A high-temperature, pressure-resistant, oil-containing microfoam drilling fluid or completion fluid and its preparation method

Abstract

This invention proposes an oil-containing, high-temperature, pressure-resistant microfoam drilling fluid or completion fluid and its preparation method, belonging to the field of petroleum drilling technology. The microfoam drilling fluid or completion fluid, by weight, comprises: 101-105 parts water; 1-3.5 parts anti-oil foam stabilizer; 0.3-0.8 parts high-temperature foaming agent; 2-5 parts high-temperature pressure-resistant filtration-reducing agent; 1-5 parts high-temperature low-density plugging agent; and 5-55 parts grease. This invention, without using special foaming agents, achieves an oil content of over 60% in the microfoam drilling fluid or completion fluid, transforming conventional grease contamination into grease performance enhancement. It improves the quality of the microfoam while reducing the solid phase, enhancing the stability, pressure resistance, temperature resistance, lubricity, inhibition, and plugging properties of the microfoam, thus broadening the application range of microfoam drilling fluid and completion fluid technology.

Description

Technical Field

[0001] This invention relates to the field of petroleum drilling technology, and in particular to an oil-containing high-temperature pressure-resistant micro-foam drilling fluid or completion fluid and its preparation method. Background Technology

[0002] Microfoam fluids utilize surfactants to reduce the surface tension of gas / liquid, forming independent spheres by encapsulating gas nuclei with multiple layers of liquid film. The gas bubbles exist in the system either individually suspended or partially interconnected, thus forming a microfoam system. As a low-density drilling fluid technology, it can reduce drilling fluid density, decrease the pressure difference between the fluid column and formation pore pressure, reduce leakage, and achieve low-density formation leakage (<1.0 g / cm³). 3 Drilling while drilling for leakage prevention and plugging. Primarily applied to fractured limestone, clastic, and ancient buried hill carbonate and igneous formations. Applied to over a hundred wells in the Shengli Oilfield, including high-angle, horizontal, and underbalanced pressure wells, this technology has successfully solved the severe leakage problem in the ancient buried hill low-pressure formations of the Shengli Oilfield, yielding significant economic and social benefits.

[0003] While this technology offers significant advantages in underbalanced drilling, it also has notable drawbacks. One is its poor ability to contaminate with pre-existing oils and its sensitivity to lubricants. The defoaming effect of oil on foam occurs through spreading on the foam surface or entering the foam as oil droplets. The process and mechanism are as follows: when oil comes into contact with the foam system, it spontaneously emulsifies to form tiny oil droplets that fill the entire foam. Oil entering the gas-liquid interface spreads rapidly on the foam surface, causing the oil-filled foam to continuously defoam during flow. When oil enters the foam structure under the influence of interfacial tension and external forces, it can damage the integrity of the foam to some extent, thus reducing the stability of the entire foam system. If a severely oil-producing formation is encountered, or if a large amount of lubricant is added during horizontal well drilling, the stability of the microfoam fluid will deteriorate sharply, or even completely defoam, leading to increased density, formation leakage, and complex downhole accidents, thus limiting the effectiveness of microfoam drilling.

[0004] The second drawback of this technology is the low compressive strength of the bubble core. As well depth increases, the foam diameter decreases while the density increases; and the deeper the well, the more severe the decrease, leading to large density variations at the bottom of the well. In some cases, the foam may even be compressed and dissolved, losing its effectiveness as a low-density drilling fluid, thus causing complex downhole conditions. Especially with the increasing number of deep wells and more complex geological conditions encountered, higher technical requirements are being placed on the stability of microfoams and the compressive strength of the liquid film under high temperature and high pressure environments at the bottom of the well.

[0005] The third drawback of this technology is the insufficient high-temperature resistance of conventional microfoam drilling fluids, especially the lack of microfoam technology to cope with high-temperature and complex geological conditions. Conventional microfoam drilling fluids can be applied to low-temperature and medium-temperature geothermal wells, but with the increase in drilling depth and the gradual increase in the exploitation of unconventional energy resources such as hot dry rock and geothermal energy, the technology of microfoam drilling fluids that can simultaneously resist high temperatures, pressure, and protect reservoirs is particularly important.

[0006] Current microfoam drilling or completion fluid oil-resistant technologies:

[0007] Chinese patent CN201610753824.5 discloses a high-lubricity microfoam drilling fluid and its preparation method. This high-lubricity microfoam drilling fluid consists of a base slurry, a lubricant, and additives. The base slurry is formulated with the following raw materials in parts by weight: 8-12 parts bentonite, 0.2-0.3 parts alkali, and 100-140 parts water. The additives are formulated with the following raw materials in parts by weight: 5-10 parts thickener, 1-5 parts alumina, 1-5 parts sodium polyquaternium, 10-15 parts sulfonate, 2-6 parts carboxymethyl cellulose, 0.5-1 part nano-titanium chloride, 0.5-1 part viscosity reducer, and 0.1-0.5 parts sodium dodecyl sulfate. The lubricant is aliphatic succinic acid, used in amounts of 5-10 parts by weight. The lubricant, being aliphatic succinic acid, has a volumetric acid content of 10%, at which point its density is 0.53-0.62 g / cm³. 3 The half-life is 16-17 hours, and the lubrication coefficient is 0.13. The technology provided by this patent is relatively specific to lubricant products and does not have broad-spectrum applicability. At the same time, it has a short half-life, no temperature resistance index, and a high lubrication coefficient, making it unsuitable for the high-temperature environment of deep wells. It is also not suitable for wells with high lubrication performance requirements, such as directional wells or horizontal wells. In addition, the bentonite content is extremely high, which is not conducive to the protection of oil and gas reservoirs.

[0008] Chinese patent CN201310078767.1 discloses a high-oil-content microfoam drilling fluid, the contents of which, by weight, are: water 100; bentonite 2.5-3; sodium carbonate 0.10-0.15; pH adjuster 0.10-0.15; anti-collapse agent (potassium polyacrylamide) 0.20-0.25; filtration loss reducer (hydrolyzed sodium polyacrylonitrile) 0.4-0.5; anti-collapse agent (sulfonated asphalt) 1.5-2.0; high-temperature filtration loss reducer (sulfonated phenolic resin) 0.8-1.0; flow pattern regulator (XC) 0.10-0.15; oil (light crude oil) 47-113; and oil-water compatible foaming agent DRfoam-Ⅱ 3-4. Its oil content is 30.15%-50.4%, and its density is 0.322-0.399 g / cm³. 3The half-life is 4–8 hours. This patent significantly improves the capacity limit of microfoam for light crude oil, but it also results in extremely low microfoam density, a short half-life, and high requirements for the key foaming agent—it must be an oil-water compatible foaming agent. This leads to the foaming agent preferentially adsorbing at the oil-water interface, significantly reducing the amount adsorbed at the gas-liquid interface, thus drastically reducing the stability of the foam in oils. In addition, the industrialization level of such oil-water compatible or oil-based foaming agents is low, making them impractical for field implementation.

