An on-line thickening agent for alkaline reservoir oil displacement surfactants and method of use thereof

Abstract

This application relates to an online thickener for oil displacement in alkaline reservoirs and its application method, which is prepared by the following steps: preparing a surfactant solution at room temperature; adding a formaldehyde solution or other formaldehyde derivatives in a molar ratio of 1:1-5 to the surfactant; and then adding salicylic acid or its salt in a molar ratio of 1:1-3 to the surfactant. While ensuring the thickening performance of the surfactant, this method can significantly reduce the critical micelle concentration and oil-water interfacial tension, improve oil-water displacement efficiency, and solve the problem of insufficient adaptability of existing oil displacement systems under alkaline reservoir conditions.

Description

Technical Field

[0001] This invention belongs to the field of oilfield chemical enhanced oil recovery (CEM), specifically relating to an online thickener of surfactants for alkaline reservoirs and its application method. This method is mainly applied in tertiary oil recovery processes in alkaline, low-permeability reservoirs and complex reservoirs. By achieving an in-situ thickening reaction of surfactants under reservoir conditions, it increases the viscosity and interfacial activity of the displacement fluid, thereby improving oil-water flow characteristics, expanding the swept volume of the oil displacement, and enhancing oil recovery. Background Technology

[0002] Currently, most oil reservoirs in my country suffer from complex conditions and poor reservoir properties, characterized by small pore throats, low permeability, and strong heterogeneity. As development progresses into the mid-to-late stages, inter-layer contradictions become increasingly prominent, water cut rises rapidly, remaining oil is dispersed, and recovery rates continue to decline. In recent years, to improve recovery rates, chemical flooding technologies such as alkaline flooding and alkali-surfactant-polymer ternary composite flooding have been widely applied. These methods typically involve injecting alkaline solutions (such as Na2CO3 or NaOH) to react with natural organic acids in the crude oil, generating in-situ surfactants in the formation to reduce interfacial tension and improve oil displacement efficiency. However, with the continuous promotion of tertiary oil recovery technologies, alkaline environments in reservoirs are becoming increasingly common. The resulting reservoir corrosion, dissolution, and scaling exacerbate reservoir heterogeneity, often causing single-well water cuts to exceed 98%, rendering the reservoir economically unviable, while large amounts of untapped or underutilized reserves remain trapped in the formation.

[0003] To address the aforementioned challenges, deep profile control technology has gradually become an important means of improving oil recovery. This technology involves injecting large doses of thickener to block high-permeability layers or fracture channels, altering the flow direction of subsequent injected fluids, increasing the oil displacement area and efficiency of the displacing agent, thereby improving the recovery rate. In recent years, betaine and other surfactants containing amino, carboxyl, or amide groups have received widespread attention and are gradually being applied to complex reservoirs due to their excellent interfacial activity, salt tolerance, and wettability regulation capabilities. However, under alkaline reservoir conditions, the molecular structure of these surfactants is prone to hydrolysis or deactivation, resulting in insufficient stability and thickening performance. At the same time, conventional thickeners, due to their high viscosity during injection, place stringent requirements on the injection pump, easily leading to excessive pump pressure and shortened equipment lifespan. Furthermore, during formation migration, thickeners inevitably suffer adsorption losses, limiting their migration distance and making it difficult to reach the target profile control area, significantly restricting their practical application in alkaline reservoirs.

[0004] Therefore, there is an urgent need to develop a new surfactant-based oil displacement method that can achieve in-situ thickening and simultaneously improve surface and interfacial properties under alkaline reservoir conditions, in order to overcome the problems of injection difficulties, insufficient migration distance, and poor performance stability in existing technologies. This invention addresses these bottlenecks by proposing an online surfactant thickener for oil displacement in alkaline reservoirs and its application method. This method utilizes the characteristic that betaine-based surfactants are completely soluble in low-carbon alcohols without forming colloids. After entering the reservoir and being diluted with water, they form viscoelastic small-molecule hydrogels, solving the problem of the difficulty in injecting viscoelastic colloids into low-permeability reservoirs. Simultaneously, it utilizes the in-situ catalytic reaction of formaldehyde with betaine-based surfactants in the reservoir's alkaline environment to enhance the hydrophilic end's interaction strength. This allows for online in-situ thickening of the surfactant under formation conditions, effectively reducing the injection pressure of the original solution, extending the radius of action, and maintaining and enhancing oil displacement performance. Therefore, it provides an efficient, simple, and promising new approach for improving oil recovery and deep profile control in alkaline reservoirs.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] Online thickener for oil displacement in alkaline reservoirs and its application method, including the following steps:

