Micro-crosslinked interlocking fluid loss reducer and preparation method therefor, and cement slurry system for well cementing

Abstract

Disclosed in the present invention are a micro-crosslinked interlocking fluid loss reducer and a preparation method therefor, and a cement slurry system for well cementing. The preparation method for the fluid loss reducer comprises: mixing 2-acrylamido-2-methylpropanesulfonic acid, a vinyl-containing carboxylic acid or a derivative monomer thereof, and water and adding a pH regulator to regulate the pH value of the system; then adding a modified acrylamide monomer, a vinyl cyclic monomer, and a crosslinking agent; then adding a molecular weight regulator, a chelating agent, and an oxidizing agent to obtain a mixed system; and dropwise adding an aqueous solution of a reducing agent to the mixed system for reaction for a period of time to obtain the fluid loss reducer. The fluid loss reducer of the present invention has better heat and salt resistance and fluid loss reduction performance, can improve the settling stability of the cement slurry system, has no adverse effects on the comprehensive performance of the cement slurry system, and has a wide range of applicable temperatures.

Description

A micro-crosslinked interlocking fluid loss reducing agent and its preparation method in cementing slurry system Technical Field

[0001] This invention relates to a micro-crosslinked interlocking fluid loss reducing agent, its preparation method, and a cementing slurry system, belonging to the field of oil and gas well cementing technology. Background Technology

[0002] Deep and ultra-deep oil and gas resources hold immense potential, making them a crucial area for increasing oil and gas reserves and production, and gradually shifting towards extra-deep formations. Currently, drilling technology for ultra-deep and extra-deep oil and gas formations has achieved leapfrog development, with well depths reaching 7000m being mature, exceeding 8000m and becoming increasingly routine, reaching 9000m, and even surpassing 10000m. Cementing slurry technology is crucial for ensuring the safety of cementing operations in deep and ultra-deep wells, achieving long-term and efficient sealing of cement sheaths, and supporting safe oil and gas production, spanning the entire lifecycle of oil and gas wells, including drilling, completion, production, and disposal. However, cementing ultra-deep and extra-deep oil and gas wells faces complex geological conditions and extreme operating conditions, such as ultra-deep (>9000m), ultra-high temperature (>200℃), and ultra-high pressure (>140MPa), posing significant challenges to key cementing slurry materials and systems. Water loss reducers are one of the core components of oil well cement slurry. They play a crucial role in reducing water loss in cement slurry, ensuring system stability, and preventing cement slurry from being lost to the formation and contaminating the reservoir.

[0003] There are many types of fluid loss control agents, among which 2-acrylamido-2-methylpropanesulfonic acid (AMPS) copolymers have become a research and application hotspot due to their excellent molecular structure designability, temperature and salt resistance, and strong adaptability. However, under harsh environments such as ultra-high temperature and ultra-high pressure, AMPS copolymer fluid loss control agents still have some problems: ① Under ultra-high temperature and strong alkaline conditions, the polymer molecular structure is prone to conformational transformation, partial hydrolysis and chain scission, and adsorption-desorption imbalance, leading to uncontrollable water loss of cement slurry and deterioration of overall performance; ② Fluid loss control agents are often linear polymers with obvious high-temperature dilution characteristics, resulting in poor sedimentation stability of cement slurry at ultra-high temperatures, affecting the safety of cementing construction and sealing quality; ③ Poor adaptability over a wide temperature range makes it difficult to meet the requirements of long cement slurry injection stroke, large friction in small gaps of the tailpipe, and large temperature difference between the top and bottom of the effective sealing section across temperature zones for the development of cement slurry rheology, stability, and mechanical strength. Therefore, there is an urgent need to develop high-performance fluid loss reducing agents suitable for cementing ultra-deep and extra-deep wells, so as to improve the overall performance of cement slurry systems and meet the technical requirements of cementing complex wells.

[0004] CN109503782A discloses an inorganic-organic polymer water loss reducing agent, which is graft copolymerized from itaconic acid, acrylamide monomers, AMPS, silane coupling agents, and inorganic materials (one of silicon carbide, silica, and alumina). It introduces inorganic non-metallic particles and modifies the polymer's micro-crosslinked structure based on existing polymers, improving the water loss reducing agent's temperature resistance; the water loss of cement slurry is controlled to within 60 mL at 230℃. However, the water loss reducing effect above 230℃ is not described, and the effect on other properties of cement slurry is not investigated.

[0005] CN106188395A discloses a micro-crosslinked, high-temperature, salt-resistant cementitious slurry fluid loss reducer, prepared by free radical aqueous solution polymerization of AMPS, acrylamide (AM), unsaturated polycarboxylic acids, N-vinylpyrrolidone (NVP), and N,N-methylenebisacrylamide (crosslinking agent). It is suitable for temperatures of 30-240℃, resists saturated brine, and reduces the API fluid loss of the cement slurry to less than 50 mL. However, the polymer contains more than 15% acrylamide by mass. Under high-temperature, strongly alkaline conditions, the amide groups hydrolyze into carboxylic acid groups with strong retarding properties. While this improves the fluid loss reduction capacity, it can easily cause adverse effects such as a "reverse" thickening time in the cement slurry and a reduction in the compressive strength of the cement paste, thus affecting the overall performance of the cement slurry system.

[0006] Although the polymer-based fluid loss reducing agents disclosed in the prior art have improved temperature and salt resistance, they still have certain defects in terms of overall performance, especially in the application of ultra-deep and ultra-high temperature cementing in ultra-deep wells. Summary of the Invention

[0007] To address the aforementioned technical problems, the present invention aims to provide a micro-crosslinked interlocking fluid loss reducing agent, its preparation method, and a cementing slurry system. The fluid loss reducing agent of the present invention exhibits superior temperature and salt resistance, excellent fluid loss reduction performance, and improves the settling stability of the cementing slurry system, while having no adverse effects on the overall performance of the cementing slurry system.

