A composite electric field control method for electrochemical treatment of produced water in oil and gas fields

Abstract

This invention provides a composite electric field control method for electrochemical treatment of produced water in oil and gas fields, applicable to an electrochemical treatment system containing an electrochemical reaction chamber, anode and cathode, electrode status monitoring module, and central control unit. The method first applies a DC electric field through the central control unit to perform electrocoagulation and electroflotation treatment. Simultaneously, the electrode status monitoring module collects operating parameters such as electrode voltage drop, current value, and surface impedance in real time and feeds them back to the central control unit. The central control unit analyzes the parameters to determine the degree of electrode scaling or passivation. When a preset threshold is reached, an alternating electric field is periodically superimposed for short periods within the DC electric field. The alternating electric field uses a sine wave or square wave of 10Hz-500Hz, with a voltage amplitude of 10%-30% of the DC electric field. By controlling its duration and interval, the newly formed scale layer and passivation film are dynamically peeled off, achieving simultaneous in-situ electrode maintenance and contaminant removal, avoiding downtime for cleaning, and improving the continuous operation stability of the system.

Description

Technical Field

[0001] This invention relates to the field of electrochemical treatment technology for produced water in oil and gas fields, specifically to a composite electric field control method for electrochemical treatment of produced water in oil and gas fields. Background Technology

[0002] As oil and gas field development enters its mid-to-late stages, the volume of produced water increases year by year. Produced water contains large amounts of suspended solids, emulsified oil, bacteria, scaling ions (such as calcium and magnesium ions), and corrosive components (such as chloride ions). Direct discharge without effective treatment will cause serious environmental pollution; direct reinjection into the formation will clog reservoir pores, corrode pipelines and equipment, and affect normal oilfield production. Therefore, efficient treatment of produced water has become a crucial aspect of oilfield development.

[0003] Electrochemical water treatment technology is widely used in produced water treatment due to its advantages such as no need for chemical reagents, high treatment efficiency, and high degree of automation. Among these technologies, composite electric field control technology, by combining various forms such as pulsed electric fields, alternating electric fields, and direct current electric fields, can enhance multiple effects such as electrolytic oxidation, electrocoagulation, and electroflotation, significantly improving pollutant removal efficiency. However, existing electrochemical technologies still face many challenges when treating produced water from oil and gas fields with high mineralization, high oil content, and high suspended solids: electrode surfaces are prone to scaling and passivation, leading to decreased treatment efficiency; electric field parameters are difficult to dynamically adjust according to water quality and electrode condition, making long-term stable operation impossible.

[0004] The invention patent CN106712745B discloses a composite high-voltage pulsed electric field, an electric field sterilization device, and a method. It achieves dual destruction of microbial cell membranes through the combined loading of microsecond- and nanosecond-level high-voltage pulsed electric fields, thereby improving sterilization efficiency. While this technology shows good results in biological inactivation, it is primarily geared towards the food and medical fields, targeting low-conductivity, clean media environments. Its application to produced water from oil and gas fields has significant shortcomings: First, the device does not consider the impact of high ion intensity on the attenuation of the pulsed electric field and lacks an adaptive adjustment mechanism for changes in conductivity; second, its electrode structure is not designed with anti-fouling and anti-scaling functions, making it prone to electrode passivation and clogging in water with high calcium and magnesium content and high suspended solids, leading to a rapid decline in treatment efficiency; third, the method focuses on sterilization and does not integrate electrocoagulation and electroflotation functions, failing to achieve the synergistic removal of multiple pollutants such as oil and suspended solids.

[0005] Patent No. N113292143B discloses a method for selectively separating anions and cations in saline wastewater using an electric field-coupled composite electrofiltration membrane. This invention combines an electric field with a composite electrofiltration membrane, utilizing an electrochemical hydrogen / oxygen evolution layer to achieve selective ion migration and resource recovery, making it suitable for saline wastewater treatment. Although this technology introduces a composite mechanism of electric field and membrane material, it still has significant drawbacks when applied to oil and gas field produced water treatment: First, this method relies on a low-voltage DC electric field, which has a single form and lacks dynamic control capabilities, making it difficult to meet the multi-scale removal requirements of complex pollutants; second, its membrane system structure is complex, easily contaminated by oily substances leading to flux decay, and is difficult to clean and maintain, making it unsuitable for continuous operation of produced water with high oil content; third, this technology does not integrate an intelligent feedback control module, and cannot dynamically adjust the electric field parameters according to real-time changes in water quality, resulting in high energy consumption and unstable treatment effects.