[0007] The first step involves preparing a 30-50% (w / w) surfactant solution using a low-carbon alcohol at room temperature. The solution is stirred until fully dissolved, resulting in a homogeneous and transparent solution. The betaine surfactant is at least one or a combination of industrial-grade or higher purity betaine surfactants such as oleamidopropyl betaine, erucamide propyl betaine, dodecyl hydroxypropyl sulfonate betaine, and octadecyl hydroxypropyl sulfonate betaine. The solvents used are industrial-grade or higher purity methanol, ethanol, n-propanol, isopropanol, ethylene glycol, and glycerol.

[0008] The second step involves adding a formaldehyde solution or other formaldehyde derivatives in a molar ratio of 1:1-5 to the surfactant solution obtained in the first step, and stirring until fully dissolved to form a homogeneous solution, for 1-3 hours. The formaldehyde solution must be of industrial grade or higher purity, and the other formaldehyde derivatives are industrial grade or higher purity formaldehyde aqueous solutions, trioxymethylene, or hexamethylenetetramine.

[0009] The third step involves adding salicylic acid or its salt to the above solution at a molar ratio of 1:1-3 with the surfactant, and stirring for 1-3 hours to obtain an online thickener for oil displacement in alkaline reservoirs. The salicylic acid or its salt is industrial grade or higher purity salicylic acid, sodium salicylate, potassium hydrochloride, or ammonium salicylate.

[0010] The application method is as follows: First, inject 1-10 cubic meters of isolation fluid into the injection well, then inject 1-3 cubic meters of the above-mentioned online thickener, then inject another 1-10 cubic meters of isolation fluid, and finally restore normal injection water to inject the aforementioned liquid downhole. Maintain normal production pressure and continue injection until the pressure is restored to the pressure before the water drive breakthrough. This is recorded as one injection cycle, which can increase production by more than 10%.

[0011] The advantages of this invention are as follows: Addressing the problems of poor stability, short effective distance, and difficult injection associated with surfactant-assisted oil displacement in existing alkaline heterogeneous reservoirs, this invention provides a method for preparing a surfactant that can be generated online and in situ under reservoir conditions and possesses thickening properties. The agent itself has low viscosity, and the injection pressure does not increase significantly, thus extending the migration distance of the thickener in the formation. After entering the reservoir, the agent automatically forms a hydrogel upon dilution with water. Furthermore, the formaldehyde-like substances in the agent, after further dilution with water, can undergo hydroxymethylation under alkaline and high reservoir conditions, enhancing the strength of its hydrophilic end and increasing the inertia of the small molecule gel. This counteracts the viscosity reduction effect caused by dilution, resulting in a hydrogel solution with high viscosity, ensuring oil displacement efficiency. In addition, while maintaining the thickening performance of the surfactant, this agent can also significantly reduce the critical micelle concentration and oil-water interfacial tension, thereby improving oil-water displacement efficiency and solving the problem of insufficient adaptability of existing oil displacement systems under alkaline reservoir conditions.

