Temperature-controllable expanding plugging agent for oil-based drilling fluid and preparation method thereof

Abstract

The present application relates to the oil-based drilling fluid additive technical field, it is a kind of oil-based drilling fluid temperature control expansion plugging agent and preparation method thereof, the present application oil-based drilling fluid temperature control expansion plugging agent is by octadecyl acrylate, butyl acrylate, isobornyl methacrylate, pore-forming agent, crosslinking agent and initiator through suspension polymerization process synthesis is obtained, it not only has excellent high-temperature stability, can stably resist 180 DEG C high temperature, meet the temperature requirement of deep well leakage plugging, also have outstanding pressure-bearing plugging capacity, under 7MPa pressure difference condition, can form high-strength gel plugging layer in leakage passage, effectively seal fissure and pore, significantly restore formation pressure-bearing capacity;At the same time, raw material is easy to get, operation is safe, process is simple, suitable for industrial production.

Description

Technical Field

[0001] This invention relates to the field of oil-based drilling fluid additives, specifically a temperature-controlled expansion plugging agent for oil-based drilling fluids and its preparation method. Background Technology

[0002] With the large-scale development of shale gas, tight oil, and ultra-deep wells, oil-based drilling fluids have become the preferred fluid for drilling in complex formations due to their excellent high-temperature resistance, pollution resistance, and lubrication properties. However, once oil-based drilling fluids are lost, not only can the cost of drilling fluid consumption per well reach millions of yuan, but it can also easily induce serious chain-reaction engineering accidents such as wellbore instability, stuck pipe, and even blowouts, hindering safe and rapid drilling. Unlike water-based drilling fluids, oil-based drilling fluids lack a polar continuous phase, making it difficult for conventional water-based plugging agents (such as water-absorbing and swelling plant fibers, cross-linked gels, and bridged plug-solidified composite slurries) to effectively wet, swell, or cross-link in the oil phase environment. This incompatibility not only results in low bonding strength, difficulty in retention, and poor pressure resistance of the plugging layer, but also easily produces negative pollution effects on the oil-based system, such as demulsification, thickening, and increased filtration loss, severely damaging the rheological properties and stability of the drilling fluid. Therefore, developing high-efficiency plugging materials that are fully compatible with oil-based drilling fluids and effective against fractures of multiple scales has become a technical bottleneck that urgently needs to be overcome in the field of drilling engineering.

[0003] Currently, existing oil-based plugging materials, both domestically and internationally, can be broadly categorized into three types, but all have significant limitations in application. The first type consists of rigid bridging particles (such as calcium carbonate, mica flakes, nut shells, and graphite). These materials primarily rely on particle size distribution for physical bridging, but they have almost no filling capacity for micro-cracks (<100μm), and the plugging layer structure is loose, with a pressure resistance generally below 7MPa. The second type comprises oil-absorbing and swelling polymers (such as styrene-butadiene rubber and acrylates). These materials can expand in volume by 2 to 6 times in the oil phase, but they suffer from insufficient strength after expansion and are prone to softening or decomposition at high temperatures (>150℃), posing a high risk of secondary leakage. The third type is chemically cross-linked systems (such as epoxy, polyurethane, and phenolic resins). Although they have high strength after curing, their rapid reaction rate and high heat release during curing result in extremely poor compatibility with oil-based drilling fluids, leading to a narrow window for on-site construction. Misjudging the location of the leaking layer can easily result in significant material waste or even trigger a stuck drill pipe accident.

[0004] Among the existing patented technologies that have been disclosed, the practical application effect of oil-based sealing materials is also subject to multiple limitations.

[0005] For example, Chinese patent document CN104232037A discloses an oil-based drilling fluid fracture plugging agent. This plugging agent comprises the following components by weight percentage, based on the total weight of the drilling fluid system: 10%–15% oil-swellable material, 15%–20% deformable particles, 2%–3% fiber material, 5%–10% plugging material, 50%–67% ultrafine calcium carbonate, and 1%–2% surfactant. This plugging agent is primarily designed to address the leakage prevention and plugging needs of oil-based drilling fluid systems encountering highly permeable and fractured formations. It achieves good results in oil absorption and volume expansion within 2 hours. For fractures ≤4mm, the compressive strength can reach over 7MPa, demonstrating excellent plugging performance. It utilizes the synergistic effect between its components to seal fractures, thereby improving the success rate of leakage prevention and plugging. The patent discloses a leak-sealing system that combines ultrafine calcium carbonate, plant fiber and oil-swellable powder. Although it can form a tough filter cake and withstand pressure up to 7MPa, its ability to fill cracks wider than 1mm is obviously insufficient. Moreover, the ultrafine particles are prone to settling under high temperature conditions, which leads to sealing failure and causes "secondary leakage".

[0006] Chinese patent document CN119331576A discloses a high-filtration-loss pressure-bearing plugging agent for oil-based drilling fluids and its preparation method. The plugging agent, by weight, comprises 30 to 40 parts of bridging support material, 10 to 15 parts of fiber material, 40 to 50 parts of filler material, and 5 to 10 parts of filter aid. The required amounts of bridging support material, fiber material, filler material, and filter aid are mixed evenly to obtain the high-filtration-loss pressure-bearing plugging agent for oil-based drilling fluids. The preparation method of this invention is simple, consisting of a mixture of various materials such as bridging support material, fiber material, filler material, and filter aid. Due to the small size of the solid particles, they easily enter leakage channels and spaces of various opening sizes, and are rapidly filtered out under pressure differential. The more severe the leakage, the faster the leakage rate, and the faster the filtration. Therefore, this invention has a wide range of applications, simple plugging construction, high safety, rapid effect, and low cost. This patent proposes a three-phase composite sealing material consisting of "bridging-filling-filtration aid," which has the advantages of convenient on-site preparation and low cost, but is only suitable for leakage velocities of less than 20m. 3 In formations with permeability loss of approximately 1000 m / h, there is a lack of expansion and filling capacity for microfractures (<50 μm), and the introduction of filter aids will increase the filtration loss of the system, which is detrimental to wellbore stability.

[0007] Chinese patent document CN115124644B discloses an oil-absorbing swelling agent and its slow-release preparation method. The oil-absorbing swelling agent comprises 170-200 parts by weight of polymeric monomer, 3-5 parts by weight of crosslinking agent, and 0.1-0.2 parts by weight of initiator. This invention's oil-absorbing swelling agent can be prepared into particles of different sizes, facilitating its mixing with cement to form cement slurry. Used as a plugging agent in oil and gas wells, it expands after absorbing oil-based fluids. After being coated with a slow-release layer, it exhibits a slow-release swelling effect, making it suitable for field applications. This material is prepared using a water-based system, and its swelling function highly depends on the penetration and absorption of the external oil phase. It requires a slow-release layer to achieve delayed expansion, making it primarily suitable for conventional plugging scenarios. However, in deep, high-temperature, and complex oil-based drilling fluid environments, such materials, which rely on external oil phase penetration and have limited temperature resistance, are difficult to meet the long-term pressure-bearing plugging requirements under harsh conditions.

