A leak-proof material for cementing preflush, a preparation method thereof, and a cementing leak-proof preflush system and application thereof

Abstract

The application provides a leakproof material for cementing preflush, a preparation method of the leakproof material, a cementing leakproof preflush system and application of the system. The method comprises the following steps: mixing an ester organic monomer, a benzene organic monomer and 2-alkenyl amide-2-methyl propanesulfonic acid, stirring to obtain a mixed solution at 200-300 rpm, adding water at a speed of 2-10 mL / min, adjusting pH to 6-8 to obtain an emulsion M1; stirring the emulsion M1 at 300-500 rpm, mixing with an initiator solution M2, and performing a first reaction at 70-75 DEG C to obtain an intermediate product M3; mixing the ester organic monomer and the 2-alkenyl amide-2-methyl propanesulfonic acid to obtain a mixture M4; mixing a self-crosslinking monomer, an initiator and water to obtain a mixture M5; adding the mixture M4 and the mixture M5 into the intermediate product M3 at a speed of 2-10 mL / min respectively to perform a second reaction, and obtaining the leakproof material for cementing preflush.

Description

Technical Field

[0001] This invention belongs to the technical field of cementing pre-flush fluid additives. Specifically, it relates to a leak-proof material for cementing pre-flush fluid, its preparation method, and a cementing leak-proof pre-flush fluid system and its application. Background Technology

[0002] With advancements in oil and gas exploration and development technologies, unconventional resources such as tight oil and gas and shale gas are becoming viable alternatives to traditional energy sources. In recent years, the issue of leakage due to micro- and nano-fractures in deep mudstone and shale oil and gas formations has received increasing attention. Particularly in drilling fluids, various leak-proof materials targeting micro- and nano-fractures have been developed, primarily based on nano-rigid materials such as micro- and nano-calcium carbonate and nano-zinc oxide whiskers. For example, CN109762541B discloses a micro- and nano-composite leak-proof agent for drilling fluids and its preparation method, containing nano-calcium carbonate, nano-zinc oxide whiskers, nano-emulsified paraffin wax, flocculants, and lubricants. The solid particles of a specific size keep the fractures open at the fracture sites, while small-sized solid particles and deformed particles construct a spatial structure at the fracture sites, forming an isolation layer with extremely low permeability. This effectively isolates the wellbore from the formation, preventing drilling fluid leakage into the formation.

[0003] Research on drilling fluid leak-proof materials can provide a reference for related research in the cementing field. However, since the density of cement slurry is often greater than that of drilling fluid, the requirements for formation pressure resistance are higher. Cementing and plugging materials have made some progress in recent years. For example, CN105062440B discloses a plugging and leak-proof material that uses a compound of fibers, polymer microspheres, polymer powder, and blast furnace slag. The polymer microspheres and fibers are intertwined, and the polymer powder bonds the polymer microspheres, fibers, and blast furnace slag, thereby improving the material's pressure resistance. However, the above materials lack strong adaptability to different lost-flow formations or fractures of different apertures. Regarding adaptive leak-proof materials, CN115029926A provides the composition and preparation method of a fiber-grafted expandable resin plugging material and its application in cementing and leak-proofing. This material is obtained through the grafting copolymerization reaction of different polymers and can be deformably extruded into the pores formed by the bridging material, effectively sealing fractures of 1–5 mm under temperature conditions of 20–120℃. This patent improves the adaptability of leak-proof and plugging materials to cracks of different opening sizes through a specific structural design. However, since its working method requires "squeezing" into the formation, its adaptability and efficiency still need to be improved. Furthermore, the impact of the above materials on the performance of the wellbore working fluid has not been analyzed and evaluated.

[0004] Currently, how to achieve efficient and adaptive cementing leakage prevention, ensure the pressure-bearing capacity of the leakage prevention layer, and ensure that the leakage prevention and plugging materials have no significant impact on the performance of the cementing fluid remains a key technical problem that urgently needs to be solved. Summary of the Invention

[0005] To address the problems in the prior art, the present invention aims to provide a pre-cementing fluid leak-proof material, its preparation method, a pre-cementing fluid leak-proof system, and its application. The pre-cementing fluid leak-proof system of the present invention exhibits stable performance and good adaptability to fractures of varying opening sizes and different types of voids.

[0006] To achieve the above objectives, according to a first aspect of the present invention, a method for preparing a leak-proof material for cementing pre-flush fluid is provided, comprising:

[0007] S1, mix 2-3 parts by weight of ester organic monomers, 1.5-2.5 parts by weight of benzene organic monomers, and 2-2.5 parts by weight of 2-acrylamido-2-methylpropanesulfonic acid, and stir at 200-300 rpm to obtain a mixture. Add water to the mixture at a rate of 2-10 mL / min to adjust the pH to 6-8 to obtain emulsion M1. Stir emulsion M1 at 300-500 rpm, and then mix it with initiator solution M2. Perform a first reaction at 70-75°C for 30-40 min to obtain intermediate product M3.

