Method for treating oilfield produced water

Abstract

The application provides a treatment method for oilfield produced water reinjection, which adopts a gravity settling device, an electric field oil removal device and a filtering device, and comprises the following steps: gravity settling, conveying produced water raw water to the gravity settling device to preliminarily separate oil, water and mud; electric field oil removal, conveying sewage after gravity settling to the electric field oil removal device to remove emulsified oil and suspended matter; and filtering, conveying water after electric field oil removal to the filtering device to further remove emulsified oil and suspended matter so that the water reaches the reinjection requirement. The treatment method realizes rapid, efficient and low-cost treatment of the oilfield produced water, and especially can improve the removal efficiency of emulsified oil.

Description

Technical Field

[0001] This invention relates to the field of oilfield water treatment machinery, and in particular to a method for treating produced water in oilfields. Background Technology

[0002] Currently, most oilfields in my country have entered the mid-to-late stages of development, with crude oil water content reaching 70%-95%. Treating produced water for use as formation reinjection water is the primary treatment method. Produced water, under high temperature and pressure conditions in the formation, dissolves and carries large amounts of petroleum-related substances, inorganic salts, bacteria, and solid particles, resulting in complex water quality and significant treatment challenges. According to my country's current formation reinjection standards, the main treatment targets for most oilfield produced water are petroleum-related substances and suspended solids. Typically, the oil content in produced water is 1000-5000 mg / L, of which approximately 90% is suspended oil (>100μm) and dispersed oil (10-100μm), about 10% is emulsified oil (0.1-10μm), and a small amount of dissolved oil (≤1%). Suspended solids consist of various solid particles, such as clay, paraffin wax, bacterial flocs, silt, and non-dissolved organic matter.

[0003] In engineering applications, the commonly used produced water treatment process is the "old three-stage" process of "gravity sedimentation + air flotation + coagulation + filtration". Depending on the characteristics of the produced water in each oilfield, the number of sedimentation and air flotation stages can be appropriately increased to ensure the quality of the injected water. For low-permeability formations, fine filtration and membrane filtration processes are also added. Traditional produced water reinjection treatment processes can operate stably and achieve compliant treatment of produced water, but they require the addition of large amounts of chemicals, leading to secondary pollution and the treatment and disposal of chemical sludge, resulting in high operating costs. Especially for emulsified oil in produced water, current methods mainly rely on the addition of demulsifiers and flocculants, lacking efficient and low-cost treatment processes.

[0004] Chinese patent CN107417019A, "A Process for Treating Oilfield Produced Water," discloses a treatment process for reinjecting compliant produced water from oilfields. The process flow is as follows: regulating tank → aerated settling tank → oil-water separator → micro-flocculation tank → high-efficiency filter → ultraviolet disinfection. In this method, after the raw water passes through the regulating tank, demulsifiers and coagulants are added. Initial separation of oil, water, and sludge is achieved in the aerated settling tank. Subsequently, an oil-water separator, micro-flocculation tank, and high-efficiency filter are used to further remove emulsified oil and suspended solids from the water. This process improves upon conventional settling tanks by replacing them with aerated settling tanks, shortening the treatment process and improving the separation efficiency of oil, water, and sludge in the settling tank. It also reduces the amount of chemicals required to remove some of the emulsified oil. However, the removal of emulsified oil mainly relies on the addition of demulsifiers and filtration. Therefore, it suffers from problems such as high sludge production and high load on the filtration device.

[0005] Chinese patent CN102153221B discloses an oilfield produced water treatment process. This process employs a combination of air flotation, a dynamic reactor, and ultrasonic filtration to treat oilfield produced water, with nitrogen as the gas source for both the air flotation and the dynamic reactor. The core of this process is the high-efficiency dissolved nitrogen air flotation and nitrogen-powered reactor, which can efficiently remove oil and suspended solids while avoiding corrosion problems caused by dissolved oxygen. However, using nitrogen as the gas source places high demands on the airtightness and operation and maintenance of the equipment, and also requires the addition of nitrogen generation and nitrogen circulation devices, increasing the initial investment cost. Furthermore, for emulsified oil, air flotation still needs to be combined with reagents to achieve a good oil removal effect.

