A composite salt solubilizer, a solid-free completion fluid and a preparation method thereof

Abstract

The application discloses a composite salt solubilizer, a solid-free well completion fluid and a preparation method thereof, and belongs to the technical field of well completion fluid preparation. The preparation method of the composite salt solubilizer comprises the following steps: mixing a ketone compound with an alkali catalyst, adding hydrogen cyanide dropwise to perform a cyano addition reaction, and obtaining an intermediate; under an inert atmosphere, performing cyclization condensation reaction on the intermediate to obtain a six-membered nitrogen heterocyclic compound; dissolving the six-membered nitrogen heterocyclic compound in a solvent, adding sulfuric acid to stir, adjusting the pH to 2-4, and then performing ripening, so that the composite salt solubilizer is obtained. The application further discloses a solid-free well completion fluid and a preparation method thereof. The application can solve the problems of poor adaptability of the solubilizer, unobvious salt concentration improvement and thermodynamic instability of the solid-free well completion fluid system, has good technical speciality, and has a high industrialization degree.

Description

Technical Field

[0001] This invention relates to the field of completion fluid preparation technology, specifically to a composite salt solubilizer, a solid-free completion fluid, and its preparation method. Background Technology

[0002] In oil and gas drilling and completion processes, completion fluid is the core fluid for maintaining wellbore pressure balance, preventing formation fluid intrusion, and protecting reservoir integrity. Its performance directly determines the safety and efficiency of completion operations. While traditional modified drilling and completion fluids are lower in cost, they suffer from inherent defects such as poor settling stability (weighting agents easily settle, leading to tubing blockage / sticking and packer mis-seatment), insufficient temperature resistance (high-temperature thickening or thinning causes performance loss of control), and high friction under high density and high solids conditions (difficulty in running tubing in small wells and packer sealing / unsealing failure). In contrast, solids-free completion fluids, due to the absence of solid particles, minimal reservoir damage, and stable performance, avoid problems such as stuck pipe and wear caused by solids, making them an important development direction for deep and ultra-deep well completions.

[0003] Existing solid-free brine completion fluids are mainly divided into two categories: inorganic salt systems and organic salt systems, but both have significant limitations: Firstly, regarding inorganic salt systems (compounds of NaCl, KCl, CaCl2, NaBr, CaBr2, or ZnBr2, etc.), their density ranges from 1.00 to 2.60 g / cm³. 3 However, the upper limit of the density increase due to chloride salts (such as NaCl and CaCl2) is ≤1.4 g / cm³. 3 This cannot meet the needs of deep wells; although bromide salts (such as ZnBr2) can achieve a density >1.8 g / cm³, they are insufficient. 3 However, it is highly corrosive; Secondly, regarding organic salt systems (sodium formate, potassium formate, cesium formate), they have low viscosity, good fluidity, and low crystallization point, but the density of the sodium / potassium formate system is ≤1.57 g / cm³. 3 The density increase is limited and cannot meet the high-density requirements of ultra-deep wells; although cesium salts (such as cesium formate) can achieve a density >1.8 g / cm³ 3 However, cesium salt resources are scarce and extremely expensive (the unit price is more than 10 times that of conventional salt), making it difficult to apply on a large scale.

[0004] To address the aforementioned limitations, the inventors previously developed an environmentally friendly, high-density, solid-free weighting agent (see CN104610937B "An Environmentally Friendly High-Density Solid-Free Weighting Agent and its Preparation Method"). This weighting agent is a composite salt system, and its saturated aqueous solution can achieve a density of 1.828 g / cm³ at 25°C. 3It is a solid-free system with advantages such as high temperature resistance (stable at 180℃), low corrosion, good compatibility, and environmental friendliness and non-toxicity. It has been widely used in complex working conditions such as deep wells and horizontal wells within 6000m, effectively solving the problems of insufficient density and strong corrosivity of traditional solid-free systems.

[0005] However, with the development of deep-sea and ultra-deep onshore wells (depth > 7000m), formation pressure is higher, and the completion fluid density needs to be further increased to 1.88g / cm³. 3 The aforementioned environmentally friendly high-density solid-free weighting agent system has a density enhancement limit; its maximum solubility density at 25°C is only 1.828 g / cm³. 3 Adding salt will immediately cause solid precipitation, which cannot meet the requirements of ultra-deep wells. In addition, the addition of existing conventional solubilizers (such as polyethylene glycol 400) has poor compatibility with environmentally friendly high-density solid-free weighting agent systems and cannot increase the salt concentration. Although traditional supersaturated dissolution techniques (such as ultrasonic-assisted and mechanical stirring) can temporarily increase the salt concentration, the system is thermodynamically unstable and prone to precipitation and crystallization at high temperatures due to ion association and water activity loss, resulting in high construction risks.

