An annular space protection fluid and its application

Abstract

The present invention provides an annulus protection fluid and its application. The annulus protection fluid comprises a magnetic liquid, a base grease, a solid filler, and a base oil. The annulus protection fluid of the present invention comprises a magnetic liquid, a base grease, a solid filler, and a base oil. The resulting fluid is a non-Newtonian fluid with high density and viscosity, thereby enhancing its sealing performance and achieving a good plugging effect. The fluid also has excellent corrosion resistance and can extend the service life of oil casing.

Description

Technical Field

[0001] The invention belongs to the technical field of oil and gas fields, and in particular relates to an annulus protection fluid and application thereof. Background Art

[0002] During oil and gas field exploration and development, the application of annular protection fluids is crucial to maintaining the integrity and functionality of the wellbore. Annular protection fluids are typically used to fill the annular space between the casing and tubing to prevent cross-flow of formation fluids (such as oil, gas, and water), reduce the pressure on the packer from the oil and gas formation, protect the integrity of the packer, protect the inner wall of the casing and the outer wall of the tubing from corrosion, and maintain the structural integrity of the wellbore.

[0003] However, with the advancement of carbon capture, utilization, and storage (CCUS) projects, traditional annular protection fluids face new challenges, particularly during high-pressure CO2 injection and alternating water-gas injection operations. For example, existing annular protection fluids fail to achieve both corrosion resistance and sealing performance, impacting the safety and effectiveness of CCUS projects while also posing potential environmental risks. Therefore, developing an annular protection fluid that balances both corrosion resistance and sealing performance has become a pressing technical challenge. Summary of the Invention

[0004] The main purpose of the present invention is to provide an annular space protection fluid, which can take into account both anti-corrosion performance and sealing performance.

[0005] The present invention also provides a method for protecting an oil and gas well, which uses the annulus protection fluid to fill the oil and gas well. Therefore, the method for protecting the oil and gas well can achieve both anti-corrosion performance and sealing performance.

[0006] In a first aspect, the present invention provides an annulus protection fluid comprising a magnetic liquid, a base grease, a solid filler and a base oil.

[0007] The annular protection fluid as described above, wherein the solid filler comprises at least one of polytetrafluoroethylene, nitrile rubber, graphite, tungsten disulfide, molybdenum disulfide, and boron nitride;

[0008] The weight average molecular weight of the polytetrafluoroethylene is 5000-10000, and the average particle size is 3 μm-10 μm;

[0009] And / or, the average particle size of the nitrile rubber is 0.1 mm to 1.2 mm;

[0010] And / or, the average particle size of the graphite is 1 μm-50 μm;

[0011] And / or, the average particle size of the tungsten disulfide is 1 μm-10 μm;

[0012] And / or, the average particle size of the molybdenum disulfide is 1 μm-10 μm;

[0013] And / or, the average particle size of the boron nitride is 0.5 μm-30 μm.

[0014] In the annular protection fluid as described above, the magnetic liquid includes Fe3O4 nanoparticles, and the average particle size of the Fe3O4 nanoparticles is 10nm~50nm.

[0015] In the annulus protection fluid as described above, the base grease includes lithium 12-hydroxystearate and / or aluminum-based grease.

[0016] In the annulus protection fluid as described above, the base oil includes at least one of 500SN base oil, poly-alpha olefin synthetic base oil (PAO10), hydrogenated cycloalkyl base oil, perfluoropolyether, and silicone oil.

[0017] The annular space protection fluid as described above comprises, in terms of mass percentage, 7.06% to 28.24% of magnetic liquid, 16.7% to 17.7% of base grease, 47% to 50% of solid filler, and the balance being base oil.

[0018] The annular space protection fluid as described above, wherein the solid filler comprises polytetrafluoroethylene, nitrile rubber and graphite;

[0019] The mass ratio of the polytetrafluoroethylene, nitrile rubber and graphite is (18.8-20): (9.4-10): (18.8-20).

[0020] The annular space protection fluid as described above further includes a tracer, and the tracer includes a tracer containing rare earth elements and / or a DNA tracer.

[0021] The annular space protection fluid as described above, wherein the annular space protection fluid further comprises a bactericide and a corrosion inhibitor;

[0022] The fungicide comprises at least one of eugenol, acetyl eugenol, cinnamaldehyde and eucalyptol;

[0023] And / or, the corrosion inhibitor includes sodium N-octylglycinate (OCT) and / or sodium N-dodecylglycinate (DOD).

[0024] In a second aspect, the present invention provides a method for protecting an oil and gas well, which uses the annulus protection fluid described above to fill the oil casing annulus of the oil and gas well.

[0025] The annular space protection fluid of the present invention includes magnetic liquid, base grease, solid filler and base oil. The formed fluid is a non-Newtonian fluid with high density and viscosity, thereby enhancing its sealing performance and achieving a good sealing effect. In addition, the fluid has excellent anti-corrosion performance and can extend the service life of the oil casing. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] To more clearly illustrate the technical solutions in the embodiments of the present invention or related technologies, the following briefly introduces the drawings required for use in the embodiments of the present invention or related technologies. Obviously, the drawings described below are only some embodiments of the present invention. Those skilled in the art can also derive other drawings based on these drawings without inventive effort.