[0009] Chinese patent CN201310012264.4 discloses a high oil-to-water ratio, water-in-oil, recyclable microfoam drilling fluid composition, comprising: foaming agent: 0.5%–8 wt%; oil: 55%–90 wt%; bentonite: 0.5%–8 wt%; viscosifier: 0.15–1 wt%; filtration reducer: 0.55%–8 wt%; diluent: 0.2%–3 wt%; shale inhibitor: 0–8 wt%; and weighting agent: based on a weighting density of 1.05 g / cm³. 3 ~2.2g / cm 3 The composition is as follows: The remainder is aqueous phase. This drilling fluid composition can form an oil-in-water recirculating micro-foam drilling fluid in both water-based and oil-containing (kerosene, diesel, or light crude oil) solutions with varying concentrations (0-80%). It exhibits excellent lubricity, low filtration loss, and leak-proof properties, while also being non-flammable and safe during drilling, and possessing good temperature resistance. The thickeners are biopolymers, acrylic-acrylamide copolymers, and cellulose-based natural polymers; the filtration loss reducers are lignite resins, phenolic resins, asphalt, acrylic polymers, modified starches, and modified celluloses; the diluents are zwitterionic or lignin polymers; and the shale inhibitors are sodium chloride, potassium chloride, and quaternary ammonium salts. Its oil content reaches 80%, while its minimum density is 1.05 g / cm³. 3 The highest concentration can reach 2.2 g / cm³. 3 It exhibits no foaming characteristics—specifically, its half-life performance. The core of this patent is to broaden the density range of drilling fluid under increased pressure. In essence, it does not form a foam system, but rather prevents the drilling fluid from being invaded by gas, thus forming a stable drilling fluid system. The gas nuclei are encapsulated within the system through foam formation, preventing excessive changes in drilling fluid properties that could lead to complex accidents.

[0010] Regarding microfoam drilling fluid or completion fluid pressure-resistant technology, there are few reports on related technologies, and previous applications have been limited to shallow wells. According to field feedback, the current maximum well depth for foam drilling fluid is 3000m, and laboratory data also supports this, showing that the density remains approximately 0.99g / cm³ at 30MPa. 3 The above methods are insufficient to achieve the goal of reducing foam density.

[0011] The November 2018 issue of the journal *Petroleum Drilling Technology*, Volume 46, Issue 6, published a paper titled "Research and Field Test of High-Temperature Resistant Foam Drilling Fluid Technology for Deep Wells," which introduces a high-temperature resistant foam drilling fluid system for deep wells. This system exhibits strong resistance to high temperatures, inhibition, and high pressure. Laboratory studies showed that its oil resistance reached 30%, and it possesses certain pressure resistance, but the bubble density variation range at 30 MPa is large: Δρ is 0.7 g / cm³. 3 The bubble particle size is unstable, resulting in unstable density of the foam drilling fluid; the foam half-life is less than 9.31 min, indicating poor foam quality; it is only suitable for use as a foam drilling fluid, and not suitable as a recyclable micro-foam drilling fluid.

[0012] Regarding current microfoam drilling fluid or completion fluid temperature-resistant technologies:

[0013] The journal *Drilling Fluids and Completion Fluids*, Volume 25, Issue 6, 2008, introduced an experimental study on a high-temperature resistant seawater micro-foam drilling fluid. The micro-foam drilling fluid prepared in this paper achieved a density of 0.6–0.95 g / cm³. 3 The high-temperature stabilizer LNW was introduced, which enabled the seawater microfoam drilling fluid to withstand temperatures up to 150℃ and maintain long-term stability for 7 days. However, after adding 5% crude oil, the density increased from 0.70 to 0.72, and the half-life decreased from 5 days to approximately 24 hours. While the density change was not significant, the stability of the microfoam film decreased sharply, posing a potential safety hazard for field use.

[0014] Chinese patent CN201911423228.0 discloses a high-temperature rigid rubber recyclable foam drilling fluid or completion fluid and its preparation method. This patent pre-prepares a high-temperature rigid rubber base fluid in clean water using 0.2-0.8 parts of a low molecular weight high-temperature resistant foam stabilizer, 1-2 parts of a foam density reducing agent, and 0.1-0.2 parts of a high-temperature wetting agent. This base fluid is then combined with 0-3 parts of high-temperature resistant sodium bentonite, 0-0.1 parts of an alkalinity regulator, 0.3-0.5 parts of a high-temperature foaming agent, 0.1-0.5 parts of a high-temperature and salt-resistant filtration loss reducing agent, and 1-3 parts of a high-temperature resistant resin filtration loss reducing agent. This invention features low solid content and strong membrane structure; half-life > 30 days at 150℃ / 16h, > 20 days at 180℃ / 16h, and > 2.3 days at 200℃ / 16h, significantly increasing the number of recyclable microfoam drilling or completion fluids. This allows recyclable microfoam drilling and completion fluids to be applied to the exploitation of high-temperature, low-pressure, easily leaking oil and gas resources and geothermal wells. However, its pressure resistance has not been reported.

[0015] In summary, current microfoam drilling fluids have achieved certain results in terms of oil resistance or temperature resistance. However, current microfoam oil-resistant technologies contain large amounts of bentonite, cellulose polymers, or barite. While these substances have some adsorption capacity for oils and greases, the capacity of these conventional treatment agents for oil or lubricants is limited to 5%–10%. After being contaminated by oil, the quality and stability of the microfoam significantly decrease, the half-life shortens, and the density increases. Alternatively, using special oil-water compatible foaming agents to increase the oil content of water-based microfoam systems can achieve an oil resistance of 30%–80%, but the half-life is short, the foam quality is severely degraded, and the density is higher than that of pure water, becoming an oil-in-water drilling fluid, thus losing its effectiveness as a low-density drilling fluid. Microfoam drilling fluids or completion fluids can withstand temperatures up to 200℃ / 16h with a half-life >2.3d, but their resistance to oil contamination is insufficient. Therefore, there is currently a significant lack of comprehensive technologies for pressure-resistant microfoam drilling fluids or completion fluids to cope with complex high-temperature and high-pressure reservoir environments.

[0016] The November 2018 issue of the journal *Petroleum Drilling Technology* (Volume 46, Issue 6) published a paper titled "Research and Field Test of High-Temperature Resistant Foam Drilling Fluid Technology for Deep Wells," which introduces a high-temperature resistant foam drilling fluid system for deep wells. Indoor experiments showed that this system possesses strong resistance to high temperatures, inhibition, and high pressure. Application results in the HaShen 2 well demonstrate that this high-temperature resistant foam drilling fluid exhibits excellent comprehensive performance and has field application value. Its oil resistance is 30%, and the bubble density variation range Δρ at 30 MPa is 0.7 g / cm³. 3 It has a half-life of less than 9.31 min and poor foam stability, making it suitable only for foam drilling fluids and not for recyclable microfoam drilling fluids.

[0017] Chinese patent CN201610753824.5 discloses a high-lubricity microfoam drilling fluid and its preparation method. This high-lubricity microfoam drilling fluid is composed of a base slurry, a lubricant, and additives. The base slurry has the following raw material proportions by weight: 8-12 parts bentonite, 0.2-0.3 parts alkali, and 100-140 parts water. The additives have the following raw material proportions by weight: 5-10 parts thickener, 1-5 parts alumina, 1-5 parts sodium polyquaternium, 10-15 parts sulfonate, 2-6 parts carboxymethyl cellulose, 0.5-1 part nano-titanium chloride, 0.5-1 part viscosity reducer, and 0.1-0.5 parts sodium dodecyl sulfate. The lubricant is aliphatic succinic acid, used in an amount of 5-10 parts by weight. The lubricant, being aliphatic succinic acid, has a volumetric capacity of 10%, at which point its density is 0.53-0.62 g / cm³. 3 It has a half-life of 16-17 hours, a lubrication coefficient of 0.13, and poor lubricity.

[0018] Chinese patent CN201310078767.1 discloses a high-oil-content microfoam drilling fluid, the contents of which, by weight, are: water 100; bentonite 2.5-3; sodium carbonate 0.10-0.15; pH adjuster 0.10-0.15; anti-collapse agent (potassium polyacrylamide) 0.20-0.25; filtration loss reducer (hydrolyzed sodium polyacrylonitrile) 0.4-0.5; anti-collapse agent (sulfonated asphalt) 1.5-2.0; high-temperature filtration loss reducer (sulfonated phenolic resin) 0.8-1.0; flow pattern regulator (XC) 0.10-0.15; oil (light crude oil) 47-113; and oil-water compatible foaming agent DRfoam-Ⅱ 3-4. Its oil content is 30.15%-50.4%, and its density is 0.322-0.399 g / cm³. 3 The half-life is 4–8 hours.