[0006] Chinese patent CN104016452B discloses a process for producing water in oilfields, particularly suitable for treating produced water containing polymers. The process flow is as follows: produced water and a reverse demulsifier are introduced into a demulsifier loaded with a high-voltage pulsed electric field. The demulsified produced water is fed into the upper part of an air flotation separator, while charged bubbles prepared by surfactants are fed into the lower part. Air bubbles are fed into the lower part of the air flotation separator. The charged bubbles adsorb emulsified oil droplets and work synergistically with the air flotation to achieve oil-water separation. This process can effectively demulsify and has a high oil-water separation efficiency. However, for produced water, the high-voltage pulsed electric field poses safety hazards. Produced water typically has a high content of inorganic ions, which significantly reduces its dielectric constant, making it prone to breakdown and short circuits. Furthermore, high voltage can cause electrode corrosion due to electrochemical reactions, increasing maintenance workload. Additionally, this process still requires the addition of a reverse demulsifier and surfactants, which can easily lead to secondary pollution. Summary of the Invention

[0007] In view of some or all of the above-mentioned technical problems existing in the prior art, the present invention proposes a method for treating oilfield produced water reinjection, which realizes rapid, efficient and low-cost treatment of oilfield produced water, and in particular can improve the removal efficiency of emulsified oil.

[0008] To achieve the above-mentioned objectives, this invention proposes a method for treating produced water reinjection from oilfields. This method employs a gravity settling device, an electric field oil removal device, and a filtration device, and includes the following steps: Gravity settling involves transporting the extracted raw water to a gravity settling device for preliminary separation of oil, water, and mud. Electric field oil removal involves transporting wastewater, after gravity settling, to an electric field oil removal device for the removal of emulsified oil and suspended solids; and The filtration process involves sending the water after oil removal by the electric field to a filtration device for further removal of emulsified oil and suspended solids, ensuring that the effluent meets the requirements for reinjection.

[0009] In this invention, the removal of emulsified oil and suspended solids is achieved through the above three physical process steps, effectively meeting the standards for oilfield produced water reinjection. Since no chemical reagents are required, secondary pollution and the treatment of chemical sludge are reduced, enabling rapid, efficient, and low-cost treatment of oilfield produced water. Furthermore, the use of different physical methods in these three steps to remove emulsified oil improves the removal efficiency and achieves better removal results.

[0010] In one embodiment, the electric field oil removal device has a water inlet at one end and a water outlet and an oil outlet at the other end, and a sludge discharge outlet at the bottom. The electric field oil removal device has electrode plates arranged in rows along the length from the water inlet to the water outlet, and the space between adjacent electrode plates is filled with agglomerated material.

[0011] In one embodiment, the electrode plate is made of carbon-based or silicon-based material, including but not limited to graphite, ceramics, and materials modified thereon, and the electrode plate operates at a pressure of 1V to 30V.

[0012] In one embodiment, the electrode plate and the coalescing material are connected by an electrode support plate and a filler support plate, both of which are porous plates; the distance between the bottom of the electrode plate and the bottom of the electric field oil removal device is 1 / 6 to 1 / 4 of the maximum working area height of the electric field oil removal device.

[0013] In one embodiment, the water inlet is located at 1 / 5 to 1 / 4 of the distance from the bottom of the electric field oil removal device. Multiple water inlets are provided corresponding to the gaps between the electrode plates. One or two oil outlets are provided. The lateral distance between the electrode plate and the oil outlet is at least 20 cm. The distance between the top of the electrode plate and the oil outlet is 1 / 5 to 1 / 3 of the maximum working height of the electric field oil removal device. An oil-separating weir is provided on the oil outlet.

[0014] In one embodiment, the water outlet is located below the oil outlet and above the water inlet, and a baffle plate is provided in front of the water outlet.