[0006] None of the aforementioned existing technologies have solved the core problem of in-situ electrode maintenance under highly complex water conditions, and lack a dynamic electric field control strategy based on dual feedback of water quality and electrode status. Summary of the Invention

[0007] The purpose of this invention is to provide a composite electric field control method for electrochemical treatment of produced water in oil and gas fields. By dynamically superimposing an alternating electric field during the DC electric field treatment process, combined with real-time monitoring and feedback correction, the method achieves synergistic optimization of in-situ electrode maintenance and efficient pollutant removal.

[0008] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0009] A composite electric field control method for electrochemical treatment of produced water in oil and gas fields is applied to an electrochemical treatment system comprising an electrochemical reaction chamber, an anode and a cathode disposed within the electrochemical reaction chamber, an electrode status monitoring module for monitoring the operating status of the electrodes, and a central control unit electrically connected to the anode, cathode, and electrode status monitoring module. The method includes the following steps:

[0010] S101: During the electrochemical treatment of produced water from oil and gas fields in the electrochemical reaction chamber, the central control unit controls the application of a DC electric field between the anode and the cathode to perform electrocoagulation and electroflotation treatment.

[0011] S102: The electrode status monitoring module collects the operating status parameters of the anode and cathode in real time. The operating status parameters include at least one of the voltage drop between the electrode pairs, the current value through the electrodes, and the electrode surface impedance, and sends the operating status parameters to the central control unit.

[0012] S103: The central control unit analyzes the received operating status parameters and determines whether the scaling or passivation degree on the anode and cathode surfaces reaches a preset threshold.

[0013] S104: When it is determined that the degree of scaling or passivation reaches a preset threshold, the central control unit controls the periodic short-term superposition of an alternating electric field during the application of the DC electric field. The alternating electric field adopts a sine wave or square wave with a frequency of 10Hz-500Hz, and the voltage amplitude of the alternating electric field is 10%-30% of the voltage amplitude of the DC electric field.

[0014] S105: The central control unit controls the duration and superposition interval of the alternating electric field to dynamically strip away the newly formed scale and passivation film on the anode and cathode surfaces, thereby maintaining the electrode's operational activity.

[0015] In one embodiment of the present invention, the operating state parameters in step S102 include at least two of the following: voltage drop between electrode pairs, current through the electrodes, electrode surface impedance, and electrode surface temperature.

[0016] In one embodiment of the present invention, in step S103, the central control unit quantifies the severity of scaling or passivation on the anode and cathode surfaces by analyzing the time series change trend of the operating status parameters. The time series analysis period is 5-30 minutes.

[0017] In one embodiment of the present invention, the alternating electric field in step S104 adopts a sine wave or a square wave with a frequency range of 20-450Hz.

[0018] In one embodiment of the present invention, the voltage amplitude of the alternating electric field in step S104 is 15%-25% of the voltage amplitude of the direct current electric field.

[0019] In one embodiment of the present invention, the duration of the alternating electric field in step S105 is 10-120 seconds.

[0020] In one embodiment of the present invention, the superposition interval of the alternating electric field in step S105 is 5-60 minutes. The superposition interval is dynamically adjusted according to the rate of change of the impedance of the electrode surface. The higher the rate of change of impedance, the smaller the superposition interval.

[0021] In one embodiment of the present invention, the alternating electric field in step S104 periodically reverses the electrode polarity, and the period of the polarity reversal is 1-5 minutes.

[0022] In one embodiment of the present invention, step S6 is further included: after the superposition of alternating electric fields is completed, the electrode state monitoring module collects the electrode operating state parameters again, and the central control unit compares them with the preset normal state parameter range. If the normal range is not reached, the superposition interval of the next alternating electric field is shortened by 10%-30%.

