Compact sandstone permeability and porosity improvement agent system and method for hole enlargement and throat enlargement thereof

Abstract

The present application relates to the technical field of fracturing fluid additive, and is a tight sandstone pore permeability improvement agent system and a method for hole expansion and throat enlargement, the former comprising multistage acid, fluoroboric acid, iron ion stabilizer and water, and the following steps are performed: a required amount of multistage acid is uniformly mixed with the iron ion stabilizer to obtain A liquid; clean water is prepositioned, and is injected into a formation from a sand mixing vehicle to replace formation water in a perforation hole, clean the perforation throat, immediately inject the obtained A liquid into the perforation throat, then immediately inject fluoroboric acid into the reservoir, and finally immediately inject clean water as a spacer fluid; after the reservoir pressure drop is greater than or equal to 12 MPa, a preflush, a sand-carrying fluid, a displacement fluid are injected, and normal fracturing operations are carried out. The present application generates hydrofluoric acid by the reaction of multistage acid and fluorine salt to achieve the purpose of expanding and enlarging the tight pore throat, has significant corrosion inhibition and strong casing protection function, and simultaneously compounding the iron ion stabilizer as a protective agent to avoid injection damage to the reservoir.

Description

Technical Field

[0001] This invention relates to the field of fracturing fluid additives, specifically a system of porosity and permeability improvers for dense sandstone and its method for enlarging pores and increasing throat width. Background Technology

[0002] Currently, unconventional energy gases (including shale gas, coalbed methane, and tight sandstone gas) account for an increasing proportion of the energy mix year by year. Tight sandstone gas, as an important component of unconventional energy gases, has achieved a series of successes while also facing numerous development challenges.

[0003] In the stimulation of tight sandstone gas wells, reservoir properties deteriorate as rolling development progresses. Due to the extremely dense pore throats (permeability generally below 0.1 mD) of tight sandstone reservoirs, fracturing operations require high pump pressures, making fracture creation difficult, and the narrow fracture openings hinder large-scale proppant injection. Artificial fractures have low conductivity, making stimulation challenging. High-tight sandstone gas often cannot be utilized on a large scale. Extremely tight sandstone reservoirs (GR > 100) frequently fail to fracture due to their excessive density, resulting in abandoned sections and preventing them from contributing to production.

[0004] In the later stages of development of most sandstone oil and gas reservoirs, high-quality reservoirs are nearly fully developed, making the efficient development of high-tightness, low-quality reservoirs particularly important. To increase the success rate of stimulation of extremely tight sandstone reservoirs, pre-modification of reservoir properties is necessary. Soil acid is a conventional acid system for acidification of sandstone reservoirs, but its rapid reaction with sandstone, short reaction distance, difficulty in deep stimulation of tight sandstone reservoirs, tendency to form secondary product precipitation, excessive reaction with clay, and damage to the sandstone framework are all challenges that severely limit its large-scale application.

[0005] Complex multi-level acids possess the characteristics of both strong and weak organic acids, contain multiple hydrogen ions, and can slowly and progressively ionize to release H+. +， Without damaging the sandstone framework, its effective range is 8 to 10 times that of conventional soil acids, enabling deep porosity and throat enhancement through pre-flush acid treatment. This fundamentally improves the porosity and permeability characteristics of tight sandstone formations. Simultaneously, its phosphate, carboxylic acid, and sulfonic acid functional groups have a strong complexing effect on calcium and magnesium ions, effectively protecting the sandstone framework and achieving porosity and permeability improvement in extremely tight sandstone. Through optimized acid design, 100% fracturing of extremely tight reservoirs can be achieved, forming the desired high-conductivity artificial fractures, significantly increasing the venting area of ​​low-quality, high-tightness sandstone gas, and significantly improving the utilization rate of tight sandstone gas reserves.

[0006] Therefore, it is necessary to develop a tight sandstone porosity and permeability improvement agent system containing multi-level acids to carry out industrial development of high-tight reservoirs. Summary of the Invention

[0007] This invention provides a tight sandstone porosity and permeability improvement agent system and its method for enlarging pores and increasing throats, overcoming the shortcomings of the prior art. It can effectively solve the problems in the development of existing sandstone oil and gas reservoirs, such as the short action distance of conventional acid systems, difficulty in deeply modifying tight sandstone reservoirs, and the easy formation of secondary product precipitation, which can cause secondary damage to sandstone reservoirs.