[0012] Indoor verification:

[0013] The online thickener, a surfactant for oil displacement in alkaline reservoirs obtained in this invention, is mixed with alkaline oilfield produced water at a volume ratio of 1:5-10 and stirred until homogeneous. The mixture is then kept at 40-90℃ for 2-10 hours to obtain a homogeneous hydrogel. The gel has an apparent viscosity of 12-35 mPa·s, a surface tension of 25.3-32.6 mN / m, and an interfacial tension of 10. -1 -10 -3 The efficiency of core oil displacement is on the order of mN / m, which increases the efficiency by more than 12.8%. Detailed Implementation

[0014] Example 1

[0015] An online thickener for oil displacement in alkaline reservoirs and its application method:

[0016] At room temperature, erucamide propyl betaine was prepared with glycerol as solvent to a surfactant solution at a mass concentration of 40%. The solution was stirred until completely dissolved to obtain a homogeneous and transparent solution. Formaldehyde solution with a molar ratio of 1:3.5 to the surfactant was added to this solution, and the mixture was stirred for 2 hours to obtain a homogeneous solution. Subsequently, sodium salicylate with a molar ratio of 1:2 to the surfactant was added to the above solution, and the mixture was stirred for 2 hours to obtain an online thickener. The erucamide propyl betaine, glycerol, formaldehyde solution, and sodium salicylate were all of industrial grade or higher purity. The online thickener was mixed with alkaline oilfield produced water at pH 9.0 at a volume ratio of 1:9 and kept at 60°C for 4.5 hours to obtain a homogeneous hydrogel. The apparent viscosity of the hydrogel was 32.1 mPa·s, the surface tension was 31.6 mN / m, and the interfacial tension was 10. -1 The efficiency of core flooding is on the order of mN / m, which improves the efficiency by 14.4%.

[0017] Practical applications:

[0018] In alkaline reservoirs with produced water pH=9.0, 9 cubic meters of isolation fluid were first injected into the treatment water well, followed by 1 cubic meter of online thickener, and then another 9 cubic meters of isolation fluid. After one injection cycle under normal injection pressure, the formation pressure recovered to the level before water drive breakthrough, increasing production by 18%.

[0019] Example 2

[0020] An online thickener for oil displacement in alkaline reservoirs and its application method:

[0021] At room temperature, oleamidopropyl betaine was prepared into a surfactant solution using methanol as a solvent at a mass concentration of 50%. The solution was stirred until completely dissolved to obtain a homogeneous and transparent solution. Trioxymethylene (TOM) was added to this solution at a molar ratio of 1:4 to the surfactant, and the mixture was stirred for 3 hours to obtain a homogeneous solution. Subsequently, salicylic acid (SAC) was added to the above solution at a molar ratio of 1:2.6 to the surfactant, and the mixture was stirred for 3 hours to obtain an online thickener. The oleamidopropyl betaine, methanol, TOM, and salicylic acid were all of industrial grade or higher purity. The online thickener was mixed with alkaline oilfield produced water at pH 10 at a volume ratio of 1:5 and kept at 80°C for 2.5 hours to obtain a homogeneous hydrogel. The apparent viscosity of the hydrogel was 15 mPa·s, the surface tension was 28.1 mN / m, and the interfacial tension was 10. -2 The efficiency of core flooding is on the order of mN / m, which increases the efficiency by 14.1% and the production by 16%.

[0022] Practical applications:

[0023] In alkaline reservoirs with produced water pH=10, 5 cubic meters of isolation fluid were first injected into the treatment water well, followed by 2 cubic meters of online thickener, and then another 5 cubic meters of isolation fluid. After two injection cycles under normal injection pressure, the formation pressure returned to the level before water drive breakthrough.

[0024] Example 3

[0025] An online thickener for oil displacement in alkaline reservoirs and its application method:

[0026] At room temperature, dodecyl hydroxypropyl sulfonate betaine was prepared into a surfactant solution at a mass concentration of 30% using ethylene glycol as a solvent. The solution was stirred until completely dissolved, yielding a homogeneous and transparent solution. Hexamethylenetetramine, with a molar ratio of 1:1.3 to the surfactant, was added to this solution and stirred for 1 hour to obtain a homogeneous solution. Subsequently, potassium salicylate, with a molar ratio of 1:1.8 to the surfactant, was added to the above solution and stirred for 1.5 hours to obtain an online thickener. The dodecyl hydroxypropyl sulfonate betaine, ethylene glycol, hexamethylenetetramine, and potassium salicylate were all of industrial grade or higher purity. The online thickener was mixed with alkaline oilfield produced water at pH 8 at a volume ratio of 1:7 and kept at 70°C for 4 hours to obtain a homogeneous hydrogel. The hydrogel had an apparent viscosity of 27 mPa·s, a surface tension of 29.0 mN / m, and an interfacial tension of 10. -2 The efficiency of core flooding is on the order of mN / m, which increases the efficiency by 15.3% and the production by 14%.

