A nanofiber-reinforced foam system for foam drilling fluid and its preparation method

Abstract

This invention belongs to the field of drilling engineering technology, specifically relating to a nanofiber-reinforced foam system for foam drilling fluid and its preparation method. The nanofiber-reinforced foam system for foam drilling fluid includes a gas phase and a liquid phase. The liquid phase comprises the following raw material components by mass percentage: 0.3-0.8 wt% foaming agent, 0.3-1.0 wt% nanofibers, and the balance being water. The foaming agent is prepared by in-situ polymerization of sodium isomeric tridecyl alcohol polyoxyethylene ether carboxylate and fatty acid methyl ester ethoxylate, followed by the introduction of hydrophilic monomers and crosslinking agents, using ammonium persulfate as an initiator. This invention's system exhibits high temperature and high salinity resistance, strong foam stability, and solves the problems of poor stability, insufficient temperature and salt resistance, high cost, and poor environmental performance of existing foam drilling fluids, achieving intelligent matching of foam performance with formation conditions.

Description

Technical Field

[0001] This invention belongs to the field of drilling engineering technology, specifically relating to a nanofiber reinforced foam system for foam drilling fluid and its preparation method. Background Technology

[0002] Foam fluids are widely used in oil and gas field development due to their high efficiency, good reservoir protection effect, low overall cost and minimal formation damage. They can be used as drilling fluid, completion fluid, fracturing fluid, etc., and have significant advantages, especially in low-permeability, low-pressure and low-saturation formations, which can increase oil and gas production and reduce production costs.

[0003] Foam drilling fluid is a gas-liquid mixed multiphase system. With its advantages of low density and low leakage, it can improve mechanical drilling speed, reduce the risk of stuck pipe and leaks, and is recyclable, making it a promising area for oil and gas well engineering. However, foam is a thermodynamically unstable system, and problems such as disproportionation, aggregation, and rupture restrict its development, especially under high temperature (≥200℃), high pressure, and high salinity (total salinity ≥20×10⁻⁶). 4 In complex formations (mg / L), foam is prone to rupture, leading to a sharp decline in drilling fluid performance and severely impacting drilling efficiency and safety. Unstable foam can lose its viscosity, producing discharged fluid, causing slug flow, resulting in temporary overequilibrium, and thus damaging the formation.

[0004] With the development of foam drilling fluid technology in recent years, the commonly used methods to improve the stability of foam drilling fluids can be mainly divided into the following two types. The first method is to increase the viscosity of the liquid phase, thereby reducing the rate of foam separation. This is mainly achieved by adding plant gums, polymers, etc., to the foam system. However, this method suffers from incomplete foam breaking, which can easily lead to pore and throat blockage in the formation, affecting the productivity of oil and gas wells. The second method is to enhance the mechanical strength of the foam film, thereby increasing its resistance to impacts and disturbances. This is mainly achieved by adding particulate foam stabilizers, such as SiO2 nanoparticles, to the foam. However, SiO2 nanoparticles are relatively expensive. Therefore, the development of a foam drilling fluid system that is temperature and salt resistant, has good stability, and is environmentally friendly and low-cost has become an industry demand. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a nanofiber-reinforced foam system for foam drilling fluid and its preparation method; it solves the problems of poor stability, insufficient temperature and salt resistance, high cost and poor environmental performance of existing foam drilling fluids, and achieves intelligent matching of foam performance with formation conditions.

[0006] To overcome the shortcomings of the prior art, the present invention provides the following technical solution:

[0007] A nanofiber-reinforced foam system for foam drilling fluid includes a gas phase and a liquid phase; the liquid phase comprises the following raw material components by mass percentage: 0.3~0.8wt% foaming agent, 0.3~1.0wt% nanofiber, and the balance being water; the foaming agent is prepared by in-situ polymerization of sodium isomeric tridecyl alcohol polyoxyethylene ether carboxylate and fatty acid methyl ester ethoxylate, followed by the introduction of hydrophilic monomers and crosslinking agents, using ammonium persulfate as an initiator.

[0008] Furthermore, the mass ratio of sodium isomeric tridecyl alcohol polyoxyethylene ether carboxylate to fatty acid methyl ester ethoxylate is 2:1.

