Cement paste for plugging wellbore under ultrahigh-temperature and high-pressure conditions and preparation method thereof

Abstract

The invention relates to the technical field of well cementation cement paste, in particular to cement paste for shaft plugging under ultrahigh-temperature and high-pressure conditions and a preparation method thereof, and the cement paste for shaft plugging under ultrahigh-temperature and high-pressure conditions is prepared by mixing oil well G-grade cement, sulphoaluminate cement, silica sand, silica powder, a fluid loss agent, a retarder, a dispersing agent, a defoaming agent and water. The cement paste for shaft plugging under the ultrahigh-temperature and high-pressure conditions is obtained by compounding sulphoaluminate cement and admixture such as silica sand and silica powder with different particle sizes, the cement paste has the advantages that the density difference is small, the stability is good, the thickening time is adjustable, the size of cement stone after curing is not shrunk, the compressive strength of the cement stone after curing for 28 days is kept stable and does not decline continuously when the compressive strength is 25 MPa or above, and the cement paste is suitable for shaft plugging under the ultrahigh-temperature and high-pressure conditions. And the requirement of long-term plugging of a shaft under the conditions of ultrahigh temperature and high pressure can be met.

Description

Technical Field

[0001] This invention relates to the field of cement slurry technology, specifically a cement slurry for wellbore sealing under ultra-high temperature and high pressure conditions and its preparation method. Background Technology

[0002] In China's domestic oilfields, shallow oil and gas development in older areas has entered its later stages. To find new replacement blocks, exploration is shifting towards deep and ultra-deep wells. Currently, there are over 80 wells with depths exceeding 8000 meters, leading to a rapid increase in wellbore temperature and pressure. After drilling, if no economically recoverable oil and gas shows are found in the target formation, cementing is often used to seal the abandoned formation, effectively preventing harmful formation fluids or gases from reaching the surface.

[0003] Existing cement slurries have the following problems under ultra-high temperature and high pressure conditions in wellbores: First, during the cement injection process, the high temperature causes shear dilution, and the slurry settles, leading to pump blockage and construction interruption. Second, the cement slurry thickening time is difficult to meet the requirement of more than 6 hours, resulting in insufficient additional time for safe construction. Third, after the cement slurry solidifies, the cement stone shrinks in volume and cannot form a good bond with the casing wall, allowing formation fluids to seep through the micro-gap between the cement stone and the casing wall to the surface. Fourth, the cement stone is eroded by formation fluids with high mineralization, damaging the cement's bonding and strength. Fifth, under ultra-high temperature conditions, the strength of the cement stone declines sharply, making it prone to breakage, detachment, and silica cracking, failing to meet the requirements for long-term effective wellbore sealing.

[0004] For the sealing of ultra-high temperature and high pressure wells, conventional cement slurry can no longer meet the requirements of on-site construction applications. Therefore, it is essential to develop a cement slurry suitable for sealing wells under ultra-deep high temperature and high pressure conditions. Summary of the Invention

[0005] This invention provides a cement slurry for wellbore plugging under ultra-high temperature and high pressure conditions and its preparation method, which overcomes the shortcomings of the prior art and can effectively solve the problem that existing cement slurries cannot meet the requirements of ultra-high temperature and high pressure wellbore plugging.

[0006] One of the technical solutions of the present invention is achieved through the following measures: a cement slurry for wellbore plugging under ultra-high temperature and high pressure conditions, the raw materials comprising, by weight, 100 parts of oil well grade G cement, 6 to 30 parts of sulfoaluminate cement, 17 to 22 parts of silica sand, 23 to 38 parts of silica powder, 6 to 10 parts of fluid loss reducing agent, 8 to 12 parts of retarder, 1.0 to 1.5 parts of dispersant, 0.1 to 0.2 parts of defoamer and 42 to 80 parts of water.

[0007] The following are further optimizations and / or improvements to one of the above-mentioned technical solutions: The aforementioned G-grade cement for oil wells is one of the two types: MSR medium sulfur-resistant cement and HSR high sulfur-resistant cement.

[0008] The above-mentioned sulfoaluminate cement is a self-stressing sulfoaluminate cement.

[0009] The aforementioned water loss reducing agent is a high-temperature resistant water loss reducing agent, which is one of the following: 2-acrylamido-2-methylpropanesulfonic acid / acrylamide / dimethyldiallylammonium chloride / acrylic acid copolymer, 2-acrylamido-2-methylpropanesulfonic acid / acrylic acid / N,N-dimethylacrylamide copolymer, 2-acrylamido-2-methylpropanesulfonic acid / maleic acid / dimethyldiallylammonium chloride copolymer, and 2-acrylamido-2-methylpropanesulfonic acid / maleic acid / itaconic acid / N,N-dimethylacrylamide copolymer.

[0010] The aforementioned retarder is a high-temperature retarder, which is one of the following: 2-acrylamido-2-methylpropanesulfonic acid / maleic acid / itaconic acid copolymer, 2-acrylamido-2-methylpropanesulfonic acid / maleic acid / acrylic acid / acrylamide copolymer, and 2-acrylamido-2-methylpropanesulfonic acid / itaconic acid / acrylic acid / dimethyldiallylammonium chloride copolymer.

[0011] The dispersant mentioned above is one of formaldehyde / acetone / sodium sulfite condensate, naphthalene / sulfuric acid / formaldehyde condensate, and sodium methacrylate sulfonate / acrylic acid / isoprene alcohol polyoxyethylene ether copolymer.