[0027] Figure 1 This is a scanning electron microscope image of the annular space protection fluid of Example 1 of the present invention;

[0028] Figure 2 This is a scanning electron microscope image of the annular space protection fluid of Example 3 of the present invention;

[0029] Figure 3 This is a scanning electron microscope image of the annular space protection fluid of Example 4 of the present invention;

[0030] Figure 4 for Figure 3 EDS map at position 23 in the middle spectrum;

[0031] Figure 5 Graphs showing the storage modulus of the annular protection fluids of Examples 1 to 5;

[0032] Figure 6 Graphs showing loss modulus of annular protection fluids according to Examples 1 to 5;

[0033] Figure 7 Annular space protection fluid loss factor curve diagram of Example 1 to Example 5;

[0034] Figure 8 Graphs showing complex viscosity of the annulus protection fluids of Examples 1 to 5;

[0035] Figure 9 Annular space protection fluid viscosity-shear rate curve diagram of Example 1-Example 5;

[0036] Figure 10 Diagram of the oil pipe used for the annulus protection fluid sealing performance test of Examples 1 to 9. DETAILED DESCRIPTION

[0037] To make the objectives, technical solutions, and advantages of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0038] During the exploration and development of oil and gas fields, the application of annular protection fluids is crucial to ensuring the integrity and functionality of the wellbore. Annular protection fluids are typically used to fill the annular area between the casing and the oil and gas pipes. Their main functions are to prevent the cross-flow of formation fluids (such as oil, gas, and water), protect the oil casing from corrosion, and maintain the structural integrity of the wellbore. Traditional annular protection fluids achieve these functions by adjusting their physical and chemical properties, such as density, viscosity, and chemical composition. However, with the advancement of carbon capture, utilization, and storage (CCUS) projects, traditional annular protection fluids face new challenges, especially in high-pressure carbon dioxide (CO2) injection and alternating water and gas injection operations.

[0039] During high-pressure CO2 injection operations, wellbore packer failures are frequent, leading to serious annular fluid leakage. This leakage not only weakens the annular fluid's anti-corrosion effectiveness but can also cause formation fluid crossflow, compromising the safety and integrity of the wellbore. Furthermore, contact between the high-pressure injected CO2 and wellbore materials can create a highly corrosive environment, exacerbating corrosion of the metal casing. This harsh environment places higher demands on the annular fluid's performance, requiring it to provide both effective sealing and excellent corrosion resistance.

[0040] Existing annular protection fluids struggle to achieve an ideal balance between corrosion resistance and sealing performance. While some traditional protection fluids offer good corrosion resistance, they are prone to leakage in high-pressure and highly corrosive environments, compromising their overall effectiveness. Therefore, developing an annular protection fluid that can remain stable under extreme conditions while maintaining both corrosion resistance and sealing performance has become a pressing technical challenge. This new protection fluid must provide long-lasting protection in high-pressure CO2 environments to ensure the safety and sustainability of CCUS projects.

[0041] Based on this, in a first aspect, the present invention provides an annulus protection fluid, comprising a magnetic liquid, a base grease, a solid filler and a base oil.

[0042] It can be understood that magnetic liquid is a new type of nanomaterial including magnetic nanoparticles, surfactants, and base carrier liquid, which has both magnetism and fluidity.

[0043] The annular protection fluid of the present invention comprises a magnetic liquid, a base grease, a solid filler, and a base oil, achieving both corrosion resistance and sealing performance. This is because the annular protection fluid, comprising the magnetic liquid, base grease, solid filler, and base oil, forms a non-Newtonian fluid with high density and viscosity, which enhances its sealing performance and achieves excellent sealing effects, enabling it to quickly seal pores in the oil casing string and leaking gaps in the packer. Furthermore, this annular protection fluid exhibits excellent corrosion resistance and can maintain stable performance even in highly corrosive media environments, thereby extending the service life of the oil casing.

[0044] Therefore, the annular space protection fluid of the present invention includes magnetic liquid, base grease, solid filler and base oil. The formed fluid is a non-Newtonian fluid with high density and viscosity, thereby enhancing its sealing performance and achieving a good sealing effect. In addition, the fluid has excellent anti-corrosion performance and can extend the service life of the oil casing.

[0045] In some embodiments of the present invention, the solid filler includes at least one of polytetrafluoroethylene, nitrile rubber, graphite, tungsten disulfide, molybdenum disulfide, and boron nitride; the weight-average molecular weight of polytetrafluoroethylene is 5000-10000, for example, it can be 5000, 6000, 7000, 8000, 9000, 10000 or a range consisting of any two thereof; the average particle size is 3μm-10μm, for example, it can be 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm or a range consisting of any two thereof.

[0046] In some embodiments, the average particle size of the nitrile rubber is 0.1 mm-1.2 mm, for example, the average particle size of the nitrile rubber is 0.1 mm, 0.3 mm, 0.5 mm, 0.7 mm, 1.0 mm, 1.2 mm or a range consisting of any two thereof.

[0047] In some embodiments, the average particle size of the graphite is 1 μm-50 μm, for example, the average particle size of the graphite is 1 μm, 5 μm, 10 μm, 20 μm, 30 μm, 40 μm, 50 μm, or a range consisting of any two thereof.

[0048] In some embodiments, the average particle size of tungsten disulfide is 1 μm, 3 μm, 5 μm, 7 μm, 9 μm, 10 μm, or a range consisting of any two thereof.

[0049] In some embodiments, the average particle size of molybdenum disulfide is 1 μm, 3 μm, 5 μm, 7 μm, 9 μm, 10 μm, or a range consisting of any two thereof.

[0050] In some embodiments, the average particle size of the boron nitride is 0.5 μm, 1 μm, 2 μm, 5 μm, 10 μm, 20 μm, 30 μm, or a range consisting of any two thereof.