[0009] Furthermore, the nanofibers are silica-cellulose composite nanofibers prepared from biomass through multi-stage pretreatment, ultrasonic-assisted acid hydrolysis, graft copolymerization, and purification; the total mass of silica and cellulose accounts for ≥80wt% of the total mass of the silica-cellulose composite nanofibers, the particle size is ≤500nm, the cluster particle size is ≤500μm, and the specific surface area is ≥100m². 2 / g.

[0010] Furthermore, the gas phase is selected from nitrogen, carbon dioxide, or air;

[0011] And / or, the hydrophilic monomer is selected from one or a mixture of two or more of acrylamide, N-hydroxymethylacrylamide, and N-ethylacrylamide;

[0012] And / or, the crosslinking agent is selected from one or both of N,N-methylenebisacrylamide and divinylbenzene.

[0013] Furthermore, when the gas phase is nitrogen, the foam mass of the foam system is 45%–90%; when the gas phase is carbon dioxide, the foam mass is 55%–90%; when the gas phase is air, the foam mass is 42%–90%; the foam mass is the percentage of the gas volume in the foam to the total foam volume.

[0014] In addition, the present invention also provides a method for preparing the nanofiber-reinforced foam system for foam drilling fluid as described above, comprising the following steps: mixing water and foaming agent according to a ratio, adding nanofibers and stirring evenly to obtain a foam base liquid; and then foaming the foam base liquid to obtain the nanofiber-reinforced foam system for foam drilling fluid.

[0015] In addition, the present invention also provides a method for preparing a foaming agent in a nanofiber reinforced foam system for foam drilling fluid as described above, comprising the following steps: mixing sodium isomeric tridecyl alcohol polyoxyethylene ether carboxylate and fatty acid methyl ester ethoxylate at a mass ratio of 2:1, adding a hydrophilic monomer and a crosslinking agent, using ammonium persulfate as an initiator, and carrying out an in-situ polymerization reaction at 60~65°C for 4~6 hours to obtain the foaming agent.

[0016] In addition, the present invention also provides a method for preparing nanofibers in the nanofiber-reinforced foam system for foam drilling fluid as described above, comprising the following steps:

[0017] S1. Multi-stage pretreatment: The alkaline solution is mixed with a eutectic solvent to form a pretreatment solution; the biomass raw material and the pretreatment solution are then mixed according to a preset solid-liquid ratio, and after stirring and reacting for a period of time, the product is filtered, washed and dried to obtain refined cellulose.

[0018] S2. Ultrasonic-assisted acid hydrolysis: The refined cellulose is mixed with sulfuric acid solution and then ultrasonically dispersed. After centrifugation, dialysis and drying, nanofiber crystals are obtained.

[0019] S3. Graft copolymerization: The nanofiber crystals, N-isopropylacrylamide and sodium silicate are mixed, and deionized water is added to control the solid content. Then, the reaction is carried out under nitrogen protection with stirring. The reaction product is neutralized and washed by centrifugation.

[0020] S4. The product after centrifugation and washing is placed into a dialysis bag, dialyzed in deionized water, and then freeze-dried to obtain silica-cellulose composite nanofibers.

[0021] Further, in step S1, the alkaline solution is a sodium hydroxide solution with a mass fraction of 1.0~2.0%; the eutectic solvent is a choline chloride-urea eutectic solvent, and the molar ratio of choline chloride to urea is 1:2; the mixing volume ratio of the alkaline solution to the eutectic solvent is 1:1; the biomass raw material is wood, cotton or agricultural waste; the solid-liquid ratio of the biomass raw material to the pretreatment liquid is 1:(12-18) g / mL; the stirring reaction conditions are: temperature 70~90℃, stirring rate 200~400rpm, time 1.5-2.5h; washing until the filtrate is neutral, and drying at 75~85℃ for 10~14h.

[0022] Further, in step S2, the mass concentration of the sulfuric acid solution is 60%; the solid-liquid ratio of the refined cellulose to the sulfuric acid solution is 1:15 g / mL; and the power of the ultrasonic dispersion treatment is 400 W and the frequency is 20 kHz.