[0008] S2, mix 20-25 parts by weight of ester organic monomers and 0.25-0.5 parts by weight of 2-acrylamido-2-methylpropanesulfonic acid to obtain mixture M4; mix 2-5 parts by weight of self-crosslinking monomers, initiator and water to obtain mixture M5; add mixture M4 and mixture M5 to intermediate product M3 at a feeding rate of 2-10 mL / min respectively to carry out a second reaction to obtain the leak-proof material for cementing pre-fill fluid.

[0009] In stage S1 above, this invention uses 2-acrylamido-2-methylpropanesulfonic acid as an emulsifier and employs a reverse emulsification method to achieve the formation of a nanoscale emulsion in water from an organic monomer mixture. This ensures the success rate of preparing the nanoscale microsphere core, improves the dispersion performance of the polymer microspheres, and simplifies the reaction process and materials. The polymerization activity of 2-acrylamido-2-methylpropanesulfonic acid, along with its initiation properties, promotes emulsion polymerization, ensuring the formation of solid-phase polymer microspheres with nanoscale dimensions. The first reaction temperature in S1 effectively balances emulsion stability and reaction rate; temperatures exceeding this range may negatively impact emulsion stability.

[0010] In the S2 stage, adding different materials separately and slowly helps to ensure the success rate of self-crosslinking monomer polymers, while ensuring that the distribution of self-crosslinking monomers on the surface of microspheres is more random, which helps to improve the crosslinking effect of the final microspheres. The specific monomer mixing sequence in this invention can improve the success rate of preparing nanoscale self-crosslinking polymer microspheres.

[0011] The rate at which water is added to the mixture is also controlled within the aforementioned range. This helps to ensure that the emulsion droplets in the emulsion polymerization have a low particle size, thereby ensuring that the polymer microspheres reach the micro-nano scale.

[0012] This preparation method uses a soap-free emulsion polymerization method, which has a simple raw material composition and relatively low process requirements, enabling industrial production and large-scale application.

[0013] In some preferred embodiments of the present invention, the ester organic monomers include methyl methacrylate and / or methyl acrylate; and / or,

[0014] The benzene-based organic monomers include divinylbenzene and / or styrene; and / or,

[0015] The initiator comprises persulfate and / or azobisisobutylamidine hydrochloride, preferably, the initiator comprises ammonium persulfate and / or potassium persulfate; and / or,

[0016] The self-crosslinking monomers include N-hydroxymethylacrylamide and / or diacetone acrylamide.

[0017] Preferential selection of the above-mentioned ester-based organic monomers and benzene-based organic monomers is beneficial to improving the temperature and salt resistance of polymer microspheres.

[0018] In some preferred embodiments of the present invention, sodium bicarbonate is used to adjust the pH.

[0019] In some preferred embodiments of the present invention, the initiator solution M2 comprises 0.05 to 0.07 parts by mass of initiator and 4 to 8 parts by mass of water.

[0020] In some preferred embodiments of the present invention, 40-60 parts by weight of water are added to the mixture to obtain the emulsion M1.

[0021] In some preferred embodiments of the present invention, the mixture M5 comprises 0.2 to 0.25 parts by weight of an initiator and 15 to 30 parts by weight of water.

[0022] In some preferred embodiments of the present invention, the temperature of the second reaction is 80-85°C, and the time is 2-3 hours. The preferred second reaction temperature is more conducive to obtaining micro / nano-scale polymer microspheres.

[0023] In some preferred embodiments of the present invention, the emulsion M1 is stirred at a stirring speed of 400-500 rpm and then mixed with the initiator solution M2.

[0024] In some preferred embodiments of the present invention, in S1, the ester organic monomer is 2-2.5 parts by weight, the benzene organic monomer is 1.5-2 parts by weight, and the 2-acrylamido-2-methylpropanesulfonic acid is 2-2.3 parts by weight; and / or,

[0025] In S2, the ester organic monomer is 20-22 parts by mass, and the 2-acrylamido-2-methylpropanesulfonic acid is 0.25-0.3 parts by mass.

[0026] According to another aspect of the present invention, a leak-proof material for cementing pre-fill fluid prepared according to the above-described preparation method is also provided.

[0027] The leak-proof material for cementing pre-flush fluid of this invention, through structural design, introduces self-crosslinking monomers on the surface of microspheres, enabling it to adapt to fractures of different apertures and improve leak-proof pressure resistance, while having no significant impact on the performance of the pre-flush fluid. Compared to rigid nanomaterials, micro- and nano-scale microspheres are elastic and can penetrate into different types of fractures, exhibiting stronger adaptability. A large number of self-crosslinking monomers are uniformly distributed on the surface of the microspheres. After entering the well, upon reaching a specific depth, crosslinking can occur between the polymer microspheres at specific concentrations and temperatures. Due to the low probability and short contact time between microspheres in the pre-flush fluid, the crosslinking behavior is not significant. When a leak occurs, the pre-flush fluid containing microspheres leaks into voids and fractures, and the microspheres accumulate in large quantities in these voids and fractures, forming a structure with high pressure resistance. Therefore, the self-crosslinking microsphere structure formed by this invention enables it to intelligently identify leaks and achieve sealing effects. Simultaneously, because the microsphere particles are extremely small, they have virtually no significant impact on the engineering performance of the pre-flush fluid.

