Annulus protection fluid and application thereof

Abstract

The invention provides an annulus protection fluid and application thereof. The annulus protection fluid comprises a magnetic liquid, base grease, a solid filler and base oil. The annulus protection fluid comprises the magnetic liquid, the base grease, the solid filler and the base oil, and the formed fluid is a non-Newtonian fluid and is high in density and viscosity, so that the sealing performance of the fluid can be enhanced, a good plugging effect is achieved, the fluid has excellent corrosion resistance, and the service life of an oil casing can be prolonged.

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] In the process of oil and gas field exploration and development, the application of annular protection fluid is crucial to maintaining the integrity and function of the wellbore. Annular protection fluid is usually used to fill the annular area between the casing and the tubing to prevent the cross-flow of formation fluids (such as oil, gas, and water), reduce the pressure of the packer from the oil and gas layer, 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, especially in high-pressure carbon dioxide injection and water-gas alternating injection operations. For example, the annular protection fluids in the existing technology cannot achieve both anti-corrosion performance and sealing performance, which not only affects the safety and effectiveness of CCUS projects, but also may cause potential risks to the environment. Therefore, the development of an annular protection fluid that can take into account both anti-corrosion performance and sealing performance has become a technical problem that needs to be solved urgently. Summary of the invention

[0004] The main purpose of the present invention is to provide an annulus 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 space 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-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] As the annular protection fluid described above, the magnetic liquid includes Fe 3 O 4 Nanoparticles, the Fe 3 O 4 The average particle size of nanoparticles is 10nm~50nm.

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

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

[0017] The annulus 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 annulus protection fluid as described above further comprises a tracer, and the tracer comprises a tracer containing rare earth elements and / or a DNA tracer.

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

[0022] The bactericide 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, using the annulus protection fluid as described above to fill the casing annulus of the oil and gas well.

[0025] The annulus protection fluid of the present invention comprises 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 plugging effect. The fluid has excellent anti-corrosion performance and can extend the service life of the oil casing. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order 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, and for ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

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

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

[0029] Figure 3 This is a scanning electron microscope image of the annulus 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 It is a storage modulus curve diagram of the annular space protection fluid of Example 1 to Example 5;

[0032] Figure 6 It is a graph of loss modulus of annular space protection fluid of Example 1 to Example 5;

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

[0034] Figure 8 The complex viscosity curve diagram of the annulus protection fluid of Example 1 to Example 5;

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

[0036] Fig.10 This is a diagram of the oil pipe used for testing the sealing performance of the annulus protection fluid in Examples 1 to 9. DETAILED DESCRIPTION

[0037] In order to make the purpose, technical solutions and advantages of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in combination with the embodiments of the present invention. Obviously, the described embodiments are 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 creative work are 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 fluid is crucial to ensure the integrity and functionality of the wellbore. Annular protection fluid is usually used to fill the annular area between the casing and the oil and gas pipe. Its main function is 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, especially in the field of carbon dioxide (CO 2 ) Traditional annular space protection fluid faces new challenges in high-pressure injection and water-gas alternating injection operations.

[0039] In CO 2 During high-pressure injection operations, wellbore packers frequently fail, resulting in serious leakage of the annular protection fluid. This leakage not only weakens the anti-corrosion effect of the annular protection fluid, but may also cause formation fluid crossflow, thus affecting the safety and integrity of the wellbore. In addition, the high-pressure injected CO 2 After contacting with wellbore materials, a highly corrosive environment may be formed, which will aggravate the corrosion of metal casing. This harsh environment places higher requirements on the performance of annular protection fluid, requiring it to have excellent anti-corrosion performance while providing effective sealing.

[0040] It is difficult for existing annular protection fluids to achieve an ideal balance between anti-corrosion performance and sealing performance. Although some traditional protection fluids have good anti-corrosion performance, they are prone to leakage under high pressure and highly corrosive environments, affecting their overall effect. Therefore, the development of an annular protection fluid that can remain stable under extreme conditions and take into account both anti-corrosion and sealing performance has become a technical problem that needs to be solved urgently. This new type of protection fluid needs to be in high pressure CO 2 Provide lasting protection in the environment 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 annulus protection fluid of the present invention includes magnetic liquid, base grease, solid filler and base oil, and can take into account both anti-corrosion performance and sealing performance. This is because the annulus protection fluid includes magnetic liquid, base grease, solid filler and base oil, and the fluid formed is a non-Newtonian fluid with high density and viscosity, thereby enhancing its sealing performance, achieving a good plugging effect, and being able to quickly plug the pores of the oil casing string and the leakage gaps of the packer. In addition, the annulus protection fluid has excellent anti-corrosion performance, can maintain stable performance in a highly corrosive medium environment, and extend the service life of the oil casing.