[0023] In one embodiment of the present invention, the current density of the DC electric field is adjustable in the range of 10-100 mA / cm², and the central control unit dynamically adjusts the current density according to the chemical oxygen demand (COD) and suspended solids (SS) concentration in the water quality baseline parameters.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] This invention achieves simultaneous in-situ electrode maintenance and contaminant removal by dynamically superimposing an alternating electric field during DC electric field treatment, solving the problem of reduced treatment efficiency caused by electrode scaling and passivation in traditional technologies. The periodic short-term superposition of the alternating electric field can dynamically peel off newly formed scale and passivation films using electric field force, avoiding production interruptions caused by downtime cleaning and significantly improving the stability of continuous system operation.

[0026] This invention addresses the pain points of existing electrochemical technologies, such as electrode scaling and passivation leading to decreased processing efficiency and the need for shutdown cleaning. It employs a composite operation mode with a primary DC electric field and a dynamically superimposed alternating electric field: While the DC electric field continuously performs electrocoagulation and electroflotation (removal of the main contaminants), when electrode status monitoring parameters (voltage drop, impedance, etc.) reach the scaling / passivation threshold, a periodically short-term alternating electric field (10Hz-500Hz sine wave or square wave) with a voltage amplitude of 10%-30% of the DC electric field is periodically superimposed. This utilizes the electric field force to dynamically peel off newly formed scale and passivation films. This breaks through the traditional shutdown maintenance mode, enabling simultaneous in-situ online electrode maintenance and contaminant removal, significantly improving the system's continuous operation stability and avoiding production interruptions.

[0027] This invention innovatively constructs a dynamic feedback control system based on electrode state, solving the problem of the lack of accurate state perception in existing technologies. By collecting at least two parameters such as voltage drop, current value, surface impedance, and temperature in real time through the electrode state monitoring module, a multi-dimensional assessment of the electrode state can be achieved.

[0028] The central control unit quantifies the changing trend of scaling / passivation levels through 5-30 minute time series analysis, avoiding misjudgments caused by instantaneous parameter fluctuations. It only triggers the superposition of alternating electric fields when a preset threshold is reached, reducing ineffective energy consumption. Compared to existing technologies that monitor only one parameter, multi-parameter collaborative analysis can more accurately identify electrode failure risks, providing a reliable basis for electric field control decisions.

[0029] This invention addresses the high salinity and scaling tendency of produced water from oil and gas fields by refining and innovating the alternating electric field parameters. It employs sinusoidal or square waves with optimized frequencies ranging from 10Hz to 500Hz to adapt to high ion intensity environments, reducing electric field attenuation and enhancing scale removal force. The voltage amplitude is limited to 10%-30% of the DC electric field, and the duration is controlled between 10-120 seconds to balance maintenance effectiveness with overall treatment efficiency and avoid interfering with the electrocoagulation reaction. The stacking interval is adaptively adjusted based on the rate of change of electrode surface impedance, ranging from 5-60 minutes. The faster the impedance change (the faster the scaling), the shorter the interval, enabling on-demand maintenance and reducing energy consumption.

[0030] This invention introduces electrode polarity reversal and secondary verification logic, extending electrode life and ensuring maintenance effectiveness. An alternating electric field periodically reverses electrode polarity every 1-5 minutes, causing the anode and cathode to alternately undergo oxidation / reduction reactions, reducing unilateral scaling and corrosion, and balancing electrode wear. After the alternating electric field is superimposed, secondary parameter acquisition is compared with the normal range. If the parameters do not meet the standards, the next superposition interval is automatically shortened by 10%-30%, forming a closed loop of monitoring, control, verification, and optimization to ensure the electrode always maintains its active state.

[0031] This invention addresses the fluctuating characteristics of produced water quality by designing an electric field parameter adjustment mechanism based on a water quality baseline. The DC electric field current density (10-100 mA / cm²) is dynamically adjusted according to the COD and suspended solids (SS) concentrations in the water. During periods of high pollution, the current density is increased to enhance flocculation, while during periods of low pollution, the density is decreased to save energy, achieving a dynamic balance between load and energy consumption. This overcomes the limitations of fixed electric field parameters in existing technologies, adapting to the treatment needs of produced water with varying pollution loads and improving system adaptability and energy efficiency.