[0015] In one embodiment, the filling coalescing material includes, but is not limited to, one or more of zeolite, PP plastic balls, and Raschig rings. Preferably, the filling coalescing material is designed in a porous shape.

[0016] In one embodiment, the gravity settling operation time is 0.5h to 10h, and the electric field oil removal operation time is 15min to 45min; the filtration device adopts a single-stage or two-stage filter, and the filler material selected in the filter includes, but is not limited to, one or a combination of walnut shells, quartz sand, anthracite, and porous ceramics.

[0017] In one embodiment, the filtration device further includes a backwash mechanism that periodically cleans the filtration device and the generated backwash water is returned to the inlet of the gravity settling device.

[0018] In one implementation scheme, the effluent after gravity settling contains no more than 100 mg / L of oil and suspended solids; after electric field oil removal, the effluent contains no more than 20 mg / L of oil and suspended solids; and after filtration, the effluent contains less than 5 mg / L of oil and less than 1 mg / L of suspended solids.

[0019] Compared with the prior art, the advantages of the present invention are as follows: 1) No chemical agents such as demulsifiers and flocculants are added, which effectively reduces the production of chemical sludge and avoids secondary pollution problems, thus significantly reducing operating costs.

[0020] 2) The processing flow is simple and the dwell time is short, which can effectively reduce the initial investment cost.

[0021] 3) The equipment is simple and easy to maintain. In particular, the electric field oil removal device does not have the problem of electrode wear and operates stably. After filtration, the oil content is less than 5 mg / L and the suspended solids content is less than 1 mg / L, which meets the oilfield's limit standards for oil content and suspended solids in reinjection water. Moreover, the quality of the effluent is better than the reinjection limit standards. Attached Figure Description

[0022] The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, in which: Figure 1 The diagram shows one embodiment of the process flow of the oilfield produced water reinjection treatment method of the present invention.

[0023] Figure 2 As shown Figure 1 A front view of one embodiment of the electric field oil removal device.

[0024] Figure 3 As shown Figure 2 A top view of the electric field oil removal device.

[0025] In the accompanying drawings, the same parts use the same reference numerals. The drawings are not drawn to scale. Detailed Implementation

[0026] To make the technical solutions and advantages of the present invention clearer, exemplary embodiments of the present invention will be described in further detail below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not an exhaustive list of all embodiments. Furthermore, without conflict, the embodiments and features in the embodiments of the present invention can be combined with each other.

[0027] During the invention process, the inventors noticed that in order to meet the reinjection requirements, existing oilfield produced water requires the addition of a large amount of chemicals during the produced water treatment process, which leads to secondary pollution and problems such as the treatment and disposal of chemical sludge, resulting in high operating costs.

[0028] To address the above shortcomings, embodiments of the present invention propose a method for treating oilfield produced water reinjection, which will be described in detail below.

[0029] Figure 1 This paper illustrates one embodiment of the process flow of the oilfield produced water reinjection treatment method of the present invention. In this embodiment, the oilfield produced water reinjection treatment method of the present invention employs a gravity settling device, an electric field oil removal device, and a filtration device, and mainly includes the following steps: gravity settling, in which the produced water is transported to the gravity settling device for preliminary separation of oil, water, and mud; electric field oil removal, in which the wastewater after gravity settling is transported to the electric field oil removal device for removal of emulsified oil and suspended solids; and filtration, in which the effluent after electric field oil removal is transported to the filtration device for further removal of emulsified oil and suspended solids, in preparation for reinjection treatment.

[0030] exist Figure 1 In this process, the treatment of produced water in oilfields to meet the standards for produced water reinjection is mainly achieved through three processes: gravity settling by a gravity settling device, removal of emulsified oil and suspended solids by an electric field oil removal device, and filtration by a filtration device. All three processes are implemented by physical means and do not involve the addition of chemicals. Therefore, there are no issues such as secondary pollution or chemical sludge treatment. Moreover, the treatment steps are relatively few, the operating cost is low, the operating efficiency is high, and it is easier to maintain.

