Composite acid liquid system for plug removal and augmented injection of profile control water injection well and preparation method of composite acid liquid system and plug removal and augmented injection method of composite acid liquid system

Abstract

The invention relates to the technical field of oilfield development, in particular to a composite acid liquid system for plug removal and augmented injection of a profile control water injection well and a preparation method of the composite acid liquid system and a plug removal and augmented injection method.The composite acid liquid system for plug removal and augmented injection of the profile control water injection well comprises composite pre-acid liquid, composite main body acid liquid, composite post-acid liquid and displacing liquid, the method comprises the following steps: adding a required amount of ammonium persulfate into a mixed solution of hydrochloric acid, a corrosion inhibitor, a viscosity stabilizer and an iron stabilizer, and uniformly stirring and mixing to obtain a composite pre-acid solution; adding a required amount of ammonium persulfate into a mixed solution of hydrochloric acid, hydrofluoric acid, fluoboric acid, a corrosion inhibitor, a viscosity stabilizer and an iron stabilizer, and uniformly stirring and mixing to obtain a composite main body acid solution; adding a required amount of ammonium persulfate into a mixed solution of hydrochloric acid, a corrosion inhibitor, a viscosity stabilizer and an iron stabilizer, and uniformly stirring and mixing to obtain a composite post-acid solution; the displacing fluid is demineralized water. The problems of high pump injection pressure and difficult water injection after profile control of the water injection well are effectively solved, and the daily water injection rate of the profile control water injection well is increased.

Description

Technical Field

[0001] This invention relates to the field of oilfield development technology, and is a composite acid system for profile control and water injection well unblocking and injection enhancement, as well as its preparation method and unblocking and injection enhancement method. Background Technology

[0002] With the development of my country's petrochemical industry, major oilfields in my country have entered the middle and late stages of development. To replenish formation energy, water injection technology is now widely used in oilfields. During water injection development, the heterogeneity of the formation in the injection well can lead to a decrease in water injection capacity, premature water breakthrough in the oil well, and the inability to effectively release reservoir energy.

[0003] Water injection well profile control technology is a commonly used oil enhancement measure in my country's oilfield development. It primarily involves injecting profile control agents to adjust the flow characteristics of crude oil within the wellbore, thereby increasing oil recovery. However, with its expanding application, problems with this technology have become increasingly apparent. After using polymeric micelle profile control agents, residues remaining in the wellbore, orifices, and formation gradually clog these areas over time. This leads to a gradual decrease in injection volume and a gradual increase in injection pressure, eventually reaching formation system pressure and causing a high-pressure injection failure. This severely impacts injection efficiency and results in a significant waste of resources during oilfield development. Therefore, effectively addressing the clogging issues caused by polymeric micelle profile control agents is a decisive factor in the success of improving water injection enhancement in profile-controlled water injection wells.

[0004] In recent years, acidizing has been performed on injection wells after profile modification to remove blockages, but some wells still cannot meet the requirements for increased injection even after multiple rounds of acidizing. The high pressure and injection difficulties encountered after profile modification of injection wells remain technical challenges that companies have been unable to solve. Summary of the Invention

[0005] This invention provides a composite acid system for unblocking and increasing injection in profile-adjusted water injection wells, along with its preparation method and unblocking and injection method. This overcomes the shortcomings of the prior art and can effectively solve the problems of high pressure and difficult water injection that exist after profile adjustment in existing water injection wells.

[0006] One of the technical solutions of this invention is achieved through the following measures: a composite acid system for profile control and injection well unblocking and injection enhancement, comprising a composite pre-acid solution, a composite main acid solution, a composite post-acid solution, and a displacement fluid, prepared according to the following method: To prepare the composite pre-acid solution, add the required amount of ammonium persulfate to a mixed solution of hydrochloric acid, corrosion inhibitor, adhesive stabilizer, and iron stabilizer, and stir until homogeneous to obtain the composite pre-acid solution. To prepare the composite main acid solution, add the required amount of ammonium persulfate to a mixed solution of hydrochloric acid, hydrofluoric acid, fluoroboric acid, corrosion inhibitor, adhesive stabilizer, and iron stabilizer, and stir until homogeneous to obtain the composite main acid solution. To prepare the composite post-acid solution, add the required amount of ammonium persulfate to a mixed solution of hydrochloric acid, corrosion inhibitor, adhesive stabilizer, and iron stabilizer, and stir until homogeneous to obtain the composite post-acid solution. Prepare a displacement solution, which is water.

[0007] The following are further optimizations and / or improvements to one of the above-mentioned technical solutions: The aforementioned composite pre-acid solution comprises, by weight percentage, 8% to 12% hydrochloric acid, 1% to 3% corrosion inhibitor, 1% to 2% adhesion stabilizer, 1% to 2% iron stabilizer, 1% to 2% ammonium persulfate, and the remainder being water.

[0008] The above-mentioned composite pre-acid solution, by weight percentage, consists of 8% hydrochloric acid, 2% corrosion inhibitor, 1% adhesion stabilizer, 1% iron stabilizer, 2% ammonium persulfate, and the remainder is water.

[0009] The aforementioned composite acid solution comprises, by weight percentage, 8% to 12% hydrochloric acid, 1% to 3% hydrofluoric acid, 3% to 5% fluoroboric acid, 1% to 3% corrosion inhibitor, 1% to 2% adhesion stabilizer, 1% to 2% iron stabilizer, 1% to 2% ammonium persulfate, and the remainder being water.

[0010] The aforementioned composite acid solution, by weight percentage, consists of 12% hydrochloric acid, 2% hydrofluoric acid, 4% fluoroboric acid, 2% corrosion inhibitor, 1% adhesion stabilizer, 1% iron stabilizer, 2% ammonium persulfate, and the remainder is water.