[0028] According to another aspect of the present invention, a pre-flooding fluid system for cementing is also provided, comprising 100 parts by weight of water, 8-15 parts by weight of pre-flooding fluid anti-leakage material, 2-5 parts by weight of fiber, 80-150 parts by weight of solid material, 1.5-3 parts by weight of suspension stabilizer, 2-3 parts by weight of fluid loss reducer, 4-7 parts by weight of anti-fouling agent, and 0.3-0.5 parts by weight of defoamer.

[0029] Preferably, the fiber comprises one or more of lignin fiber, polyvinyl alcohol fiber, and polyester fiber; preferably, the fiber has a length of 0.5-3 mm and a diameter of 5-15 μm.

[0030] Preferably, the solid material includes one or more of the following: quartz sand, dolomite powder, barite, and microsilica.

[0031] Preferably, the suspension stabilizer is an AMPS-type medium-temperature pre-solvent suspension stabilizer; preferably, the water loss reducing agent includes an AMPS-type medium-temperature cement slurry water loss reducing agent; preferably, the antifouling agent includes an organophosphonate antifouling agent; preferably, the defoaming agent includes an organosilicon defoaming agent.

[0032] In some preferred embodiments of the present invention, when preparing the anti-leakage material for cementing pre-fluid, the mixture is stirred at a stirring speed of 4000~12000 rpm.

[0033] The leak-proof material for cementing pre-flush fluid of the present invention is a stable, nano-sized microsphere in the form of pre-flush fluid with a hydrophilic surface. Therefore, it has good stability and dispersibility in pre-flush fluid, does not require additional emulsifiers or dispersants, and has little impact on the rheology and stability of pre-flush fluid.

[0034] According to another aspect of the present invention, an application of the above-mentioned pre-filling fluid system for cementing and preventing leakage is provided, which is suitable for sealing cracks with a width of 0.5mm-5mm and different types of pores under conditions of 100℃-180℃.

[0035] In some preferred embodiments of the present invention, the pre-filled cementing fluid system has a pressure greater than 6.9 MPa and a filtration loss of less than 40 mL.

[0036] Compared with existing technologies, the beneficial effects of the pre-flooding liquid system for cementing and leak prevention of the present invention include:

[0037] 1. The cementing and leak prevention pre-flush fluid system of the present invention consists of nano-sized, stable solid particles, which have strong adaptability to different types of pre-flush fluids and good compatibility with pre-flush fluids.

[0038] 2. The pre-filling fluid system for cementing leak prevention of the present invention has good adaptability to different opening cracks and different types of voids. It can adapt to voids and cracks of various shapes and types, and play an intelligent leak prevention role.

[0039] 3. The pre-flush liquid anti-leakage structure of the present invention has high strength and strong pressure bearing capacity, which can effectively achieve the purpose of preventing leakage and reducing filtration loss, and has no adverse effect on the performance of the pre-flush liquid and cement slurry. Attached Figure Description

[0040] Figure 1 The particle size distribution diagram of emulsion M1 in Example 1 is shown.

[0041] Figure 2 The particle size distribution in emulsion M1 of Comparative Example 4 is shown. Detailed Implementation

[0042] In order to provide a clearer understanding of the technical features, objectives and beneficial effects of the present invention, the technical solution of the present invention will now be described in detail below, but it should not be construed as limiting the scope of implementation of the present invention.

[0043] Performance testing of smart polymer leak-proof materials for cementing pre-filling fluid:

[0044] 1. Particle size evaluation

[0045] The experiment was conducted at room temperature. Before the experiment, the quartz sample cell was washed sequentially with ethanol and deionized water. After the sample cell was allowed to dry naturally, it was moistened with the liquid to be tested. Using a pipette close to the bottom of the sample cell, the liquid to be tested was slowly squeezed into the sample cell to avoid generating air bubbles. The size and distribution of the nanoemulsion droplets were measured using a Mastersizer 3000 laser particle size analyzer. Each experiment was performed three times, and the final result was the average.

[0046] 2. Self-crosslinking effect

[0047] The self-crosslinking properties were determined using solvent extraction, with sol content as the indicator. Different samples were dried at different temperatures, and the dried products were then wrapped in filter paper and placed in a Soxhlet extractor. After reflux extraction with acetone for 24 h, the samples were dried at room temperature to constant weight. The gel content was calculated as the ratio of the final weight to the initial weight.

[0048] Example 1

[0049] This embodiment provides a leak-proof material for cementing pre-flush fluid and its preparation method. The specific preparation method includes:

[0050] S1. Weigh 2.5 parts by mass of methyl methacrylate and 2 parts by mass of styrene, add 2.3 parts by mass of 2-acrylamido-2-methylpropanesulfonic acid, and stir at 200 RPM for 3 min to form a mixture; use a metering pump to add 40 parts by mass of water to the mixture at a rate of 2 mL / min, and adjust the pH value to 7 with NaHCO3 to obtain emulsion M1; transfer mixture M1 to a three-necked flask, and then place it in a water bath, stir M1 with a stirrer at 400 rpm, and then raise the water bath temperature to 70℃; add 0.06 parts by mass of potassium persulfate to 5 parts by mass of deionized water to prepare initiator solution M2; add solution M2 to the three-necked flask containing M1, and then react to obtain intermediate product M3.

