Well-washing fluids suitable for heavy oil deposition in oilfield wellbores, their preparation methods and applications

Abstract

This invention relates to the field of oilfield chemical technology, specifically to a well-washing fluid suitable for heavy oil deposits in oilfield wellbores, its preparation method, and its application. The well-washing fluid, by weight percentage, consists of the following raw materials: 3%–5% organic solvent, 10%–12% sodium silicate aqueous solution, 0.05%–0.15% sodium chloride, 0.25%–0.5% surfactant, 0.25%–0.5% additives, and water as the balance. The well-washing fluid of this invention can be used in well-washing operations. No additional heating equipment is required at the oilfield site; self-heating within the well is sufficient to achieve a good cleaning effect. It achieves low-temperature cleaning, and the oil washing efficiency on the casing inner wall can reach over 95% within 30 minutes. After cleaning, the solution system allows for rapid oil-water separation at the surface, with a separation time of less than 10 minutes, which is beneficial for heavy oil recovery.

Description

Technical Field

[0001] This invention relates to the field of oilfield chemical technology, specifically to a well-washing fluid suitable for heavy oil deposition in oilfield wellbores, its preparation method, and its application. Background Technology

[0002] Heavy oil refers to crude oil with high viscosity and poor fluidity. It is characterized by high content of gums, asphaltenes, and waxes, and a low pour point. During extraction, the drop in temperature often causes heavy oil to deposit and adhere to the casing walls and drill strings, making it difficult to clean. This situation severely affects the normal operation of equipment and production efficiency. Heavy oil well-washing fluid is a key chemical used in the petroleum industry for cleaning oil pipelines, crude oil storage tanks, casing walls, and other equipment. Traditional heavy oil well-washing fluids often suffer from poor permeability and unsatisfactory oil-washing effects, and require high temperatures (typically 50-80℃) during the cleaning process. This not only wastes energy but also increases construction risks and costs.

[0003] In recent years, the research and development of heavy oil well-washing fluids has gradually shifted towards low-temperature, environmentally friendly methods and rapid separation of oil and water at the surface. While some heavy oil well-washing fluids based on surfactants have improved cleaning effectiveness to some extent, their preparation processes are complex, requiring high temperatures (80℃), and they cannot achieve rapid separation at the surface, remaining in an emulsion state, which fails to meet the demands for low-temperature, high-efficiency cleaning. Furthermore, these well-washing fluids often require specific surfactants, which are not only expensive but also pollute the environment. Currently, there are also heavy oil well-washing fluids based on organic solvents, but these contain aromatic hydrocarbons, such as xylene, which are highly toxic to humans and pollute the environment. Moreover, these organic solvents are expensive, resulting in low economic benefits.

[0004] Currently, there are some heavy oil well washing fluid products on the market, but these products generally have the following problems:

[0005] (1) Poor permeability: Due to the high viscosity of heavy oil, traditional well cleaning fluids have difficulty penetrating into the interior of heavy oil, resulting in poor cleaning effect;

[0006] (2) Low oil washing efficiency: Even under high temperature conditions, the traditional well washing fluid is still not ideal for cleaning heavy oil, and multiple cleanings are required to achieve satisfactory results;

[0007] (3) High energy consumption: Because cleaning needs to be carried out at a high temperature, a large amount of energy is consumed;

[0008] (4) Environmental pollution: Some well washing fluids will generate harmful wastewater and waste gas during production and use. Summary of the Invention

[0009] To address the aforementioned problems, this invention proposes a well-washing fluid suitable for heavy oil deposition in oilfield wellbores, its preparation method, and its application. The well-washing fluid is prepared primarily from organic solvents, sodium silicate aqueous solution, and surfactants. It exhibits rapid oil-water separation at the surface, good permeability, high oil washing efficiency, non-solidification at low temperatures, low energy consumption, and environmental friendliness.

[0010] The well-washing fluid for heavy oil deposition in oilfield wellbores described in this invention is composed of the following raw materials by weight percentage: 3%~5% organic solvent, 10%~12% sodium silicate aqueous solution, 0.05%~0.15% sodium chloride, 0.25%~0.5% surfactant, 0.25%~0.5% additives, and water as the balance.