[0019] Chinese patent CN201310012264.4 discloses a high oil-to-water ratio, water-in-oil, recyclable microfoam drilling fluid composition, comprising: foaming agent: 0.5%–8 wt%; oil: 55%–90 wt%; bentonite: 0.5%–8 wt%; viscosifier: 0.15–1 wt%; filtration reducer: 0.55%–8 wt%; diluent: 0.2%–3 wt%; shale inhibitor: 0–8 wt%; and weighting agent: based on a weighting density of 1.05 g / cm³. 3 ~2.2g / cm 3 The remainder is water phase. This drilling fluid composition can form a water-in-oil circulating micro-foam drilling fluid in both water-based drilling fluids and oil (kerosene, diesel or light crude oil) containing different amounts (0-80%). It has good lubricity, low filtration loss, and leak-proof properties. It is also non-flammable and safe during the drilling process, and has good temperature resistance. Summary of the Invention

[0020] To address the problems of existing microfoam drilling fluids, such as low oil content, poor stability of oil-bearing foam, insufficient foam compressive strength, unstable density, insufficient high-temperature resistance, poor foam quality, and insufficient high-temperature microfoam compressive strength and oil contamination resistance, and to improve the adaptability of microfoam fluids to formation crude oil contamination and their suitability for drilling in high-temperature, high-pressure deep wells, directional wells, horizontal wells, and extended reach wells, this invention provides an oil-bearing, high-temperature, high-pressure resistant microfoam drilling fluid or completion fluid for complex high-temperature, high-pressure reservoir environments, and its preparation method.

[0021] According to one aspect of the present invention, a microfoam drilling fluid or completion fluid is provided, comprising, by weight:

[0022] 101-105 parts water;

[0023] Oil-resistant foam stabilizer: 0.8–3.3 parts;

[0024] High-temperature resistant foaming agent: 0.3–0.8 parts;

[0025] 2-5 parts of a high-temperature and pressure resistant, pressure-resistant, and filtration-reducing agent;

[0026] 1-5 parts of high-temperature resistant, low-density sealing agent;

[0027] 5-55 parts of oil;

[0028] The anti-oil and foam stabilizer comprises, by weight, parts of:

[0029] Emulsifier 0.5-2.0 parts, viscoelastic polymer 0.1-0.3 parts, modified starch 0.2-1.0 parts.

[0030] Optionally, the high-temperature resistant foaming agent is selected from at least one of anionic foaming agents or nonionic foaming agents.

[0031] Optionally, the high-temperature and pressure-resistant filtration agent is selected from... Ultra-high temperature filtration loss reducer At least one of the following: ultra-high temperature filtration reducer, high temperature foam protectant TFP, or sodium sulfite.

[0032] Optionally, the high-temperature resistant low-density plugging agent is selected from at least one of soda ash, sodium bentonite, sepiolite fiber, water glass resin silane coupling agent composite plugging agent.

[0033] The water glass resin silane coupling agent composite sealing agent of the present invention comprises, by volume, 20-40 parts of water glass, 5-18 parts of resin, and 2-5 parts of silane coupling agent; the specific preparation method can be referred to Chinese invention patent application number 202010714140.0, which is incorporated herein by reference to the extent that it is consistent with the content of the present invention.

[0034] Optionally, the grease is selected from at least one of diesel oil, kerosene, white oil, synthetic base oil, or crude oil.

[0035] Optionally, the anionic foaming agent is selected from at least one of sodium dodecylbenzene sulfonate (SDBS), fatty alcohol glyceryl ether sulfonate (AGES), or sodium α-olefin sulfonate (AOS).

[0036] Optionally, the nonionic foaming agent is selected from at least one of polyoxyethylene octylphenol ether-10, alkylphenol polyoxyethylene ether OP-10, or oleamidopropyl dimethyl tertiary amine PKO-O.

[0037] Optionally, the emulsifier is a polyhydroxy surfactant.

[0038] Optionally, the polyhydroxy surfactant is polyvinyl alcohol.

[0039] Optionally, the polyvinyl alcohol is selected from at least one of polyvinyl alcohol BP05, polyvinyl alcohol 1288, polyvinyl alcohol 1488 or polyvinyl alcohol 1788.

[0040] Optionally, the viscoelastic polymer is an organic polymer with an elastic modulus / viscosity modulus greater than 1.

[0041] The elastic modulus (G′), also known as the storage modulus, refers to the amount of energy stored in a viscoelastic fluid during elastic deformation (reversible), reflecting the elasticity of the viscoelastic fluid. An AR1500ex rotational rheometer (manufactured in the USA) can be used to perform oscillation scanning on the polymer aqueous solution at a frequency of 0.01–100 Hz.

[0042] The viscous modulus (G″), also known as the loss modulus, refers to the amount of energy lost by a viscoelastic fluid during deformation due to viscous deformation (irreversible), reflecting the viscosity of the viscoelastic fluid.

[0043] Optionally, the viscoelastic polymer is selected from at least one of low molecular weight high-temperature foam stabilizer TFS or hydroxyethyl cellulose HEC.

[0044] Optionally, the modified starch is obtained by etherification of starch under alkaline conditions.

[0045] Optionally, the modified starch is selected from at least one of the heat-resistant starch CMS-K or the heat-resistant starch SHR-1.

[0046] In this invention, the low molecular weight high-temperature foam stabilizer TFS comprises a nonionic cellulose ether backbone structure, a hydrophobic structure, and sulfonate groups, with a weight-average molecular weight between 1 million and 2 million. When compounded with commonly used foaming agents, it forms microfoam with a density of 0.3–0.8 g / cm³. 3 The microfoam half-life is ≥56h at room temperature, ≥42h after hot rolling at 120℃, ≥37h after hot rolling at 150℃, and ≥4.5h after hot rolling at 200℃. It can resist saturated NaCl and CaCl2 solutions.

[0047] The density of the high-temperature resistant, low-density plugging agent is ≤1.65 g / cm³. 3 Lightweight and porous, resistant to high temperatures and mineralization, possessing both inorganic rigidity and organic flexible plugging properties. Temperature resistance ≥200℃, excellent plugging performance, filtrate penetration depth reduced by 68.6% compared to the base liquid. Inert material, highly compatible, and effective against Na+. + Ca 2+ Cl - It is not sensitive to pollution.

[0048] The high-temperature protective agent TFP has little impact on the foaming performance of microfoam base liquids, but can improve the temperature resistance of microfoam base liquids by 30–90℃. It also improves the microfoam plugging performance by at least 39.1% at both room temperature and before and after high temperatures, and reduces the density of ultrafine CaCO3 by 39.5% compared to inorganic plugging agents. Temperature resistance is ≥180℃.

[0049] According to another aspect of the present invention, a method for preparing the above-mentioned microfoam drilling fluid or completion fluid is provided, wherein the water is divided into two parts: water I and water II; and the oil is divided into two parts: oil I and oil II.

[0050] The preparation method includes: mixing a mixture containing water I, an oil-resistant foam stabilizer, a high-temperature foaming agent, a high-temperature pressure-reducing and filtration-loss agent, and a high-temperature low-density plugging agent, then adding oil I, stirring, and then adding water II and oil II to obtain the micro-foam drilling fluid or completion fluid.

[0051] The anti-oil and foam stabilizer includes an emulsifier, a viscoelastic polymer, and modified starch.

