Temporary plugging type workover fluid as well as preparation method and application thereof

Abstract

The invention relates to temporary plugging type workover fluid as well as a preparation method and application thereof, and belongs to the technical field of oil production engineering. The temporary plugging type workover fluid comprises the following components in percentage by mass: 0.4-2% of a discharge aiding agent, 2.5-5% of an oil-soluble temporary plugging agent, 0.04-0.1% of a filtrate reducer and the balance of water, wherein the cleanup additive is prepared from sodium dioctyl sulfosuccinate and alkyl glucoside; the oil-soluble temporary plugging agent comprises EVA (Ethylene Vinyl Acetate) resin, C9 petroleum resin and calcium carbonate; the filtrate reducer comprises hydrolyzed polyacrylamide. The EVA resin and the C9 petroleum resin are compounded to serve as the oil-soluble temporary plugging agent, meanwhile, the discharge aiding agent and the filtrate reducer are combined, the temporary plugging type workover fluid for medium-high permeability heavy oil reservoirs is formed, and compared with a conventional workover fluid, the temporary plugging type workover fluid has better compatibility to the heavy oil reservoirs and can be applied to workover operation of the medium-low temperature heavy oil reservoirs.

Description

Technical Field

[0001] This invention belongs to the field of oil production engineering technology, and in particular relates to a temporary plugging well workover fluid, its preparation method and application. Background Technology

[0002] For medium-to-high permeability heavy oil reservoirs, the kill fluid used in well workover operations is mainly fresh water or clean brine. Although these kill fluids have low solid content, the reservoir pressure coefficient is low, the reservoir properties are good, and the pressure fluctuations in the wellbore during the operation process lead to high fluid loss. After the kill fluid enters the formation, it is very easy to form a water-in-oil emulsion, which increases the viscosity sharply, leading to emulsification and blockage in the near-wellbore zone and prolonging the high water cut drainage period.

[0003] To address leakage issues, commonly used workover fluids include solidified water workover fluids, polymer workover fluids, and oil-soluble temporary plugging workover fluids. Solidified water workover fluids use superabsorbent polymers as solidifying agents, exhibiting strong binding force on free water and significantly reducing workover fluid leakage. However, their stable structure makes post-treatment complex. Polymer workover fluids increase viscosity and reduce filtration through polymers (polyacrylamide, xanthan gum, carboxymethyl cellulose, etc.), but high polymer concentrations are required for medium-to-high permeability reservoirs, increasing workover fluid costs. Oil-soluble temporary plugging workover fluids typically use materials such as asphalt, paraffin wax, and petroleum resins as shielding plugging particles, combined with a low-concentration polymer solution to suspend the plugging agent and reduce filtration. While these oil-soluble temporary plugging workover fluids can significantly reduce workover fluid leakage, the softening point of the plugging materials is generally above 75℃, making them unsuitable for medium-to-low temperature reservoir applications. Furthermore, the high asphalt and paraffin content in the plugging materials can further increase the viscosity of heavy oil, exacerbating wellbore waxing and scaling.

[0004] For example, patent CN 103087694 A discloses a soft-particle oil-soluble temporary plugging agent, comprising 50-60 wt% water, 1-5 wt% carboxymethyl modified cellulose, 1-4 wt% low-viscosity PAC, 30-38 wt% linear paraffin oil, 1-4 wt% linear alkyl polyoxyethylene ether, 1-3 wt% glycerol, and 2-6 wt% calcium oxide. This product is simple to use; the specific application method is to add 3%-4% of the agent directly to the drilling fluid by volume before it enters the oil and gas formation, thereby achieving protection of the oil and gas formation. This product is heat resistant up to 140℃, has good dispersibility in drilling fluid, and can reduce bentonite drilling fluid filtration loss by 60% and reduce bentonite swelling rate by 90%. However, the high paraffin content in this oil-soluble temporary plugging agent can easily lead to a further increase in the viscosity of heavy oil, exacerbating wax and scale formation in the wellbore.

[0005] Patent CN 104388068 A discloses a high-temperature oil-soluble temporary plugging agent, which comprises the following components by weight percentage: 10%-40% asphalt, 20%-50% C9 petroleum resin, 15%-50% coumarone resin, 5%-15% surfactant, 2%-15% polymer fiber, and 1%-10% softening point additive. The surfactant is selected from polyoxyethyl alkyl phenyl ether, polyoxyethyl alkyl ether, and polyoxyethyl fatty acid ether ester; the polymer fiber is selected from polyvinyl alcohol fiber, modified polyester fiber, and polyurethane fiber; and the softening point additive is selected from cationic starch or lignite. This temporary plugging agent exhibits good oil solubility, acid resistance, salt resistance, and high-temperature degradation resistance. Furthermore, the softening point can be adjusted within the range of the softening point additive, thus achieving the purpose of protecting high-temperature oil layers. However, the asphalt content in this patented oil-soluble temporary plugging agent is relatively high. Summary of the Invention

[0006] In view of this, the present invention provides a temporary plugging workover fluid, its preparation method and application. The temporary plugging workover fluid is suitable for medium and low temperature (40℃~90℃) heavy oil reservoirs, and has excellent plugging and filtration loss reduction properties as well as heavy oil viscosity reduction properties. It can solve the problems of excessively high heavy oil viscosity and wellbore wax and scale formation caused by high asphalt or paraffin content in the prior art.

[0007] To achieve the above objectives, the present invention adopts the following technical solution.

[0008] In a first aspect, the present invention provides a temporary plugging workover fluid, wherein, by mass percentage, the temporary plugging workover fluid comprises 0.4% to 2% of a flow aid, 2.5% to 5% of an oil-soluble temporary plugging agent, 0.04% to 0.1% of a filtration loss reducer, and the remainder being water.

[0009] The aforementioned temporary plugging workover fluid includes sodium dioctyl sulfonate (e.g., OT-70) and alkyl glucoside (e.g., APG0810).

[0010] The aforementioned temporary plugging workover fluid includes sodium dioctyl sulfonate and alkyl glucoside, wherein the alkyl group in the alkyl glucoside has 8 to 12 carbon atoms.

[0011] The aforementioned temporary plugging workover fluid includes sodium dioctyl sulfonate and alkyl glucoside as the drainage aid, wherein the mass ratio of sodium dioctyl sulfonate to alkyl glucoside is 1:1 to 2.

[0012] In this invention, the drainage aid is composed of anionic surfactant sodium dioctyl sulfosuccinate (e.g., OT-70) and nonionic surfactant alkyl glucoside (APG0810). Sodium dioctyl sulfosuccinate acts as a drainage agent, which can quickly pass through the oil-water interface and accelerate the formation of oil-in-water emulsions. APG0810 has excellent wetting and solubilizing ability for heavy oil and can form micro-foam oil with crude oil, which can significantly reduce the viscosity of heavy oil. The synergistic effect of the two enhances the flowability of heavy oil in the near-wellbore zone.

[0013] The aforementioned temporary plugging workover fluid uses an oil-soluble plugging agent that is a composite resin comprising EVA resin, C9 petroleum resin, and calcium carbonate. The EVA resin is an ethylene-vinyl acetate copolymer resin.

[0014] The aforementioned temporary plugging workover fluid uses an oil-soluble temporary plugging agent that is a composite resin comprising EVA resin, C9 petroleum resin, and calcium carbonate; wherein the mass ratio of the EVA resin to the C9 petroleum resin is 1.8 to 2.2:1.