[0011] The organic solvent is n-dodecane, n-tetradecane, isotetradecane, n-hexadecane, or white oil. Organic solvents are key components of well-washing fluids, with n-tetradecane and white oil being the two most effective. These organic solvents were chosen because they are environmentally friendly, effective even at low temperatures (reducing construction costs and difficulty, eliminating the need for surface heating equipment, requiring only internal heating within the well, with wellhead temperatures typically between 35-40°C), and facilitate rapid separation and recovery of heavy oil at the surface. Both n-tetradecane and white oil are non-toxic, odorless, and environmentally friendly organic solvents, and do not possess the flammability of gasoline or kerosene. Heavy oil is mainly composed of high-molecular-weight alkanes, cycloalkanes, and aromatics, exhibiting complex chemical structures and strong intermolecular forces. Straight-chain alkanes such as n-tetradecane have high lipophilicity, effectively dissolving long-chain alkanes and non-polar components in heavy oil. Due to the principle of "like dissolves like," straight-chain alkane molecules have good compatibility with non-polar components in heavy oil, thus dissolving heavy oil more efficiently. Straight-chain alkanes are more flexible and have a tighter intermolecular packing than branched or cyclic carbon atoms, which helps them penetrate into the interior of heavy oil, disrupting its intermolecular forces. Furthermore, with the assistance of appropriate surfactants, straight-chain alkanes are more likely to form stable oil-water emulsions, promoting the emulsification and dispersion of heavy oil and improving washing efficiency.

[0012] Straight-chain alkanes can reduce the interfacial tension between heavy oil and solid surfaces, thus facilitating the detachment of heavy oil from the surface. Straight-chain alkanes are more flexible and have a tighter molecular packing than branched or cyclic alkanes, which helps them penetrate the interior of the heavy oil and disrupt its intermolecular forces.

[0013] The ratio of organic solvent to sodium silicate aqueous solution is 1:2 to 1:4 by mass.

[0014] Sodium silicate has a modulus greater than 2, preferably 3.2. The sodium silicate aqueous solution has a mass fraction of 40%, resulting in a relatively thin solution with low viscosity and good fluidity. If the modulus is too small, the fluidity will be poor, making pumping and circulation well washing operations impossible; if the modulus is too large, it will not effectively reduce the viscosity of heavy oil.

[0015] This invention uses an aqueous solution of sodium silicate, in which sodium ions (Na+) are present. + Sodium silicate can interact with molecules in oil, reducing the attraction between oil molecules, improving the interfacial tension between oil and water, thereby lowering the viscosity of heavy oil and increasing its permeability. Furthermore, sodium silicate aqueous solution is alkaline and can significantly increase the pH value of the aqueous solution. Under high pH conditions, some acidic components in heavy oil (such as natural fatty acids) will transform into anionic surfactants, enhancing the emulsification effect at the oil-water interface. Simultaneously, it can disrupt the strong interfacial adsorption between heavy oil and solid surfaces, and promote the dissociation of heavy oil molecules.

[0016] Adding a trace amount of sodium chloride can effectively increase the interfacial tension between oil and water, thereby achieving rapid oil-water separation. Due to the ion shielding effect, sodium chloride dissociates into sodium ions (Na+) in water. + ) and chloride ions (Cl - These ions are distributed in the aqueous phase and form an electrical double layer near the oil-water interface, restricting direct interactions between oil and water molecules. Furthermore, sodium chloride ions competitively adsorb at the aqueous interface, displacing some surfactant molecules and weakening the surfactant's ability to reduce interfacial tension. For systems containing naturally occurring surfactants (such as gums and asphaltenes in heavy oil), sodium chloride inhibits their adsorption at the interface, causing the interfacial tension to rise again.

[0017] The additives mentioned are Span-80, polysorbate-80, lecithin, or lauric acid.

[0018] The surfactant is sodium dodecyl sulfate, sodium dodecyl sulfonate, glyceryl monostearate, or sodium dioctyl sulfosuccinate.

[0019] The preparation method of the well cleaning fluid suitable for heavy oil deposition in oilfield wellbores according to the present invention is as follows: weigh each raw material according to the proportion, mix them, stir at room temperature for 30 min until uniform and transparent to obtain the finished product. The stirring speed is 60 r / min. The preferred order of material addition is water, surfactant, sodium chloride, sodium silicate aqueous solution, organic solvent, and additives.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] (1) The well cleaning fluid described in this invention reduces construction costs and difficulty. No additional heating equipment is required at the oilfield site. It can achieve a good cleaning effect simply by self-heating inside the well, thus realizing low-temperature cleaning, reducing the risk of well cleaning operations, and reducing both costs and energy consumption.

