Cement slurry type plugging material resistant to downhole fluid dilution and its preparation method and application

Abstract

The application provides a cement slurry type plugging material resistant to dilution of downhole fluid and a preparation method and application thereof. The cement slurry type plugging material comprises oil well cement, spherical weighting agent, high-temperature resistant fluid loss additive, high-temperature resistant suspending agent, high-temperature resistant retarder, high-temperature resistant toughening agent and high-temperature resistant flocculating agent. The high-temperature resistant flocculating agent has a molecular chain structure of mutual adsorption and winding, and the molecular chain is connected with an amide group and / or a sulfonate group, so that the anti-dilution capacity of the plugging material to downhole fluid can be significantly improved. The cement slurry type plugging material provided by the application has strong anti-dilution capacity to downhole fluid, good residence capacity and high pressure sealing strength, can quickly treat the malignant leakage of high-temperature deep wells and super-deep wells, and is expected to solve the malignant leakage problem faced by deep complex formations.

Description

Technical Field

[0001] This invention belongs to the field of drilling technology and relates to a plugging material, particularly a cement slurry-based plugging material resistant to downhole fluid dilution, its preparation method, and its application. Background Technology

[0002] Well leakage is a serious and complex issue during drilling and completion that remains unresolved. It significantly increases non-productive time, consumes large amounts of drilling fluid and plugging materials, causing substantial economic losses, and can lead to complex accidents such as well collapse, stuck pipe, or blowouts, impacting the achievement of geological objectives. Currently, major basins all face prominent well leakage problems, severely restricting the efficient development of oil and gas resources. In particular, severe well leakage is the primary drilling technology challenge hindering the improvement of quality and efficiency in oil and gas drilling projects.

[0003] As exploration and development delve deeper into complex formations, the probability of severe well leakage is increasing, potentially leading to significant economic losses. Leakage pathways for severe well leakage primarily include dissolution pores, fractures / faults, caverns, and underground rivers, with fractures / cavities being the most common. These pathways are characterized by difficulties in determining their size and shape, limited material transport space, and stringent requirements for effective plugging. Large fractures and cavernous complex formations have large leakage channels, making conventional plugging materials easily diluted, eroded, and washed away by formation fluids, thus failing to effectively remain in the leakage zone and form an effective sealing layer. Furthermore, conventional plugging materials are also ineffective at sealing large-channel leakage zones such as fractures and caverns.

[0004] Plugging large fractures and complex karst formations presents significant challenges, placing higher demands on the performance of leak prevention and plugging materials. Currently, a wide variety of plugging materials are available to address severe leaks, such as polymer gels, expandable particles, shape memory materials, and curable materials. However, these materials still face bottlenecks such as insufficient retention capacity and frequent re-leakage in some formations. They generally suffer from drawbacks such as low success rates, long processing times, low pressure resistance after plugging, and difficulty in replicating the effectiveness of plugging work.

[0005] Therefore, it is evident that providing a plugging material that enhances resistance to downhole fluid dilution and pressure bearing capacity, improves retention capacity, and increases plugging strength, thereby enabling rapid repair of severe leakage in high-temperature deep and ultra-deep wells, has become an urgent problem that needs to be solved by those skilled in the art. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the present invention aims to provide a cement slurry-based plugging material resistant to downhole fluid dilution, its preparation method, and its application. The cement slurry-based plugging material has strong resistance to downhole fluid dilution, good retention capacity, and high pressure-bearing sealing strength. It can quickly treat severe leakage in high-temperature deep wells and ultra-deep wells, and is expected to solve the problem of severe leakage in deep and complex formations.

[0007] To achieve this objective, the present invention adopts the following technical solution:

[0008] In a first aspect, the present invention provides a cement slurry-based plugging material that resists dilution by downhole fluids. The cement slurry-based plugging material includes oil well cement, spherical weighting agent, high-temperature fluid loss reducing agent, high-temperature suspending agent, high-temperature retarder, high-temperature toughening agent, and high-temperature flocculant.

[0009] The high-temperature resistant flocculant has a molecular chain structure in which the molecules are mutually adsorbed and entangled, and the molecular chains are connected with amide groups and / or sulfonate groups.

[0010] The high-temperature resistant water loss reducing agent, high-temperature resistant suspending agent, high-temperature resistant retarder, high-temperature resistant toughening agent, and high-temperature resistant flocculant have a temperature tolerance of ≥200℃, for example, 200℃, 210℃, 220℃, 230℃, 240℃, 250℃, 260℃, 270℃, or 280℃, but are not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0011] The cement slurry-based plugging material provided by this invention contains a high-temperature resistant flocculant with a specific molecular structure. The amide and / or sulfonate groups on its molecular chain readily form hydrogen bonds with water molecules, thereby enhancing its affinity for water. Furthermore, the mutually adsorbed and entangled molecular chain structure and hydrogen bonds together form a three-dimensional network structure, encapsulating the mixing water and solid particles, thus making them less susceptible to scouring by formation water molecules. Ultimately, this significantly improves the plugging material's resistance to dispersion and flocculation, giving it excellent resistance to downhole fluid dilution. Combined with the synergistic effect of other components, it further enhances... This method enhances the retention capacity, temperature resistance, and pressure-bearing sealing capacity of plugging materials, with a leakage channel adaptability range of up to 10mm, a pressure-bearing sealing capacity exceeding 20MPa, and a flexural strength greater than 10MPa. It can solve the problems of poor applicability of conventional leakage prevention and plugging technologies, low success rate of plugging on the first attempt, and serious repeated leakage caused by malignant well leakage in complex formations such as large fractures and karst caves. It can adapt to malignant well leakage formations with different fracture widths, significantly saves drilling time, reduces drilling costs, and enables safe and rapid drilling in complex formations of deep and ultra-deep wells, which is conducive to large-scale promotion and application.