[0015] In some embodiments of the first aspect of the present invention, the oil-soluble temporary plugging agent comprises a composite resin formed by the EVA resin and the C9 petroleum resin, which includes two particle sizes: composite resin A and composite resin B.

[0016] In existing technologies, EVA resin is commonly used as a crude oil pour point depressant. In this invention, EVA resin is used as a temporary plugging agent, serving both a temporary plugging function and improving crude oil fluidity after dissolving in oil. Petroleum resin, as a commonly used oil-soluble temporary plugging agent, has a high oil solubility. This invention combines petroleum resin and EVA resin, which facilitates a wider range of adjustment of the softening point of the temporary plugging agent, overcoming the problem of a narrow application temperature range when using a single petroleum resin as a temporary plugging agent.

[0017] The calcium carbonate in the aforementioned temporary plugging workover fluid has a particle size in the nanometer range.

[0018] This invention adds ultrafine calcium carbonate to a mixed resin of EVA resin and C9 petroleum resin, which facilitates further fine-tuning of the softening point of the temporary plugging agent. By using this nano-sized ultrafine calcium carbonate to adjust the softening point of the composite resin temporary plugging agent, the resulting temporary plugging agent does not damage the reservoir.

[0019] The aforementioned temporary plugging workover fluid uses an oil-soluble temporary plugging agent that is a composite resin comprising EVA resin, C9 petroleum resin, and calcium carbonate; wherein the calcium carbonate has a particle size of 0.02 μm to 0.1 μm.

[0020] The aforementioned temporary plugging workover fluid uses an oil-soluble temporary plugging agent that is a composite resin comprising EVA resin, C9 petroleum resin, and calcium carbonate; wherein the calcium carbonate accounts for 2% to 10% of the total mass of the EVA resin and the C9 petroleum resin.

[0021] In this invention, the amount of ultrafine calcium carbonate added is such that the softening point of the composite resin exhibits an approximately linear relationship with it, that is, the softening point of the composite temporary plugging agent and the amount of calcium carbonate added approximately exhibit a relationship of Y = aX + b, so as to more rationally adjust the softening point of the oil-soluble temporary plugging agent.

[0022] The aforementioned temporary plugging workover fluid uses an oil-soluble temporary plugging agent that is a composite resin comprising EVA resin, C9 petroleum resin, and calcium carbonate; wherein the C9 petroleum resin has a softening point of 95℃~100℃.

[0023] The aforementioned temporary plugging workover fluid uses an oil-soluble temporary plugging agent that is a composite resin comprising EVA resin, C9 petroleum resin, and calcium carbonate; wherein the EVA resin contains 25% to 28% VA (vinyl acetate).

[0024] The aforementioned temporary plugging workover fluid uses an oil-soluble temporary plugging agent that is a composite resin comprising EVA resin, C9 petroleum resin, and calcium carbonate; wherein the softening point of the EVA resin is 45℃~50℃.

[0025] In this invention, an oil-soluble temporary plugging agent is formed by using EVA resin with a lower softening point and C9 petroleum resin with a higher softening point. This can broaden the temperature range of the oil-soluble temporary plugging agent in the field of heavy oil reservoirs, making it suitable for well workover operations in medium and low temperature heavy oil reservoirs of 40℃ to 90℃.

[0026] The aforementioned temporary plugging workover fluid contains an oil-soluble temporary plugging agent prepared by mixing two composite resins with different particle sizes, namely EVA resin and C9 petroleum resin, after melting and adding ultrafine calcium carbonate.

[0027] In some embodiments of the first aspect of the present invention, the composite resin includes composite resin A and composite resin B, wherein the particle size of composite resin A is 1 / 3 to 2 / 3 times the median throat diameter of the pore size in the natural core of the reservoir, and the particle size of composite resin B is 1 / 3 to 1 / 4 times the throat diameter.

[0028] In this invention, the oil-soluble temporary plugging agent is uniformly dispersed in the workover fluid under the suspension effect of the filtration reducer. During the operation, the temporary plugging agent slowly enters the formation along with the workover fluid leakage. Large-diameter temporary plugging agent particles form bridging in the wellbore or near-wellbore zone according to the 2 / 3 bridging theory, while small-diameter temporary plugging agent particles form a dense filter membrane for sealing. Together, they reduce further leakage of the workover fluid into the formation. During normal production, the temporary plugging agent dissolves rapidly in the oil, opening the seepage channels. At the same time, the EVA component with a specific structure can play a role in reducing pour point and viscosity, improving the fluidity of heavy oil.

[0029] The aforementioned temporary plugging workover fluid includes hydrolyzed polyacrylamide as the filtration loss reducing agent.

[0030] In this invention, the filtration loss reducer hydrolyzed polyacrylamide is a hydrophobic associative polymer that forms a low-viscosity solution after dissolution. On the one hand, it reduces the filtration loss of the workover fluid, and on the other hand, it can regulate the settling velocity of the temporary plugging agent particles.

[0031] The aforementioned temporary plugging workover fluid includes hydrolyzed polyacrylamide as a filtration loss reducer, wherein the molecular weight of the polyacrylamide is 18 million g / mol to 25 million g / mol. That is, the molecular weight of the polyacrylamide is 1.8 × 10⁻⁶ g / mol. 7 g / mol ~ 2.5*10 7 g / mol.

[0032] The aforementioned temporary plugging workover fluid includes a filtration loss reducing agent comprising hydrolyzed polyacrylamide, wherein the degree of hydrolysis of the polyacrylamide is 20% to 25%.

[0033] In this invention, hydrolyzed polyacrylamide is used as a filtration reducer. Hydrolyzed polyacrylamide, after dissolving in water, has a certain viscosity. Before the temporary plugging agent forms a filter membrane, it reduces the filtration rate of the workover fluid and suspends the temporary plugging agent, preventing it from settling too quickly to the bottom of the well. As the workover fluid is lost to the formation, the temporary plugging agent forms a seal, completely isolating the wellbore from the formation channel. During production recovery, as crude oil flows into the wellbore, the oil-soluble temporary plugging agent dissolves in the oil. EVA improves crude oil flowability, and the flow aid forms an oil-in-water emulsion with the crude oil, significantly reducing crude oil viscosity. This synergistic effect enhances the permeability of crude oil in the near-wellbore zone, accelerating the recovery of well productivity.

[0034] A second aspect of the present invention provides a method for preparing the above-mentioned temporary plugging workover fluid, comprising the following steps:

[0035] 1) Mix C9 petroleum resin and EVA resin according to the formula, and then add calcium carbonate to obtain an oil-soluble temporary plugging agent;

[0036] 2) Add drainage aid to water according to the formula, then add hydrolyzed polyacrylamide to dissolve and mature it; then add oil-soluble temporary plugging agent to prepare temporary plugging workover fluid.

[0037] In the above-mentioned method for preparing temporary plugging workover fluid, in step 1), C9 petroleum resin and EVA resin are mixed according to the formula, and then calcium carbonate is added to obtain an oil-soluble temporary plugging agent, wherein the oil-soluble temporary plugging agent includes composite resin A and composite resin B.

[0038] In the above-mentioned method for preparing temporary plugging workover fluid, in step 1), the particle size of the composite resin A is 1 / 3 to 2 / 3 times the median throat diameter of the natural core pores in the reservoir.