[0032] This invention solves the core problems of existing technologies, such as difficult electrode maintenance, rigid parameter control, and poor continuous operation stability under highly complex water conditions. It forms an intelligent control system covering the entire process of monitoring, decision-making, regulation, and verification, which significantly improves the efficiency and economy of electrochemical treatment of produced water in oil and gas fields. Attached Figure Description

[0033] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained from these drawings without creative effort.

[0034] Figure 1 This is a block diagram illustrating the overall principle of the present invention. Detailed Implementation

[0035] In the following description, only certain exemplary embodiments are briefly described. As those skilled in the art will recognize, the described embodiments can be modified in various ways without departing from the spirit or scope of the embodiments of the invention. Therefore, the drawings and description are considered to be exemplary in nature and not restrictive. Embodiments of the invention will now be described in detail with reference to the accompanying drawings.

[0036] See Figure 1 A composite electric field control method for electrochemical treatment of produced water in oil and gas fields is disclosed. The method is applied to an electrochemical treatment system comprising an electrochemical reaction chamber, an anode and a cathode disposed within the electrochemical reaction chamber, an electrode status monitoring module for monitoring the operating status of the electrodes, and a central control unit electrically connected to the anode, cathode, and electrode status monitoring module. The method includes the following steps:

[0037] S101: During the electrochemical treatment of produced water from oil and gas fields in the electrochemical reaction chamber, the central control unit controls the application of a DC electric field between the anode and the cathode to perform electrocoagulation and electroflotation treatment.

[0038] S102: The electrode status monitoring module collects the operating status parameters of the anode and cathode in real time. The operating status parameters include at least one of the voltage drop between the electrode pairs, the current value through the electrodes, and the electrode surface impedance, and sends the operating status parameters to the central control unit.

[0039] S103: The central control unit analyzes the received operating status parameters and determines whether the scaling or passivation degree on the anode and cathode surfaces reaches a preset threshold.

[0040] S104: When it is determined that the degree of scaling or passivation reaches a preset threshold, the central control unit controls the periodic short-term superposition of an alternating electric field during the application of the DC electric field. The alternating electric field adopts a sine wave or square wave with a frequency of 10Hz-500Hz, and the voltage amplitude of the alternating electric field is 10%-30% of the voltage amplitude of the DC electric field.

[0041] S105: The central control unit controls the duration and superposition interval of the alternating electric field to dynamically strip away the newly formed scale and passivation film on the anode and cathode surfaces, thereby maintaining the electrode's operational activity.

[0042] This invention achieves simultaneous in-situ electrode maintenance and contaminant removal by dynamically superimposing an alternating electric field during DC electric field treatment, solving the problem of reduced treatment efficiency caused by electrode scaling and passivation in traditional technologies. The periodic short-term superposition of the alternating electric field can dynamically peel off newly formed scale and passivation films using electric field force, avoiding production interruptions caused by downtime cleaning and significantly improving the stability of continuous system operation.

[0043] In one embodiment of this invention, the operating status parameters in step S102 include at least two of the following: voltage drop between the electrode pairs, current through the electrodes, electrode surface impedance, and electrode surface temperature. By adding monitoring parameters such as electrode surface temperature, a multi-dimensional assessment of the electrode status is achieved. Compared to single-parameter monitoring, multi-parameter collaborative analysis can more accurately determine scaling, passivation, or corrosion phenomena, reduce the false judgment rate, and provide a more reliable decision-making basis for electric field control.

[0044] In one embodiment of this invention, in step S103, the central control unit quantifies the severity of scaling or passivation on the anode and cathode surfaces by analyzing the time-series changes in operating status parameters. The time-series analysis period is 5-30 minutes. Using a 5-30 minute time-series analysis period captures the gradual change trend of the electrode state, avoiding mis-controls caused by instantaneous parameter fluctuations. By quantifying the scaling / passivation degree, precise triggering of the electric field superposition strategy is achieved, reducing ineffective energy consumption.

[0045] In one embodiment of this invention, the alternating electric field in step S104 uses a sine wave or square wave with a frequency range of 20-450Hz. Optimizing the alternating electric field frequency to 20-450Hz, compared to a wider range of 10-500Hz, is more suitable for the high salinity characteristics of produced water from oil and gas fields. This frequency range reduces electric field attenuation, enhances the peeling force on scale, and avoids energy waste at high frequencies, thus improving maintenance efficiency.