[0008] To achieve the above objectives, the first aspect of the present invention provides a method for preparing a micro-crosslinked interlocking type dehydration reducing agent, comprising the following steps:

[0009] (1) Mix 30-90 parts by weight of 2-acrylamido-2-methylpropanesulfonic acid, 3-20 parts by weight of vinyl-containing carboxylic acid or its derivative monomers and water, and add a pH adjuster to adjust the pH of the system to 6-7; then add 5-30 parts by weight of modified acrylamide monomer, 2-30 parts by weight of vinyl cyclic monomer and 0.1-3 parts by weight of crosslinking agent, wherein the crosslinking agent includes compounds containing three alkenyl or four alkenyl groups; then add 0.02-3 parts by weight of molecular weight adjuster, 0.05-2 parts by weight of chelating agent and 0.2-1 parts by weight of oxidant to obtain a mixed system;

[0010] (2) Add an aqueous solution containing 0.2-1 parts by weight of reducing agent dropwise to the mixed system. After the addition is complete, react for a period of time to obtain the micro-crosslinked interlocking type dehydration reducer.

[0011] According to a specific embodiment of the present invention, preferably, the weight ratio of 2-acrylamido-2-methylpropanesulfonic acid, vinyl-containing carboxylic acid or derivative monomer, modified acrylamide monomer, vinyl cyclic monomer, crosslinking agent, molecular weight regulator, chelating agent, oxidizing agent and reducing agent is (37-74):(5-15):(15-28):(5-20):(0.5-2):(0.05-3):(0.05-1.5):(0.3-1):(0.23-0.56).

[0012] According to a specific embodiment of the present invention, preferably, in step (1), the vinyl-containing carboxylic acid or its derivative monomer includes one or more of acrylic acid, itaconic acid, maleic anhydride, maleic acid and fumaric acid.

[0013] According to a specific embodiment of the present invention, preferably, in step (1), the amount of water used is 230-850 parts by weight, based on 30-90 parts by weight of 2-acrylamido-2-methylpropanesulfonic acid.

[0014] According to a specific embodiment of the present invention, preferably, in step (1), the pH adjuster includes alkaline compounds such as sodium hydroxide and / or potassium hydroxide.

[0015] According to a specific embodiment of the present invention, preferably, in step (1), the modified acrylamide monomer includes one or more of N-butoxymethacrylamide, N,N-diethylacrylamide, N-hydroxyethylacrylamide, diacetone acrylamide and N-isopropylacrylamide.

[0016] According to a specific embodiment of the present invention, preferably, in step (1), the vinyl cyclic monomer includes one or more of N-vinylpyrrolidone, N-vinylcaprolactam and vinylcyclopentane.

[0017] According to a specific embodiment of the present invention, preferably, in step (1), the crosslinking agent includes one or two of triallylamine and pentaerythritol tetraallyl ether.

[0018] According to a specific embodiment of the present invention, preferably, in step (1), the molecular weight regulator includes one or more of mercaptopropionic acid, mercaptoethanol, isopropanol, dodecyl mercaptoethanol, hydroquinone and 2-mercaptobenzoic acid.

[0019] According to a specific embodiment of the present invention, preferably, in step (1), the chelating agent includes one or more of ethylenediaminetetraacetic acid, disodium ethylenediaminetetraacetic acid, tetrasodium ethylenediaminetetraacetic acid, and diethylenetriaminepentaacetic acid.

[0020] According to a specific embodiment of the present invention, preferably, in step (1), the oxidant includes one or more of the following: ammonium persulfate, potassium persulfate, azobisisobutyrazoline hydrochloride, azobisisobutyramidine hydrochloride, hydrogen peroxide, benzoyl peroxide, and cumene hydrogen peroxide.

[0021] According to a specific embodiment of the present invention, preferably, in step (2), before adding the aqueous solution containing 0.2-1 parts by weight of reducing agent to the mixed system, the mixture is further heated to 30-60°C under stirring at 150±50 rpm.

[0022] According to a specific embodiment of the present invention, preferably, in step (2), the reducing agent includes one or more of sodium sulfite, sodium bisulfite, ferrous sulfate, ferrous chloride, N,N-dimethylaniline and sodium dithionite.

[0023] According to a specific embodiment of the present invention, preferably, in step (2), the mass concentration of the reducing agent in the aqueous solution containing 0.2-1 parts by weight of reducing agent is 0.4-2%.

[0024] According to a specific embodiment of the present invention, preferably, in step (2), the aqueous solution containing 0.2-1 parts by weight of reducing agent is added to the mixed system over a time of 30-60 minutes, and the temperature of the mixed system is 30-60°C during the process of adding the aqueous solution containing 0.2-1 parts by weight of reducing agent to the mixed system.

[0025] According to a specific embodiment of the present invention, preferably, in step (2), the temperature of the reaction is 60-90°C and the reaction time is 1-6h.

[0026] The second aspect of the present invention provides a micro-crosslinked interlocking type water loss reducing agent, which is prepared by the above-mentioned method for preparing the micro-crosslinked interlocking type water loss reducing agent.

[0027] According to a specific embodiment of the present invention, preferably, the micro-crosslinked interlocking water loss reducing agent comprises: structural units derived from 2-acrylamido-2-methylpropanesulfonic acid, structural units derived from monomers containing vinyl carboxylic acids or their derivatives, structural units derived from modified acrylamide monomers, structural units derived from vinyl cyclic monomers, and structural units derived from crosslinking agents, wherein the crosslinking agent comprises compounds containing three alkenyl groups or four alkenyl groups.

[0028] A third aspect of the present invention provides a cementing slurry system, the cementing slurry system comprising at least: cement, and the above-mentioned micro-crosslinked interlocking fluid loss reducing agent.