[0011] The above-mentioned components, by weight percentage, are 8% to 12% hydrochloric acid, 1% to 3% corrosion inhibitor, 1% to 2% adhesion stabilizer, 1% to 2% iron stabilizer, 1% to 2% ammonium persulfate, and the remainder is water.

[0012] The above-mentioned composite post-acid solution, by weight percentage, consists of 10% hydrochloric acid, 2% corrosion inhibitor, 1% adhesion stabilizer, 1% iron stabilizer, 2% ammonium persulfate, and the remainder is water.

[0013] The iron stabilizer is citric acid, the viscosity stabilizer is a cationic quaternary ammonium salt, the fluoroboric acid is a 50% aqueous solution by weight, the corrosion inhibitor is alkylphenol polyoxyethylene ether, the alkylphenol polyoxyethylene ether is a 30% to 40% aqueous solution by weight, the hydrochloric acid is a 31% aqueous solution by weight, and the hydrofluoric acid is a 40% aqueous solution by weight.

[0014] The second technical solution of the present invention is achieved through the following measures: a method for preparing a composite acid system for profile control, unblocking, and increasing injection in water injection wells, comprising: To prepare the composite pre-acid solution, add the required amount of ammonium persulfate to a mixed solution of hydrochloric acid, corrosion inhibitor, adhesive stabilizer, and iron stabilizer, and stir until homogeneous to obtain the composite pre-acid solution. To prepare the composite main acid solution, add the required amount of ammonium persulfate to a mixed solution of hydrochloric acid, hydrofluoric acid, fluoroboric acid, corrosion inhibitor, adhesive stabilizer, and iron stabilizer, and stir until homogeneous to obtain the composite main acid solution. To prepare the composite post-acid solution, add the required amount of ammonium persulfate to a mixed solution of hydrochloric acid, corrosion inhibitor, adhesive stabilizer, and iron stabilizer, and stir until homogeneous to obtain the composite post-acid solution. Prepare a displacement solution, which is water.

[0015] The third technical solution of the present invention is achieved through the following measures: a method for unblocking and increasing injection in profile-adjusting water injection wells using a composite acid system, comprising: The first step is to close the wellhead passage of the profile control injection well, inject clean water into the acidizing surface pipeline of the profile control injection well, and conduct a leakage pressure test on the acidizing surface pipeline to determine the sealing performance of the acidizing surface pipeline. The second step is to open the wellhead passage of the profile control injection well and inject the required amount of clean water into the profile control injection well through the acidification surface pipeline to conduct a limited internal pressure test to confirm the normal water absorption of the formation below the profile control injection well. The third step involves injecting the composite pre-acid, composite main acid, and composite post-acid into the profile control injection well in sequence at varying rates to establish a downhole pulse wave hydraulic oscillation field and remove blockages in the near-wellbore area. Then, a displacement fluid is injected into the profile control injection well to displace and squeeze the acid to a deeper depth, thus achieving deep unblocking of the profile control injection well. The fourth step involves not flushing back the acid solution from the injection well, and injecting it directly after the required reaction time has elapsed.

[0016] This invention can not only effectively solve the problem of blockage caused by polymeric micelle profile control agents in water injection wells, but also remove blockages caused by inorganic scale, mechanical impurities, clay expansion and particle migration accumulated in the near-wellbore zone, as well as blockages caused by drilling solid particles. At the same time, it maintains a low pH environment in the near-wellbore zone to prevent precipitation and accumulation, thus preventing secondary precipitation. It effectively solves the problems of high pumping pressure and difficult water injection after profile control in water injection wells, thereby ensuring an increase in the daily injection volume of profile-controlled water injection wells. Detailed Implementation

[0017] This invention is not limited to the following embodiments, and specific implementation methods can be determined according to the technical solutions and actual conditions of this invention. Unless otherwise specified, all chemical reagents and chemicals mentioned in this invention are well-known and commonly used chemical reagents and chemicals in the prior art; unless otherwise specified, all percentages in this invention are weight percentages; unless otherwise specified, the solvent in the solutions in this invention is an aqueous solution of water; room temperature in this invention generally refers to a temperature between 15°C and 25°C, generally defined as 25°C.

[0018] The present invention will be further described below with reference to embodiments: Example 1: The composite acid system for profile control and injection well unblocking and injection enhancement includes composite pre-acid, composite main acid, composite post-acid, and displacement fluid, and is prepared according to the following method: To prepare the composite pre-acid solution, add the required amount of ammonium persulfate to a mixed solution of hydrochloric acid, corrosion inhibitor, adhesive stabilizer, and iron stabilizer, and stir until homogeneous to obtain the composite pre-acid solution. To prepare the composite main acid solution, add the required amount of ammonium persulfate to a mixed solution of hydrochloric acid, hydrofluoric acid, fluoroboric acid, corrosion inhibitor, adhesive stabilizer, and iron stabilizer, and stir until homogeneous to obtain the composite main acid solution. To prepare the composite post-acid solution, add the required amount of ammonium persulfate to a mixed solution of hydrochloric acid, corrosion inhibitor, adhesive stabilizer, and iron stabilizer, and stir until homogeneous to obtain the composite post-acid solution. Prepare a displacement solution, which is water; Prepare a displacement solution, which is demineralized water.

[0019] As needed, the method for optimizing the dosage of ammonium persulfate includes: adding different amounts of ammonium persulfate to the required concentration of profile control agent, measuring the final viscosity of the profile control agent under different dosages of ammonium persulfate at the same reaction time and temperature, and optimizing the ammonium persulfate concentration to 1% to 2% by weight when the degradation rate of the profile control agent is the highest. The experimental basis for optimizing the dosage of ammonium persulfate (APS) is shown in Table 1.