[0023] And / or, in step S3, the mass ratio of the nanofiber crystals, N-isopropylacrylamide, and sodium silicate is 1:(0.1~0.3):(0.2~0.5); the solid content is 3~8%; the stirring reaction conditions are: reaction temperature 60~80℃, stirring speed 200~400rpm, time 4~6h; the neutralization alkaline solution is a 10% sodium hydroxide solution, and the pH of the system after neutralization is 6.5~7.0; the centrifugation conditions are: centrifugation speed 8000~10000rpm, centrifugation time 15~20min, and centrifugation washing 3~5 times;

[0024] And / or, in step S4, dialysis is performed in flowing deionized water and dialysis continues until the pH of the system stabilizes at 6.5~7.0; the molecular weight cutoff of the dialysis bag is 8000~14000, the dialysis time is 48-72h, the freeze-drying temperature is -50℃, and the drying time is 24~48h.

[0025] Compared with the prior art, the technical solution of the present invention has at least the following technical effects:

[0026] (1) The nanofibers in the reinforced foam system proposed in this invention are nanofiber crystals grafted with N-isopropylacrylamide (NIPAM) monomer and sodium silicate. The grafting of SiO2 particles improves mechanical strength and thermal stability. The SiO2 particles are firmly attached to the fiber surface, constructing a relatively rough nano-armor interface structure, forming an armor effect; improving roughness and reducing interfacial tension. The grafted and modified nanofibers adsorb on the liquid-liquid and gas-liquid interfaces, increasing the mechanical strength of the liquid film and improving the surfactant and stability, thus making the foam performance more stable. It is compounded with a foaming agent to achieve synergistic interfacial stability. Compared with unmodified nanofibers, the foam drilling fluid system with modified nanofibers has significantly improved temperature and salt resistance.

[0027] (2) The system of the present invention can maintain good foam stability under extreme conditions such as high temperature and high salinity, with a half-life of more than 151 min. The principle is due to the synergistic protective effect of multiple components in the system: under high temperature conditions, the polymer chains will shrink and collapse, tightly adhering to the surface of the bubbles, enhancing the viscoelasticity and mechanical strength of the liquid film; while silica-cellulose provides a rigid skeleton that is resistant to high temperature, effectively inhibiting bubble aggregation; at the same time, the system mainly relies on physical spatial barrier to maintain stability and is not easily affected by the salt in the water. This multi-protection mechanism ensures the stability of the foam under complex geological conditions.

[0028] (3) The reinforced foam system proposed in this invention uses wood, cotton, and agricultural waste as raw materials, fully considering the renewability and resource utilization efficiency of the raw materials, and strives to achieve efficient conversion of lignocellulose materials, thereby reducing production costs and improving product quality. Through multi-stage pretreatment and grafting technology, the prepared nanofibers significantly improve the adaptability and stability of the foam. The principle is that when encountering high-temperature formations, the polymer chains on the surface of the nanofibers will automatically shrink and more firmly adsorb onto the surface of the bubbles, enhancing the mechanical strength of the liquid film; when encountering acidic or alkaline environments, the surface charge of the nanofibers will change, and the interface state will be adjusted by mutual attraction or repulsion. This intelligent response mechanism enables the foam system to automatically adjust its interface behavior according to formation conditions, and maintain excellent stability in complex formations with different temperatures and pH levels, significantly improving the adaptability of foam drilling fluid.

[0029] (4) Formation adaptive foaming technology forms a distribution of bubbles from large to small by pre-modulating formation water and step foaming technology. It can adaptively seal pores and fractures of different sizes, avoid the limitations of single-size bubbles, improve sweep efficiency, and the bubbles of different sizes support each other to form a more stable foam system with better rheological properties. It has stronger rock carrying and sealing capabilities, realizes precise matching between foam performance and formation conditions, and improves drilling efficiency.