[0051] The solid filler of the present invention includes the above-mentioned substances, which can further enhance the sealing performance of the annular space protection fluid and achieve a good plugging effect.

[0052] PTFE offers excellent chemical resistance, resisting attack by most chemicals, including strong acids and bases, making it highly stable in corrosive environments. PTFE's low friction helps reduce flow resistance during annular protection fluid injection, improving flow efficiency. Furthermore, PTFE maintains stable performance over a wide temperature range. Furthermore, PTFE's high weight-average molecular weight ensures the material's mechanical strength and wear resistance.

[0053] Nitrile rubber has good tolerance to oil substances and is suitable for use in oil and gas environments. Its good elasticity enables it to effectively fill and seal irregular gaps and enhance the sealing performance of annular protection fluids.

[0054] Graphite has excellent thermal conductivity, which helps dissipate heat and prevent localized overheating. Its natural lubricity reduces friction and wear. Furthermore, graphite maintains a stable structure and performance even in high-temperature environments.

[0055] In some embodiments of the present invention, the magnetic liquid includes Fe3O4 nanoparticles, and the average particle size of the Fe3O4 nanoparticles is 10nm~50nm, for example, it can be 10nm, 20nm, 30nm, 40nm, 50nm or a range consisting of any two thereof.

[0056] The magnetic fluid of the present invention includes Fe3O4 nanoparticles. These particles exhibit superparamagnetism, meaning they rapidly respond and align in the presence of an applied magnetic field, thereby altering the fluid's rheological properties. This property can be used to enhance the fluid's sealing properties when needed, creating a more effective barrier. Furthermore, under the influence of an applied magnetic field, the Fe3O4 nanoparticles can form dense particle chains or networks within the wellbore, filling tiny cracks and voids. This enhances the annular protection fluid's ability to plug leaks and improves its sealing properties.

[0057] Fe3O4 nanoparticles with an average particle size of 10nm to 50nm have a large specific surface area, which helps improve their ability to interact with other components. This high specific surface area facilitates uniform dispersion in the fluid, prevents particle agglomeration, and improves the overall stability and performance of the fluid.

[0058] In one embodiment, the surface of the Fe3O4 nanoparticles may be coated with a silane coupling agent.

[0059] In some embodiments of the present invention, the base grease includes lithium 12-hydroxystearate and / or aluminum-based grease.

[0060] The base grease in this invention, including the aforementioned substances, further enhances the corrosion resistance and sealing properties of the annular protection fluid. Among them, lithium 12-hydroxystearate exhibits excellent thermal stability, maintaining its consistency and performance at high temperatures. It also provides effective protection against moisture in humid environments and resists softening or loss under shear forces, maintaining its sealing and lubricating properties.

[0061] In some embodiments of the present invention, the base oil includes at least one of 500SN base oil, poly-alpha olefin synthetic base oil (PAO10), hydrogenated cycloalkyl base oil, perfluoropolyether, and silicone oil.

[0062] The base oils used in the present invention include the aforementioned substances. Acting as both a carrier and lubricant, the base oils play a crucial role in the corrosion resistance and sealing properties of the annular protection fluid. Synthetic base oils, for example, typically possess higher thermal stability and can maintain their viscosity and lubricity under extreme temperature conditions. Furthermore, synthetic base oils have a more uniform molecular structure and excellent antioxidant properties, extending the service life of the annular protection fluid. Even at low temperatures, synthetic base oils maintain excellent fluidity, ensuring the full performance of the annular protection fluid's properties.

[0063] In some embodiments of the present invention, the annular space protection fluid comprises, by mass percentage, 7.06% to 28.24% magnetic liquid, 16.7% to 17.7% base grease, 47% to 50% solid filler, and the balance is base oil.

[0064] Illustratively, the mass content of the magnetic liquid can be 7.06%, 8%, 9%, 10%, 12%, 15%, 18%, 20%, 25%, 28.24% or a range consisting of any two thereof; the mass content of the base fat can be 16.7%, 16.8%, 16.9%, 17%, 17.1%, 17.3%, 17.5%, 17.7% or a range consisting of any two thereof; the mass content of the solid filler can be 47%, 47.5%, 48%, 48.5%, 49%, 49.5%, 50% or a range consisting of any two thereof.

[0065] The annular protection fluid of the present invention contains a magnetic liquid at a mass percentage of 7.06% to 28.24%. This proportion of magnetic liquid allows the fluid's viscosity and fluidity to be adjusted under an applied magnetic field, thereby enhancing sealing and leak-proofing capabilities. The appropriate amount of magnetic liquid ensures that the fluid can quickly form an effective barrier when needed, preventing fluid channeling. The base grease, which contains a mass percentage of 16.7% to 17.7%, provides excellent lubricity, reduces friction between the fluid and the wellbore wall, and forms a durable seal. The base grease's thermal stability and water resistance help maintain the fluid's performance in high-temperature and humid environments. The solid filler, which contains a mass percentage of 47% to 50%, provides a physical barrier, filling micro-cracks and preventing fluid channeling. Some solid fillers also have anti-corrosion properties. The presence of the solid filler increases the fluid's density and viscosity, enhancing the annular protection fluid's stability under high-pressure conditions. The base oil, acting as a carrier, ensures the annular protection fluid maintains stable fluidity and performance under varying temperature and pressure conditions. The base oil synergizes with the other components to enhance the overall anti-corrosion and sealing effects.