[0051] S2. Mix 22.5 parts by mass of methyl methacrylate with 0.3 parts by mass of 2-acrylamido-2-methylpropanesulfonic acid to prepare mixture M4; dissolve 3 parts by mass of N-hydroxymethylacrylamide and 0.23 parts by mass of potassium persulfate in 25 parts by mass of deionized water to prepare mixture M5; use a metering pump to simultaneously add solutions M4 and M5 to a three-necked flask containing M3 at a rate of 2 mL / min, and then heat to 85°C to react to obtain a polymer microsphere emulsion, which is SSL1, a leak-proof material for cementing pre-fill fluid.

[0052] Example 2

[0053] This embodiment provides a leak-proof material for cementing pre-flush fluid and its preparation method. The specific preparation method includes:

[0054] S1. Weigh 2 parts by mass of methyl acrylate and 2.5 parts by mass of divinylbenzene, add 2.3 parts by mass of 2-acrylamido-2-methylpropanesulfonic acid, and stir at 200 RPM for 3 min to form a mixture; use a metering pump to add 40 parts by mass of water to the mixture at a rate of 2 mL / min, and adjust the pH value to 7 with NaHCO3 to obtain emulsion M1; transfer mixture M1 to a three-necked flask, and then place it in a water bath, stir M1 with a stirrer at 400 rpm, and then raise the water bath temperature to 70℃; add 0.05 parts by mass of ammonium persulfate to 5 parts by mass of deionized water to prepare initiator solution M2; add solution M2 to the three-necked flask containing M1, and then react to obtain intermediate product M3.

[0055] S2. Mix 20 parts by mass of methyl acrylate with 0.3 parts by mass of 2-acrylamido-2-methylpropanesulfonic acid to prepare mixture M4; dissolve 2.2 parts by mass of diacetone acrylamide and 0.23 parts by mass of ammonium persulfate in 25 parts by mass of deionized water to prepare mixture M5; use a metering pump to simultaneously add solutions M4 and M5 to a three-necked flask containing M3 at a rate of 2 mL / min, and then heat to 85°C to react to obtain a polymer microsphere emulsion, which is SSL2, a leak-proof material for cementing pre-fill fluid.

[0056] Example 3

[0057] This embodiment provides a leak-proof material for cementing pre-flush fluid and its preparation method. The specific preparation method includes:

[0058] S1. Weigh 2.0 parts by mass of methyl methacrylate and 1.5 parts by mass of styrene, add 2 parts by mass of 2-acrylamido-2-methylpropanesulfonic acid, and stir at 200 RPM for 3 min to form a mixture; use a metering pump to add 40 parts by mass of water to the mixture at a rate of 4 mL / min, and adjust the pH value to 7 with NaHCO3 to obtain emulsion M1; transfer mixture M1 to a three-necked flask, and then place it in a water bath, stir M1 with a stirrer at 500 rpm, and then raise the water bath temperature to 75℃; add 0.05 parts by mass of potassium persulfate to 5 parts by mass of deionized water to prepare initiator solution M2; add solution M2 to the three-necked flask containing M1, and then react to obtain intermediate product M3.

[0059] S2. Mix 20 parts by mass of diacetone acrylamide with 0.3 parts by mass of 2-acrylamido-2-methylpropanesulfonic acid to prepare mixture M4; dissolve 2 parts by mass of N-hydroxymethylacrylamide and 0.2 parts by mass of potassium persulfate in 25 parts by mass of deionized water to prepare mixture M5; use a metering pump to simultaneously add solutions M4 and M5 to a three-necked flask containing M3 at a rate of 2 mL / min, and then heat to 85°C to react to obtain a polymer microsphere emulsion, which is SSL3, a leak-proof material for cementing pre-fill fluid.

[0060] Implement column 4

[0061] This embodiment provides a leak-proof material for cementing pre-flush fluid and its preparation method. The specific preparation method includes:

[0062] S1. Weigh 3.0 parts by weight of methyl methacrylate and 2.5 parts by weight of styrene, add 2.5 parts by weight of 2-acrylamido-2-methylpropanesulfonic acid, and stir at 200 RPM for 3 min to form a mixture; use a metering pump to add 50 parts by weight of water to the mixture at a rate of 6 mL / min, and adjust the pH value to 7 with NaHCO3 to obtain emulsion M1; transfer mixture M1 to a three-necked flask, and then place it in a water bath, stir M1 with a stirrer at 300 rpm, and then raise the water bath temperature to 70℃; add 0.07 parts by weight of potassium persulfate to 5 parts by weight of deionized water to prepare initiator solution M2; add solution M2 to the three-necked flask containing M1, and then react to obtain intermediate product M3.