[0030] (5) Compared with traditional nanofibers, the nanofibers prepared by the present invention have the following characteristics: by grafting, the nanofibers are modified, which not only enhances the foam stability but also maintains good stability in high temperature and high mineralization geological environments. They can adapt to geological conditions and work with foaming agents to regulate the stability of the system. In terms of raw materials, renewable biological resources are used and prepared through green processes, which has environmental advantages. Attached Figure Description

[0031] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. Wherein:

[0032] Figure 1 This is a particle size distribution diagram of the modified nanofibers;

[0033] Figure 2 This is a particle size distribution diagram of the modified nanofiber clusters;

[0034] Figure 3 This is a characterization diagram of the adsorption-desorption isotherms of the modified nanofibers;

[0035] Figure 4 This is a comparison chart of the liquid separation time and foam volume of the reinforced foam system under different nanofiber concentrations;

[0036] Figure 5 This is a comparison chart of the overall foam values ​​of reinforced foam systems under different nanofiber concentrations;

[0037] Figure 6 It is a foaming agent composite system formed by continuous reaction at 60-65℃ for 4-6 hours;

[0038] Figure 7 It is a foaming agent composite system formed by continuous reaction at 50-55℃ for 4-6 hours;

[0039] Figure 8 It is a foaming agent composite system formed by continuous reaction at 70-75℃ for 4-6 hours;

[0040] Figure 9 These are silica-cellulose composite nanofibers prepared by continuous reaction at 60-80℃ for 4-6 hours.

[0041] Figure 10 These are silica-cellulose composite nanofibers prepared by continuous reaction at 60-80℃ for 1-3 hours.

[0042] Figure 11 These are silica-cellulose composite nanofibers prepared by continuous reaction at 60-80℃ for 7-9 hours.

[0043] Figure 12 These are silica-cellulose composite nanofibers prepared by continuous reaction at 50-70℃ for 4-6 hours.

[0044] Figure 13 It is a silica-cellulose composite nanofiber prepared by continuous reaction at 90-110℃ for 4-6 hours;

[0045] Figure 14 It is the crushed biomass raw material;

[0046] Figure 15 This describes the foaming behavior of the system of this invention under high mineralization conditions;

[0047] Figure 16 This is a SEM image of purified silica-cellulose composite nanofibers;

[0048] Figure 17 This is a magnified SEM image of silica-cellulose composite nanofibers;

[0049] Figure 18 This is a further enlarged SEM image of the silica-cellulose composite nanofibers. Detailed Implementation

[0050] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Those skilled in the art should understand that the embodiments described are merely illustrative of the invention and should not be considered as specific limitations thereof. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention. Process parameters not specifically specified in the following embodiments are generally performed under conventional conditions.

[0051] The endpoints and any values ​​of the ranges disclosed in this invention are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this invention.

[0052] Terminology Explanation: Foam mass refers to the percentage of gas volume in the total foam volume. The Waring Blender method is a commonly used laboratory stirring foaming method, which generates foam by stirring a foam base liquid at a certain speed in a high-speed stirrer for a period of time. Critical temperature refers to the temperature at which nanofibers transition from a hydrophilic to a hydrophobic state; in this invention, it is 50-60℃. Nanoscale armor effect refers to the effect of SiO2 particles forming a dense coating layer on the surface of cellulose, enhancing the particle's mechanical strength and interfacial adsorption capacity. In-situ polymerization reaction refers to the free radical polymerization at the gas-liquid interface initiated by ammonium persulfate, using a compound of sodium isomeric tridecyl alcohol polyoxyethylene ether carboxylate and fatty acid methyl ester ethoxylate, introducing hydrophilic monomers and crosslinking agents.

[0053] This invention provides a nanofiber-reinforced foam system for foam drilling fluids, comprising a gas phase and a liquid phase. The liquid phase contains the following raw material components by mass percentage: 0.3-0.8 wt% foaming agent, 0.3-1.0 wt% nanofibers, and the balance being water. The foaming agent is prepared by in-situ polymerization of sodium isomeric tridecyl alcohol polyoxyethylene ether carboxylate and fatty acid methyl ester ethoxylate, followed by the introduction of hydrophilic monomers and crosslinking agents, using ammonium persulfate as an initiator. Both the foaming agent and nanofibers in the liquid phase are soluble in tap water, river water, or formation water. The foaming agent is heat resistant up to 200℃, has a foaming rate of up to 560%, and a foam half-life of 1.5 h at 200℃, maintaining excellent foaming performance at high temperatures (200℃) and exhibiting excellent surface activity at low concentrations.