[0046] In one embodiment of this invention, the voltage amplitude of the alternating electric field in step S104 is 15%-25% of the voltage amplitude of the direct current electric field. Limiting the alternating electric field voltage amplitude to 15%-25% of the direct current voltage ensures effective scale removal while avoiding interference from excessively high voltage on the electrocoagulation reaction dominated by the direct current electric field. This range balances maintenance effectiveness with overall treatment efficiency, reducing overall energy consumption.

[0047] In one embodiment of the present invention, the duration of the alternating electric field in step S105 is 10-120 seconds. This 10-120 second duration design allows for dynamic adjustment based on the scale thickness: thin scale layers can be peeled off quickly, while thick scale layers can be peeled off with a slightly longer duration, avoiding the impact of excessive accumulation on the main treatment process and achieving efficient and energy-saving maintenance.

[0048] In one embodiment of this invention, the superposition interval of the alternating electric field in step S105 is 5-60 minutes. This superposition interval is dynamically adjusted according to the rate of change of the electrode surface impedance; the higher the impedance change rate, the smaller the superposition interval. This dynamic superposition interval of 5-60 minutes can be adaptively adjusted according to the impedance change rate, shortening the interval when the impedance changes rapidly (rapid scaling) and lengthening the interval when the impedance changes slowly. This on-demand control mode avoids the problems of insufficient maintenance or excessive energy consumption caused by fixed intervals.

[0049] In one embodiment of the present invention, the alternating electric field in step S104 periodically reverses the electrode polarity, with a polarity reversal period of 1-5 minutes. This 1-5 minute periodic electrode polarity reversal allows the anode and cathode to alternately undergo oxidation and reduction reactions, reducing directional scaling and corrosion on one side of the electrode, balancing electrode wear, and extending electrode lifespan.

[0050] In one embodiment of this invention, step S6 is further included: after the alternating electric field superposition ends, the electrode state monitoring module collects the electrode operating state parameters again, and the central control unit compares them with the preset normal state parameter range. If the parameters do not reach the normal range, the superposition interval of the next alternating electric field is shortened by 10%-30%. The feedback correction step forms a closed-loop control of monitoring, regulation, verification, and optimization through secondary monitoring and interval adjustment. When the initial maintenance does not meet expectations, shortening the interval can provide timely remediation, ensuring that the electrode is always in an active state and guaranteeing the stability of the treatment effect.

[0051] After the alternating electric field superposition ends, the electrode state monitoring module collects the electrode operating status parameters again, and the central control unit compares them with the preset normal state parameter range. This changes the traditional unidirectional control mode in electrochemical treatment, introducing a feedback loop and constructing a closed-loop control system from parameter monitoring and regulation to effect verification. Through this closed-loop control, the system no longer blindly operates according to fixed parameters, but can dynamically adjust according to the actual state of the electrodes, making the entire treatment process more intelligent and precise. For example, when treating high-mineralized produced water, the electrode scaling rate is fast. Through real-time feedback, the system can adjust the alternating electric field superposition interval in a timely manner to ensure that the electrodes are always in good operating condition.

[0052] If the collected parameters are not within the normal range, the system automatically shortens the superposition interval of the alternating electric field by 10%-30%. This method of dynamically adjusting the electric field superposition interval based on actual conditions gives the system stronger adaptability. Different oil and gas fields have significantly different produced water qualities, and the scaling and passivation of electrodes also vary. This adaptive adjustment can effectively cope with complex and changing water quality conditions. For example, in cases of poor water quality and easy electrode scaling, the system will automatically increase the maintenance frequency to ensure the stability of the treatment effect; while in cases of relatively good water quality, it can appropriately extend the superposition interval to reduce unnecessary energy consumption.