[0006] Therefore, there is an urgent need to develop a highly efficient solubilizer specifically for the aforementioned environmentally friendly high-density solid-free weighting agent system, which can stably increase the density without introducing a solid phase. At the same time, it is necessary to establish a complete process method of "solvent preparation - compound salt compounding - completion fluid preparation" to achieve industrial application and break through the core path of the bottleneck of ultra-deep well completion fluid density. Summary of the Invention

[0007] The problem to be solved by this invention is to provide a composite salt solubilizer, a solid-free completion fluid and its preparation method, so as to solve the problems of poor solubilizer compatibility, insignificant salt concentration increase and thermodynamic instability of the solid-free completion fluid system.

[0008] The technical solution adopted to solve its technical problem is a method for preparing a composite salt solubilizer, comprising the following steps: (1) Mix ketone compounds with a base catalyst and add hydrogen cyanide dropwise to carry out a cyano addition reaction to obtain an intermediate; (2) Under an inert atmosphere, the intermediate is subjected to a cyclization condensation reaction to obtain a six-membered nitrogen heterocyclic compound; (3) Dissolve the six-membered nitrogen heterocyclic compound in a solvent, add sulfuric acid and stir, adjust the pH to 2-4, and then ripen it to obtain a composite salt solubilizer.

[0009] The beneficial effects of the above-mentioned technical solution of this invention are as follows: The composite salt solubilizer prepared by this invention contains a six-membered nitrogen heterocyclic skeleton, which is generated by the condensation reaction of ketone compounds with hydrogen cyanide. After sulfonation modification, sulfonic acid groups (-SO3H) are introduced to form a synergistic structure of "steric hindrance of nitrogen heterocycle + hydrogen bond network of sulfonic acid group". The six-membered nitrogen heterocycle contains two amide bonds (-CO-NH-), one methyl (-CH3) substituent and a terminal amino group (-NH2), which provides 0.8 nm of steric hindrance, which can effectively inhibit the ion association and crystallization of composite salt in environmentally friendly high-density solid-free weighting agent. The sulfonic acid group forms a six-fold hydrogen bond network with water molecules, which reduces water activity, enhances ion exchange capacity and improves the solubility of composite salt. The steric hindrance effect of nitrogen heterocycle and the hydrogen bond network of sulfonic acid group work together to break through the density limit of environmentally friendly high-density solid-free weighting agent composite salt without forming a supersaturated system.

[0010] Preferably, in step (1), the ketone compound is acetone or acetone oxime; the alkaline catalyst is a 5-15% (w / w) potassium hydroxide ethanol solution, sodium hydroxide ethanol solution, or sodium ethoxide ethanol solution; the molar ratio of the ketone compound to hydrogen cyanide is 1:(1-1.4); the hydrogen cyanide dropping rate is 0.6-1 mol / L; the cyano addition reaction temperature is 25-35℃, and the time is 1.5-2.5 h.

[0011] The beneficial effects of the above technical solution adopted in this invention are: controlling the hydrogen cyanide dropping rate to 0.6~1 mol / L to avoid incomplete reaction caused by excessively high local concentration.

[0012] More preferably, in step (1), the ketone compound is acetone oxime; the base catalyst is a 10% (w / w) potassium hydroxide ethanol solution; the molar ratio of the ketone compound to hydrogen cyanide is 1:1.2; the hydrogen cyanide dropping rate is 0.8 mol / L; the cyano addition reaction temperature is 25°C and the time is 2 h.

[0013] More preferably, the ratio of ketone compound to base catalyst is 1 mol: (50~60) g.

[0014] More preferably, the ratio of ketone compound to base catalyst is 1 mol: 56 g.

[0015] Preferably, the cyclization condensation reaction in step (2) is carried out at a temperature of 110~130℃ for 3.5~4.5h.

[0016] More preferably, the cyclization condensation reaction in step (2) is carried out at a temperature of 120°C for 4 hours.

[0017] Preferably, step (3) includes the following steps: dissolving the six-membered nitrogen heterocyclic compound in a solvent, cooling it to 3~6°C in an ice bath, adding sulfuric acid dropwise and stirring for 1.5~2.5h, adjusting the pH to 2.8~3.2, and then aging it at 35~45°C for 0.5~1.5h to obtain the composite salt solubilizer.