[0029] According to a specific embodiment of the present invention, preferably, the cementing slurry system comprises: 100 parts by weight of cement, 3-5 parts by weight of the micro-crosslinked interlocking fluid loss reducing agent, 0-80 parts by weight of quartz sand, 0-6 parts by weight of stabilizer, 0-3 parts by weight of dispersant, 0-6 parts by weight of retarder, 0-0.5 parts by weight of defoamer, 0-15 parts by weight of high-temperature strength degradation inhibitor, and 40-70 parts by weight of water. More preferably, the quartz sand has a particle size of 200-600 mesh.

[0030] According to a specific embodiment of the present invention, preferably, the density of the cementing slurry system is 1.90 ± 0.02 g / cm³. 3 .

[0031] According to a specific embodiment of the present invention, the cement includes Grade G oil well cement. The stabilizer, dispersant, retarder, and defoamer can all be products of the prior art. Specifically, the stabilizer may include biopolymer-based high-temperature stabilizers, acrylamide-based polymer ultra-high-temperature suspension stabilizers, etc., such as one or two of high-temperature stabilizer DRK-3S and ultra-high-temperature suspension stabilizer DRK-4L. The dispersant may include aldehyde-ketone condensate dispersants and / or polystyrene sulfonate dispersants, such as one or more of dispersant DRS-1S, dispersant SAF, dispersant SXY, dispersant USZ, and dispersant SDJZ-1. The high-temperature retarder may include acrylamide polymer retarders and / or 2-acrylamide-2-methylpropanesulfonic acid polymer retarders, such as one or more of retarders DRH-2L, retarder DRH-3L, retarder JXH-2L, and retarder HX-36L. The defoamer may include one or more of organic esters, polyoxypropylene glycerol ethers, and polydimethylsiloxanes, such as defoamer DRX-1L. The high-temperature strength degradation inhibitor may include mineral powders, such as the high-temperature strength degradation inhibitor DRB-3S.

[0032] The present invention has at least the following beneficial effects:

[0033] This invention employs micro-crosslinking polymerization technology to introduce reactive active sites of "triple double bonds" or "quadruple double bonds" into the polymer molecular structure. These sites are linked by chemical bonds to form a rigid, interlocked network polymer. Through the synergistic effect of the monomers, crosslinking agents, molecular weight regulators, and chelating agents, the water loss reducing agent of this invention exhibits significantly improved temperature, pressure, and salt resistance, along with excellent water loss reducing performance. Furthermore, it can significantly improve the settling stability of cement slurry systems and the mechanical properties of cement paste under ultra-high temperature conditions. Simultaneously, the water loss reducing agent of this invention has virtually no adverse effect on the thickening performance of cement slurry systems, maintaining a normal thickening curve. Moreover, the water loss reducing agent of this invention has a wide applicable temperature range, applicable from 20-245℃, without adversely affecting the overall performance of cement slurry systems within this temperature range. In addition, the preparation method of the water loss reducing agent of this invention is simple and mild, enabling large-scale production and widespread application. The fluid loss reducing agent of this invention is applicable to various cementing slurry systems, including conventional density, low density, and high density cement slurry systems at medium, high, and ultra-high temperatures. It can meet the cementing technology requirements under complex working conditions such as deep wells, ultra-deep wells, extra-deep wells, high-pressure gas wells, unconventional oil and gas wells, gas storage wells, and geothermal wells, and has a broad application market. Attached Figure Description

[0034] Figure 1 shows the effect of different curing times at 245℃ and 130MPa on the API water loss of cement slurry systems containing 5% of the water loss reducing agent prepared in Example 1 and Comparative Example 1, respectively.

[0035] Figure 2 shows the effect of different salt concentrations on the API water loss of the cement slurry system containing the water loss reducing agent prepared in Example 1 at 245℃ and 130MPa.

[0036] Figure 3 shows the thickening curve of the cement slurry system with 4% of the water loss reducing agent prepared in Example 1 at 245°C and 130 MPa. Detailed Implementation

[0037] To provide a clearer understanding of the technical features, objectives, and beneficial effects of the present invention, the present invention will now be described in detail below, but this should not be construed as limiting the scope of the invention.

[0038] It should be noted that, unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0039] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0040] It should be understood that the terms “comprising,” “including,” and / or “containing” as used herein specify the presence of the stated features, integers, steps, components, or combinations thereof, but do not exclude the presence or addition of one or more other features, integers, steps, components, or combinations thereof.

[0041] The endpoints and any values ​​of the ranges disclosed in this invention are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this invention.

[0042] Example 1

[0043] Weigh 74g of 2-acrylamido-2-methylpropanesulfonic acid, 2g of maleic anhydride, and 4g of acrylic acid, dissolve them in 350g of water, and slowly add sodium hydroxide to adjust the pH of the system to 6-7; then add 15g of N-n-butoxymethacrylamide, 5g of N-vinylpyrrolidone, and 1g of triallylamine and mix well; then add 0.05g of mercaptopropionic acid, 0.05g of disodium ethylenediaminetetraacetate, and 0.5g of ammonium persulfate to obtain a mixed system; heat the mixed system to 45℃ under stirring at 200 rpm, and dissolve 0.23g of sodium bisulfite in 50g of water to prepare a reducing agent solution. Slowly add the reducing agent solution dropwise to the mixed system at 45℃ over 30min. After the addition is complete, slowly heat to 70℃ and maintain this temperature for 4h of reaction, then allow it to cool naturally to room temperature to obtain a micro-crosslinked interlocking type dehydration reducer.

[0044] The structure of the micro-crosslinked interlocking type water loss reducing agent in this embodiment is presumably as follows:

[0045] It can be seen that the three C=C bonds in triallylamine undergo copolymerization reactions with other polymeric monomers, and the chain segment length between each crosslinking point is controlled by a molecular weight regulator to generate a network copolymer-type dehydration reducer with a micro-crosslinked interlocking structure.