[0020] Table 1 shows that as the amount of ammonium persulfate (APS) increases, the final viscosity of the profile control agent decreases rapidly. When the amount of ammonium persulfate (APS) exceeds 1%, the rate of degradation of the profile control agent slows down, and when the amount of ammonium persulfate (APS) exceeds 2%, the degradation rate of the profile control agent remains essentially unchanged. 1% to 2% of ammonium persulfate (APS) achieves the oxidative destruction of the polymer structure and removes the organic pollution blockage from the profile control injection well.

[0021] Example 2: As an optimization of the above example, the composite pre-acid solution comprises, by weight percentage, 8% to 12% hydrochloric acid, 1% to 3% corrosion inhibitor, 1% to 2% adhesion stabilizer, 1% to 2% iron stabilizer, 1% to 2% ammonium persulfate, and the remainder being water.

[0022] Example 3: As an optimization of the above example, the composite pre-acid solution consists of 8% hydrochloric acid, 2% corrosion inhibitor, 1% adhesion stabilizer, 1% iron stabilizer, 2% ammonium persulfate, and the remainder is water by weight percentage.

[0023] As needed, composite pre-acid solutions can remove inorganic scale and mechanical impurities accumulated in the near-wellbore zone.

[0024] Example 4: As an optimization of the above example, the composite main acid solution, by weight percentage, is 8% to 12% hydrochloric acid, 1% to 3% hydrofluoric acid, 3% to 5% fluoroboric acid, 1% to 3% corrosion inhibitor, 1% to 2% adhesion stabilizer, 1% to 2% iron stabilizer, 1% to 2% ammonium persulfate, and the remainder is water.

[0025] Example 5: As an optimization of the above example, the composite main acid solution, by weight percentage, is 12% hydrochloric acid, 2% hydrofluoric acid, 4% fluoroboric acid, 2% corrosion inhibitor, 1% adhesion stabilizer, 1% iron stabilizer, 2% ammonium persulfate, and the remainder is water.

[0026] As needed, the composite main acid solution is prepared by using hydrochloric acid to dissolve hydrochloric acid-soluble substances such as calcium. In the subsequent acidizing process of profile control injection wells, hydrofluoric acid can effectively dissolve exposed sand and clay minerals downhole, relieve the blockage caused by clay expansion in the downhole formation and the migration and blockage of downhole formation particles, as well as blockage caused by drilling solid particles, such as bentonite (soluble in hydrofluoric acid) and barium salts (barium sulfate and barium sulfide are soluble in hydrofluoric acid), and expand the pore throat space, thereby achieving the purpose of increasing injection in profile control injection wells.

[0027] Example 6: As an optimization of the above example, the composition by weight percentage is 8% to 12% hydrochloric acid, 1% to 3% corrosion inhibitor, 1% to 2% adhesion stabilizer, 1% to 2% iron stabilizer, 1% to 2% ammonium persulfate, and the remainder is water.

[0028] Example 7: As an optimization of the above example, the composite post-acid solution consists of 10% hydrochloric acid, 2% corrosion inhibitor, 1% adhesion stabilizer, 1% iron stabilizer, 2% ammonium persulfate, and the remainder is water, by weight percentage.

[0029] As needed, the composite post-acid solution can maintain a low pH environment in the near-wellbore zone, preventing sediment from accumulating in the near-wellbore zone and thus preventing secondary sedimentation.

[0030] Example 8: As an optimization of the above example, the iron stabilizer is citric acid, the viscosity stabilizer is a cationic quaternary ammonium salt, the fluoroboric acid is a 50% aqueous solution by weight, the corrosion inhibitor is alkylphenol polyoxyethylene ether, the alkylphenol polyoxyethylene ether is a 30% to 40% aqueous solution by weight, the hydrochloric acid is a 31% aqueous solution by weight, and the hydrofluoric acid is a 40% aqueous solution by weight.

[0031] As needed, a 50% fluoroboric acid aqueous solution can stabilize downhole clay and downhole formation particles. This effect is due to both chemical and physical factors. The main factor is that the hydrofluoric acid produced by the hydrolysis of fluoroboric acid destroys the nature of clay minerals and reduces the cation exchange capacity of the residual soil.

[0032] As needed, during the acidizing process of profile control injection wells, alkylphenol polyoxyethylene ethers can slow down the chemical corrosion of the well casing, tubing and other metal equipment that the acid solution contacts.

[0033] Depending on the need, cationic quaternary ammonium salts can be used to prevent the swelling of downhole formation clay and stabilize downhole formation clay particles.

[0034] As needed, during the acidizing process of profile control injection wells, citric acid (C6H8O7) can reduce Fe... 3+ Reduced to Fe 2+ It can also form stable iron complexes with iron ions in acid solutions, thereby reducing the formation of Fe(OH)3 precipitate and achieving the purpose of stabilizing iron ions.

[0035] Example 9: A method for preparing the composite acid system for profile control and injection well unblocking and injection enhancement, comprising: To prepare the composite pre-acid solution, add the required amount of ammonium persulfate to a mixed solution of hydrochloric acid, corrosion inhibitor, adhesive stabilizer, and iron stabilizer, and stir until homogeneous to obtain the composite pre-acid solution. To prepare the composite main acid solution, add the required amount of ammonium persulfate to a mixed solution of hydrochloric acid, hydrofluoric acid, fluoroboric acid, corrosion inhibitor, adhesive stabilizer, and iron stabilizer, and stir until homogeneous to obtain the composite main acid solution. To prepare the composite post-acid solution, add the required amount of ammonium persulfate to a mixed solution of hydrochloric acid, corrosion inhibitor, adhesive stabilizer, and iron stabilizer, and stir until homogeneous to obtain the composite post-acid solution. Prepare a displacement solution, which is water.