[0012] The aforementioned defoamer is one of the following: alcohol polyether type defoamer, organosilicon type defoamer, and tributyl phosphate defoamer.

[0013] The aforementioned silica sand is silica sand with a D90 particle size of 140 mesh, and the silica powder is silica powder with a D90 particle size of 800 mesh; and / or the water is one of fresh water, groundwater, and salt water.

[0014] The cement slurry used for wellbore plugging under the above-mentioned ultra-high temperature and high pressure conditions is obtained by the following method: The first step is to mix the required amount of oil well grade G cement, sulfoaluminate cement, silica sand and silica powder evenly to obtain solid material; The second step is to add the required amount of water loss reducing agent to the required amount of water and stir for 20 seconds at a stirring speed of 800 r / min to 1200 r / min, then add the required amount of retarder and stir for 10 seconds to obtain a mixture. Add the required amount of dispersant and defoamer to the mixture, adjust the stirring speed to 3000 r / min and stir for 30 seconds to obtain the slurry. The third step involves adding solid materials to the slurry at a stirring speed of 3800 r / min to 4200 r / min, completing the addition within 20 to 30 seconds. Then, the stirring speed is adjusted to 10000 r / min to 12000 r / min and stirred for 40 to 60 seconds to obtain cement slurry for wellbore plugging under ultra-high temperature and high pressure conditions.

[0015] The cement slurry used for wellbore plugging under the above-mentioned ultra-high temperature and high pressure conditions is obtained by the following method: S1. At a stirring speed of 800 r / min to 1200 r / min, add the required amount of water loss reducing agent to the required amount of water and stir for 20 seconds. Then add the required amount of retarder and stir for 10 seconds to obtain a mixture. Add the required amount of dispersant and defoamer to the mixture and adjust the stirring speed to 3000 r / min and stir for 30 seconds to obtain the slurry. S2, at a stirring speed of 3800 r / min to 4200 r / min, add the required amount of oil well grade G cement, silica sand, silica powder and sulfoaluminate cement to the slurry in sequence, and complete the addition within 30 s to 50 s. Adjust the stirring speed to 10000 r / min to 12000 r / min and stir for 40 s to 60 s to obtain cement slurry for wellbore plugging under ultra-high temperature and high pressure conditions.

[0016] The second technical solution of the present invention is achieved through the following measures: a method for preparing cement slurry for wellbore plugging under ultra-high temperature and high pressure conditions, which is carried out according to the following method: The first step is to mix the required amount of oil well grade G cement, sulfoaluminate cement, silica sand and silica powder evenly to obtain solid material; The second step is to add the required amount of water loss reducing agent to the required amount of water and stir for 20 seconds at a stirring speed of 800 r / min to 1200 r / min, then add the required amount of retarder and stir for 10 seconds to obtain a mixture. Add the required amount of dispersant and defoamer to the mixture, adjust the stirring speed to 3000 r / min and stir for 30 seconds to obtain the slurry. The third step involves adding solid materials to the slurry at a stirring speed of 3800 r / min to 4200 r / min, completing the addition within 20 to 30 seconds. Then, the stirring speed is adjusted to 10000 r / min to 12000 r / min and stirred for 40 to 60 seconds to obtain cement slurry for wellbore plugging under ultra-high temperature and high pressure conditions.

[0017] The third technical solution of the present invention is achieved through the following measures: a method for preparing cement slurry for wellbore plugging under ultra-high temperature and high pressure conditions, which is carried out according to the following method: S1. At a stirring speed of 800 r / min to 1200 r / min, add the required amount of water loss reducing agent to the required amount of water and stir for 20 seconds. Then add the required amount of retarder and stir for 10 seconds to obtain a mixture. Add the required amount of dispersant and defoamer to the mixture and adjust the stirring speed to 3000 r / min and stir for 30 seconds to obtain the slurry. S2, at a stirring speed of 3800 r / min to 4200 r / min, add the required amount of oil well grade G cement, silica sand, silica powder and sulfoaluminate cement to the slurry in sequence, and complete the addition within 30 s to 50 s. Adjust the stirring speed to 10000 r / min to 12000 r / min and stir for 40 s to 60 s to obtain cement slurry for wellbore plugging under ultra-high temperature and high pressure conditions.

[0018] This invention relates to a cement slurry for wellbore plugging under ultra-high temperature and high pressure conditions, which is formulated with sulfoaluminate cement and admixtures such as silica sand and silica powder of different particle sizes. It has excellent properties such as small density difference, good stability, adjustable thickening time, no volume shrinkage of cement stone after curing, stable compressive strength of cement stone above 25MPa after 28 days of curing without further decline, and low permeability. It can meet the requirements of long-term wellbore plugging under ultra-high temperature and high pressure conditions. Detailed Implementation

[0019] This invention is not limited to the following embodiments, and specific implementation methods can be determined according to the technical solutions and actual conditions of this invention. Unless otherwise specified, all chemical reagents and chemicals mentioned in this invention are well-known and commonly used chemical reagents and chemicals in the prior art; unless otherwise specified, all percentages in this invention are mass percentages; unless otherwise specified, all solutions in this invention are aqueous solutions with water as the solvent, for example, hydrochloric acid solution is an aqueous solution of hydrochloric acid; room temperature in this invention generally refers to a temperature between 15°C and 25°C, generally defined as 25°C.