[0012] Preferably, the cement slurry-based sealing material comprises the following components by weight:

[0013]

[0014] The spherical weighting agent comprises 20-60 parts by weight, for example, 20, 25, 30, 35, 40, 45, 50, 55, or 60 parts; the high-temperature water loss reducing agent comprises 1-4 parts by weight, for example, 1, 1.5, 2, 2.5, 3, 3.5, or 4 parts; the high-temperature suspending agent comprises 2-8 parts by weight, for example, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, or 8 parts; and the high-temperature retarder comprises 3-6 parts by weight, for example, 3, 3.5, 4, 5, 6, 7, 8 parts. The high-temperature toughening agent can be 4, 4.5, 5, 5.5, or 6 parts by weight, and the high-temperature toughening agent can be 5-12 parts by weight, for example, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10, 10.5, 11, 11.5, or 12 parts by weight. The high-temperature flocculant can be 1-8 parts by weight, for example, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, or 8 parts by weight, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0015] Preferably, the oil well cement includes Grade G oil well cement.

[0016] Preferably, the G-grade oil well cement comprises the following components by mass percentage;

[0017]

[0018] The CaO mass percentage is 60%-70%, for example, it can be 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, or 70%; the Al2O3 mass percentage is 1%-2%, for example, it can be 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, or 2%; the SiO2 mass percentage is 15%-20%, for example, it can be 15%, 15.5%, 16%, 16.5%, 17%, 17.5%, 18%, 18.5%, 19%, 19.5%, or 20%; and the Fe2O3 mass percentage is 2%-6%, for example, it can be 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, or 5.5%. The percentage of MgO is 1%-2%, for example, it can be 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, or 2%. The percentage of SO3 is 2%-4%, for example, it can be 2%, 2.2%, 2.4%, 2.6%, 2.8%, 3%, 3.2%, 3.4%, 3.6%, 3.8%, or 4%. The percentage of loss on ignition is 0.5%-2%, for example, it can be 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, or 2%, but is not limited to the listed values; other unlisted values ​​within this range also apply.

[0019] Preferably, the spherical weighting agent comprises any one or a combination of at least two of spherical manganese tetroxide powder, spherical ilmenite powder, or spherical galena powder. Typical but non-limiting combinations include combinations of spherical manganese tetroxide powder and spherical ilmenite powder, combinations of spherical ilmenite powder and spherical galena powder, combinations of spherical manganese tetroxide powder and spherical galena powder, or combinations of spherical manganese tetroxide powder, spherical ilmenite powder, and spherical galena powder. More preferably, it comprises spherical manganese tetroxide powder and / or spherical ilmenite powder, and more preferably, it comprises spherical manganese tetroxide powder.

[0020] Preferably, the high-temperature dehydration agent comprises a quaternary polymer of 2-acrylamido-2-methylpropanesulfonic acid / N-vinylpyrrolidone / diallyldimethylammonium chloride / itaconic acid and / or a terpolymer of 2-acrylamido-2-methylpropanesulfonic acid / N,N-dimethylacrylamide / maleic anhydride, and more preferably a quaternary polymer of 2-acrylamido-2-methylpropanesulfonic acid / N-vinylpyrrolidone / diallyldimethylammonium chloride / itaconic acid.

[0021] Preferably, the high-temperature suspending agent comprises any one or a combination of at least two of polyacrylamide, magnesium aluminum silicate, or warming agent. Typical but non-limiting combinations include a combination of polyacrylamide and magnesium aluminum silicate, a combination of magnesium aluminum silicate and warming agent, a combination of polyacrylamide and warming agent, or a combination of polyacrylamide, magnesium aluminum silicate, and warming agent. Preferably, it is magnesium aluminum silicate and / or warming agent, and more preferably magnesium aluminum silicate.

[0022] Preferably, the high-temperature retarder comprises any one or a combination of at least two of aluminum sulfate, sodium ethylenediaminetetramethylenephosphonate, or borax. Typical but non-limiting combinations include a combination of aluminum sulfate and sodium ethylenediaminetetramethylenephosphonate, a combination of sodium ethylenediaminetetramethylenephosphonate and borax, a combination of aluminum sulfate and borax, or a combination of aluminum sulfate, sodium ethylenediaminetetramethylenephosphonate, and borax. More preferably, it is a combination of sodium ethylenediaminetetramethylenephosphonate and borax.