[0036] Example 10: As an optimization of the above examples, the preparation method of the composite acid system for profile control injection well unblocking and injection enhancement is carried out according to the following steps: To prepare a composite pre-acid solution, by weight percentage, add 2% ammonium persulfate to a mixed solution of 8% hydrochloric acid, 2% corrosion inhibitor, 1% adhesion stabilizer, and 1% iron stabilizer, and stir until homogeneous to obtain the composite pre-acid solution. To prepare the composite main acid solution, by weight percentage, add 2% ammonium persulfate to a mixed solution of 12% hydrochloric acid, 2% hydrofluoric acid, 4% fluoroboric acid, 2% corrosion inhibitor, 1% adhesion stabilizer, and 1% iron stabilizer, and stir to mix evenly to obtain the composite main acid solution. To prepare a composite post-acid solution, by weight percentage, add 2% ammonium persulfate to a mixed solution of 10% hydrochloric acid, 2% corrosion inhibitor, 1% adhesion stabilizer, and 1% iron stabilizer, and stir until homogeneous to obtain the composite post-acid solution. Prepare a displacement solution, which is water.

[0037] As required, the specific steps for evaluating the corrosion inhibition performance of the composite acid system used for profile control and injection well unblocking in this invention include: First, immersing the N80 steel sheet (of the same or similar material as the well casing, well casing, and other metal equipment at the injection site) in acetone for 15 minutes; Second, cleaning the N80 steel sheet with degreased cotton balls and then immersing it in anhydrous ethanol for 15 minutes; Third, air-drying the soaked N80 steel sheet on filter paper, weighing it on a balance, recording the weight of the N80 steel sheet as W1, and measuring the length L, width C, and thickness H of the N80 steel sheet; Fourth, using the suspension method, placing the N80 steel sheet into an experimental bottle containing the composite acid system of this invention, and placing the experimental bottle in a water bath heater, heating it to 70°C, and then keeping it at a constant temperature for 4 hours; Fifth, cleaning the N80 steel sheet taken out of the experimental bottle and weighing it again as W2.

[0038] The corrosion rate of N80 metal materials by the composite acid system is calculated according to the following formula: Surface area of ​​the test piece: S 表 =[(L×C)+(L×H)+(C×H)]×2 Corrosion rate: V = [(W1 - W2) / (h × S)] 表 )] Among them, S 表 denoted as , where L is the surface area of ​​the N80 steel sheet; L is the length of the N80 steel sheet; C is the width of the N80 steel sheet; H is the thickness of the N80 steel sheet; h is the deepest corrosion depth of the N80 steel sheet surface in the composite acid system; W1 is the weight of the N80 steel sheet before acid etching by the composite acid system; and W2 is the weight of the N80 steel sheet after acid etching by the composite acid system.

[0039] Using the same corrosion inhibition performance evaluation experimental methods and conditions as described above, the corrosion rates of the composite acid system on three types of N80 steel sheets of the same specifications are shown in Table 2.

[0040] The data in Table 2 show that the average corrosion rate (η=2.7525) of the composite acid system of the present invention on well casing, well string and other metal equipment at the injection site made of N80 material and similar materials meets the national standard requirements (η≤6).

[0041] Example 11: This composite acid system is used for unblocking and increasing injection in profile-adjusting water injection wells, and is carried out according to the following steps: The first step is to close the wellhead passage of the profile control injection well, inject clean water into the acidizing surface pipeline of the profile control injection well, and conduct a leakage pressure test on the acidizing surface pipeline to determine the sealing performance of the acidizing surface pipeline. The second step is to open the wellhead passage of the profile control injection well and inject the required amount of clean water into the profile control injection well through the acidification surface pipeline to conduct a limited internal pressure test to confirm the normal water absorption of the formation below the profile control injection well. The third step involves injecting the composite pre-acid, composite main acid, and composite post-acid into the profile control injection well in sequence at varying rates to establish a downhole pulse wave hydraulic oscillation field and remove blockages in the near-wellbore area. Then, a displacement fluid is injected into the profile control injection well to displace and squeeze the acid to a deeper depth, thus achieving deep unblocking of the profile control injection well. The fourth step involves not flushing back the acid solution from the injection well, and injecting it directly after the required reaction time has elapsed.

[0042] The total volume V of the composite acid solution required should be calculated according to the following formula: V = πR 2 ×h×Φ Where V is the total volume of the composite main acid solution used, m 3 R is the radius of acid treatment for profile control injection wells, in meters; h is the effective thickness of the injection layer in profile control injection wells, in meters; Φ is the average porosity of the injection layer in profile control injection wells, in percent.

[0043] The displacement fluid is either clean water or water from the injection network process. The displacement fluid injection volume is calculated according to the following formula: S = H1 × L1 + H2 × L2 Where S is the displacement fluid injection volume, m 3 H1 is the position of the pipe foot, in meters; H2 is the thickness from H1 to the bottom of the perforated section, in meters; L1 is the internal volume of the well casing, in meters. 3 / 1000m; L2 is the annulus volume of the well casing, in m³. 3 / 1000m.

[0044] Example 12: A method for unblocking and increasing injection in a profile control well using a composite acid system, which is carried out according to the following steps: Historical production overview of a certain profile control and water injection well No. 1 in a certain oilfield: Drilling began on November 10, 2015, and was completed on November 18, 2015, with a total depth of 1825m and a completed formation J2x. Five profile control measures (composite gel profile control) and one conventional acidizing treatment (clay slow-release acid and chelated acid) were performed; however, none of these measures achieved the required increase in water injection.