[0027] Practical applications:

[0028] In alkaline reservoirs with produced water pH=8, 8 cubic meters of isolation fluid were first injected into the treatment water well, followed by 2 cubic meters of online thickener, and then another 8 cubic meters of isolation fluid. After two injection cycles while maintaining conventional water injection pressure, the formation pressure recovered to the level before water drive breakthrough, increasing production by 20%.

[0029] Example 4

[0030] An online thickener for oil displacement in alkaline reservoirs and its application method:

[0031] At room temperature, octadecylhydroxypropyl sulfonate betaine was dissolved in ethanol at a concentration of 45% to prepare a surfactant solution. The solution was stirred until completely dissolved to obtain a homogeneous and transparent solution. Formaldehyde solution with a molar ratio of 1:4.2 to the surfactant was added to this solution, and the mixture was stirred for 3 hours to obtain a homogeneous solution. Subsequently, ammonium salicylate with a molar ratio of 1:4 to the surfactant was added to the above solution, and the mixture was stirred for 3 hours to obtain an online thickener. The octadecylhydroxypropyl sulfonate betaine, ethanol, formaldehyde solution, and ammonium salicylate were all of industrial grade or higher purity. The online thickener was mixed with alkaline oilfield produced water at pH 7.5 at a volume ratio of 1:6 and kept at 55°C for 8 hours to obtain a homogeneous hydrogel. The apparent viscosity of the hydrogel was 18.3 mPa·s, the surface tension was 28.8 mN / m, and the interfacial tension was 10. -1 The efficiency of core flooding is on the order of mN / m, which improves the efficiency by 15.0%.

[0032] Practical applications:

[0033] In alkaline reservoirs with produced water pH=7.5, 8 cubic meters of isolation fluid were first injected into the treatment water well, followed by 2 cubic meters of online thickener, and then another 8 cubic meters of isolation fluid. After two injection cycles while maintaining conventional water injection pressure, the formation pressure recovered to the level before water drive breakthrough, increasing production by 12%.

[0034] Example 5

[0035] An online thickener for oil displacement in alkaline reservoirs and its application method:

[0036] At room temperature, erucamide propyl betaine and oleamide propyl betaine were prepared with methanol as solvent at a mass concentration of 35% to obtain a surfactant solution. The solution was stirred until completely dissolved to obtain a homogeneous and transparent solution. Formaldehyde solution with a molar ratio of 1:1.8 to the surfactant was added to this solution, and the mixture was stirred for 1.5 hours to obtain a homogeneous solution. Subsequently, sodium salicylate with a molar ratio of 1:2.5 to the surfactant was added to the above solution, and the mixture was stirred for 2 hours to obtain an online thickener. The erucamide propyl betaine, oleamide propyl betaine, methanol, formaldehyde solution, and sodium salicylate were all of industrial grade or higher purity. The online thickener was mixed with alkaline oilfield produced water at pH 9 at a volume ratio of 1:10 and kept at 90℃ for 2 hours to obtain a homogeneous hydrogel. The apparent viscosity of the hydrogel was 35 mPa·s, the surface tension was 30.7 mN / m, and the interfacial tension was 10. -2 The efficiency of core flooding is on the order of mN / m, which improves the efficiency by 16.1%.

[0037] Practical applications:

[0038] In alkaline reservoirs with produced water pH=9, 10 cubic meters of isolation fluid were first injected into the treatment water well, followed by 2 cubic meters of online thickener, and then another 10 cubic meters of isolation fluid. After one injection cycle under the condition of maintaining conventional water injection pressure, the formation pressure recovered to the level before water drive breakthrough, increasing production by 12%.