[0023] Preferably, the mass ratio of sodium ethylenediaminetetramethylenephosphonate and borax in the high-temperature retarder is 1:(4-6), for example, it can be 1:4, 1:4.2, 1:4.4, 1:4.6, 1:4.8, 1:5, 1:5.2, 1:5.4, 1:5.6, 1:5.8 or 1:6, but it is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0024] Preferably, the high-temperature toughening agent comprises any one or a combination of at least two of engineering fibers, sepiolite fibers, or asbestos fibers. Typical but non-limiting combinations include combinations of engineering fibers and sepiolite fibers, combinations of sepiolite fibers and asbestos fibers, combinations of engineering fibers and asbestos fibers, or combinations of engineering fibers, sepiolite fibers, and asbestos fibers. It is more preferably sepiolite fibers and / or asbestos fibers, and more preferably sepiolite fibers.

[0025] Preferably, the density of the cement slurry-based sealing material is 1.60-2.70 g / cm³. 3 For example, it could be 1.60 g / cm³ 3 1.65g / cm 3 1.70g / cm 3 1.75g / cm 3 1.80g / cm 3 1.85g / cm 3 1.90g / cm 3 1.95g / cm 3 2.00g / cm 3 2.05g / cm 3 2.10 g / cm 3 2.15g / cm 3 2.20g / cm 32.25g / cm 3 2.30g / cm 3 2.35g / cm 3 2.40 g / cm 3 2.45g / cm 3 2.50g / cm 3 2.55g / cm 3 2.60g / cm 3 2.65g / cm 3 Or 2.70 g / cm 3 However, this does not apply to all values ​​listed; other unlisted values ​​within the same range also apply.

[0026] Secondly, the present invention provides a method for preparing a cement slurry-based sealing material as described in the first aspect, the method comprising the following steps:

[0027] (1) High-temperature resistant flocculant was prepared by soap-free emulsion polymerization;

[0028] (2) Mix well cement, spherical weighting agent, high temperature water loss reducing agent, high temperature suspension agent, high temperature retarder, high temperature toughening agent and high temperature flocculant obtained in step (1), add water and stir evenly to obtain cement slurry-type plugging material that resists dilution of downhole fluid.

[0029] Preferably, the soap-free emulsion polymerization method in step (1) includes: adding sodium styrene sulfonate, methacrylic acid, acrylamide, N,N-diethyl-2-acrylamide, N-vinylpyrrolidone and sodium 2-(methacrylic acid)ethanesulfonate to deionized water, stirring evenly, and adding ammonium persulfate solution dropwise during stirring, carrying out the polymerization reaction in a protective gas atmosphere, and washing and drying the solid and liquid in sequence to obtain a white powdery anti-high temperature flocculant.

[0030] Preferably, the polymerization reaction temperature is 70-80°C, for example, 70°C, 71°C, 72°C, 73°C, 74°C, 75°C, 76°C, 77°C, 78°C, 79°C or 80°C, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0031] Preferably, the polymerization reaction time is 20-30 hours, for example, 20 hours, 21 hours, 22 hours, 23 hours, 24 hours, 25 hours, 26 hours, 27 hours, 28 hours, 29 hours or 30 hours, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0032] Preferably, the protective gas includes any one or a combination of at least two of nitrogen, helium, or argon. Typical but non-limiting combinations include combinations of nitrogen and helium, helium and argon, nitrogen and argon, or combinations of nitrogen, helium, and argon, with nitrogen being more preferred.

[0033] Preferably, the washing solution used in the washing process includes ethanol.

[0034] Thirdly, the present invention provides an application of cement slurry-based plugging material as described in the first aspect in preventing or treating well leakage.

[0035] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0036] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0037] The cement slurry-based plugging material provided by this invention contains a high-temperature resistant flocculant with a specific molecular structure. The amide and / or sulfonate groups on its molecular chain readily form hydrogen bonds with water molecules, thereby enhancing its affinity for water. Furthermore, the mutually adsorbed and entangled molecular chain structure and hydrogen bonds together form a three-dimensional network structure, encapsulating the mixing water and solid particles, thus making them less susceptible to scouring by formation water molecules. Ultimately, this significantly improves the plugging material's resistance to dispersion and flocculation, giving it excellent resistance to downhole fluid dilution. Combined with the synergistic effect of other components, it further enhances... This method enhances the retention capacity, temperature resistance, and pressure-bearing sealing capacity of plugging materials, with a leakage channel adaptability range of up to 10mm, a pressure-bearing sealing capacity exceeding 20MPa, and a flexural strength greater than 10MPa. It can solve the problems of poor applicability of conventional leakage prevention and plugging technologies, low success rate of plugging on the first attempt, and serious repeated leakage caused by malignant well leakage in complex formations such as large fractures and karst caves. It can adapt to malignant well leakage formations with different fracture widths, significantly saves drilling time, reduces drilling costs, and enables safe and rapid drilling in complex formations of deep and ultra-deep wells, which is conducive to large-scale promotion and application. Detailed Implementation

[0038] The technical solution of the present invention will be further illustrated below through specific embodiments.

