled to be 0.1%-5%, and the concentration of the ferric ion in the iron salt is 0.01%-0.5%. The concentration water of the tubular membrane system has a mud content of 1%-30% before entering the solid-liquid separation device. The water containing floating oil in the primary flotation tank enters the secondary flotation tank, and the content of the floating oil is controlled to be 0.01%-5%.

[0050] The application will be further described below in combination with the drawings and specific embodiments:

[0051] As shown in the drawings Figure 1 and the drawings Figure 2 The oilfield produced water system includes a flotation tank, a coagulation and sedimentation device, an oxidation tank, a high-concentration membrane device, and a forced evaporation device connected in sequence.

[0052] The flotation tank is a two-stage flotation tank, the secondary flotation tank takes the water containing floating oil in the primary flotation tank as the feed, and is provided with a reflux component to reflux the clear liquid of the stage to the primary flotation tank, and the clear liquid of the primary flotation tank is taken as the product water. The water containing floating oil in the primary flotation tank enters the secondary flotation tank, and the content of the oil is controlled to be 0.01%-5%. The secondary flotation tank contains a coalescence resin having an oil-water separation function, the clear liquid after the secondary flotation is pumped into the coalescence resin part in the flotation tank, the oil produced by the coalescence resin is discharged, and the clear liquid produced by the coalescence resin is taken as the clear liquid of the secondary flotation.

[0053] The clear liquid of the secondary flotation enters the coagulation and sedimentation device, the device contains a tubular membrane part and a solid-liquid separation part, the solid-liquid separation device is a filter press, the clear liquid of the primary flotation is added with a coagulant, then is concentrated by the tubular membrane, and then enters the filter press, the concentration water has a solid content of 1%-30% before entering the solid-liquid separation device. The solid filter cake obtained after the filter press is the oil sludge, and the clear liquid is refluxed to the tubular membrane system for secondary treatment. The permeate water of the tubular membrane is taken as the product water and enters the oxidation tank.

[0054] The oxidation tank is a two-stage oxidation tank. The oxidation tank is oxidized by micro-nano ozone bubbles and cooperates with oxidizing agents. Through two-stage parallel connection, the oxidizing agents are fully utilized to remove organic matter. At the same time, the oxidation effect is adjusted and controlled by the diversion of the raw water. The gas collecting device is arranged above the two-stage oxidation tank, and is connected with the first air flotation tank. The unreacted ozone is transported to the bubble generating device in the air flotation tank. The purpose is to use the unreacted ozone in the oxidation process as the added gas in the air flotation process. Not only the ozone is fully utilized, but also the oxidation treatment is carried out in the air flotation part. In addition, the water inlet of the multi-stage oxidation tank is diverted. The water production of the tubular membrane system is diverted to the second-stage oxidation tank by 5% to 50%. The oxidation process is adjusted and controlled by the diversion amount. The water after the first-stage oxidation enters the second-stage oxidation, and then the unoxidized tubular membrane water is added. The oxidation effect is accurately adjusted by the diversion adjustment.

[0055] The oxidizing agent added in the first-stage oxidation tank is a mixed solution of hydrogen peroxide and iron salt. The mass content of hydrogen peroxide is controlled to be 0.1% to 5%, and the concentration of trivalent iron ions in the iron salt is 0.01% to 0.5%.

[0056] The produced water after oxidation is treated by a high-concentration membrane device. The high-concentration membrane device includes a tubular reverse osmosis membrane and a tubular nanofiltration membrane part. The concentrated water of the tubular reverse osmosis membrane enters the tubular nanofiltration membrane group. The water produced by the tubular nanofiltration membrane is returned to the tubular reverse osmosis membrane. The water produced by the tubular reverse osmosis membrane is the water produced by the part.

[0057] Before entering the high-concentration membrane device, according to the concentration of boron, calcium and magnesium ions in the solution, the adsorption resin can be selectively connected to remove boron, calcium and magnesium impurity ions. The purpose is to reduce the pollution of the subsequent membrane system.

[0058] The concentrated solution of the tubular nanofiltration membrane part enters a forced evaporation device. The device is a multiple-effect evaporation or mechanical compression evaporation (MVR). The solid salt is obtained as the product of the system. The fresh water is mixed with the water produced by the tubular reverse osmosis membrane in the membrane device to be the water produced by the system.

[0059] The treatment effect of the device system is as follows: (1)

[0061] (2)

[0063] (3)

[0065]

[0066] In conclusion, the application discloses an oilfield produced water treatment system, which comprises a gas floatation tank, a coagulation and precipitation device, an oxidation tank, a high-concentration membrane device and a forced evaporation device connected in sequence.

[0067] The contents not described in detail in the specification belong to the prior art known by the person skilled in the art, the standard parts used can be purchased from the market, the special-shaped parts can be ordered according to the description and the drawings, the specific connection mode of each part adopts the conventional means such as bolt, rivet and welding in the prior art, the mechanical parts and equipment adopt the conventional types in the prior art, the circuit connection adopts the conventional connection mode in the prior art, and the details are not described herein.

[0068] The application is not limited by the above-mentioned embodiments, and any change, modification, replacement, combination and simplification made without departing from the spirit and principle of the application shall be equivalent replacement, and all shall be included in the protection scope of the application.

