Electrochemically controllable gel-breaking gel-breaking agent-free fracturing fluid, preparation method and application thereof

Abstract

The application discloses an electrochemical controllable gel-breaking guar fracturing fluid without gel-breaking agent and a preparation method and application thereof, and belongs to the technical field of fracturing fluids.The components of the fracturing fluid are as follows: 0.3-0.6% modified guar gum, 5-15% composite conductive electrolyte, 0.05-0.30% stabilizer, and the rest is clean water.The application discards the traditional chemical gel-breaking agent system, and realizes gel-breaking by relying on a multi-stage electrochemical degradation mechanism of electric field polarization-acid-base microfield coupling.Through the step-by-step action of electric field activation, coordination dissociation and deep degradation of the main chain, the guar gum polymer can be completely degraded into water-soluble small molecular carboxylic acid without the generation of difficultly soluble residues; the stratum pore blockage and permanent reservoir damage caused by the chemical gel-breaking agent residues are eliminated from the root, which is favorable for protecting the reservoir permeability and improving the oil and gas recovery rate.

Description

Technical Field

[0001] This invention relates to the field of fracturing fluid technology, specifically to an electrochemically controllable gel-breaking fracturing fluid without a gel-breaking agent, its preparation method, and its application. Background Technology

[0002] Fracturing technology in oil and gas fields is a core process for efficiently increasing the production of tight oil and shale gas. Fracturing fluids need to possess both high viscosity and proppant-carrying capacity for fracturing, and the ability to quickly break down and flow back after fracturing. Currently, the industry mainstream uses plant-based fracturing fluids such as guar gum and hydroxypropyl guar gum, combined with chemical breaker agents such as peroxides and bio-enzymes. Breaking down the fracturing fluid is achieved through the oxidative degradation of polymer chains by these agents. This is currently the most mature and widely used conventional fracturing fracturing breaking technology system both domestically and internationally.

[0003] Existing conventional fracturing and gel breaking technology systems require the addition of gel breaking agents. Agent residues can easily clog formation pores, causing permanent damage to the reservoir and directly reducing oil and gas recovery rates. The gel breaking effect is highly susceptible to formation temperature, salinity, and on-site construction conditions. The gel breaking rate cannot be precisely controlled manually, often resulting in premature gel breaking leading to failure of proppant transport operations, or premature gel breaking leading to difficulties in flowback.

[0004] Based on this, the present invention designs an electrochemically controllable gel-breaking agent-free fracturing fluid, its preparation method, and its application to solve the above problems. Summary of the Invention

[0005] To address the aforementioned shortcomings of existing technologies, this invention provides an electrochemically controllable gel-breaking fracturing fluid without a gel-breaking agent, which, by mass percentage, consists of the following components: 0.3-0.6% modified guar gum, 5-15% composite conductive electrolyte, 0.05-0.30% stabilizer, and the balance being water.

[0006] The method for preparing the modified guar gum is as follows: S1. Preparation of zirconium oxychloride complex solution: Take 7.5 parts by mass of zirconium oxychloride octahydrate and dissolve it in 30 parts of deionized water. Stir until completely dissolved, then add hydrochloric acid dropwise and stir. S2. Add 260 parts of isopropanol to the reactor, add 50 parts of 32% sodium hydroxide solution under stirring at room temperature and mix well; add 100 parts of guar gum powder, heat to 43°C and alkalize, add 42 parts of sodium chloroacetate and further heat to 66°C, and react at a constant temperature. S3. Cool to 50°C and add the zirconium hydroxychloride complex solution dropwise into the reaction vessel. During the dropwise addition process, maintain the pH at 5.0-5.5. After the dropwise addition is complete, continue the reaction. Then, wash, filter, vacuum dry, pulverize and sieve to obtain the final product.

[0007] Furthermore, in step S2, the alkalization treatment time is 50-70 min, and the isothermal reaction time is 140-160 min.

[0008] The composite conductive electrolyte is composed of potassium chloride, sodium chloride, and anhydrous sodium citrate in a mass ratio of 6:3:1; the stabilizer is composed of 0.20 parts sodium thiosulfate and 0.10 parts disodium ethylenediaminetetraacetate (EDTA-2Na).

