Thickened oil viscosity-reducing formation working fluid, working system, preparation method and application thereof

Abstract

The present application belongs to the field of oilfield chemistry and workover engineering process, and discloses a stratum working fluid for thick oil viscosity reduction, a working system, a preparation method and application thereof. The stratum working fluid for thick oil viscosity reduction comprises the following components by weight: 60-91 parts of water, 1-5 parts of anti-swelling agent, 5-20 parts of stratum cleaning agent and 3-15 parts of thick oil viscosity reducer. The working system for thick oil viscosity reduction comprises the above-mentioned stratum working fluid and a wellbore working fluid for cleaning dead oil in the wellbore. The stratum working fluid of the present application reduces the viscosity of crude oil in the near wellbore zone through viscosity reduction and dispersion, wetting drag reduction and surfactant assisted cleanup, reduces organic plugging, and has little corrosion to the pipe string. When the working system of the present application is applied, the soak time is greatly shortened, the entire construction process can be completed within three days, the construction period is greatly shortened, and the production efficiency is improved.

Description

Technical Field

[0001] This invention relates to the fields of oilfield chemistry and well workover engineering, and particularly to a formation working fluid, working system, preparation method and application for reducing viscosity of heavy oil. Background Technology

[0002] Heavy oil has a high content of asphaltenes and gums, resulting in high viscosity, poor fluidity, and a tendency to form organic blockages near the wellbore. Some heavy oil reservoirs, due to their poor crude oil properties, small reservoir blocks, large burial depth, and poor reservoir airtightness, cannot utilize thermal development methods such as steam injection, steam drive, or SAGD; currently, water drive development is employed. Due to long-term water injection development, reservoir temperature decreases, and crude oil viscosity increases accordingly, further deteriorating fluidity. The high content of gums and asphaltenes in heavy oil crude oil leads to strong adhesion, easily forming organic blockages in narrow channels such as pores and throats. Simultaneously, it is susceptible to the influence of external fluids and solid phases during operation, causing organic blockages such as sludge in the near-wellbore area. These organic blockages gradually cause a decrease in the permeability of the liquid phase (especially the oil phase), manifested as a decline in dynamic fluid level, a decrease in single-well production, and a significant challenge in stabilizing oil well production.

[0003] To address this issue, the industry has experimented with measures such as CO2 huff and puff. CO2 huff and puff is an effective measure to increase the production of low-yield and inefficient heavy oil wells. The injected CO2 is a supercritical fluid that dissolves the remaining oil around the reservoir, causing the volume of the remaining oil in the formation to expand. This increases the oil saturation in the pores, improves the relative permeability of oil and water, and enhances the fluidity of crude oil, thereby reducing water cut and increasing crude oil production.

[0004] Patent CN115288644A discloses a method for enhancing oil recovery in low-permeability reservoirs using composite carbon dioxide huff and puff. The mechanism of this CO2 huff and puff technology for increasing oil production mainly utilizes the fact that CO2's solubility in crude oil is 4.4 times that in water. When CO2 dissolves in crude oil, it can increase the crude oil volume by 10% to 30%, significantly reducing crude oil viscosity, lowering the interfacial tension between oil and water, improving the oil-water mobility ratio, and extracting and vaporizing light hydrocarbon components from the crude oil. Combined with nano-displacement agents, this achieves enhanced oil recovery and improved drainage.

[0005] Patent CN112360408A discloses a method for enhancing heavy oil recovery by injecting carbon dioxide thermal fluid. This method involves heating carbon dioxide gas to 80-100°C at the surface and then injecting it into the formation to heat and reduce the viscosity of the heavy oil. The resulting heavy oil-carbon dioxide mixture is then separated, and the carbon dioxide gas is recovered. Heavy oil production can be increased using huff and puff and displacement techniques.

[0006] Although CO2 huff and puff can increase heavy oil production, the amount of CO2 used per well is generally over 500 tons, with a daily injection volume of 20-100 tons, an injection time of more than a week, and a well shut-in period of 1-2 months, resulting in a long construction cycle. Furthermore, CO2 is an acidic gas, which causes significant corrosion to the tubing.

[0007] Therefore, measures to increase the production of heavy oil wells using CO2 huff and puff still have many shortcomings, and there is an urgent need in this field to develop more efficient single-well production enhancement technologies. Summary of the Invention

[0008] To address the above problems, this invention provides a formation working fluid for reducing viscosity of heavy oil, a working system, its preparation method, and its application.

[0009] According to one aspect of the present invention, a formation working fluid for reducing viscosity of heavy oil is provided, the formation working fluid comprising the following components by weight: 60 to 91 parts water, 1 to 5 parts anti-swelling agent, 5 to 20 parts formation cleaning agent, and 3 to 15 parts heavy oil viscosity reducer.

[0010] According to one embodiment of the present invention, the anti-swelling agent is selected from at least one of potassium chloride, ammonium chloride, tetraethylammonium sulfate, and hexadecyltrimethylammonium fluoride.

[0011] According to one embodiment of the present invention, the formation cleaning agent comprises the following components: alcohol ether, fatty alcohol polyoxyethylene ether, alkali, ethylene glycol, and emulsifier.

[0012] According to one embodiment of the present invention, the formation cleaning agent comprises the following components: oleyl alcohol polyoxyethylene ether, fatty alcohol polyoxyethylene ether, cocamidopropyl betaine, brine, ethylene glycol, fluorocarbon surfactant, alpha amylase, triethanolamine, and water.

[0013] According to one embodiment of the present invention, the mass percentages of each component of the formation cleaning agent are as follows: 5%~10% oleyl alcohol polyoxyethylene ether, 1%~2% fatty alcohol polyoxyethylene ether, 1%~2% cocamidopropyl betaine, 5%~10% brine, 1%~5% ethylene glycol, 1%~3% fluorocarbon surfactant, 1%~5% alpha amylase, 1%~3% triethanolamine, and the balance being water.