[0046] Example 2

[0047] Weigh 58g of 2-acrylamido-2-methylpropanesulfonic acid and 12g of maleic anhydride, dissolve them in 510g of water, and slowly add sodium hydroxide to adjust the pH of the system to 6-7; then add 20g of N,N-diethylacrylamide, 10g of N-vinylcaprolactam and 1.5g of triallylamine and mix well; then add 0.2g of mercaptoethanol, 0.1g of tetrasodium ethylenediaminetetraacetate and 0.8g of potassium persulfate to obtain a mixed system; heat the mixed system to 50℃ under stirring at 200 rpm, and dissolve 0.37g of sodium sulfite in 50g of water to prepare a reducing agent solution. Slowly add the reducing agent solution dropwise to the mixed system at 50℃ over 40min. After the addition is complete, slowly heat to 75℃ and maintain this temperature for 3h. Then, allow it to cool naturally to room temperature to obtain a micro-crosslinked interlocking type dehydration reducer.

[0048] Example 3

[0049] Weigh 55g of 2-acrylamido-2-methylpropanesulfonic acid and 5g of itaconic acid, dissolve them in 680g of water, and slowly add sodium hydroxide to adjust the pH of the system to 6-7; then add 25g of N-hydroxyethylacrylamide, 15g of N-vinylcaprolactam and 0.5g of pentaerythritol tetraallyl ether and mix well; then add 3g of isopropanol, 0.5g of disodium ethylenediaminetetraacetate and 1g of azobisisobutyramidine hydrochloride to obtain a mixed system; heat the mixed system to 55℃ under stirring at 150 rpm, and dissolve 0.56g of ferrous sulfate in 50g of water to prepare a reducing agent solution. Slowly add the reducing agent solution dropwise to the mixed system at 55℃ over 60min. After the addition is complete, slowly heat to 80℃ and maintain this temperature for 5h. Then, allow it to cool naturally to room temperature to obtain a micro-crosslinked interlocking type dehydration reducer.

[0050] Example 4

[0051] Weigh 37g of 2-acrylamido-2-methylpropanesulfonic acid, 5g of maleic acid, and 10g of fumaric acid, dissolve them in 750g of water, and slowly add sodium hydroxide to adjust the pH of the system to 6-7; then add 28g of diacetone acrylamide, 20g of vinylcyclopentane, and 2g of triallylamine and mix well; then add 1.5g of 2-mercaptobenzoic acid, 1.5g of diethylenetriaminepentaacetic acid, and 0.6g of benzoyl peroxide to obtain a mixed system; heat the mixed system to 60℃ under stirring at 100 rpm, and dissolve 0.3g of N,N-dimethylaniline in 50g of water to prepare a reducing agent solution. Slowly add the reducing agent solution dropwise to the 60℃ mixed system over 30min. After the addition is complete, slowly heat to 65℃ and maintain this temperature for 6h. Then, allow it to cool naturally to room temperature to obtain a micro-crosslinked interlocking type dehydration reducer.

[0052] Example 5

[0053] Weigh 67g of 2-acrylamido-2-methylpropanesulfonic acid, 4g of itaconic acid, and 4g of acrylic acid, dissolve them in 250g of water, and slowly add sodium hydroxide to adjust the pH of the system to 6-7; then add 15g of N-isopropylacrylamide, 10g of N-vinylcaprolactam, and 0.5g of pentaerythritol tetraallyl ether and mix well; then add 0.8g of mercaptopropionic acid, 1.2g of diethylenetriaminepentaacetic acid, and 0.3g of cumene hydroperoxide to obtain a mixed system; heat the mixed system to 50℃ under stirring at 150 rpm, and dissolve 0.35g of sodium dithionite in 50g of water to prepare a reducing agent solution. Slowly add the reducing agent solution dropwise to the mixed system at 50℃ over 50 minutes. After the addition is complete, slowly heat to 75℃ and maintain this temperature for 2 hours. Then, allow it to cool naturally to room temperature to obtain a micro-crosslinked interlocking type dehydration reducer.

[0054] Example 6

[0055] Weigh 64g of 2-acrylamido-2-methylpropanesulfonic acid, 2g of maleic anhydride, and 4g of acrylic acid, dissolve them in 350g of water, and slowly add sodium hydroxide to adjust the pH of the system to 6-7; then add 15g of N-n-butoxymethacrylamide, 5g of vinylcyclopentane, and 1g of triallylamine and mix well; then add 0.05g of mercaptopropionic acid, 0.1g of disodium ethylenediaminetetraacetate, and 0.5g of ammonium persulfate to obtain a mixed system; heat the mixed system to 40℃ under stirring at 200 rpm, and dissolve 0.23g of sodium bisulfite in 50g of water to prepare a reducing agent solution. Slowly add the reducing agent solution dropwise to the mixed system at 40℃ over 60min. After the addition is complete, slowly heat to 70℃ and maintain this temperature for 4h of reaction, then allow it to cool naturally to room temperature to obtain a micro-crosslinked interlocking type dehydration reducer.

[0056] Comparative Example 1

[0057] Weigh 74g of 2-acrylamido-2-methylpropanesulfonic acid, 2g of maleic anhydride, and 4g of acrylic acid, dissolve them in 350g of water, and slowly add sodium hydroxide to adjust the pH of the system to 6-7; then add 15g of N-n-butoxymethacrylamide and 5g of N-vinylpyrrolidone and mix well; then add 0.05g of mercaptopropionic acid, 0.05g of disodium ethylenediaminetetraacetate, and 0.5g of ammonium persulfate to obtain a mixed system; heat the mixed system to 45℃ under stirring at 200 rpm, and dissolve 0.23g of sodium bisulfite in 50g of water to prepare a reducing agent solution. Slowly add the reducing agent solution dropwise to the mixed system at 45℃ over 30min. After the addition is complete, slowly heat to 70℃ and maintain this temperature for 4h. Then, allow it to cool naturally to room temperature to obtain a dehydration reducer.