[0008] One of the technical solutions of the present invention is achieved through the following measures: a dense sandstone porosity and permeability improvement agent system, comprising multi-stage acid, fluoroboric acid, iron ion stabilizer and water, wherein, by mass percentage, the multi-stage acid is 15% to 30%, the fluoroboric acid is 2% to 8%, the iron ion stabilizer is 0.5% to 1.5%, and the balance is water.

[0009] The following are further optimizations and / or improvements to one of the above-mentioned inventive technical solutions: The aforementioned multi-level acid is a mixture of polyisopropylene phosphate-acrylic acid copolymer and phosphonocarboxylic acid copolymer, wherein the molar ratio of polyisopropylene phosphate-acrylic acid copolymer to phosphonocarboxylic acid copolymer is 1:5.

[0010] The molecular weights of the above-mentioned polyisopropylene phosphate-acrylic acid copolymers and phosphonocarboxylic acid copolymers are all between 1500 and 2500.

[0011] The above-mentioned polyisopropylene phosphate-acrylic acid copolymer was obtained by the following method: S01, phosphorous acid, acetic anhydride and glacial acetic acid are mixed and stirred until the solution is clear to obtain the first mixture; S02, add the required amount of acetone to the first mixture, react and then distill to obtain isopropenylated phosphoric acid monomer, wherein the molar ratio of added phosphorous acid, acetic anhydride, glacial acetic acid and acetone is 1:1.95:1.3:1.3. S03, add the required amount of potassium persulfate and acrylic acid mixture to isopropylene phosphate monomer, and after reaction, obtain polyisopropylene phosphate-acrylic acid copolymer.

[0012] In step S01 above, the mixing temperature is 18°C ​​to 20°C, and the mixing time is 15 min to 18 min.

[0013] In step S02 above, the reaction temperature is 18°C ​​to 20°C, the reaction time is 1.0h to 1.5h, and acetone is added within 1h. The distillation conditions include distillation under complete vacuum at 170°C until no more fractions are distilled off.

[0014] In step S03 above, according to the mass percentage, a mixture of 0.01% potassium persulfate and 15% acrylic acid is added to every 50% isopropyl phosphate monomer, and the mixture of potassium persulfate and acrylic acid is added within 1 hour. The reaction temperature is 75°C to 80°C, and the reaction time is 35 min to 40 min.

[0015] In the synthesis of the above-mentioned phosphonocarboxylic acid copolymer, the raw materials include sodium hydroxide, ammonium persulfate, sodium bisulfite, phosphoric acid, acrylic acid, 2-acrylamide-2-methylpropanesulfonic acid, and water. The mass fraction of sodium hydroxide is 0.015%, the sum of the mass fractions of ammonium persulfate and sodium bisulfite is 0.05%, the sum of the mass fractions of phosphoric acid, acrylic acid, and 2-acrylamide-2-methylpropanesulfonic acid is 30%, and the remainder is water. The molar ratio of ammonium persulfate to sodium bisulfite is 1:1, and the molar ratio of phosphoric acid, acrylic acid, and 2-acrylamide-2-methylpropanesulfonic acid is 1:1:1.

[0016] The above phosphonocarboxylic acid copolymer was synthesized according to the following method: S11, after mixing the required amounts of phosphorous acid, sodium hydroxide and water evenly, heat under reflux to obtain the second mixture; S12, the required amounts of sodium hydroxide, acrylic acid, 2-acrylamide-2-methylpropanesulfonic acid and sodium bisulfite are mixed evenly in sequence to obtain the third mixture. Immediately after obtaining the third mixture, it is mixed with the second mixture to obtain the fourth mixture. S13, add the required amount of ammonium persulfate to the fourth mixture, and after reaction, obtain the phosphonocarboxylic acid copolymer.

[0017] In step S12 above, the specific process of mixing the third mixture with the second mixture includes: after obtaining the third mixture, immediately adding the third mixture to the second mixture at a linear speed of 2 mL / min while stirring.

[0018] In step S13 above, the reaction temperature is 25°C to 35°C, and the reaction time is 2h to 3h.