[0008] Therefore, existing oil-based sealing materials still have problems such as easy softening and decomposition at high temperatures, low pressure resistance, and insufficient filling of microcracks. Summary of the Invention

[0009] This invention provides a temperature-controlled expansion plugging agent for oil-based drilling fluids and its preparation method, which overcomes the shortcomings of the prior art and can effectively solve the problems of insufficient temperature resistance and pressure bearing capacity of existing oil-based plugging materials.

[0010] One of the technical solutions of the present invention is achieved through the following measures: a temperature-controlled expansion plugging agent for oil-based drilling fluid, wherein the raw materials comprise, by mass ratio (5 to 7): (1 to 3): (1 to 2), octadecyl acrylate, butyl acrylate, and isobornyl methacrylate, and the raw materials further include a pore-forming agent, a crosslinking agent, and an initiator, wherein the amount of pore-forming agent added is 50% to 74% of the total mass of octadecyl acrylate, butyl acrylate, and isobornyl methacrylate, the amount of crosslinking agent added is 1.0% to 2.0% of the total mass of octadecyl acrylate, butyl acrylate, and isobornyl methacrylate, and the amount of initiator added is 2.0% of the total mass of octadecyl acrylate, butyl acrylate, and isobornyl methacrylate.

[0011] The following are further optimizations and / or improvements to one of the above-mentioned technical solutions: The above-mentioned raw materials include octadecyl acrylate, butyl acrylate, and isobornyl methacrylate in a mass ratio of 6:2:2. The raw materials also include a pore-forming agent, a crosslinking agent, and an initiator. The amount of pore-forming agent added is 50% of the total mass of octadecyl acrylate, butyl acrylate, and isobornyl methacrylate; the amount of crosslinking agent added is 1.0% of the total mass of octadecyl acrylate, butyl acrylate, and isobornyl methacrylate; and the amount of initiator added is 2.0% of the total mass of octadecyl acrylate, butyl acrylate, and isobornyl methacrylate.

[0012] The pore-forming agent mentioned above is ethyl acetate.

[0013] The crosslinking agent mentioned above is divinylbenzene.

[0014] The initiator mentioned above is azobisisobutyronitrile.

[0015] The above-mentioned raw materials also include an organic dispersant, the amount of which is 5% to 15% of the total mass of octadecyl acrylate, butyl acrylate and isobornyl methacrylate, and the organic dispersant is one of polyvinylpyrrolidone, sodium dodecylbenzenesulfonate, ammonium polyacrylate and ethylene glycol monobutyl ether.

[0016] The above-mentioned raw materials also include inorganic dispersants, the amount of which is 15% to 25% of the total mass of octadecyl acrylate, butyl acrylate and isobornyl methacrylate, and the inorganic dispersant is one of calcium carbonate, sodium hexametaphosphate and sodium silicate.

[0017] The above-mentioned oil-based drilling fluid temperature-controlled expansion plugging agent is obtained by the following method: S1, after adding organic and inorganic dispersants to water and stirring to dissolve them, a mixture is obtained; S2, after mixing and dissolving octadecyl acrylate, butyl acrylate, isobornyl methacrylate, pore-forming agent, crosslinking agent and initiator, a mixture is obtained; S3, after adding the mixture to the feedstock and heating and reacting, the product is obtained. After filtering, soaking, washing and drying, the product is obtained as a temperature-controlled expansion plugging agent for oil-based drilling fluid.

[0018] In step S1 above, the total mass concentration of organic and inorganic dispersants in the mixture is 2.5% to 3.5%, and the stirring and dissolving time is 10 min to 15 min.

[0019] In step S2 above, the mixing and dissolving time is 5 to 10 minutes.

[0020] In step S3 above, the temperature is heated to 75°C to 80°C, and the reaction time is 6.0h to 6.5h.

[0021] In step S3 above, anhydrous ethanol is used for soaking, and drying is carried out under vacuum at 60°C to 65°C for 12 to 14 hours.

[0022] The second technical solution of the present invention is achieved through the following measures: a method for preparing a temperature-controlled expansion plugging agent for oil-based drilling fluid, which is carried out according to the following method: S1, after adding organic and inorganic dispersants to water and stirring to dissolve them, a mixture is obtained; S2, after mixing and dissolving octadecyl acrylate, butyl acrylate, isobornyl methacrylate, pore-forming agent, crosslinking agent and initiator, a mixture is obtained; S3, after adding the mixture to the feedstock and heating and reacting, the product is obtained. After filtering, soaking, washing and drying, the product is obtained as a temperature-controlled expansion plugging agent for oil-based drilling fluid.

[0023] Compared with the prior art, the beneficial effects of the present invention are as follows: First, in the oil-based drilling fluid temperature-controlled expansion plugging agent of this invention, isobornyl methacrylate is introduced as a temperature-resistant rigid monomer in the raw material. Its molecular structure contains a rigid alicyclic structure with significant volume steric hindrance effect. This structure can not only effectively increase the glass transition temperature of polymer segments, enabling them to maintain excellent mechanical skeleton strength under high temperature environments, avoiding the softening and degradation problems that are prone to occur in conventional oil-absorbing expansion materials when the temperature exceeds 150°C; at the same time, the introduction of the rigid alicyclic structure restricts excessive molecular motion of the polymer at high temperatures, so that the expanded material can still maintain a high-strength three-dimensional network structure under the high temperature and high pressure conditions of deep and ultra-deep wells, greatly improving the pressure-bearing capacity of the plugging layer; Secondly, in the temperature-controlled expansion plugging agent for oil-based drilling fluids of this invention, butyl acrylate is selected as the structure-adjusting monomer, and its short butyl chain endows the polymer with high flexibility and deformation capability. The addition of this characteristic balances the brittleness brought by the temperature-resistant rigid monomer, enabling the plugging agent particles to undergo moderate plastic deformation rather than brittle fragmentation under the action of high temperature and high pressure downhole. This not only allows it to closely adhere to the irregular crack wall, forming a tight-fitting plugging layer with high bonding strength and good sealing performance, but also provides a good sealing effect. Third, in the temperature-controlled expansion plugging agent for oil-based drilling fluid of the present invention, octadecyl acrylate is introduced as the core oil-absorbing functional monomer. Its long-chain aliphatic alkyl (18-carbon) structure has excellent affinity with the continuous phase of oil-based drilling fluid, fundamentally avoiding the problems of conventional water-based plugging materials being difficult to wet and disperse in the oil phase and causing demulsification. More importantly, the specific ratio of the three monomers (octadecyl acrylate, butyl acrylate, and isobornyl methacrylate) synergistically enables the temperature-controlled expansion plugging agent for oil-based drilling fluid of the present invention to have temperature-controlled expansion characteristics. During the preparation and pumping stages at room temperature, the material structure is stable and the swelling rate is low, ensuring good pumping rheology. When it enters the high-temperature lost circulation zone at the bottom of the well, the heat triggers the intensified movement of the material chain segments, the oil-absorbing expansion function is efficiently activated, and the material rapidly swells and deforms and adaptively squeezes into multi-scale fractures. Fourth, in this invention, based on the introduction of octadecyl acrylate, butyl acrylate, and isobornyl methacrylate, divinylbenzene is selected as a crosslinking agent to further enhance the high-temperature skeleton stability and pressure-bearing sealing capability. Divinylbenzene contains a rigid benzene ring structure, and its crosslinking agent not only has extremely high thermal stability but also significantly enhances the bonding force between polymer molecular chains. In the high-temperature environment of deep and ultra-deep wells, this rigid three-dimensional crosslinking network works synergistically with the rigid alicyclic structure of isobornyl methacrylate to effectively suppress the violent thermal motion of polymer chain segments at high temperatures. This allows the plugging agent to maintain excellent mechanical strength after absorbing oil and expanding, without losing its pressure-bearing capacity due to high-temperature softening or deformation, thereby significantly improving the long-term pressure-bearing sealing performance of the sealing layer under complex geostress.