[0044] Therefore, the annulus 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 plugging effect. 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 graphite is 1 μm-50 μm, for example, the average particle size of 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] Among them, polytetrafluoroethylene has excellent chemical corrosion resistance and can resist the erosion of most chemicals, including strong acids and strong bases, making it very stable in corrosive environments. And the low friction characteristics of polytetrafluoroethylene help reduce the flow resistance of the fluid during the annular protection fluid filling process and improve the flow efficiency. In addition, polytetrafluoroethylene can maintain stable performance over a wide temperature range. At the same time, the weight average molecular weight of polytetrafluoroethylene ensures the mechanical strength and wear resistance of the material.

[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 the annular protection fluid.

[0054] Graphite has good thermal conductivity, which can help dissipate heat and prevent local overheating. And the natural lubricity of graphite can reduce friction and wear. In addition, graphite can maintain a stable structure and performance in high temperature environments.

[0055] In some embodiments of the present invention, the magnetic liquid includes Fe 3 O 4 Nanoparticles, Fe 3 O 4 The average particle size of the nanoparticles is 10 nm to 50 nm, for example, 10 nm, 20 nm, 30 nm, 40 nm, 50 nm or a range consisting of any two thereof.

[0056] The magnetic liquid of the present invention comprises Fe 3 O 4 Nanoparticles, Fe 3 O 4 The nanoparticles are superparamagnetic, which means they can quickly respond and form an oriented alignment in the presence of an external magnetic field, thereby changing the rheological properties of the fluid. This property can be used to enhance the sealing performance of the fluid when needed, forming a more effective barrier. In addition, under the action of an external magnetic field, Fe 3 O 4 Nanoparticles can form dense particle chains or network structures in the wellbore, filling tiny cracks and gaps, thereby enhancing the plugging ability of the annulus protection fluid and improving the sealing performance.

[0057] Fe with an average particle size of 10nm~50nm3 O 4 Nanoparticles have a large specific surface area, which is beneficial for improving their ability to interact with other components. This high specific surface area is conducive to forming a uniform dispersion in the fluid, preventing particle agglomeration, and improving the overall stability and performance of the fluid.

[0058] In one embodiment, Fe 3 O 4 The surface of the nanoparticles can 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 the present invention includes the above-mentioned substances, which can further improve the anti-corrosion performance and sealing performance of the annular protection fluid. Among them, 12-hydroxy lithium stearate has good thermal stability, can maintain its consistency and performance in a high temperature environment, and can provide effective protection in a humid environment to prevent the intrusion of water, is not easy to soften or lose under the action of shear force, and maintains 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 cycloalkane base oil, perfluoropolyether, and silicone oil.

[0062] The base oil in the present invention includes the above-mentioned substances. The base oil, as a carrier and lubricant, plays a vital role in the anti-corrosion performance and sealing performance of the annular space protection fluid. Taking synthetic base oil as an example, it usually has higher thermal stability and can maintain its viscosity and lubrication performance under extreme temperature conditions. In addition, the molecular structure of synthetic base oil is more uniform, and its antioxidant performance is excellent, which prolongs the service life of the annular space protection fluid. In a low temperature environment, the synthetic base oil can still maintain good fluidity, ensuring the performance of the annular space protection fluid.

[0063] In some embodiments of the present invention, the annulus protection fluid includes, 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] Exemplarily, 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] In the annulus protection fluid of the present invention, the mass percentage of the magnetic liquid is 7.06% to 28.24%, and the proportion of the magnetic liquid allows the viscosity and fluidity of the fluid to be adjusted under an external magnetic field, thereby enhancing the sealing performance and plugging ability. And an appropriate amount of magnetic liquid ensures that the fluid can quickly form an effective barrier when needed to prevent fluid channeling. The mass percentage of the base grease is 16.7% to 17.7%, and the base grease provides good lubricity, reduces the friction between the fluid and the wellbore wall, and forms a durable sealing layer. And the thermal stability and water resistance of the base grease help to maintain the performance of the fluid in high temperature and humid environments. The mass percentage of the solid filler is 47% to 50%, and a high proportion of solid fillers provides a physical barrier, fills tiny cracks, and prevents fluid channeling. At the same time, some solid fillers also have anti-corrosion properties. And the presence of solid fillers increases the density and viscosity of the fluid, and enhances the stability of the annulus protection fluid under high pressure environments. The base oil acts as a carrier to ensure that the annulus protection fluid maintains stable fluidity and performance under different temperature and pressure conditions. And the base oil synergizes with 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, so that the density of the annular space protection fluid is relatively high, and it can 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 the solid filler of the present invention comprises polytetrafluoroethylene, nitrile rubber and graphite, the mass ratio of polytetrafluoroethylene, nitrile rubber and graphite is within the above range, and the balance of material properties can be achieved, so that the comprehensive performance of the fluid in terms of sealing, corrosion resistance and thermal stability is better. And this mass ratio can form a more dense and uniform filler, fill the cracks and gaps in the wellbore, and improve the sealing and leakproof performance of the fluid. In addition, the above-mentioned solid filler enhances the performance of the annular space protection fluid under extreme conditions through synergistic effect, so that the long-term safety and integrity of the wellbore are improved.