[0009] A method for preparing the electrochemically controllable gel-breaking, gel-free fracturing fluid includes the following steps: Modified guar gum is added to water, and the mixture is stirred at 60-120 r / min to obtain a mixture. A composite conductive electrolyte and a stabilizer are added to the mixture, and the mixture is stirred to obtain a dispersion. The temperature is raised to 25-45℃, and the mixture is stirred for 20-30 min to swell and mature, thus obtaining an electrochemically controllable debonding fracturing fluid without a debonding agent.

[0010] A method for applying the electrochemically controllable gel-breaking, gel-free fracturing fluid includes the following steps: A1. Reservoir fracturing operations; The fracturing fluid is injected into the oil and gas reservoir to complete the fracturing, sand carrying and sand laying operations, and then the pressure is stabilized and left to stand. A2. Electrochemically controlled gel breaking; By deploying bipolar electrodes downhole and connecting them to a low-voltage DC power supply, the fracturing fluid undergoes a multi-stage coupled electrochemical reaction triggered by the electric field, breaking the cross-linked bonds of polymers and achieving controllable gel breaking. A3. Flowback completion; The viscosity of the flowback fluid is monitored in real time using a viscometer. Once the viscosity is found to be ≤5 mPa·s, low-viscosity fluid flowback operation is carried out. Well completion is completed once the residue content is found to be ≤200 mg / L by filtration and weighing.

[0011] Furthermore, in A1, the voltage stabilization settling time is 5-10 minutes.

[0012] Furthermore, in A2, the current density of the low-voltage DC power supply is 5-15 mA / cm². 2 Voltage 5-20V.

[0013] Furthermore, in A2, a tiered power-on mode is adopted, with each tier lasting 30-60 seconds, followed by a 2-5 second pause, repeated 3-10 times.

[0014] Furthermore, in A3, the backflow pressure differential is 2-5 MPa, and the backflow velocity is ≤15 m / s. 3 / h.

[0015] In the above scheme, by utilizing the electrochemical degradation mechanism of electric field polarization-acid-base microfield coupling, a multi-field coupled controllable de-gelling system is constructed, which differs from the traditional single chemical oxidation de-gelling method. Specifically: 1. Electric field activation stage: A low-voltage DC electric field acts on the conductive de-gelling fluid system, and the freely moving Na in the solution... + K + Cl - 1. **Directional migration of electrolyte ions to form a stable ionic current, uniformly polarizing the guar gum polymer cross-linked network, and weakening intermolecular hydrogen bonds, van der Waals forces, and metal coordination bonds;** 2. **Microfield construction stage:** Redox reactions occur on the electrode surface, and H+ is enriched at the anode. + The formation of localized weakly acidic microregions allows for the enrichment of OH groups at the cathode. - 1. Formation of weakly alkaline micro-regions: The alternating acid-base environment throughout the region disrupts the stable cross-linking system of the fracturing fluid; 2. Coordination dissociation stage: Modified guar gum relies on metal ion coordination to form a high-viscosity network structure. The acid-base micro-field can precisely replace coordinated water molecules and break coordination bonds, causing the macroscopic viscosity of the colloid to decrease rapidly; 3. Deep degradation stage: Under the continuous action of the electric field, the C-C bonds and CO bonds of the polymer backbone undergo oxidative breakage, and the long-chain macromolecules are degraded into short-chain organic matter step by step, and finally hydrolyzed into water-soluble small molecule carboxylic acids, with no insoluble residue; 4. Controllable regulation stage: The gel breaking reaction rate follows the laws of electrochemical kinetics and can be precisely controlled by voltage gradient, energizing time, and current density to avoid the lag and runaway problems of traditional chemical gel breaking. At the same time, the micro-gas production of the electrode can form micro-disturbances, which assist in the disintegration of the network structure and further improve the thoroughness of gel breaking.