[0024] Therefore, the temperature-controlled expansion plugging agent for oil-based drilling fluid of the present invention is synthesized by suspension polymerization of octadecyl acrylate, butyl acrylate, isobornyl methacrylate, pore-forming agent, crosslinking agent and initiator. It not only has excellent high-temperature stability, can stably withstand high temperature of 180℃, and meet the temperature requirements for deep well leakage plugging, but also has outstanding pressure-bearing plugging ability. Under a pressure difference of 7MPa, it can quickly form a high-strength gel plugging layer in the leakage channel, effectively sealing fractures and pores, and significantly restoring the formation's pressure-bearing capacity. At the same time, the raw materials are readily available, the operation is safe, the process is simple, and it is suitable for industrial production. Attached Figure Description

[0025] Figure 1 The graph shows the effect of different amounts of crosslinking agents on the oil absorption rate of the temperature-controlled expansion plugging agent for oil-based drilling fluids of the present invention.

[0026] Figure 2 The graph shows the effect of different amounts of pore-forming agents on the oil absorption rate of the temperature-controlled expansion plugging agent for oil-based drilling fluid of the present invention.

[0027] Figure 3 The infrared spectrum is shown for the temperature-controlled expansion plugging agent for oil-based drilling fluid prepared in Example 1 of this invention. Detailed Implementation

[0028] This invention is not limited to the following embodiments, and specific implementation methods can be determined according to the technical solutions and actual conditions of this invention. Unless otherwise specified, all chemical reagents and chemicals mentioned in this invention are well-known and commonly used chemical reagents and chemicals in the prior art; unless otherwise specified, all percentages in this invention are mass percentages; unless otherwise specified, all solutions in this invention are aqueous solutions with water as the solvent, for example, hydrochloric acid solution is an aqueous solution of hydrochloric acid; room temperature in this invention generally refers to a temperature between 15°C and 25°C, generally defined as 25°C.

[0029] The present invention will be further described below with reference to embodiments: Example 1: This oil-based drilling fluid temperature-controlled expansion plugging agent is obtained according to the following method: S1. Disperse 5g of organic dispersant (polyvinylpyrrolidone) and 10g of inorganic dispersant (calcium carbonate) in 500mL of deionized water, and stir magnetically for 10min to dissolve and obtain a mixture. S2, 30g of octadecyl acrylate, 10g of butyl acrylate, 10g of isobornyl methacrylate, 25g of pore-forming agent (ethyl acetate, accounting for 50% of the total mass of octadecyl acrylate, butyl acrylate and isobornyl methacrylate), 0.5g of crosslinking agent (divinylbenzene, accounting for 1.0% of the total mass of octadecyl acrylate, butyl acrylate and isobornyl methacrylate), and 1.0g of initiator (azobisisobutyronitrile, accounting for 2.0% of the total mass of octadecyl acrylate, butyl acrylate and isobornyl methacrylate) were magnetically stirred and dissolved for 5 minutes to obtain a mixture. S3. The mixture was added dropwise to a four-necked flask containing the mixture using a constant pressure dropping funnel. The four-necked flask was placed in a 76°C water bath for 6 hours. After the reaction was completed, the product was obtained. The product was filtered through a stainless steel sieve to collect the resin particles. While still hot, the resin particles were soaked in anhydrous ethanol, then washed several times with 60°C hot water, and then vacuum dried at 60°C for 12 hours to obtain a temperature-controlled expansion plugging agent for oil-based drilling fluid, labeled as W1.

[0030] Example 2: This oil-based drilling fluid temperature-controlled expansion plugging agent is obtained according to the following method: S1. Disperse 5g of organic dispersant (polyvinylpyrrolidone) and 10g of inorganic dispersant (calcium carbonate) in 500mL of deionized water, and stir magnetically for 10min to dissolve and obtain a mixture. S2, 25g of octadecyl acrylate, 15g of butyl acrylate, 10g of isobornyl methacrylate, 37g of pore-forming agent (ethyl acetate, accounting for 74% of the total mass of octadecyl acrylate, butyl acrylate and isobornyl methacrylate), 0.75g of crosslinking agent (divinylbenzene, accounting for 1.5% of the total mass of octadecyl acrylate, butyl acrylate and isobornyl methacrylate), and 1.0g of initiator (azobisisobutyronitrile, accounting for 2.0% of the total mass of octadecyl acrylate, butyl acrylate and isobornyl methacrylate) were magnetically stirred and dissolved for 5 minutes to obtain a mixture. S3. The mixture was added dropwise to a four-necked flask containing the mixture using a constant pressure dropping funnel. The four-necked flask was placed in a 76°C water bath for 6 hours. After the reaction was completed, the product was obtained. The product was filtered through a stainless steel sieve to collect the resin particles. While still hot, the resin particles were soaked in anhydrous ethanol, then washed several times with 60°C hot water, and then vacuum dried at 60°C for 12 hours to obtain a temperature-controlled expansion plugging agent for oil-based drilling fluid, labeled as W2.