[0019] The second technical solution of the present invention is achieved through the following measures: a method for using a dense sandstone porosity-permeability improver system to enlarge pores and increase throat size, comprising the following steps: The first step is to mix the required amount of multi-stage acid with iron ion stabilizer evenly to obtain solution A; The second step is to pre-set 10m. 3 Clean water is injected into the formation from the sand mixing truck to replace the formation water in the perforation holes and clean the perforation throats; The third step is to immediately fill the 10m of clean water after pouring it in. 3 up to 20m 3 The obtained liquid A is injected into the perforation throat; Step 4: After injecting solution A, immediately add 3m 3 up to 5m 3 Fluoroboronic acid is injected into the reservoir; Step 5: Immediately after the fluoroboric acid injection is completed, inject 10m... 3 Up to 15m 3 Water is used as the isolation fluid. After the reservoir pressure drop reaches ≥12MPa, pre-flush fluid, proppant-carrying fluid, and displacement fluid are injected, and normal fracturing operations are carried out.

[0020] The following are further optimizations and / or improvements to the second technical solution of the above invention: In steps two, three, and four above, the discharge rate for injecting clean water, solution A, and fluoroboric acid is 0.5 m³. 3 / min to 3.0m 3 / min.

[0021] This invention achieves the purpose of expanding and increasing the pore throat by reacting multi-stage acids with fluoride salts to generate hydrofluoric acid. It has a significant corrosion inhibition effect and a strong casing protection function. At the same time, it is compounded with an iron ion stabilizer as a protective agent to avoid injection damage to the reservoir. Attached Figure Description

[0022] Appendix Figure 1 This is a construction physical image of the eighth section of well Zhao 51-xx-xxH1 in Embodiment 9 of the present invention (pressure drop of 35MPa after modification of the tight sandstone pore permeability improver system). Detailed Implementation

[0023] 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 mass percentages; unless otherwise specified, all solutions in this invention are aqueous solutions with water as the solvent, for example, hydrochloric acid solution is an aqueous solution of hydrochloric acid; room temperature in this invention generally refers to a temperature between 15°C and 25°C, generally defined as 25°C.

[0024] The present invention will be further described below with reference to embodiments: Example 1: The tight sandstone porosity and permeability improver system includes multi-stage acid, fluoroboric acid, iron ion stabilizer and water, wherein, by mass percentage, the multi-stage acid is 15% to 30%, the fluoroboric acid is 2% to 8%, the iron ion stabilizer is 0.5% to 1.5%, and the balance is water.

[0025] Example 2: As an optimization of the above example, the multi-level acid is a mixture of polyisopropylene phosphate-acrylic acid copolymer and phosphonocarboxylic acid copolymer, wherein the molar ratio of polyisopropylene phosphate-acrylic acid copolymer to phosphonocarboxylic acid copolymer is 1:5.

[0026] Example 3: As an optimization of the above examples, the molecular weight of the polyisopropylene phosphate-acrylic acid copolymer and the phosphonocarboxylic acid copolymer are both 1500 to 2500.

[0027] The molecular weights of both the isopropylene phosphate-acrylic acid copolymer and the phosphonocarboxylic acid copolymer are between 1500 and 2500. The phosphonocarboxylic acid copolymer is the main agent, which takes into account a series of properties such as strong acid ionization, multi-level weak acid, high-valence ion complexation, prevention of secondary precipitation, corrosion inhibition, and deep penetration, and has good comprehensive performance. At the same time, the polyisopropylene phosphate-acrylic acid copolymer is used as an auxiliary agent to supplement the main agent, further enhancing the functions of penetration, scale inhibition and slow release.