[0052] Optionally, the preparation method includes:

[0053] S1: Prepare mixture 1 containing water I and emulsifier;

[0054] S2: Add mixture a containing viscoelastic polymer, modified starch and high-temperature foaming agent to mixture 1 to obtain mixture 2;

[0055] S3: Add mixture b, which contains high-temperature and pressure-resistant filtration loss agent and high-temperature and low-density sealing agent, to mixture 2 to obtain mixture 3;

[0056] S4: Add grease I to mixture 3, stir, and then add water II and grease II in sequence to obtain the micro-foam drilling fluid or completion fluid.

[0057] Optionally, the mass ratio of water I to water II is 100:1 to 5; the mass ratio of oil I to oil II is 5 to 10:0 to 45.

[0058] Optionally, the preparation method includes:

[0059] S1: Mix water I with emulsifier, stir at 300r / min to 800r / min and heat to 80℃ to 90℃, keep stirring for 10 to 20min, and obtain mixture 1 after cooling;

[0060] S2: Mix the viscoelastic polymer, modified starch and high-temperature foaming agent and add them to mixture 1. Stir at 800-1200 rpm for 2-3 hours to obtain mixture 2.

[0061] S3: Mix the high-temperature and pressure-resistant filtration loss agent and the high-temperature and low-density sealing agent and add them to mixture 2. Stir at 1000-1200 rpm for 2-5 hours to obtain mixture 3.

[0062] S4: Add oil I to mixture 3, stir for 20-30 minutes, then add water II, stir for another 10-30 minutes, then add oil II again to obtain the micro-foam drilling fluid or completion fluid.

[0063] This invention uses a viscoelastic polymer, modified starch, and emulsifier to form an anti-oil foam stabilizer, combined with a high-temperature, high-pressure, and filtration-reducing agent and a high-temperature, low-density plugging agent, to form a high-oil, high-temperature, and high-pressure resistant microfoam drilling or completion fluid. It can achieve an oil content of over 60% in the microfoam drilling or completion fluid without the use of special foaming agents, transforming conventional oil contamination into oil performance enhancement. While improving microfoam quality, it also reduces the solid phase of the microfoam, enhancing its stability, pressure resistance, temperature resistance, lubricity, inhibition, and plugging properties, thus broadening the application range of microfoam drilling and completion fluid technology. Its specific technical advantages and effects include:

[0064] (1) The modified starch and viscoelastic polymer work together to tightly bind the free water in the system and adsorb a small amount of oil film: the viscoelastic polymer enhances the cohesive force of the microfoam fluid molecules through the temporary supramolecular network structure, thereby enhancing the liquid film strength; the swelling of the modified starch in water increases the fluid viscosity; the extended chains of the modified starch can form an interpenetrating structure with the network structure of the viscoelastic polymer, thereby further promoting its binding effect on free water; the structure formed by the two forms a high-quality oil-containing liquid film with a small amount of oil under the action of the emulsifier.

[0065] (2) When a large amount of oil invades from the outside, by adding free water, the emulsifier in this invention emulsifies the high content of oil under high-speed shearing action. Moreover, under the network structure formed by modified starch and viscoelastic polymer, its emulsification effect is further improved; the stable micro foam community is not disturbed, the oil resistance of micro foam fluid is increased to more than 60%, and its half-life is more than 17 days.

[0066] (3) The micro foam drilling fluid or completion fluid of the present invention does not require special oil-water compatible foaming agent or oil-based foaming agent. It transforms oil pollution into oil performance promotion, improves the oil capacity limit of micro foam fluid technology, improves micro foam stability, prolongs micro foam half-life, and increases drilling fluid recycling efficiency.

[0067] (4) The high-temperature foam protectant TFP is a rigid, lightweight, porous microstructure with nanoparticle size, which can reduce the density of the foam film surface and slow down the foam drainage rate. Sodium sulfite enhances the high-temperature oxidation effect of the microfoam treatment agent. The two work together to improve the capacity limit of the microfoam fluid at high temperatures. Its porous structure can not only reduce the liquid film density, but also firmly adsorb the high content of oil in the fluid, minimize the liquid film evaporation rate, and ultimately make the liquid film form an elastic core, rigid pressure stabilization and flexible outer film from the inside out. In addition, the high-temperature and pressure filtration loss reducing agent and the high-temperature and low-density plugging agent work together to reduce filtration loss and enhance plugging performance from the perspective of rigidity and flexibility, thereby improving the overall quality of microfoam under high temperature environment and stability under high pressure environment. This makes the microfoam fluid resistant to temperature above 200℃. Under the bottom hole pressure of 30MPa, the density of the foam can still be maintained at 0.90g / cm³. 3 Below, and with a narrow density variation range Δρ≤0.10g / cm³ 3 This ensures that the underground pressure remains stable at all times.

[0068] (5) The extreme pressure lubrication coefficient of the micro foam drilling fluid or completion fluid of the present invention reaches 0.05, which is comparable to the lubrication coefficient of all oil-based drilling fluid. It also has a strong ability to suspend rock cuttings and is suitable for drilling horizontal wells or extended reach wells.

[0069] (6) The micro foam drilling fluid or completion fluid of the present invention has a filtration loss of up to 1.6 mL, a shale recovery rate of up to 98.8%, good sealing effect, excellent inhibition, and good wellbore stabilization effect on mudstone, shale, and mud-shale. It can be used not only for preventing leakage and perforation in limestone formations, but also for safe drilling in mud-shale formations with unstable wellbore. Attached Figure Description

[0070] Figure 1 The graph shows the density change of the samples obtained in Examples 2, 4, 6, and 8 under high temperature and high pressure. Detailed Implementation

[0071] The present invention will be further described below with reference to specific embodiments, but this does not constitute any limitation on the present invention.

[0072] The sources of the raw materials used in the various embodiments of this invention are as follows:

[0073] The water glass resin silane coupling agent composite plugging agent is selected from the low-density high-temperature plugging agent prepared in Example 1 of Chinese Invention Patent "A Low-Density High-Temperature Plugging Agent, Preparation Method and Application Thereof", application number 202010714140.0.

[0074] The low molecular weight high temperature foam stabilizer TFS is selected from the low molecular weight high temperature foam stabilizer prepared in Example 2 of Chinese Invention Patent "A low molecular weight high temperature foam stabilizer and its preparation method", application number 201911401646.X.

[0075] The foam high-temperature protective agent TFP is selected from the high-temperature protective agent prepared in Example 1 of Chinese Invention Patent "A high-temperature protective agent for microfoam drilling fluid and its preparation method", application number 202010714095.9.

[0076] Sodium α-olefin sulfonate was purchased from China National Light Industry Chemical Co., Ltd.

[0077] Sepiolite fiber was purchased from Hebei Hengguang Mineral Products Co., Ltd.

[0078] The remaining raw materials are any commercially available products.

[0079] Example 1

[0080] S1: Take 100 parts of water, add 0.6 parts of polyvinyl alcohol 1788 and 0.4 parts of polyvinyl alcohol BP05, heat to 90°C while stirring, keep stirring for 20 minutes until fully dissolved, and obtain mixture 1 after cooling;

[0081] S2: Accurately weigh 0.2 parts of low molecular weight high temperature foam stabilizer TFS, 0.5 parts of high temperature resistant starch CMS-K, 0.2 parts of alkylphenol polyoxyethylene ether OP-10 and 0.3 parts of sodium α-olefin sulfonate, mix them thoroughly and add them to mixture 1. Stir continuously at 1100 rpm for 2 hours with a low speed high force stirrer to obtain mixture 2.