[0018] The beneficial effects of the above technical solution in this invention are as follows: sulfonation of six-membered nitrogen heterocyclic compounds with concentrated sulfuric acid and adjustment of pH to 2.8-3.2 can optimize the efficiency of sulfonic acid group introduction and introduce sulfonic acid groups to improve water solubility.

[0019] More preferably, step (3) includes the following steps: dissolving the six-membered nitrogen heterocyclic compound in a solvent, cooling it to 5°C in an ice bath, adding sulfuric acid dropwise and stirring for 2 hours, adjusting the pH to 2.8~3.2, and then aging it at 40°C for 1 hour to obtain the composite salt solubilizer.

[0020] More preferably, the mass ratio of the six-membered nitrogen heterocyclic compound to the solvent is 1:4.

[0021] More preferably, after aging, the solvent is removed by vacuum distillation, the mixture is washed three times with acetone, and finally dried under vacuum at 60°C and 0.1 MPa for 8 hours to obtain the composite salt solubilizer.

[0022] Preferably, the solvent is dichloromethane, chloroform, 1,2-dichloroethane or ethyl acetate; the sulfuric acid mass concentration is 70~98%; and the molar ratio of the six-membered nitrogen heterocyclic compound to sulfuric acid is 1:(1.1~1.3).

[0023] More preferably, the solvent is dichloromethane; the sulfuric acid mass concentration is 98%; and the molar ratio of the six-membered nitrogen heterocyclic compound to sulfuric acid is 1:1.2.

[0024] The present invention also provides a composite salt solubilizer prepared by the above preparation method.

[0025] This invention also provides a solids-free completion fluid, comprising the following raw materials in parts by weight: 90-110 parts water, 1-5 parts compound salt solubilizer, 0.5-1.5 parts corrosion inhibitor, 2-6 parts temperature stabilizer, and 180-240 parts environmentally friendly high-density solid-free weighting agent.

[0026] The beneficial effects of the above-mentioned technical solution in this invention are as follows: This invention uses a composite salt solubilizer in the preparation of a solid-free completion fluid based on an environmentally friendly, high-density, solid-free weighting agent. This high-density solid-free completion fluid achieves a stable density increase to 1.88 g / cm³ through the synergistic effect of "nitrogen heterocyclic steric hindrance + sulfonic acid group hydrogen bonding". 3 The density increase is 0.06 g / cm³. 3It does not form a supersaturated system, which is significantly different from traditional salt addition crystallization; it can be well applied to the completion of ultra-deep wells with a depth >7000m.

[0027] Preferred solids-free completion fluid comprises the following raw materials in parts by weight: 100 parts water, 2-4 parts compound salt solubilizer, 0.9-1.2 parts corrosion inhibitor, 4-5 parts temperature stabilizer, and 202-222 parts environmentally friendly high-density solid-free weighting agent.

[0028] Preferably, the corrosion inhibitor is an imidazoline derivative corrosion inhibitor; the temperature stabilizer is a sulfite, acid sulfite, metabisulfite, dithionite, trithionite, thiosulfate, or nitrite.

[0029] More preferably, the temperature stabilizer is sodium sulfite, sodium metabisulfite, or sodium thiosulfate.

[0030] This invention also provides a method for preparing solids-free completion fluid, comprising the following steps: Under stirring conditions, the composite salt solubilizer is dissolved in water, then the corrosion inhibitor and temperature stabilizer are added and stirred until dissolved and mixed. Finally, the environmentally friendly high-density solid-free weighting agent is added and dissolved completely to obtain the solid-free completion fluid.

[0031] Preferably, the stirring speed is 400~500 r / min; the dissolution temperature of the environmentally friendly high-density solid-free weighting agent is 70~80℃.

[0032] More preferably, the stirring speed is 450 r / min; and the dissolution temperature of the environmentally friendly high-density solid-free weighting agent is 75°C.

[0033] The present invention has the following beneficial effects: First, the composite salt solubilizer prepared in this invention possesses the synergistic effect of steric hindrance of a six-membered nitrogen heterocycle and hydrogen bond network of sulfonic acid groups. This enables a breakthrough in the solid-free density of the environmentally friendly high-density solid-free weighting agent system described in the basic patent CN104610937B, stably increasing the density at 25℃ to 1.88 g / cm³. 3 The density increased by 0.06 g / cm³. 3 It meets the requirement of 1.88 g / cm³ for ultra-deep wells (>7000m). 3 The above density requirements solve the problems of instability in traditional salting crystallization and supersaturation techniques.