[0039] Example 6

[0040] An online thickener for oil displacement in alkaline reservoirs and its application method:

[0041] At room temperature, oleamidopropyl betaine and dodecyl hydroxypropyl sulfobetaine were used as solvents, and a surfactant solution was prepared at a mass concentration of 50% using ethylene glycol. The solution was stirred until completely dissolved to obtain a homogeneous and transparent solution. Trioxymethylene (trioxymethylene) with a molar ratio of 1:4.5 to the surfactant was added to this solution, and the mixture was stirred for 2.5 hours to obtain a homogeneous solution. Subsequently, potassium salicylate (trioxymethylene) with a molar ratio of 1:3.6 to the surfactant was added to the above solution, and the mixture was stirred for 160 minutes to obtain an online thickener. The oleamidopropyl betaine, dodecyl hydroxypropyl sulfobetaine, ethylene glycol, trioxymethylene, and potassium salicylate were all of industrial grade or higher purity. The online thickener was mixed with alkaline oilfield produced water at pH 8 at a volume ratio of 1:8 and kept at 75°C for 3 hours to obtain a homogeneous hydrogel. The apparent viscosity of the hydrogel was 21.3 mPa·s, the surface tension was 27.9 mN / m, and the interfacial tension was 10. -1 The efficiency of core flooding is on the order of mN / m, which improves the efficiency by 14.9%.

[0042] Practical applications:

[0043] In alkaline reservoirs with produced water pH=8, 8 cubic meters of isolation fluid were first injected into the treatment water well, followed by 1 cubic meter of online thickener, and then another 8 cubic meters of isolation fluid. After one injection cycle under normal injection pressure, the formation pressure returned to the level before water drive breakthrough, increasing production by 19%.

[0044] Example 7

[0045] An online thickener for oil displacement in alkaline reservoirs and its application method:

[0046] At room temperature, erucamide propyl betaine and octadecyl hydroxypropyl sulfobetaine were used as solvent in methanol to prepare a surfactant solution at a mass concentration of 45%. The solution was stirred until completely dissolved to obtain a homogeneous and transparent solution. Polyoxymethylene (POM) with a molar ratio of 1:4.6 to the surfactant was added to this solution, and the mixture was stirred for 160 minutes to obtain a homogeneous solution. Subsequently, salicylic acid with a molar ratio of 1:4.4 to the surfactant was added to the above solution, and the mixture was stirred for 2.5 hours to obtain an online thickener. The erucamide propyl betaine, octadecyl hydroxypropyl sulfobetaine, methanol, POM, and salicylic acid were all of industrial grade or higher purity. The online thickener was mixed with alkaline oilfield produced water at pH 10 at a volume ratio of 1:7 and kept at 40°C for 10 hours to obtain a homogeneous hydrogel. The apparent viscosity of the hydrogel was 18.6 mPa·s, the surface tension was 29.4 mN / m, and the interfacial tension was 10. -1 The efficiency of core flooding is on the order of mN / m, which improves the efficiency by 15.2%.

[0047] Practical applications:

[0048] In alkaline reservoirs with produced water pH=10, 7 cubic meters of isolation fluid were first injected into the treatment water well, followed by 1 cubic meter of online thickener, and then another 7 cubic meters of isolation fluid. After two injection cycles while maintaining conventional water injection pressure, the formation pressure recovered to the level before water drive breakthrough, increasing production by 16%.

[0049] Example 8

[0050] An online thickener for oil displacement in alkaline reservoirs and its application method:

[0051] Under normal temperature conditions, erucamide propyl betaine, oleamide propyl betaine, and dodecyl hydroxypropyl sulfobetaine were prepared into a surfactant solution at a mass concentration of 40% using glycerol as a solvent. The solution was stirred until completely dissolved to obtain a homogeneous and transparent solution. Hexamethylenetetramine at a molar ratio of 1:3.2 to the surfactant was added to this solution, and the mixture was stirred for 2 hours to obtain a homogeneous solution. Subsequently, sodium salicylate at a molar ratio of 1:3 to the surfactant was added to the above solution, and the mixture was stirred for 2 hours to obtain an online thickener. The erucamide propyl betaine, oleamide propyl betaine, dodecyl hydroxypropyl sulfobetaine, glycerol, hexamethylenetetramine, and sodium salicylate were all of industrial grade or higher purity. The online thickener was mixed with alkaline oilfield produced water at a volume ratio of 1:9 and kept at 85°C for 2.5 hours to obtain a homogeneous hydrogel. The hydrogel has an apparent viscosity of 34.2 mPa·s, a surface tension of 30.3 mN / m, and an interfacial tension of 10. -1 The efficiency of core flooding is on the order of mN / m, which improves the efficiency by 15.8%.