[0069] In some embodiments of the present invention, the annulus 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 adds tracers to the annular protection fluid, which can facilitate the monitoring and management of wellbore integrity. On the one hand, the introduction of tracers makes it possible to monitor the flow and distribution of fluids in real time, helping to timely detect and locate leaks. On the other hand, by quickly detecting and responding to potential leakage problems, tracers help improve the overall safety of wellbore operations. In addition, the data provided by tracers can be used to optimize fluid management strategies and improve operational efficiency and effectiveness. At the same time, by accurately detecting and controlling fluid leakage, tracers help reduce the impact on the environment.

[0071] In some embodiments of the present invention, the annulus protection fluid further includes a bactericide and a corrosion inhibitor; the bactericide 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 adds a bactericide to the annular protection fluid, which can effectively prevent corrosion problems caused by microorganisms and protect metal casings and other wellbore materials. And by inhibiting the growth of microorganisms, the bactericide helps to maintain the chemical and physical stability of the annular protection fluid. In addition, it can also reduce equipment failures and damage caused by microorganisms and extend the service life of the wellbore and related equipment. At the same time, by reducing microbial-related problems, the bactericide helps to improve the overall safety and reliability of wellbore operations.

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

[0075] The annular space protection fluid of the present invention has no heavy metal components and can improve environmental protection.

[0076] The preparation method of the annulus 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 fat 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 into the second system, the gradient speed is 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 as 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 annulus 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 in conjunction with 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, wherein 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, 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, and the speed was increased gradually to 60 r / min and mixed evenly to obtain the second system.

[0087] 3) Adding magnetic liquid (MF-35 type) to the second system, wherein the magnetic liquid (MF-35 type) includes Fe 3 O 4 Nanoparticles, Fe 3 O 4 The average particle size of the nanoparticles was 30 nm, and the speed was gradually increased to 60 r / min and stirred for 30 min to obtain the 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 annulus protection fluid of Example 2 is basically the same as that of Example 1, except that the annulus 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 annulus protection fluid of Example 3 is basically the same as that of Example 1, except that the annulus 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 annulus protection fluid of Example 4 is basically the same as that of Example 1, except that the annulus 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 annulus protection fluid of Example 5 is basically the same as that of Example 1, except that the annulus 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 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, and Fe 3 O 4The average particle size of the 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 10000 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, and Fe 3 O 4 The average particle size of the 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 annulus 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, and 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 it is 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 high temperature corrosion inhibitor WTH-2600 were added to the first solution in sequence until they were completely dissolved, to obtain a second solution.

[0109] 3) 6 hours before use, add 4 g of sodium sulfite deoxidizer to the second solution until it is completely dissolved to obtain an annulus 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 annulus protection fluid of Comparative Example 3 is substantially the same as that of Example 1, except that the annulus protection fluid does not include magnetic liquid.

[0116] Comparative Example 4

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

[0118] Test example:

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

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

[0121] 3. Anti-corrosion performance: The evaluation is 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, the air sealing test was carried out for the annular protection fluid with different magnetic liquid contents. The test selected J55 NU oil pipe with a specification of Φ73.02×5.51 mm (such as Fig.10 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 of dynamic thermomechanical properties test and shear viscosity test were set to a constant shear rate of 1s -1, heating rate 3℃ / min, temperature range 25℃~80℃. Shear thinning rheological behavior evaluation collects parameters such as viscosity and angular velocity. Reference standard ISO 6721-10:2015 "Determination of dynamic mechanical properties".

[0124] In Example 8, the addition of tracers can significantly improve the accuracy of wellbore monitoring and management. Through the unique chemical or physical properties of tracers, the migration path and dynamic changes of protective fluids can be tracked in real time, thereby quickly identifying problems such as seal failure and fluid leakage. This technology helps to evaluate the protection effect and detect potential risks (such as corrosion perforation or abnormal annular pressure) at an early stage, providing a key basis for timely remedial measures, ultimately improving wellbore integrity, extending service life, and reducing environmental and safety risks.