[0045] On January 5, 2023, acidizing and boosting injection using the composite acid system described in this invention was carried out on this well. A 73mm tubing and a K341 packer were used for injection. The average formation porosity was 13.4%, the pretreatment radius for acidizing and boosting injection was 2.6m, the tubing toe position was 1797.69m, and the designed injection volume was 10m³. 3 / day, the composite acid system of the present invention for unblocking and increasing injection in the section of this well (1765.0-1775.6m / 10.6m) is used for acidizing and increasing injection. The composite pre-acid solution consists of the following components by weight percentage: hydrochloric acid 8%, corrosion inhibitor 2%, adhesion stabilizer 1%, iron stabilizer 1%, and ammonium persulfate 2%.

[0046] The total volume of the composite pre-acid solution used is 10m³. 3 (Designed to allocate 10m³ of water per day) 3 Based on the density of water, the total weight of the composite pre-acid solution is estimated to be 10,000 kg. The amounts of each component in the composite pre-acid solution are as follows: 800 kg of hydrochloric acid aqueous solution (containing 31% hydrochloric acid), 200 kg of corrosion inhibitor, 100 kg of adhesion stabilizer, 100 kg of iron stabilizer, 200 kg of ammonium persulfate, and 8,600 kg of water.

[0047] The composite acid solution consists of the following components by weight percentage: hydrochloric acid 12%, hydrofluoric acid 2%, fluoroboric acid 4%, corrosion inhibitor 2%, adhesion stabilizer 1%, iron stabilizer 1%, and ammonium persulfate 2%.

[0048] The total volume V of the composite acid solution is calculated according to the following formula: V = πR 2 ×h×Φ=3.14×2.6×2.6×10.6×13.4%=30.14≈30m 3 Where V is the total volume of the composite main acid solution used, m 3 R is the pretreatment radius of the profile-adjusting injection well (m); h is the effective thickness of the injection layer in the profile-adjusting injection well (m); Φ is the average formation porosity of the injection layer in the profile-adjusting injection well (%).

[0049] The total volume of the composite acid solution used is 30m³. 3 Based on the density of water, the total weight of the composite acid solution is estimated to be 30,000 kg. The components in the composite acid solution include: 3,600 kg of hydrochloric acid aqueous solution (containing 31% hydrochloric acid), 600 kg of hydrofluoric acid aqueous solution (containing 40% hydrofluoric acid), 1,200 kg of fluoroboric acid aqueous solution (containing 50% fluoroboric acid), 600 kg of corrosion inhibitor, 300 kg of adhesion stabilizer, 300 kg of iron stabilizer, 600 kg of ammonium persulfate, and 22,800 kg of water.

[0050] The composite post-acid solution consists of the following components by weight percentage: hydrochloric acid 10%, corrosion inhibitor 2%, adhesion stabilizer 1%, iron stabilizer 1%, and ammonium persulfate 2%.

[0051] The total volume of the composite post-acid solution used is 10m³. 3 (Designed to allocate 10m³ of water per day) 3Based on the density of water, the total weight of the composite post-acid solution is estimated to be 10,000 kg. The amounts of each component in the composite post-acid solution are as follows: 1,000 kg of hydrochloric acid aqueous solution (containing 31% hydrochloric acid), 200 kg of corrosion inhibitor, 100 kg of adhesion stabilizer, 100 kg of iron stabilizer, 200 kg of ammonium persulfate, and 8,400 kg of water.

[0052] The displacement fluid is entirely composed of clean water or water from the injection pipeline process, which displaces the acid into deeper layers of the formation to achieve the purpose of deep unblocking.

[0053] The injection volume S of the displacement fluid is calculated using the following formula: S=H1×L1+H2×L2=1775.6×3.02 / 1000+(1797.69-1775.6)×(11.56-3.02) / 1000 =5.36 + 0.19 = 5.55 ≈ 6m 3 Where S is the displacement fluid injection volume, m 3 H1 is the position of the pipe foot, in meters; H2 is the thickness from H1 to the bottom of the perforated section, in meters; L1 is the internal volume of the well casing, in meters. 3 / 1000m; L2 is the annulus volume of the well casing, in m³. 3 / 1000m.

[0054] The total weight of the displacement solution is calculated to be 6000 kg based on the density of water.

[0055] The composite acid system of the present invention is used in a method for unclogging and increasing injection in profile-adjusting water injection wells, and is carried out according to the following steps: The first step is to close the wellhead passage of the profile control injection well, inject clean water into the acidizing surface pipeline of the profile control injection well, and conduct a leakage pressure test on the acidizing surface pipeline to determine the sealing performance of the acidizing surface pipeline (high pressure and low pressure pipelines). The second step is to open the wellhead passage of the profile control injection well and pour 2m... 3 Clean water was injected into the profile control injection well through the acidified surface pipeline. The internal pressure was limited to 34MPa for test squeezing to confirm the normal water absorption of the formation below the profile control injection well. 50m³ of the prepared compound acid solution, used for profile control, unclogging, and enhanced injection in water injection wells, was transported using a specialized acid tanker truck. 3 (10m of composite pre-acid solution) 3 Composite main acid solution 30m 3 10m of composite post-acid solution 3 Transport the equipment to the well site and seal the outlet of the acidizing surface pipeline (high-pressure and low-pressure pipelines) to the wellhead of the profile control injection well; The third step involves injecting the composite pre-acid, composite main acid, and composite post-acid into the profile control injection well in sequence at varying rates to establish a downhole pulse wave hydraulic oscillation field and remove blockages in the near-wellbore area. Then, a displacement fluid is injected into the profile control injection well to displace and squeeze the acid to a deeper depth, thus achieving deep unblocking of the profile control injection well. In the third step, the composite pre-acid solution variable displacement injection method includes: the first injection of 5m 3 Displacement is 300 L / min, pump pressure is less than 34 MPa; second injection is 5 m 3 The displacement is 400L / min, and the pump pressure is less than 34MPa. The composite main body acid solution variable displacement injection method includes: the first injection of 10m 3 Displacement is 300 L / min, pump pressure is less than 34 MPa; second injection is 10 m 3 Displacement is 400 L / min, pump pressure is less than 34 MPa; third injection is 10 m 3 The displacement is 300 L / min, and the pump pressure is less than 34 MPa. The composite post-acid variable displacement injection method includes: initial injection of 5m 3 Displacement is 400 L / min, pump pressure is less than 34 MPa; second injection is 5 m 3 The displacement is 300 L / min, and the pump pressure is less than 34 MPa. The displacement fluid injection volume is 6 cubic meters, the discharge rate is 300 L / min, and the pump pressure is less than 34 MPa. The fourth step is to prevent the acid in the injection well from being flushed back and to inject it directly after the well has been shut in for 2 hours (to start production).