[0039] Example 1

[0040] This embodiment provides a cement slurry-based plugging material resistant to downhole fluid dilution and its preparation method. The preparation method includes the following steps:

[0041] (1) Using soap-free emulsion polymerization, 10 parts of sodium p-styrene sulfonate, 2 parts of methacrylic acid, 20 parts of acrylamide, 4 parts of N,N-diethyl-2-acrylamide, 6 parts of N-vinylpyrrolidone and 6 parts of sodium 2-(methacrylic acid) ethanesulfonate were added to 100 parts of deionized water and stirred evenly. During the stirring process, 1.6 parts of ammonium persulfate (dissolved in 5 parts of water) were added dropwise. The reaction temperature was controlled at 75°C and the reaction was stirred for 24 hours in a nitrogen atmosphere. After cooling to room temperature, the mixture was filtered, washed with ethanol and dried to obtain a white powdery anti-high temperature flocculant.

[0042] (2) According to the weight proportions, 100 parts of Grade G oil well cement, 40 parts of spherical weighting agent, 3 parts of high-temperature anti-water loss agent, 4 parts of high-temperature anti-suspending agent, 3 parts of high-temperature anti-retarding agent, 8 parts of high-temperature anti-toughening agent, and 3 parts of high-temperature anti-flocculator are mixed in a mixer, and then water is added and stirred evenly. The mixture is stirred at room temperature for 1 hour to obtain a density of 2.01 g / cm³. 3 The sealing grout is an aqueous solution of the sealing material.

[0043] In this embodiment, the chemical composition of the G-grade oil well cement by mass percentage is: 65% CaO, 2% Al2O3, 20% SiO2, 5% Fe2O3, 2% MgO, 4% SO3, and 2% loss on ignition; the spherical weighting agent is spherical manganese tetroxide powder; the high-temperature water loss reducing agent is a quaternary polymer of 2-acrylamido-2-methylpropanesulfonic acid / N-vinylpyrrolidone / diallyldimethylammonium chloride / itaconic acid; the high-temperature suspending agent is magnesium aluminum silicate; the high-temperature retarder is a mixture of sodium ethylenediaminetetramethylenephosphonate and borax in a mass ratio of 1:4; and the high-temperature toughening agent is sepiolite fiber.

[0044] Example 2

[0045] This embodiment provides a cement slurry-based plugging material resistant to downhole fluid dilution and its preparation method. The preparation method includes the following steps:

[0046] (1) Using soap-free emulsion polymerization, 10 parts of sodium p-styrene sulfonate, 2 parts of methacrylic acid, 20 parts of acrylamide, 4 parts of N,N-diethyl-2-acrylamide, 6 parts of N-vinylpyrrolidone and 6 parts of sodium 2-(methacrylic acid) ethanesulfonate were added to 100 parts of deionized water and stirred evenly. During the stirring process, 1.6 parts of ammonium persulfate (dissolved in 5 parts of water) were added dropwise. The reaction temperature was controlled at 75°C and the reaction was stirred for 24 hours in a nitrogen atmosphere. After cooling to room temperature, the mixture was filtered, washed with ethanol and dried to obtain a white powdery anti-high temperature flocculant.

[0047] (2) According to the weight proportions, 100 parts of Grade G oil well cement, 30 parts of spherical weighting agent, 1 part of high-temperature anti-water loss agent, 3 parts of high-temperature anti-suspending agent, 6 parts of high-temperature anti-retarding agent, 10 parts of high-temperature anti-toughening agent, and 2 parts of high-temperature anti-flocculation agent are mixed in a mixer, and then water is added and stirred evenly. The mixture is stirred at room temperature for 1 hour to prepare a solution with a density of 1.92 g / cm³. 3 The sealing grout is an aqueous solution of the sealing material.

[0048] In this embodiment, the chemical composition of the G-grade oil well cement by mass percentage is: 65% CaO, 2% Al2O3, 20% SiO2, 5% Fe2O3, 2% MgO, 4% SO3, and 2% loss on ignition; the spherical weighting agent is spherical manganese tetroxide powder; the high-temperature water loss reducing agent is a quaternary polymer of 2-acrylamido-2-methylpropanesulfonic acid / N-vinylpyrrolidone / diallyldimethylammonium chloride / itaconic acid; the high-temperature suspending agent is magnesium aluminum silicate; the high-temperature retarder is a mixture of sodium ethylenediaminetetramethylenephosphonate and borax in a mass ratio of 1:6; and the high-temperature toughening agent is sepiolite fiber.

[0049] Example 3

[0050] This embodiment provides a cement slurry-based plugging material resistant to downhole fluid dilution and its preparation method. The preparation method includes the following steps:

[0051] (1) Using soap-free emulsion polymerization, 10 parts of sodium p-styrene sulfonate, 2 parts of methacrylic acid, 20 parts of acrylamide, 4 parts of N,N-diethyl-2-acrylamide, 6 parts of N-vinylpyrrolidone and 6 parts of sodium 2-(methacrylic acid) ethanesulfonate were added to 100 parts of deionized water and stirred evenly. During the stirring process, 1.6 parts of ammonium persulfate (dissolved in 5 parts of water) were added dropwise. The reaction temperature was controlled at 75°C and the reaction was stirred for 24 hours in a nitrogen atmosphere. After cooling to room temperature, the mixture was filtered, washed with ethanol and dried to obtain a white powdery anti-high temperature flocculant.