[0031] In one embodiment, such as Figure 1 The process flow of the oilfield produced water reinjection treatment method shown is as follows: The raw produced water undergoes gravity settling in a gravity settling device to remove suspended oil, dispersed oil, a small amount of emulsified oil, and suspended solids. The settled sludge is discharged through a sludge pipeline, and the suspended oil is discharged through an oil collection pipeline located above the gravity settling device. The wastewater after gravity settling is then transported to an electric field oil removal device. An external electric field is applied through electrodes, causing the surface-charged emulsified oil droplets to accelerate under the influence of the electric field, thereby increasing the collision frequency and aggregation rate of the droplets. The emulsified oil is discharged from the outlet of the electric field oil removal device, achieving the removal of emulsified oil. Similarly, suspended solids particles, which are also usually charged, aggregate into larger particles under the influence of the electric field and settle, being discharged through the sludge pipeline below. The output water after electric field oil removal is transported to a filtration device for further removal of emulsified oil and suspended solids. After the treated output water meets the reinjection standards, it is transported to the reinjection system for reinjection.

[0032] In one embodiment, such as Figure 2 and Figure 3 As shown, one end of the electric field oil removal device ( Figure 2 The left side (middle) has an inlet 1, and the other end ( Figure 2 The middle section (right side) is equipped with a water outlet 11 and an oil outlet 10. A sludge discharge port 12 is located at the bottom. The electric field oil removal device has an outlet 11 and an oil outlet 10 along its length from the water inlet 1 to the water outlet 11. Figure 3 Multiple rows of electrode plates 3 are arranged (from left to right), and the spaces between adjacent electrode plates 3 are filled with agglomerating material 5. In a preferred embodiment, an inlet is respectively provided on the side wall of the water inlet of the electric field oil removal device between two electrode plates 3. Therefore, the electric field oil removal device has multiple water inlets 1 corresponding to the gaps between the electrode plates 3 and located on the side wall of the water inlet.

[0033] In one embodiment, such as Figure 2 and Figure 3 As shown, electrode plate 3 is made of carbon-based or silicon-based materials. Carbon-based or silicon-based materials include, but are not limited to, graphite, ceramics, and materials modified from these. During operation, the working pressure of electrode plate 3 is 1V-30V. Figure 3 As shown, during operation, one end of electrode plate 3 is connected to the positive terminal of DC power supply 7, while the farthest end of the adjacent electrode plate 3 is connected to the negative terminal of DC power supply 7. The electrode plate terminals are sealed for waterproofing. This increases the probability of collisions between emulsified oil droplets and suspended particles flowing from the inlet to the outlet.

[0034] In one embodiment, such as Figure 2 and Figure 3 As shown, electrode plate 3 and coalescing material 5 are also connected to electrode support plate 4 and packing support plate 6, respectively. Both electrode support plate 4 and packing support plate 6 are porous plates, thus not affecting the overall flow of emulsified oil, sludge, and treated produced water. In one embodiment, as... Figure 2 As shown, the distance between the bottom of electrode plate 3 and the bottom of the electric field oil removal device is 1 / 6 to 1 / 4 of the maximum working zone height of the device. The maximum working zone height refers to the height of the uppermost oil layer when the electric field oil removal device is functioning normally and filled with produced water to be treated. Generally, the outside of the electric field oil removal device will have an indicator or marking for the maximum working zone height.

[0035] In one embodiment, such as Figure 2 As shown, the water inlet 1 is located at 1 / 5 to 1 / 4 of the distance from the bottom of the electric field oil removal device. One or two oil outlets 10 are provided. The tail of the electrode plate 3 ( Figure 2The distance from the rightmost point (middle) to the oil outlet 10 is at least 20 cm. The distance between the top of the electrode plate 3 and the location of the oil outlet 10 is 1 / 5 to 1 / 3 of the maximum working height of the electric field oil removal device. An oil-separating weir 9 is provided on the oil outlet 10. The oil-separating weir 9 is constructed in a sloping shape to prevent water from entering the oil outlet 10. The oil phase enters the oil outlet 10 through the oil-separating weir 9 by overflowing.