[0014] According to one embodiment of the present invention, the heavy oil viscosity reducer comprises the following components: various surfactants, mutual solvents, and organic solvents.

[0015] According to one embodiment of the present invention, the heavy oil viscosity reducer comprises the following components: sorbitan stearate, sodium fatty alcohol polyoxyethylene ether sulfate, fluorocarbon surfactant, demulsifier, tetrasodium aminotrimethylene phosphonate, and water.

[0016] According to one embodiment of the present invention, the mass percentages of each component of the heavy oil viscosity reducer are as follows: sorbitan stearate 15%~18%, sodium fatty alcohol polyoxyethylene ether sulfate 20%~30%, fluorocarbon surfactant 2%~5%, demulsifier 3%~10%, tetrasodium aminotrimethylene phosphonate 3%~10%, and the balance being water.

[0017] According to one embodiment of the present invention, the water is selected from at least one of clean water, oil well electric pump fluid, and oily wastewater treated by a combined station.

[0018] According to another aspect of the present invention, a method for preparing a formation working fluid for reducing viscosity of heavy oil according to any of the above embodiments is provided, the method comprising the following steps: Water is used as the base liquid. Anti-swelling agent and formation cleaning agent are added to the base liquid and stirred evenly to obtain a first mixture. Add a thick oil viscosity reducer to the first mixture and stir until homogeneous to obtain a second mixture; The second mixture is heated to a set temperature to obtain the formation working fluid.

[0019] According to one embodiment of the present invention, the stirring time for preparing the first mixture is 10 to 30 minutes.

[0020] According to one embodiment of the present invention, the stirring time for preparing the second mixture is 5 to 10 minutes.

[0021] According to one embodiment of the present invention, the set temperature is not lower than 50°C.

[0022] According to another aspect of the present invention, a working system for reducing the viscosity of heavy oil is provided, the working system comprising the following: Formation working fluid for heavy oil viscosity reduction as described in any of the above embodiments; and Wellbore working fluid used to clean dead oil in wellbores.

[0023] According to one embodiment of the present invention, the wellbore working fluid comprises the following components by weight: 35-87 parts water, 2-15 parts clay anti-swelling agent, 10-40 parts well washing fluid, and 1-10 parts heavy oil viscosity reducer.

[0024] According to one embodiment of the present invention, the clay anti-swelling agent comprises 50% to 75% by mass of polyquaternary ammonium salt and 25% to 50% by mass of ammonium chloride.

[0025] According to one embodiment of the present invention, the well-washing fluid comprises the following components by mass percentage: 8%~15% oleyl alcohol polyoxyethylene ether, 1%~2% fatty alcohol polyoxyethylene ether, 1%~2% cocamidopropyl betaine, 1%~5% ethylene glycol, 0.5%~3% fluorocarbon surfactant, 1%~5% alpha amylase, 1%~3% triethanolamine, and the balance being water.

[0026] According to another aspect of the present invention, an application of the working system according to any of the above embodiments is provided, wherein the working system is applied using any of the following four processes: Process 1: First, use the wellbore working fluid for reverse circulation to flush the well, then squeeze the formation working fluid into the casing, and then shut the well in. Process 2: First, use the wellbore working fluid for positive circulation to flush the well, then squeeze the formation working fluid into the tubing, and then shut the well in. Process 3: First, use the wellbore working fluid for reverse circulation to wash the well, then squeeze the formation working fluid into the casing, use hot water to displace the formation working fluid into the formation, and then shut off the well. Process 4: First, use the wellbore working fluid for positive circulation to flush the well, then squeeze the formation working fluid into the tubing, use hot water to displace the formation working fluid into the formation, and then shut off the well.

[0027] According to one embodiment of the present invention, the well-sealing time is 12 to 48 hours.

[0028] According to one embodiment of the present invention, the temperature of the hot water is above 50°C.

[0029] By adopting the above technical solutions, the formation working fluid, working system, preparation method, and application for heavy oil viscosity reduction provided by this invention have at least one of the following advantages compared with the prior art: (1) The formation working fluid of the present invention reduces the viscosity of crude oil in the near-wellbore zone and reduces organic blockage through viscosity reduction and dispersion, wetting and drag reduction, and surface activity to aid drainage; (2) The main components of the formation working fluid of the present invention are water, surfactants, etc., which have almost no corrosive effect on the tubing; (3) The working system for reducing viscosity of heavy oil in this invention includes a wellbore working fluid that can effectively clean dead oil in the wellbore and a formation working fluid that can reduce the viscosity of crude oil in the near-wellbore zone. Through the synergy of the two, organic blockage in the wellbore and near-wellbore zone is reduced, while water-sensitive and water-locking damage is reduced, and oil phase permeability is improved, ultimately achieving the goal of increasing crude oil production per well. (4) The working system for reducing viscosity of heavy oil of the present invention significantly shortens the well simmering time when applied, and the entire construction process can be completed within three days, greatly shortening the construction cycle and improving production efficiency. Attached Figure Description

[0030] The accompanying drawings are provided to further illustrate the present disclosure and form part of the specification. They are used together with the following detailed description to explain the present disclosure, but do not constitute a limitation thereof. In the drawings: Figure 1 A flowchart of a method for preparing a formation working fluid for reducing viscosity of heavy oil according to an embodiment of the present invention is shown. Detailed Implementation

[0031] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0032] The terms "comprising" and "having," and any variations thereof, used in the specification and accompanying drawings of this invention are intended to cover non-exclusive inclusion; the terms "first," "second," etc., used in the specification, claims, or accompanying drawings of this invention are used to distinguish different objects, not to describe a particular order. "A plurality of" means two or more, unless otherwise explicitly specified.