[0039] In the above-mentioned method for preparing temporary plugging workover fluid, in step 1), the particle size of the composite resin B is 1 / 3 to 1 / 4 times the throat diameter.

[0040] In the above-mentioned method for preparing temporary plugging workover fluid, in step 1), C9 petroleum resin and EVA resin are mixed according to the formula, heated to a molten state, then calcium carbonate is added, cooled, ground, and sieved to obtain composite resin A and composite resin B; then composite resin A and composite resin B are mixed to obtain an oil-soluble temporary plugging agent.

[0041] In the above-mentioned method for preparing temporary plugging workover fluid, in step 1), calcium carbonate, preferably ultrafine calcium carbonate, is added to the mixed resin of C9 petroleum resin and EVA resin. The amount of calcium carbonate added should be such that the softening point of the final composite resin and the amount of calcium carbonate added show an approximately linear relationship. This is beneficial to broaden the application temperature range of the obtained temporary plugging workover fluid product and solve the problem that the application temperature range of the obtained temporary plugging workover fluid is narrow due to the narrow softening point range of a single resin.

[0042] In the above-mentioned method for preparing temporary plugging workover fluid, in step 1), C9 petroleum resin and EVA resin are mixed according to the formula, and then calcium carbonate is added to obtain an oil-soluble temporary plugging agent. The oil-soluble temporary plugging agent includes composite resin A and composite resin B, and the mass ratio of composite resin A to composite resin B is 3.8 to 4.2:1.

[0043] In this invention, according to the required throat diameter of the reservoir, composite resin A with a particle size of 1 / 3 to 2 / 3 times the throat diameter and composite resin B with a particle size of 1 / 3 to 1 / 4 times the throat diameter are mixed in a mass ratio of 3.8 to 4.2:1 to form an oil-soluble temporary plugging agent. The softening point of the obtained temporary plugging agent is generally 5 to 10°C higher than the formation temperature.

[0044] In the above-mentioned method for preparing temporary plugging workover fluid, in step 2), a drainage aid is added to water according to the formula, and then hydrolyzed polyacrylamide is added for dissolution and maturation; wherein, the dissolution and maturation time is 1 to 3 hours.

[0045] In this invention, hydrolyzed polyacrylamide is fully dissolved in a mixed solution of water and extrusion aids through dissolution and aging.

[0046] A third aspect of the present invention provides an application of any of the above-mentioned temporary plugging workover fluids in medium-to-high permeability heavy oil reservoirs.

[0047] In the application of the above-mentioned temporary plugging workover fluid in medium-high permeability heavy oil reservoirs, the temporary plugging workover fluid is suitable for workover operations in medium-low temperature heavy oil reservoirs with temperatures ranging from 40℃ to 90℃.

[0048] When applying the aforementioned temporary plugging workover fluid to medium-to-high permeability heavy oil reservoirs, conventional workover methods in this field can be employed. For example:

[0049] Water at a certain temperature is added to the casing to replace the crude oil in the casing space;

[0050] Add OT-7 and APG to clean water and stir evenly. Continue stirring and add hydrolyzed polyacrylamide. Let it mature for a period of time. Add temporary plugging agent powder while stirring to obtain a uniform suspension.

[0051] Inject the prepared workover fluid into the casing opening until the workover fluid is seen at the tubing outlet, and maintain stable well control.

[0052] The next well repair operation will be carried out.

[0053] In this invention, when the temporary plugging workover fluid is injected into a heavy oil reservoir for workover operations, the filtration loss reducer, polyacrylamide, is a hydrophobic associative polymer. After dissolving in the seeping heavy oil, it forms a low-viscosity solution. This reduces filtration loss of the workover fluid and regulates the settling velocity of the oil-soluble plugging agent particles. The oil-soluble plugging agent dissolves in the heavy oil and permeates into the wellbore and near-wellbore zone, thereby blocking the seepage channels and forming a seal. During normal production, under pressure, the heavy oil surges upwards, and the oil-soluble plugging agent quickly dissolves in the oil, opening the seepage channels. Simultaneously, the EVA component with a specific structure can reduce pour point and viscosity, improving the fluidity of the heavy oil.

[0054] In this invention, the above-mentioned technical features can be freely combined to form new technical solutions, provided they do not conflict with each other.

[0055] The technical solutions provided in the embodiments of the present invention have the following advantages compared with the prior art:

[0056] (1) This invention uses hydrolyzed polyacrylamide as a filter loss reducer. Before the temporary plugging agent forms a filter membrane to seal, the hydrolyzed polyacrylamide plays the role of reducing the filtration rate of the workover fluid and at the same time plays the role of suspending the temporary plugging agent to prevent the temporary plugging agent from settling to the bottom of the well too quickly. As the workover fluid is lost to the formation, the temporary plugging agent forms a seal, completely isolating the wellbore from the formation channel.

[0057] (2) This invention uses petroleum resin and EVA resin to prepare an oil-soluble temporary plugging agent by adding ultrafine calcium carbonate. The combination of petroleum resin and EVA resin is beneficial to adjust the softening point of the temporary plugging agent over a wider range, and improves the problem of narrow application temperature range when using a single petroleum resin as a temporary plugging agent. The addition of nano-sized ultrafine calcium carbonate is beneficial to further adjust the softening point of the temporary plugging agent, forming an oil-soluble temporary plugging agent that does not damage the reservoir.

[0058] (3) The oil-soluble temporary plugging agent according to the present invention has two different particle sizes. Under the suspension effect of the filtration reducer, it is uniformly dispersed in the workover fluid. During the operation, the temporary plugging agent slowly enters the formation with the loss of the workover fluid. The large-diameter temporary plugging agent particles form bridges on the well wall or near the well, and the small-diameter temporary plugging agent particles form a dense filter membrane to seal. Together, they reduce the further loss of the workover fluid to the formation. During normal production, the temporary plugging agent dissolves quickly in the oil and opens the seepage channel. At the same time, the EVA component with a specific structure can play the role of reducing pour point and viscosity, and improving the fluidity of heavy oil.

[0059] (4) This invention changes the viscosity of crude oil by using a drainage aid. Specifically, anionic surfactant sodium dioctyl sulfosuccinate and nonionic surfactant alkyl glucoside are used to form a drainage aid. Sodium dioctyl sulfosuccinate, as a drainage agent, can quickly pass through the oil-water interface and accelerate the formation of oil-in-water emulsion. Alkyl glucoside has excellent wetting and solubilizing ability for heavy oil and can form micro foam oil with crude oil, which can significantly reduce the viscosity of heavy oil. The synergistic effect of the two enhances the fluidity of heavy oil in the near-wellbore zone.

[0060] (5) The temporary plugging workover fluid in this invention can break the W / O state after contacting crude oil and form an oil-in-water emulsion, which greatly reduces the viscosity of crude oil. When applied to oil well operations, it can accelerate the return flow of workover fluid and at the same time play a role in clearing the near-well zone.

[0061] (6) This invention uses EVA resin and C9 petroleum resin as an oil-soluble temporary plugging agent, and combines it with drainage aid and filtration loss reducer to form a temporary plugging workover fluid for medium-high permeability heavy oil reservoirs. It has better compatibility with heavy oil reservoirs than conventional workover fluids and can be applied to workover operations in medium-low temperature heavy oil reservoirs.