[0020] The present invention will be further described below with reference to embodiments: Example 1: The cement slurry for wellbore plugging under ultra-high temperature and high pressure conditions comprises, by weight, 100 parts of oil well grade G cement, 6 to 30 parts of sulfoaluminate cement, 17 to 22 parts of silica sand, 23 to 38 parts of silica powder, 6 to 10 parts of fluid loss reducer, 8 to 12 parts of retarder, 1.0 to 1.5 parts of dispersant, 0.1 to 0.2 parts of defoamer, and 42 to 80 parts of water.

[0021] Example 2: As an optimization of the above example, the G-grade cement for oil wells is one of the sulfur-resistant cement in MSR and the high sulfur-resistant cement in HSR.

[0022] Example 3: As an optimization of the above examples, the sulfoaluminate cement is a self-stressing sulfoaluminate cement.

[0023] Example 4: As an optimization of the above examples, the water loss reducing agent is a high-temperature resistant water loss reducing agent, which is one of the following: 2-acrylamido-2-methylpropanesulfonic acid / acrylamide / dimethyldiallylammonium chloride / acrylic acid copolymer, 2-acrylamido-2-methylpropanesulfonic acid / acrylic acid / N,N-dimethylacrylamide copolymer, 2-acrylamido-2-methylpropanesulfonic acid / maleic acid / dimethyldiallylammonium chloride copolymer, and 2-acrylamido-2-methylpropanesulfonic acid / maleic acid / itaconic acid / N,N-dimethylacrylamide copolymer.

[0024] Example 5: As an optimization of the above examples, the retarder is a high-temperature retarder, which is one of the following: 2-acrylamido-2-methylpropanesulfonic acid / maleic acid / itaconic acid copolymer, 2-acrylamido-2-methylpropanesulfonic acid / maleic acid / acrylic acid / acrylamide copolymer, and 2-acrylamido-2-methylpropanesulfonic acid / itaconic acid / acrylic acid / dimethyldiallylammonium chloride copolymer.

[0025] Example 6: As an optimization of the above examples, the dispersant is one of formaldehyde / acetone / sodium sulfite condensate, naphthalene / sulfuric acid / formaldehyde condensate, and sodium methacrylate sulfonate / acrylic acid / isoprene alcohol polyoxyethylene ether copolymer.

[0026] Example 7: As an optimization of the above examples, the defoamer is one of the following: alcohol polyether type defoamer, organosilicon type defoamer, and tributyl phosphate defoamer.

[0027] Example 8: As an optimization of the above example, the silica sand is silica sand with a D90 particle size of 140 mesh, and the silica powder is silica powder with a D90 particle size of 800 mesh.

[0028] Example 9: As an optimization of the above examples, the water is one of fresh water, groundwater and salt water.

[0029] Example 10: As an optimization of the above examples, the cement slurry for wellbore plugging under ultra-high temperature and high pressure conditions is obtained by the following method: The first step is to mix the required amount of oil well grade G cement, sulfoaluminate cement, silica sand and silica powder evenly to obtain solid material; The second step is to add the required amount of water loss reducing agent to the required amount of water and stir for 20 seconds at a stirring speed of 800 r / min to 1200 r / min, then add the required amount of retarder and stir for 10 seconds to obtain a mixture. Add the required amount of dispersant and defoamer to the mixture, adjust the stirring speed to 3000 r / min and stir for 30 seconds to obtain the slurry. The third step involves adding solid materials to the slurry at a stirring speed of 3800 r / min to 4200 r / min, completing the addition within 20 to 30 seconds. Then, the stirring speed is adjusted to 10000 r / min to 12000 r / min and stirred for 40 to 60 seconds to obtain cement slurry for wellbore plugging under ultra-high temperature and high pressure conditions.

[0030] Example 11: As an optimization of the above examples, the cement slurry for wellbore plugging under ultra-high temperature and high pressure conditions is obtained by the following method: S1. At a stirring speed of 800 r / min to 1200 r / min, add the required amount of water loss reducing agent to the required amount of water and stir for 20 seconds. Then add the required amount of retarder and stir for 10 seconds to obtain a mixture. Add the required amount of dispersant and defoamer to the mixture and adjust the stirring speed to 3000 r / min and stir for 30 seconds to obtain the slurry. S2, at a stirring speed of 3800 r / min to 4200 r / min, add the required amount of oil well grade G cement, silica sand, silica powder and sulfoaluminate cement to the slurry in sequence, and complete the addition within 30 s to 50 s. Adjust the stirring speed to 10000 r / min to 12000 r / min and stir for 40 s to 60 s to obtain cement slurry for wellbore plugging under ultra-high temperature and high pressure conditions.