[0033] Furthermore, the reference to "embodiment" herein means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of the invention. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0034] One objective of this invention is to provide a formation working fluid for reducing the viscosity of heavy oil. This fluid comprises, by weight, the following components: 60-91 parts water, 1-5 parts anti-swelling agent, 5-20 parts formation cleaning agent, and 3-15 parts heavy oil viscosity reducer. This working fluid reduces the viscosity of crude oil in the formation through viscosity reduction and dispersion, wetting and drag reduction, and surface-active drainage enhancement, thereby facilitating extraction and increasing single-well production.

[0035] In some embodiments, the water may be selected from at least one of clean water, oil well electric pump fluid, and oily wastewater treated by the combined station. By flexibly selecting at least one of clean water, oil well electric pump fluid, and oily wastewater treated by the combined station as the base liquid, resources can be saved, pollution reduced, oil production efficiency improved, system flexibility and adaptability enhanced, and economic benefits increased.

[0036] Expansive clay minerals in formations swell upon contact with water, potentially sealing off pores that are not inherently porous, thus reducing formation permeability. Anti-swelling agents effectively prevent clay swelling, thereby avoiding pore blockage and maintaining formation permeability. In some embodiments, the anti-swelling agent is selected from at least one of potassium chloride, ammonium chloride, tetraethylammonium sulfate, and hexadecyltrimethylammonium fluoride.

[0037] Due to long-term geological processes and oil and gas extraction activities, rocks in geological formations often have a large amount of crude oil adhering to their surfaces. This crude oil not only reduces the permeability of the formation and affects the efficiency of oil and gas extraction, but may also damage the formation structure, causing problems such as rock expansion and fracture closure. Therefore, this invention uses a formation cleaning agent to remove the crude oil adhering to the rocks in the formation. The formation cleaning agent needs not only to have good solubility for crude oil, but also to have low corrosiveness to the formation rocks to avoid secondary damage to the formation. In some embodiments, the formation cleaning agent may include the following components: alcohol ethers, fatty alcohol polyoxyethylene ethers, alkalis, ethylene glycol, and emulsifiers. For example, a formation cleaning agent may specifically include oleyl alcohol polyoxyethylene ether, fatty alcohol polyoxyethylene ether, cocamidopropyl betaine, brine, ethylene glycol, fluorocarbon surfactant, alpha amylase, triethanolamine, and water, with the following mass percentages: oleyl alcohol polyoxyethylene ether 5%–10%, fatty alcohol polyoxyethylene ether 1%–2%, cocamidopropyl betaine 1%–2%, brine 5%–10%, ethylene glycol 1%–5%, fluorocarbon surfactant 1%–3%, alpha amylase 1%–5%, triethanolamine 1%–3%, and the balance being water. The oleyl alcohol polyoxyethylene ether can be oleyl alcohol polyoxyethylene ether 1602, the fatty alcohol polyoxyethylene ether can be fatty alcohol polyoxyethylene ether AEO-3, and the fluorocarbon surfactant can be FC-03. Oil alcohol polyoxyethylene ether in formation cleaning agents can disperse crude oil, gradually loosening solid crude oil particles and promoting crude oil stripping from the rock; fatty alcohol polyoxyethylene ether can break the adhesion between crude oil and rock, making crude oil easier to wash away; cocamidopropyl betaine acts as a surface active wetting agent and improves permeability, promoting crude oil stripping; brine can reduce the adhesion between crude oil and rock; ethylene glycol can reduce the viscosity of crude oil, making it easier to flush away; fluorocarbon surfactants can improve the wettability, permeability, diffusivity of formation rocks and the fluidity of crude oil, more effectively stripping crude oil from the rock surface and promoting the flow and discharge of crude oil in the formation; alpha amylase improves the permeability of the formation by decomposing organic matter in crude oil, thereby helping to clean and discharge crude oil; triethanolamine is used as an adjuvant to help other cleaning components penetrate the formation better and improve the cleaning effect.

[0038] Heavy oil viscosity reducers are mainly used to reduce crude oil viscosity and improve oil recovery. In some embodiments, heavy oil viscosity reducers include the following components: various surfactants, miscible solvents, and organic solvents. For example, a heavy oil viscosity reducer may specifically include the following components: sorbitan stearate, sodium fatty alcohol polyoxyethylene ether sulfate, fluorocarbon surfactant, demulsifier, tetrasodium aminotrimethylene phosphonate, and water, with the following mass percentages: sorbitan stearate 15%~18%, sodium fatty alcohol polyoxyethylene ether sulfate 20%~30%, fluorocarbon surfactant 2%~5%, demulsifier 3%~10%, tetrasodium aminotrimethylene phosphonate 3%~10%, and the balance being water. The fluorocarbon surfactant can be FC-03. The demulsifier can be BP-2040. Sorbitan stearate helps disperse heavy oil in water through emulsification, forming an emulsion, thereby reducing the viscosity of the heavy oil. Sodium fatty alcohol polyoxyethylene ether sulfate can effectively reduce the interfacial tension between oil and water, helping heavy oil to disperse in water as oil droplets, forming an oil-in-water emulsion, thereby reducing the viscosity of heavy oil. Fluorocarbon surfactants can reduce the interfacial tension between oil and water, promoting the dispersion and emulsification of heavy oil, thus reducing its viscosity. Demulsifiers, used in combination with other surfactants, first reduce the viscosity of heavy oil through emulsification, and then, at an appropriate time, break the emulsion, achieving effective oil-water separation. Tetrasodium aminotrimethylene phosphonate helps disperse solid particles and colloidal substances in water through dispersion, thereby reducing the viscosity of heavy oil.