[0056] This invention relates to a composite acid system for unblocking and enhancing injection in profile-adjusting injection wells. After unblocking and enhancing injection in profile-adjusting injection well 1, the pump injection pressure of well 1 decreased from 24 MPa to 12.54 MPa after acidizing. The designed injection volume is 10 m³ / s. 3 / day, the actual injection volume after acidification is reduced from 2m³ / day. 3 / rise to 10m 3 / sky.

[0057] Example 13: A method for unblocking and increasing injection in a profile control well using a composite acid system, which is carried out according to the following steps: Historical production overview of well 2 in a certain oilfield: Drilling began on October 11, 2018, and was completed on November 6, 2018. The completed formation was J2s, and the completed well depth was 3732m. On May 10, 2019, to improve the regional injection-production well network, a conversion to injection was implemented. On May 9, 2021, due to uneven activation of the injection profile shown by water absorption profile testing, inorganic gel profile control measures were implemented on the well. The inorganic gel consisted of sodium silicate and sodium hydroxide. On October 16, 2021, during the profile control operation, the injection pressure was 26.4MPa, and the actual injected water volume was 3.5m³. 3 / day, injection has been suspended due to severe under-injection; on May 22, 2022, conventional acidizing (clay slow-release acid, chelating acid) was performed on the well without setting the tubing string, followed by profile adjustment; on May 30, 2022, water absorption profile testing of the well showed uneven mobilization within the formation, with strong water absorption zones and prominent internal contradictions, leading to a decision to conduct profile adjustment operations; in November 2022, the well was used as a profile adjustment injection well, with nanospheres injected as the reagent, and a cumulative injection dose of 865 kg; the well is currently undergoing pressurized profile adjustment, but injection is difficult, with a pump injection pressure of 34 MPa and a designed injection volume of 30 m³ / min. 3 / day, actual water injection volume is 10m³ 3 After the flushing and water absorption test is completed, it was decided, based on research, to use a composite acid system of the present invention for profile control, unblocking, and increasing injection in water injection wells for acidizing and increasing injection: The composite pre-acid solution consists of the following components by weight percentage: hydrochloric acid 8%, corrosion inhibitor 2%, adhesion stabilizer 1%, iron stabilizer 1%, and ammonium persulfate 2%.

[0058] The total volume of the composite pre-acid solution used is 10m³. 3 (This represents the actual daily water injection volume of 10m³) 3 Based on the density of water, the total weight of the pre-acid solution is estimated to be 10,000 kg. The components in the composite pre-acid solution include: 800 kg of hydrochloric acid aqueous solution (containing 31% hydrochloric acid), 200 kg of corrosion inhibitor, 100 kg of adhesion stabilizer, 100 kg of iron stabilizer, 200 kg of ammonium persulfate, and 8,600 kg of water.

[0059] The composite acid solution consists of the following components by weight percentage: hydrochloric acid 12%, hydrofluoric acid 2%, fluoroboric acid 4%, corrosion inhibitor 2%, adhesion stabilizer 1%, iron stabilizer 1%, and ammonium persulfate 2%.

[0060] The total volume V of the composite acid solution is calculated according to the following formula: V = πR 2 ×h×Φ=3.14×2.0×2.0×11.5×13.9%=20.07≈20m 3 Where V is the total volume of the composite main acid solution used, m 3R is the pretreatment radius of the profile-adjusting injection well (m); h is the effective thickness of the injection layer in the profile-adjusting injection well (m); Φ is the average formation porosity of the injection layer in the profile-adjusting injection well (%).

[0061] The total volume of the composite acid solution used is 20m³. 3 Based on the density of water, the total weight of the main acid solution is estimated to be 20,000 kg. The components in the composite main acid solution include: 2,400 kg of hydrochloric acid aqueous solution (containing 31% hydrochloric acid), 400 kg of hydrofluoric acid aqueous solution (containing 40% hydrofluoric acid), 800 kg of fluoroboric acid aqueous solution (containing 50% fluoroboric acid), 400 kg of corrosion inhibitor, 200 kg of adhesion stabilizer, 200 kg of iron stabilizer, 400 kg of ammonium persulfate, and 15,200 kg of water.

[0062] The composite post-acid solution consists of the following components by weight percentage: hydrochloric acid 10%, corrosion inhibitor 2%, adhesion stabilizer 1%, iron stabilizer 1%, and ammonium persulfate 2%.

[0063] The total volume of the composite post-acid solution used is 10m³. 3 (This represents the actual daily water injection volume of 10m³) 3 Based on the density of water, the total weight of the composite post-acid solution is estimated to be 10,000 kg. The amounts of each component in the composite post-acid solution are as follows: 800 kg of hydrochloric acid aqueous solution (containing 31% hydrochloric acid), 200 kg of corrosion inhibitor, 100 kg of adhesion stabilizer, 100 kg of iron stabilizer, 200 kg of ammonium persulfate, and 8,600 kg of water.

[0064] The displacement fluid is entirely composed of clean water or water from the injection pipeline process, which displaces the acid into deeper layers of the formation to achieve the purpose of deep unblocking.