[0031] Compared with the prior art, the beneficial effects of the present invention are as follows: First, the density of the cement slurry for wellbore plugging under ultra-high temperature and high pressure conditions of this invention is adjustable within the range of 1.75 g / cm³ to 1.90 g / cm³. After curing under ultra-high temperature and high pressure conditions, the rheological properties of the cement slurry for wellbore plugging under ultra-high temperature and high pressure conditions are compared with those under normal temperature conditions. There is no shear dilution phenomenon. The density difference between the upper, middle and lower parts of the slurry can be controlled within ±0.03 g / cm³. It has good settling stability and can effectively avoid the risk of pump blockage caused by slurry settling, which would lead to construction interruption. Secondly, the cement slurry for well plugging under ultra-high temperature and high pressure conditions of this invention has an adjustable thickening time. It can be adjusted to more than 360 minutes by adjusting the amount of retarder according to the actual needs of on-site construction, thus meeting the requirements of additional time for on-site construction safety. Third, the cement slurry for well casing plugging under ultra-high temperature and high pressure conditions has a certain expansion effect during the hydration process. After forming cement stone, the volume does not shrink and the volume expansion rate of cement stone is low. It can be tightly bonded to the casing, effectively solving the problem of cement stone volume shrinkage and the formation of micro gaps in the casing wall. Fourth, the cement stone cured by the cement slurry used for wellbore plugging under ultra-high temperature and high pressure conditions has low permeability. The hydration products of the cement slurry used for wellbore plugging under ultra-high temperature and high pressure conditions can effectively fill the micropores of the cement stone, improve the density of the cement stone, and have good resistance to the erosion of high-mineralization formation fluids. Fifth, the cement slurry for wellbore plugging under ultra-high temperature and high pressure conditions of this invention, after being cured for 28 days under ultra-high temperature and high pressure conditions, has a compressive strength of 25MPa, which can meet the requirements for long-term wellbore plugging under ultra-high temperature and high pressure conditions. Sixth, this invention provides two methods for preparing cement slurry for wellbore plugging under ultra-high temperature and high pressure conditions. Both methods can be prepared in the laboratory and on-site, with no special requirements for the preparation environment. During on-site construction, cement trucks can be used for self-preparation and self-injection, or fixed tank and quantitative preparation can be carried out by pump truck for suction and injection. The operation is flexible and convenient, and the silica sand and silica powder have a reasonable particle size distribution, making on-site preparation simple.

[0032] In this invention, the raw material sulfoaluminate cement has the advantage that it is composed of anhydrous calcium sulfoaluminate and dicalcium silicate as the main minerals, and has the characteristics of early strength, high strength, high impermeability, and corrosion resistance. The raw materials silica sand and silica powder have the advantage that they are made of silica sand and silica powder of different particle sizes, and the particle size distribution fills and blocks the microporous structure of the well shaft. 800-mesh silica powder can enter the micro gaps to block the flow channels. In addition, because silica powder has a large specific surface area, it can adsorb the free water that is diluted and separated by high temperature shear, and prevent the cement slurry used for well shaft sealing from settling at high temperature under ultra-high temperature and high pressure conditions.

[0033] In this invention, all raw materials used in the following embodiments are commercially available products. Specifically, the raw material, oil well grade G cement, is HSR high-sulfur-resistant cement, provided by Hoboksar County Qingsong Nangangtun Nanjian Building Materials Co., Ltd.; the raw material, sulfoaluminate cement, is self-stressing sulfoaluminate cement with a strength grade of 52.5 MPa, provided by Tangshan Arctic Bear Building Materials Co., Ltd.; the raw material, silica sand, is silica sand with a D90 particle size of 140 mesh and an SiO2 content ≥98%, provided by Sichuan Kai'er Oil and Gas Field Technology Service Co., Ltd.; the raw material, silica powder, is silica powder with a D90 particle size of 800 mesh and an SiO2 content ≥98%, provided by Sichuan Kai'er Oil and Gas Field Technology Service Co., Ltd.; and the raw material, loss-reduction... The aqueous solution is a water-loss reducing agent HX-12L (2-acrylamido-2-methylpropanesulfonic acid / acrylamide / dimethyldiallyl ammonium chloride / acrylic acid copolymer), supplied by Chengdu Omec Petroleum Technology Co., Ltd.; the raw material retarder is a retarder XZ-R11L (2-acrylamido-2-methylpropanesulfonic acid / maleic acid / itaconic acid copolymer), supplied by CNPC Western Drilling Engineering Technology Research Institute; the raw material dispersant is a dispersant HX-21L (naphthalene / sulfuric acid / formaldehyde condensate), supplied by Chengdu Omec Petroleum Technology Co., Ltd.; and the raw material defoamer is a defoamer XP-1 (alcohol polyether type defoamer), supplied by Henan Weihui Chemical Co., Ltd.

[0034] Example 12: This cement slurry for wellbore plugging under ultra-high temperature and high pressure conditions comprises, by weight, 100 parts of oil well grade G cement (HSR high sulfur-resistant cement), 12 parts of sulfoaluminate cement, 20 parts of silica sand, 30 parts of silica fume, 7 parts of fluid loss reducer (fluid loss reducer HX-12L), 9 parts of retarder (retarder XZ-R11L), 1.3 parts of dispersant (dispersant HX-21L), 0.1 parts of defoamer (defoamer XP-1), and 64 parts of water, obtained according to the following method: The first step is to mix the required amount of oil well grade G cement, sulfoaluminate cement, silica sand and silica powder evenly to obtain solid material; The second step is to use a corrugated mixer at a stirring speed of 1000 r / min to add the required amount of water loss reducer and stir for 20 seconds, then add the required amount of retarder and stir for 10 seconds to obtain a mixture. Add the required amount of dispersant and defoamer to the mixture, adjust the stirring speed to 3000 r / min and stir for 30 seconds to obtain the slurry. The third step involves using a corrugated mixer at a stirring speed of 4000 r / min to add solid materials to the slurry and complete the addition within 25 seconds. Then, adjust the stirring speed to 11000 r / min and stir for 50 seconds to obtain cement slurry for well plugging under ultra-high temperature and high pressure conditions.