[0022] (2) The well cleaning fluid of the present invention has good penetration and cleaning ability for heavy oil and can be used for cleaning casing and drill string of heavy oil wells. Traditional well cleaning fluid usually requires a long time of circulation to achieve a cleaning efficiency of 90%. The present invention can achieve an oil washing efficiency of more than 95% on the inner wall of the casing in only 30 minutes at 35℃, and can reach up to 99%.

[0023] (3) The raw materials of the well washing fluid described in this invention are cheap, readily available, environmentally friendly, non-toxic, and odorless. They do not pose a risk of flammability or explosion, which greatly reduces the cost of well washing operations and improves the safety of well washing operations.

[0024] (4) The solution system after the well cleaning fluid described in this invention is used can achieve rapid oil-water separation on the ground. The separation time is less than 10 minutes. After the oil phase and water phase are rapidly separated, the heavy oil is present in the organic solvent, which is beneficial to the recovery of the washed heavy oil. Attached Figure Description

[0025] Figure 1 The image shows the cleaning effect of the well-washing fluid described in this invention. In the image, A is the hollow steel column before cleaning, B is the well-washing fluid before cleaning, C is the hollow steel column after cleaning, D is the hollow steel column after cleaning and rinsing with clean water for 1 second, and E is the solution system after cleaning.

[0026] Figure 2 The image shows the cleaning effect of the well-washing fluid described in Comparative Example 1. In the image, A is the hollow steel column before cleaning, B is the well-washing fluid before cleaning, C is the hollow steel column after cleaning, and D is the solution system after cleaning. Detailed Implementation

[0027] Example 1

[0028] The well-washing fluid suitable for heavy oil deposits in oilfield wellbores is composed of the following raw materials by weight percentage:

[0029] 3% organic solvent

[0030] 10% sodium silicate aqueous solution

[0031] Sodium chloride 0.05%

[0032] Surfactant 0.25%

[0033] 0.25% of the additives

[0034] Water 86.4%

[0035] The organic solvent is n-dodecane, the surfactant is sodium dodecyl sulfonate, the additive is Span-80, the sodium silicate modulus is 3.2, and the mass fraction of the sodium silicate aqueous solution is 40%.

[0036] Preparation method: Pour 86.4 parts of water into a stirring container, set the speed of the constant speed magnetic stirrer to 60 r / min, and then add 0.25 parts of surfactant, 0.05 parts of sodium chloride, 10 parts of sodium silicate aqueous solution, 3 parts of organic solvent, and 0.25 parts of additives to the stirring container in sequence. Stir at room temperature for 30 min until uniform and transparent to obtain the finished product.

[0037] Example 2

[0038] The well-washing fluid suitable for heavy oil deposits in oilfield wellbores is composed of the following raw materials by weight percentage:

[0039] 4% organic solvent

[0040] 11% sodium silicate aqueous solution

[0041] Sodium chloride 0.05%

[0042] Surfactant 0.5%

[0043] 0.3% of additives

[0044] Water 85.1%

[0045] The organic solvent is isotetradecane, the surfactant is sodium dioctyl sulfosuccinate, the auxiliary agent is lecithin, the sodium silicate modulus is 3.2, and the mass fraction of the sodium silicate aqueous solution is 40%.

[0046] Preparation method: Pour 85.1 parts of water into a stirring container, set the speed of the constant speed magnetic stirrer to 60 r / min, and then add 0.5 parts of surfactant, 0.05 parts of sodium chloride, 11 parts of sodium silicate aqueous solution, 4 parts of organic solvent, and 0.3 parts of additives to the stirring container in sequence. Stir at room temperature for 30 min until uniform and transparent to obtain the finished product.

[0047] Example 3

[0048] The well-washing fluid suitable for heavy oil deposits in oilfield wellbores is composed of the following raw materials by weight percentage:

[0049] 5% organic solvent

[0050] 12% sodium silicate aqueous solution

[0051] Sodium chloride 0.15%

[0052] Surfactant 0.5%

[0053] 0.5% of the additives

[0054] Water 83.4%

[0055] The organic solvent is hexadecane, the surfactant is glyceryl monostearate, the auxiliary agent is lauric acid, the sodium silicate modulus is 3.2, and the mass fraction of the sodium silicate aqueous solution is 40%.

[0056] Preparation method: Take 83.4 parts of water and pour it into a stirring container. Use a constant speed magnetic stirrer set to 60 r / min. Then add 0.5 parts of surfactant, 0.15 parts of sodium chloride, 12 parts of sodium silicate aqueous solution, 5 parts of organic solvent, and 0.5 parts of additives to the stirring container in sequence. Stir at room temperature for 30 min until uniform and transparent to obtain the finished product.