[0039] Another object of the present invention is to provide a method for preparing a formation working fluid for reducing viscosity of heavy oil according to any of the above embodiments. For example... Figure 1 As shown, the method generally includes the following steps: Step S1: Using water as the base liquid, add anti-swelling agent and formation cleaning agent to the base liquid, stir evenly, and obtain the first mixture; Step S2: Add heavy oil viscosity reducer to the first mixture, stir well to obtain the second mixture; Step S3: Heat the second mixture to a set temperature to obtain the formation working fluid.

[0040] The formation working fluid preparation method provided by this invention is convenient to prepare, simple in process, low in cost, and highly feasible for industrial production, with good industrial application prospects and high market value.

[0041] In some embodiments, the stirring time in step S1 is 10 to 30 minutes.

[0042] In some embodiments, the stirring time in step S2 is 5 to 10 minutes.

[0043] In some embodiments, the set temperature in step S3 is not lower than 50°C.

[0044] The working fluid enters the formation at a temperature above 40°C. This physical heating helps reduce the viscosity of the asphaltene and enhances its fluidity. The emulsifying dispersants, anionic surfactants, and nonionic surfactants in the working fluid have a strong dispersing effect on the asphaltene, gums, waxes, and other organic matter in the crude oil. The higher the temperature, the stronger the dispersing effect, reducing the oil-water interfacial tension and transforming the heavy oil from a water-in-oil emulsion to a water-based emulsion, significantly reducing its viscosity and enhancing its fluidity.

[0045] Another object of the present invention is to provide a working system for reducing the viscosity of heavy oil, comprising: a formation working fluid for reducing the viscosity of heavy oil as described in any of the above embodiments, and a wellbore working fluid for cleaning dead oil in the wellbore.

[0046] During the lift process, crude oil with poor properties gradually changes from a liquid to a solid state due to temperature decrease and pressure changes, forming "dead oil" that adheres to the annulus, tubing inner wall, polished rod, and pump barrel, potentially clogging the wellbore. To ensure that subsequent formation working fluid can smoothly enter the formation, the dead oil in the wellbore needs to be cleaned out with wellbore working fluid before injection.

[0047] In some embodiments, the wellbore working fluid comprises the following components by weight: 35 to 87 parts water, 2 to 15 parts clay anti-swelling agent, 10 to 40 parts well washing fluid, and 1 to 10 parts heavy oil viscosity reducer.

[0048] In some embodiments, the water may be selected from at least one of clean water, oil well electric pump fluid, and oily wastewater treated by a combined station.

[0049] Clay anti-swelling agents are used to prevent clay from swelling. In some embodiments, the clay anti-swelling agent comprises 50% to 75% by mass of a polyquaternary ammonium salt and 25% to 50% by mass of ammonium chloride.

[0050] Well-washing fluid is mainly used to clean dead oil in the wellbore. In some embodiments, the well-washing fluid comprises the following components by weight percentage: 8%~15% oleic alcohol polyoxyethylene ether, 1%~2% fatty alcohol polyoxyethylene ether, 1%~2% cocamidopropyl betaine, 1%~5% ethylene glycol, 0.5%~3% fluorocarbon surfactant, 1%~5% alpha amylase, 1%~3% triethanolamine, and the balance being water.

[0051] Heavy oil viscosity reducers are mainly used to reduce the viscosity of crude oil in stagnant oil, making it easier to drain. In some embodiments, a heavy oil viscosity reducer may include the following components: sorbitan stearate, sodium fatty alcohol polyoxyethylene ether sulfate, fluorocarbon surfactant, demulsifier, tetrasodium aminotrimethylene phosphonate, and water, with the following mass percentages: sorbitan stearate 15%~18%, sodium fatty alcohol polyoxyethylene ether sulfate 20%~30%, fluorocarbon surfactant 2%~5%, demulsifier 3%~10%, tetrasodium aminotrimethylene phosphonate 3%~10%, and the balance being water.

[0052] The working mechanism of the heavy oil viscosity-reducing system according to the present invention is as follows: (1) High-temperature dispersion and dissolution Under high temperature and high salinity conditions, the wellbore working fluid has a strong dispersing effect on organic matter such as asphaltenes, gums, and waxes in dead oil in the wellbore. The higher the temperature, the stronger the dispersing effect. Solid crude oil particles gradually loosen and are easy to peel off. At the same time, it has a strong dissolving effect on organic matter in crude oil, which can continuously reduce the volume of organic matter. (2) Viscosity reduction and dispersion After the formation working fluid enters the oil layer, under the reservoir temperature conditions, it transforms the high-viscosity water-in-oil emulsion into a low-viscosity oil-in-water emulsion through emulsification. At the same time, it disperses the large molecular aggregates formed by colloids and asphaltenes, reduces the cohesiveness of crude oil, and achieves viscosity reduction in heavy oil. (3) Wetting and drag reduction Starting with wettability, the formation working fluid enters the oil layer and changes the rock from oil-wetted to water-wetted, reducing the adhesion of crude oil and improving the crude oil stripping efficiency, thereby solving the problem of difficult extraction. (4) Surface-active excretion aid Based on the anti-swelling principle, the surfactants contained in the formation working fluid can reduce the interfacial tension of the working fluid, reduce water lock and Jamin effect, and achieve rapid backflow and rapid production.