[0062] (7) When using the temporary plugging workover fluid of the present invention, as crude oil flows into the wellbore during production recovery, the oil-soluble temporary plugging agent dissolves in the oil. EVA can improve the flowability of crude oil, and the drainage aid forms an oil-in-water state with the crude oil, which greatly reduces the viscosity of crude oil. The synergistic effect improves the seepage capacity of crude oil in the near-wellbore zone and accelerates the recovery of oil well production capacity. Attached Figure Description

[0063] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention.

[0064] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or related technologies will be briefly introduced below. Obviously, those skilled in the art can obtain other drawings based on these drawings without creative effort.

[0065] Figure 1 This is a viscosity-temperature curve showing the effect of the temporary plugging workover fluid obtained in Examples 1-3 of this invention on the viscosity reduction performance of heavy oil. Detailed Implementation

[0066] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0067] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this application can be purchased from the market or prepared by existing methods.

[0068] Some embodiments of the first aspect of the present invention provide a temporary plugging workover fluid, which, by mass percentage, comprises 0.4% to 2% (e.g., 0.5%, 0.7%, 1.0%, 1.2%, 1.5%, 1.7%, or 1.9%) of a flow-through aid, 2.5% to 5% (e.g., 2.5%, 2.7%, 3.0%, 3.2%, 3.5%, 3.7%, 4.0%, 4.2%, 4.5%, 4.7%, or 4.8%) of an oil-soluble temporary plugging agent, 0.04% to 0.1% (e.g., 0.05%, 0.06%, 0.07%, 0.08%, or 0.09%) of a filtration loss reducer, with the remainder being water; wherein,

[0069] The excretion aid includes sodium dioctyl sulfosuccinate and alkyl glucoside;

[0070] The oil-soluble temporary plugging agent is a composite resin comprising EVA resin, C9 petroleum resin and calcium carbonate; wherein, the EVA resin is an ethylene-vinyl acetate copolymer resin.

[0071] The filtration loss reducing agent includes hydrolyzed polyacrylamide.

[0072] According to some embodiments of the first aspect of the present invention, in the temporary plugging workover fluid, the drainage aid comprises sodium dioctyl sulfonate and alkyl glucoside; wherein, in the alkyl glucoside, the alkyl group has 8 to 12 carbon atoms (e.g., 8, 9, 10, 11 or 12).

[0073] In some embodiments of the first aspect of the present invention, the temporary plugging workover fluid contains a drainage aid comprising sodium dioctyl sulfonate and alkyl glucoside; wherein the mass ratio of sodium dioctyl sulfonate (e.g., OT-70) to alkyl glucoside (APG0810) is 1:1 to 2 (e.g., 1:1.0, 1:1.2, 1:1.4, 1:1.5, 1:1.7, 1:1.8, or 1:1.9).

[0074] In this invention, the drainage aid is composed of anionic surfactant sodium dioctyl sulfosuccinate (e.g., OT-70) and nonionic surfactant alkyl glucoside (APG0810). Sodium dioctyl sulfosuccinate acts as a drainage agent, which can quickly pass through the oil-water interface and accelerate the formation of oil-in-water emulsions. APG0810 has excellent wetting and solubilizing ability for heavy oil and can form micro-foam oil with crude oil, which can significantly reduce the viscosity of heavy oil. The synergistic effect of the two enhances the flowability of heavy oil in the near-wellbore zone.

[0075] In some embodiments of the first aspect of the present invention, the oil-soluble temporary plugging agent is a composite resin comprising EVA resin, C9 petroleum resin and calcium carbonate; wherein the mass ratio of the EVA resin to the C9 petroleum resin is 1.8 to 2.2:1 (e.g., 1.8:1, 1.9:1, 2.0:1, 2.1:1 or 2.2:1).

[0076] In existing technologies, EVA resin is commonly used as a crude oil pour point depressant. In this invention, EVA resin is used as a temporary plugging agent, serving both a temporary plugging function and improving crude oil fluidity after dissolving in oil. Petroleum resin, as a commonly used oil-soluble temporary plugging agent, has a high oil solubility. This invention combines petroleum resin and EVA resin, which facilitates a wider range of adjustment of the softening point of the temporary plugging agent, overcoming the problem of a narrow application temperature range when using a single petroleum resin as a temporary plugging agent.

[0077] In some embodiments of the first aspect of the present invention, the oil-soluble temporary plugging agent in the temporary plugging workover fluid is a composite resin comprising EVA resin, C9 petroleum resin and calcium carbonate; wherein the calcium carbonate has a particle size of nanoscale.

[0078] In this invention, nano-sized ultrafine calcium carbonate is added to a mixed resin of EVA resin and C9 petroleum resin, which helps to further fine-tune the softening point of the temporary plugging agent, thereby ensuring that the prepared temporary plugging agent does not damage the reservoir.

[0079] In some embodiments of the first aspect of the present invention, the oil-soluble temporary plugging agent in the temporary plugging workover fluid is a composite resin comprising EVA resin, C9 petroleum resin and calcium carbonate; wherein the particle size of the calcium carbonate is 0.02 μm to 0.1 μm (e.g., 0.04 μm, 0.05 μm, 0.07 μm, 0.08 μm or 0.09 μm).

[0080] In some embodiments of the first aspect of the present invention, the oil-soluble temporary plugging agent in the temporary plugging workover fluid is a composite resin comprising EVA resin, C9 petroleum resin and calcium carbonate; wherein the mass of the calcium carbonate accounts for 2% to 10% (e.g., 3%, 4%, 5%, 6%, 7%, 8% or 9%) of the total mass of the EVA resin and the C9 petroleum resin.

[0081] In this invention, the amount of ultrafine calcium carbonate added is such that the softening point of the composite resin exhibits an approximately linear relationship with it, that is, the softening point of the composite temporary plugging agent and the amount of calcium carbonate added approximately exhibit a relationship of Y = aX + b, so as to more rationally adjust the softening point of the oil-soluble temporary plugging agent.

[0082] In some embodiments of the first aspect of the present invention, the oil-soluble temporary plugging agent in the temporary plugging workover fluid is a composite resin comprising EVA resin, C9 petroleum resin and calcium carbonate; wherein the VA (vinyl acetate) content in the EVA resin is 25% to 28% (e.g., 26% or 27%).

[0083] In some embodiments of the first aspect of the present invention, the oil-soluble temporary plugging agent in the temporary plugging fluid is a composite resin comprising EVA resin, C9 petroleum resin and calcium carbonate; wherein the C9 petroleum resin has a softening point of 95°C to 100°C (e.g., 96°C, 97°C or 98°C), and the EVA resin has a softening point of 45°C to 50°C (e.g., 46°C, 47°C or 48°C).

[0084] In this invention, an oil-soluble temporary plugging agent is formed by using EVA resin with a lower softening point and C9 petroleum resin with a higher softening point. This can broaden the temperature range of the oil-soluble temporary plugging agent in the field of heavy oil reservoirs, making it suitable for well workover operations in medium and low temperature heavy oil reservoirs of 40℃ to 90℃.

[0085] In some embodiments of the first aspect of the present invention, the oil-soluble temporary plugging agent is prepared by mixing two composite resins with different particle sizes, which are obtained by melting EVA resin and C9 petroleum resin and then adding ultrafine calcium carbonate.