[0058] Comparative Example 2

[0059] Weigh 79g of 2-acrylamido-2-methylpropanesulfonic acid, 2g of maleic anhydride, and 4g of acrylic acid, dissolve them in 350g of water, and slowly add sodium hydroxide to adjust the pH of the system to 6-7; then add 15g of N,N-dimethylacrylamide and mix well; then add 0.05g of disodium ethylenediaminetetraacetate and 0.5g of ammonium persulfate to obtain a mixed system; heat the mixed system to 45℃ under stirring at 200 rpm, and dissolve 0.23g of sodium bisulfite in 50g of water to prepare a reducing agent solution. Slowly add the reducing agent solution dropwise to the mixed system at 45℃ over 30min. After the addition is complete, slowly heat to 70℃ and maintain this temperature for 4h. Then, allow it to cool naturally to room temperature to obtain a dehydration reducer.

[0060] Comparative Example 3

[0061] Weigh 74g of 2-acrylamido-2-methylpropanesulfonic acid and dissolve it in 350g of water. Slowly add sodium hydroxide to adjust the pH of the system to 6-7. Then add 15g of N-butoxymethacrylamide, 5g of N-vinylpyrrolidone, and 1g of triallylamine and mix well. Then add 0.05g of mercaptopropionic acid, 0.05g of disodium ethylenediaminetetraacetate, and 0.5g of ammonium persulfate to obtain a mixed system. Heat the mixed system to 45℃ under stirring at 200 rpm. Dissolve 0.23g of sodium bisulfite in 50g of water to prepare a reducing agent solution. Slowly add the reducing agent solution dropwise to the mixed system at 45℃ over 30min. After the addition is complete, slowly heat to 70℃ and maintain this temperature for 4h. Then allow it to cool naturally to room temperature to obtain the dehydration reducer.

[0062] Comparative Example 4

[0063] Weigh 74g of 2-acrylamido-2-methylpropanesulfonic acid, 2g of maleic anhydride, and 4g of acrylic acid, dissolve them in 350g of water, and slowly add sodium hydroxide to adjust the pH of the system to 6-7; then add 15g of N-n-butoxymethacrylamide and 1g of triallylamine and mix well; then add 0.05g of mercaptopropionic acid, 0.05g of disodium ethylenediaminetetraacetate, and 0.5g of ammonium persulfate to obtain a mixed system; heat the mixed system to 45℃ under stirring at 200 rpm, and dissolve 0.23g of sodium bisulfite in 50g of water to prepare a reducing agent solution. Slowly add the reducing agent solution dropwise to the mixed system at 45℃ over 30min. After the addition is complete, slowly heat to 70℃ and maintain this temperature for 4h of reaction, then allow it to cool naturally to room temperature to obtain a dehydration reducer.

[0064] Comparative Example 5

[0065] Weigh 74g of 2-acrylamido-2-methylpropanesulfonic acid, 2g of maleic anhydride, and 4g of acrylic acid, dissolve them in 350g of water, and slowly add sodium hydroxide to adjust the pH of the system to 6-7; then add 15g of acrylamide, 5g of N-vinylpyrrolidone, and 1g of N,N-methylenebisacrylamide and mix well; then add 0.05g of mercaptopropionic acid, 0.05g of disodium ethylenediaminetetraacetate, and 0.5g of ammonium persulfate to obtain a mixed system; heat the mixed system to 45℃ under stirring at 200 rpm, and dissolve 0.23g of sodium bisulfite in 50g of water to prepare a reducing agent solution. Slowly add the reducing agent solution dropwise to the mixed system at 45℃ over 30min. After the addition is complete, slowly heat to 70℃ and maintain this temperature for 4h. Then, allow it to cool naturally to room temperature to obtain a dehydration reducer.

[0066] Comparative Example 6

[0067] Weigh 74g of 2-acrylamido-2-methylpropanesulfonic acid, 2g of maleic anhydride, and 4g of acrylic acid, dissolve them in 350g of water, and slowly add sodium hydroxide to adjust the pH of the system to 6-7; then add 15g of N-n-butoxymethacrylamide, 5g of N-vinylpyrrolidone, and 1g of triallylamine and mix well; then add 0.5g of ammonium persulfate to obtain a mixed system; heat the mixed system to 45℃ under stirring at 200 rpm, and dissolve 0.23g of sodium bisulfite in 50g of water to prepare a reducing agent solution. Slowly add the reducing agent solution dropwise to the mixed system at 45℃ over 30min. After the addition is complete, slowly heat to 70℃ and maintain this temperature for 4h of reaction, then allow it to cool naturally to room temperature to obtain a dehydration reducer.

[0068] Comparative Example 7

[0069] Weigh 100g of 2-acrylamido-2-methylpropanesulfonic acid, 2g of maleic anhydride, and 4g of acrylic acid, dissolve them in 350g of water, and slowly add sodium hydroxide to adjust the pH of the system to 6-7; then add 3g of N-butoxymethacrylamide, 5g of N-vinylpyrrolidone, and 1g of triallylamine and mix well; then add 0.05g of mercaptopropionic acid, 0.05g of disodium ethylenediaminetetraacetate, and 0.5g of ammonium persulfate to obtain a mixed system; heat the mixed system to 45℃ under stirring at 200 rpm, and dissolve 0.23g of sodium bisulfite in 50g of water to prepare a reducing agent solution. Slowly add the reducing agent solution dropwise to the mixed system at 45℃ over 30min. After the addition is complete, slowly heat to 70℃ and maintain this temperature for 4h. Then, allow it to cool naturally to room temperature to obtain a dehydration reducer.