[0065] The injection volume S of the displacement fluid is calculated using the following formula: S=H1×L1+H2×L2=3235.6×3.02 / 1000+(3345.5-3235.6)×(11.56-3.02) / 1000 =6.75 + 0.94 = 7.69 ≈ 8m 3 Where S is the displacement fluid injection volume, m 3 H1 is the position of the pipe foot, in meters; H2 is the thickness from H1 to the bottom of the perforated section, in meters; L1 is the internal volume of the well casing, in meters. 3 / 1000m; L2 is the annulus volume of the well casing, in m³. 3 / 1000m.

[0066] Based on the density of water, the total weight of the displacement solution is 8000 kg.

[0067] The present invention discloses a method for unclogging and increasing injection in profile-adjusting water injection wells using a composite acid system, which is carried out according to the following steps: The first step is to close the wellhead passage of the profile control injection well, inject clean water into the acidizing surface pipeline of the profile control injection well, and conduct a leakage pressure test on the acidizing surface pipeline to determine the sealing performance of the acidizing surface pipeline (high pressure and low pressure pipelines). The second step is to open the wellhead passage of the profile control injection well and pour 2m... 3 Clean water was injected into the profile control injection well through the acidified surface pipeline. The internal pressure was limited to 34MPa for test squeezing to confirm the normal water absorption of the formation below the profile control injection well. 40m³ of the prepared compound acid solution, used for profile control, unclogging, and enhanced injection in water injection wells, was transported using a specialized acid tanker truck. 3 (10m of composite pre-acid solution) 3 Composite main acid solution 20m 3 10m of composite post-acid solution 3 Transport the equipment to the well site and seal the outlet of the acidizing surface pipeline (high-pressure and low-pressure pipelines) to the wellhead of the profile control injection well; The third step involves injecting the composite pre-acid, composite main acid, and composite post-acid into the profile control injection well in sequence at varying rates to establish a downhole pulse wave hydraulic oscillation field and remove blockages in the near-wellbore area. Then, a displacement fluid is injected into the profile control injection well to displace and squeeze the acid to a deeper depth, thus achieving deep unblocking of the profile control injection well. In the third step, the composite pre-acid solution variable displacement injection method includes: the first injection of 5m 3 Displacement is 300 L / min, pump pressure is less than 34 MPa; second injection is 5 m 3 The displacement is 400L / min, and the pump pressure is less than 34MPa. The composite main body acid solution variable displacement injection method includes: the first injection of 5m 3 Displacement is 300 L / min, pump pressure is less than 34 MPa; second injection is 5 m 3 Displacement is 400 L / min, pump pressure is less than 34 MPa; third injection is 5 m 3 Displacement is 300 L / min, pump pressure is less than 34 MPa; fourth injection is 5 m 3 The displacement is 400L / min, and the pump pressure is less than 34MPa. The composite post-acid variable displacement injection method includes: initial injection of 5m 3 Displacement is 400 L / min, pump pressure is less than 34 MPa; second injection is 5 m 3 The displacement is 300 L / min, and the pump pressure is less than 34 MPa. The displacement fluid injection volume is 8m 3 The displacement is 300 L / min, and the pump pressure is less than 34 MPa. The fourth step is to prevent the acid in the injection well from being flushed back and to inject it directly after the well has been shut in for 2 hours (to start production).

[0068] The composite acid system of this invention for unblocking and increasing injection in profile-adjusting injection wells, after unblocking and increasing injection in profile-adjusting injection well 2, resulted in a decrease in pump injection pressure from 34 MPa to 21 MPa after acidizing. The designed injection volume was 30 m³ / s. 3 / day, the actual injection volume after acidification is reduced from 10m³ / day. 3 / rise to 30m 3 / sky.

[0069] In summary, the advantages of this invention are as follows: (1) The present invention is a composite acid system for profile control and water injection well unblocking and injection enhancement. The liquid preparation is simple and the operation is convenient. After the conventional acid preparation is completed, a certain amount of ammonium persulfate is added according to the weight percentage. After it is fully dissolved, it is loaded into an acid tanker truck and transported directly to the site for use. (2) The composite acid system of the present invention for profile control and unblocking water injection wells has good oxidation performance, which can effectively destroy the high molecular micelles in the profile control agent of water injection wells, oxidize and destroy the high molecular structure, and has high degradation and dispersion efficiency. (3) The composite acid system of the present invention for unblocking and increasing injection in profile-adjusting injection wells has a good corrosion inhibition effect during the acidizing process of profile-adjusting injection wells, and can slow down the corrosion rate of the acid to the well casing, well pipe and other metal equipment in contact with the well during the acidizing process. (4) The composite acid system of the present invention for profile control water injection well unblocking and injection increases the unblocking radius after profile control water injection well unblocking and injection. When the acid reaches the formation with the injection, the discharge rate is rapidly increased and high and low discharge rates are alternately injected to form a hydraulic pulse wave at the bottom of the well, establish a pulse wave hydraulic oscillation field, and act on the rock and cemented blockage, so that the blockage in the near well zone is vibrated and automatically falls off and is fully exposed in the acid, thereby achieving the purpose of completely removing the blockage in the near well zone. Then, the displacement fluid is injected to displace the acid into the deeper part of the formation to achieve the purpose of deep unblocking and expand the unblocking radius. (5) The composite acid system of the present invention for unblocking and increasing injection in profile-adjusting water injection wells significantly reduces the pump pressure after unblocking and increases injection, resulting in a significant increase in injection volume and effectively ensuring the increase in daily injection volume of the water injection well, thereby improving the injection efficiency.

[0070] The above technical features constitute various embodiments of the present invention, which have strong adaptability and implementation effect. Unnecessary technical features can be added or removed according to actual needs to meet the needs of different situations.