[0082] S3: Accurately weigh 0.8 parts of ultra-high temperature filtration loss reducer, 2 parts of foam high temperature protection agent TFP, 1 part of sodium bentonite, 0.03 parts of soda ash, 0.5 parts of sepiolite fiber and 1 part of water glass resin silane coupling agent composite blocker were thoroughly mixed and then added to mixture 2. The mixture was stirred continuously at 1100 rpm for 4 hours to obtain mixture 3.

[0083] S4: Oil phase emulsification: At the same stirring speed, 5 parts of diesel oil were added to mixture 3, and after stirring for 30 minutes, 1 part of water was added. After stirring for 30 minutes, the remaining 20 parts of white oil were added to obtain the sample of Example 1.

[0084] Example 2

[0085] The preparation details are the same as in Example 1, except that different amounts of white oil are added in S4. The specific details are as follows:

[0086] S4: At the same stirring speed, add 5 parts of diesel oil to mixture 3, stir for 30 minutes, add 1 part of water, stir for 30 minutes, and then add the remaining 40 parts of white oil to obtain the sample of Example 2.

[0087] Comparative Example 1

[0088] This comparative example uses the preparation steps of Example 1 of the present invention, except that no excess free water and diesel oil are added in S4. The other steps are the same, and the specific details are as follows:

[0089] S1: Take 100 parts of water, add 0.6 parts of polyvinyl alcohol 1788 and 0.4 parts of polyvinyl alcohol BP05, heat to 90°C while stirring, keep stirring for 20 minutes until fully dissolved, and obtain mixture 1 after cooling;

[0090] S2: Accurately weigh 0.2 parts of low molecular weight high temperature foam stabilizer TFS, 0.5 parts of high temperature resistant starch CMS-K, 0.2 parts of alkylphenol polyoxyethylene ether OP-10 and 0.3 parts of sodium α-olefin sulfonate, mix them thoroughly and add them to mixture 1. Stir continuously at 1100 rpm for 2 hours with a low speed high force stirrer to obtain mixture 2.

[0091] S3: Accurately weigh 0.8 parts of ultra-high temperature filtration loss reducer, 2 parts of foam high temperature protection agent TFP, 1 part of sodium bentonite, 0.03 parts of soda ash, 0.5 parts of sepiolite fiber and 1 part of water glass resin silane coupling agent composite blocker were thoroughly mixed and then added to mixture 2. The mixture was stirred continuously at 1100 rpm for 4 hours to obtain mixture 3.

[0092] S4: After stirring at the same speed for 30 minutes, add 5 parts of white oil to obtain the Comparative Example 1 sample.

[0093] Comparative Example 2

[0094] This comparative example uses the steps of Example 1 of the present invention, except that in step S4, no residual free water is added. The other steps are the same, and the specific details are as follows:

[0095] S1: Take 100 parts of water, add 0.6 parts of polyvinyl alcohol 1788 and 0.4 parts of polyvinyl alcohol BP05, heat to 90°C while stirring, keep stirring for 20 minutes until fully dissolved, and obtain mixture 1 after cooling;

[0096] S2: Accurately weigh 0.2 parts of low molecular weight high temperature foam stabilizer TFS, 0.5 parts of high temperature resistant starch CMS-K, 0.2 parts of alkylphenol polyoxyethylene ether OP-10 and 0.3 parts of sodium α-olefin sulfonate, mix them thoroughly and add them to mixture 1. Stir continuously at 1100 rpm for 2 hours with a low speed high force stirrer to obtain mixture 2.

[0097] S3: Accurately weigh 0.8 parts of ultra-high temperature filtration loss reducer, 2 parts of foam high temperature protection agent TFP, 1 part of sodium bentonite, 0.03 parts of soda ash, 0.5 parts of sepiolite fiber and 1 part of water glass resin silane coupling agent composite blocker were thoroughly mixed and then added to mixture 2. The mixture was stirred continuously at 1100 rpm for 4 hours to obtain mixture 3.

[0098] S4: At the same stirring speed, add 5 parts of diesel oil to mixture 3, stir for 30 minutes, and then add the remaining 10 parts of white oil to obtain the comparative example 2 sample.

[0099] Test 1: Density Test. A YM-7 type measuring instrument with a range of 0.1–1.5 g / cm³ was used. 3 A liquid density meter was used to test and record the microbubble fluid density of samples from Example 1, Example 2, Comparative Example 1, and Comparative Example 2. Specific data are shown in Table 1.

[0100] Test 2: Rheological properties and filtration loss test. A ZNN-D6 six-speed rotational viscometer was used to measure and record the Φ600 and Φ300 readings of the samples from Example 1, Example 2, Comparative Example 1, and Comparative Example 2. The apparent viscosity (AV), plastic viscosity (PV), and dynamic shear force (YP) of the microfoam fluid were calculated. Specific data are shown in Table 1. A triple medium-pressure filtration loss meter was used to measure the filtration loss (FL) of the samples from Example 1, Example 2, Comparative Example 1, and Comparative Example 2 at 0.69 MPa pressure for 30 minutes. Specific data are shown in Table 1.

[0101] Test 3: Half-life test. Samples from Example 1, Example 2, Comparative Example 1, and Comparative Example 2 were poured into 250mL graduated cylinders respectively. The time required for the volume of liquid discharged from the foam to be half of the total liquid volume when the foam had not been discharged, or the time required for the volume of foam to decrease and settle to be half of the total liquid volume when the foam had not been discharged, were tested. Specific data are shown in Table 1.

[0102] Test 4: Lubrication performance test.

[0103] Using an EP extreme pressure lubrication tester manufactured by OFI Testing Equipment Company, USA, the extreme pressure lubrication coefficients (K) of the samples from Example 1, Example 2, Comparative Example 1, and Comparative Example 2 under different diesel fuel dosages were tested. f The experimental steps are as follows:

[0104] First, preheat the EP extreme pressure lubricator by running it at 300 rpm for 15 minutes. Then, calibrate the instrument using distilled water and run it at 60 rpm and 150 psi for 5 minutes, recording the instrument readings. Finally, test the lubrication coefficient of samples with different oil contents under the following conditions: 60 rpm, 150 psi, and 5 minutes. Record the instrument readings after 5 minutes.

[0105] Test 5: Inhibition Test. The inhibition of micro-foam drilling fluid or completion fluid was tested using the shale recovery rate method. Dark gray mudstone cuttings with a water recovery rate of 35%–40% were selected from the core sample and immersed in the sample of Example 2 and Comparative Example 2. After hot rolling at 200℃ for 16 hours, the shale recovery rate was tested. The data obtained are shown in Table 1.

[0106] Test 6: Temperature resistance test. The slurries of the sample from Example 2 and the sample from Comparative Example 2 were placed in a high-temperature aging tank and aged in a hot roller furnace at 200°C for 16 hours. After being removed and naturally cooled, they were stirred at the same stirring speed for 30-60 minutes. Their density, rheology, half-life, extreme pressure lubrication coefficient and shale recovery rate were tested. The data obtained are shown in Table 1.

[0107] Table 1. Overall performance test results of Examples 1-2 and Comparative Examples 1-2

[0108]

[0109] As shown in Table 1, the density of the solution prepared according to the present invention is 0.75 g / cm³. 3 When the oil content of the high-oil-content, temperature- and pressure-resistant microfoam drilling fluid or completion fluid reaches 45%, the density is stable, the quality of the microfoam increases, the half-life becomes longer, the dynamic-plastic ratio increases, and the suspension stability is further increased. Moreover, after aging at 200℃, the stability and lubrication performance are good, and it has a strong inhibitory effect on shale.