[0066] In the annular space protection fluid of the present invention, the mass percentage of each substance is within the above range, which can make the density of the annular space protection fluid higher, resist the pressure imbalance in the high-pressure injection operation, and effectively support and protect the packer.

[0067] In some embodiments of the present invention, the solid filler includes polytetrafluoroethylene, nitrile rubber and graphite; the mass ratio of polytetrafluoroethylene, nitrile rubber and graphite is (18.8~20):(9.4~10):(18.8~20), for example, it can be 18.8:9.4:18.8, 19:9.4:18.8, 19.5:9.4:18.8, 20:9.4:18.8, 18.8:9.6:18.8, 18.8:9.8:18.8, 18.8:10:18.8, 18.8:9.4:19, 18.8:9.4:19.2, 18.8:9.4:19.5, 18.8:9.4:20 or a range consisting of any two of them.

[0068] When solid filler of the present invention comprises polytetrafluoroethylene (PTFE), acrylonitrile-butadiene rubber (ABC) and graphite, the mass ratio of polytetrafluoroethylene (PTFE), acrylonitrile-butadiene rubber (ABC) and graphite, in the above-mentioned scope, can realize the balance of material characteristic, makes the comprehensive property of fluid in sealing, corrosion resistance and thermal stability better.And this mass ratio can form comparatively dense and uniform filler, fills the crack and the space in the wellbore, improves the sealing and leakproof performance of fluid.In addition, above-mentioned solid filler, by synergistic effect, strengthens the performance of annular space protection fluid under extreme conditions, makes the long-term safety and integrity of wellbore be improved.

[0069] In some embodiments of the present invention, the annular space protection fluid further includes a tracer, and the tracer includes a tracer containing a rare earth element and / or a DNA tracer.

[0070] The present invention incorporates tracers into the annular protection fluid, facilitating the monitoring and management of wellbore integrity. On one hand, the introduction of tracers enables real-time monitoring of fluid flow and distribution, helping to promptly detect and locate leaks. On the other hand, by rapidly detecting and responding to potential leaks, tracers contribute to improving the overall safety of wellbore operations. Furthermore, the data provided by tracers can be used to optimize fluid management strategies, improving operational efficiency and effectiveness. Furthermore, by accurately detecting and controlling fluid leaks, tracers help reduce environmental impact.

[0071] In some embodiments of the present invention, the annular space protection fluid further includes a fungicide and a corrosion inhibitor; the fungicide includes at least one of eugenol, acetyl eugenol, cinnamaldehyde, and eucalyptol.

[0072] In some embodiments, the corrosion inhibitor includes sodium N-octylglycinate (OCT) and / or sodium N-dodecylglycinate (DOD).

[0073] The present invention incorporates a biocide into the annular protection fluid, effectively preventing microbial corrosion and protecting metal casing and other wellbore materials. By inhibiting microbial growth, the biocide helps maintain the chemical and physical stability of the annular protection fluid. Furthermore, it reduces microbial-induced equipment failures and damage, extending the service life of the wellbore and related equipment. Furthermore, by reducing microbial-related issues, the biocide helps improve the overall safety and reliability of wellbore operations.

[0074] The present invention adds a corrosion inhibitor to the annular space protection fluid to form a protective film on the metal surface, reducing the contact between corrosive substances and the metal, thereby reducing the corrosion rate and extending the service life of the oil pipe and casing.

[0075] The annular space protection fluid of the present invention does not contain heavy metal components, and can improve environmental protection.

[0076] The preparation method of the annular space protection fluid of the present invention may include the following steps:

[0077] The base oil is heated to a certain temperature to dissolve the base grease to obtain the first system;

[0078] Then, solid fillers are sequentially added to the first system and stirred at a low speed to obtain a second system;

[0079] After adding the magnetic liquid to the second system, the speed was increased to 60 r / min and mixed evenly to obtain the annular protection fluid.

[0080] In a second aspect, the present invention provides a method for protecting an oil and gas well, which uses the annulus protection fluid described above to fill the casing annulus of the oil and gas well.

[0081] The oil and gas well protection method of the present invention uses the annular space protection fluid to fill the casing annulus of the oil and gas well. Therefore, the oil and gas well protection method can achieve both anti-corrosion performance and sealing performance.

[0082] The technical solution of the present invention is further described below with reference to specific embodiments.

[0083] Example 1

[0084] The preparation method of the annular space protection fluid of this embodiment comprises the following steps:

[0085] 1) The base oil perfluoropolyether is heated to 70° C., and then the base fat 12-hydroxystearate lithium is added thereto and stirred until completely dissolved to obtain the first system.

[0086] 2) Solid fillers polytetrafluoroethylene, nitrile rubber (P830E), and graphite were added to the first system in sequence. The weight-average molecular weight of polytetrafluoroethylene was 8000, the average particle size was 5 μm, the average particle size of nitrile rubber was 0.6 mm, and the average particle size of graphite was 25 μm. The mass ratio M of polytetrafluoroethylene, nitrile rubber, and graphite was 18.8:9.4:18.8. The mixture was gradually accelerated to 60 r / min and mixed uniformly to obtain a second system.

[0087] 3) Add magnetic liquid (MF-35 type) to the second system, wherein the magnetic liquid (MF-35 type) includes Fe3O4 nanoparticles with an average particle size of 30 nm. The speed is gradually increased to 60 r / min and stirred for 30 minutes to obtain an annular protection fluid.

[0088] The annular space protection fluid includes, by mass percentage, 7.06% magnetic liquid (MF-35 type), 17.7% base fat 12-hydroxystearate lithium, 18.8% polytetrafluoroethylene, 9.4% nitrile rubber, 18.8% graphite powder, and 28.24% base oil perfluoropolyether.