[0031] Example 3: This oil-based drilling fluid temperature-controlled expansion plugging agent is obtained according to the following method: S1. Disperse 5g of organic dispersant (polyvinylpyrrolidone) and 10g of inorganic dispersant (calcium carbonate) in 500mL of deionized water, and stir magnetically for 10min to dissolve and obtain a mixture. S2, 35g of octadecyl acrylate, 5g of butyl acrylate, 5g of isobornyl methacrylate, 22.5g of pore-forming agent (ethyl acetate, accounting for 50% of the total mass of octadecyl acrylate, butyl acrylate and isobornyl methacrylate), 0.9g of crosslinking agent (divinylbenzene, accounting for 2.0% of the total mass of octadecyl acrylate, butyl acrylate and isobornyl methacrylate), and 0.9g of initiator (azobisisobutyronitrile, accounting for 2.0% of the total mass of octadecyl acrylate, butyl acrylate and isobornyl methacrylate) were magnetically stirred and dissolved for 5 minutes to obtain a mixture. S3, the mixture was added dropwise to a four-necked flask containing the mixture using a constant pressure dropping funnel. The four-necked flask was placed in a 76°C water bath for 6 hours. After the reaction was completed, the product was obtained. The product was filtered through a stainless steel sieve to collect the resin particles. While still hot, the resin particles were soaked in anhydrous ethanol, then washed several times with 60°C hot water, and then vacuum dried at 60°C for 12 hours to obtain a temperature-controlled expansion plugging agent for oil-based drilling fluid, labeled as W3.

[0032] Comparative Example 1: The difference from Example 1 is that the raw material isobornyl methacrylate and crosslinking agent (divinylbenzene) are not added, while the other steps remain unchanged. The resulting plugging agent is labeled as D1.

[0033] Comparative Example 2: The difference from Example 1 is that no raw material crosslinking agent (divinylbenzene) is added, and "10g of isobornyl methacrylate in step S2" is replaced with "10g of methyl methacrylate in step S2". All other steps remain unchanged. The resulting sealing agent is labeled as D2.

[0034] Experimental Example 1: Investigating the effect of different proportions of monomers (octadecyl acrylate, butyl acrylate, and isobornyl methacrylate) on the oil absorption performance of a temperature-controlled expansion plugging agent for oil-based drilling fluids.

[0035] Experimental sample: Sample Example 1: This oil-based drilling fluid temperature-controlled expansion plugging agent was obtained according to the following method: S1. Disperse 5g of organic dispersant (polyvinylpyrrolidone) and 10g of inorganic dispersant (calcium carbonate) in 500mL of deionized water, and stir magnetically for 10min to dissolve and obtain a mixture. S2, 20g octadecyl acrylate, 15g butyl acrylate, 15g isobornyl methacrylate, 50g ethyl acetate, 0.5g divinylbenzene (accounting for 1.0% of the total mass of octadecyl acrylate, butyl acrylate and isobornyl methacrylate), and 1.0g azobisisobutyronitrile (accounting for 2.0% of the total mass of octadecyl acrylate, butyl acrylate and isobornyl methacrylate) were magnetically stirred and dissolved for 5 minutes to obtain a mixture. S3. The mixture was added dropwise to a four-necked flask containing the mixture using a constant pressure dropping funnel. The four-necked flask was placed in a 76°C water bath for 6 hours. After the reaction was completed, the product was obtained. The product was filtered through a stainless steel sieve to collect the resin particles. While still hot, the resin particles were soaked in anhydrous ethanol, then washed several times with 60°C hot water, and then vacuum dried at 60°C for 12 hours to obtain a temperature-controlled expansion plugging agent for oil-based drilling fluid, labeled as DL-1.

[0036] Sample Example 2: The difference from Sample Example 1 is that in step S2, "20g of octadecyl acrylate, 15g of butyl acrylate, and 15g of isoborneol methacrylate" is replaced with "25g of octadecyl acrylate, 15g of butyl acrylate, and 10g of isoborneol methacrylate". The other steps remain unchanged, and the resulting oil-based drilling fluid temperature-controlled expansion plugging agent is labeled as DL-2.

[0037] Sample Example 3: The difference from Sample Example 1 is that in step S2, "20g of octadecyl acrylate, 15g of butyl acrylate, and 15g of isoborneol methacrylate" is replaced with "30g of octadecyl acrylate, 10g of butyl acrylate, and 10g of isoborneol methacrylate". The other steps remain unchanged, and the resulting oil-based drilling fluid temperature-controlled expansion plugging agent is labeled as DL-3.

[0038] Sample Example 4: The difference from Sample Example 1 is that in step S2, "20g of octadecyl acrylate, 15g of butyl acrylate, and 15g of isoborneol methacrylate" is replaced with "35g of octadecyl acrylate, 5g of butyl acrylate, and 5g of isoborneol methacrylate". The other steps remain unchanged, and the resulting oil-based drilling fluid temperature-controlled expansion plugging agent is labeled as DL-4.

[0039] Sample Example 5: The difference from Sample Example 1 is that in step S2, "20g of octadecyl acrylate, 15g of butyl acrylate, and 15g of isoborneol methacrylate" is replaced with "40g of octadecyl acrylate, 5g of butyl acrylate, and 5g of isoborneol methacrylate". The other steps remain unchanged, and a temperature-controlled expansion plugging agent for oil-based drilling fluid is obtained, labeled as DL-5.

[0040] Experimental Method: The oil absorption rate of DL-1 to DL-5 prepared from Samples 1 to 5 was tested. The oil absorption rate test method is as follows: DL-1 to DL-5 with a mass of 20g were placed in non-woven bags and sealed. The sealed non-woven bags were then placed in pre-prepared No. 3 white oil. At certain intervals, the non-woven bags were removed from the No. 3 white oil, and the residual oil droplets on the surface of the non-woven bags were thoroughly wiped off with filter paper. Then, the mass M of DL-1 to DL-5 after oil absorption was weighed and recorded. The oil absorption amount of DL-1 to DL-5 was tested and calculated according to formula (1). Formula (1) is S=(M-20) / 20, where S is the oil absorption rate, g / g; M is the mass after oil absorption, g.

[0041] Experimental results: The oil absorption rates of DL-1 to DL-5 prepared by Sample Examples 1 to 5 of the present invention are shown in Table 1.

[0042] Table 1. Effect of different monomer addition amounts on oil absorption performance .

[0043] As shown in Table 1, DL-3 prepared in Sample Example 3 of this invention exhibits the highest oil absorption rate, reaching 13.79 g / g at 160℃ for 20 h, with a volume expansion of approximately 2.3 times. This indicates that the optimal oil absorption performance is achieved when the mass ratio of octadecyl acrylate (oil-absorbing monomer), butyl acrylate (structural monomer), and isobornyl methacrylate (thermosensitive monomer) is 6:2:2. This is because changing the monomer ratio affects the oil absorption rate of the product. The amount of each monomer added significantly impacts the oil absorption performance and particle state of the product. When the monomer ratio is inappropriate, the functional groups in the monomers fail to fully participate in the reaction, and the residual monomer substances can affect the structure of the product.

[0044] Experimental Example 2: Investigating the effect of different amounts of crosslinking agents on the oil absorption performance of temperature-controlled expansion plugging agents for oil-based drilling fluids.