[0016] Furthermore, the modified fracturing fluid employs a compound system of inorganic coordination-modified guar gum, composite conductive electrolyte, and buffer stabilizer, distinguishing it from ordinary water-based fracturing fluids. It possesses stable conductivity and sensitive electrochemical response characteristics. Upon energization, the system undergoes a four-stage coupled reaction: electrode water electrolysis, coordination bond dissociation, polymer backbone oxidative degradation, and residual functional group hydrolysis. This completely destroys the three-dimensional network cross-linked structure of the fracturing fluid, achieving gradient, controllable, and complete gel breaking. The complete reaction equations are as follows: Compared with the prior art, the beneficial effects of this invention are as follows: 1. This invention exhibits low reservoir damage and excellent environmental performance. It abandons the traditional chemical de-gelling agent system, relying instead on a multi-stage electrochemical degradation mechanism involving electric field polarization and acid-base micro-field coupling to achieve de-gelling. Through the step-by-step action of electric field activation, micro-field construction, coordination dissociation, and deep degradation of the main chain, guar gum polymers can be completely degraded into water-soluble small-molecule carboxylic acids, without the formation of insoluble residues. This eliminates the formation pore blockage and permanent reservoir damage caused by chemical de-gelling agent residues, which is beneficial for protecting reservoir permeability and improving oil and gas recovery. Simultaneously, the flowback fluid has low pollutant content, making it easy to purify, recover, and recycle, reducing the risk of soil and groundwater pollution and aligning with the development direction of green oil and gas field exploitation.

[0017] 2. This invention offers strong controllability in gel breaking and a wide range of operational adaptability. The gel breaking process follows electrochemical kinetics, allowing for precise control of the reaction rate and degree of gel breaking through parameters such as voltage gradient, energizing duration, and current density. This overcomes the limitations of traditional chemical oxidation gel breaking, which is greatly affected by formation temperature, salinity, and water quality conditions. It avoids premature gel breaking leading to sand-carrying fracture failure and also prevents difficulties in backflow caused by delayed gel breaking. Simultaneously, the micro-disturbances created by the trace gas production at the electrodes assist in the disintegration of the network structure, ensuring thorough gel breaking. This invention is adaptable to complex fracturing conditions such as conventional oil and gas reservoirs and high-temperature deep wells, significantly improving operational stability and adaptability.

[0018] 3. This invention simplifies the construction process and reduces overall application costs. It eliminates the need for additional procurement, preparation, and addition of chemical breaker agents, saving on corresponding material costs and on-site preparation procedures. This simplifies the fracturing site construction process and reduces labor costs. The downhole electrical triggering method provides rapid response, and combined with real-time monitoring of the flowback fluid viscosity, it allows for quick determination of the breaker endpoint, shortening post-fracturing waiting and construction cycles. Furthermore, the downhole electrode device is reusable, further reducing the overall cost of on-site operations. This invention demonstrates excellent economic efficiency and promotional value in engineering applications. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0020] Unless otherwise specified, the experimental methods used in this invention are conventional methods; unless otherwise specified, the materials and reagents used are commercially available. The guar gum powder used in this invention is hydroxypropyl guar gum powder, purchased from Guangrao Liuhe Chemical Co., Ltd.

[0021] Example 1: This example provides a method for preparing modified guar gum: 1. Preparation of zirconium oxychloride complex solution: Dissolve 7.5 parts of zirconium oxychloride octahydrate in 30 parts of deionized water by weight, stir at 25°C until completely dissolved, then slowly add 4.5 parts of 6 mol / L hydrochloric acid and stir for 30 min. 2. Add 260 parts of isopropanol to the reactor, add 50 parts of 32% sodium hydroxide solution under stirring at 25°C and mix well; add 100 parts of guar gum powder and heat to 43°C for alkalization for 65 min; add 42 parts of sodium chloroacetate and heat to 66°C for constant temperature reaction for 150 min. 3. Cool down to 50℃, and add the above zirconium hydroxychloride complex solution dropwise into the reaction vessel within 15 min. During the dropwise addition, maintain the pH at 5.0-5.5 with 5% NaOH solution. After the dropwise addition is complete, react for 90 min. 4. The above product was washed and filtered three times with an ethanol-water solution (volume ratio 7:3), then dried under vacuum at 55℃ and -0.08MPa for 240 min, and pulverized through an 180-mesh sieve to obtain inorganic coordination-modified guar gum.

[0022] Example 2: The composite conductive electrolyte provided in this example is composed of potassium chloride, sodium chloride, and anhydrous sodium citrate in a mass ratio of 6:3:1; the stabilizer is composed of 0.20 parts sodium thiosulfate and 0.10 parts disodium ethylenediaminetetraacetate (EDTA-2Na).