[0028] Example 4: As an optimization of the above examples, the polyisopropylene phosphate-acrylic acid copolymer was obtained according to the following method: S01, place a three-necked flask equipped with a reflux condenser into a low-temperature cooling device, and mix phosphorous acid, acetic anhydride and glacial acetic acid in sequence. Stir at 19°C for 15 minutes until the solution is clear to obtain the first mixture. S02, the required amount of acetone is slowly added dropwise through a funnel to the first mixture in the flask, and the addition is completed within 1 hour. After reacting for 1.5 hours, it is placed in a rotary evaporator for distillation under a complete vacuum at 170°C until no more fractions are distilled off, resulting in a viscous golden-yellow liquid, which is isopropenylated phosphoric acid monomer. The molar ratio of added phosphorous acid, acetic anhydride, glacial acetic acid and acetone is 1:1.95:1.3:1.3. S03. Place a three-necked flask equipped with a reflux condenser in a heat-collecting magnetic stirrer (water bath). Slowly add the required amount of a mixture of potassium persulfate and acrylic acid to the isopropylene phosphate monomer in the three-necked flask through a dropping funnel. Complete the addition within 1 hour. Then, keep the mixture at 75°C for 40 minutes to obtain a semi-transparent liquid with a certain viscosity, namely polyisopropylene phosphate-acrylic acid copolymer. In this copolymer, 0.01% potassium persulfate and 15% acrylic acid are added to every 50% isopropylene phosphate monomer by mass percentage.

[0029] In this invention, the synthesis equation for isopropenyl phosphate monomer is as follows: The synthesis equation for polyisopropyl phosphate-acrylic acid copolymer is as follows: Where m and n can both take values ​​from 1 to 8 (integers). Example 5: As an optimization of the above example, in the synthesis of the phosphonocarboxylic acid copolymer, the raw materials include sodium hydroxide, ammonium persulfate, sodium bisulfite, phosphoric acid, acrylic acid, 2-acrylamide-2-methylpropanesulfonic acid, and water. The mass fraction of sodium hydroxide is 0.015%, the sum of the mass fractions of ammonium persulfate and sodium bisulfite is 0.05%, the sum of the mass fractions of phosphoric acid, acrylic acid, and 2-acrylamide-2-methylpropanesulfonic acid is 30%, and the remainder is water. The molar ratio of ammonium persulfate to sodium bisulfite is 1:1, and the molar ratio of phosphoric acid, acrylic acid, and 2-acrylamide-2-methylpropanesulfonic acid is 1:1:1.

[0030] Example 6: As an optimization of the above examples, the phosphonocarboxylic acid copolymer was synthesized according to the following method: S11, after mixing the required amounts of phosphorous acid, sodium hydroxide and water in a reaction flask, heat under reflux to obtain a second mixture; S12, the required amounts of sodium hydroxide, acrylic acid, 2-acrylamide-2-methylpropanesulfonic acid and sodium bisulfite are mixed sequentially at a linear speed of 2 mL / min to obtain a third mixture. Immediately after obtaining the third mixture, it is mixed with the second mixture to obtain a fourth mixture. S13, add the required amount of ammonium persulfate to the fourth mixture at a linear velocity of 2 mL / min, control the reaction temperature at 35℃ in a cold bath for 3 hours, and consider the reaction to be complete when the temperature no longer changes within 4 hours, thus obtaining the phosphonocarboxylic acid copolymer.

[0031] In this invention, the synthesis equation for the phosphonocarboxylic acid copolymer is as follows: Where m and n can both take values ​​from 1 to 8 (integers).

[0032] Phosphonocarboxylic acid copolymers exhibit good water solubility. The molecular chain contains -CONH2, -COOH, -OH, and -SO3H, with an average molecular weight of 1500 to 2500. The carboxylic acid groups in this molecular structure are weak acid groups, exhibiting strong affinity for polyvalent cations, enhancing surface activity and action distance, and readily adsorbing particles to prevent scale formation, especially carbonate scale. The sulfonic acid groups, being strong acid groups, significantly enhance the copolymer's organic strong acid properties and water solubility, promoting polymer chain extension in water and improving acidity and penetration. The phosphonic acid groups in the molecule can form insoluble chelates with metallic iron ions to form a protective film, primarily acting as corrosion inhibitors. Simultaneously, the phosphonic acid groups contribute to inhibiting carbonate precipitation. The entire molecule combines strong acid, multi-level weak acid, high-valence ion complexation, corrosion inhibition, and deep penetration properties, resulting in excellent overall performance.