[0110] Example 3

[0111] S1: Take 100 parts of water, add 1 part of polyvinyl alcohol 1488 and 1 part of polyvinyl alcohol 1288, heat to 90°C while stirring, keep stirring for 20 minutes until fully dissolved, and obtain mixture 1 after cooling;

[0112] S2: Accurately weigh 0.2 parts of low molecular weight high temperature foam stabilizer TFS, 0.1 parts of hydroxyethyl cellulose, 0.5 parts of high temperature resistant starch CMS-K, 0.5 parts of high temperature resistant starch SHR-1, 0.5 parts of sodium dodecylbenzene sulfonate and 0.3 parts of oleamide propyl dimethyl tertiary amine, mix them thoroughly and add them to mixture 1. Stir continuously at 1200 rpm for 3 hours with a low speed high force stirrer to obtain mixture 2;

[0113] S3: Accurately weigh 2 portions The ultra-high temperature filtration loss reducer, 2 parts of foam high temperature protection agent TFP, 0.2 parts of sodium sulfite, 1 part of sodium bentonite, 0.03 parts of soda ash, 1 part of sepiolite fiber and 2 parts of water glass resin silane coupling agent composite plugging agent are thoroughly mixed and then added to mixture 2. The mixture is stirred continuously at 1200 rpm for 4 hours to obtain mixture 3.

[0114] S4: At the same stirring speed, add 10 parts of crude oil to mixture 3, stir for 30 minutes, add 2 parts of water, stir for 30 minutes, and then add the remaining 30 parts of diesel to obtain the sample of Example 3.

[0115] Example 4

[0116] The preparation details are the same as in Example 3, except that different amounts of oil are added in S4. The specific details are as follows:

[0117] S4: At the same stirring speed, add 10 parts of crude oil to mixture 3, stir for 30 minutes, add 2 parts of water, stir for 30 minutes, and then add the remaining 50 parts of diesel to obtain the sample of Example 3.

[0118] Comparative Example 3

[0119] This comparative example uses the steps of Example 3, except that no excess free water and oil are added in S4. Specific details are as follows:

[0120] S1: Take 100 parts of water, add 1 part of polyvinyl alcohol 1488 and 1 part of polyvinyl alcohol 1288, heat to 90°C while stirring, keep stirring for 20 minutes until fully dissolved, and obtain mixture 1 after cooling;

[0121] S2: Accurately weigh 0.2 parts of low molecular weight high temperature foam stabilizer TFS, 0.1 parts of hydroxyethyl cellulose, 0.5 parts of high temperature resistant starch CMS-K, 0.5 parts of high temperature resistant starch SHR-1, 0.5 parts of sodium dodecylbenzene sulfonate and 0.3 parts of oleamide propyl dimethyl tertiary amine, mix them thoroughly and add them to mixture 1. Stir continuously at 1200 rpm for 3 hours with a low speed high force stirrer to obtain mixture 2;

[0122] S3: Accurately weigh 2 portions The ultra-high temperature filtration loss reducer, 2 parts of foam high temperature protection agent TFP, 0.2 parts of sodium sulfite, 1 part of sodium bentonite, 0.03 parts of soda ash, 1 part of sepiolite fiber and 2 parts of water glass resin silane coupling agent composite plugging agent are thoroughly mixed and then added to mixture 2. The mixture is stirred continuously at 1200 rpm for 4 hours to obtain mixture 3.

[0123] S4: At the same stirring speed, add 10 parts of crude oil to mixture 3 and stir for 30 minutes to obtain comparative example 3 sample.

[0124] Comparative Example 4

[0125] This comparative example uses the steps of Example 3, except that no excess free water is added in S4. Specific details are as follows:

[0126] S1: Take 100 parts of water, add 1 part of polyvinyl alcohol 1488 and 1 part of polyvinyl alcohol 1288, heat to 90°C while stirring, keep stirring for 20 minutes until fully dissolved, and obtain mixture 1 after cooling;

[0127] S2: Accurately weigh 0.2 parts of low molecular weight high temperature foam stabilizer TFS, 0.1 parts of hydroxyethyl cellulose, 0.5 parts of high temperature resistant starch CMS-K, 0.5 parts of high temperature resistant starch SHR-1, 0.5 parts of sodium dodecylbenzene sulfonate and 0.3 parts of oleamide propyl dimethyl tertiary amine, mix them thoroughly and add them to mixture 1. Stir continuously at 1200 rpm for 3 hours with a low speed high force stirrer to obtain mixture 2;

[0128] S3: Accurately weigh 2 portions The ultra-high temperature filtration loss reducer, 2 parts of foam high temperature protection agent TFP, 0.2 parts of sodium sulfite, 1 part of sodium bentonite, 0.03 parts of soda ash, 1 part of sepiolite fiber and 2 parts of water glass resin silane coupling agent composite plugging agent are thoroughly mixed and then added to mixture 2. The mixture is stirred continuously at 1200 rpm for 4 hours to obtain mixture 3.

[0129] S4: At the same stirring speed, add 10 parts of crude oil to mixture 3, stir for 30 minutes, and then add the remaining 5 parts of diesel to obtain the comparative sample 4.

[0130] The density, rheology, filtration loss, half-life, and lubricity of the samples from Example 3, Example 4, Comparative Example 3, and Comparative Example 4 at room temperature were tested using the same method described above. The experimental data obtained are shown in Table 2. Simultaneously, the rheology, filtration loss, half-life, lubricity, and inhibition properties of the samples from Example 4 and Comparative Example 4 after being heated to 200℃ for 16 hours were tested. The experimental data obtained are shown in Table 2.

[0131] Table 2. Overall performance test results of Examples 3-4 and Comparative Examples 3-4

[0132]

[0133] As shown in Table 2 above, the density prepared using the formulation method of this invention is 0.82 g / cm³. 3When the oil content of the high-efficiency anti-oil microfoam drilling fluid reaches 60%, the density is stable, the quality of microfoam increases, the half-life becomes longer, the dynamic-plastic ratio increases, and the suspension stability is further increased. Moreover, the stability and lubrication performance index after high-temperature aging at 200℃ are comparable to the lubrication coefficient of full diesel, and the inhibition of shale is significantly enhanced.

[0134] Comparative Example 5

[0135] This comparative example uses the preparation steps of Example 3, except that polyvinyl alcohol is not added in S1 and no emulsifier is prepared; the remaining free water and oil are not added in S4. Specific details are as follows:

[0136] S1: Accurately weigh 0.2 parts of low molecular weight high temperature foam stabilizer TFS, 0.1 parts of hydroxyethyl cellulose, 0.5 parts of high temperature resistant starch CMS-K, 0.5 parts of high temperature resistant starch SHR-1, 0.5 parts of sodium dodecylbenzene sulfonate and 0.3 parts of oleamide propyl dimethyl tertiary amine, mix thoroughly and add to 100 parts of water, and stir continuously at 1200 rpm for 3 hours with a low speed high force stirrer to obtain mixture 1;

[0137] S2: Accurately weigh 2 portions The ultra-high temperature filtration loss reducer, 2 parts of foam high temperature protection agent TFP, 0.2 parts of sodium sulfite, 1 part of sodium bentonite, 0.03 parts of soda ash, 1 part of sepiolite fiber and 2 parts of water glass resin silane coupling agent composite plugging agent are thoroughly mixed and then added to mixture 1. The mixture is stirred continuously at 1200 rpm for 4 hours to obtain mixture 2.

[0138] S3: At the same stirring speed, add 10 parts of crude oil to mixture 2 and stir for 30 minutes to obtain the sample of comparative example 5.