[0089] Example 2

[0090] The preparation method of the annular space protection fluid of Example 2 is basically the same as that of Example 1, except that the annular space protection fluid includes, by mass percentage, 14.12% magnetic liquid (MF-35 type), 17.7% base fat 12-hydroxystearate lithium, 18.8% polytetrafluoroethylene, 9.4% nitrile rubber, 18.8% graphite, and 21.18% base oil perfluoropolyether.

[0091] Example 3

[0092] The preparation method of the annular space protection fluid of Example 3 is basically the same as that of Example 1, except that the annular space protection fluid includes, by mass percentage, 21.18% magnetic liquid (MF-35 type), 17.7% base fat 12-hydroxystearate lithium, 18.8% polytetrafluoroethylene, 9.4% nitrile rubber, 18.8% graphite powder, and 14.12% base oil perfluoropolyether.

[0093] Example 4

[0094] The preparation method of the annular space protection fluid of Example 4 is basically the same as that of Example 1, except that the annular space protection fluid includes, by mass percentage, 28.24% magnetic liquid (MF-35 type), 17.7% base fat 12-hydroxystearate lithium, 18.8% polytetrafluoroethylene, 9.4% nitrile rubber, 18.8% graphite powder, and 7.06% base oil perfluoropolyether.

[0095] Example 5

[0096] The preparation method of the annular space protection fluid of Example 5 is basically the same as that of Example 1, except that the annular space protection fluid includes, by mass percentage, 26.64% magnetic liquid (MF-35 type), 16.7% base fat 12-hydroxystearate lithium, 20% polytetrafluoroethylene, 10% nitrile rubber, 20% graphite powder, and 6.66% base oil perfluoropolyether.

[0097] Example 6

[0098] The preparation method of the annular space protection fluid of Example 6 is basically the same as that of Example 1, except that the weight average molecular weight of polytetrafluoroethylene is 5000 and the average particle size is 3 μm; the average particle size of nitrile rubber is 1.2 mm, the average particle size of graphite is 50 μm, the average particle size of Fe3O4 nanoparticles is 10 nm, and the mass ratio M of polytetrafluoroethylene, nitrile rubber and graphite is 18.4:10:20.

[0099] Example 7

[0100] The preparation method of the annular space protection fluid of Example 7 is basically the same as that of Example 1, except that the weight average molecular weight of polytetrafluoroethylene is 10,000 and the average particle size is 10 μm; the average particle size of nitrile rubber is 0.1 mm, the average particle size of graphite is 1 μm, the average particle size of Fe3O4 nanoparticles is 50 nm, and the mass ratio M of polytetrafluoroethylene, nitrile rubber and graphite is 20:9.4:18.8.

[0101] Example 8

[0102] The preparation method of the annular space protection fluid of Example 8 is basically the same as that of Example 1, except that the solid filler includes tungsten disulfide, molybdenum disulfide, and boron nitride, wherein the average particle size of tungsten disulfide is 1 μm, the average particle size of molybdenum disulfide is 10 μm, and the average particle size of boron nitride is 0.5 μm; the base grease is aluminum-based grease, the base oil is silicone oil, and a DNA tracer is additionally added.

[0103] Example 9

[0104] The preparation method of the annular space protection fluid of Example 9 is basically the same as that of Example 1, except that the solid filler includes tungsten disulfide, molybdenum disulfide, and boron nitride, wherein the average particle size of tungsten disulfide is 10 μm, the average particle size of molybdenum disulfide is 1 μm, and the average particle size of boron nitride is 30 μm. Eugenol is additionally added as a bactericide, and sodium N-octylglycinate (OCT) is added as a corrosion inhibitor.

[0105] Comparative Example 1

[0106] The preparation method of the annular space protection fluid of Comparative Example 1 comprises the following steps:

[0107] 1) Dissolve 880 g of sodium formate in 1 kg of water until completely dissolved to obtain a first solution.

[0108] 2) 50 g of sodium carbonate, 50 g of sodium bicarbonate, and 30 g of modified imidazoline-based high-temperature corrosion inhibitor WTH-2600 were sequentially added to the first solution until they were completely dissolved to obtain a second solution.

[0109] 3) Six hours before use, add 4 g of sodium sulfite scavenger to the second solution until it is completely dissolved to obtain an annular protection fluid.

[0110] Comparative Example 2

[0111] The preparation method of the annular space protection fluid of Comparative Example 2 comprises the following steps:

[0112] Under stirring conditions of 4000 rpm, formate, inorganic phosphate and hydroxycarboxylate are added to water; stirring is continued at 4000 rpm, and then thiourea and dodecylthiourea imidazoline are added; stirring is continued, and then sodium sulfite is added; stirring is continued until completely dissolved to obtain an annulus protection fluid.

[0113] The annular space protection fluid includes the following components in parts by mass: 12 parts of water, 10 parts of formate (potassium formate), 25 parts of inorganic phosphate (dipotassium hydrogen phosphate), 1 part of hydroxycarboxylate (sodium citrate), 0.25 parts of thiourea, 0.16 parts of dodecylthiourea imidazoline, and 0.3 parts of sodium sulfite.

[0114] Comparative Example 3

[0115] The preparation method of the annular space protection fluid of Comparative Example 3 is substantially the same as that of Example 1, except that the annular space protection fluid does not include magnetic liquid.