[0045] Experimental sample: Sample Example 6: This oil-based drilling fluid temperature-controlled expansion plugging agent was obtained according to the following method: S1. Disperse 5g of organic dispersant (polyvinylpyrrolidone) and 10g of inorganic dispersant (calcium carbonate) in 500mL of deionized water, and stir magnetically for 10min to dissolve and obtain a mixture. S2, 30g octadecyl acrylate, 10g butyl acrylate, 10g isobornyl methacrylate, 50g ethyl acetate, 0.075g divinylbenzene (0.15% of the total mass of octadecyl acrylate, butyl acrylate and isobornyl methacrylate), and 1.0g azobisisobutyronitrile (2.0% of the total mass of octadecyl acrylate, butyl acrylate and isobornyl methacrylate) were magnetically stirred and dissolved for 5 minutes to obtain a mixture. S3. The mixture was added dropwise to a four-necked flask containing the mixture using a constant pressure dropping funnel. The four-necked flask was placed in a 76°C water bath for 6 hours. After the reaction was completed, the product was obtained. The product was filtered through a stainless steel sieve to collect the resin particles. While still hot, the resin particles were soaked in anhydrous ethanol, then washed several times with 60°C hot water, and then vacuum dried at 60°C for 12 hours to obtain a temperature-controlled expansion plugging agent for oil-based drilling fluid, labeled as DL-6.

[0046] Sample Example 7: The difference from Sample Example 6 is that in step S2, "0.075g divinylbenzene (0.15% of the total mass of octadecyl acrylate, butyl acrylate and isobornyl methacrylate)" is replaced with "0.125g divinylbenzene (0.25% of the total mass of octadecyl acrylate, butyl acrylate and isobornyl methacrylate)". The rest of the steps remain unchanged. The resulting oil-based drilling fluid is used as a temperature-controlled expansion plugging agent and is labeled as DL-7.

[0047] Sample Example 8: The difference from Sample Example 6 is that in step S2, "0.075g divinylbenzene (0.15% of the total mass of octadecyl acrylate, butyl acrylate and isobornyl methacrylate)" is replaced with "0.25g divinylbenzene (0.5% of the total mass of octadecyl acrylate, butyl acrylate and isobornyl methacrylate)". The rest of the steps remain unchanged. The resulting oil-based drilling fluid is used as a temperature-controlled expansion plugging agent and is labeled as DL-8.

[0048] Sample Example 9: The difference from Sample Example 6 is that in step S2, "0.075g divinylbenzene (0.15% of the total mass of octadecyl acrylate, butyl acrylate and isobornyl methacrylate)" is replaced with "0.5g divinylbenzene (1.0% of the total mass of octadecyl acrylate, butyl acrylate and isobornyl methacrylate)". The rest of the steps remain unchanged. The resulting oil-based drilling fluid is used as a temperature-controlled expansion plugging agent and is labeled as DL-9.

[0049] Sample Example 10: The difference from Sample Example 6 is that in step S2, "0.075g divinylbenzene (0.15% of the total mass of octadecyl acrylate, butyl acrylate and isobornyl methacrylate)" is replaced with "0.75g divinylbenzene (1.5% of the total mass of octadecyl acrylate, butyl acrylate and isobornyl methacrylate)". The rest of the steps remain unchanged. The resulting oil-based drilling fluid is used as a temperature-controlled expansion plugging agent and is labeled as DL-10.

[0050] Sample Example 11: The difference from Sample Example 6 is that in step S2, "0.075g divinylbenzene (0.15% of the total mass of octadecyl acrylate, butyl acrylate and isobornyl methacrylate)" is replaced with "1.0g divinylbenzene (2.0% of the total mass of octadecyl acrylate, butyl acrylate and isobornyl methacrylate)". The rest of the steps remain unchanged. The resulting oil-based drilling fluid is used as a temperature-controlled expansion plugging agent and is labeled as DL-11.

[0051] Sample Example 12: The difference from Sample Example 6 is that in step S2, "0.075g divinylbenzene (0.15% of the total mass of octadecyl acrylate, butyl acrylate and isobornyl methacrylate)" is replaced with "1.25g divinylbenzene (2.5% of the total mass of octadecyl acrylate, butyl acrylate and isobornyl methacrylate)". The rest of the steps remain unchanged. The resulting oil-based drilling fluid is used as a temperature-controlled expansion plugging agent and is labeled as DL-12.

[0052] Experimental method: The oil absorption rate of DL-6 to DL-12 prepared from Samples 6 to 12 was tested. The oil absorption rate test method is the same as in Experimental Example 1.

[0053] Experimental results: The oil absorption rates of DL-6 to DL-12 prepared from Samples 6 to 12 of this invention are shown in Table 2. Figure 1 As shown.

[0054] Table 2 Effect of different crosslinking agent addition amounts on oil absorption performance .

[0055] From Table 2 and Figure 1 It can be seen that DL-9 prepared in Sample Example 9 of this invention has the highest oil absorption rate, with an oil absorption rate of 13.80 g / g at 160℃ / 20h. Therefore, the optimal oil absorption performance is achieved when the amount of crosslinking agent (divinylbenzene) added is 1.0% of the total mass of octadecyl acrylate, butyl acrylate, and isobornyl methacrylate. This is because changing the amount of crosslinking agent added affects the oil absorption rate of the product. When the amount of crosslinking agent added is small, the crosslinking density of the formed product will decrease accordingly, increasing the dispersion of monomer particles and reducing the oil absorption rate of the product. When the amount of crosslinking agent added is large, the crosslinking density of the polymer will increase significantly, reducing the internal network space of the polymer and thus reducing the oil absorption rate of the product, which is consistent with the Flory theory. Only when an appropriate amount of crosslinking agent is added can the internal space of the reaction product reach its optimal state, at which point the obtained product has the best oil absorption capacity.

[0056] Experimental Example 3: Investigating the effect of different amounts of pore-forming agents on the oil absorption performance of temperature-controlled expansion plugging agents for oil-based drilling fluids.

[0057] Experimental sample: Sample Example 13: This oil-based drilling fluid temperature-controlled expansion plugging agent was obtained according to the following method: S1, Disperse 2.5g of organic dispersant (polyvinylpyrrolidone) and 5g of inorganic dispersant (calcium carbonate) in 250mL of deionized water, and dissolve by magnetic stirring for 10min to obtain a mixture; S2, 15g of octadecyl acrylate, 5g of butyl acrylate, 5g of isobornyl methacrylate, 3.13g of ethyl acetate (accounting for 12.52% of the total mass of octadecyl acrylate, butyl acrylate and isobornyl methacrylate), 0.25g of divinylbenzene (accounting for 1.0% of the total mass of octadecyl acrylate, butyl acrylate and isobornyl methacrylate) and 0.5g of azobisisobutyronitrile were magnetically stirred and dissolved for 5 minutes to obtain a mixture. S3. The mixture was added dropwise to a four-necked flask containing the mixture using a constant pressure dropping funnel. The four-necked flask was placed in a 76°C water bath for 6 hours. After the reaction was completed, the product was obtained. The product was filtered through a stainless steel sieve to collect the resin particles. While still hot, the resin particles were soaked in anhydrous ethanol, then washed several times with 60°C hot water, and then vacuum dried at 60°C for 12 hours to obtain a temperature-controlled expansion plugging agent for oil-based drilling fluid, labeled as DL-13.