[0054] The foaming agent compound system of this invention has the appearance of an amber or light brown viscous liquid, is easily soluble in water, and remains soluble at high temperatures (≥200℃) and high mineralization (total mineralization can reach 20×10⁻⁶). 4 It maintains excellent foaming properties and stability even under conditions of mg / L, making it particularly suitable for water-based foam drilling fluid systems in high-temperature and high-salinity formations. This system is mainly composed of sodium isomeric tridecyl alcohol polyoxyethylene ether carboxylate (anionic) and fatty acid methyl ester ethoxylate (nonionic) in a mass ratio of 2:1. By adding hydrophilic monomers and crosslinking agents to this system, an in-situ polymerization reaction is carried out for 4-6 hours under ammonium persulfate initiation. There are no special requirements for the mass ratio of the hydrophilic monomers, crosslinking agents, and initiators. In this invention, the mass ratio of the hydrophilic monomers, crosslinking agents, and initiators is 1:(0.0001-0.005):(0.00001-0.00002) to exemplify the advantages of this invention, but does not limit its scope. The reaction temperature is set at 60-65℃ to form a foaming agent composite system (such as...). Figure 6 As shown in Figures 7 and 8, the foaming agent composite systems obtained by reacting at 50-55℃ and 70-75℃, respectively, combine interfacial activity and polymer thickening properties. This system primarily achieves this through the synergistic effect of anions and cations, forming a dense composite film at the gas-liquid interface. This significantly enhances the mechanical strength and anti-interference ability of the foam liquid film, avoiding the problem of single surfactants easily failing under extreme conditions.

[0055] In the aforementioned nanofiber-reinforced foam system for foam drilling fluid, as a preferred embodiment, the nanofibers are made from biomass (including but not limited to wood, cotton, or agricultural waste, such as pulverized biomass raw materials) Figure 14 Using the sample (shown) as raw material, silica-cellulose composite nanofibers were prepared through multi-stage pretreatment, ultrasonic-assisted acid hydrolysis, graft copolymerization, and purification. Under acid-catalyzed conditions, silicic acid generated from the hydrolysis of sodium silicate undergoes a condensation reaction with the hydroxyl groups on the surface of cellulose, forming strong Si-OC covalent grafting sites. Subsequently, the continuously hydrolyzed silicic acid uses these as core centers to form a silica nanoparticle coating through in-situ deposition and condensation, ultimately constructing a composite structure with cellulose chains as the core and a rigid silica network as the shell. The total mass of silica and cellulose accounts for ≥80wt% of the total mass of the silica-cellulose composite nanofibers, with a particle size ≤500nm, a cluster particle size ≤500μm, and a specific surface area ≥100m². 2 / g.

[0056] SEM image of purified silica-cellulose composite nanofibers as shown below Figure 16 As shown, the magnified structure is as follows Figure 17 , Figure 18As shown, the surface of cellulose fibers is covered with a large number of silica nanoparticles, forming a core-shell composite structure. This structure endows the nanofibers with good mechanical strength and thermal stability. The composite nanofibers prepared by reacting at 60-80℃ for 4-6 hours have the best structure (as shown in Figure 9), while the structural integrity and performance of the products obtained by reacting at 1-3 hours (Figure 10), 7-9 hours (Figure 11), or at 50-70℃ (Figure 12) or 90-110℃ (Figure 13) all decreased.

[0057] In the above-mentioned nanofiber-reinforced foam system for foam drilling fluid, as a preferred embodiment, the gas phase includes, but is not limited to, nitrogen, carbon dioxide, or air; the hydrophilic monomer includes, but is not limited to, one or a mixture of two or more of acrylamide, N-hydroxymethylacrylamide, and N-ethylacrylamide; and the crosslinking agent includes, but is not limited to, one or two of N,N-methylenebisacrylamide and divinylbenzene.

[0058] The foam mass of the foam system is as follows: the foam mass refers to the percentage of gas volume in the foam to the total foam volume; when the gas phase is nitrogen, the foam mass of the foam system is 45%–90%, more preferably 50%–80%; when the gas phase is carbon dioxide, the foam mass of the foam system is 55%–90%, more preferably 65%–80%; when the gas phase is air, the foam mass of the foam system is 42%–90%, more preferably 49%–80%. According to the present invention, preferably, the gas phase is nitrogen. Nitrogen foam has better foaming ability and foam stability after foaming than carbon dioxide foam and air foam. Moreover, nitrogen gas is low in cost, widely available, and is a non-flammable, highly stable, non-toxic, colorless, odorless, and non-corrosive gas. The foaming behavior of the system of the present invention under high mineralization conditions is as follows: Figure 15 As shown, it exhibits excellent salt resistance.