[0053] When processing produced water from oil and gas fields with high oil content and suspended solids, electrodes are prone to scaling and passivation, which can affect treatment efficiency. The feedback correction mechanism can promptly detect abnormal electrode conditions and maintain electrode activity by adjusting the alternating electric field superposition interval, preventing a decrease in treatment efficiency. Taking an actual treatment process as an example, after the initial superposition of the alternating electric field, the scale and passivation film on the electrode surface may not be completely removed. In this case, parameters are collected again and compared with a preset range. If the parameters are found to be substandard, the superposition interval is shortened, and treatment is repeated to ensure the electrode maintains a good working condition, thereby stabilizing the treatment effect and ensuring the continuous and efficient treatment of produced water.

[0054] Meanwhile, the feedback correction mechanism optimizes the entire processing flow. In traditional processing methods, untimely or excessive electrode maintenance often occurs, leading to increased processing costs and unstable processing results. This invention can adjust the maintenance strategy in a timely manner based on the real-time state of the electrodes without interrupting the processing flow, reducing ineffective maintenance operations, improving system operating efficiency, and also reducing energy consumption and maintenance costs, making the entire electrochemical treatment system more efficient, energy-saving, and economical.

[0055] In one embodiment of this invention, the current density of the DC electric field is adjustable within a range of 10-100 mA / cm², and the central control unit dynamically adjusts the current density based on the chemical oxygen demand (COD) and suspended solids (SS) concentrations in the water quality baseline parameters. The 10-100 mA / cm² current density range can match water quality loads with different COD and SS concentrations. Increasing the current density enhances the flocculation effect during periods of high pollution, while decreasing the current density saves energy during periods of low pollution, thus achieving a dynamic balance between load and energy consumption.

[0056] To facilitate a better understanding of the present invention by those skilled in the art, the present invention will be further described below.

[0057] Example 1:

[0058] This embodiment mainly targets produced water from oil and gas fields with an oil content of 450 mg / L and an SS concentration of 280 mg / L. The specific treatment steps are as follows:

[0059] Step S101: The water quality sensing module collects baseline water quality parameters in real time, including oil concentration (450 mg / L), COD value (350 mg / L), suspended solids (SS) concentration (280 mg / L), and total bacterial count (1.2 × 10⁻⁶). 5 CFU / mL; The electrode status monitoring module collects the voltage drop between the electrode pairs (initial value 2.5V) and the current through the electrodes (initial value 1.8A) in real time, and sends the above parameters to the central control unit.

[0060] Step S102: The central control unit calls the multi-mode electric field control model and combines water quality and electrode state parameters to generate a composite electric field application strategy: pulse electric field preprocessing, DC electric field main processing, and periodic superposition of alternating electric field maintenance.

[0061] Step S103: First, apply the pulsed electric field mode and adjust the parameters according to the oil content and total number of colonies: pulse voltage amplitude 12kV / cm, pulse frequency 5kHz, duration T1=15 minutes to achieve oil droplet demulsification and microbial inactivation.

[0062] Then, the system was switched to DC electric field mode, and the current density was adjusted to 60 mA / cm² based on the COD and SS concentrations for a duration of T2=40 minutes to enhance electrocoagulation and electroflotation effects.

[0063] During DC processing, the electrode condition monitoring module collects voltage drop and current values ​​every 10 minutes (time series analysis cycle). When the voltage drop is detected to rise to 3.8V, which is 52% higher than the initial value, it is determined that the degree of electrode scaling exceeds the preset threshold.

[0064] Triggering the superposition of alternating electric fields: A sine wave with a frequency of 200Hz is used, and the voltage amplitude is 20% of the DC voltage amplitude. The electrode polarity is periodically reversed, with a reversal period of 3 minutes, a duration of T3=40 seconds, and a superposition interval of Δt=20 minutes.

[0065] Feedback correction step S104: After the treatment cycle is completed, the water quality sensing module collects the target parameters of the effluent water quality. The COD removal rate is 88% and the SS removal rate is 92%, which meets the preset treatment effect standard. There is no need to adjust the model weight coefficient.

[0066] Example 2:

[0067] This embodiment is for produced water from oil and gas fields with high mineralization and high scaling tendency, with a conductivity of 18000 μS / cm and a total calcium and magnesium ion concentration of 1400 mg / L.