[0058] Sample Example 14: The difference from Sample Example 13 is that in step S2, “3.13g ethyl acetate (accounting for 12.52% of the total mass of octadecyl acrylate, butyl acrylate and isobornyl methacrylate)” is replaced with “6.25g ethyl acetate (accounting for 25% of the total mass of octadecyl acrylate, butyl acrylate and isobornyl methacrylate)”, while the other steps remain unchanged, to obtain a temperature-controlled expansion plugging agent for oil-based drilling fluid, labeled as DL-14.

[0059] Sample Example 15: The difference from Sample Example 13 is that in step S2, “3.13g ethyl acetate (accounting for 12.52% of the total mass of octadecyl acrylate, butyl acrylate and isobornyl methacrylate)” is replaced with “12.5g ethyl acetate (accounting for 50% of the total mass of octadecyl acrylate, butyl acrylate and isobornyl methacrylate)”, while the other steps remain unchanged, to obtain a temperature-controlled expansion plugging agent for oil-based drilling fluid, labeled as DL-15.

[0060] Sample Example 16: The difference from Sample Example 13 is that in step S2, “3.13g ethyl acetate (accounting for 12.52% of the total mass of octadecyl acrylate, butyl acrylate and isobornyl methacrylate)” is replaced with “18.5g ethyl acetate (accounting for 74% of the total mass of octadecyl acrylate, butyl acrylate and isobornyl methacrylate)”, while the other steps remain unchanged, to obtain a temperature-controlled expansion plugging agent for oil-based drilling fluid, labeled as DL-16.

[0061] Sample Example 17: The difference from Sample Example 13 is that in step S2, “3.13g ethyl acetate (accounting for 12.52% of the total mass of octadecyl acrylate, butyl acrylate and isobornyl methacrylate)” is replaced with “25g ethyl acetate (accounting for 100% of the total mass of octadecyl acrylate, butyl acrylate and isobornyl methacrylate)”, while the other steps remain unchanged, to obtain a temperature-controlled expansion plugging agent for oil-based drilling fluid, labeled as DL-17.

[0062] Experimental method: The oil absorption rate of DL-13 to DL-17 prepared from Samples 13 to 17 was tested. The oil absorption rate test method is the same as in Experiment 1.

[0063] Experimental results: The oil absorption rates of DL-6 to DL-12 prepared from Samples 13 to 17 of this invention are shown in Table 3. Figure 2 As shown.

[0064] Table 3 Effect of different pore-forming agent dosages on oil absorption performance .

[0065] From Table 3 and Figure 2 It can be seen that the pore-forming agent can increase the oil absorption rate by forming physical oil absorption channels inside. As the amount of pore-forming agent added continues to increase, the oil absorption rate of the sample at 160℃ / 5h also increases rapidly. The DL-15 prepared in Sample Example 15 of the present invention, when the amount of pore-forming agent added is 12.5g (accounting for 50% of the total mass of octadecyl acrylate, butyl acrylate and isobornyl methacrylate), has a moderate oil absorption rate of 4.76g / g at 160℃ / 5h, which can prevent it from completely expanding before reaching the bottom of the well.

[0066] Based on the single-factor analysis experiments of Examples 1 to 3 above, the optimal synthesis ratio of raw materials for the temperature-controlled expansion plugging agent for oil-based drilling fluid of the present invention is as follows: the preferred mass ratio of raw materials octadecyl acrylate, butyl acrylate, and isobornyl methacrylate is 6:2:2; the preferred amount of crosslinking agent (divinylbenzene) is 1.0% of the total mass of octadecyl acrylate, butyl acrylate, and isobornyl methacrylate; and the preferred amount of pore-forming agent is 50% of the total mass of octadecyl acrylate, butyl acrylate, and isobornyl methacrylate.

[0067] Experimental Example 4: Structural characterization of the temperature-controlled expansion plugging agent for oil-based drilling fluid of the present invention.

[0068] Experimental method: Infrared spectroscopy was performed on W1 prepared in Example 1 of this invention.

[0069] Experimental results: The infrared spectrum of W1 prepared in Example 1 of this invention is as follows. Figure 3 As shown, from Figure 3 It can be seen that the fingerprint area is 796cm. -1 Location and characteristic area 1604cm -1 The vibrations are attributed to the out-of-plane deformation vibrations of the CH bonds in the benzene ring and the bending vibrations of the C=C skeleton in the crosslinking agent (divinylbenzene); 1052 cm⁻¹ -1 The stretching vibration of CO in the thermoresistant monomer (isobornyl methacrylate) is also attributed to this vibration. In addition, the 1165 cm⁻¹ is influenced by the oil-absorbing monomer (octadecyl acrylate) and the structural monomer (butyl acrylate). -1 and 1212cm -1 Bending and stretching vibrations of COC at 1388 cm -1 and 1458cm -1 Bending vibration of CH3 at 2877 cm -1 and 2956cm -1 Asymmetric stretching vibration of the main chain -CH2 and 1730 cm -1 The stretching vibration intensity at C=O was significantly enhanced, indicating that the temperature-controlled expansion plugging agent for oil-based drilling fluids of this invention was successfully synthesized.

[0070] Experimental Example 5: Investigating the expansion performance of the temperature-controlled expansion plugging agent for oil-based drilling fluids of the present invention.

[0071] Experimental method: The expansion properties of W1 to W3 prepared in Examples 1 to 3 of the present invention were tested, that is, the expansion rate of W1 was tested at different temperatures (room temperature to 220°C), and D1 prepared in Comparative Example 1 and D2 prepared in Comparative Example 2 were used as controls.

[0072] Experimental results: The expansion rates of W1 to W3 prepared in Examples 1 to 3 of the present invention are shown in Tables 4-1 to 4-3, the expansion rate of D1 prepared in Comparative Example 1 is shown in Table 5, and the expansion rate of D2 prepared in Comparative Example 2 is shown in Table 6.

[0073] Table 4-1 Expansion rate of W1 prepared in Example 1 (20h) .

[0074] Table 4-2 Expansion rate of W2 prepared in Example 1 (20h) .

[0075] Table 4-3 Expansion rate of W3 prepared in Example 1 (20h) .