[0057] Example 4

[0058] The well-washing fluid suitable for heavy oil deposits in oilfield wellbores is composed of the following raw materials by weight percentage:

[0059] 3% organic solvent

[0060] 10% sodium silicate aqueous solution

[0061] Sodium chloride 0.1%

[0062] Surfactant 0.25%

[0063] 0.25% of the additives

[0064] Water 86.4%

[0065] The organic solvent is white oil, the surfactant is sodium dodecyl sulfate, the additive is polysorbate-80, the sodium silicate modulus is 3.2, and the mass fraction of the sodium silicate aqueous solution is 40%.

[0066] Preparation method: Pour 86.4 parts of water into a stirring container, set the speed of the constant speed magnetic stirrer to 60 r / min, and then add 0.25 parts of surfactant, 0.1 parts of sodium chloride, 10 parts of sodium silicate aqueous solution, 3 parts of organic solvent, and 0.25 parts of additives to the stirring container in sequence. Stir at room temperature for 30 min until uniform and transparent to obtain the finished product.

[0067] Example 5

[0068] The well-washing fluid suitable for heavy oil deposits in oilfield wellbores is composed of the following raw materials by weight percentage:

[0069] 3% organic solvent

[0070] 10% sodium silicate aqueous solution

[0071] Sodium chloride 0.1%

[0072] Surfactant 0.25%

[0073] 0.25% of the additives

[0074] Water 86.4%

[0075] The organic solvent is n-tetradecane, the surfactant is sodium dodecyl sulfate, the additive is polysorbate-80, the sodium silicate modulus is 3.2, and the mass fraction of the sodium silicate aqueous solution is 40%.

[0076] Preparation method: Pour 86.4 parts of water into a stirring container, set the speed of the constant speed magnetic stirrer to 60 r / min, and then add 0.25 parts of surfactant, 0.1 parts of sodium chloride, 10 parts of sodium silicate aqueous solution, 3 parts of organic solvent, and 0.25 parts of additives to the stirring container in sequence. Stir at room temperature for 30 min until uniform and transparent to obtain the finished product.

[0077] Comparative Example 1

[0078] Heavy oil well washing fluid, by weight percentage, is composed of the following raw materials:

[0079] 10% sodium silicate aqueous solution

[0080] Sodium chloride 0.1%

[0081] Surfactant 0.25%

[0082] 0.25% of the additives

[0083] Water 89.4%

[0084] It contains no organic solvents, the surfactant is sodium dodecyl sulfate, the additive is polysorbate-80, the sodium silicate modulus is 3.2, and the mass fraction of the sodium silicate aqueous solution is 40%.

[0085] Preparation method: Pour 89.4 parts of water into a stirring container, set the speed of the constant speed magnetic stirrer to 60 r / min, and then add 0.25 parts of surfactant, 0.1 parts of sodium chloride, 10 parts of sodium silicate aqueous solution and 0.25 parts of additives to the stirring container in sequence. Stir at room temperature for 30 min until uniform and transparent to obtain the finished product.

[0086] Comparative Example 2

[0087] Heavy oil well washing fluid, by weight percentage, is composed of the following raw materials:

[0088] 3% organic solvent

[0089] Sodium chloride 0.1%

[0090] Surfactant 0.25%

[0091] 0.25% of the additives

[0092] Water 96.4%

[0093] The organic solvent is n-tetradecane, the surfactant is sodium dodecyl sulfate, and the additive is polysorbate-80.

[0094] Preparation method: Pour 96.4 parts of water into a stirring container, set the speed of the constant speed magnetic stirrer to 60 r / min, and then add 0.25 parts of surfactant, 0.1 parts of sodium chloride, 3 parts of organic solvent and 0.25 parts of additives to the stirring container in sequence. Stir at room temperature for 30 min until uniform and transparent to obtain the finished product.

[0095] Comparative Example 3

[0096] Heavy oil well washing fluid, by weight percentage, is composed of the following raw materials:

[0097] 3% organic solvent

[0098] 10% sodium silicate aqueous solution

[0099] Surfactant 0.25%

[0100] 0.25% of the additives

[0101] Water 86.5%

[0102] The organic solvent is n-tetradecane, the surfactant is sodium dodecyl sulfate, the additive is polysorbate-80, the sodium silicate modulus is 3.2, and the mass fraction of the sodium silicate aqueous solution is 40%.