[0052] Practical applications:

[0053] In alkaline reservoirs with produced water pH=9, 9 cubic meters of isolation fluid were first injected into the treatment water well, followed by 1 cubic meter of online thickener, and then another 9 cubic meters of isolation fluid. After one injection cycle under normal injection pressure, the formation pressure returned to the level before water drive breakthrough, increasing production by 15%.

Claims

1. An online thickener for oil displacement surfactants in alkaline oil reservoirs, characterized in that... It is prepared by the following steps: The first step is to take betaine-based surfactants at room temperature and prepare a surfactant solution with a mass concentration of 30-50% using low-carbon alcohols. Stir until fully dissolved to obtain a uniform and transparent solution. The second step is to add formaldehyde solution or other formaldehyde derivatives in a molar ratio of 1:1-5 to the surfactant solution obtained in the first step, and stir until it is fully dissolved to form a homogeneous solution, stirring for 1-3 hours. The third step is to add salicylic acid or its salt in a molar ratio of 1:1-3 to the surfactant to the above solution, and stir for 1-3 hours to obtain an online thickener for oil displacement in alkaline reservoirs.

2. The thickener according to claim 1, characterized in that: The betaine surfactant is selected from at least one or a combination of betaine surfactants such as oleamidopropyl betaine, erucamide propyl betaine, dodecyl hydroxypropyl sulfobetaine, and octadecyl hydroxypropyl sulfobetaine, with industrial grade or higher purity; the solvent is selected from one or more of methanol, ethanol, n-propanol, isopropanol, ethylene glycol, and glycerol, with industrial grade or higher purity. The second step is that the formaldehyde solution is an industrial grade or higher purity product, and the other forms of formaldehyde derivatives are industrial grade or higher purity formaldehyde aqueous solution, trioxymethylene, and hexamethylenetetramine. The third step is that the salicylic acid or its salt is salicylic acid, sodium salicylate, potassium hydrochloride, or ammonium salicylate of industrial grade or higher purity.

3. The thickener according to claim 1, characterized in that: The first step is to take betaine-based surfactants at room temperature and prepare a surfactant solution with a mass concentration of 30-50% using low-carbon alcohols. Stir until fully dissolved to obtain a uniform and transparent solution. The second step is to add formaldehyde solution or other formaldehyde derivatives in a molar ratio of 1:1-5 to the surfactant solution obtained in the first step, and stir until it is fully dissolved to form a homogeneous solution, stirring for 1-3 hours. The third step is to add salicylic acid or its salt in a molar ratio of 1:1-3 to the surfactant to the above solution, and stir for 1-3 hours to obtain an online thickener for oil displacement in alkaline reservoirs.

4. The method for preparing an online thickener for alkaline reservoir displacement surfactant according to any one of claims 1-3, characterized in that... Includes the following steps: The first step is to take betaine-based surfactants at room temperature and prepare a surfactant solution with a mass concentration of 30-50% using low-carbon alcohols. Stir until fully dissolved to obtain a uniform and transparent solution. The second step is to add formaldehyde solution or other formaldehyde derivatives in a molar ratio of 1:1-5 to the surfactant solution obtained in the first step, and stir until it is fully dissolved to form a homogeneous solution, stirring for 1-3 hours. The third step is to add salicylic acid or its salt in a molar ratio of 1:1-3 to the surfactant to the above solution, and stir for 1-3 hours to obtain an online thickener for oil displacement in alkaline reservoirs.

5. Use of the online thickener for alkaline reservoir displacement surfactant as described in any one of claims 1-3 in the petrochemical field.