[0086] In some embodiments of the first aspect of the present invention, the oil-soluble temporary plugging agent comprises a composite resin A and a composite resin B, wherein the particle size of the composite resin A is 1 / 3 to 2 / 3 times (e.g., 1 / 3, 1 / 2, or 2 / 3 times) the median throat diameter of the reservoir's natural core pores, and the particle size of the composite resin B is 1 / 3 to 1 / 4 times (e.g., 1 / 3, 7 / 24, or 1 / 4 times) the throat diameter.

[0087] In this invention, the oil-soluble temporary plugging agent is uniformly dispersed in the workover fluid under the suspension effect of the filtration reducer. During the operation, the oil-soluble temporary plugging agent slowly enters the formation along with the workover fluid leakage. Large-diameter temporary plugging agent particles form bridging in the wellbore or near-wellbore zone according to the 2 / 3 bridging theory, while small-diameter temporary plugging agent particles form a dense filter membrane for sealing. Together, they reduce further leakage of the workover fluid into the formation. During normal production, the temporary plugging agent dissolves rapidly in the oil, opening the seepage channels. At the same time, the EVA component with a specific structure can play a role in reducing pour point and viscosity, improving the fluidity of heavy oil.

[0088] According to some embodiments of the first aspect of the present invention, in the oil-soluble temporary plugging agent, the mass ratio of the composite resin A to the composite resin B is 3.8 to 4.2:1 (e.g., 3.9:1, 4.0:1 or 4.11).

[0089] In some embodiments of the first aspect of the present invention, the polyacrylamide has a molecular weight of 18 million g / mol to 25 million g / mol (e.g., 19 million g / mol, 20 million g / mol, 21 million g / mol, 22 million g / mol, 23 million g / mol, or 24 million g / mol). That is, the molecular weight of the polyacrylamide is 1.8 × 10⁻⁶. 7 g / mol ~ 2.5*10 7 g / mol (e.g., 1.8*10) 7 g / mol, 1.9*10 7 g / mol, 2.0*10 7 g / mol, 2.1*10 7 g / mol, 2.2*10 7 g / mol, 2.3*10 7 g / mol or 2.4*10 7 g / mol).

[0090] In this invention, the filtration loss reducer hydrolyzed polyacrylamide is a hydrophobic associative polymer that forms a low-viscosity solution after dissolution. On the one hand, it reduces the filtration loss of the workover fluid, and on the other hand, it can regulate the settling velocity of the temporary plugging agent particles.

[0091] In some embodiments of the first aspect of the present invention, the filtration loss reducing agent in the temporary plugging workover fluid comprises hydrolyzed polyacrylamide; the degree of hydrolysis of the polyacrylamide is 20% to 25% (e.g., 21%, 22%, 23% or 24%).

[0092] In this invention, hydrolyzed polyacrylamide is used as a filtration reducer in the temporary plugging workover fluid. Hydrolyzed polyacrylamide, after dissolving in water, has a certain viscosity. Before the temporary plugging agent forms a filter membrane for sealing, it reduces the filtration rate of the workover fluid and suspends the temporary plugging agent, preventing it from settling too quickly to the bottom of the well. As the workover fluid filtrations into the formation, the temporary plugging agent forms a seal, completely isolating the wellbore from the formation channel. During production recovery, as crude oil flows into the wellbore, the oil-soluble temporary plugging agent dissolves in the oil. EVA improves crude oil flowability, and the flow aid forms an oil-in-water emulsion with the crude oil, significantly reducing crude oil viscosity. This synergistic effect enhances the permeability of crude oil in the near-wellbore zone, accelerating the recovery of well productivity.

[0093] Some embodiments of the second aspect of the present invention provide a method for preparing the above-mentioned temporary plugging workover fluid, comprising the following steps:

[0094] 1) Mix C9 petroleum resin and EVA resin according to the formula, and then add calcium carbonate to obtain an oil-soluble temporary plugging agent;

[0095] 2) Add drainage aid to water according to the formula, then add hydrolyzed polyacrylamide to dissolve and mature it; then add oil-soluble temporary plugging agent to prepare temporary plugging workover fluid.

[0096] According to some embodiments of the second aspect of the present invention, in step 1), C9 petroleum resin and EVA resin are mixed according to the formulation, and then calcium carbonate is added to obtain an oil-soluble temporary plugging agent, wherein the oil-soluble temporary plugging agent includes composite resin A and composite resin B, the particle size of composite resin A is 1 / 3 to 2 / 3 times (e.g., 1 / 3, 1 / 2, or 2 / 3 times) the median throat diameter of the reservoir's natural core pores, and the particle size of composite resin B is 1 / 3 to 1 / 4 times (e.g., 1 / 3, 7 / 24, or 1 / 4 times) the throat diameter.

[0097] According to some embodiments of the second aspect of the present invention, in step 1), C9 petroleum resin and EVA resin are mixed according to the formula, heated to a molten state, and then calcium carbonate is added (the amount of ultrafine calcium carbonate added has an approximately linear relationship with the softening point of the composite resin). After cooling, the mixture is ground and sieved to obtain composite resin A and composite resin B; then composite resin A and composite resin B are mixed to obtain an oil-soluble temporary plugging agent.

[0098] According to some embodiments of the second aspect of the present invention, in step 1), C9 petroleum resin and EVA resin are mixed according to the formulation, and then calcium carbonate is added to obtain an oil-soluble temporary plugging agent, wherein the oil-soluble temporary plugging agent comprises composite resin A and composite resin B, and the mass ratio of composite resin A to composite resin B is 3.8 to 4.2:1 (e.g., 3.9:1, 4.0:1 or 4.11).

[0099] In this invention, according to the required throat diameter of the reservoir, composite resin A with a particle size of 1 / 3 to 2 / 3 times the throat diameter and composite resin B with a particle size of 1 / 3 to 1 / 4 times the throat diameter are mixed in a mass ratio of 3.8 to 4.2:1 to form an oil-soluble temporary plugging agent. The softening point of the obtained temporary plugging agent is generally 5 to 10°C higher than the formation temperature.

[0100] According to some embodiments of the second aspect of the present invention, in step 2), a drainage aid is added to water according to the formula, and then hydrolyzed polyacrylamide is added for dissolution and maturation, wherein the dissolution and maturation time is 1 to 3 hours (e.g., 1.5 hours, 2 hours or 2.5 hours).

[0101] Some embodiments of the third aspect of the present invention provide an application of any of the above-mentioned temporary plugging workover fluids in medium-to-high permeability heavy oil reservoirs.

[0102] According to some embodiments of the third aspect of the present invention, the temporary plugging workover fluid is suitable for workover operations in medium- and low-temperature heavy oil reservoirs at temperatures ranging from 40°C to 90°C (e.g., 50°C, 60°C, 70°C, or 80°C).

[0103] According to some embodiments of the third aspect of the present invention, when the temporary plugging workover fluid is applied in medium-to-high permeability heavy oil reservoirs, conventional workover methods in the art can be employed. For example:

[0104] Water at a certain temperature is added to the casing to replace the crude oil in the casing space;

[0105] Add OT-7 and APG to clean water and stir evenly. Continue stirring and add hydrolyzed polyacrylamide. Let it mature for a period of time. Add temporary plugging agent powder while stirring to obtain a uniform suspension.

[0106] Inject the prepared workover fluid into the casing opening until the workover fluid is seen at the tubing outlet, and maintain stable well control.

[0107] The next well repair operation will be carried out.