[0103] Preparation method: Pour 86.5 parts of water into a stirring container, set the speed of the constant speed magnetic stirrer to 60 r / min, and then add 0.25 parts of surfactant, 10 parts of sodium silicate aqueous solution, 3 parts of organic solvent and 0.25 parts of additives to the stirring container in sequence. Stir at room temperature for 30 min until uniform and transparent to obtain the finished product.

[0104] Comparative Example 4

[0105] Heavy oil well washing fluid, by weight percentage, is composed of the following raw materials:

[0106] 3% organic solvent

[0107] 10% sodium silicate aqueous solution

[0108] Sodium chloride 0.1%

[0109] 0.25% of the additives

[0110] Water 86.65%

[0111] The organic solvent is n-tetradecane, the additive is polysorbate-80, the sodium silicate modulus is 3.2, and the mass fraction of the sodium silicate aqueous solution is 40%.

[0112] Preparation method: Pour 86.65 parts of water into a stirring container, set the speed of the constant speed magnetic stirrer to 60 r / min, and then add 0.1 parts of sodium chloride, 10 parts of sodium silicate aqueous solution, 3 parts of organic solvent and 0.25 parts of additives to the stirring container in sequence. Stir at room temperature for 30 min until uniform and transparent to obtain the finished product.

[0113] Test case

[0114] Cleaning performance test:

[0115] Experimental methods:

[0116] 1. Apply heavy oil to the outer surface of a hollow steel column with a diameter of 100 mm and a wall thickness of 3 mm until no steel column surface is exposed (the viscosity of the heavy oil is greater than 2500 mPa·s, measured at 25℃).

[0117] 2. Heat the prepared well-washing fluid to 35°C in a water bath, and use a homemade stirring clamp to hold the hollow steel column coated with thick oil and immerse it in the well-washing fluid;

[0118] 3. Turn on the agitator, set the speed to 150 r / min, and rotate and rinse for 30 minutes. Then remove the clamp and steel column, remove the surface moisture, and the cleaning is complete.

[0119] The well-washing fluids obtained in Examples 1-5 and Comparative Examples 1-4 were used to clean the outer surface of the steel column according to the above-described cleaning steps. The experimental results are as follows:

[0120] .

[0121] The well-cleaning fluid of this invention achieves ideal cleaning results. At a temperature of 35°C, the cleaning efficiency exceeds 90%, reaching a maximum of 99%, thus meeting the cleaning requirements for petroleum equipment. Using the well-cleaning fluid of this invention, the heavy oil and aqueous solution can be rapidly separated within 10 minutes after cleaning. Specific effects are as follows: Figure 1 As shown in Comparative Example 1, after cleaning with the well-washing fluid, only a small portion of the steel column surface was exposed. The specific effects of the well-washing fluid solution are as follows: Figure 2 As shown in the figure, although the cleaning efficiency exceeded 90% when using the well washing fluid described in Comparative Example 3, the separation time between heavy oil and aqueous solution was significantly prolonged.

Claims

1. A well-washing fluid suitable for rapid recovery of heavy oil deposits in oilfield wellbores, characterized in that, The well-washing fluid, by weight percentage, comprises the following raw materials: 3%–5% organic solvent, 10%–12% sodium silicate aqueous solution, 0.05%–0.15% sodium chloride, 0.25%–0.5% surfactant, 0.25%–0.5% additives, and water as the balance; the sodium silicate aqueous solution has a modulus greater than 2 and a mass fraction of 40%; the well-washing fluid is used in well-washing operations. The organic solvent is n-tetradecane, isotetradecane, or n-hexadecane; The additives mentioned are Span-80, polysorbate-80, lecithin, or lauric acid; The surfactant is sodium dodecyl sulfate, sodium dodecyl sulfonate, glyceryl monostearate, or sodium dioctyl sulfosuccinate.

2. The well-washing fluid for rapid recovery of heavy oil deposits in oilfield wellbores according to claim 1, characterized in that, The ratio of organic solvent to sodium silicate aqueous solution is 1:2 to 1:4 by mass.

3. The method for preparing the well-washing fluid suitable for rapid recovery of heavy oil deposits in oilfield wellbores according to any one of claims 1-2, characterized in that, Weigh out each ingredient in proportion, mix them, and stir at room temperature until uniform and transparent to obtain the finished product.

4. The application of the well-washing fluid according to any one of claims 1-2, suitable for rapid recovery of heavy oil deposits in oilfield wellbores, in well-washing operations.

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