[0063] S2. Mix 25 parts by mass of methyl methacrylate with 0.5 parts by mass of 2-acrylamido-2-methylpropanesulfonic acid to prepare mixture M4; dissolve 5 parts by mass of N-hydroxymethylacrylamide and 0.25 parts by mass of potassium persulfate in 25 parts by mass of deionized water to prepare mixture M5; use a metering pump to simultaneously add solutions M4 and M5 to a three-necked flask containing M3 at a rate of 6 mL / min, and then heat to 85°C to react, to obtain a polymer microsphere emulsion, which is SSL4, a leak-proof material for cementing pre-fill fluid.

[0064] Comparative Example 1

[0065] The difference from Example 1 is that 2-acrylamido-2-methylpropanesulfonic acid was not added in step S1, and the resulting leak-proof material is DBL1.

[0066] Comparative Example 2

[0067] The difference from Example 1 is that in step S1, the mixture M1 is transferred to a three-necked flask and then placed in a water bath. M1 is stirred at 200 rpm using a stirrer, and the resulting leak-proof material is DBL2.

[0068] Comparative Example 3

[0069] The difference from Example 1 is that in step S1, the mixture M1 is transferred to a three-necked flask, then placed in a water bath, and M1 is stirred at 400 rpm using a stirrer. Then the water bath temperature is raised to 85°C, and the resulting leak-proof material is DBL3.

[0070] Comparative Example 4

[0071] The difference from Example 1 is that the preparation steps of mixture M1 in step S1 are as follows: 2.3 parts by mass of 2-acrylamido-2-methylpropanesulfonic acid were dissolved in 40 parts by mass of water beforehand; 2.5 parts by mass of methyl methacrylate and 2 parts by mass of styrene were added to the pre-prepared aqueous solution of 2-acrylamido-2-methylpropanesulfonic acid, and the pH was adjusted to 7 using Na2CO3 to obtain emulsion M1. The leak-proof material obtained in this comparative example is DBL4.

[0072] Comparative Example 5

[0073] The difference from Example 1 is that in step S1, 2.5 parts by weight of methyl methacrylate and 2 parts by weight of styrene were weighed and mixed, and 2.3 parts by weight of 2-acrylamido-2-methylpropanesulfonic acid were added. The mixture was stirred at 100 RPM for 3 minutes to form a mixture. 40 parts by weight of water were added to the mixture at a rate of 2 mL / min using a metering pump, and the pH was adjusted to 7 using NaHCO3 to obtain emulsion M1. Mixture M1 was transferred to a three-necked flask and placed in a water bath. M1 was stirred at 100 rpm using a stirrer, and then the water bath temperature was raised to 70°C. The leak-proof material obtained in this comparative example is DBL5.

[0074] Comparative Example 6

[0075] The difference from Example 1 is that in step S2, 22.5 parts by weight of methyl methacrylate are weighed to prepare M4; 0.3 parts by weight of 2-acrylamido-2-methylpropanesulfonic acid, 3 parts by weight of N-hydroxymethylacrylamide, and 0.23 parts by weight of potassium persulfate are dissolved in 25 parts by weight of deionized water to obtain mixture M5. The leak-proof material obtained in this comparative example is DBL6.

[0076] Comparative Example 7

[0077] The difference from Example 1 is that, in step S2, a metering pump is used to simultaneously and directly add solutions M4 and M5 to the three-necked flask containing M3. The leak-proof material obtained in this comparative example is DBL7.

[0078] The particle size of the leak-proof materials prepared in the above embodiments and comparative examples at room temperature is shown in Table 1.

[0079] Table 1

[0080]

[0081] As shown in Table 1, the cementing and leak-proof materials SSL1 to SSL4 all have nanoscale particle sizes, indicating the formation of nanopolymer microspheres. These nanoscale microspheres easily adapt to cracks of different apertures and different types of pores, demonstrating strong adaptability. In Comparative Example 1, 2-acrylamido-2-methylpropanesulfonic acid was not added, so an emulsion could not be formed for emulsion polymerization, and therefore no polymer microspheres were formed, with no particle size data available. In Comparative Example 2, the stirring speed was lower than the specified speed, which failed to emulsify the organic monomers into smaller emulsion droplets, thus no polymer microspheres were formed, and no particle size data was available. In Comparative Example 3, the water bath temperature was higher than the specified temperature, and temperature is a key factor affecting emulsion stability, resulting in an unstable emulsion formed by the organic monomers, making it difficult to ensure the emulsion polymerization process, and no polymer microspheres were formed, with no particle size data available. In Comparative Example 4, the specified mixing sequence was not used, so polymer microspheres with nanoscale particle sizes could not be formed, and the product had a large particle size and wide distribution. In Comparative Example 5, the specified rotation speed was not used, making it difficult to ensure that the emulsion droplets were reduced to nanoscale size through mechanical energy, resulting in a large product particle size and wide distribution. This is because the synthesis of nanopolymer microspheres requires the organic monomers to be dispersed into nanoscale droplets during the emulsion polymerization reaction, which requires a large energy input, one from mechanical energy such as vigorous stirring and ultrasound, and the other from chemical energy. The reverse emulsification method can fully utilize the chemical energy of 2-acrylamido-2-methylpropanesulfonic acid as an emulsifier to form an emulsion with a smaller particle size, thereby preparing nanoscale polymer microspheres. However, it is difficult to directly emulsify organic monomers into nanoscale emulsions by directly mixing organic monomers, water, and emulsifiers.