[0053] Compared with other production enhancement measures for heavy oil reservoirs, the heavy oil viscosity reduction system, its preparation method, and application process of the present invention have the following advantages: It is easy to prepare, and the preparation time is generally 1 to 2 hours. It can be prepared on the construction site or prepared at the preparation station and then transported to the construction site. The process is simple. When using the heavy oil viscosity reduction system, it is only necessary to circulate it to wash the well and squeeze it into the formation. There is no need to run the tubing string. It generally takes 4 to 8 hours. Low cost: Compared with CO2 huff and puff, natural gas huff and puff, the heavy oil viscosity reduction system of this invention uses fewer raw materials, has lower cost, and is easy to scale up. Safe and environmentally friendly, the heavy oil viscosity reduction system of this invention uses water as the base liquid, and the raw materials used are water-soluble and all are environmentally friendly materials, with no safety risks such as high temperature and corrosion. It is fast-acting; noticeable results can be seen within a week after applying the heavy oil viscosity reduction system to a single well.

[0054] The density of the formation working fluid in this system is approximately 1.01~1.05 (g / cm³). 3 With a pH value between 7 and 9, the viscosity reduction rate (50℃) is ≥80%.

[0055] The wellbore working fluid can be prepared using the following method: Use water as the base fluid, add anti-swelling agent and well washing fluid to the base fluid, and stir for 10-30 minutes; Add the thick oil viscosity reducer to the mixture and stir for 5-10 minutes; The stirred mixture is heated to above 50°C to obtain the wellbore working fluid.

[0056] Another object of the present invention is to provide an application of the working system according to any of the above embodiments, wherein the working system is applied using any of the following four processes: Process 1: First, use the wellbore working fluid for reverse circulation to flush the well, then squeeze the formation working fluid into the casing, and then shut the well in. Process 2: First, use the wellbore working fluid to flush the well in a positive circulation manner, then squeeze the formation working fluid into the tubing, and then shut the well in. Process 3: First, use the wellbore working fluid for reverse circulation to wash the well, then squeeze the formation working fluid into the casing, use hot water to displace the formation working fluid into the formation, and then shut off the well. Process 4: First, use the wellbore working fluid to flush the well in a positive circulation manner. Then, squeeze the formation working fluid into the tubing, use hot water to displace the formation working fluid into the formation, and then shut off the well.

[0057] In some embodiments, the well is simmered for 12 to 48 hours.

[0058] In some embodiments, the temperature of the hot water is above 50°C.

[0059] The present invention will be further illustrated below with specific examples, but the scope of protection of the present invention is not limited thereto. Unless otherwise specified, all percentages in the following examples are mass percentages, all parts are parts by weight, and the viscosity reduction test method is a conventional method in the art.

[0060] Example 1 Prepare the working fluid for wellbore #1. Use 35 parts of clean water as the base fluid, add 2 parts of clay anti-swelling agent and 10 parts of well washing fluid to the clean water, and stir for 10 minutes. The clay anti-swelling agent contains 50% polyquaternary ammonium salt and 50% ammonium chloride. The well washing fluid contains 8% oleic alcohol polyoxyethylene ether, 1% fatty alcohol polyoxyethylene ether, 1% cocamidopropyl betaine, 1% ethylene glycol, 0.5% fluorocarbon surfactant, 1% alpha amylase, 1% triethanolamine, and the balance is water. Add 1 part of heavy oil viscosity reducer to the mixture and stir for 5 minutes. The heavy oil viscosity reducer consists of: 15% sorbitan stearate, 20% sodium fatty alcohol polyoxyethylene ether sulfate, 2% fluorocarbon surfactant, 3% demulsifier, 3% tetrasodium aminotrimethylene phosphonate, and the balance is water. The stirred mixture was kept at a constant temperature of 50°C in a water bath for 1 hour to obtain the wellbore working fluid.

[0061] Preparation of Formation Working Fluid #1: Using 60 parts water as the base solution, add 1 part potassium chloride and 5 parts formation cleaning agent to the water, and stir for 10 minutes. The formation cleaning agent consists of: 5% oleic alcohol polyoxyethylene ether, 1% fatty alcohol polyoxyethylene ether, 1% cocamidopropyl betaine, 5% brine, 1% ethylene glycol, 1% fluorocarbon surfactant, 1% alpha amylase, 1% triethanolamine, with the remainder being water. Add 3 parts heavy oil viscosity reducer to the mixture and stir for 5 minutes. The heavy oil viscosity reducer consists of: 15% sorbitan stearate, 20% fatty alcohol polyoxyethylene ether sodium sulfate, 2% fluorocarbon surfactant, 3% demulsifier, 3% tetrasodium aminotrimethylene phosphonate, with the remainder being water. Incubate the stirred mixture in a 50°C water bath for 1 hour to obtain the formation working fluid.

[0062] Viscosity reduction experiments were conducted on the prepared wellbore working fluid and formation working fluid, and the experimental parameters and results are shown in Table 1 below.

[0063] Table 1 Experimental parameters and results

[0064] The above viscosity reduction experiment results show that the wellbore working fluid and formation working fluid prepared according to the scheme of the present invention have a high viscosity reduction rate.

[0065] Example 2 Preparation of working fluid for wellbore #2: 50 parts of oil well electric pump fluid were used as the base fluid. 6 parts of clay anti-swelling agent and 20 parts of well-washing fluid were added to the oil well electric pump fluid, and the mixture was stirred for 15 minutes. The clay anti-swelling agent contained 55% polyquaternium salt and 45% ammonium chloride. The well-washing fluid contained 10% oleic alcohol polyoxyethylene ether, 1.5% fatty alcohol polyoxyethylene ether, 1.2% cocamidopropyl betaine, 2% ethylene glycol, 1% fluorocarbon surfactant, 2% alpha amylase, 1.5% triethanolamine, and the balance being water. 3 parts of heavy oil viscosity reducer were added to the mixture and stirred for 6 minutes. The heavy oil viscosity reducer consisted of: 16% sorbitan stearate, 22% sodium fatty alcohol polyoxyethylene ether sulfate, 2.5% fluorocarbon surfactant, 4% demulsifier, 4% tetrasodium aminotrimethylene phosphonate, and the balance being water. The stirred mixture was kept at a constant temperature of 52°C in a water bath for 1.5 hours to obtain the wellbore working fluid.