[0108] In this invention, when the temporary plugging workover fluid is injected into a heavy oil reservoir for workover operations, the filtration loss reducer, polyacrylamide, is a hydrophobic associative polymer. After dissolving in the seeping heavy oil, it forms a low-viscosity solution. This reduces filtration loss of the workover fluid and regulates the settling velocity of the oil-soluble plugging agent particles. The oil-soluble plugging agent dissolves in the heavy oil and permeates into the wellbore and near-wellbore zone, thereby blocking the seepage channels and forming a seal. During normal production, under pressure, the heavy oil surges upwards, and the oil-soluble plugging agent quickly dissolves in the oil, opening the seepage channels. Simultaneously, the EVA component with a specific structure can reduce pour point and viscosity, improving the fluidity of the heavy oil.

[0109] The technical solution of the present invention will be further explained clearly and completely below with reference to specific embodiments and accompanying drawings.

[0110] Example 1

[0111] A temporary plugging workover fluid can be used for workover operations in oil reservoirs with a formation temperature of 45℃ and a median core throat diameter of 200μm. Its preparation method includes the following steps.

[0112] S1: Preparation of oil-soluble temporary plugging agent

[0113] 10g of C9 petroleum resin powder (softening point: 95℃) and 20g of EVA powder (softening point: 48℃) were mixed and heated until melted. Then, 0.6g of ultrafine calcium carbonate was added while stirring. After cooling, the mixture was ground to obtain a composite resin with a softening point of 50℃. The particles of the composite resin that passed through a 115-mesh sieve were then sorted through a 200-mesh sieve. The powder that did not pass through the 200-mesh sieve was collected to obtain composite resin A with a particle size of 1 / 3 to 2 / 3 times the throat diameter. The powder that passed through the 200-mesh sieve was sorted through a 300-mesh sieve. The powder that did not pass through the 300-mesh sieve was collected to obtain composite resin B with a particle size of 1 / 3 to 1 / 4 times the throat diameter. Composite resin A and composite resin B were mixed uniformly at a mass ratio of 4:1 to obtain an oil-soluble temporary plugging agent.

[0114] Weigh 10.00g of oil-soluble temporary plugging agent and place it in a 250ml beaker. Add 100ml of kerosene and dissolve the agent at 50℃ for 1 hour. Filter the solution with high-speed filter paper, air dry, and place it in a 60℃ constant temperature drying oven for 2 hours. Weigh the remaining mass and find that it is 0.04g. The oil solubility of the oil-soluble temporary plugging agent is 99.6%.

[0115] S2: Preparation of Temporary Positive Well Workover Fluid

[0116] Take 200ml of formation water, add 0.5g TO-7 and 0.5g APG, stir well, and add 0.1g of a molecule with a molecular weight of 18 million g / mol (i.e., 1.8*10). 7Hydrolyzed polyacrylamide KY-2 (g / mol) was matured for 2 hours to ensure no fish eyes, and 6g of the oil-soluble temporary plugging agent prepared in this example was added. The mixture was stirred evenly to obtain a temporary plugging workover fluid.

[0117] Example 2

[0118] A temporary plugging workover fluid can be used for workover operations in oil reservoirs with a formation temperature of 60℃ and a median core throat diameter of 100μm. Its preparation method includes the following steps.

[0119] S1: Preparation of oil-soluble temporary plugging agent

[0120] Weigh 10g of C9 petroleum resin powder and 20g of EVA powder, mix and heat until melted, add 1.62g of ultrafine calcium carbonate while stirring, cool and grind to obtain a composite resin with a softening point of 67℃; the particles of the composite resin that pass through a 230-mesh sieve are then sorted through a 400-mesh sieve, and the powder that does not pass through the 400-mesh sieve is taken, which is composite resin A with a particle size of 1 / 3 to 2 / 3 times the throat diameter; the powder that passes through the 400-mesh sieve is sorted through a 500-mesh sieve, and the powder that does not pass through the 500-mesh sieve is taken, which is composite resin B with a particle size of 1 / 3 to 1 / 4 times the throat diameter. Composite resin A and composite resin B are mixed uniformly at a mass ratio of 4:1 to obtain an oil-soluble temporary plugging agent.

[0121] S2: Preparation of Temporary Positive Well Workover Fluid

[0122] Take 200ml of formation water, add 1g TO-7 and 1g APG, stir well, and add 0.15g of a 2*10 molecular weight compound. 7 Add g / mol of hydrolyzed polyacrylamide KY-2, mature for 2 hours to ensure no fish eyes, add 8g of the oil-soluble temporary plugging agent prepared in step S1, stir evenly to obtain the temporary plugging workover fluid.

[0123] Example 3

[0124] A temporary plugging workover fluid can be used for workover operations in oil reservoirs with a formation temperature of 80℃ and a median core throat diameter of 50μm. Its preparation method includes the following steps.

[0125] S1: Preparation of oil-soluble temporary plugging agent

[0126] Weigh 10g of C9 petroleum resin powder and 20g of EVA powder, mix and heat until melted, add 3g of ultrafine calcium carbonate while stirring, cool and grind to obtain a composite resin with a softening point of 90℃. The particles of the composite resin that pass through a 400-mesh sieve are then sorted through an 800-mesh sieve. The powder that does not pass through the 800-mesh sieve is taken to obtain composite resin A with a particle size of 1 / 3 to 2 / 3 times the throat diameter. The powder that passes through the 800-mesh sieve is sorted through a 1000-mesh sieve. The powder that does not pass through the 1000-mesh sieve is taken to obtain composite resin B with a particle size of 1 / 3 to 1 / 4 times the throat diameter. Composite resin A and composite resin B are mixed uniformly at a mass ratio of 4:1 to obtain an oil-soluble temporary plugging agent.

[0127] S2: Preparation of Temporary Positive Well Workover Fluid

[0128] Take 200ml of formation water, add 2g TO-7 and 2g APG0810, stir well, and then add 0.2g of a substance with a molecular weight of 2.4*10. 7 After hydrolyzing polyacrylamide KY-2 at a concentration of g / mol and aging for 2 hours to ensure no fish eyes, add 10g of oil-soluble temporary plugging agent from step 1 and stir evenly to obtain a temporary plugging workover fluid.

[0129] Comparative Example 1

[0130] A method for preparing a temporary plugging well workover fluid differs from Example 3 in that the mixing ratio of composite resin A and composite resin B in step S1 is different, while other technical aspects remain the same. Specifically, the preparation method includes the following steps:

[0131] S1: Preparation of oil-soluble temporary plugging agent

[0132] Weigh 10g of C9 petroleum resin powder and 20g of EVA powder, mix and heat until melted, add 3g of ultrafine calcium carbonate while stirring, cool and grind to obtain a composite resin with a softening point of 90℃. The particles of the composite resin that pass through a 400-mesh sieve are then sorted through an 800-mesh sieve. The powder that does not pass through the 800-mesh sieve is taken to obtain composite resin A with a particle size of 1 / 3 to 2 / 3 times the throat diameter. The powder that passes through the 800-mesh sieve is sorted through a 1000-mesh sieve. The powder that does not pass through the 1000-mesh sieve is taken to obtain composite resin B with a particle size of 1 / 3 to 1 / 4 times the throat diameter. Composite resin A and composite resin B are mixed uniformly at a mass ratio of 1:1 to obtain an oil-soluble temporary plugging agent.