[0035] Example 13: This cement slurry for wellbore plugging under ultra-high temperature and high pressure conditions comprises, by weight, 100 parts of oil well grade G cement (HSR high sulfur-resistant cement), 12 parts of sulfoaluminate cement, 20 parts of silica sand, 30 parts of silica fume, 7 parts of fluid loss reducer (fluid loss reducer HX-12L), 9 parts of retarder (retarder XZ-R11L), 1.3 parts of dispersant (dispersant HX-21L), 0.1 parts of defoamer (defoamer XP-1), and 64 parts of water, obtained according to the following method: S1. Using a corrugated mixer at a stirring speed of 1000 r / min, add the required amount of water loss reducer to the required amount of water and stir for 20 seconds. Then add the required amount of retarder and stir for 10 seconds to obtain a mixture. Add the required amount of dispersant and defoamer to the mixture and adjust the stirring speed to 3000 r / min and stir for 30 seconds to obtain the slurry. S2. Using a corrugated mixer at 4000 r / min, the required amounts of oil well grade G cement, silica sand, silica powder and sulfoaluminate cement are added to the slurry in sequence and added within 45 seconds. The mixing speed is then adjusted to 11000 r / min and mixed for 50 seconds to obtain cement slurry for wellbore plugging under ultra-high temperature and high pressure conditions.

[0036] The cement slurry for wellbore plugging under ultra-high temperature and high pressure conditions prepared in Example 13 of this invention differs from that in Example 12 in that the preparation method is different.

[0037] Example 14: This cement slurry for wellbore plugging under ultra-high temperature and high pressure conditions comprises, by weight, 100 parts of oil well grade G cement (HSR high sulfur-resistant cement), 20 parts of sulfoaluminate cement, 22 parts of silica sand, 38 parts of silica fume, 6 parts of fluid loss reducer (fluid loss reducer HX-12L), 9 parts of retarder (retarder XZ-R11L), 1.5 parts of dispersant (dispersant HX-21L), 0.1 parts of defoamer (defoamer XP-1), and 70 parts of water, obtained according to the following method: The first step is to mix the required amount of oil well grade G cement, sulfoaluminate cement, silica sand and silica powder evenly to obtain solid material; The second step is to use a corrugated mixer at a stirring speed of 1000 r / min to add the required amount of water loss reducer and stir for 20 seconds, then add the required amount of retarder and stir for 10 seconds to obtain a mixture. Add the required amount of dispersant and defoamer to the mixture, adjust the stirring speed to 3000 r / min and stir for 30 seconds to obtain the slurry. The third step involves using a corrugated mixer at a stirring speed of 4000 r / min to add solid materials to the slurry and complete the addition within 25 seconds. Then, adjust the stirring speed to 11000 r / min and stir for 60 seconds to obtain cement slurry for well plugging under ultra-high temperature and high pressure conditions.

[0038] Example 15: This cement slurry for wellbore plugging under ultra-high temperature and high pressure conditions comprises, by weight, 100 parts of oil well grade G cement (HSR high sulfur-resistant cement), 6 parts of sulfoaluminate cement, 17 parts of silica sand, 23 parts of silica fume, 8 parts of fluid loss reducer (fluid loss reducer HX-12L), 11 parts of retarder (retarder XZ-R11L), 1 part of dispersant (dispersant HX-21L), 0.1 parts of defoamer (defoamer XP-1), and 42 parts of water, obtained according to the following method: The first step is to mix the required amount of oil well grade G cement, sulfoaluminate cement, silica sand and silica powder evenly to obtain solid material; The second step is to use a corrugated mixer at a stirring speed of 1000 r / min to add the required amount of water loss reducer and stir for 20 seconds, then add the required amount of retarder and stir for 10 seconds to obtain a mixture. Add the required amount of dispersant and defoamer to the mixture, adjust the stirring speed to 3000 r / min and stir for 30 seconds to obtain the slurry. The third step involves using a corrugated mixer at a stirring speed of 4000 r / min to add solid materials to the slurry and complete the addition within 25 seconds. Then, adjust the stirring speed to 11000 r / min and stir for 50 seconds to obtain cement slurry for well plugging under ultra-high temperature and high pressure conditions.

[0039] Example 16: This cement slurry for wellbore plugging under ultra-high temperature and high pressure conditions comprises, by weight, 100 parts of oil well grade G cement (HSR high sulfur-resistant cement), 25 parts of sulfoaluminate cement, 22 parts of silica sand, 38 parts of silica fume, 10 parts of fluid loss reducer (fluid loss reducer HX-12L), 12 parts of retarder (retarder XZ-R11L), 1.5 parts of dispersant (dispersant HX-21L), 0.1 parts of defoamer (defoamer XP-1), and 80 parts of water, obtained according to the following method: The first step is to mix the required amount of oil well grade G cement, sulfoaluminate cement, silica sand and silica powder evenly to obtain solid material; The second step is to use a corrugated mixer at a stirring speed of 1000 r / min to add the required amount of water loss reducer and stir for 20 seconds, then add the required amount of retarder and stir for 10 seconds to obtain a mixture. Add the required amount of dispersant and defoamer to the mixture, adjust the stirring speed to 3000 r / min and stir for 30 seconds to obtain the slurry. The third step involves using a corrugated mixer at a stirring speed of 4000 r / min to add solid materials to the slurry and complete the addition within 25 seconds. Then, adjust the stirring speed to 11000 r / min and stir for 50 seconds to obtain cement slurry for well plugging under ultra-high temperature and high pressure conditions.