[0052] (2) According to the weight percentages, mix 100 parts of Grade G oil well cement, 50 parts of spherical weighting agent, 3 parts of high-temperature water loss reducing agent, 6 parts of high-temperature suspending agent, 5 parts of high-temperature retarder, 9 parts of high-temperature toughening agent, and 8 parts of high-temperature flocculant in a mixer, then add water and stir evenly. Stir at room temperature for 1 hour to obtain a solution with a density of 2.38 g / cm³. 3 The sealing grout is an aqueous solution of the sealing material.

[0053] In this embodiment, the chemical composition of the G-grade oil well cement by mass percentage is: 65% CaO, 2% Al2O3, 20% SiO2, 5% Fe2O3, 2% MgO, 4% SO3, and 2% loss on ignition; the spherical weighting agent is spherical manganese tetroxide powder; the high-temperature water loss reducing agent is a quaternary polymer of 2-acrylamido-2-methylpropanesulfonic acid / N-vinylpyrrolidone / diallyldimethylammonium chloride / itaconic acid; the high-temperature suspending agent is magnesium aluminum silicate; the high-temperature retarder is a mixture of sodium ethylenediaminetetramethylenephosphonate and borax in a mass ratio of 1:5; and the high-temperature toughening agent is sepiolite fiber.

[0054] Example 4

[0055] This embodiment provides a cement slurry-based plugging material resistant to downhole fluid dilution and its preparation method. The preparation method includes the following steps:

[0056] (1) Using soap-free emulsion polymerization, 10 parts of sodium p-styrene sulfonate, 2 parts of methacrylic acid, 20 parts of acrylamide, 4 parts of N,N-diethyl-2-acrylamide, 6 parts of N-vinylpyrrolidone and 6 parts of sodium 2-(methacrylic acid) ethanesulfonate were added to 100 parts of deionized water and stirred evenly. During the stirring process, 1.6 parts of ammonium persulfate (dissolved in 5 parts of water) were added dropwise. The reaction temperature was controlled at 75°C and the reaction was stirred for 24 hours in a nitrogen atmosphere. After cooling to room temperature, the mixture was filtered, washed with ethanol and dried to obtain a white powdery anti-high temperature flocculant.

[0057] (2) According to the weight percentages, mix 100 parts of Grade G oil well cement, 60 parts of spherical weighting agent, 2 parts of high-temperature water loss reducing agent, 2 parts of high-temperature suspending agent, 3 parts of high-temperature retarder, 5 parts of high-temperature toughening agent, and 3 parts of high-temperature flocculant in a mixer, then add water and stir evenly. Stir at room temperature for 1 hour to obtain a solution with a density of 2.66 g / cm³. 3 The sealing grout is an aqueous solution of the sealing material.

[0058] In this embodiment, the chemical composition of the G-grade oil well cement by mass percentage is: 65% CaO, 2% Al2O3, 20% SiO2, 5% Fe2O3, 2% MgO, 4% SO3, and 2% loss on ignition; the spherical weighting agent is spherical manganese tetroxide powder; the high-temperature water loss reducing agent is a quaternary polymer of 2-acrylamido-2-methylpropanesulfonic acid / N-vinylpyrrolidone / diallyldimethylammonium chloride / itaconic acid; the high-temperature suspending agent is magnesium aluminum silicate; the high-temperature retarder is a mixture of sodium ethylenediaminetetramethylenephosphonate and borax in a mass ratio of 1:4; and the high-temperature toughening agent is sepiolite fiber.

[0059] Example 5

[0060] This embodiment provides a cement slurry-based plugging material resistant to downhole fluid dilution and its preparation method. The preparation method includes the following steps:

[0061] (1) Using soap-free emulsion polymerization, 10 parts of sodium p-styrene sulfonate, 2 parts of methacrylic acid, 20 parts of acrylamide, 4 parts of N,N-diethyl-2-acrylamide, 6 parts of N-vinylpyrrolidone and 6 parts of sodium 2-(methacrylic acid) ethanesulfonate were added to 100 parts of deionized water and stirred evenly. During the stirring process, 1.6 parts of ammonium persulfate (dissolved in 5 parts of water) were added dropwise. The reaction temperature was controlled at 75°C and the reaction was stirred for 24 hours in a nitrogen atmosphere. After cooling to room temperature, the mixture was filtered, washed with ethanol and dried to obtain a white powdery anti-high temperature flocculant.

[0062] (2) According to the weight proportions, 100 parts of Grade G oil well cement, 20 parts of spherical weighting agent, 4 parts of high-temperature water loss reducing agent, 8 parts of high-temperature suspending agent, 3 parts of high-temperature retarder, 6 parts of high-temperature toughening agent, and 4 parts of high-temperature flocculant are mixed in a mixer, and then water is added and stirred evenly. The mixture is stirred at room temperature for 1 hour to obtain a density of 1.61 g / cm³. 3 The sealing grout is an aqueous solution of the sealing material.