Claims

1. An oilfield produced water treatment system, characterized in that: It includes a flotation tank, a coagulation sedimentation unit, an oxidation tank, a high-concentration membrane unit, and a forced evaporation unit connected in sequence. The flotation tank includes a primary flotation tank and a secondary flotation tank. The oil-water outlet of the primary flotation tank is connected to the inlet of the secondary flotation tank through a pipeline. The secondary flotation tank is equipped with a return port, which is connected to the primary flotation tank through a pipeline and returns the clarified liquid from the secondary flotation tank to the primary flotation tank. The clarified liquid production outlet of the primary flotation tank is connected to a coagulation sedimentation device through a pipeline. The coagulation and sedimentation device includes a tubular membrane system and a solid-liquid separation device, wherein the solid-liquid separation device is a filter press. The inlet of the tubular membrane system is connected to the clear liquid product outlet of the primary flotation tank through a pipeline. The tubular membrane system is provided with a coagulant inlet. The muddy water outlet of the tubular membrane system is connected to the inlet of the solid-liquid separation device through a pipeline. The solid-liquid separation device is provided with a second reflux port, through which the clear liquid is returned to the tubular membrane system. The permeate product outlet of the tubular membrane system is connected to the oxidation tank through a pipeline. The oxidation tank includes a primary oxidation tank and a secondary oxidation tank. The permeate product outlet of the tubular membrane system is connected to the primary oxidation tank and the secondary oxidation tank respectively through pipes. The primary oxidation tank and the secondary oxidation tank are arranged in parallel. The primary oxidation tank is provided with an oxidant inlet. The outlet of the primary oxidation tank is connected to the inlet of the secondary oxidation tank through a pipe. The outlet of the secondary oxidation tank is connected to a high-concentration membrane device through a pipe. The high-concentration membrane device includes a disc-tube reverse osmosis membrane and a disc-tube nanofiltration membrane. The inlet of the disc-tube reverse osmosis membrane is connected to a secondary oxidation tank through a pipeline. The concentrate outlet of the disc-tube reverse osmosis membrane is connected to the inlet of the disc-tube nanofiltration membrane. The permeate from the disc-tube nanofiltration membrane is returned to the disc-tube reverse osmosis membrane through a pipeline. The disc-tube reverse osmosis membrane is provided with a freshwater outlet. The outlet of the disc-tube nanofiltration membrane is connected to a forced evaporation device through a pipeline. The forced evaporation device is a multi-effect evaporator or a mechanical compression evaporator (MVR). A gas collection device is provided above the primary oxidation tank and the secondary oxidation tank. The gas collection device is connected to the primary flotation tank and is used to transport unreacted ozone to the bubble generator in the primary flotation tank. An adsorption resin is installed between the secondary oxidation tank and the disc tube reverse osmosis membrane. Before entering the disc tube reverse osmosis membrane, the permeate from the secondary oxidation tank is first removed by the adsorption resin to remove boron, calcium, and magnesium impurity ions.

2. The oilfield produced water treatment system as described in claim 1, characterized in that: The forced evaporation device is equipped with a fixed salt outlet and a fresh water outlet. Solid salt products are obtained through the fixed salt outlet, and fresh water is obtained through the fresh water outlet. This fresh water is mixed with the fresh water produced by the disc tube reverse osmosis membrane as the system product water.

3. A method for treating produced water in an oilfield produced water treatment system as described in claim 1 or 2, characterized in that, Includes the following steps: 1) The produced water from the oilfield is fed into the primary flotation tank. The secondary flotation tank uses the oil-containing water from the primary flotation tank as feed and is equipped with a reflux device to return the clarified liquid from the secondary flotation tank to the primary flotation tank, and the clarified liquid from the primary flotation tank is used as the product water. 2) After adding coagulant to the primary air flotation clarified water, it is concentrated by tubular membrane. The concentrated muddy water enters the filter press to obtain solid filter cake, i.e. oil sludge. The clarified water is returned to the tubular membrane system for secondary treatment. The permeate from the tubular membrane is used as the permeate to enter the next stage of treatment. 3) The permeate from the tubular membrane is diverted into the primary oxidation tank and the secondary oxidation tank. The two oxidation tanks use micro-nano ozone bubbles for oxidation, in conjunction with an oxidant. The two parallel stages remove organic matter using the oxidant, while the oxidation effect is controlled by the diversion of the raw water. 4) The permeate from the secondary oxidation tank enters the disc tube reverse osmosis membrane, the concentrate from the disc tube reverse osmosis membrane enters the disc tube nanofiltration membrane, the permeate from the disc tube nanofiltration membrane is returned to the disc tube reverse osmosis membrane, and the freshwater permeate from the disc tube reverse osmosis membrane is the system's permeate. 5) The outlet of the disc tube nanofiltration membrane is connected to a forced evaporation device, and solid salt is obtained as the system product. The obtained fresh water is mixed with the permeate from the disc tube reverse osmosis membrane to form the system's permeate.

4. The oilfield produced water treatment method as described in claim 3, characterized in that: The influent to the primary oxidation tank and the secondary oxidation tank are diverted, with 5%-50% of the permeate from the tubular membrane system being diverted to the secondary oxidation tank.

5. The oilfield produced water treatment method as described in claim 3, characterized in that: The oxidant added to the primary oxidation tank is a mixed solution of hydrogen peroxide and iron salt, wherein the mass content of hydrogen peroxide is controlled at 0.1%-5%, and the concentration of ferric ions in the iron salt is in the range of 0.01%-0.5%.

6. The oilfield produced water treatment method as described in claim 3, characterized in that: The concentrated water from the tubular membrane system has a mud content of 1%-30% before entering the solid-liquid separation device.

7. The oilfield produced water treatment method as described in claim 3, characterized in that: The oil content in the water entering the secondary air flotation tank from the primary air flotation tank is controlled between 0.01% and 5%.

Images