[0076] Table 5. Expansion rate of D1 prepared in Comparative Example 1 (20h) .

[0077] Table 6. Expansion rate of D2 prepared in Comparative Example 2 (20h) .

[0078] As shown in Tables 4 to 6, the expansion rates of W1 to W3 prepared in Examples 1 to 3, D1 prepared in Comparative Example 1, and D2 prepared in Comparative Example 2 differed at different temperatures, but all reached their highest expansion rates after 10 hours. Compared to W1 to W3 prepared in Examples 1 to 3, the overall expansion rates of D1 prepared in Comparative Example 1 and D2 prepared in Comparative Example 2 were lower after 10 hours. This indicates that W1 to W3 prepared in Examples 1 to 3 of the present invention have better expansion performance.

[0079] Experimental Example 6: Investigating the sealing performance of the temperature-controlled expansion plugging agent for oil-based drilling fluids of the present invention.

[0080] Experimental method: The pressure-bearing sealing capacity of the expansion sealant on a 20-40 mesh sand bed was tested using a high-temperature and high-pressure water loss tester. The experimental slurry was an oil-based slurry (density 1.8 g / cm³). 3 + 5% of W1 to W3 prepared in Examples 1 to 3 of the present invention, or D1 prepared in Comparative Example 1, or D2 prepared in Comparative Example 2.

[0081] The specific experimental steps are as follows: The pressure-bearing sealing capacity of the expansion sealant on a 20-40 mesh sand bed was tested using a high-temperature, high-pressure water loss meter. The experimental slurry was an oil-based slurry (density 1.8 g / cm³). 3 + 5% W1 prepared in Example 1 of the present invention, or D1 prepared in Comparative Example 1, or D2 prepared in Comparative Example 2.

[0082] The specific experimental steps are as follows: (1) Place the drilling fluid cup with the bottom cover facing up and the top cover facing down on the drilling fluid cup support platform. Tighten the bottom cover with a hex wrench and tighten the bottom cover screw valve with a regular wrench (distinguish between the top and bottom covers: the bottom cover has a larger hole and can be fixed in the heating device; the top cover has a smaller hole and can be used to insert a thermometer). (2) Invert the drilling fluid cup, i.e., the bottom cover is facing down and the top cover is facing up, and place it on the drilling fluid cup support platform. Open the top cover of the drilling fluid cup and use a vernier caliper to measure the depth inside the drilling fluid cup (Note: When measuring the depth, do not measure the thickness of the top cover). (3) Using a vernier caliper, pour 20 to 40 mesh sand into the drilling fluid cup to a depth of 6 cm; (4) Using a vernier caliper, pour each experimental slurry into the drilling fluid cup until the liquid level in the cup is 1 cm (320 mL) from the cup opening. (5) Tighten the top cover with a hex wrench and tighten the top cover screw valve with a regular wrench; (6) Finally, check again whether the upper and lower covers are tightened with a hex wrench, and check whether the screw valves of the upper and lower covers are tightened with a regular wrench; (7) Place the drilling fluid cup with the top cover facing up and the bottom cover facing down in the heating device, and use a regular wrench to turn the top cover screw valve clockwise until the drilling fluid cup is fixed in the heating device and cannot be rotated. (8) Check the three-way pressure regulating valve connected to the nitrogen cylinder. Connect the pressure regulating valve with the larger range, i.e. the pressure head, to the upper cover and use the safety pin to insert and fix it. Connect the pressure regulating valve with the smaller range, i.e. the filtrate receiver, to the lower cover and use the safety pin to insert and fix it. (9) First, rotate the large range pressure regulating valve clockwise to adjust the pressure to 0.69 MPa, then turn the top cover screw counterclockwise by 45° < angle < 90° to inject 0.69 MPa pressure into the drilling fluid cup. After 3 seconds, tighten the top cover screw clockwise to seal the pressure inside the cup. (10) Insert the thermometer into the hole of the top cover, set the temperature of the heating device to 150°C, observe the thermometer rise to 150°C and then keep it warm, and control the total heating time to 10h. (11) After heat preservation for 10 hours, first rotate the large-range pressure regulating valve clockwise to adjust the pressure to 1 MPa. Then rotate the small-range pressure regulating valve clockwise to adjust the pressure to 0.69 MPa; (12) Use a regular wrench to turn the top cover screw counterclockwise by 45° < angle < 90° and inject 1MPa pressure into the drilling fluid cup. In order to prevent the water in the filtrate from vaporizing under HTHP conditions and causing inaccurate measurement of filtrate loss, it is necessary to use a regular wrench to turn the bottom cover screw counterclockwise by 45° < angle < 90° and inject 0.69MPa pressure into the filtrate receiver. (13) Time for 15 minutes. If the pressure of the small-range pressure gauge is >0.8MPa within 15 minutes, the filtrate needs to be released so that the value of the small-range pressure gauge returns to 0.69MPa. After 15 minutes, tighten the lower cover screw counterclockwise (do not tighten the upper cover screw) to release the liquid in the filtrate receiver and record the filtrate loss in the measuring cylinder. (14) Next, rotate the large-range pressure gauge clockwise to adjust the pressure to 2MPa, and use a regular wrench to turn the lower cover screw 45° < angle < 90° to inject 0.69MPa pressure into the filtrate receiver; (15) Time for 15 minutes. If the pressure of the small-range pressure gauge is >0.8MPa within 15 minutes, the filtrate needs to be released so that the value of the small-range pressure gauge returns to 0.69MPa. After 15 minutes, tighten the lower cover screw counterclockwise (do not tighten the upper cover screw) to release the liquid in the filtrate receiver and record the filtrate loss in the measuring cylinder. (16) Repeat steps (14) to (15) until the injection pressure of the top cover reaches 6MPa (the maximum pressure of the drilling fluid cup is 7.1MPa), and record the filtration loss after 15 minutes under 6MPa pressure. In order to test the pressure resistance of the expansion plugging layer formed between the sand beds, the liquid loss (leakage) test is performed using experimental slurry.

[0083] Experimental results: The sand bed leakage test results of W1 to W3 prepared in Examples 1 to 3 of the present invention are shown in Tables 7-1 to 7-3, the sand bed leakage test results of D1 prepared in Comparative Example 1 are shown in Table 8, and the sand bed leakage test results of D2 prepared in Comparative Example 2 are shown in Table 9.

[0084] Table 7-1 Results of sand bed leakage test of W1 prepared in Example 1 .

[0085] Table 7-2 Results of sand bed leakage test of W2 prepared in Example 2 .

[0086] Table 7-3 Results of sand bed leakage test of W3 prepared in Example 3 .

[0087] Table 8. Results of sand bed leakage test for D1 prepared in Comparative Example 1 .

[0088] Table 9. Results of sand bed leakage test of D2 prepared in Comparative Example 2 .