[0063] In this embodiment, the chemical composition of the G-grade oil well cement by mass percentage is: 65% CaO, 2% Al2O3, 20% SiO2, 5% Fe2O3, 2% MgO, 4% SO3, and 2% loss on ignition; the spherical weighting agent is spherical manganese tetroxide powder; the high-temperature water loss reducing agent is a quaternary polymer of 2-acrylamido-2-methylpropanesulfonic acid / N-vinylpyrrolidone / diallyldimethylammonium chloride / itaconic acid; the high-temperature suspending agent is magnesium aluminum silicate; the high-temperature retarder is a mixture of sodium ethylenediaminetetramethylenephosphonate and borax in a mass ratio of 1:6; and the high-temperature toughening agent is sepiolite fiber.

[0064] Example 6

[0065] This embodiment provides a cement slurry-based plugging material resistant to downhole fluid dilution and its preparation method. The preparation method includes the following steps:

[0066] (1) Using soap-free emulsion polymerization, 10 parts of sodium p-styrene sulfonate, 2 parts of methacrylic acid, 20 parts of acrylamide, 4 parts of N,N-diethyl-2-acrylamide, 6 parts of N-vinylpyrrolidone and 6 parts of sodium 2-(methacrylic acid) ethanesulfonate were added to 100 parts of deionized water and stirred evenly. During the stirring process, 1.6 parts of ammonium persulfate (dissolved in 5 parts of water) were added dropwise. The reaction temperature was controlled at 75°C and the reaction was stirred for 24 hours in a nitrogen atmosphere. After cooling to room temperature, the mixture was filtered, washed with ethanol and dried to obtain a white powdery anti-high temperature flocculant.

[0067] (2) According to the weight percentages, mix 100 parts of Grade G oil well cement, 45 parts of spherical weighting agent, 3 parts of high-temperature resistant fluid loss reducing agent, 5 parts of high-temperature resistant suspending agent, 4 parts of high-temperature resistant retarder, 12 parts of high-temperature resistant toughening agent, and 5 parts of high-temperature resistant flocculant in a mixer, then add water and stir evenly. Stir at room temperature for 1 hour to obtain a solution with a density of 2.29 g / cm³. 3 The sealing grout is an aqueous solution of the sealing material.

[0068] In this embodiment, the chemical composition of the G-grade oil well cement by mass percentage is: 65% CaO, 2% Al2O3, 20% SiO2, 5% Fe2O3, 2% MgO, 4% SO3, and 2% loss on ignition; the spherical weighting agent is spherical manganese tetroxide powder; the high-temperature water loss reducing agent is a quaternary polymer of 2-acrylamido-2-methylpropanesulfonic acid / N-vinylpyrrolidone / diallyldimethylammonium chloride / itaconic acid; the high-temperature suspending agent is magnesium aluminum silicate; the high-temperature retarder is a mixture of sodium ethylenediaminetetramethylenephosphonate and borax in a mass ratio of 1:5; and the high-temperature toughening agent is sepiolite fiber.

[0069] Comparative Example 1

[0070] This comparative example provides a cement slurry-based plugging material and its preparation method. The preparation method includes: mixing 100 parts by weight of Grade G oil well cement, 30 parts by weight of spherical weighting agent, 2 parts by weight of high-temperature resistant fluid loss reducing agent, 4 parts by weight of high-temperature resistant suspending agent, 3 parts by weight of high-temperature resistant retarder, and 8 parts by weight of high-temperature resistant toughening agent in a mixer, then adding water and stirring evenly, stirring at room temperature for 1 hour to obtain a material with a density of 1.86 g / cm³. 3 The sealing grout is an aqueous solution of the sealing material.

[0071] In this comparative example, the chemical composition of the G-grade oil well cement by mass percentage is: 65% CaO, 2% Al2O3, 20% SiO2, 5% Fe2O3, 2% MgO, 4% SO3, and 2% loss on ignition; the spherical weighting agent is spherical manganese tetroxide powder; the high-temperature water loss reducing agent is a quaternary polymer of 2-acrylamido-2-methylpropanesulfonic acid / N-vinylpyrrolidone / diallyldimethylammonium chloride / itaconic acid; the high-temperature suspending agent is magnesium aluminum silicate; the high-temperature retarder is a mixture of sodium ethylenediaminetetramethylenephosphonate and borax in a mass ratio of 1:5; and the high-temperature toughening agent is sepiolite fiber.

[0072] Impact resistance test:

[0073] The sieving residue method was used to determine the anti-dilution ability of the sealing material obtained in Example 1. The specific test method was as follows: the sealing material was accurately weighed according to the weight parts, added to clean water at a dilution ratio of 1:5, and stirred at a speed of 500±10 rpm for 10-60 min. The anti-dilution ability of the sealing material was evaluated by measuring the sieving residue of the sealing material under different stirring time conditions. The relevant test results are shown in Table 1 below.

[0074] Table 1

[0075]

[0076] As shown in Table 1, the weight loss of the plugging material obtained by the present invention only increases slightly after stirring for 1 hour, and it still has strong resistance to erosion.

[0077] Stayability test:

[0078] The retention of plugging material in the leakage channel is a prerequisite for the formation of a sealant. In this invention, the retention capacity of the 60% concentration cement slurry-based plugging material with resistance to downhole fluid dilution obtained in Example 1 under natural gravity was evaluated in a leak simulation device with different sizes of slotted plates. The relevant test results are shown in Table 2 below.