[0040] Comparative Example 1: The formula for this conventional wellbore plugging cement slurry (density 1.75 g / cm³) is as follows: 100 parts of oil well grade G cement (HSR high sulfur-resistant cement), 6 parts of fluid loss reducer (fluid loss reducer HX-12L), 9 parts of retarder (retarder XZ-R11L), 0.1 parts of defoamer (defoamer XP-1), and 47 parts of water. It is obtained by adding the required amount of water to the slurry cup of a corrugated mixer and adjusting the stirring speed to 4000 r / min. Then, add the required amount of fluid loss reducer, retarder, and defoamer to the slurry cup and stir for 30 seconds. Then, add the oil well grade G HSR high sulfur-resistant cement and add it within 19 seconds until it is finished. Adjust the stirring speed to 12000 r / min and stir for 50 seconds to obtain the conventional wellbore plugging cement slurry.

[0041] Comparative Example 2: The formula for this conventional wellbore plugging cement slurry (density 1.90 g / cm³) is as follows: 100 parts of oil well grade G cement (HSR high sulfur-resistant cement), 6 parts of fluid loss reducer (HX-12L), 9 parts of retarder (XZ-R11L), 0.5 parts of dispersant (HX-21L), 0.1 parts of defoamer (XP-1), and 47 parts of water. It is obtained as follows: Add the required amount of water to the slurry cup of a corrugated mixer, adjust the stirring speed to 4000 r / min, add the required amounts of fluid loss reducer, retarder, and defoamer to the slurry cup, and stir for 30 seconds. Then, add the oil well grade G HSR high sulfur-resistant cement within 19 seconds until the addition is complete, adjust the stirring speed to 12000 r / min, and stir for 50 seconds to obtain the conventional wellbore plugging cement slurry.

[0042] Experimental Example 1: Investigating the performance of the cement slurry for wellbore sealing under ultra-high temperature and high pressure conditions according to the present invention.

[0043] Experimental Methods: The performance of the cement slurry for wellbore plugging under ultra-high temperature and high pressure conditions of the present invention was investigated according to the methods specified in GB / T 19139-2012 "Test Methods for Cement in Oil Wells". First, the density and rheological properties of the cement slurry for wellbore plugging under ultra-high temperature and high pressure conditions prepared in Examples 12 to 16 of the present invention were investigated. Then, since the raw materials of Examples 12 and 13 of the present invention are the same and only the preparation methods are different, only the thickening time of the cement slurry for wellbore plugging under ultra-high temperature and high pressure conditions prepared in Examples 13 to 16 of the present invention was investigated. Finally, the settling stability of the cement slurry for wellbore plugging under ultra-high temperature and high pressure conditions prepared in Examples 13 to 16 of the present invention was investigated. Meanwhile, Comparative Examples 1 to 2 were used as controls.

[0044] Experimental results: The density and rheological properties of the cement slurry for wellbore plugging under ultra-high temperature and high pressure conditions prepared in Examples 12 to 16 of this invention are shown in Table 1. As can be seen from Table 1, the density of the cement slurry for wellbore plugging under ultra-high temperature and high pressure conditions of this invention is adjustable in the range of 1.75 g / cm³ to 1.90 g / cm³, and the rheological properties are good. The thickening time of the cement slurry for wellbore plugging under ultra-high temperature and high pressure prepared in Examples 13 to 16 of the present invention is shown in Table 2. As can be seen from Table 2, under the experimental conditions of 190℃ and 103MPa, the thickening time of the cement slurry for wellbore plugging under ultra-high temperature and high pressure of the present invention is greater than 360min, indicating that the thickening time of the cement slurry for wellbore plugging under ultra-high temperature and high pressure of the present invention can be adjusted according to the technical conditions. The settlement stability of the cement slurry for wellbore plugging under ultra-high temperature and high pressure conditions prepared in Examples 13 to 16 of this invention is shown in Table 3. As can be seen from Table 3, the density difference between the upper, middle and lower parts of the cement slurry for wellbore plugging under ultra-high temperature and high pressure conditions prepared in Examples 13 to 16 of this invention can be controlled within the range of ±0.03 g / cm³, while the density difference between the upper and lower parts of the conventional cement slurry for wellbore plugging prepared in Comparative Examples 1 to 2 is larger. This indicates that the settlement stability of the cement slurry for wellbore plugging under ultra-high temperature and high pressure conditions of this invention is better than that of the conventional cement slurry for wellbore plugging prepared in Comparative Examples 1 to 2.

[0045] Experimental Example 2: Investigating the compressive strength of cement stone after curing the cement slurry used for well plugging under ultra-high temperature and high pressure conditions of the present invention.

[0046] Experimental Methods: Following the methods specified in GB / T 19139-2012 "Test Methods for Cement in Oil Wells", cement slurry used for wellbore plugging under ultra-high temperature and high pressure conditions in Examples 13 to 16 of this invention was cured for 24h, 48h, 7d, 14d, and 28d respectively under ultra-high temperature and high pressure (200℃×20.7MPa) to obtain cement stone with different curing times. The compressive strength of the cement stone with different curing times was measured. Comparative Example 2 was used as a control.