[0125] In Example 9, due to the addition of bactericide, the growth of microorganisms (such as sulfate-reducing bacteria, saprophytes, etc.) can be effectively inhibited, and the biocorrosion (MIC) and harmful byproducts (such as hydrogen sulfide) caused by their metabolic activities can be avoided, thereby significantly reducing the corrosion risk of oil casing. In addition, the bactericide can prevent microorganisms from forming biofilms on the inner wall of the annulus, reduce local electrochemical corrosion caused by biofilm accumulation, and ensure the long-term stability and sealing effect of the protective fluid. By controlling microbial contamination, the degradation of annular fluid performance can also be delayed, the probability of wellbore integrity failure can be reduced, and ultimately the safety and economy of oil and gas well operation can be improved.

[0126] In Example 9, the corrosion inhibitor was added to inhibit the corrosion of the oil pipe and casing caused by electrochemical action. The corrosion inhibitor forms a dense and stable passivation film on the metal surface, effectively isolating the corrosive medium (such as CO 2 , H 2 S, Cl⁻) contact with the oil casing matrix, reducing the reaction rate, thereby delaying the occurrence of uniform corrosion, pitting and stress corrosion cracking. In addition, the corrosion inhibitor can also work synergistically with other functional additives (such as fungicides) in the annular protection fluid to reduce the risk of local corrosion, ensure the long-term integrity of the oil 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 annulus protection fluid of Example 1 of the present invention.

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

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

[0130] from Figure 1-3It 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 in 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 Fe 3 O 4 The introduction of nanoparticles, Fe 3 O 4 Nanoparticles, due to their high specific surface area and surface activity, can effectively fill the microscopic gaps in the annular protection fluid and form a synergistic effect with solid particles, thereby enhancing the density and stability of the overall structure. This phenomenon not only confirms the significant regulatory effect of magnetic liquid content on the microstructure of the annular protection fluid, but also reveals its role in promoting the dispersion 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 of Example 3, the content of iron is 27.45%, and the content of oxygen is 3.81%. 3 O 4 The stoichiometric ratio of 3 O 4 Nanoparticles. In addition, the presence of fluorine and trace chlorine was detected at position 23 of the spectrum, which was 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 was as high as 61.67%, and its main source was graphite. The introduction of graphite not only enhanced the lubrication performance of the annular protection fluid, but also further optimized its mechanical strength and thermal stability.

[0133] Figure 5 It is a storage modulus curve diagram of the annulus 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 increases 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 modulus of Examples 4 and 5 is close to that of Example 3 and tends to be stable. This phenomenon shows that the Fe in the magnetic liquid3 O 4 When introduced in small amounts, nanoparticles 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, indicating that the introduction of magnetic fluid 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 annulus protection fluid of Examples 1 to 5.

[0136] from Figure 6 It 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 gentle until the temperature reaches 55°C, when the loss modulus increases slightly with slight oscillations. This behavior may be related to the Fe in the magnetic liquid. 3 O 4 The magnetorheological effect of nanoparticles is related to their interaction with the matrix.

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

[0138] from Figure 7 It can be seen that the magnetic liquid content has little effect on the loss factor of the annular protection fluid, that is, increasing or decreasing the magnetic liquid content does not significantly change the value of the loss factor. This shows that the loss factor of the annular protection fluid is not sensitive to temperature changes, and further confirms that the introduction of magnetic liquid can significantly improve the overall stability of the annular protection fluid during the heating process. Based on the above results, the addition of magnetic liquid not only optimizes the rheological properties of the annular protection fluid, but also significantly improves 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 8It 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 Fe in the magnetic liquid 3 O 4 Nanoparticles play an important role in the system, not only promoting the formation of solid particle network structure, but also enhancing the stability and density of the network through their 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, the increase in 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 a high rheological stability in a high temperature environment, which is mainly attributed to the Fe 3 O 4 Nanoparticles strengthen the network structure of solid particles and their thermal stability at high temperatures. Therefore, the introduction of magnetic fluid not only optimizes the rheological properties of the annular protection fluid through its lubrication effect, but also through Fe 3 O 4 The nano effect of nanoparticles significantly enhances the stability of the solid particle network structure.

[0142] Fig. 9 Annular space protection fluid viscosity-shear rate curve diagram of Example 1-Example 5.