[0133] S2: Preparation of Temporary Positive Well Workover Fluid

[0134] Take 200ml of formation water, add 2g TO-7 and 2g APG0810, stir well, and then add 0.2g of a substance with a molecular weight of 2.4*10. 7After hydrolyzing polyacrylamide KY-2 at a concentration of g / mol for 2 hours to ensure no fish eyes, add 10g of the oil-soluble temporary plugging agent obtained in step S1, stir evenly, and obtain a temporary plugging well workover fluid.

[0135] In this comparative example, since the composition of the drainage aid in the temporary plugging workover fluid is the same as that in Example 3, the viscosity-reducing performance of the obtained temporary plugging workover fluid on crude oil is similar to that of the temporary plugging workover fluid obtained in Example 3.

[0136] Comparative Example 2

[0137] A method for preparing a temporary plugging workover fluid includes the following steps:

[0138] S1: Preparation of oil-soluble temporary plugging agent

[0139] Weigh 10g of C9 petroleum resin powder and 40g of EVA powder, mix and heat until melted, add 3g of ultrafine calcium carbonate while stirring, cool and grind to obtain a composite resin with a softening point of about 70℃. The particles of the composite resin that pass through a 400-mesh sieve are then sorted through an 800-mesh sieve. The powder that does not pass through the 800-mesh sieve is collected, which yields composite resin A with a particle size of 1 / 3 to 2 / 3 times the throat diameter. The powder that passes through the 800-mesh sieve is then sorted through a 1000-mesh sieve. The powder that does not pass through the 1000-mesh sieve is collected, which yields composite resin B with a particle size of 1 / 3 to 1 / 4 times the throat diameter. Composite resin A and composite resin B are uniformly mixed at a mass ratio of 4:1 to obtain an oil-soluble temporary plugging agent.

[0140] S2: Preparation of Temporary Positive Well Workover Fluid

[0141] Take 200ml of formation water, add 2g TO-7 and 2g APG0810, stir well, and then add 0.2g of a substance with a molecular weight of 2.4*10. 7 After hydrolyzing polyacrylamide KY-2 at a concentration of g / mol and aging for 2 hours to ensure no fish eyes, add 10g of oil-soluble temporary plugging agent from step 1 and stir evenly to obtain a temporary plugging workover fluid.

[0142] In this comparative example, since the softening point of the oil-soluble temporary plugging agent prepared in step S1 is lower than the formation temperature of 80°C, the temporary plugging workover fluid prepared in this comparative example has softened and agglomerated during the accumulation of temporary plugging agent particles. Therefore, it is ultimately impossible to achieve effective bridging and plugging.

[0143] Performance testing of temporary plugging workover fluid

[0144] (1) System stability

[0145] The stability of the temporary plugging workover fluid systems prepared in Examples 1, 2, and 3 was tested. Premature instability of solid particles in the workover fluid is detrimental to the formation of the temporary plugging zone during well entry.

[0146] Table 1. Stability Test of Temporary Plugging Type Well Workover Fluid System

[0147]

[0148] As the temperature rises, the viscosity of the workover fluid decreases, and the stability of the system decreases. Within 90℃, the solid phase of this temporary plugging workover fluid remains stable for more than 24 hours, which meets the time requirement for the workover fluid to form a shielding temporary plugging zone.

[0149] (2) Crude oil viscosity reduction performance

[0150] Using formation water and dehydrated crude oil (containing 8.5% wax and 59.8% asphalt) from a certain oilfield as the test objects for the performance of temporary plugging workover fluid, 100 ml of temporary plugging workover fluid (hereinafter referred to as workover fluid) was prepared according to the preparation method of the temporary plugging workover fluid provided in Examples 1-3, and labeled as workover fluid 1, workover fluid 2 and workover fluid 3 respectively. A sample of dehydrated crude oil was taken, and the dehydrated crude oil and workover fluid were mixed and stirred evenly according to a mass ratio of 7:3. The viscosity-temperature (i.e., viscosity-temperature) curves of the dehydrated crude oil, the mixture of dehydrated crude oil and formation water with a mass ratio of 7:3 (i.e., 30% water-containing blank crude oil), and the mixture of dehydrated crude oil and workover fluid with a mass ratio of 7:3 were tested in the temperature range of 30℃~70℃. Figure 1 Viscosity-temperature curves showing the effect of the temporary plugging workover fluids obtained in Examples 1-3 of this invention on the viscosity-reducing properties of heavy oil are shown. Workover fluid 1 was prepared according to the preparation method of the temporary plugging workover fluid in Example 1, workover fluid 2 was prepared according to the preparation method of the temporary plugging workover fluid in Example 2, and workover fluid 3 was prepared according to the preparation method of the temporary plugging workover fluid in Example 3.

[0151] Depend on Figure 1 It can be seen that for high-colloidal asphalt crude oil (i.e., dehydrated crude oil), the viscosity of the dehydrated crude oil is significantly reduced after contact with the workover fluids 1-3 obtained according to Examples 1-3. Furthermore, as the molecular weight of the hydrolyzed polyacrylamide raw material used in Examples 1-3 increases, the viscosity of the resulting workover fluid increases, and the viscosity-reducing effect decreases somewhat, but the viscosity reduction rate is still greater than 90%, meeting the viscosity reduction standard for heavy oil viscosity reducers specified in Q / SY HB 0192 (when the emulsion viscosity is greater than 2000 mPa·s, the viscosity reduction rate of water-based viscosity reducers should not be less than 90%). When applied to oil well operations, it can accelerate the return flow rate of the workover fluid and simultaneously clear the near-wellbore area.

[0152] (3) Static filtration loss

[0153] According to GB / T16783.1-2014, the static filtration loss of the workover fluids prepared in Examples 1, 2, and 3 was determined using an SD6 six-unit medium-pressure filtration loss meter (Qingdao Bairuida Petroleum Machinery Manufacturing Co., Ltd.). The specific method is as follows:

[0154] Take 100 ml of the workover fluid sample obtained according to Examples 1-3 and put it into the filtrate loser cup, making the liquid level 1-1.5 cm from the top of the cup. Then place the filter paper, install the medium-pressure filtrate loser, and place the dry measuring cylinder under the discharge pipe to collect the filtrate. Adjust the pressure regulator to reach 690 kPa (100 psi ± 5 psi), and start timing while pressurizing. After 30 minutes, measure the volume of the collected filtrate. For comparative analysis, the filtrate loss was determined using conventional workover fluid (2% KCl solution) under the same conditions. Table 2 shows the filtrate loss of the workover fluid sample obtained according to Examples 1-3 and the 2% KCl solution (conventional workover fluid), where the filtrate loss rate is the filtrate loss of the workover fluid sample relative to the conventional workover fluid.

[0155] Table 2. Filtration rate of the temporary plugging workover fluid system

[0156]

[0157] As can be seen from Table 2, the experimental results of static filtration loss show that, compared with conventional inorganic salt workover fluid (2% KCl solution), the static filtration loss of the temporary plugging workover fluid according to the present invention is significantly reduced. This indicates that the plugging zone formed by the temporary plugging workover fluid obtained by the technical solution of the present invention can effectively reduce the leakage of fluid entering the well during the workover process.

[0158] (4) Blocking rate and permeability recovery rate

[0159] Based on the workover fluids prepared in Examples 1, 2, 3 and Comparative Example 1, the plugging rate and permeability recovery rate of the workover fluids on the core at different temperatures were measured.