[0059] This invention also provides a method for preparing temperature- and salt-resistant nanofibers for foam drilling fluids, comprising the following steps:

[0060] Step 1: Raw material refining

[0061] A pretreatment mixture was prepared by mixing a 1.0-2.0% (w / w) sodium hydroxide solution with a choline chloride-urea eutectic solvent (molar ratio 1:2) at a volume ratio of 1:1. The pulverized biomass feedstock and the pretreatment mixture were added to a three-necked glass flask equipped with a mechanical stirrer, a reflux condenser, and a thermometer for stirring and reaction. The reaction temperature was 70-90℃, the reaction time was 1.5-2.5 h, and the stirring speed was controlled at 200-400 rpm. The solid-liquid ratio of the pretreatment mixture to the biomass feedstock was controlled at 1:(12-18) (g / mL). Immediately after the reaction, vacuum filtration was performed using a Buchner funnel and a suction flask. The solid product was repeatedly washed with deionized water until the filtrate was neutral. The washed solid was placed in a drying oven and dried at 75-85℃ for 10-14 h to obtain a refined cellulose product, which appeared as a white fibrous solid. Because low-concentration alkali can break down the structure of biomass, making it loose, the choline chloride and urea in the eutectic solvent form a hydrogen bond network, which can selectively dissolve the lignin damaged by the alkali, while hemicellulose is hydrolyzed under acidic conditions. Therefore, this process can achieve efficient removal of 85-95% lignin and 90-97% hemicellulose, while maintaining the integrity of the cellulose crystalline structure.

[0062] Step 2: Preparation of nanofiber crystals

[0063] The refined cellulose product obtained in step 1 above was added to a 500 mL three-necked flask with 60% concentrated sulfuric acid solution at a solid-liquid ratio of 1:15 (g / mL). Hydrolysis was assisted by an ultrasonic disperser (400W power, 20kHz frequency) under constant temperature water bath conditions of 50-70℃. The reaction temperature was controlled within the range of 50-70℃, and the reaction was terminated immediately by adding ice water after ultrasonic treatment for 45 minutes. The mixture was transferred to a high-speed centrifuge and centrifuged at 8000 rpm for 15 minutes. The supernatant was removed, and the precipitate was collected. The precipitate was placed in a dialysis bag with a molecular weight cutoff of 8000-14000 and dialyzed in flowing deionized water for 72 hours until the pH value stabilized at 6.5-7.0. Finally, after drying, white powdery nanofiber crystals were obtained. The calculated yield of nanocellulose using this process reached 87.3%.

[0064] Step 3: Preparation of silica-cellulose composite nanofibers

[0065] The refined nanocellulose and N-isopropylacrylamide (NIPAM) monomers obtained in step 2 above were added to sodium silicate at a mass ratio of 1:(0.1-0.3):(0.2-0.5) in a three-necked glass flask equipped with a stirrer, a nitrogen purging tube, and a thermometer. Deionized water was added to control the solid content to 3-8%. Under nitrogen purging, the reaction was carried out in a water bath at 60-80℃ for 4-6 hours to complete the graft copolymerization, with the stirring speed controlled at 200-400 rpm. The acidic suspension after the reaction was completed was transferred to a 2000 mL beaker, and a 10% sodium hydroxide solution was slowly added dropwise under ice-water bath conditions to adjust the pH to 6.5-7.0 and terminate the reaction. During the neutralization process, the stirring speed was controlled at 200-400 rpm, and the dropping rate was controlled to keep the system temperature below 25℃. Aliquot the neutralized suspension into 500mL centrifuge tubes and centrifuge at 8000-10000rpm for 15-20 minutes. Remove the supernatant to obtain a solid precipitate. Add an equal volume of deionized water to the centrifuged precipitate, redisperse it using a vortex mixer, and repeat the above centrifugation and washing process 3-5 times.