[0089] As can be seen from Tables 7 to 9, the leakage of D1 prepared in Comparative Example 1 and D2 prepared in Comparative Example 2 is higher than that of W1 prepared in Example 1 of this invention, indicating that the sealing and filtration effects of D1 prepared in Comparative Example 1 and D2 prepared in Comparative Example 2 are poor. For W1 to W3 prepared in Examples 1 to 3 of this invention, and D1 prepared in Comparative Example 1 and D2 prepared in Comparative Example 2, the filtration loss of each plugging agent gradually decreases with increasing temperature, indicating that the oil absorption and expansion capacity of each plugging agent is positively correlated with the bottom layer sealing effect. Due to insufficient expansion performance, D1 prepared in Comparative Example 1 and D2 prepared in Comparative Example 2 cannot form a dense sealing skeleton in the sand layer pores, and their overall leak prevention and plugging performance is inferior to that of W1 to W3 prepared in Example 1. A comparison of the data of W1 to W3 prepared in the embodiments of the present invention shows that the data of W1 to W3 prepared in embodiments 1 to 3 of the present invention are all better than those of D1 and D2 prepared in the comparative example. Among them, the performance of W1 prepared in embodiment 1 of the present invention is particularly outstanding, indicating that the temperature-controlled expansion plugging agent for oil-based drilling fluid of the present invention can exhibit good plugging performance at a high temperature of 180°C.

[0090] In summary, the temperature-controlled expansion plugging agent for oil-based drilling fluid of this invention is synthesized by suspension polymerization of octadecyl acrylate, butyl acrylate, isobornyl methacrylate, pore-forming agent, crosslinking agent, and initiator. It not only has excellent high-temperature stability, capable of withstanding 180°C to meet the temperature requirements for plugging lost circulation in deep wells, but also has outstanding pressure-bearing plugging capacity. Under a pressure differential of 7 MPa, it can quickly form a high-strength gel plugging layer in the lost circulation channel, effectively sealing fractures and pores and significantly restoring the formation's pressure-bearing capacity. At the same time, the raw materials are readily available, the operation is safe, the process is simple, and it is suitable for industrial production.

[0091] The above technical features constitute the embodiments of the present invention, which have strong adaptability and implementation effect. Unnecessary technical features can be added or removed according to actual needs to meet the needs of different situations.

Claims

1. A temperature-controlled expansion plugging agent for oil-based drilling fluids, characterized in that... The raw materials include octadecyl acrylate, butyl acrylate, and isobornyl methacrylate in a mass ratio of 5 to 7:1 to 3:1 to 2. The raw materials also include a pore-forming agent, a crosslinking agent, and an initiator. The amount of pore-forming agent added is 50% to 74% of the total mass of octadecyl acrylate, butyl acrylate, and isobornyl methacrylate. The amount of crosslinking agent added is 1.0% to 2.0% of the total mass of octadecyl acrylate, butyl acrylate, and isobornyl methacrylate. The amount of initiator added is 2.0% of the total mass of octadecyl acrylate, butyl acrylate, and isobornyl methacrylate.

2. The temperature-controlled expansion plugging agent for oil-based drilling fluid according to claim 1, characterized in that... The raw materials include octadecyl acrylate, butyl acrylate, and isobornyl methacrylate in a mass ratio of 6:2:

2. The raw materials also include a pore-forming agent, a crosslinking agent, and an initiator. The amount of pore-forming agent added is 50% of the total mass of octadecyl acrylate, butyl acrylate, and isobornyl methacrylate; the amount of crosslinking agent added is 1.0% of the total mass of octadecyl acrylate, butyl acrylate, and isobornyl methacrylate; and the amount of initiator added is 2.0% of the total mass of octadecyl acrylate, butyl acrylate, and isobornyl methacrylate.

3. The temperature-controlled expansion plugging agent for oil-based drilling fluid according to claim 1 or 2, characterized in that... The pore-forming agent is ethyl acetate; and / or the crosslinking agent is divinylbenzene; and / or the initiator is azobisisobutyronitrile.

4. The temperature-controlled expansion plugging agent for oil-based drilling fluid according to claim 3, characterized in that... The raw materials also include an organic dispersant, which is added at a rate of 5% to 15% of the total mass of octadecyl acrylate, butyl acrylate and isobornyl methacrylate. The organic dispersant is one of polyvinylpyrrolidone, sodium dodecylbenzenesulfonate, ammonium polyacrylate and ethylene glycol monobutyl ether.

5. The temperature-controlled expansion plugging agent for oil-based drilling fluid according to claim 1, 2, or 4, characterized in that... The raw materials also include an inorganic dispersant, the amount of which is 15% to 25% of the total mass of octadecyl acrylate, butyl acrylate and isobornyl methacrylate, and the inorganic dispersant is one of calcium carbonate, sodium hexametaphosphate and sodium silicate.

6. The temperature-controlled expansion plugging agent for oil-based drilling fluid according to claim 5, characterized in that... Obtained using the following method: S1, after adding organic and inorganic dispersants to water and stirring to dissolve them, a mixture is obtained; S2, after mixing and dissolving octadecyl acrylate, butyl acrylate, isobornyl methacrylate, pore-forming agent, crosslinking agent and initiator, a mixture is obtained; S3, after adding the mixture to the feedstock and heating and reacting, the product is obtained. After filtering, soaking, washing and drying, the product is obtained as a temperature-controlled expansion plugging agent for oil-based drilling fluid.

7. The temperature-controlled expansion plugging agent for oil-based drilling fluid according to claim 6, characterized in that... In step S1, the total mass concentration of organic and inorganic dispersants in the mixture is 2.5% to 3.5%, and the stirring and dissolving time is 10 min to 15 min.

8. The temperature-controlled expansion plugging agent for oil-based drilling fluids according to claim 6 or 7, characterized in that... In step S2, the mixing and dissolving time is 5 to 10 minutes.

9. The temperature-controlled expansion plugging agent for oil-based drilling fluid according to claim 8, characterized in that... In step S3, the temperature is heated to 75°C to 80°C, and the reaction time is 6.0h to 6.5h; or / and, in step S3, anhydrous ethanol is used for soaking, and drying is carried out under vacuum at 60°C to 65°C for 12h to 14h.

10. A method for preparing a temperature-controlled expansion plugging agent for oil-based drilling fluid according to any one of claims 1 to 5, 7 to 9, characterized in that... Perform it as follows: S1, after adding organic and inorganic dispersants to water and stirring to dissolve them, a mixture is obtained; S2, after mixing and dissolving octadecyl acrylate, butyl acrylate, isobornyl methacrylate, pore-forming agent, crosslinking agent and initiator, a mixture is obtained; S3, after adding the mixture to the feedstock and heating and reacting, the product is obtained. After filtering, soaking, washing and drying, the product is obtained as a temperature-controlled expansion plugging agent for oil-based drilling fluid.

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