Claims

1. A composite acid system for unclogging and increasing injection in profile control water injection wells, characterized in that... The composite pre-acid solution, composite main acid solution, composite post-acid solution, and displacement solution are prepared according to the following method: To prepare the composite pre-acid solution, add the required amount of ammonium persulfate to a mixed solution of hydrochloric acid, corrosion inhibitor, adhesive stabilizer, and iron stabilizer, and stir until homogeneous to obtain the composite pre-acid solution. To prepare the composite main acid solution, add the required amount of ammonium persulfate to a mixed solution of hydrochloric acid, hydrofluoric acid, fluoroboric acid, corrosion inhibitor, adhesive stabilizer, and iron stabilizer, and stir until homogeneous to obtain the composite main acid solution. To prepare the composite post-acid solution, add the required amount of ammonium persulfate to a mixed solution of hydrochloric acid, corrosion inhibitor, adhesive stabilizer, and iron stabilizer, and stir until homogeneous to obtain the composite post-acid solution. Prepare a displacement solution, which is water.

2. The composite acid system for profile control and unblocking / enhancing water injection wells according to claim 1, characterized in that... The composite pre-acid solution, by weight percentage, consists of 8% to 12% hydrochloric acid, 1% to 3% corrosion inhibitor, 1% to 2% adhesion stabilizer, 1% to 2% iron stabilizer, 1% to 2% ammonium persulfate, and the remainder is water.

3. The composite acid system for profile control and unblocking / enhancing water injection wells according to claim 2, characterized in that... The composite pre-acid solution, by weight percentage, consists of 8% hydrochloric acid, 2% corrosion inhibitor, 1% adhesion stabilizer, 1% iron stabilizer, 2% ammonium persulfate, and the remainder is water.

4. The composite acid system for profile control, unblocking, and enhanced injection in water injection wells according to claim 1, 2, or 3, characterized in that... The composite acid solution, by weight percentage, consists of 8% to 12% hydrochloric acid, 1% to 3% hydrofluoric acid, 3% to 5% fluoroboric acid, 1% to 3% corrosion inhibitor, 1% to 2% adhesion stabilizer, 1% to 2% iron stabilizer, 1% to 2% ammonium persulfate, and the remainder is water.

5. The composite acid system for profile control and unblocking / enhancing water injection wells according to claim 4, characterized in that... The composite acid solution, by weight percentage, consists of 12% hydrochloric acid, 2% hydrofluoric acid, 4% fluoroboric acid, 2% corrosion inhibitor, 1% adhesion stabilizer, 1% iron stabilizer, 2% ammonium persulfate, and the remainder is water.

6. The composite acid system for unblocking and increasing injection in profile control water injection wells according to any one of claims 1 to 5, characterized in that... The composition by weight percentage is 8% to 12% hydrochloric acid, 1% to 3% corrosion inhibitor, 1% to 2% adhesion stabilizer, 1% to 2% iron stabilizer, 1% to 2% ammonium persulfate, and the remainder is water.

7. The composite acid system for profile control and unblocking / enhancing water injection wells according to claim 6, characterized in that... The composite post-acid solution, by weight percentage, consists of 10% hydrochloric acid, 2% corrosion inhibitor, 1% adhesion stabilizer, 1% iron stabilizer, 2% ammonium persulfate, and the remainder is water.

8. The composite acid system for unblocking and increasing injection in profile control water injection wells according to any one of claims 1 to 7, characterized in that... The iron stabilizer is citric acid, the viscosity stabilizer is a cationic quaternary ammonium salt, the fluoroboric acid is a 50% aqueous solution by weight, the corrosion inhibitor is alkylphenol polyoxyethylene ether, the alkylphenol polyoxyethylene ether is a 30% to 40% aqueous solution by weight, the hydrochloric acid is a 31% aqueous solution by weight, and the hydrofluoric acid is a 40% aqueous solution by weight.

9. A method for preparing a composite acid system for unblocking and increasing injection in profile control water injection wells according to any one of claims 2 to 8, characterized in that... include: To prepare the composite pre-acid solution, add the required amount of ammonium persulfate to a mixed solution of hydrochloric acid, corrosion inhibitor, adhesive stabilizer, and iron stabilizer, and stir until homogeneous to obtain the composite pre-acid solution. To prepare the composite main acid solution, add the required amount of ammonium persulfate to a mixed solution of hydrochloric acid, hydrofluoric acid, fluoroboric acid, corrosion inhibitor, adhesive stabilizer, and iron stabilizer, and stir until homogeneous to obtain the composite main acid solution. To prepare the composite post-acid solution, add the required amount of ammonium persulfate to a mixed solution of hydrochloric acid, corrosion inhibitor, adhesive stabilizer, and iron stabilizer, and stir until homogeneous to obtain the composite post-acid solution. Prepare a displacement solution, which is water.

10. A method for unblocking and increasing injection in a profile control water injection well using a composite acid system according to any one of claims 1 to 8, characterized in that... include: The first step is to close the wellhead passage of the profile control injection well, inject clean water into the acidizing surface pipeline of the profile control injection well, and conduct a leakage pressure test on the acidizing surface pipeline to determine the sealing performance of the acidizing surface pipeline. The second step is to open the wellhead passage of the profile control injection well and inject the required amount of clean water into the profile control injection well through the acidification surface pipeline to conduct a limited internal pressure test to confirm the normal water absorption of the formation below the profile control injection well. The third step involves injecting the composite pre-acid, composite main acid, and composite post-acid into the profile control injection well in sequence at varying rates to establish a downhole pulse wave hydraulic oscillation field and remove blockages in the near-wellbore area. Then, a displacement fluid is injected into the profile control injection well to displace and squeeze the acid to a deeper depth, thus achieving deep unblocking of the profile control injection well. The fourth step involves not flushing back the acid solution from the injection well, and injecting it directly after the required reaction time has elapsed.

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