[0034] Secondly, when the composite salt solubilizer prepared by this invention is used in solid-free completion fluid, it can achieve excellent stability across the entire temperature range and adapt to extreme downhole environments. Under high temperature conditions, the system does not precipitate solid phase and the density does not decrease significantly, making it suitable for use in ultra-deep well environments. Under low temperature conditions, it has good fluidity and adapts to low temperature well conditions. Moreover, it does not precipitate / crystallize under long-term static conditions, avoiding tubing blockage and packer mis-seating caused by solid phase sedimentation.

[0035] Meanwhile, the composite salt solubilizer prepared by this invention is only highly effective in solubilizing the environmentally friendly high-density solid-free weighting agent system in the basic patent CN104610937B, and is ineffective for other salts. Its technical specificity is obvious, avoiding the inefficiency problem of general-purpose solubilizers. This invention also proves that chemical solubilization can replace physical supersaturation to achieve density improvement, providing a new path for breakthroughs in the density of solid-free completion fluids, which is different from the unstable solutions of traditional salt crystallization or ultrasonic assistance.

[0036] In summary, this invention systematically solves the core problems of insufficient density, easy solid phase precipitation, and high-temperature failure of completion fluids in ultra-deep wells through the design of a special composite salt solubilizer and the preparation of completion fluids. It also has the advantages of high performance, low cost, and green environmental protection, providing key technical support for safe and efficient completion of ultra-deep wells and has important industrial application value. Detailed Implementation

[0037] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are only for explaining the invention and are not intended to limit the invention; that is, the described embodiments are only a part of the embodiments of this invention, and not all of them.

[0038] Therefore, the following detailed description of the embodiments of the present invention is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0039] The features and performance of the present invention will be further described in detail below with reference to the embodiments. The imidazoline derivative corrosion inhibitor and its preparation method used in the present invention refer to "CN115449359B An imidazoline derivative corrosion inhibitor and its preparation method"; the environmentally friendly high-density solid-free weighting agent and its preparation method refer to "CN104610937B An environmentally friendly high-density solid-free weighting agent and its preparation method".

[0040] Example 1 A method for preparing a composite salt solubilizer includes the following steps: (1) 1 mol of acetone oxime and 56 g of 10% potassium hydroxide ethanol solution were added to a reaction vessel and mixed. 1.2 mol of hydrogen cyanide was added dropwise to the reaction vessel at a rate of 0.8 mol / L. The cyano addition reaction was carried out at 25 °C for 2 h to obtain the intermediate. (2) The intermediate was transferred to another glass reactor, nitrogen was introduced to replace the air, and then the temperature was raised to 120°C. Under the nitrogen atmosphere, the intermediate was subjected to a cyclization condensation reaction for 4 hours to obtain a six-membered nitrogen heterocyclic compound. (3) Dissolve the six-membered nitrogen heterocyclic compound in dichloromethane to form an intermediate solution with a mass percentage concentration of 20%. Cool the intermediate solution to 5°C in an ice bath. Add sulfuric acid with a mass concentration of 98% dropwise to the intermediate solution at a molar ratio of 1:1.2 of the six-membered nitrogen heterocyclic compound and sulfuric acid and stir for 2 hours. Adjust the pH to 2.8~3.2 and then mature at 40°C for 1 hour. After maturity, remove the solvent by vacuum distillation, wash three times with acetone, and finally dry under vacuum at 60°C and 0.1 MPa for 8 hours to obtain the composite salt solubilizer.

[0041] Example 2 A method for preparing a composite salt solubilizer includes the following steps: (1) Add 1 mol of acetone oxime and 56 g of 10% potassium hydroxide ethanol solution to a reaction vessel and mix. Add 1 mol of hydrogen cyanide dropwise to the reaction vessel at a rate of 0.6 mol / L and carry out a cyano addition reaction at 30°C for 2.5 h to obtain an intermediate. (2) The intermediate was transferred to another glass reactor, nitrogen was introduced to replace the air, and then the temperature was raised to 110°C. Under the nitrogen atmosphere, the intermediate was subjected to a cyclization condensation reaction for 3.5 h to obtain a six-membered nitrogen heterocyclic compound. (3) Dissolve the six-membered nitrogen heterocyclic compound in dichloromethane to form an intermediate solution with a mass percentage concentration of 20%. Cool the intermediate solution to 3°C in an ice bath. Add 95% sulfuric acid dropwise to the intermediate solution at a molar ratio of 1:1.2 for the six-membered nitrogen heterocyclic compound and sulfuric acid, and stir for 1.5 h. Adjust the pH to 2.8~3.2, and then age it at 35°C for 1.5 h. After aging, remove the solvent by vacuum distillation, wash three times with acetone, and finally dry it under vacuum at 60°C and 0.1 MPa for 8 h to obtain the composite salt solubilizer.