[0047] Experimental Results: The compressive strength of each cement stone is shown in Table 4. As can be seen from Table 4, the cement slurry for wellbore plugging under ultra-high temperature and high pressure conditions prepared in Examples 13 to 16 of this invention, after curing under ultra-high temperature and high pressure conditions, all exhibited a compressive strength exceeding 40 MPa after 48 hours of curing. After 28 days of curing, the compressive strength of the cement stone decreased to a minimum of 26 MPa before stabilizing. In contrast, the conventional cement slurry for wellbore plugging prepared in Comparative Example 2, after curing under ultra-high temperature and high pressure conditions, showed a decrease in compressive strength of the cement stone after 48 hours of curing, decreasing to 6 MPa after 28 days. This indicates that the cement stone of the cement slurry for wellbore plugging under ultra-high temperature and high pressure conditions of this invention exhibits excellent compressive strength performance under high temperature and high pressure. After 28 days of curing, the compressive strength remains above 25 MPa, which can meet the long-term requirements for the compressive strength of cement stone in wellbore plugging under ultra-high temperature and high pressure conditions.

[0048] Experimental Example 3: Investigating the permeability of cement stone after curing the cement slurry used for well plugging under ultra-high temperature and high pressure conditions of the present invention.

[0049] Experimental methods: In accordance with the methods specified in GB / T 19139-2012 "Test Methods for Cement in Oil Wells", cement slurry for wellbore plugging under ultra-high temperature and high pressure conditions prepared in Examples 13 to 16 of this invention was cured for 7 days to obtain cement stone. The permeability and porosity of the cement stone were investigated. Meanwhile, Comparative Example 1 and Comparative Example 2 were used as controls.

[0050] Experimental Results: The permeability and porosity of each cement stone are shown in Table 5. As can be seen from Table 5, compared to Comparative Examples 1 and 2, the cement stones prepared in Examples 13 to 16 of this invention for wellbore plugging under ultra-high temperature and high pressure conditions, after 7 days of curing, exhibit significantly lower 7-day liquid phase permeability and porosity, demonstrating a clear advantage. This indicates that the particle size distribution of various solid materials in the cement slurry for wellbore plugging under ultra-high temperature and high pressure conditions of this invention is reasonable, and the appropriate ratio of silica powder to silica sand further reduces the porosity of the cement stone under ultra-high temperature and high pressure conditions, maintaining a dense structure.

[0051] Experimental Example 4: Investigating the permeability and volume shrinkage rate of the cement stone after curing the cement slurry used for well plugging under ultra-high temperature and high pressure conditions of the present invention.

[0052] Experimental method: In accordance with the method specified in SY / T 5504.8 "Evaluation method of cement admixtures for oil wells - Part 8 - Expansion agent", cement slurry for wellbore plugging under ultra-high temperature and high pressure conditions prepared in Examples 13 to 16 of this invention was cured for 24 hours to obtain cement stone. The volume expansion rate of each cement stone was investigated. Meanwhile, Comparative Example 1 and Comparative Example 2 were used as controls.

[0053] Experimental results: The volume expansion rate of cement stone is shown in Table 6. As can be seen from Table 6, compared with Comparative Examples 1 to 2, the cement stone prepared by the cement slurry for wellbore plugging under ultra-high temperature and high pressure conditions in Examples 13 to 16 of the present invention does not shrink in volume after 24 hours of curing. This indicates that the cement slurry for wellbore plugging under ultra-high temperature and high pressure conditions of the present invention can form a good bond with the casing wall, preventing the formation fluid from passing through the micro gaps between the cement stone and the casing wall and reaching the surface due to the shrinkage of the cement stone volume.

[0054] In summary, this invention uses sulfoaluminate cement and admixtures such as silica sand and silica powder of different particle sizes to obtain cement slurry for well plugging under ultra-high temperature and high pressure conditions. It has excellent properties such as small density difference, good stability, adjustable thickening time, no volume shrinkage of cement stone after curing, stable compressive strength of cement stone above 25MPa after 28 days of curing without further decline, and low permeability, which can meet the requirements of long-term well plugging under ultra-high temperature and high pressure conditions.

[0055] The above technical features constitute the embodiments of the present invention, which have strong adaptability and implementation effect. Unnecessary technical features can be added or removed according to actual needs to meet the needs of different situations.

Claims

1. A cement slurry for use in plugging a wellbore under ultra-high temperature and high pressure conditions, characterized in that The raw materials include 100 parts of oil well G-grade cement, 6 to 30 parts of sulphoaluminate cement, 17 to 22 parts of silica sand, 23 to 38 parts of silica powder, 6 to 10 parts of fluid loss additive, 8 to 12 parts of retarder, 1.0 to 1.5 parts of dispersant, 0.1 to 0.2 parts of defoamer and 42 to 80 parts of water by weight.

2. The cement slurry for use in wellbore plugging under ultra-high temperature and high pressure conditions according to claim 1, characterized in that The oil well G-grade cement is one of MSR sulphur-resistant cement and HSR high sulphur-resistant cement; or / and, the sulphoaluminate cement is self-stress sulphoaluminate cement.

3. The cement slurry for use in wellbore plugging under ultra-high temperature and high pressure conditions according to claim 1 or 2, characterized in that The fluid loss additive is high-temperature resistant fluid loss additive, which is one of 2-acrylamido-2-methylpropanesulfonic acid / acrylamide / dimethyldiallylammonium chloride / acrylic acid copolymer, 2-acrylamido-2-methylpropanesulfonic acid / acrylic acid / N,N-dimethylacrylamide copolymer, 2-acrylamido-2-methylpropanesulfonic acid / maleic acid / dimethyldiallylammonium chloride copolymer and 2-acrylamido-2-methylpropanesulfonic acid / maleic acid / itaconic acid / N,N-dimethylacrylamide copolymer.