[0066] Step 4: Purification of composite particles

[0067] The reaction product obtained in step 3 above was placed in a dialysis bag with a molecular weight cutoff of 8000-14000 and dialyzed in flowing deionized water for 48-72 hours. Finally, the washed and dialyzed nanofibers were placed in a freeze dryer for freeze-drying at -50°C for 24-48 hours, followed by restoring to room temperature to obtain further purified silica-cellulose nanocomposite particles. This purification process effectively removes residual acid and inorganic salt impurities, yielding nanofibers with a purity ≥98%.

[0068] The SEM image of the silica-cellulose composite nanofibers is shown below. Figure 16 As shown;

[0069] In the nanofibers, the total proportion of silicon dioxide and nanocellulose is ≥80wt%.

[0070] In the above preparation method, as a preferred embodiment, the nanofiber particle size is ≤500nm, the cluster particle size is ≤500μm, and the specific surface area is ≥100m². 2 / g, such as Figures 1-3 As shown; from Figure 1 It can be seen that the particle size is mainly distributed in the range of 100-200nm, with an average particle size of 110nm, and particles larger than 500nm account for less than 1%.

[0071] In the above preparation method, as a preferred embodiment, the nanofibers have a temperature resistance of up to 200℃, a foaming rate of ≥500%, and a foam half-life of up to 2h.

[0072] In the above preparation method, as a preferred embodiment, the amide groups on the polymer chain form hydrogen bonds with water molecules under normal temperature and pressure. Under the action of these hydrogen bonds, the polymer chain is fully hydrated, and the nanofibers exhibit hydrophilicity under normal temperature and pressure conditions. They can be well dispersed in tap water, river water, or formation water to form a stable base liquid. The extended chain structure within the foam allows the nanofibers to be better stabilized in the aqueous phase. When the ambient temperature exceeds its critical temperature, the polymer chain dehydrates and collapses, exhibiting a hydrophobic state, and the particles change from a hydrophilic state to a hydrophobic state. This promotes the migration of the nanofibers from the aqueous phase and their tight adsorption at the liquid interface, forming a dense armor layer at the gas-liquid interface. This adaptive behavior not only effectively prevents bubble aggregation by significantly increasing the mechanical strength of the interfacial film but also significantly slows down the liquid film drainage rate by enhancing interfacial viscoelasticity, thereby extending the foam half-life under extreme conditions.

[0073] In the above preparation method, as a preferred embodiment, the nanofibers are in the form of white to light gray powder, which can significantly enhance the durability and strength of foam, effectively resist foam rupture under high temperature of 200°C, and maintain the stability of foam performance.

[0074] In the above preparation method, as a preferred embodiment, the nano-armor, through the dense hydrogen bond network formed between molecular chains, constitutes a stable entangled structure, thereby significantly enhancing the overall stability of the foam. Silicon is uniformly distributed on the surface of the nano-armor, achieving a silanization-enhanced effect.

[0075] According to the present invention, preferably, the concentration ratio of the nanofibers to the foaming agent is (1-1.5):1. At this concentration ratio, the foaming agent and nanofibers have a good synergistic effect, which macroscopically manifests as a large foam volume and a long half-life of the generated foam; microscopically manifests as nanoparticles adsorbed on the bubble liquid film, effectively enhancing the mechanical strength of the liquid film and reducing the evaporation rate and separation rate of the liquid film.

[0076] This invention also provides a formation adaptive foaming process, the specific steps of which are as follows:

[0077] (1) Formation water preconditioning: Collect target formation water samples, analyze their ionic composition, and adjust the Ca content in the foam base solution. 2+ Mg 2 + The concentration should be within the range compatible with formation water to avoid salting out and demulsification.

[0078] (2) Stepped foaming: After the foam base liquid is pumped into the foam generator, gas is injected using a stepped pressurization method. By controlling the foam generator to sequentially increase the pressure within a certain pressure range, the foam forms a multi-level bubble structure at different pressure levels: In the low-pressure stage, a small number of large bubbles are generated as a transport skeleton, preferentially entering high-permeability channels to generate the Jamin effect; in the medium-pressure stage, the shear force increases, and the large bubbles are broken into medium-sized bubbles to fill the pores; in the high-pressure stage, a large number of micro bubbles are generated to fill the pore space, entering the low-permeability area to expand the sweep area. Finally, through the synergistic effect of bubbles of various sizes, adaptive regulation is achieved, enhancing its migration and sealing capabilities in the formation.