[0042] Example 3 A method for preparing a composite salt solubilizer includes the following steps: (1) Add 1 mol of acetone oxime and 56 g of 10% potassium hydroxide ethanol solution to a reaction vessel and mix. Add 1.4 mol of hydrogen cyanide dropwise to the reaction vessel at a rate of 1 mol / L and carry out a cyano addition reaction at 35°C for 1.5 h to obtain an intermediate. (2) The intermediate was transferred to another glass reactor, nitrogen was introduced to replace the air, and then the temperature was raised to 130°C. Under the nitrogen atmosphere, the intermediate was subjected to a cyclization condensation reaction for 3.5 h to obtain a six-membered nitrogen heterocyclic compound. (3) Dissolve the six-membered nitrogen heterocyclic compound in dichloromethane to form an intermediate solution with a mass percentage concentration of 20%. Cool the intermediate solution to 6°C in an ice bath. Add sulfuric acid with a mass concentration of 80% dropwise to the intermediate solution at a molar ratio of 1:1.2 for the six-membered nitrogen heterocyclic compound and sulfuric acid. Stir for 2.5 h. Adjust the pH to 2.8~3.2 and then mature at 45°C for 0.5 h. After maturity, remove the solvent by vacuum distillation. Wash with acetone three times. Finally, dry under vacuum at 60°C and 0.1 MPa for 8 h to obtain the composite salt solubilizer.

[0043] Example 4 A solids-free completion fluid comprises the following raw materials in parts by weight: 100 parts water, 2 parts of the composite salt solubilizer prepared in Example 1, 0.9 parts imidazoline derivative corrosion inhibitor, 4 parts sodium metabisulfite, and 202 parts environmentally friendly high-density solid-free weighting agent.

[0044] This embodiment also provides a method for preparing solids-free completion fluid, including the following steps: Under stirring conditions of 450 r / min, the composite salt solubilizer and water are added to the reactor and stirred for 5 min to dissolve. Then, imidazoline derivative corrosion inhibitor and sodium metabisulfite are added and stirred for 5 min to dissolve. Finally, environmentally friendly high-density solid-free weighting agent is added at 75℃ and stirred until completely dissolved to obtain solid-free completion fluid.

[0045] Example 5 A solids-free completion fluid comprises the following raw materials in parts by weight: 100 parts water, 3 parts of the composite salt solubilizer prepared in Example 1, 1 part of imidazoline derivative corrosion inhibitor, 5 parts of sodium metabisulfite, and 212 parts of environmentally friendly high-density solid-free weighting agent.

[0046] This embodiment also provides a method for preparing solids-free completion fluid, including the following steps: Under stirring conditions of 450 r / min, the composite salt solubilizer and water are added to the reactor and stirred for 5 min to dissolve. Then, imidazoline derivative corrosion inhibitor and sodium metabisulfite are added and stirred for 5 min to dissolve. Finally, environmentally friendly high-density solid-free weighting agent is added at 75℃ and stirred until completely dissolved to obtain solid-free completion fluid.

[0047] Example 6 A solids-free completion fluid comprises the following raw materials in parts by weight: 100 parts water, 4 parts of the composite salt solubilizer prepared in Example 1, 1.2 parts imidazoline derivative corrosion inhibitor, 4 parts sodium thiosulfate, and 222 parts of environmentally friendly high-density solid-free weighting agent.

[0048] This embodiment also provides a method for preparing solids-free completion fluid, including the following steps: Under stirring conditions of 450 r / min, the composite salt solubilizer and water are added to the reactor and stirred for 5 min to dissolve. Then, imidazoline derivative corrosion inhibitor and sodium thiosulfate are added and stirred for 5 min to dissolve. Finally, environmentally friendly high-density solid-free weighting agent is added at 75℃ and stirred until completely dissolved to obtain solid-free completion fluid.

[0049] Comparative Example 1 A solids-free completion fluid comprises the following raw materials in parts by weight: 100 parts water, 0.8 parts imidazoline derivative corrosion inhibitor, 3 parts sodium sulfite, and 192 parts environmentally friendly high-density solid-free weighting agent.