[0070] Comparative Example 8

[0071] Weigh 20g of 2-acrylamido-2-methylpropanesulfonic acid, 2g of maleic anhydride, and 4g of acrylic acid, dissolve them in 350g of water, and slowly add sodium hydroxide to adjust the pH of the system to 6-7; then add 15g of N-butoxymethacrylamide, 40g of N-vinylpyrrolidone, and 8g of triallylamine and mix well; then add 0.05g of mercaptopropionic acid, 0.05g of disodium ethylenediaminetetraacetate, and 0.5g of ammonium persulfate to obtain a mixed system; heat the mixed system to 45℃ under stirring at 200 rpm, and dissolve 0.23g of sodium bisulfite in 50g of water to prepare a reducing agent solution. Slowly add the reducing agent solution dropwise to the mixed system at 45℃ over 30min. After the addition is complete, slowly heat to 70℃ and maintain this temperature for 4h. Then, allow it to cool naturally to room temperature to obtain a dehydration reducer.

[0072] Test case

[0073] When the experimental temperature is less than 180℃, the performance of the fluid loss reducer shall be evaluated in accordance with the methods described in GB / T 19139-2012 "Test Methods for Oil Well Cement" and SY / T 5504.2-2013 "Evaluation Methods for Oil Well Cement Admixtures Part 2: Fluid Loss Reducers". When the experimental temperature is greater than or equal to 180℃, the evaluation method for the water loss reduction performance of the water loss reducing agent is as follows: Place the cement slurry system containing the water loss reducing agent in the slurry cup of the high-temperature and high-pressure thickener. After completing the thickening test steps in the above standard, raise the temperature to the corresponding experimental temperature and pressure within the set time, and maintain constant temperature and pressure for 30 minutes. Then, cool down to about 90℃, remove the cement slurry system, and clean the oil on the top of the cement slurry system. Then, use a constant speed stirrer to stir the cement slurry system evenly, and place it in the preheated high-temperature and high-pressure water loss tester cylinder. After completing the operation in the above standard, slowly raise the temperature to the corresponding experimental temperature, and ensure that the pressure difference between the top of the cylinder and the bottom condenser is 6.9MPa. After raising the temperature to the experimental temperature, conduct the water loss test and record the water loss in 30 minutes. The API water loss of the cement slurry system is twice the water loss in 30 minutes.

[0074] The formula for cement slurry system with an experimental temperature of 20-90℃ is: 600g Grade G oil well cement (HSR) + x% fluid loss reducer + (44-x)% water.

[0075] The cement slurry system formula for an experimental temperature of 120-150℃ is as follows: 600g Grade G oil well cement (HSR) + x% fluid loss reducer + 35% quartz sand (200 mesh) + 0.6% high-temperature stabilizer DRK-3S + 1% dispersant DRS-1S + 2% ultra-high temperature retarder DRH-3L + 0.5% defoamer DRX-1L + (55-x)% water. The density of the cement slurry system is 1.90 g / cm³. 3 .

[0076] The cement slurry system formula for an experimental temperature of 180-200℃ is as follows: 500g Grade G oil well cement (HSR) + x% fluid loss reducer + 50% quartz sand (200 mesh) + 1% high-temperature stabilizer DRK-3S + 3% ultra-high temperature suspension stabilizer DRK-4L + 2% dispersant DRS-1S + 3% ultra-high temperature retarder DRH-3L + 0.5% defoamer DRX-1L + (60-x)% water. The density of the cement slurry system is 1.90 g / cm³. 3 .

[0077] The cement slurry system formulation for experimental temperatures of 220-245℃ is as follows: 500g Grade G oil well cement (HSR) + x% fluid loss reducer + 70% quartz sand (200 mesh) + 1% high-temperature stabilizer DRK-3S + 3% ultra-high temperature suspension stabilizer DRK-4L + 2% dispersant DRS-1S + 5% ultra-high temperature retarder DRH-3L + 0.5% defoamer DRX-1L + 10% high-temperature strength degradation inhibitor DRB-3S + (70-x)% water. The density of the cement slurry system is 1.90 g / cm³. 3 .

[0078] It should be noted that the percentages (%) in the above cement slurry system formulation represent the mass percentage of each material in the G-grade oil well cement, that is, the proportion of each material based on the mass of the G-grade oil well cement as 100%. The dosage of the fluid loss reducing agent in the above cement slurry system is shown in Table 1. In addition, the water in the above cement slurry system formulation is fresh water or saturated brine (i.e., 36% NaCl aqueous solution), as specifically shown in Table 1.

[0079] The comprehensive performance evaluation results of the water loss reducing agents prepared in the above embodiments and comparative examples are shown in Table 1.

[0080] Table 1

[0081] In Table 1, "*" represents the mass concentration of water, and "—" represents that it was not measured.

[0082] As shown in Table 1, with increasing experimental temperature, the API water loss of the cement slurry system with the same formulation containing the water-reducing agent of this invention changes little, and the water-reducing agent of this invention has a temperature resistance of up to 245℃ and is also resistant to saturated salt water. When the experimental temperature is 20-150℃, the API water loss of the cement slurry system with 3% of the water-reducing agent prepared in Example 1 of this invention can be controlled below 50mL, and it has good settling stability, no free liquid, and high 24h cement stone compressive strength. When the experimental temperature is 180-245℃, by appropriately increasing the dosage of the water-reducing agent, the API water loss of the cement slurry system can also be reduced to below 50mL, and the cement slurry settling time does not exceed 30s, which can meet the requirements of on-site mixing. In addition, with increasing experimental temperature, the density difference of the cement slurry system increases slightly, but the settling stability (i.e., density difference) can be controlled within 0.03 / cm³. 3 Below this, and with no free liquid, it has no adverse effect on the mechanical strength of high-temperature cement stone. Under saturated saline conditions at 245℃, the API water loss of the cement slurry system with 5% of the water-reducing agent of Example 1 of this invention is also less than 50 mL. Simultaneously, under 245℃ conditions, the cement slurry systems with the water-reducing agents of Examples 1-6 of this invention exhibit higher API water loss, mortar settling time, settling stability, and mechanical strength of the cement stone.