[0023] Example 1: This example provides an application of an electrochemically controllable gel-breaking, gel-free fracturing fluid, including the following steps: S1: Weigh out 0.6 parts of modified guar gum, 15 parts of composite conductive electrolyte, 0.30 parts of stabilizer, and the remainder is water, based on a total mass of 100 parts of the final fracturing fluid. S2: Add the modified guar gum to the water in 5 portions, with an interval of 10 minutes between each addition. After all the gum has been added, stir at 120 r / min for 15 minutes to obtain the mixture. S3: Add composite conductive electrolyte and stabilizer to the mixture. After all the electrolyte is added, continue stirring for 20 minutes to obtain a dispersion. Heat the mixture to 45°C and continue stirring for 30 minutes to allow it to swell and mature, thus obtaining an electrochemically controllable debonding fracturing fluid without a debonding agent.

[0024] S4: Reservoir fracturing operation; The fracturing fluid is injected into the oil and gas reservoir at a high pressure of 50 MPa to complete the fracturing, sand carrying and sand laying operations, and then the pressure is stabilized and left to stand for 10 minutes. S5: Electrochemically controlled gel breaking; Bipolar electrodes (2m apart, with the positive electrode located in the fracture extension zone) were installed downhole and connected to a low-voltage DC power supply (current density 15mA / cm²). 2 (voltage 20V) triggers a multi-stage coupled electrochemical reaction in the fracturing fluid through the action of an electric field, breaking the cross-linked bonds of polymers and achieving controllable gel breaking. The system employs a tiered power-on mode, with each tier lasting 60 seconds followed by a 5-second pause, repeated 10 times. S6: Well runoff completion; The viscosity of the return fluid was monitored in real time using a viscometer, and the detected viscosity was ≤5 mPa·s (170 s⁻¹). -1 Afterwards, low-viscosity liquid flowback operations were carried out (flowback pressure differential 5MPa, flowback velocity ≤15m). 3 The residue content was detected to be 75 mg / L by filtration and weighing method (method based on: "SY / T 5107-2016 Performance Evaluation Method of Water-based Fracturing Fluid"). This is significantly better than the standard requirement of ≤600 mg / L for conventional guar gum fracturing fluid and the recommended value of ≤200 mg / L for low-damage fracturing fluid in existing technology. After that, well completion was completed (running production tubing, installing wellhead, and delivering for production).

[0025] The method for purifying and recovering flowback fluid is as follows: A flocculant (such as polyaluminum chloride or nonionic polyacrylamide) is added to the flowback fluid after electrochemical gel breaking. After thorough mixing, the fluid is allowed to settle to remove suspended residues and fine colloidal particles, resulting in a supernatant. The supernatant is then filtered to remove residual fine suspended matter, yielding a clarified filtrate. This filtrate is then subjected to an electrochemical reaction to oxidize and degrade soluble organic pollutants in the liquid phase. The effluent after electrochemical oxidation is passed through an activated carbon adsorption device to adsorb and remove residual trace organic matter, resulting in purified water that is reused in the preparation of conductive fracturing fluids.

[0026] The test results showed that the reservoir damage rate of this method was 4.8%, which is less than 5% (method basis: "SY / T 6540-2021 Indoor Evaluation Method for Damage to Oil Reservoirs by Drilling Fluid and Completion Fluid").

[0027] Example 2: This example provides an application of an electrochemically controllable gel-breaking, gel-free fracturing fluid, including the following steps: S1: Weigh out 0.3 parts of modified guar gum, 5 parts of composite conductive electrolyte, 0.05 parts of stabilizer, and the remainder is water, based on a total mass of 100 parts of the final fracturing fluid. S2: Add the modified guar gum to the water in three portions, with a 5-minute interval between each addition. After all the gum has been added, stir at 60 rpm for 10 minutes to obtain the mixture. S3: Add composite conductive electrolyte and stabilizer to the mixture. After all the electrolyte is added, continue stirring for 10 minutes to obtain a dispersion. Heat the mixture to 25°C and continue stirring for 20 minutes to allow it to swell and mature, thus obtaining an electrochemically controllable debonding fracturing fluid without a debonding agent.