[0050] This comparative example also provides a method for preparing solids-free completion fluid, including the following steps: Under stirring conditions of 450 r / min, water is added to the reactor, followed by imidazoline derivative corrosion inhibitor and sodium sulfite, and stirred for 5 min to dissolve. Finally, environmentally friendly high-density solid-free weighting agent is added at 75℃ and stirred until completely dissolved to obtain solid-free completion fluid.

[0051] Comparative Example 2 A solids-free completion fluid comprises the following raw materials in parts by weight: 100 parts water, 2 parts polyethylene glycol 400, 0.8 parts imidazoline derivative corrosion inhibitor, 3 parts sodium sulfite, and 192 parts environmentally friendly high-density solid-free weighting agent.

[0052] This comparative example also provides a method for preparing solids-free completion fluid, including the following steps: Under stirring conditions of 450 r / min, polyethylene glycol 400 and water are added to the reactor and stirred for 5 min to dissolve. Then, imidazoline derivative corrosion inhibitor and sodium sulfite are added and stirred for 5 min to dissolve. Finally, environmentally friendly high-density solid-free weighting agent is added at 75℃ and stirred until completely dissolved to obtain solid-free completion fluid.

[0053] Comparative Example 3 A solids-free completion fluid comprises the following raw materials in parts by weight: 100 parts water, 3 parts of the composite salt solubilizer prepared in Example 1, 0.8 parts imidazoline derivative corrosion inhibitor, 3 parts sodium metabisulfite, and 413 parts potassium formate.

[0054] This comparative example also provides a method for preparing solids-free completion fluid, including the following steps: Under stirring conditions of 450 r / min, the composite salt solubilizer and water are added to the reactor and stirred for 5 min to dissolve. Then, imidazoline derivative corrosion inhibitor and sodium metabisulfite are added and stirred for 5 min to dissolve. Finally, potassium formate is added at 75℃ and stirred until completely dissolved to obtain solids-free completion fluid.

[0055] Comparative Example 4 A solids-free completion fluid comprises the following raw materials in parts by weight: 100 parts water, 3 parts of the composite salt solubilizer prepared in Example 1, 0.8 parts imidazoline derivative corrosion inhibitor, 3 parts sodium metabisulfite, and 37 parts potassium chloride.

[0056] This comparative example also provides a method for preparing solids-free completion fluid, including the following steps: Under stirring conditions of 450 r / min, the composite salt solubilizer and water are added to the reactor and stirred for 5 min to dissolve. Then, imidazoline derivative corrosion inhibitor and sodium metabisulfite are added and stirred for 5 min to dissolve. Finally, potassium chloride is added at 75℃ and stirred until completely dissolved to obtain solids-free completion fluid.

[0057] Comparative Example 5 A solids-free completion fluid comprises the following raw materials in parts by weight: 100 parts water, 3 parts of the composite salt solubilizer prepared in Example 1, 0.8 parts imidazoline derivative corrosion inhibitor, 3 parts sodium metabisulfite, and 100 parts calcium chloride.

[0058] This comparative example also provides a method for preparing solids-free completion fluid, including the following steps: Under stirring conditions of 450 r / min, the composite salt solubilizer and water are added to the reactor and stirred for 5 min to dissolve. Then, imidazoline derivative corrosion inhibitor and sodium metabisulfite are added and stirred for 5 min to dissolve. Finally, calcium chloride is added at 75℃ and stirred until completely dissolved to obtain solids-free completion fluid.

[0059] Experimental Example 1: Temperature Resistance Test The solid-free completion fluids prepared in Examples 4-6 and Comparative Examples 1-5 were subjected to room temperature, high temperature, and low temperature performance tests. The specific test methods are as follows: (1) Performance at room temperature: The prepared solid-free completion fluid was sealed and left to stand for 24 hours at 25°C. The appearance was observed to see if there was any sediment, and the density of the clear fluid was tested with a mud densitometer.

[0060] (2) High temperature performance: The solid-free completion fluid was loaded into an aging kettle with a polytetrafluoroethylene inner liner, 1 MPa of nitrogen was injected, and it was placed at a constant temperature of 180℃ for 24 hours. The fluid was then removed and the bottom of the completion fluid was observed for any sedimentation. The density was tested at 25℃ using a mud densitometer.

[0061] (3) Low temperature performance: The prepared solid-free completion fluid was placed in a -21℃ freezer for 24 hours and the low temperature solidification was observed.