[0033] Example 7: The method for using this dense sandstone porosity-permeability improver system to enlarge pores and increase throat size is carried out according to the following steps: The first step is to mix the required amount of multi-stage acid with iron ion stabilizer evenly to obtain solution A; The second step is to pre-set 10m. 3 Clean water is injected into the formation from the sand mixing truck to replace the formation water in the perforation holes and clean the perforation throats; The third step is to immediately fill the 10m of clean water after pouring it in. 3 up to 20m 3 The obtained liquid A is injected into the perforation throat; Step 4: After injecting solution A, immediately add 3m 3 up to 5m 3 Fluoroboronic acid is injected into the reservoir; Step 5: Immediately after the fluoroboric acid injection is completed, inject 10m... 3 Up to 15m 3 Water is used as the isolation fluid. After the reservoir pressure drop reaches ≥12MPa, pre-flush fluid, proppant-carrying fluid, and displacement fluid are injected, and normal fracturing operations are carried out.

[0034] Example 8: As an optimization of the above example, in steps two, three, and four, the discharge rate for injecting clean water, solution A, and fluoroboric acid is 0.5 m³. 3 / min to 3.0m 3 / min.

[0035] Example 9: The fracturing string for the Zhao 51-xx-xxH1 well in the Zhao 51 block of Inner Mongolia was a 5-inch N80 steel pipe. The reservoir permeability in the 8th section was 0.02mD to 0.12mD, with a tested GR value of approximately 120. Physical properties indicated strong reservoir tightness, making stimulation difficult. Gas logging showed poor performance. To fully utilize this reservoir, a moderately scaled design was implemented, and initial fluid absorption tests were conducted with a displacement of 1m³. 3 The pump stopped due to overpressure at a rate of / min, and continuous oscillating extrusion failed to induce liquid flow. Therefore, a pre-treatment modification with a pore-enlarging and throat-increasing agent was implemented, reducing the discharge rate to 0.5m³. 3 / min, inject a tight sandstone porosity and permeability improvement agent system (by mass percentage, including: Solution A (25% multi-stage acid + 1% iron ion stabilizer) 20m 3 +4% fluoroboric acid 5m 3 After complete injection, the pressure decreased by 35 MPa, allowing for successful construction of this highly compact reservoir (as shown in the construction photos). Figure 1 (As shown).

[0036] The specific implementation steps are as follows: The first step is to prepare solution A (25% multi-stage acid + 1% iron ion stabilizer mixed evenly) to prepare for construction. The multi-stage acid can prevent casing corrosion. The second step is to pre-set 10m.3 Clean water, under a pump pressure not exceeding 60 MPa, is supplied at a rate of 0.5 m... 3 The discharge rate is gradually increased to 3.0 m³ / min. 3 The sand-mixing truck injects water into the formation at a rate of / min to replace the formation water in the perforation holes, clean the perforation throats, and at the same time pre-squeeze out clean water to determine the reservoir's liquid absorption capacity. The third step is to pour in clean water, then add 20m... 3 The prepared solution A (25% multi-stage acid + 1% iron ion stabilizer) was immediately injected into the 10m... 3 Clean water, under a pump pressure not exceeding 60 MPa, is supplied at a rate of 0.5 m... 3 The discharge rate is gradually increased to 3.0 m³ / min. 3 Injecting water at a rate of / min into the perforation throat creates a strong acid environment for the perforation throat after it has been cleaned with water, which facilitates deep complexation of high-valence ions. The fourth step is to prepare 5mg of fluoroboric acid with a mass percentage of 2% to 8%. 3 After liquid A is injected, under the condition that the pump pressure does not exceed 60 MPa, at a speed of 0.5 m 3 The discharge rate is gradually increased to 3.0 m³ / min. 3 The injection rate of / min immediately injects fluoroboric acid into the reservoir. The fluoroboric acid and the multi-level acid in the A solution injected in the third step work together to slowly form hydrofluoric acid, which acts on the sandstone pore throat and achieves the purpose of uniform acid distribution, pore enlargement and throat expansion, pressure reduction and injection enhancement. Step 5: Immediately after the fluoroboric acid injection is completed, inject 10m... 3 Water is used as the isolation fluid. After the reservoir pressure drop reaches ≥12MPa, pre-flush fluid, proppant-carrying fluid, and displacement fluid are injected, and normal fracturing operations are carried out.

[0037] During implementation, to facilitate observation of pressure changes, a constant flow rate of the pore-enlarging and throat-increasing modifier can be injected within a certain range. During fracturing operations, the highest sand ratio measured was 30%, and the average sand ratio was 20%. Figure 1 This indicates that the strong tight reservoir was successfully modified.