[0028] S4: Reservoir fracturing operation; The fracturing fluid is injected into the oil and gas reservoir at a high pressure of 50 MPa to complete the fracturing, sand carrying and sand laying operations, and then the pressure is stabilized and left to stand for 5 minutes. S5: Electrochemically controlled gel breaking; Bipolar electrodes (0.5m spacing, with the positive electrode located in the fracture extension zone) were installed downhole and connected to a low-voltage DC power supply (current density 5mA / cm²). 2 (5V voltage) triggers a multi-stage coupled electrochemical reaction in the fracturing fluid through the action of an electric field, breaking the cross-linked bonds of polymers and achieving controllable gel breaking. The system employs a tiered power-on mode, with each tier lasting 30 seconds followed by a 2-second pause, repeated 3 times. S6: Well runoff completion; The viscosity of the return fluid was monitored in real time using a viscometer, and the detected viscosity was ≤5 mPa·s (170 s⁻¹). -1 Afterwards, low-viscosity liquid flowback operations were carried out (flowback pressure differential 2MPa, flowback velocity ≤15m). 3 The residue content was found to be 67 mg / L after filtration and weighing, and the well was then completed (production tubing was run, wellhead was installed, and the well was handed over for production).

[0029] The method for purifying and recovering flowback fluid is as follows: A flocculant (such as polyaluminum chloride or nonionic polyacrylamide) is added to the flowback fluid after electrochemical gel breaking. After thorough mixing, the fluid is allowed to settle to remove suspended residues and fine colloidal particles, resulting in a supernatant. The supernatant is then filtered to remove residual fine suspended matter, yielding a clarified filtrate. This filtrate is then subjected to an electrochemical reaction to oxidize and degrade soluble organic pollutants in the liquid phase. The effluent after electrochemical oxidation is passed through an activated carbon adsorption device to adsorb and remove residual trace organic matter, resulting in purified water that is reused in the preparation of conductive fracturing fluids.

[0030] Testing showed that this method caused a reservoir damage rate of 3.8%, which is less than 5%.

[0031] Example 3: This example provides an application of an electrochemically controllable gel-breaking, gel-free fracturing fluid, including the following steps: S1: Weigh out 0.5 parts of modified guar gum, 10 parts of composite conductive electrolyte, 0.20 parts of stabilizer, and the remainder is water, based on a total mass of 100 parts of the final fracturing fluid. S2: Add the modified guar gum to the water in 5 portions, with an interval of 5 minutes between each addition. After all the gum has been added, stir at 100 r / min for 12 minutes to obtain a mixture. S3: Add composite conductive electrolyte and stabilizer to the mixture. After all the electrolyte is added, continue stirring for 16 minutes to obtain a dispersion. Heat the mixture to 40°C and continue stirring for 20 minutes to allow it to swell and mature, thus obtaining an electrochemically controllable debonding fracturing fluid without a debonding agent.

[0032] S4: Reservoir fracturing operation; The fracturing fluid is injected into the oil and gas reservoir at a high pressure of 50 MPa to complete the fracturing, sand carrying and sand laying operations, and then stabilized and allowed to stand for 8 minutes. S5: Electrochemically controlled gel breaking; Bipolar electrodes (1m apart, with the positive electrode located in the fracture extension zone) were installed downhole and connected to a low-voltage DC power supply (current density 10mA / cm²). 2 (voltage 10V) triggers a multi-stage coupled electrochemical reaction in the fracturing fluid through the action of an electric field, breaking the cross-linked bonds of polymers and achieving controllable gel breaking. The system employs a tiered power-on mode, with each tier lasting 40 seconds followed by a 5-second pause, repeated 8 times. S6: Well runoff completion; The viscosity of the return fluid was monitored in real time using a viscometer, and the detected viscosity was ≤5 mPa·s (170 s⁻¹). -1 Afterwards, low-viscosity liquid flowback operations were carried out (flowback pressure differential 3MPa, flowback velocity ≤15m). 3 / h), the residue content was detected by filtration and weighing method to be 79mg / L, and then the well completion was completed (running production tubing, installing wellhead, and handing over to production).

[0033] The method for purifying and recovering flowback fluid is as follows: A flocculant (such as polyaluminum chloride or nonionic polyacrylamide) is added to the flowback fluid after electrochemical gel breaking. After thorough mixing, the fluid is allowed to settle to remove suspended residues and fine colloidal particles, resulting in a supernatant. The supernatant is then filtered to remove residual fine suspended matter, yielding a clarified filtrate. This filtrate is then subjected to an electrochemical reaction to oxidize and degrade soluble organic pollutants in the liquid phase. The effluent after electrochemical oxidation is passed through an activated carbon adsorption device to adsorb and remove residual trace organic matter, resulting in purified water that is reused in the preparation of conductive fracturing fluids.