[0083] Furthermore, compared with Comparative Example 1, the water loss reduction performance, settling stability, and cement stone compressive strength of the cement slurry system with the water loss reduction agent prepared in Example 1 of this invention at 90℃ are not significantly different from those of Comparative Example 1; however, the various properties of the fresh water and saturated salt water cement slurry systems with the water loss reduction agent prepared in Example 1 of this invention at 245℃ are far superior to those of Comparative Example 1; indicating that the micro-crosslinked interlocking water loss reduction agent of this invention has a superior molecular structure and excellent water loss reduction performance, settling stability, and resistance to ultra-high temperature and salt.

[0084] The water loss reducing agent prepared in Comparative Example 2 is a typical linear anionic polymer. At 90°C, its performance is not much different from that of the water loss reducing agent prepared in Example 1 of this invention. However, at 245°C, the freshwater cement slurry system with the water loss reducing agent prepared in Comparative Example 2 has a large API water loss, poor settling stability, and a significant impact on the compressive strength of cement stone. The water loss of the brine cement slurry system is uncontrollable, and other properties are further reduced.

[0085] The difference between Comparative Example 3 and Example 1 is that the vinyl-containing carboxylic acid or its derivative monomers are omitted; the difference between Comparative Example 4 and Example 1 is that the vinyl cyclic monomer is omitted; the difference between Comparative Example 5 and Example 1 is that N-n-butoxymethacrylamide is replaced with acrylamide, and the crosslinking agent is replaced with N,N-methylenebisacrylamide; the difference between Comparative Example 6 and Example 1 is that the molecular weight regulator and chelating agent are omitted; Comparative Examples 7 and 8 are examples where the proportions of certain monomers or crosslinking agents used in Example 1 are adjusted to be outside the scope of this invention. It can be seen that the water loss reducing agents of Comparative Examples 3-8 all exhibit problems such as high API water loss, poor sedimentation stability, and significant impact on the compressive strength of cement stone at 245°C, and their thickening curves show bulging.

[0086] Figure 1 shows the effect of different curing times at 245℃ and 130MPa on the API water loss of cement slurry systems (fresh water) containing 5% of the water loss reducing agent prepared in Example 1 and Comparative Example 1, respectively. As can be seen from Figure 1, the water loss of the cement slurry system containing Example 1 changes less with curing time, and the API water loss of the cement slurry system within the 10-hour curing time at 245℃ is consistently below 50mL, indicating that its molecular structure and performance are stable under ultra-high temperature conditions, meeting the technical requirements for ultra-deep and ultra-long cementing operations at ultra-high temperatures. In contrast, the water loss of the cement slurry system containing Comparative Example 1 gradually increases with prolonged curing time. The API water loss of the cement slurry system cured at 245℃ for 2 hours exceeds 100mL, with even greater water loss in the later stages, severely affecting the overall performance and construction safety of the ultra-deep and ultra-high temperature cement slurry system for ultra-high temperature cementing.

[0087] Figure 2 shows the effect of different salt concentrations on the API water loss of the cement slurry system doped with the water loss reducing agent prepared in Example 1 at 245℃ and 130MPa. As can be seen from Figure 2, the water loss of the cement slurry system doped with 4% of Example 1 gradually increases with increasing salt concentration, but the API water loss of the saturated brine system remains below 100mL. The water loss of the cement slurry system doped with 5% of Example 1 is less affected by salt concentration, and the API water loss of the saturated brine cement slurry system can be controlled below 50mL, indicating that the water loss reducing agent prepared in Example 1 of this invention has strong resistance to ultra-high temperature and salt.

[0088] Figure 3 shows the thickening curve of the cement slurry system with 4% of the water loss reducing agent prepared in Example 1 at 245℃ and 130MPa. As can be seen from Figure 3, the thickening curve of the cement slurry system under ultra-high temperature and high pressure conditions is normal, with no abnormal fluctuations in temperature and pressure. The initial consistency of the system is 15 Bc, and the consistency changes only slightly with increasing temperature, eventually maintaining around 11 Bc. The thickening time of the cement slurry system is 450 min. This indicates that the water loss reducing agent has virtually no adverse effect on the initial flow state, high-temperature settling stability, and thickening performance of the cement slurry system.

[0089] In summary, the micro-crosslinked interlocking fluid loss reducing agent of this invention exhibits excellent temperature, pressure, and salt resistance, with a temperature and pressure resistance up to 245℃ and 130MPa, and salt resistance up to saturation. It also demonstrates excellent fluid loss reducing performance and significantly improves the settling stability and mechanical properties of cement paste under ultra-high temperature conditions. Furthermore, it has virtually no adverse effect on the thickening performance of the cement paste system, maintaining a normal thickening curve. Moreover, it has a wide applicable temperature range, suitable for temperatures from 20℃ to 245℃. Therefore, the micro-crosslinked interlocking fluid loss reducing agent of this invention possesses superior comprehensive performance, overcoming the shortcomings of existing polymer-based fluid loss reducing agents, such as poor temperature and salt resistance, strong high-temperature dilution, poor settling stability of cement paste systems, inverted thickening time, and significant impact on the mechanical strength of cement paste. It shows promising application prospects in cementing fields such as deep wells, ultra-deep wells, extra-deep wells, high-pressure gas wells, unconventional oil and gas wells, gas storage wells, and geothermal wells.