[0079] Table 2

[0080]

[0081]

[0082] As shown in Table 2, the cement slurry-based plugging material resistant to downhole fluid dilution obtained in this invention can quickly adhere and seal fractures of 1mm, 3mm, 5mm, 8mm, and 10mm. Analysis reveals that although the plugging slurry does not contain large-particle bridging material, the network-forming effect of the high-temperature resistant flocculant polymer chains and the high-temperature resistant toughening agent fibers in the plugging material achieves excellent automatic bridging and network-forming retention. As the fracture width increases, the retention difficulty of the cement slurry-based plugging material resistant to downhole fluid dilution gradually increases, but it can still effectively retain in large fractures of 8mm and 10mm.

[0083] Furthermore, as the crack size increases, the concentration and particle size of the high-temperature resistant flocculant and high-temperature resistant toughening agent introduced into the cement slurry-type plugging material resistant to downhole fluid dilution need to be increased accordingly. This creates conditions for the cement slurry-type plugging material resistant to downhole fluid dilution to remain in place and form a plug, thus expanding the adaptability of the cement slurry-type plugging material resistant to downhole fluid dilution to cracks of different sizes.

[0084] Pressure sealing capability test:

[0085] The pressure-bearing and sealing capacity of the cement slurry-based plugging materials obtained in Examples 1-6 and Comparative Example 1 were determined according to the methods specified in industry standard SY / T 5840-2007 "Indoor Test Methods for Bridging and Plugging Materials for Drilling Fluids". The specific process of the high-temperature and high-pressure dynamic plugging simulation experiment is as follows:

[0086] The cement slurry-based sealing materials obtained in Examples 1-6 and Comparative Example 1 were added to clean water, with the mass of the cement slurry-based sealing material controlled to be 110% of the mass of the clean water. Test modules with joint widths of 5-3 mm, 8-5 mm, and 10-8 mm were selected, installed in the high-temperature and high-pressure dynamic and static sealing simulation experimental device, and sealed. The heating temperature was set to 200℃, and the sealing slurry to be tested was added. The overburden pressure was simulated by pressurizing with a mechanically assisted pump. When the pressure values ​​were 1.0 MPa, 3.0 MPa, 5.0 MPa, 7.0 MPa, 10.0 MPa, 15.0 MPa, 20.0 MPa, 25.0 MPa, and 30.0 MPa, respectively, the pressure was stabilized for more than 5 minutes, and the pressure changes were recorded. The final pressure displayed is the pressure-bearing sealing capacity of the sealing material. The test results of the highest pressure-bearing sealing capacity corresponding to each example and comparative example are shown in Table 3 below.

[0087] Table 3

[0088]

[0089]

[0090] As shown in Table 3, the cement slurry-based plugging materials resistant to downhole fluid dilution obtained in Examples 1-6 can form dense pressure-bearing sealing layers in 5-3mm, 8-5mm, and 10-8mm fractured leak layers at 200℃, with a maximum pressure-bearing capacity of over 20MPa. This indicates that the cement slurry-based plugging materials resistant to downhole fluid dilution obtained in this invention have high pressure-bearing sealing capacity and can meet the needs of high-pressure plugging operations in deep and complex formations.

[0091] Compared with Examples 1-6, the cement slurry-based plugging material obtained in Comparative Example 1 did not contain a high-temperature resistant flocculant, and its maximum pressure-bearing sealing capacity was around 16 MPa. This is because the lack of a high-temperature resistant flocculant resulted in poor flocculation and dispersion of the plugging slurry. After being washed by water, some solid particles separated from the plugging slurry and were suspended in layers, which would affect the curing quality and pressure-bearing strength of the sealing layer. The cement slurry-based plugging materials resistant to downhole fluid dilution obtained in Examples 1-6 all contained a high-temperature resistant flocculant, and their maximum pressure-bearing sealing capacity was above 20 MPa (the upper limit of the instrument is 20 MPa). This indicates that the high-temperature resistant flocculant can effectively improve the anti-dispersion properties of the plugging slurry, enabling the solid particles to reach a relatively stable flocculation state, thereby improving the pressure-bearing sealing capacity of the plugging material.

[0092] Flexural strength test:

[0093] The flexural strength of the cement slurry-based sealing materials obtained in Examples 1-6 and Comparative Example 1 was determined according to the method specified in the national standard GB / T 3001-2007 "Refractory Materials - Test Method for Flexural Strength at Room Temperature". The specific process is as follows:

[0094] Standard prism specimens with dimensions of 40mm×40mm×160mm were used. Cement slurry-based sealing material was filled into the mold and covered with a cover plate. After solidification at room temperature, the mold was removed and placed in a high-temperature curing autoclave at the required temperature of 100℃×20MPa for 24 hours. The flexural strength was evaluated using a flexural strength tester. The relevant test results are shown in Table 4 below.

[0095] Table 4

[0096] Example 1 11.1 Example 2 10.5 Example 3 12.1 Example 4 10.9 Example 5 10.2 Example 6 12.6 Comparative Example 1 8.9

[0097] As shown in Table 4, the flexural strength of the cement slurry-based sealing materials obtained in Examples 1-6 is generally above 10 MPa, with the highest flexural strength in Examples 3 and 6, both reaching above 12 MPa. In contrast, the flexural strength of the cement slurry-based sealing material obtained in Comparative Example 1 is only 8.9 MPa.