[0066] Preparation of Formation Working Fluid #2: 70 parts of oil well electric pump fluid were used as the base fluid. 2 parts of ammonium chloride and 8 parts of formation cleaning agent were added to the oil well electric pump fluid and stirred for 15 minutes. The formation cleaning agent consisted of: 6% oleic alcohol polyoxyethylene ether, 1.4% fatty alcohol polyoxyethylene ether, 1.4% cocamidopropyl betaine, 6% brine, 1.5% ethylene glycol, 2% fluorocarbon surfactant, 2% alpha amylase, 1.5% triethanolamine, and the remainder being water. 6 parts of heavy oil viscosity reducer were added to the mixture and stirred for 6 minutes. The heavy oil viscosity reducer consisted of: 15.5% sorbitan stearate, 22% fatty alcohol polyoxyethylene ether sodium sulfate, 2.5% fluorocarbon surfactant, 4% demulsifier, 4% tetrasodium aminotrimethylene phosphonate, and the remainder being water. The stirred mixture was kept at a constant temperature of 51°C in a water bath for 1.2 hours to obtain the formation working fluid.

[0067] Viscosity reduction experiments were conducted on the prepared wellbore working fluid and formation working fluid, and the experimental parameters and results are shown in Table 2 below.

[0068] Table 2 Experimental parameters and results

[0069] The above viscosity reduction experiment results show that the wellbore working fluid and formation working fluid prepared according to the scheme of the present invention have a high viscosity reduction rate.

[0070] Example 3 Prepare the working fluid for wellbore #3. Use 60 parts of clean water as the base fluid, add 8 parts of clay anti-swelling agent and 25 parts of well washing fluid to the clean water, and stir for 20 minutes. The clay anti-swelling agent contains 60% polyquaternary ammonium salt and 40% ammonium chloride. The well washing fluid contains 11% oleic alcohol polyoxyethylene ether, 1.5% fatty alcohol polyoxyethylene ether, 1.5% cocamidopropyl betaine, 3% ethylene glycol, 1.7% fluorocarbon surfactant, 3% alpha amylase, 2% triethanolamine, and the balance is water. Add 5 parts of heavy oil viscosity reducer to the mixture and stir for 8 minutes. The heavy oil viscosity reducer consists of: 16% sorbitan stearate, 25% sodium fatty alcohol polyoxyethylene ether sulfate, 3.5% fluorocarbon surfactant, 7% demulsifier, 6% tetrasodium aminotrimethylene phosphonate, and the balance is water. The stirred mixture was kept at a constant temperature of 53°C in a water bath for 1 hour to obtain the wellbore working fluid.

[0071] Preparation of Formation Working Fluid #3: 75 parts water were used as the base solution. 3 parts tetraethylammonium sulfate and 12 parts formation cleaning agent were added to the water, and the mixture was stirred for 20 minutes. The formation cleaning agent consisted of: 7% oleic alcohol polyoxyethylene ether, 1.5% fatty alcohol polyoxyethylene ether, 1.5% cocamidopropyl betaine, 7% brine, 3% ethylene glycol, 2% fluorocarbon surfactant, 3% alpha amylase, 2% triethanolamine, and the remainder being water. 9 parts heavy oil viscosity reducer were added to the mixture and stirred for 8 minutes. The heavy oil viscosity reducer consisted of: 16% sorbitan stearate, 25% sodium fatty alcohol polyoxyethylene ether sulfate, 3.5% fluorocarbon surfactant, 6% demulsifier, 6% tetrasodium aminotrimethylene phosphonate, and the remainder being water. The stirred mixture was kept at a constant temperature of 52°C in a water bath for 1.2 hours to obtain the formation working fluid.

[0072] Viscosity reduction experiments were conducted on the prepared wellbore working fluid and formation working fluid, and the experimental parameters and results are shown in Table 3 below.

[0073] Table 3 Experimental parameters and results

[0074] The above viscosity reduction experiment results show that the wellbore working fluid and formation working fluid prepared according to the scheme of the present invention have a high viscosity reduction rate.

[0075] Example 4 Preparation of working fluid for well No. 4: 75 parts of oily wastewater treated by the joint station were used as the base fluid. 12 parts of clay anti-swelling agent and 35 parts of well-washing fluid were added to the treated oily wastewater, and the mixture was stirred for 25 minutes. The clay anti-swelling agent contained 70% polyquaternium salt and 30% ammonium chloride. The well-washing fluid contained 12% oleic alcohol polyoxyethylene ether, 1.8% fatty alcohol polyoxyethylene ether, 1.7% cocamidopropyl betaine, 4% ethylene glycol, 2.5% fluorocarbon surfactant, 4% alpha amylase, 2.5% triethanolamine, and the balance being water. 8 parts of heavy oil viscosity reducer were added to the mixture and stirred for 8 minutes. The heavy oil viscosity reducer consisted of: 17% sorbitan stearate, 28% sodium fatty alcohol polyoxyethylene ether sulfate, 4% fluorocarbon surfactant, 8% demulsifier, 9% tetrasodium aminotrimethylene phosphonate, and the balance being water. The stirred mixture was kept at a constant temperature of 50°C in a water bath for 1 hour to obtain the wellbore working fluid.