[0062] The results are shown in Table 1.

[0063] Table 1. Results of Temperature Resistance Tests for Solid-Free Completion Fluids

[0064] As can be seen from Table 1, firstly, the composite salt solubilizer has a significant effect on improving the specificity of the environmentally friendly high-density solid-free weighting agent system.

[0065] Specifically, the environmentally friendly high-density solid-free weighting agent systems with added composite salt solubilizers in Examples 4-6 showed no precipitation or crystallization at either room temperature or high temperature. At room temperature, compared to Comparative Example 1 (1.828 g / cm³) without added composite salt solubilizers... 3 Comparative Example 2 (1.826 g / cm³) with added conventional solubilizer polyethylene glycol 400 3 The concentration increased by 0.02~0.056 g / cm³. 3 The highest concentration can reach 1.882 g / cm³. 3 This demonstrates that the composite salt solubilizer of the present invention can effectively improve the solubility of the environmentally friendly high-density solid-free weighting agent system, exceeding 1.88 g / cm³. 3 The density limit. With increasing amounts of the composite salt solubilizer and the environmentally friendly high-density solid-free weighting agent (Example 4 → Example 6), the system density gradually increased (1.848 → 1.882 g / cm³). 3 Furthermore, it exhibits excellent high-temperature stability (density changes by only 0.001~0.002 g / cm³ after aging at 180℃). 3 This meets the needs of ultra-deep wells.

[0066] Meanwhile, the composite salt solubilizer of this invention is ineffective against other salt systems. After adding the composite salt solubilizer to Comparative Example 3 (potassium formate, an organic salt) and Comparative Example 4 (potassium chloride, a low-density inorganic salt), a large amount of crystals still precipitated, with densities only 1.163~1.599 g / cm³. 3 This indicates that the ionic complexation effect of the composite salt solubilizer of this invention is only suitable for environmentally friendly, high-density systems without solid-phase weighting agents, and has no solubilizing effect on non-target salts; in Comparative Example 5 (calcium chloride, a single high-concentration salt), the addition of the composite salt solubilizer of this invention actually accelerated crystallization (almost complete crystallization), because the sulfonic acid groups of the composite salt solubilizer react with Ca... 2+ Complexation is insufficient to inhibit the crystallization of high-concentration salts; on the contrary, the additional ionic strength introduced by the molecular structure exacerbates crystallization.

[0067] Furthermore, all examples and comparative examples (except for comparative examples 4-5 which were completely solidified) did not solidify at -21°C and exhibited good fluidity, demonstrating that the composite salt solubilizer of the present invention has no negative impact on the low-temperature stability of the environmentally friendly high-density solid-free weighting agent system, and ensures fluidity in ultra-deep well low-temperature sections (such as shallow formations).

[0068] Experiment Example 2: Long-term stability test The solid-free completion fluid prepared in Example 6 was placed in an aging vessel lined with polytetrafluoroethylene (PTFE), and nitrogen gas was injected at 1 MPa. The vessel was then placed at a constant temperature of 180°C for 3, 5, and 7 days. After aging, the fluid was removed, and the presence of sediment at the bottom was observed. The density was also tested using a mud densitometer at 25°C. The results are shown in Table 2.

[0069] Table 2. Long-term stability test results of the solids-free completion fluid prepared in Example 6

[0070] As shown in Table 2, the solid-free completion fluid prepared in Example 6 did not exhibit crystallization after 3, 5, and 7 days of static constant temperature at 180℃*1MPa, demonstrating controllable overall stability and good settling stability; furthermore, its density change was only ≤0.002 g / cm³. 3 This indicates that the system has good high-temperature density stability; it also indicates that the solid-free completion fluid of the present invention has no risk of settling and its density is controllable under the extreme working conditions of "high temperature (180℃), high pressure and long time" in ultra-deep wells, thus meeting the long-term stability requirements for engineering applications.

[0071] Experiment Example 3: Corrosion Resistance Test Referring to the static method for testing corrosion rate in the standard SY / T 0026-1999 "Water Corrosion Test Method", the test object was: Example 6 (density 1.882 g / cm³). 3 Corrosion test pieces: 2 pieces of 13Cr material, labeled as test piece 1# and test piece 2# respectively; experimental conditions: static constant temperature at 180℃ for 7 days. The results are shown in Table 3.