[0139] Comparative Example 6

[0140] This comparative example follows the steps of Example 3, except that viscoelastic polymer is not added in S2, and the remaining free water and oil are not added in S4. The stirring speed is also different. Specific details are as follows:

[0141] S1: Take 100 parts of water, add 1 part of polyvinyl alcohol 1488 and 1 part of polyvinyl alcohol 1288, heat to 90°C while stirring, keep stirring for 20 minutes until fully dissolved, and obtain mixture 1 after cooling;

[0142] S2: Accurately weigh 0.5 parts of high-temperature resistant starch CMS-K, 0.5 parts of high-temperature resistant starch SHR-1, 0.5 parts of sodium dodecylbenzenesulfonate and 0.3 parts of oleamide propyl dimethyl tertiary amine, mix them thoroughly and add them to mixture 1. Stir continuously at 800 rpm for 3 hours with a low-speed high-power stirrer to obtain mixture 2.

[0143] S3: Accurately weigh 2 portions The ultra-high temperature filtration loss reducer, 2 parts of foam high temperature protection agent TFP, 0.2 parts of sodium sulfite, 1 part of sodium bentonite, 0.03 parts of soda ash, 1 part of sepiolite fiber and 2 parts of water glass resin silane coupling agent composite plugging agent are thoroughly mixed and then added to mixture 2. The mixture is stirred continuously at 1200 rpm for 4 hours to obtain mixture 3.

[0144] S4: At the same stirring speed, add 10 parts of crude oil to mixture 3 and stir for 30 minutes to obtain the sample of comparative example 6.

[0145] Comparative Example 7

[0146] This comparative example follows the steps of Example 3, except that modified starch is not added in S2, and the remaining free water and oil are not added in S4. Specific details are as follows:

[0147] S1: Take 100 parts of water, add 1 part of polyvinyl alcohol 1488 and 1 part of polyvinyl alcohol 1288, heat to 90°C while stirring, keep stirring for 20 minutes until fully dissolved, and obtain mixture 1 after cooling;

[0148] S2: Accurately weigh 0.2 parts of low molecular weight high temperature foam stabilizer TFS, 0.1 parts of hydroxyethyl cellulose, 0.5 parts of sodium dodecylbenzene sulfonate and 0.3 parts of oleamide propyl dimethyl tertiary amine, mix them thoroughly and add them to mixture 1. Stir continuously at 1200 rpm for 3 hours with a low speed high force stirrer to obtain mixture 2.

[0149] S3: Accurately weigh 2 portions The ultra-high temperature filtration loss reducer, 2 parts of foam high temperature protection agent TFP, 0.2 parts of sodium sulfite, 1 part of sodium bentonite, 0.03 parts of soda ash, 1 part of sepiolite fiber and 2 parts of water glass resin silane coupling agent composite plugging agent are thoroughly mixed and then added to mixture 2. The mixture is stirred continuously at 1200 rpm for 4 hours to obtain mixture 3.

[0150] S4: At the same stirring speed, 10 parts of crude oil were added to mixture 3 to obtain comparative example 7 sample.

[0151] Comparative Example 8

[0152] This comparative example follows the steps of Example 3, except that no high-temperature and pressure resistant filtration loss reducer is added in S3, and no remaining free water and oil are added in S4. Specific details are as follows:

[0153] S1: Take 100 parts of water, add 1 part of polyvinyl alcohol 1488 and 1 part of polyvinyl alcohol 1288, heat to 90°C while stirring, keep stirring for 20 minutes until fully dissolved, and obtain mixture 1 after cooling;

[0154] S2: Accurately weigh 0.2 parts of low molecular weight high temperature foam stabilizer TFS, 0.1 parts of hydroxyethyl cellulose, 0.5 parts of high temperature resistant starch CMS-K, 0.5 parts of high temperature resistant starch SHR-1, 0.5 parts of sodium dodecylbenzene sulfonate and 0.3 parts of oleamide propyl dimethyl tertiary amine, mix them thoroughly and add them to mixture 1. Stir continuously at 1200 rpm for 3 hours with a low speed high force stirrer to obtain mixture 2;

[0155] S3: Accurately weigh 1 part sodium bentonite, 0.03 parts soda ash, 1 part sepiolite fiber and 2 parts water glass resin silane coupling agent composite sealant, mix them thoroughly and add them to mixture 2. Stir continuously at 1200 rpm for 4 hours to obtain mixture 3.

[0156] S4: At the same stirring speed, 10 parts of crude oil were added to mixture 3 to obtain comparative sample 8.

[0157] Comparative Example 9

[0158] This comparative example uses the sample from Example 3, except that no high-temperature resistant low-density plugging agent is added in S3, and no excess free water and grease are added in S4. Specific details are as follows:

[0159] S1: Take 100 parts of water, add 1 part of polyvinyl alcohol 1488 and 1 part of polyvinyl alcohol 1288, heat to 90°C while stirring, keep stirring for 20 minutes until fully dissolved, and obtain mixture 1 after cooling;

[0160] S2: Accurately weigh 0.2 parts of low molecular weight high temperature foam stabilizer TFS, 0.1 parts of hydroxyethyl cellulose, 0.5 parts of high temperature resistant starch CMS-K, 0.5 parts of high temperature resistant starch SHR-1, 0.5 parts of sodium dodecylbenzene sulfonate and 0.3 parts of oleamide propyl dimethyl tertiary amine, mix them thoroughly and add them to mixture 1. Stir continuously at 1200 rpm for 3 hours with a low speed high force stirrer to obtain mixture 2;

[0161] S3: Accurately weigh 2 portions Mix the ultra-high temperature filtration loss reducer, 2 parts of foam high temperature protectant TFP and 0.2 parts of sodium sulfite thoroughly and add them to mixture 2. Stir continuously at 1200 rpm for 4 hours to obtain mixture 3.

[0162] S4: At the same stirring speed, 10 parts of crude oil were added to mixture 3 to obtain comparative example 9 sample.

[0163] The density, rheology, filtration loss, and half-life of Comparative Examples 5–9 were tested at room temperature using the same method described above. The experimental data obtained are shown in Table 3.

[0164] Table 3. Comparative Examples 5–9: Microfoam quality and rheological properties test results.

[0165]

[0166]

[0167] As shown in Table 3, the absence of emulsifiers and modified starch in microfoam fluids leads to a significant increase in foam density, water loss, and a shorter half-life after the introduction of oils, resulting in poorer foam stability. Conversely, the absence of viscoelastic polymers, while significantly reducing foam density, results in a decrease in microfoam film quality and a shorter half-life. Furthermore, the lack of high-temperature and pressure-reducing filtration agents and high-temperature low-density plugging agents not only slightly worsens foam stability but also significantly increases filtration loss, leading to a decrease in the leak prevention and plugging effectiveness of microfoam drilling or completion fluids.

[0168] Test 7: Pressure Resistance Test. This test mainly examines the density changes of microfoam samples from Example 2, Example 4, Comparative Example 6, and Comparative Example 8 under high temperature and high pressure conditions at the bottom of the well. An MDT (Multi-Drilling Test) device was used to simulate the circulation of drilling fluid under high temperature and high pressure conditions to determine the density change pattern. The test steps are as follows:

[0169] (1) Prepare for the experiment.

[0170] (2) Check the temperature control system, check the pressure control system, check all instruments, check the oil pump to ensure it is working properly, and check the steam source pressure, etc.

[0171] (3) Inhale the sample from the example or comparative example, and expel the mixed air. Note: The standard is that the test solution flows out steadily without any air bubbles, indicating that the vessel is free of gas. Repeat the above steps if necessary.

[0172] (4) Programmed heating process. The preset temperature is 220℃. When the temperature reaches 200℃, it is kept constant (manual assistance in maintaining the temperature is generally required).

[0173] (5) Then adjust the pressure gauge to raise the pressure to 10, 15, 20, 25, 30, 40, 60, 100, 150, 200, 250 and 300 atm respectively. During the pressure increase, record the amount of oil extruded at each point and represent it as M.