[0068] The specific processing steps are as follows:

[0069] Step S101: The water quality sensing module collects baseline water quality parameters, including conductivity of 18000 μS / cm, COD value of 220 mg / L, and pH value of 7.8; the electrode status monitoring module collects electrode surface impedance with an initial value of 5 Ω and an initial electrode surface temperature of 32℃.

[0070] Step S102: Central control unit generation strategy: pulse electric field preprocessing, DC electric field main body processing, and high-frequency alternating electric field superposition maintenance.

[0071] Step S103:

[0072] Pulsed electric field mode: pulse voltage amplitude 8kV / cm, pulse frequency 2kHz, duration T1=10 minutes.

[0073] DC electric field mode: current density 40mA / cm², duration T2=50 minutes.

[0074] Electrode condition monitoring uses a 25-minute analysis cycle. When the electrode surface impedance rises to 9Ω (an 80% increase) and the temperature rises to 38℃, an alternating electric field is triggered.

[0075] The alternating electric field uses a square wave with a frequency of 400Hz and a voltage amplitude of 25% of the DC voltage amplitude. The polarity reversal period is 2 minutes, the duration is T3=80 seconds, and the superposition interval is Δt=15 minutes. The interval is shortened due to the high impedance change rate.

[0076] Feedback correction step S104: After the first superposition, the electrode surface impedance drops to 7Ω, which is below the normal range (5-6Ω). The central control unit increases the alternating electric field weight coefficient of the multi-mode electric field control model by 15%, and the superposition interval of the next cycle is shortened to 12 minutes.

[0077] Example 3:

[0078] This example focuses on produced water from low-pollution oil and gas fields, with COD of 130 mg / L and SS of 45 mg / L. The specific treatment steps are as follows:

[0079] Step S101: The water quality sensor module collects COD value (130 mg / L), SS concentration (45 mg / L), and total bacterial count (3 × 10⁻⁶). 4 CFU / mL; the electrode status monitoring module collects the initial voltage drop value of 2.0V and the initial current value of 1.2A.

[0080] Step S102: The central control unit generates a low-energy consumption strategy: short-time pulse preprocessing, low current density DC processing, and long-interval alternating electric field superposition.

[0081] Step S103:

[0082] Pulsed electric field mode: pulse voltage amplitude 5kV / cm, pulse frequency 1kHz, duration T1=5 minutes.

[0083] DC electric field mode: current density 15mA / cm², duration T2=30 minutes.

[0084] Electrode status monitoring is performed in 30-minute cycles. When the voltage drops to 2.4V, an alternating electric field is triggered. A sine wave with a frequency of 50Hz is used, and the voltage amplitude is 15% of the DC voltage amplitude. The duration is T3 = 30 seconds, and the superposition interval is Δt = 50 minutes.

[0085] Treatment results: COD removal rate of effluent is 85%, no obvious passivation of electrodes after 120 hours of continuous operation, and energy consumption is reduced by 30% compared with traditional methods.

[0086] This invention addresses the complex water quality characteristics of produced water from oil and gas fields, characterized by high salinity, high oil content, and high suspended solids. It achieves multi-dimensional innovations based on existing electrochemical water treatment technologies. The core innovations are as follows:

[0087] This invention establishes a dynamic control system with water quality parameters and electrode state parameters as dual inputs. A water quality sensing module collects pollution indicators such as oil content, COD, and suspended solids in real time, while an electrode state monitoring module captures operating parameters such as voltage drop and surface impedance. This forms a dual sensing mechanism for pollution status and equipment health, solving the problem of insufficient adaptability caused by single-parameter control in existing technologies.

[0088] This invention designs a functional partitioning and timing coupling mechanism for three electric fields: pulse, alternating, and direct current. The pulse electric field is specifically used for oil droplet demulsification and microbial inactivation, the direct current electric field is responsible for electrocoagulation and electroflotation of the main body, and the alternating electric field realizes in-situ electrode maintenance. The three modes are precisely switched according to the timing sequence of pretreatment, main body treatment, and dynamic maintenance, which breaks through the limitations of existing technologies with single or simple superposition of electric field forms.