4. The cement slurry for use in wellbore plugging under ultra-high temperature and high pressure conditions according to claim 1 or 2 or 3, characterized in that The retarder is high-temperature resistant retarder, which is one of 2-acrylamido-2-methylpropanesulfonic acid / maleic acid / itaconic acid copolymer, 2-acrylamido-2-methylpropanesulfonic acid / maleic acid / acrylic acid / acrylamide copolymer and 2-acrylamido-2-methylpropanesulfonic acid / itaconic acid / acrylic acid / dimethyldiallylammonium chloride copolymer.

5. The cement slurry for use in wellbore plugging under ultra-high temperature and high pressure conditions according to any one of claims 1 to 4, characterized in that The dispersant is one of formaldehyde / ketone / sodium sulfite condensate, naphthalene / sulfuric acid / formaldehyde condensate and sodium methallylsulfonate / acrylic acid / polyoxyethylene isopentenyl ether copolymer; or / and, the defoamer is one of alcohol polyether type defoamer, silicone type defoamer and phosphoric acid tributyl ester defoamer.

6. The cement slurry for use in wellbore plugging under ultra-high temperature and high pressure conditions according to any one of claims 1 to 5, characterized in that The silica sand is D90 particle size 140 mesh silica sand, and the silica powder is D90 particle size 800 mesh silica powder; or / and, the water is one of fresh water, underground water and salt water.

7. The cement slurry for use in wellbore plugging under ultra-high temperature and high pressure conditions according to any one of claims 1 to 6, characterized in that The cement slurry for wellbore plugging under ultra-high temperature and high pressure conditions is obtained by the following method: In the first step, the required amount of oil well G-grade cement, sulphoaluminate cement, silica sand and silica powder are uniformly mixed and stirred to obtain solid phase materials; In the second step, the required amount of fluid loss additive is added to the required amount of water under stirring at a speed of 800 to 1200 r / min, and stirred for 20 s, and then the required amount of retarder is added and stirred for 10 s to obtain a mixture, and then the required amount of dispersant and defoamer are added to the mixture, and the stirring speed is adjusted to 3000 r / min and stirred for 30 s to obtain a slurry preparation liquid; In the third step, the solid phase materials are added to the slurry preparation liquid under stirring at a speed of 3800 to 4200 r / min, and the stirring is completed within 20 to 30 s, and then the stirring speed is adjusted to 10000 to 12000 r / min and stirred for 40 to 60 s to obtain the cement slurry for wellbore plugging under ultra-high temperature and high pressure conditions.

8. The cement slurry for use in wellbore plugging under ultra-high temperature and high pressure conditions according to any one of claims 1 to 6, characterized in that The cement slurry for wellbore plugging under ultra-high temperature and high pressure conditions is obtained by the following method: S1, under the stirring speed of 800r / min to 1200r / min, a required amount of fluid loss additive was added into a required amount of water and stirred for 20s, then a required amount of retarder was added and stirred for 10s to obtain a mixture, a required amount of dispersant and defoaming agent was added into the mixture, the stirring speed was adjusted to 3000r / min and stirred for 30s to obtain a slurry preparation liquid; S2, under the stirring speed of 3800r / min to 4200r / min, a required amount of oil well G grade cement, silica sand, silicon powder and sulphoaluminate cement was sequentially added into the slurry preparation liquid and added completely within 30s to 50s, the stirring speed was adjusted to 10000r / min to 12000r / min and stirred for 40s to 60s to obtain a cement slurry for wellbore plugging under superhigh temperature and high pressure conditions.

9. A method of preparing a cement slurry for use in wellbore plugging under ultra-high temperature and high pressure conditions according to any one of claims 1 to 6, characterized in that The following method was used: First step, a required amount of oil well G grade cement, sulphoaluminate cement, silica sand and silicon powder was uniformly mixed and stirred to obtain a solid phase material; Second step, under the stirring speed of 800r / min to 1200r / min, a required amount of fluid loss additive was added into a required amount of water and stirred for 20s, then a required amount of retarder was added and stirred for 10s to obtain a mixture, a required amount of dispersant and defoaming agent was added into the mixture, the stirring speed was adjusted to 3000r / min and stirred for 30s to obtain a slurry preparation liquid; Third step, under the stirring speed of 3800r / min to 4200r / min, the solid phase material was added into the slurry preparation liquid and added completely within 20s to 30s, the stirring speed was adjusted to 10000r / min to 12000r / min and stirred for 40s to 60s to obtain a cement slurry for wellbore plugging under superhigh temperature and high pressure conditions.

10. A method of preparing a cement slurry for use in wellbore plugging under ultra-high temperature and high pressure conditions according to any one of claims 1 to 6, characterized in that The following method was used: S1, under the stirring speed of 800r / min to 1200r / min, a required amount of fluid loss additive was added into a required amount of water and stirred for 20s, then a required amount of retarder was added and stirred for 10s to obtain a mixture, a required amount of dispersant and defoaming agent was added into the mixture, the stirring speed was adjusted to 3000r / min and stirred for 30s to obtain a slurry preparation liquid; S2, under the stirring speed of 3800r / min to 4200r / min, a required amount of oil well G grade cement, silica sand, silicon powder and sulphoaluminate cement was sequentially added into the slurry preparation liquid and added completely within 30s to 50s, the stirring speed was adjusted to 10000r / min to 12000r / min and stirred for 40s to 60s to obtain a cement slurry for wellbore plugging under superhigh temperature and high pressure conditions.

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