[0116] Comparative Example 4

[0117] The preparation method of the annular space protection fluid of Comparative Example 4 is substantially the same as that of Example 1, except that the annular space protection fluid does not include a solid filler.

[0118] Test example:

[0119] 1. Micromorphology characterization: The annular protection fluid was tested using an S-3400N scanning electron microscope.

[0120] 2. Density test: Use a density meter to test the annular space protection fluid, referring to GB / T 4472-2011 "Determination of density and relative density of chemical products".

[0121] 3. Anti-corrosion performance: The evaluation shall be carried out using the method in Appendix A or Appendix B of GB / T 35509-2017 “Application and Evaluation of Corrosion Inhibitors in Oil and Gas Fields”.

[0122] 4. Sealing performance: At room temperature (25°C) and 60°C, airtightness tests were conducted on annular protection fluids with different magnetic liquid contents. The test selected J55 NU tubing with a specification of Φ73.02×5.51 mm (such as Figure 10 as shown) as the test object.

[0123] 5. Dynamic thermomechanical properties test, shear viscosity test and shear thinning rheological behavior evaluation: Anton Paar MCR502 dynamic rheometer was used. The parameters for dynamic thermomechanical properties test and shear viscosity test were set to a constant shear rate of 1s. -1 The temperature was increased at a rate of 3°C / min over a temperature range of 25°C to 80°C. Shear thinning rheological behavior was evaluated by collecting parameters such as viscosity and angular velocity. Reference was made to ISO 6721-10:2015, "Determination of dynamic mechanical properties."

[0124] In Example 8, the addition of a tracer significantly enhances the accuracy of wellbore monitoring and management. The tracer's unique chemical or physical properties allow real-time tracking of the migration path and dynamic changes of protective fluids, enabling rapid identification of issues such as seal failure and fluid leakage. This technology helps assess protective effectiveness and enables early detection of potential risks (such as corrosion perforation or abnormal annular pressure), providing critical evidence for timely remedial measures. Ultimately, this improves wellbore integrity, extends wellbore service life, and reduces environmental and safety risks.

[0125] In Example 9, the addition of a biocide effectively inhibits the growth of microorganisms (such as sulfate-reducing bacteria and saprophytes), preventing the metabolically induced microbial corrosion (MIC) and the production of harmful byproducts (such as hydrogen sulfide), thereby significantly reducing the risk of corrosion of the casing and tubing. Furthermore, the biocide prevents microorganisms from forming biofilms on the inner wall of the annulus, reducing localized electrochemical corrosion caused by biofilm accumulation and ensuring the long-term stability and sealing effectiveness of the protective fluid. By controlling microbial contamination, the degradation of the annular fluid performance can be delayed, reducing the probability of wellbore integrity failure, and ultimately improving the safety and economic efficiency of oil and gas well operations.

[0126] Furthermore, in Example 9, the addition of a corrosion inhibitor can suppress corrosion of the tubing and casing caused by electrochemical reactions. The corrosion inhibitor forms a dense and stable passivation film by adsorbing on the metal surface, effectively isolating corrosive media (such as CO2, H2S, and Cl⁻) from the tubing and casing matrix, reducing the reaction rate and thereby delaying the occurrence of uniform corrosion, pitting, and stress corrosion cracking. Furthermore, the corrosion inhibitor can synergize with other functional additives (such as fungicides) in the annular protection fluid to reduce the risk of localized corrosion, safeguard the long-term integrity of the tubing and casing structure, significantly extend the service life of the equipment, and reduce the probability of wellbore failure and maintenance costs caused by corrosion.

[0127] Figure 1 This is a scanning electron microscope image of the annular space protection fluid of Example 1 of the present invention.

[0128] Figure 2 This is a scanning electron microscope image of the annular space protection fluid of Example 3 of the present invention.

[0129] Figure 3 This is a scanning electron microscope image of the annular space protection fluid of Example 4 of the present invention.

[0130] from Figure 1-3 It can be seen that with the increase of magnetic liquid content, the distribution of solid particles in the annular protection fluid shows a densification trend. In Example 4 with a magnetic liquid content of 28.24%, the solid particles are almost evenly distributed throughout the entire observation field of view, forming a continuous and dense network structure, and no obvious particle agglomeration phenomenon is observed. This result shows that the introduction of magnetic liquid significantly improves the dispersibility of solid particles and promotes their uniform distribution in the annular protection fluid. Further analysis found that a large number of solid particles with smaller particle sizes appeared in Example 4, which was mainly attributed to the introduction of Fe3O4 nanoparticles in the magnetic liquid. Due to their high specific surface area and surface activity, Fe3O4 nanoparticles can effectively fill the microscopic voids in the annular protection fluid and form a synergistic effect with the solid particles, thereby enhancing the density and stability of the overall structure. This phenomenon not only confirms the significant regulatory effect of the magnetic liquid content on the microstructure of the annular protection fluid, but also reveals its promoting effect on the dispersibility of solid particles and the formation of network structure.

[0131] Figure 4 for Figure 3 EDS map at position 23 in the spectrum.

[0132] from Figure 4 It can be seen that at position 23 of the spectrum in Example 3, the iron content is 27.45% and the oxygen content is 3.81%. This ratio is highly consistent with the stoichiometric ratio of Fe3O4, indicating that this position is mainly composed of Fe3O4 nanoparticles in the magnetic liquid. In addition, the presence of fluorine and trace chlorine elements were also detected at position 23 of the spectrum, mainly attributed to the uniform dispersion of polytetrafluoroethylene and nitrile rubber in the solid filler. At the same time, the carbon content at this position is as high as 61.67%, and its main source is graphite. The introduction of graphite not only enhances the lubrication performance of the annular protection fluid, but also further optimizes its mechanical strength and thermal stability.