[0038] In this invention, multi-level acids release H+ slowly. + It allows the acid to be released uniformly within the dense pore throat, and under reservoir conditions, it reacts with fluoride salts to generate an appropriate amount of hydrofluoric acid, thereby achieving the purpose of enlarging and increasing the pore throat. This is achieved through the slow release of H... +By controlling the acid release time to achieve deep acidification, the problem of short-range action distance of conventional soil acids is overcome. Addressing the challenge of fluoride ions reacting with calcium and magnesium ions to form insoluble precipitates, the developed multi-stage acid incorporates phosphate and carboxylic acid functional groups with strong complexing and scale-inhibiting capabilities. These groups, through high-strength chelation, complex calcium and magnesium ions in the solution. The injection sequence is designed: first, the multi-stage acid is injected to create a strong acid environment and complex high-valence ions, followed by the injection of fluoride salts. This combination allows fluoride and hydrogen ions to effectively bind and act on sandstone reservoirs, preventing secondary damage to the reservoir from precipitation while improving the efficiency of sandstone treatment and achieving clean stimulation of tight sandstone reservoirs. For casing protection in stimulated wells, this multi-stage acid combination also exhibits significant corrosion inhibition and strong casing protection functions. Furthermore, it incorporates iron ion stabilizers and other protective agents to prevent injection-induced damage to the reservoir.

[0039] Compared with the prior art, the present invention has the following beneficial effects: (1) Calcium and magnesium ion complexation rate: 100%; (2) Calcium carbonate and magnesium carbonate have a scale inhibition rate of 100%; (3) After the treatment, the core permeability increased to 135%; (4) Pump pressure drop during fracturing operations ≥12MPa; (5) The distance of dynamic acid etching on the core profile is 8 to 10 times that of soil acid; (6) 120℃, N80 corrosion rate 4.25g / (m 2 The corrosion rate of P110 is 1.23 g / (m·h), with a corrosion rate of 1.23 g / (m·h). 2 ·h).

[0040] Meanwhile, in the Su77, ​​Zhao51, and Su19 blocks of Changqing Oilfield, a total of 52 wells and 156 layers have been applied, increasing the hydraulic fracturing stimulation rate of ultra-tight reservoirs with permeability below 0.1mD and GR > 100 from 23% to 96%. It is evident that this tight sandstone porosity and permeability improver system significantly increases the oil and gas utilization rate of low-grade reservoirs. With the deepening of rolling development, this tight sandstone porosity and permeability improver system will become a key tool for the industrial development of low-grade, high-tight reservoirs.

[0041] In summary, this invention achieves the purpose of expanding and increasing the pore throat by reacting multi-stage acids with fluoride salts to generate hydrofluoric acid. It has significant corrosion inhibition effect and strong casing protection function. At the same time, it is compounded with iron ion stabilizers as protective agents to avoid injection damage to the reservoir.

[0042] The above technical features constitute the 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 system for improving the porosity and permeability of dense sandstone, characterized in that... It includes multi-stage acid, fluoroboric acid, iron ion stabilizer and water, wherein, by mass percentage, the multi-stage acid is 15% to 30%, the fluoroboric acid is 2% to 8%, the iron ion stabilizer is 0.5% to 1.5%, and the balance is water.

2. The dense sandstone porosity and permeability improvement agent system according to claim 1, characterized in that... The multi-level acid is a mixture of polyisopropylene phosphate-acrylic acid copolymer and phosphonocarboxylic acid copolymer, wherein the molar ratio of polyisopropylene phosphate-acrylic acid copolymer to phosphonocarboxylic acid copolymer is 1:

5.

3. The dense sandstone porosity and permeability improvement agent system according to claim 2, characterized in that... The molecular weights of the polyisopropylene phosphate-acrylic acid copolymer and the phosphonocarboxylic acid copolymer are both between 1500 and 2500.

4. The dense sandstone porosity and permeability improvement agent system according to claim 2 or 3, characterized in that... The polyisopropylene phosphate-acrylic acid copolymer is obtained by the following method: S01, phosphorous acid, acetic anhydride and glacial acetic acid are mixed and stirred until the solution is clear to obtain the first mixture; S02, add the required amount of acetone to the first mixture, react and then distill to obtain isopropenylated phosphoric acid monomer, wherein the molar ratio of added phosphorous acid, acetic anhydride, glacial acetic acid and acetone is 1:1.95:1.3:1.