[0072] Table 3. Corrosion resistance test results of the solid-free completion fluid prepared in Example 6

[0073] As can be seen from the results in Table 3, after the 13Cr material specimen was kept at a constant temperature of 180°C for 7 days in the solution of Example 6, the average corrosion rate was 0.1405 mm / a, which is low. This indicates that the solid-free completion fluid prepared by the composite salt solubilizer of the present invention has low corrosivity to commonly used downhole metals (such as 13Cr), which can not only ensure the performance of the completion fluid, but also extend the equipment life and reduce maintenance costs.

[0074] In summary, the composite salt solubilizer of this invention has the core advantages of specialized solubilization, full-temperature stability, and low corrosion for environmentally friendly, high-density, solid-free completion fluid systems without solids weighting agents, breaking through the density limit (≥1.88 g / cm³). 3 It achieves both solid-free properties at room temperature and high temperature while maintaining low-temperature fluidity and long-term stability at high temperature, and exhibits low corrosivity to metals such as 13Cr. However, it has no solubilizing effect on other salt systems such as potassium formate, potassium chloride, and calcium chloride (and may even cause negative effects), fully demonstrating its technical specificity and irreplaceability, and providing core support for ultra-deep well high-density completion fluids from formulation to performance.

[0075] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a composite salt solubilizer, characterized in that, Includes the following steps: (1) Mix ketone compounds with a base catalyst and add hydrogen cyanide dropwise to carry out a cyano addition reaction to obtain an intermediate; (2) Under an inert atmosphere, the intermediate is subjected to a cyclization condensation reaction to obtain a six-membered nitrogen heterocyclic compound; (3) Dissolve the six-membered nitrogen heterocyclic compound in a solvent, add sulfuric acid and stir, adjust the pH to 2-4, and then ripen it to obtain a composite salt solubilizer.

2. The method for preparing the composite salt solubilizer as described in claim 1, characterized in that, In step (1), the ketone compound is acetone or acetone oxime; the alkaline catalyst is a 5-15% (w / w) potassium hydroxide ethanol solution, sodium hydroxide ethanol solution, or sodium ethoxide ethanol solution; the molar ratio of the ketone compound to hydrogen cyanide is 1:(1-1.4); the hydrogen cyanide dropping rate is 0.6-1 mol / L; the cyano addition reaction temperature is 25-35℃, and the time is 1.5-2.5 h.

3. The method for preparing the composite salt solubilizer as described in claim 1, characterized in that, The cyclization condensation reaction in step (2) is carried out at a temperature of 110~130℃ for 3.5~4.5h.

4. The method for preparing the composite salt solubilizer as described in claim 1, characterized in that, Step (3) includes the following steps: dissolve the six-membered nitrogen heterocyclic compound in a solvent, cool it in an ice bath to 3~6℃, add sulfuric acid dropwise and stir for 1.5~2.5h, adjust the pH to 2.8~3.2, and then ripen it at 35~45℃ for 0.5~1.5h to obtain the composite salt solubilizer.

5. The method for preparing the composite salt solubilizer as described in claim 4, characterized in that, The solvent is dichloromethane, chloroform, 1,2-dichloroethane, or ethyl acetate; the sulfuric acid has a mass concentration of 70-98%; and the molar ratio of the six-membered nitrogen heterocyclic compound to sulfuric acid is 1:(1.1-1.3).

6. A composite salt solubilizer prepared by any one of claims 1 to 5.

7. A solids-free completion fluid, characterized in that, Including the following parts by weight of raw materials: The ingredients are: 90-110 parts water, 1-5 parts composite salt solubilizer as described in claim 6, 0.5-1.5 parts corrosion inhibitor, 2-6 parts temperature stabilizer, and 180-240 parts environmentally friendly high-density solid-free weighting agent.

8. The solid-free completion fluid as described in claim 7, characterized in that, The corrosion inhibitor is an imidazoline derivative corrosion inhibitor; the temperature stabilizer is a sulfite, acid sulfite, metabisulfite, dithionite, trithionite, thiosulfate, or nitrite.

9. The method for preparing the solid-free completion fluid according to any one of claims 7-8, characterized in that, Includes the following steps: Under stirring conditions, the composite salt solubilizer is dissolved in water, then the corrosion inhibitor and temperature stabilizer are added and stirred until dissolved and mixed. Finally, the environmentally friendly high-density solid-free weighting agent is added and dissolved completely to obtain the solid-free completion fluid.

10. The method for preparing solid-free completion fluid as described in claim 9, characterized in that, The stirring conditions are: a stirring speed of 400-500 r / min; and a dissolution temperature of 70-80℃ for the environmentally friendly high-density solid-free weighting agent.

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