[0034] The test results showed that this method caused a reservoir damage rate of 4.1%, which is less than 5%.

[0035] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions will not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. An electrochemically controllable, non-breakable fracturing fluid, characterized in that, By mass percentage, it consists of the following components: 0.3-0.6% modified guar gum, 5-15% composite conductive electrolyte, 0.05-0.30% stabilizer, and the balance being water.

2. A fracturing fluid with electrochemically controllable gel breaking and no gel breaking agent as described in claim 1, characterized in that, The method for preparing the modified guar gum is as follows: S1. Preparation of zirconium oxychloride complex solution: Take 7.5 parts by mass of zirconium oxychloride octahydrate and dissolve it in 30 parts of deionized water. Stir until completely dissolved, then add hydrochloric acid dropwise and stir. S2. Add 260 parts of isopropanol to the reactor, add 50 parts of 32% sodium hydroxide solution under stirring at room temperature and mix well; add 100 parts of guar gum powder, heat to 43°C and alkalize, add 42 parts of sodium chloroacetate and further heat to 66°C, and react at a constant temperature. S3. Cool to 50°C and add the zirconium hydroxychloride complex solution dropwise into the reaction vessel. During the dropwise addition process, maintain the pH at 5.0-5.

5. After the dropwise addition is complete, continue the reaction. Then, wash, filter, vacuum dry, pulverize and sieve to obtain the final product.

3. A fracturing fluid with electrochemically controllable gel breaking as described in claim 1, characterized in that, The composite conductive electrolyte is composed of potassium chloride, sodium chloride, and anhydrous sodium citrate in a mass ratio of 6:3:1; the stabilizer is composed of 0.20 parts sodium thiosulfate and 0.10 parts disodium ethylenediaminetetraacetate (EDTA-2Na).

4. A fracturing fluid with electrochemically controllable gel breaking and no gel breaking agent as described in claim 2, characterized in that, In step S2, the alkalization treatment time is 50-70 min, and the isothermal reaction time is 140-160 min.

5. A method for preparing an electrochemically controllable, breaker-free fracturing fluid as described in claim 1, characterized in that, Includes the following steps: Modified guar gum is added to water, and the mixture is stirred at 60-120 r / min to obtain a mixture. A composite conductive electrolyte and a stabilizer are added to the mixture, and the mixture is stirred to obtain a dispersion. The temperature is raised to 25-45℃, and the mixture is stirred for 20-30 min to swell and mature, thus obtaining an electrochemically controllable debonding fracturing fluid without a debonding agent.

6. A method for applying the electrochemically controllable gel-breaking fracturing fluid without a gel-breaking agent as described in claims 1-5, characterized in that, Includes the following steps: A1. Reservoir fracturing operations; The fracturing fluid is injected into the oil and gas reservoir to complete the fracturing, sand carrying and sand laying operations, and then the pressure is stabilized and left to stand. A2. Electrochemically controlled gel breaking; By deploying bipolar electrodes downhole and connecting them to a low-voltage DC power supply, the fracturing fluid undergoes a multi-stage coupled electrochemical reaction triggered by the electric field, breaking the cross-linked bonds of polymers and achieving controllable gel breaking. A3. Flowback completion; Real-time monitoring of the flowback fluid viscosity; once the viscosity is ≤5 mPa·s, low-viscosity fluid flowback operation is carried out; once the residue content is ≤200 mg / L, well completion is completed.

7. The application of the electrochemically controllable gel-breaking, gel-free fracturing fluid according to claim 6, characterized in that, In A1, the voltage stabilization and settling time is 5-10 minutes.

8. The application of the electrochemically controllable gel-breaking, gel-free fracturing fluid according to claim 6, characterized in that, In A2, the current density of the low-voltage DC power supply is 5-15 mA / cm². 2 Voltage 5-20V.

9. The application of the electrochemically controllable gel-breaking, gel-free fracturing fluid according to claim 6, characterized in that, In A2, a graded power-on mode is adopted, with each stage lasting 30-60 seconds, followed by a 2-5 second pause, and repeated 3-10 times.

10. The application of the electrochemically controllable gel-breaking, gel-free fracturing fluid according to claim 6, characterized in that, In A3, the backflow pressure differential is 2-5 MPa, and the backflow velocity is ≤15 m / s. 3 / h.

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