[0076] Preparation of working fluid for Formation #4: 83 parts of oily wastewater treated at the combined station were used as the base fluid. 4 parts of hexadecyltrimethylammonium fluoride and 15 parts of formation cleaning agent were added to the treated oily wastewater, and the mixture was stirred for 25 minutes. The formation cleaning agent consisted of: 9% oleic alcohol polyoxyethylene ether, 1.8% fatty alcohol polyoxyethylene ether, 1.8% cocamidopropyl betaine, 8% brine, 4% ethylene glycol, 2.5% fluorocarbon surfactant, 4% alpha amylase, 2.5% triethanolamine, and the remainder being water. 12 parts of heavy oil viscosity reducer were added to the mixture and stirred for 9 minutes. The heavy oil viscosity reducer consisted of: 17% sorbitan stearate, 27% sodium fatty alcohol polyoxyethylene ether sulfate, 4% fluorocarbon surfactant, 8% demulsifier, 7% tetrasodium aminotrimethylene phosphonate, and the remainder being water. The stirred mixture was kept at a constant temperature of 50°C in a water bath for 1 hour to obtain the formation working fluid.

[0077] Viscosity reduction experiments were conducted on the prepared wellbore working fluid and formation working fluid, and the experimental parameters and results are shown in Table 4 below.

[0078] Table 4 Experimental parameters and results

[0079] The above viscosity reduction experiment results show that the wellbore working fluid and formation working fluid prepared according to the scheme of the present invention have a high viscosity reduction rate.

[0080] Example 5 Preparation of working fluid for wellbore #5: 87 parts of oily wastewater treated at the joint station were used as the base fluid. 15 parts of clay anti-swelling agent and 40 parts of well-washing fluid were added to the oily wastewater and stirred for 30 minutes. The clay anti-swelling agent contained 75% polyquaternium salt and 25% ammonium chloride. The well-washing fluid contained 15% oleic alcohol polyoxyethylene ether, 2% fatty alcohol polyoxyethylene ether, 2% cocamidopropyl betaine, 5% ethylene glycol, 3% fluorocarbon surfactant, 5% alpha amylase, 3% triethanolamine, and the balance being water. 10 parts of heavy oil viscosity reducer were added to the mixture and stirred for 10 minutes. The heavy oil viscosity reducer consisted of: 18% sorbitan stearate, 30% sodium fatty alcohol polyoxyethylene ether sulfate, 5% fluorocarbon surfactant, 10% demulsifier, 10% tetrasodium aminotrimethylene phosphonate, and the balance being water. The stirred mixture was kept at a constant temperature of 52°C in a water bath for 1 hour to obtain the wellbore working fluid.

[0081] Preparation of Formation Working Fluid #5: 91 parts of oily wastewater treated at the combined station were used as the base fluid. 5 parts of potassium chloride and 20 parts of formation cleaning agent were added to the oily wastewater and stirred for 30 minutes. The formation cleaning agent consisted of: 10% oleic alcohol polyoxyethylene ether, 2% fatty alcohol polyoxyethylene ether, 2% cocamidopropyl betaine, 10% brine, 5% ethylene glycol, 3% fluorocarbon surfactant, 5% alpha amylase, 3% triethanolamine, and the remainder being water. 15 parts of heavy oil viscosity reducer were added to the mixture and stirred for 10 minutes. The heavy oil viscosity reducer consisted of: 18% sorbitan stearate, 30% sodium fatty alcohol polyoxyethylene ether sulfate, 5% fluorocarbon surfactant, 10% demulsifier, 10% tetrasodium aminotrimethylene phosphonate, and the remainder being water. The stirred mixture was kept at a constant temperature of 50°C in a water bath for 1 hour to obtain the formation working fluid.

[0082] Viscosity reduction experiments were conducted on the prepared wellbore working fluid and formation working fluid, and the experimental parameters and results are shown in Table 5 below.

[0083] Table 5 Experimental parameters and results

[0084] The above viscosity reduction experiment results show that the wellbore working fluid and formation working fluid prepared according to the scheme of the present invention have a high viscosity reduction rate.

[0085] Application Example 1 The No. 2 wellbore working fluid and No. 2 formation working fluid prepared in Example 2 were subjected to field application tests.

[0086] The crude oil viscosity of Well X in Dagang Oilfield is 10417 mPa·s (50℃), the pour point is 33℃, and the wax content is 4.17%. Ten days after the new well was put into production, no fluid was produced at the wellhead. Analysis indicated that the high-viscosity oil was clogging the wellbore. During the well workover operation, following procedure two, 10 tons of No. 2 wellbore working fluid were used for positive circulation well flushing, followed by the injection of 50 tons of No. 2 formation working fluid through the tubing, and the well was left to stand for 24 hours. After the operation was completed, the well returned to normal production capacity and has been producing continuously for more than 12 months, with an initial daily increase of 4.83 tons and a cumulative increase of 719 tons.

[0087] Application Example 2 The No. 3 wellbore working fluid and No. 3 formation working fluid prepared in Example 3 were subjected to field application tests.

[0088] The crude oil viscosity of Well X in Dagang Oilfield was 4451 mPa·s (50℃). Before the operation, the daily production of fluid was 1.38 cubic meters and the daily production of oil was 1.12 tons, with a water cut of 19%, a significant decrease compared to the initial production period. Analysis showed that during the long-term production process, heavy oil caused organic blockage in the near-wellbore area. After the well was shut down, the operation was carried out according to process three, using 30 tons of No. 3 wellbore working fluid for reverse circulation well washing, squeezing 100 tons of No. 3 formation working fluid through the casing, and using 20 tons of oily wastewater treated at the joint station at a temperature above 50℃ to displace the formation working fluid into the formation, and then simmering the well for 24 hours. After the operation, the daily production of fluid was 13.64 cubic meters and the daily production of oil was 3.30 tons, with a water cut of 75.8%. The initial daily oil increase was 2.18 tons, and the cumulative oil increase was 253 tons.