[0082] In Example 1 and Comparative Example 4, the particle size distribution of emulsion M1 is as follows: Figure 1 , Figure 2 As shown.

[0083] Emulsion droplets were formed in both Comparative Examples 6 and 7, therefore their self-crosslinking properties need to be further investigated.

[0084] Table 2 shows the gel content of different self-crosslinking polymer microspheres after heat treatment at different temperatures. The increased gel content of microspheres containing self-crosslinking monomers after heat treatment indicates the presence of self-crosslinking behavior. The cementing and leak-proof materials SSL1~SSL5 all formed a large amount of gel after heating at 60℃, 120℃, and 140℃. The polymer can effectively crosslink at 120℃, and completely crosslink at 140℃, highlighting the self-crosslinking phenomenon of the prepared microspheres under high-temperature conditions. Comparative Example 5 also formed a large amount of gel. However, the polymer microspheres formed in Comparative Example 6 had almost zero gel content after heating at 60℃, 120℃, and 140℃. Comparative Example 6 introduced self-crosslinking monomers in step S2; although the self-crosslinking monomers were not uniformly distributed on the microsphere surface, they still exhibited self-crosslinking characteristics. In Comparative Example 7, the monomer solution was added too quickly in step 2, and the self-crosslinking monomers failed to be successfully introduced onto the microspheres, therefore, they did not exhibit self-crosslinking characteristics.

[0085] Table 2

[0086]

[0087] Performance evaluation test of intelligent pre-flush fluid system for cementing leak prevention:

[0088] The filtration loss reduction capability of self-crosslinked microspheres was analyzed using HTHP (High-Temperature High-Pressure Hydrocarbon) analysis. The filtration loss was measured using a Trinelle high-temperature high-pressure hydrocarbon analyzer at 140℃, a pressure differential of 6.9 MPa, and a filtration time of 30 min. Two test media were used: API-recommended filter paper and a microporous membrane with a pore size of 220 nm, which better simulates microfractures and micropores to evaluate the leakage prevention capability of the self-crosslinked microspheres in this type of formation. To evaluate the temperature response characteristics of the self-crosslinked microdomains, the cementing fluid containing the self-crosslinked microspheres was first cured at different temperatures for a period of time to simulate the circulation process of the cementing fluid in the formation. Afterward, the fluid was removed and evaluated using an HTHP analyzer.

[0089] Application Example 1

[0090] Dissolve 10 parts by weight of SSL1 (a pre-flooding fluid material for cementing), 2 parts by weight of DRY-S1 (a suspension stabilizer from China Petroleum Engineering Technology Research Institute Co., Ltd.), 3 parts by weight of DRF-2L (a fluid loss reducer from China Petroleum Engineering Technology Research Institute Co., Ltd.), 5 parts by weight of DRP-1L (a contaminant from China Petroleum Engineering Technology Research Institute Co., Ltd.), and 0.5 parts by weight of DRX-1L (a defoamer from China Petroleum Engineering Technology Research Institute Co., Ltd.) in 100 parts by weight of water and stir thoroughly. Mix 120 parts by weight of dolomite powder with 3 parts by weight of fibers with a length of 2-10 mm thoroughly. While stirring at 4000 rpm, slowly pour the solid mixture into the solution. After pouring, continue stirring at high speed to mix evenly to obtain the pre-flooding fluid system SP1 for cementing.

[0091] Application Example 2

[0092] Dissolve 10 parts by weight of SSL3 (a pre-flooding fluid for cementing), 2 parts by weight of DRY-S1 (a suspension stabilizer from China Petroleum Engineering & Technology Research Institute Co., Ltd.), 3 parts by weight of DRF-2L (a fluid loss reducer from China Petroleum Engineering & Technology Research Institute Co., Ltd.), 5 parts by weight of DRP-1L (a contaminant from China Petroleum Engineering & Technology Research Institute Co., Ltd.), and 0.5 parts by weight of DRX-1L (a foam suppressant from China Petroleum Engineering & Technology Research Institute Co., Ltd.) in 100 parts by weight of water and stir thoroughly. Mix 120 parts by weight of dolomite powder with 3 parts by weight of fibers with a length of 2-10 mm thoroughly. Stir at 4000 rpm and slowly pour the solid mixture into the solution. After pouring, continue to stir at high speed until the mixture is homogeneous to obtain the pre-flooding fluid system SP2 for cementing.