[0133] Figure 5 This is a storage modulus curve diagram of the annular space protection fluid of Example 1 to Example 5.

[0134] from Figure 5 It can be seen that when the mass percentage of the magnetic liquid is increased from 7.06% to 14.12%, the storage modulus of Example 1 and Example 2 remains relatively stable. However, when the mass percentage of the magnetic liquid is 21.18%, the storage modulus of Example 3 increases significantly, while the storage moduli of Examples 4 and 5 are close to that of Example 3 and tend to be stable. This phenomenon shows that when a small amount of Fe3O4 nanoparticles in the magnetic liquid are introduced, they have a significant effect on the solid particle network structure of the annular protection fluid, further enhancing its elastic characteristics. In addition, as the temperature increases, the storage modulus of Examples 1 to 5 all show a trend of first decreasing and then increasing, and an inflection point appears in the range of 68°C to 70°C. After the inflection point, the storage modulus increases slightly as the temperature further increases, which shows that the introduction of the magnetic liquid significantly improves the thermal stability of the solid particle network structure inside the annular protection fluid.

[0135] Figure 6 This is a graph showing the loss modulus of the annular protection fluid of Examples 1 to 5.

[0136] from Figure 6It can be seen that with the increase in the mass percentage of magnetic liquid, the loss modulus also shows an upward trend, and its evolution law is similar to that of the storage modulus. The loss modulus of Example 1 and Example 2 is relatively stable, while the loss modulus of Example 3 increases significantly, and Examples 4 and 5 remain stable. In the temperature range of 25°C to 35°C, the loss modulus decreases with increasing temperature, which is mainly attributed to the decrease in the viscosity of the base fat; when the temperature exceeds 35°C, the change in the loss modulus tends to be flat until the temperature reaches 55°C, when the loss modulus shows a slight increase accompanied by slight oscillations. This behavior may be related to the magnetorheological effect of Fe3O4 nanoparticles in the magnetic liquid and its interaction with the matrix.

[0137] Figure 7 This is a graph showing the loss factor of the annulus protection fluid for Examples 1 to 5.

[0138] from Figure 7 It can be seen that the magnetic fluid content has a minimal effect on the loss factor of the annular protection fluid; increasing or decreasing the magnetic fluid content does not significantly change the loss factor. This indicates that the loss factor of the annular protection fluid is insensitive to temperature changes and further confirms that the introduction of magnetic fluid can significantly improve the overall stability of the annular protection fluid during heating. Taken together, these results indicate that the addition of magnetic fluid not only optimizes the rheological properties of the annular protection fluid but also significantly enhances its application potential in high-temperature environments by enhancing the thermal stability of the solid particle network structure.

[0139] Figure 8 This is a complex viscosity curve of the annulus protection fluid of Example 1 to Example 5.

[0140] from Figure 8 It can be seen that as the mass percentage of the magnetic liquid increases from 7.06% to 14.12%, the complex viscosity of the air protection fluids of Examples 1 and 2 decreases significantly. This phenomenon is mainly attributed to the lower viscosity of the magnetic liquid compared to the base oil, which plays a lubricating role in the system, thereby reducing the overall viscosity. However, when the mass percentage of the magnetic liquid increases further, the complex viscosity gradually increases. This change shows that the Fe3O4 nanoparticles in the magnetic liquid play an important role in the system, not only promoting the formation of the solid particle network structure, but also enhancing the stability and density of the network through its nano effect.

[0141] When the temperature is below 60°C, the complex viscosity of the annular protection fluids of Examples 1 to 5 gradually decreases with increasing temperature, which is consistent with the typical rheological behavior of non-Newtonian fluids, that is, increasing temperature leads to intensified molecular motion, thereby reducing the viscosity of the system. However, in the temperature range of 60°C to 80°C, the complex viscosity-temperature curve tends to be flat, indicating that the effect of further increasing the temperature on the complex viscosity is significantly weakened. This phenomenon reveals that the annular protection fluid has high rheological stability in a high temperature environment, which is mainly attributed to the strengthening effect of Fe3O4 nanoparticles on the solid particle network structure and its thermal stability at high temperatures. Therefore, the introduction of magnetic fluid not only optimizes the rheological properties of the annular protection fluid through its lubricating effect, but also significantly enhances the stability of the solid particle network structure through the nano effect of Fe3O4 nanoparticles.

[0142] Figure 9 Graphs showing viscosity-shear rate curves of the annular protection fluids of Examples 1 to 5.

[0143] from Figure 9 It can be seen that the viscosity of the annular protection fluid does not change significantly with the increase in the mass percentage of magnetic liquid, indicating that the introduction of magnetic liquid has a limited effect on the rheological properties of the annular protection fluid. This is attributed to the weak interaction between the magnetic liquid and other components or the concentration not reaching the threshold that significantly changes the rheological behavior of the system. At the same time, with the increase in shear rate, the viscosity of the annular protection fluid shows a clear linear downward trend, exhibiting typical shear thinning characteristics, indicating that at high shear rates, the microstructure within the annular protection fluid (such as molecular chain orientation, particle dispersion state, or interaction forces) is reorganized or destroyed under the action of shear force. Specifically, the increase in shear force may weaken the weak interactions within the annular protection fluid (such as van der Waals forces, hydrogen bonds, or electrostatic interactions) or promote the rearrangement of particles or molecular chains, thereby reducing flow resistance and significantly enhancing fluidity. Therefore, the increase in the mass percentage of magnetic liquid has little effect on the rheological properties of the annular protection fluid, while the increase in shear rate significantly reduces the viscosity of the annular protection fluid, reflecting the non-Newtonian fluid behavior of the material at high shear rate, and providing an important theoretical basis for its application in the lubrication and sealing fields under high shear conditions.