[0098] Based on the above test results, the cement slurry-based plugging material provided by this invention has the characteristics of strong resistance to downhole fluid dilution, good retention capacity, and high pressure-bearing and plugging capacity. Moreover, the pressure-bearing and plugging capacity of this plugging material is higher than 20MPa, the flexural strength is greater than 10MPa, and the leakage channel adaptability range can reach 10mm. It can adapt to complex formations such as dissolution pores, large fractures, faults, and caverns with different leakage velocities, and can solve the problem of severe well leakage in complex formations. It ensures safe and rapid drilling of high-temperature deep wells and ultra-deep wells, and meets the needs of efficient development of ultra-deep and ultra-deep oil and gas reservoirs.

[0099] 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 present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A cement slurry-based plugging material resistant to downhole fluid dilution, characterized in that, The cement slurry-based sealing material comprises the following components by weight: 100 parts of oil well cement; 20-60 parts of spherical weighting agent; 1-4 parts of high-temperature water loss reducing agent; 2-8 parts of high-temperature resistant suspending agent; 3-6 parts of high-temperature retarder; 5-12 parts of high-temperature toughening agent; 1-8 parts of high-temperature resistant flocculant; The spherical weighting agent is spherical manganese tetroxide powder; The high-temperature water loss reducing agent is a quaternary polymer of 2-acrylamido-2-methylpropanesulfonic acid / N-vinylpyrrolidone / diallyldimethylammonium chloride / itaconic acid. The high-temperature resistant suspending agent is magnesium aluminum silicate; The high-temperature retarder is a combination of sodium ethylenediaminetetramethylenephosphonate and borax. The mass ratio of sodium ethylenediaminetetramethylenephosphonate and borax in the high-temperature retarder is 1:(4-6); The high-temperature toughening agent is sepiolite fiber; The density of the cement slurry-based sealing material is 1.90-2.70 g / cm³. 3 ; The high-temperature resistant flocculant has a molecular chain structure in which the molecules are mutually adsorbed and entangled, and the molecular chains are connected with amide groups and / or sulfonate groups. The high-temperature resistant flocculant is prepared by soap-free emulsion polymerization, which includes: adding sodium styrene sulfonate, methacrylic acid, acrylamide, N,N-diethyl-2-acrylamide, N-vinylpyrrolidone and sodium 2-(methacrylic acid)ethanesulfonate to deionized water, stirring evenly, and adding ammonium persulfate solution dropwise during stirring. The polymerization reaction is carried out in a protective gas atmosphere. After solid-liquid separation, the mixture is washed and dried sequentially to obtain a white powdery high-temperature resistant flocculant. The high-temperature resistant water loss reducing agent, high-temperature resistant suspending agent, high-temperature resistant retarding agent, high-temperature resistant toughening agent, and high-temperature resistant flocculant have a temperature tolerance of ≥200℃.

2. The cement slurry-based sealing material according to claim 1, characterized in that, The oil well cement includes Grade G oil well cement.

3. The cement slurry-based leak-sealing material according to claim 2, characterized in that, The G-grade oil well cement comprises the following components by mass percentage; CaO 60%-70%; Al2O3 1%-2%; SiO2 15%-20%; Fe2O3 2%-6%; MgO 1%-2%; SO3 2%-4%; Loss on ignition: 0.5%-2%.

4. A method for preparing a cement slurry-based sealing material as described in any one of claims 1-3, characterized in that, The preparation method includes the following steps: (1) High-temperature resistant flocculant was prepared by soap-free emulsion polymerization; The soap-free emulsion polymerization method includes: adding sodium styrene sulfonate, methacrylic acid, acrylamide, N,N-diethyl-2-acrylamide, N-vinylpyrrolidone and sodium 2-(methacrylic acid)ethanesulfonate to deionized water, stirring evenly, and adding ammonium persulfate solution dropwise during stirring. The polymerization reaction is carried out in a protective gas atmosphere. After solid-liquid separation, the mixture is washed and dried sequentially to obtain a white powdery anti-high temperature flocculant. (2) Mix well cement, spherical weighting agent, high temperature water loss reducing agent, high temperature suspending agent, high temperature retarder, high temperature toughening agent and high temperature flocculant obtained in step (1), add water and stir evenly to obtain cement slurry-type plugging material that resists dilution of downhole fluid.

5. The preparation method according to claim 4, characterized in that, The polymerization reaction is carried out at a temperature of 70-80℃.

6. The preparation method according to claim 4, characterized in that, The polymerization reaction takes 20-30 hours.

7. The preparation method according to claim 4, characterized in that, The protective gas includes any one or a combination of at least two of nitrogen, helium, or argon.

8. The preparation method according to claim 7, characterized in that, The protective gas is nitrogen.

9. The preparation method according to claim 4, characterized in that, The washing solution used includes ethanol.

10. The application of a cement slurry-based sealing material as described in any one of claims 1-3 in the prevention or treatment of well leakage.

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