3. S03, add the required amount of potassium persulfate and acrylic acid mixture to isopropylene phosphate monomer, and after reaction, obtain polyisopropylene phosphate-acrylic acid copolymer.

5. The dense sandstone porosity and permeability improvement agent system according to claim 4, characterized in that... In step S01, the mixing temperature is 18°C ​​to 20°C, and the mixing time is 15 min to 18 min; or / and in step S02, the reaction temperature is 18°C ​​to 20°C, the reaction time is 1.0 h to 1.5 h, and acetone is added within 1 h, and the distillation conditions include: distillation under complete vacuum at 170°C until no fraction is distilled off; or / and in step S03, a mixture of 0.01% potassium persulfate and 15% acrylic acid is added per 50% isopropenylated phosphoric acid monomer by mass percentage, and the mixture of potassium persulfate and acrylic acid is added within 1 h, the reaction temperature is 75°C to 80°C, and the reaction time is 35 min to 40 min.

6. The tight sandstone porosity and permeability improvement agent system according to any one of claims 2 to 5, characterized in that... In the synthesis of phosphonocarboxylic acid copolymers, the raw materials include sodium hydroxide, ammonium persulfate, sodium bisulfite, phosphoric acid, acrylic acid, 2-acrylamide-2-methylpropanesulfonic acid, and water. The mass fraction of sodium hydroxide is 0.015%, the sum of the mass fractions of ammonium persulfate and sodium bisulfite is 0.05%, the sum of the mass fractions of phosphoric acid, acrylic acid, and 2-acrylamide-2-methylpropanesulfonic acid is 30%, and the remainder is water. The molar ratio of ammonium persulfate to sodium bisulfite is 1:1, and the molar ratio of phosphoric acid, acrylic acid, and 2-acrylamide-2-methylpropanesulfonic acid is 1:1:

1.

7. The tight sandstone porosity and permeability improvement agent system according to any one of claims 2 to 6, characterized in that... The phosphonocarboxylic acid copolymer was synthesized according to the following method: S11, after mixing the required amounts of phosphorous acid, sodium hydroxide and water evenly, heat under reflux to obtain the second mixture; S12, the required amounts of sodium hydroxide, acrylic acid, 2-acrylamide-2-methylpropanesulfonic acid and sodium bisulfite are mixed evenly in sequence to obtain the third mixture. Immediately after obtaining the third mixture, it is mixed with the second mixture to obtain the fourth mixture. S13, add the required amount of ammonium persulfate to the fourth mixture, and after reaction, obtain the phosphonocarboxylic acid copolymer.

8. The dense sandstone porosity and permeability improver system according to claim 7, characterized in that... In step S12, the specific process of mixing the third mixture with the second mixture includes: after obtaining the third mixture, immediately adding the third mixture to the second mixture at a linear speed of 2 mL / min while stirring; or / and, in step S13, the reaction temperature is 25℃ to 35℃, and the reaction time is 2h to 3h.

9. A method for using a tight sandstone porosity-permeability improver system according to any one of claims 1 to 8 to enlarge pores and increase throat size, characterized in that... Follow these steps: The first step is to mix the required amount of multi-stage acid with iron ion stabilizer evenly to obtain solution A; The second step is to pre-set 10m. 3 Clean water is injected into the formation from the sand mixing truck to replace the formation water in the perforation holes and clean the perforation throats; The third step is to immediately fill the 10m of clean water after pouring it in. 3 up to 20m 3 The obtained liquid A is injected into the perforation throat; Step 4: After injecting solution A, immediately add 3m 3 up to 5m 3 Fluoroboronic acid is injected into the reservoir; Step 5: Immediately after the fluoroboric acid injection is completed, inject 10m... 3 Up to 15m 3 Water is used as the isolation fluid. After the reservoir pressure drop reaches ≥12MPa, pre-flush fluid, proppant-carrying fluid, and displacement fluid are injected, and normal fracturing operations are carried out.

10. The method for using the dense sandstone porosity and permeability improvement agent system according to claim 9 for pore enlargement and throat thickening, characterized in that... In steps two, three, and four, the discharge rate for injecting clean water, solution A, and fluoroboric acid is 0.5 m³. 3 / min to 3.0m 3 / min.

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