[0089] This invention proposes a composite operation mode in which a periodic superimposed alternating electric field is used in the operation of a DC electric field. The superimposed alternating electric field adopts a 10-500Hz sine wave or square wave, and the voltage amplitude is 10%-30% of the DC voltage. By dynamically peeling off the newly formed scale layer and passivation film on the electrode surface through polarity reversal, the traditional shutdown cleaning is transformed into online real-time maintenance, which solves the problem of electrode passivation and blockage under high calcium and magnesium water quality.

[0090] 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 both the preferred embodiments and all changes and modifications falling within the scope of the invention.

[0091] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. It should be noted that any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A composite electric field control method for electrochemical treatment of produced water in oil and gas fields, applied to an electrochemical treatment system comprising an electrochemical reaction chamber, an anode and a cathode disposed within the electrochemical reaction chamber, an electrode state monitoring module for monitoring the operating status of the electrodes, and a central control unit electrically connected to the anode, cathode, and electrode state monitoring module, characterized in that, The method includes the following steps: S101: During the electrochemical treatment of produced water from oil and gas fields in the electrochemical reaction chamber, the central control unit controls the application of a DC electric field between the anode and the cathode to perform electrocoagulation and electroflotation treatment. S102: The electrode status monitoring module collects the operating status parameters of the anode and cathode in real time. The operating status parameters include at least one of the voltage drop between the electrode pairs, the current value through the electrodes, and the electrode surface impedance, and sends the operating status parameters to the central control unit. S103: The central control unit analyzes the received operating status parameters and determines whether the scaling or passivation degree on the anode and cathode surfaces reaches a preset threshold. S104: When it is determined that the degree of scaling or passivation reaches a preset threshold, the central control unit controls the periodic short-term superposition of an alternating electric field during the application of the DC electric field. The alternating electric field adopts a sine wave or square wave with a frequency of 10Hz-500Hz, and the voltage amplitude of the alternating electric field is 10%-30% of the voltage amplitude of the DC electric field. S105: The central control unit controls the duration and superposition interval of the alternating electric field to dynamically peel off the newly formed scale and passivation film on the anode and cathode surfaces, and maintain the electrode operation activity; the superposition interval of the alternating electric field is 5-60 minutes, and the superposition interval is dynamically adjusted according to the rate of change of the electrode surface impedance. The higher the rate of change of impedance, the smaller the superposition interval. It also includes step S6: After the alternating electric field superposition ends, the electrode state monitoring module collects the electrode operating state parameters again, and the central control unit compares them with the preset normal state parameter range. If the normal range is not reached, the superposition interval of the next alternating electric field is shortened by 10%-30%.

2. The composite electric field control method for electrochemical treatment of produced water in oil and gas fields according to claim 1, characterized in that: The operating status parameters in step S102 include at least two of the following: voltage drop between electrode pairs, current through the electrodes, electrode surface impedance, and electrode surface temperature.

3. The composite electric field control method for electrochemical treatment of produced water in oil and gas fields according to claim 1, characterized in that: In step S103, the central control unit analyzes the time series change trend of the operating status parameters to quantitatively determine the severity of scaling or passivation on the anode and cathode surfaces. The time series analysis period is 5-30 minutes.

4. The composite electric field control method for electrochemical treatment of produced water in oil and gas fields according to claim 1, characterized in that: The alternating electric field in step S104 uses a sine wave or a square wave with a frequency range of 20-450Hz.

5. The composite electric field control method for electrochemical treatment of produced water in oil and gas fields according to claim 1, characterized in that: In step S104, the voltage amplitude of the alternating electric field is 15%-25% of the voltage amplitude of the direct current electric field.

6. The composite electric field control method for electrochemical treatment of produced water in oil and gas fields according to claim 1, characterized in that: The duration of the alternating electric field in step S105 is 10-120 seconds.

7. A composite electric field control method for electrochemical treatment of produced water in oil and gas fields according to claim 1, characterized in that: In step S104, the alternating electric field periodically reverses the electrode polarity, and the period of polarity reversal is 1-5 minutes.

8. The composite electric field control method for electrochemical treatment of produced water in oil and gas fields according to claim 1, characterized in that: The current density of the DC electric field is adjustable from 10 to 100 mA / cm², and the central control unit dynamically adjusts the current density based on the chemical oxygen demand (COD) and suspended solids (SS) concentration in the water quality baseline parameters.

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