[0093] Application Example 3

[0094] Dissolve 15 parts by weight of SSL1 (a pre-flooding fluid material for cementing), 2 parts by weight of DRY-S1 (a suspension stabilizer from China Petroleum Engineering Technology Research Institute Co., Ltd.), 3 parts by weight of DRF-2L (a fluid loss reducer from China Petroleum Engineering Technology Research Institute Co., Ltd.), 5 parts by weight of DRP-1L (a contaminant from China Petroleum Engineering Technology Research Institute Co., Ltd.), and 0.5 parts by weight of DRX-1L (a defoamer from China Petroleum Engineering Technology Research Institute Co., Ltd.) in 100 parts by weight of water and stir thoroughly. Mix 120 parts by weight of dolomite powder with 3 parts by weight of fibers with a length of 2-10 mm thoroughly. While stirring at 4000 rpm, slowly pour the solid mixture into the solution. After pouring, continue stirring at high speed to mix evenly to obtain the pre-flooding fluid system SP3 for cementing.

[0095] Application Example 4

[0096] Eight parts by weight of SSL1 (a pre-flooding fluid material for cementing), two parts by weight of DRY-S1 (a suspension stabilizer from China Petroleum Engineering & Technology Research Institute Co., Ltd.), three parts by weight of DRF-2L (a fluid loss reducer from China Petroleum Engineering & Technology Research Institute Co., Ltd.), five parts by weight of DRP-1L (a contaminant from China Petroleum Engineering & Technology Research Institute Co., Ltd.), and 0.5 parts by weight of DRX-1L (a defoamer from China Petroleum Engineering & Technology Research Institute Co., Ltd.) were dissolved in 100 parts by weight of water and stirred thoroughly. 120 parts by weight of dolomite powder and two parts by weight of fibers with a length of 2-10 mm were thoroughly mixed. The solid mixture was slowly poured into the solution while stirring at 4000 rpm. After pouring, the mixture was stirred at high speed until homogeneous, thus obtaining the pre-flooding fluid system SP4 for cementing.

[0097] Application Comparative Example 1

[0098] SPD1, a pre-cementing fluid for preventing leakage, was prepared according to the method in Application Example 1, except that no pre-cementing fluid leakage prevention material was used.

[0099] Application Comparative Example 2

[0100] SPD2, a pre-cementing fluid for preventing leakage, was prepared according to the method in Application Example 1, except that no fibers were used.

[0101] Application Comparative Example 3

[0102] The cementing pre-flush fluid SPD3 was prepared according to the method of Application Example 1, except that the amount of the pre-flush fluid anti-leakage material SSL1 added was 5 parts by mass.

[0103] Application Comparative Example 4

[0104] SPD4, a pre-cementing fluid for preventing leakage, was prepared according to the method of Application Example 1, except that the leakage prevention material DBL4 prepared in Comparative Example 4 was used instead of SSL1, the leakage prevention material for the pre-cementing fluid.

[0105] Application Comparative Example 5

[0106] SPD5, a pre-cementing fluid for preventing leakage, was prepared according to the method of Application Example 1, except that the leakage prevention material DBL5 prepared in Comparative Example 5 was used instead of the leakage prevention material SSL1 for the pre-cementing fluid.

[0107] The leakage prevention and plugging performance of the above-mentioned cementing pre-fill fluid was tested at 60℃, 120℃ and 140℃ for different simulated media. The results are shown in Tables 3, 4, 5 and 6.

[0108] Table 3

[0109]

[0110] Table 4

[0111]

[0112] Table 5

[0113]

[0114] Table 6

[0115]

[0116] As shown in Table 4, the self-crosslinked microspheres did not perform their leak-proof function at a temperature of 60℃. This is because the self-crosslinking temperature was not reached, and no crosslinking structure was formed between the microspheres, making it difficult to meet the pressure resistance of 6.9MPa. As shown in Table 5, at a temperature of 120℃, the application examples all showed good leak-proof performance, with a pressure resistance >6.9MPa and a cumulative leakage of less than 40mL. In Comparative Example 1, no anti-leakage material for the cementing pre-fluid was added, so the pre-fluid failed to prevent leakage and caused gas perforation. In Comparative Example 2, no fiber material was added, so it could not bridge the gap, resulting in significant leakage. In Comparative Example 3, the amount of anti-leakage material for the cementing pre-fluid was less than the specified amount, resulting in significant leakage. In Comparative Example 4, the microspheres used in the anti-leakage material for the cementing pre-fluid had large particle sizes, making it difficult to intelligently adapt to fractures and form a dense anti-leakage sealing structure, thus resulting in poor anti-leakage and plugging capabilities. In Comparative Example 5, the self-crosslinking monomers on the surface of the microspheres were unevenly distributed, causing premature crosslinking of the self-crosslinking microspheres during high-temperature cycling, thus reducing the anti-leakage capability. Table 5 shows that after reaching the self-crosslinking temperature, the microspheres can have a good anti-leakage effect over a wide temperature range. Table 6 shows that the viscosity change in Application Example 1 was small under curing at 140℃, while the apparent viscosity of Comparative Example 5 increased significantly, indicating that the self-crosslinking microspheres in Comparative Example 5 underwent crosslinking, increasing the system viscosity.

[0117] As can be seen from Table 5, after reaching the self-crosslinking temperature, the microspheres can have a good leak-proof effect over a wide temperature range.

[0118] As can be seen from Table 6, the viscosity of Example 1 under curing at 140℃ changed little, while the apparent viscosity of Comparative Example 5 increased significantly. This indicates that the self-crosslinked microspheres in Comparative Example 5 underwent crosslinking, which increased the viscosity of the system.