[0144] Table 1

[0145]

[0146] Table 2

[0147]

[0148] As can be seen from Table 1-2, compared with the comparative example, the annular space protection fluid provided by the present invention includes magnetic liquid, base grease, solid filler and base oil. The formed fluid is a non-Newtonian fluid with high density and viscosity, which can enhance its sealing performance and achieve a good sealing effect. In addition, the fluid has excellent anti-corrosion performance and can extend the service life of the oil casing.

[0149] As shown in Table 2, under test pressures of 28 MPa, 35 MPa, and 42 MPa, the annular protection fluids of Examples 1-5 exhibited no gas leakage. All annular protection fluids with varying magnetic liquid contents exhibited excellent airtightness. This indicates that the addition of magnetic liquid did not significantly alter the sealing capability of the annular protection fluid, primarily due to the good compatibility between the magnetic liquid and the matrix material and the uniform dispersion of the magnetic liquid at the sealing interface. Furthermore, the introduction of magnetic liquid may improve the filling performance of the annular protection fluid under high pressure through its unique rheological properties (such as shear-thinning behavior), thereby enhancing the stability of the sealing interface. Notably, the annular protection fluid maintained a seal even under a high pressure of 42 MPa, indicating that the addition of magnetic liquid did not weaken the pressure resistance of the annular protection fluid and may even improve its sealing reliability under high pressure by enhancing the material's deformation resistance, further confirming the annular protection fluid's excellent pressure resistance and adaptability to extreme operating conditions.

[0150] At 60°C and 65 MPa, 77 MPa, and 90 MPa, the annular protection fluids of Examples 1-5 exhibited no gas leakage, demonstrating that the annular protection fluids can effectively fill leaking gaps and form a stable sealing interface under high temperature and high pressure, exhibiting excellent gas sealing performance in extreme high-pressure environments. This further demonstrates that the introduction of magnetic fluids may improve the filling performance of the annular protection fluid under high pressure through their unique rheological properties (such as shear-thinning behavior), thereby enhancing the stability of the sealing interface. This demonstrates that the annular protection fluids possess excellent high-temperature and pressure resistance and adaptability to extreme operating conditions.

[0151] Finally, it should be noted that those skilled in the art will readily identify other embodiments of the present invention after considering the specification and practicing the invention disclosed herein. The present invention is intended to cover any variations, uses, or adaptations of the present invention that follow the general principles of the present invention and include common knowledge or customary techniques in the art not disclosed herein. The present invention is not limited to the precise structure described above and illustrated in the accompanying drawings, and various modifications and variations may be made without departing from the scope thereof. The scope of the present invention is limited solely by the appended claims.

Claims

1. An annulus protection fluid, characterized in that: The invention comprises a magnetic liquid, a base grease, a solid filler and a base oil; the solid filler comprises at least one of polytetrafluoroethylene, nitrile rubber, graphite, tungsten disulfide, molybdenum disulfide and boron nitride; the magnetic liquid comprises Fe3O4 nanoparticles, and the average particle size of the Fe3O4 nanoparticles is 10nm to 50nm; The base grease includes 12-hydroxystearate lithium and / or aluminum-based grease; The base oil includes at least one of 500SN base oil, poly-alpha olefin synthetic base oil, hydrogenated cycloalkyl base oil, perfluoropolyether, and silicone oil; The annular space protection fluid comprises, by mass percentage, 7.06% to 28.24% of magnetic liquid, 16.7% to 17.7% of base grease, 47% to 50% of solid filler, and the balance of base oil; The annular space protection fluid is a non-Newtonian fluid.

2. The annulus protection fluid according to claim 1, characterized in that: The weight average molecular weight of the polytetrafluoroethylene is 5000-10000, and the average particle size is 3 μm-10 μm; And / or, the average particle size of the nitrile rubber is 0.1 mm to 1.2 mm; And / or, the average particle size of the graphite is 1 μm-50 μm; And / or, the average particle size of the tungsten disulfide is 1 μm-10 μm; And / or, the average particle size of the molybdenum disulfide is 1 μm-10 μm; And / or, the average particle size of the boron nitride is 0.5 μm-30 μm.

3. The annulus protection fluid according to claim 1, characterized in that: The solid filler includes polytetrafluoroethylene, nitrile rubber and graphite; The mass ratio of the polytetrafluoroethylene, nitrile rubber and graphite is (18.8-20): (9.4-10): (18.8-20).

4. The annulus protection fluid according to any one of claims 1 to 3, characterized in that: The annular space protection fluid further includes a tracer, and the tracer includes a tracer containing rare earth elements and / or a DNA tracer.

5. The annulus protection fluid according to claim 4, characterized in that: The annular space protection fluid also includes a bactericide and a corrosion inhibitor; The fungicide comprises at least one of eugenol, acetyl eugenol, cinnamaldehyde and eucalyptol; And / or, the corrosion inhibitor includes sodium N-octylglycinate and / or sodium N-dodecylglycinate.

6. A method for protecting an oil and gas well, characterized in that: The annulus protection fluid according to any one of claims 1 to 5 is used to fill the casing annulus of the oil and gas well.

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