[0160] Three Bailey core samples (Φ2.5*30) were collected and numbered 1, 2, 3 and 4. The diameter of the pores is shown in Table 3. The simulated oil was kerosene and the formation water was simulated formation water with a salinity of 5100 mg / L.

[0161] Experimental Procedure: Four core samples were vacuumed and saturated with simulated formation water until the pressure stabilized. The following experiments were conducted at different experimental temperatures (see Table 3). The workover fluid for core number 1 was the workover fluid prepared in Example 1; the workover fluid for core number 2 was the workover fluid prepared in Example 2; the workover fluid for core number 3 was the workover fluid prepared in Example 3; and the workover fluid for core number 4 was the workover fluid prepared in Example 1. The specific experimental steps are as follows:

[0162] (1) Calculate the core pore volume using positive saturated water; where pv is the unit of pore volume (for example: if the pore volume of a core is 100ml, injecting 100ml of water can represent 1pv of water injection).

[0163] (2) Reverse injection of kerosene until the pressure stabilizes, then record the stable pressure P. O1 Calculate the oil phase permeability K O1 ;

[0164] (3) Inject clean water in the forward direction to displace the kerosene. Record the stable pressure P after the pressure stabilizes. W1 Calculate the water phase permeability K w1 ;

[0165] (4) Inject 1pv of temporary plugging workover fluid in the forward direction, maintain the experimental temperature and pressure difference for 24 hours, and inject 1pv of simulated formation water in the forward direction to record the stable pressure P. W2 Calculate the aqueous phase permeability K after temporary plugging. w2 ;

[0166] (5) Inject 2pv of kerosene in the reverse direction, let it stand for 1 hour, then continue injecting kerosene until the pressure stabilizes and record the stable pressure P. O2 Calculate the oil phase permeability K o2 .

[0167] Table 3 shows the data on the effects of the temporary plugging workover fluids obtained in Examples 1-3 and Comparative Example 1 on core plugging and permeability recovery.

[0168] As can be seen from the experimental data in Table 3, under different experimental temperatures, the temporary plugging workover fluids prepared in Examples 1, 2, and 3 achieved a temporary plugging rate of over 70% for Bailey core samples. After being unblocked with kerosene, the core permeability recovered well, with a permeability recovery rate of over 80%. The workover fluid prepared in Comparative Example 1 had a poor sealing effect due to an improper ratio of resin A to resin B, and its temporary plugging rate decreased significantly under the same conditions.

[0169] Table 3. Data on the impact of temporary plugging fluids on core plugging and permeability recovery.

[0170]

[0171] Note: Temporary congestion rate = (K) w1 -K w2 ) / K w1 *100%; Permeability recovery rate = K o2 / K o1 *100%.

[0172] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A temporary plugging well workover fluid, characterized in that, By weight percentage, the temporary plugging workover fluid comprises 0.4%–2% flow aid, 2.5%–5% oil-soluble temporary plugging agent, 0.04%–0.1% filtration loss reducer, and the remainder is water; wherein, The excretion aid includes sodium dioctyl sulfosuccinate and alkyl glucoside; The oil-soluble temporary plugging agent is a composite resin comprising EVA resin, C9 petroleum resin and calcium carbonate. The filtration loss reducing agent includes hydrolyzed polyacrylamide.

2. The temporary plugging workover fluid according to claim 1, characterized in that, In the alkyl glucoside, the alkyl group has 8 to 12 carbon atoms.

3. The temporary plugging well workover fluid according to claim 1, characterized in that, In the discharge aid, the mass ratio of sodium dioctyl sulfosuccinate and alkyl glucoside is 1:1 to 2.

4. The temporary plugging workover fluid according to claim 1, characterized in that, The calcium carbonate has a particle size in the nanometer range.

5. The temporary plugging workover fluid according to claim 4, characterized in that, The calcium carbonate has a particle size of 0.02 μm to 0.1 μm.

6. The temporary plugging workover fluid according to claim 1, characterized in that, In the oil-soluble temporary plugging agent, the mass ratio of the EVA resin to the C9 petroleum resin is 1.8 to 2.2:

1.

7. The temporary plugging workover fluid according to claim 1, characterized in that, In the oil-soluble temporary plugging agent, the calcium carbonate accounts for 2% to 10% of the total mass of the EVA resin and the C9 petroleum resin.

8. The temporary plugging workover fluid according to claim 1, characterized in that, The softening point of the EVA resin is 45℃~50℃, and the softening point of the C9 petroleum resin is 95℃~100℃.

9. The temporary plugging workover fluid according to claim 1, characterized in that, The EVA resin contains 25% to 28% VA (vinyl acetate).

10. The temporary plugging workover fluid according to claim 1, characterized in that, The oil-soluble temporary plugging agent is a mixture of two composite resins with different particle sizes, prepared by melting EVA resin and C9 petroleum resin and adding calcium carbonate.

11. The temporary plugging workover fluid according to claim 10, characterized in that, The composite resin includes composite resin A and composite resin B. The particle size of composite resin A is 1 / 3 to 2 / 3 times the median throat diameter of the pores in the natural core of the reservoir, and the particle size of composite resin B is 1 / 3 to 1 / 4 times the throat diameter.

12. The temporary plugging workover fluid according to claim 11, characterized in that, The mass ratio of composite resin A to composite resin B is 3.8 to 4.2:

1.

13. The temporary plugging workover fluid according to claim 1, characterized in that, The polyacrylamide has a molecular weight of 18 million g / mol to 25 million g / mol; the degree of hydrolysis of the polyacrylamide is 20% to 25%.

14. A method for preparing a temporary plugging workover fluid according to any one of claims 1-13, characterized in that, The preparation method includes the following steps: 1) Mix C9 petroleum resin and EVA resin according to the formula, and then add calcium carbonate to obtain an oil-soluble temporary plugging agent; 2) Add the drainage aid to the water according to the formula, then add hydrolyzed polyacrylamide to dissolve and mature it; then add the oil-soluble temporary plugging agent to prepare a temporary plugging workover fluid.

15. The method for preparing the temporary plugging workover fluid according to claim 14, characterized in that, In step 1), the oil-soluble temporary plugging agent includes composite resin A and composite resin B, wherein the particle size of composite resin A is 1 / 3 to 2 / 3 times the throat diameter in the pores of the natural core of the reservoir, and the particle size of composite resin B is 1 / 3 to 1 / 4 times the throat diameter.

16. The method for preparing the temporary plugging workover fluid according to claim 14 or 15, characterized in that, In step 1), C9 petroleum resin and EVA resin are mixed according to the formula, heated to a molten state, then calcium carbonate is added, cooled, ground, and sieved to obtain composite resin A and composite resin B; then composite resin A and composite resin B are mixed to obtain an oil-soluble temporary plugging agent.

17. The application of a temporary plugging workover fluid in medium-to-high permeability heavy oil reservoirs, characterized in that... The temporary plugging workover fluid is the temporary plugging workover fluid according to any one of claims 1-13, or is prepared by the preparation method of the temporary plugging workover fluid according to any one of claims 14-16.

18. The application of the temporary plugging workover fluid according to claim 17 in medium-to-high permeability heavy oil reservoirs, characterized in that, The temporary plugging workover fluid is suitable for workover operations in medium-low temperature heavy oil reservoirs with temperatures ranging from 40℃ to 90℃.

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