[0119] Compatibility evaluation of cement slurry with pre-cementing fluid system for well leakage prevention:

[0120] The influence of leak-proof materials used in cementing pre-flush fluid on the rheological properties of the pre-flush fluid was tested according to the national standard GB / T19139-2012 "Test Methods for Cement in Oil Wells". The results are shown in Table 7.

[0121] Table 7

[0122]

[0123] SPD1 did not contain microspheres for preventing leakage in cementing pre-flush fluid. SP1 contained 10 parts by weight of microspheres, and SP3 contained 15 parts by weight. It can be seen that after adding microspheres for preventing leakage in cementing pre-flush fluid, the increase in apparent viscosity at room temperature was relatively small with increasing microsphere content, meeting the construction requirements. This is mainly because the microspheres do not form polymer colloids with large hydrodynamic radii in water, resulting in less binding of free water and therefore no significant thickening effect.

[0124] In summary, the anti-leakage material for cementing pre-flush fluid of the present invention has strong adaptability and can seal different types of micro-nano level cracks and pores. It has a pressure resistance greater than 6.9 MPa and a filtration loss of less than 40 mL, achieving the purpose of preventing leakage and reducing filtration loss. Moreover, it has no adverse effects on the performance of pre-flush fluid and cement slurry, meeting the anti-leakage requirements of cementing in shale formations with micro-cracks and pores.

Claims

1. A method for preparing a leak-proof material for cementing pre-filling fluid, characterized in that, include: S1, mix 2-3 parts by weight of ester organic monomers, 1.5-2.5 parts by weight of benzene organic monomers, and 2-2.5 parts by weight of 2-acrylamido-2-methylpropanesulfonic acid, and stir at 200-300 rpm to obtain a mixture. Add water to the mixture at a rate of 2-10 mL / min to adjust the pH to 6-8 to obtain emulsion M1. Stir emulsion M1 at 300-500 rpm, and then mix it with initiator solution M2. Perform a first reaction at 70-75°C for 30-40 min to obtain intermediate product M3. S2, mix 20-25 parts by weight of ester organic monomers and 0.25-0.5 parts by weight of 2-acrylamido-2-methylpropanesulfonic acid to obtain mixture M4; mix 2-5 parts by weight of self-crosslinking monomers, initiator and water to obtain mixture M5; add mixture M4 and mixture M5 to intermediate product M3 at a feeding rate of 2-10 mL / min respectively to carry out a second reaction to obtain the leak-proof material for cementing pre-fill fluid.

2. The preparation method according to claim 1, characterized in that, The ester organic monomers include methyl methacrylate and / or methyl acrylate; and / or, The benzene-based organic monomers include divinylbenzene and / or styrene.

3. The preparation method according to claim 1, characterized in that, The self-crosslinking monomers include N-hydroxymethylacrylamide and / or diacetone acrylamide.

4. The preparation method according to claim 1, characterized in that, The initiator solution M2 comprises 0.05 to 0.07 parts by mass of initiator and 4 to 8 parts by mass of water.

5. The preparation method according to claim 1, characterized in that, Add 40-60 parts by weight of water to the mixture to obtain the emulsion M1.

6. The preparation method according to claim 1, characterized in that, The mixture M5 comprises 0.2 to 0.25 parts by weight of initiator and 15 to 30 parts by weight of water.

7. The preparation method according to claim 1, characterized in that, The second reaction is carried out at a temperature of 80-85°C for 2-3 hours.

8. The preparation method according to claim 1, characterized in that, The initiator includes persulfate and / or azobisisobutylamidine hydrochloride.

9. The preparation method according to claim 1, characterized in that, The emulsion M1 is stirred at a stirring speed of 400~500 rpm and then mixed with the initiator solution M2.

10. The preparation method according to claim 1, characterized in that, In S1, the ester organic monomer is 2-2.5 parts by weight, the benzene organic monomer is 1.5-2 parts by weight, and the 2-acrylamido-2-methylpropanesulfonic acid is 2-2.3 parts by weight; and / or, In S2, the ester organic monomer is 20-22 parts by mass, and the 2-acrylamido-2-methylpropanesulfonic acid is 0.25-0.3 parts by mass.

11. A leak-proof material for cementing pre-fill fluid prepared by the preparation method according to any one of claims 1 to 10.

12. A pre-filling fluid system for cementing leak prevention, characterized in that, It includes 100 parts by weight of water, 8-15 parts by weight of the leak-proof material for cementing pre-fill fluid as described in claim 11, 2-5 parts by weight of fiber, 80-150 parts by weight of solid material, 1.5-3 parts by weight of suspension stabilizer, 2-3 parts by weight of fluid loss reducer, 4-7 parts by weight of anti-fouling agent, and 0.3-0.5 parts by weight of antifoaming agent.

13. The application of the pre-filled cementing fluid system of claim 12 in sealing fractures and pores, characterized in that, The applicable temperature is 100~180℃, and the crack width is 0.5~5mm.

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