[0036] In one embodiment, such as Figure 2 As shown, the water outlet 11 is located below the oil outlet 10 and above the water inlet 1. A baffle plate 8 is provided in front of the water outlet 11. Under the action of the electric field, the emulsified oil demulsifies and coalesces, and is separated by gravity. The oil phase moves upward and overflows through the oil outlet 10, while the output water after being de-oiled by the electric field flows downward through the baffle plate 8 to the water outlet 11.

[0037] In one embodiment, such as Figure 2 and Figure 3 As shown, the filling coalescing material 5 includes, but is not limited to, one or more of zeolite, PP plastic balls, and Raschig rings. The filling coalescing material 5 is designed with a porous shape.

[0038] In one embodiment, such as Figures 1 to 3 As shown, the working time for gravity settling is 0.5 h to 10 h. The working time for electric field oil removal is 15 min to 45 min.

[0039] In one embodiment, such as Figure 1 As shown, the filtration device employs a single-stage or two-stage filter. The filter media selected includes, but is not limited to, one or a combination of several of the following: walnut shells, quartz sand, anthracite, and porous ceramics.

[0040] In one embodiment, such as Figure 1 As shown, the filtration device also includes a backwashing mechanism, which periodically cleans the filtration device and the generated backwash water is returned to the inlet of the gravity settling device.

[0041] In a preferred embodiment, the main water quality characteristics of the oilfield produced water used for testing are as follows: oil content 1000-5000 mg / L, suspended solids 100-1000 mg / L. First, the produced water is transported to a gravity settling device for the removal of suspended oil, dispersed oil, a small amount of emulsified oil, and easily settled suspended solids. The operating conditions are: inlet water temperature 40℃, operating pressure at atmospheric pressure, and settling residence time 30-60 min. Second, the effluent from the gravity settling device is transported to an electric field oil removal device for the removal of emulsified oil and some difficult-to-settle suspended solids. The operating conditions are: inlet water temperature 40℃, applied voltage 2-10V, residence time 20 min, and operating pressure at atmospheric pressure. Finally, the effluent from the electric field oil removal device is transported to a filtration device for reinjection treatment to meet standards for oil and suspended solids. The operating conditions are: inlet water temperature 40℃, filtration residence time 3-5 min, and operating pressure at atmospheric pressure.

[0042] In a preferred embodiment, the oilfield produced water reinjection treatment device further includes a gravity settling device, an electric field oil removal device, and a filtration device. The gravity settling device is a conventional oil removal tank, and the filtration device is a walnut shell filter. Figure 2 and Figure 3 As shown, the electric field oil removal device includes an inlet pipe 1, a perforated water distribution pipe 2, electrode plates 3, electrode support plates 4, coalescing material 5, packing support plates 6, a DC power supply 7, a baffle plate 8, an oil weir 9, an oil outlet 10, a water outlet 11, and a sludge discharge port 12. The inlet pipe 1 is located in the lower part of the device and is connected to the perforated water distribution pipe 2. The perforated water distribution pipe 2 has multiple small holes, each corresponding to a set of electrode plates 3. The electrode support plate 4 is fixed in the lower part of the device, and the electrode plates 3 are installed on top of the electrode support plate 4. The coalescing material 5 fills the spaces between adjacent electrode plates 3, and the packing support plates 6 are located on both sides of the electrode plates 3. Both the electrode support plate 4 and the packing support plate 6 are perforated plates, whose main function is to fix the packing material and prevent it from being lost. Each electrode plate 3 has a terminal block on its top, which is connected sequentially to the positive and negative terminals of the DC power supply 7, meaning that adjacent electrode plates have opposite polarities. The terminal blocks on the electrode plates are sealed for waterproofing. The baffle plate 8 is connected to the bottom of the device, and its main function is to create a better flow field to improve the oil removal effect. The oil weir 9 is located at the top of the device and is connected to the oil outlet 10. The water outlet 11 is located in the lower middle part of the device, and the sludge discharge port 12 is located at the bottom of the device.