[0174] (6) After the previous step is completed, depressurize and then repeat steps five and six after setting the temperature to 150℃.

[0175] (7) After the experiment, depressurize, cool, rinse the vessel, tidy up the instruments, turn off the power, and compile the test data. The results are shown in [link to results]. Figure 1 .

[0176] from Figure 1It can be seen that in a 200℃ environment, the density of microfoam drilling fluid initially increases gradually with increasing pressure, then tends to stabilize. When the pressure reaches a certain value, the pressure on the inner wall of the bubble reaches equilibrium with the external environmental pressure, and the bubble diameter no longer decreases significantly. Comparative Example 6, lacking an elastic core, and Comparative Example 8, lacking a high-temperature, pressure-resistant, and filtration-reducing agent, exhibited significant density decay, with the density exceeding 1.0 g / cm³ after pressure exceeded 10 MPa. 3 The density variation range of the samples in Example 2 and Example 4 was narrower, with Δρ ≤ 0.1 g / cm³. 3 Approximately, and the final density is ≤0.89 g / cm³. 3 Compared with the comparative example, the temperature and pressure resistance of the foam in the system of the present invention is significantly enhanced.

[0177] Any numerical value mentioned in this invention, if there is only a two-unit interval between any minimum and any maximum value, includes all values ​​that increase by one unit each time from the minimum to the maximum value. For example, if the amount of a component, or the value of a process variable such as temperature, pressure, or time, is stated as 50-90, in this specification it means specifically listing values ​​such as 51-89, 52-88… and 69-71 and 70-71, etc. For non-integer values, it may be appropriately considered that a unit is 0.1, 0.01, 0.001, or 0.0001. These are merely some specifically specified examples. In this application, in a similar manner, all possible combinations of numerical values ​​between the listed minimum and maximum values ​​are considered to have been disclosed.

[0178] It should be noted that the embodiments described above are only for explaining the present invention and do not constitute any limitation on the present invention. The present invention has been described with reference to typical embodiments, but it should be understood that the words used therein are descriptive and explanatory terms, not limiting terms. Modifications can be made to the present invention within the scope of the claims, and revisions can be made to the present invention without departing from the scope and spirit of the present invention. Although the present invention described herein relates to specific methods, materials, and embodiments, it does not mean that the present invention is limited to the specific examples disclosed herein; on the contrary, the present invention can be extended to all other methods and applications with the same function.

Claims

1. A microfoam drilling fluid or completion fluid, characterized in that, By weight, it includes: 101-105 parts water; Oil-resistant foam stabilizer: 0.8~3.3 parts; High-temperature resistant foaming agent: 0.3~0.8 parts; 2-5 parts of a high-temperature and pressure resistant, pressure-resistant, and filtration-reducing agent; 1-5 parts of high-temperature resistant, low-density sealing agent; 5-55 parts oil; The anti-oil and foam stabilizer comprises, by weight, parts of: Emulsifier 0.5~2.0 parts, viscoelastic polymer 0.1~0.3 parts, modified starch 0.2~1.0 parts; The high-temperature and pressure filtration reduction agent is selected from at least one of WHITETROL®X ultra-high temperature filtration reduction agent, WHITEMP® ultra-high temperature filtration reduction agent, foam high-temperature protectant TFP, or sodium sulfite. The high-temperature resistant low-density plugging agent is selected from at least one of soda ash, sodium bentonite, sepiolite fiber, water glass resin silane coupling agent composite plugging agent; The emulsifier is polyvinyl alcohol; The viscoelastic polymer is selected from at least one of the low molecular weight high temperature foam stabilizer TFS or hydroxyethyl cellulose. The modified starch is selected from at least one of the heat-resistant starch CMS-K or heat-resistant starch SHR-1.

2. The microfoam drilling fluid or completion fluid according to claim 1, characterized in that, The high-temperature resistant foaming agent is selected from at least one of anionic foaming agents or nonionic foaming agents; And / or, the grease is selected from at least one of diesel oil, kerosene, white oil, synthetic base oil or crude oil.

3. The microfoam drilling fluid or completion fluid according to claim 2, characterized in that, The anionic foaming agent is selected from at least one of sodium dodecylbenzenesulfonate, fatty alcohol glyceryl ether sulfonate, or α-olefin sulfonate.

4. The microfoam drilling fluid or completion fluid according to claim 2, characterized in that, The nonionic foaming agent is selected from at least one of polyoxyethylene octylphenol ether-10, alkylphenol polyoxyethylene ether OP-10, or oleamidopropyl dimethyl tertiary amine PKO-O.

5. The microfoam drilling fluid or completion fluid according to claim 1, characterized in that, The polyvinyl alcohol is selected from at least one of polyvinyl alcohol BP05, polyvinyl alcohol 1288, polyvinyl alcohol 1488 or polyvinyl alcohol 1788.

6. The microfoam drilling fluid or completion fluid according to any one of claims 1 to 5, characterized in that, The viscoelastic polymer is an organic polymer with an elastic modulus / viscosity modulus greater than 1; And / or, the modified starch is obtained by etherification of starch under alkaline conditions.

7. A method for preparing the microfoam drilling fluid or completion fluid according to any one of claims 1 to 6, characterized in that, The water is divided into two parts: water I and water II; the oil is divided into two parts: oil I and oil II. The preparation method includes: mixing a mixture containing water I, an oil-resistant foam stabilizer, a high-temperature foaming agent, a high-temperature pressure-reducing and filtration-loss agent, and a high-temperature low-density plugging agent, then adding oil I, stirring, and then adding water II and oil II to obtain the micro-foam drilling fluid or completion fluid. The anti-oil and foam stabilizer includes an emulsifier, a viscoelastic polymer, and modified starch.

8. The preparation method according to claim 7, characterized in that, The preparation method includes: S1: Prepare mixture 1 containing water I and emulsifier; S2: Add mixture a containing viscoelastic polymer, modified starch and high-temperature foaming agent to mixture 1 to obtain mixture 2; S3: Add mixture b, which contains high-temperature and pressure-resistant filtration loss agent and high-temperature and low-density sealing agent, to mixture 2 to obtain mixture 3; S4: Add oil I to mixture 3, stir, and then add water II and oil II in sequence to obtain the micro-foam drilling fluid or completion fluid; And / or, the mass ratio of water I to water II is 100:1~5; the mass ratio of oil I to oil II is 5~10:0~45.

9. The preparation method according to claim 8, characterized in that, The preparation method includes: S1: Mix water I with emulsifier, stir at 300r / min~800r / min and heat to 80℃~90℃, keep stirring for 10~20min, and after cooling, obtain mixture 1; S2: Mix the viscoelastic polymer, modified starch and high-temperature foaming agent and add them to mixture 1. Stir at 800~1200 rpm for 2~3 hours to obtain mixture 2. S3: Mix the high-temperature and pressure-resistant filtration loss agent and the high-temperature and low-density sealing agent and add them to mixture 2. Stir at 1000~1200 rpm for 2~5 hours to obtain mixture 3. S4: Add grease I to mixture 3, stir for 20-30 minutes, then add water II, stir for another 10-30 minutes, then add grease II to obtain the micro-foam drilling fluid or completion fluid.

10. The preparation method according to claim 7, characterized in that, The microfoam drilling fluid or completion fluid has a temperature resistance of over 200℃, and / or an oil resistance of over 60%, and / or a half-life of over 17 days; and / or the microfoam drilling fluid or completion fluid has a density of less than 0.90 g / cm³ under a bottom hole pressure of 30 MPa, and a density variation range Δρ ≤ 0.10 g / cm³. 3 .

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