[0090] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a micro-crosslinked interlocking type water loss reducing agent, comprising the following steps: (1) Mix 30-90 parts by weight of 2-acrylamido-2-methylpropanesulfonic acid, 3-20 parts by weight of vinyl-containing carboxylic acid or its derivative monomers and water, and add a pH adjuster to adjust the pH of the system to 6-7; then add 5-30 parts by weight of modified acrylamide monomer, 2-30 parts by weight of vinyl cyclic monomer and 0.1-3 parts by weight of crosslinking agent, wherein the crosslinking agent includes compounds containing three alkenyl or four alkenyl groups; then add 0.02-3 parts by weight of molecular weight adjuster, 0.05-2 parts by weight of chelating agent and 0.2-1 parts by weight of oxidant to obtain a mixed system; (2) Add an aqueous solution containing 0.2-1 parts by weight of reducing agent dropwise to the mixed system. After the addition is complete, react for a period of time to obtain the micro-crosslinked interlocking type dehydration reducer.

2. The preparation method of the micro-crosslinked interlocking type water loss reducing agent according to claim 1, wherein, The weight ratio of the 2-acrylamido-2-methylpropanesulfonic acid, the vinyl-containing carboxylic acid or its derivative monomer, the modified acrylamide monomer, the vinyl cyclic monomer, the crosslinking agent, the molecular weight regulator, the chelating agent, the oxidizing agent and the reducing agent is (37-74):(5-15):(15-28):(5-20):(0.5-2):(0.05-3):(0.05-1.5):(0.3-1):(0.23-0.56).

3. The preparation method of the micro-crosslinked interlocking type water loss reducing agent according to claim 1, wherein, In step (1), the vinyl-containing carboxylic acid or derivative monomer includes one or more of acrylic acid, itaconic acid, maleic anhydride, maleic acid and fumaric acid.

4. The preparation method of the micro-crosslinked interlocking type water loss reducing agent according to claim 1, wherein, In step (1), the amount of water used is 230-850 parts by weight, based on 30-90 parts by weight of 2-acrylamido-2-methylpropanesulfonic acid.

5. The preparation method of the micro-crosslinked interlocking type water loss reducing agent according to claim 1, wherein, In step (1), the modified acrylamide monomer includes one or more of N-butoxymethacrylamide, N,N-diethylacrylamide, N-hydroxyethylacrylamide, diacetone acrylamide and N-isopropylacrylamide.

6. The preparation method of the micro-crosslinked interlocking type water loss reducing agent according to claim 1, wherein, In step (1), the vinyl cyclic monomer includes one or more of N-vinylpyrrolidone, N-vinylcaprolactam, and vinylcyclopentane.

7. The preparation method of the micro-crosslinked interlocking type water loss reducing agent according to claim 1, wherein, In step (1), the crosslinking agent includes one or both of triallylamine and pentaerythritol tetraallyl ether.

8. The preparation method of the micro-crosslinked interlocking type water loss reducing agent according to claim 1, wherein, In step (1), the molecular weight regulator includes one or more of mercaptopropionic acid, mercaptoethanol, isopropanol, dodecyl mercaptoethanol, hydroquinone, and 2-mercaptobenzoic acid.

9. The preparation method of the micro-crosslinked interlocking type water loss reducing agent according to claim 1, wherein, In step (1), the chelating agent includes one or more of ethylenediaminetetraacetic acid, disodium ethylenediaminetetraacetic acid, tetrasodium ethylenediaminetetraacetic acid, and diethylenetriaminepentaacetic acid.

10. The preparation method of the micro-crosslinked interlocking type water loss reducing agent according to claim 1, wherein, In step (1), the oxidant includes one or more of ammonium persulfate, potassium persulfate, azobisisobutyrazoline hydrochloride, azobisisobutyramidine hydrochloride, hydrogen peroxide, benzoyl peroxide and cumene hydrogen peroxide.

11. The preparation method of the micro-crosslinked interlocking type water loss reducing agent according to claim 1, wherein, In step (2), before adding the aqueous solution containing 0.2-1 parts by weight of reducing agent to the mixed system, the process further includes heating the mixed system to 30-60°C under stirring at 150±50 rpm.

12. The preparation method of the micro-crosslinked interlocking type water loss reducing agent according to claim 1, wherein, In step (2), the reducing agent includes one or more of sodium sulfite, sodium bisulfite, ferrous sulfate, ferrous chloride, N,N-dimethylaniline, and sodium dithionite.

13. The preparation method of the micro-crosslinked interlocking type water loss reducing agent according to claim 1, wherein, In step (2), the aqueous solution containing 0.2-1 parts by weight of reducing agent is added dropwise to the mixed system over a time of 30-60 minutes, and the temperature of the mixed system is 30-60°C during the process of adding the aqueous solution containing 0.2-1 parts by weight of reducing agent to the mixed system.

14. The preparation method of the micro-crosslinked interlocking type water loss reducing agent according to claim 1, wherein, In step (2), the reaction temperature is 60-90℃ and the reaction time is 1-6h.

15. A micro-crosslinked interlocking type water loss reducing agent, prepared by the method of any one of claims 1-14.

16. A cementing slurry system, said cementing slurry system comprising at least: Cement, and the micro-crosslinked interlocking water loss reducing agent as described in claim 15.

17. The cementing slurry system according to claim 16, wherein, The cementing slurry system comprises: 100 parts by weight of cement, 3-5 parts by weight of the micro-crosslinked interlocking fluid loss reducing agent, 0-80 parts by weight of quartz sand, 0-6 parts by weight of stabilizer, 0-3 parts by weight of dispersant, 0-6 parts by weight of retarder, 0-0.5 parts by weight of defoamer, 0-15 parts by weight of high-temperature strength degradation inhibitor, and 40-70 parts by weight of water.

18. The cementing slurry system according to claim 16, wherein, The density of the cement slurry system is 1.90 ± 0.02 g / cm³. 3 .

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