[0089] The embodiments described above are merely illustrative of implementation methods of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention.

Claims

1. A formation working fluid for reducing viscosity of heavy oil, characterized in that, It includes the following components by weight: 60-91 parts water, 1-5 parts anti-swelling agent, 5-20 parts formation cleaning agent, and 3-15 parts heavy oil viscosity reducer.

2. The formation working fluid for reducing viscosity of heavy oil according to claim 1, characterized in that, The anti-swelling agent is selected from at least one of potassium chloride, ammonium chloride, tetraethylammonium sulfate, and hexadecyltrimethylammonium fluoride.

3. The formation working fluid for reducing viscosity of heavy oil according to claim 1, characterized in that, The formation cleaning agent comprises the following components: alcohol ether, fatty alcohol polyoxyethylene ether, alkali, ethylene glycol, and emulsifier.

4. The formation working fluid for reducing viscosity of heavy oil according to claim 3, characterized in that, The formation cleaning agent comprises the following components: oleyl alcohol polyoxyethylene ether, fatty alcohol polyoxyethylene ether, cocamidopropyl betaine, brine, ethylene glycol, fluorocarbon surfactant, alpha amylase, triethanolamine, and water.

5. The formation working fluid for reducing viscosity of heavy oil according to claim 4, characterized in that, The mass percentages of each component in the formation cleaning agent are as follows: 5%~10% oleyl alcohol polyoxyethylene ether, 1%~2% fatty alcohol polyoxyethylene ether, 1%~2% cocamidopropyl betaine, 5%~10% brine, 1%~5% ethylene glycol, 1%~3% fluorocarbon surfactant, 1%~5% alpha amylase, 1%~3% triethanolamine, and the remainder is water.

6. The formation working fluid for reducing viscosity of heavy oil according to claim 1, characterized in that, The heavy oil viscosity reducer comprises the following components: various surfactants, mutual solvents, and organic solvents.

7. The formation working fluid for reducing viscosity of heavy oil according to claim 6, characterized in that, The heavy oil viscosity reducer comprises the following components: sorbitan stearate, sodium fatty alcohol polyoxyethylene ether sulfate, fluorocarbon surfactant, demulsifier, tetrasodium aminotrimethylene phosphonate, and water.

8. The formation working fluid for reducing viscosity of heavy oil according to claim 7, characterized in that, The mass percentages of each component in the heavy oil viscosity reducer are as follows: sorbitan stearate 15%~18%, sodium fatty alcohol polyoxyethylene ether sulfate 20%~30%, fluorocarbon surfactant 2%~5%, demulsifier 3%~10%, tetrasodium aminotrimethylene phosphonate 3%~10%, and the balance is water.

9. The formation working fluid for reducing viscosity of heavy oil according to claim 1, characterized in that, The water is selected from at least one of clean water, oil well electric pump fluid, and oily wastewater treated by the combined station.

10. A method for preparing a formation working fluid for reducing viscosity of heavy oil according to any one of claims 1-9, characterized in that, Includes the following steps: Water is used as the base liquid. Anti-swelling agent and formation cleaning agent are added to the base liquid and stirred evenly to obtain a first mixture. Add a thick oil viscosity reducer to the first mixture and stir until homogeneous to obtain a second mixture; The second mixture is heated to a set temperature to obtain the formation working fluid.

11. The method according to claim 10, characterized in that, The stirring time for preparing the first mixture is 10-30 minutes.

12. The method according to claim 10, characterized in that, The stirring time for preparing the second mixture is 5 to 10 minutes.

13. The method according to claim 10, characterized in that, The set temperature is not lower than 50°C.

14. A working system for reducing the viscosity of heavy oil, characterized in that, Including the following: The formation working fluid for reducing viscosity of heavy oil as described in any one of claims 1-9; and Wellbore working fluid used to clean dead oil in wellbores.

15. The working system for reducing viscosity of heavy oil according to claim 14, characterized in that, The wellbore working fluid comprises the following components by weight: 35-87 parts water, 2-15 parts clay anti-swelling agent, 10-40 parts well washing fluid, and 1-10 parts heavy oil viscosity reducer.

16. The working system for reducing viscosity of heavy oil according to claim 15, characterized in that, The clay anti-swelling agent comprises 50% to 75% polyquaternary ammonium salt and 25% to 50% ammonium chloride by mass.

17. The working system for reducing viscosity of heavy oil according to claim 15, characterized in that, The well-washing fluid comprises the following components by mass percentage: 8%~15% oleyl alcohol polyoxyethylene ether, 1%~2% fatty alcohol polyoxyethylene ether, 1%~2% cocamidopropyl betaine, 1%~5% ethylene glycol, 0.5%~3% fluorocarbon surfactant, 1%~5% alpha amylase, 1%~3% triethanolamine, and the balance being water.

18. The application of the working system according to any one of claims 14-17, characterized in that, The working system can be applied using any of the following four processes: Process 1: First, use the wellbore working fluid for reverse circulation to flush the well, then squeeze the formation working fluid into the casing, and then shut the well in. Process 2: First, use the wellbore working fluid for positive circulation to flush the well, then squeeze the formation working fluid into the tubing, and then shut the well in. Process 3: First, use the wellbore working fluid for reverse circulation to wash the well, then squeeze the formation working fluid into the casing, use hot water to displace the formation working fluid into the formation, and then shut off the well. Process 4: First, use the wellbore working fluid for positive circulation to flush the well, then squeeze the formation working fluid into the tubing, use hot water to displace the formation working fluid into the formation, and then shut off the well.

19. The application of the working system according to claim 18, characterized in that, The well-sealing time is 12 to 48 hours.

20. The application of the working system according to claim 18, characterized in that, The temperature of the hot water is above 50°C.

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