[0143] from Fig. 9It can be seen that with the increase of the mass percentage of magnetic liquid, the viscosity of the annular protection fluid does not change significantly, indicating that the introduction of magnetic liquid has limited effect on the rheological properties of the annular protection fluid, which is attributed to the weak interaction between the magnetic liquid and other components or its concentration does not reach the threshold of significantly changing the rheological behavior of the system; at the same time, with the increase of shear rate, the viscosity of the annular protection fluid shows an obvious linear downward trend, showing typical shear thinning characteristics, indicating that at high shear rate, the microstructure inside the annular protection fluid (such as molecular chain orientation, particle dispersion state or interaction force) is reorganized or destroyed under the action of shear force. Specifically, the increase in shear force may weaken the weak interactions inside the annular protection fluid (such as van der Waals forces, hydrogen bonds or electrostatic effects), 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 annulus protection fluid, while the increase in shear rate significantly reduces the viscosity of the annulus protection fluid, reflecting the non-Newtonian fluid behavior of the material at high shear rate, and provides 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] It can be seen from Table 1-2 that, compared with the comparative example, the annulus 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, thereby enhancing its sealing performance and achieving a good plugging effect. The fluid has excellent anti-corrosion performance and can extend the service life of the oil casing.

[0149] As can be seen from Table 2, under the conditions of test pressures of 28 MPa, 35 MPa and 42 MPa, the annular protection fluids of Examples 1 to 5 did not leak gas, and the annular protection fluids with different magnetic liquid contents all showed excellent gas sealing performance. This shows that the addition of magnetic liquid did not significantly change the sealing ability of the annular protection fluid, which is mainly attributed to the good compatibility between the magnetic liquid and the matrix material, and the uniform dispersion of the magnetic liquid in the sealing interface. In addition, 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. It should be noted that under a high pressure of 42 MPa, the annular protection fluid can still remain sealed, indicating that the addition of magnetic liquid does 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 anti-deformation ability, further confirming that the annular protection fluid has excellent pressure resistance and adaptability to extreme working conditions.

[0150] At 60°C, 65 MPa, 77 MPa, and 90 MPa, the annular protection fluids of Examples 1 to 5 did not leak gas, indicating that the annular protection fluids can effectively fill the leakage gaps and form a stable sealing interface under high temperature and high pressure, and have excellent gas sealing performance in extreme high-pressure environments. This once again proves that the introduction of magnetic fluids may improve the filling performance of annular protection fluids under high pressure through their unique rheological properties (such as shear thinning behavior), thereby enhancing the stability of the sealing interface. This shows that the annular protection fluid has excellent high temperature and pressure resistance and adaptability to extreme working conditions.

[0151] Finally, it should be noted that those skilled in the art will readily conceive of 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, which follow the general principles of the present invention and include common knowledge or customary technical means in the art not disclosed by the present invention, are not limited to the precise structure described above and shown in the drawings, and may be modified and changed in various ways without departing from the scope thereof. The scope of the present invention is limited only by the appended claims.

Claims

1. An annulus protection fluid, characterized in that: Includes magnetic fluid, base grease, solid filler and base oil.

2. The annulus protection fluid according to claim 1, characterized in that: 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 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-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 or 2, characterized in that: The magnetic liquid comprises Fe3O4 nanoparticles, and the average particle size of the Fe3O4 nanoparticles is 10nm-50nm.

4. The annulus protection fluid according to any one of claims 1 to 3, characterized in that: The base grease includes lithium 12-hydroxystearate and / or aluminum-based grease.

5. The annulus protection fluid according to any one of claims 1 to 4, characterized in that: The base oil includes at least one of 500SN base oil, poly-alpha olefin synthetic base oil (PAO10), hydrogenated cycloalkane base oil, perfluoropolyether, and silicone oil.

6. The annulus protection fluid according to any one of claims 1 to 5, characterized in that: The annular space protection fluid includes, 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 is base oil.

7. The annulus protection fluid according to claim 2, 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).

8. The annulus protection fluid according to any one of claims 1 to 7, characterized in that: The annulus protection fluid further includes a tracer, and the tracer includes a tracer containing a rare earth element and / or a DNA tracer.

9. The annulus protection fluid according to any one of claims 1 to 8, characterized in that: The annular space protection fluid also includes a bactericide and a corrosion inhibitor; The bactericide comprises at least one of eugenol, acetyl eugenol, cinnamaldehyde and eucalyptol; And / or, the corrosion inhibitor includes sodium N-octylglycinate (OCT) and / or sodium N-dodecylglycinate (DOD).

10. A method for protecting an oil and gas well, characterized in that: The annulus protection fluid described in any one of claims 1 to 9 is used to fill the casing annulus of the oil and gas well.

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