[0043] In one embodiment, after testing using the apparatus and process conditions of the two preferred embodiments, the oilfield produced water used in the test, after gravity settling, contained less than 100 mg / L of oil and suspended solids. After electric field oil removal, the oil and suspended solids content of the effluent was less than 20 mg / L. After filtration, the oil content was less than 5 mg / L and the suspended solids content was less than 1 mg / L, meeting the oilfield's limits on oil and suspended solids content in reinjected water.

[0044] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and / or modifications falling within the scope of the invention, and all changes and / or modifications made according to embodiments of the invention should be covered within the protection scope of the invention.

Claims

1. A method for treating produced water from an oilfield, characterized in that, It employs a gravity settling device, an electric field oil removal device, and a filtration device, and includes the following steps: Gravity settling involves transporting the raw produced water to a gravity settling device for preliminary separation of oil, water, and mud. The oil content of the produced water is 1000-5000 mg / L. Electric field oil removal involves transporting gravity-sedimented wastewater to an electric field oil removal device. Under the influence of an electric field, charged emulsified oil droplets are accelerated to break down and coalesce, thus removing emulsified oil and suspended solids. The electric field oil removal device includes electrode plates with an operating voltage of 1V-30V; and... The filtration process involves sending the water effluent after the electric field oil removal to a filtration unit for further removal of emulsified oil and suspended solids, ensuring the effluent meets reinjection requirements. The electric field oil removal device has a water inlet at one end and a water outlet and an oil outlet at the other end, with a sludge discharge outlet at the bottom. Multiple rows of electrode plates are arranged along the length from the water inlet to the water outlet inside the device. The electrode plates are made of carbon-based or silicon-based materials and extend along both the longitudinal and longitudinal directions. The spaces between adjacent rows of electrode plates are filled with a coalescing material, including one or more of zeolite, PP plastic balls, and Raschig rings. The electrode plate and the coalescing material are connected by an electrode support plate and a packing support plate. Both the electrode support plate and the packing support plate are porous plates. The distance between the bottom of the electrode plate and the bottom of the electric field oil removal device is 1 / 6 to 1 / 4 of the maximum working area height of the electric field oil removal device. The water inlet is located at 1 / 5 to 1 / 4 of the distance from the bottom of the electric field oil removal device, and multiple water inlets are provided in the gaps between the electrode plates. There is one or two oil outlets. The lateral distance between the electrode plate and the oil outlet is at least 20 cm. The distance between the top of the electrode plate and the oil outlet is 1 / 5 to 1 / 3 of the maximum working area height of the electric field oil removal device.

2. The processing method according to claim 1, characterized in that, An oil-separating weir is provided in front of the oil outlet.

3. The processing method according to claim 1 or 2, characterized in that, The water outlet is located below the oil outlet and above the water inlet, and a baffle plate is provided in front of the water outlet.

4. The processing method according to claim 1 or 2, characterized in that, The working time of gravity settling is 0.5h to 10h, and the working time of electric field oil removal is 15min to 45min; the filtration device adopts a single-stage or two-stage filter, and the filler material selected in the filter includes one or a combination of walnut shells, quartz sand, anthracite, and porous ceramics.

5. The processing method according to claim 4, characterized in that, The filtration device also includes a backwash mechanism, which periodically cleans the filtration device and the generated backwash water flows back to the inlet of the gravity settling device.

6. The processing method according to claim 1 or 5, characterized in that, After gravity settling, the effluent contains no more than 100 mg / L of oil and suspended solids; after electric field oil removal, the effluent contains no more than 20 mg / L of oil and suspended solids; after filtration, the oil content is less than 5 mg / L and the suspended solids content is less than 1 mg / L.

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