[0079] This invention also provides two methods for preparing nanofiber-reinforced foam for foam drilling fluid: one is a foam preparation method for laboratory evaluation, and the other is a foam ground preparation method for field construction in oil and gas fields.

[0080] The method for preparing foam for laboratory evaluation according to the present invention comprises the following steps:

[0081] Foaming agent was added to water according to the specified ratio and stirred for 15-20 minutes to prepare a foaming agent solution. Then, nanofibers were added and stirred for 15-20 minutes to obtain a foam base solution. The foam base solution was then stirred and foamed using the Waring Blender method at a speed of 6000-8000 rpm for 5-10 minutes. After stirring, the foam was poured into a 1000 mL graduated cylinder, and the initial volume of the foam and the time required for 50 mL of liquid to separate from the foam were recorded at room temperature and pressure to verify the foam's stability.

[0082] The method for preparing a foamed surface for drilling site construction according to the present invention comprises the following steps:

[0083] Empty and rinse the ground circulation tank. Add water and foaming agent to the mixing tank according to the specified ratio, stir for 1-3 minutes, then add nanofibers and stir for 5-10 minutes to ensure uniform mixing and prepare the foam base liquid. Pump the foam base liquid into the foam generator and mix it with nitrogen according to the formation adaptive foaming process to obtain the reinforced foam system.

[0084] The present invention will now be described in detail with reference to embodiments thereof. These examples are provided by way of explanation and not by way of limitation. In fact, those skilled in the art will recognize that modifications and variations can be made to the present invention without departing from its scope or spirit. For example, a feature shown or described as part of one embodiment may be used in another embodiment to produce yet another embodiment. Therefore, it is desirable that the present invention encompass such modifications and variations that fall within the scope of the appended claims and their equivalents.

[0085] In the embodiments of the present invention, unless otherwise specified, the experimental methods used are conventional methods, and the materials and reagents used are commercially available unless otherwise specified.

[0086] Example 1

[0087] A nanofiber-reinforced foam system for foam drilling fluid includes a gas phase and a liquid phase; the gas phase is nitrogen, and the mass percentages of the raw material components in the liquid phase are as follows:

[0088] 0.3 wt% foaming agent, 0.3 wt% nanofibers, balance water;

[0089] The foaming agent is a foaming agent system formed by compounding sodium isomeric tridecyl alcohol polyoxyethylene ether carboxylate and fatty acid methyl ester ethoxylate in a mass ratio of 2:1 and introducing hydrophilic monomers and crosslinking agents, and then undergoing in-situ polymerization at 60-65℃ for 4-6 hours initiated by ammonium persulfate.

[0090] The nanofibers are prepared by mixing pulverized biomass raw materials with a 1.0-2.0% sodium hydroxide solution and a choline chloride-urea eutectic solvent (molar ratio 1:2) at a 1:1 volume ratio. This pretreatment solution is then subjected to pretreatment at 70-90℃, followed by ultrasonic-assisted hydrolysis with sulfuric acid solution at 50-70℃ to obtain nanocellulose crystals. The nanocellulose is then mixed with N-isopropylacrylamide monomer and sodium silicate in a specific ratio and reacted at 60-80℃ for 4-6 hours under nitrogen protection to complete graft copolymerization. Finally, the nanofibers are purified by dialysis and freeze-dried to obtain silica-cellulose composite nanofibers.

[0091] The preparation method includes the following steps:

[0092] Add the foaming agent to 100 mL of water according to the specified ratio, and stir on a magnetic stirrer for 15-20 min to obtain a foaming agent solution. Then add silica-cellulose nanofibers and continue stirring for 20 min to obtain a foam base solution. Take 100 mL of the prepared foam base solution and stir and foam it using the Waring Blender method under a nitrogen atmosphere at a stirring speed of 7000 r / min for 10 min to obtain a reinforced foam system. After stirring, pour the prepared reinforced foam system into a 1000 mL graduated cylinder. Record the initial volume of the foam as 310 mL and the time taken for 50 mL of foam base solution to precipitate from the foam system as 31 min at room temperature and pressure, demonstrating good foaming and foam stability.

[0093] Example 2

[0094] A nanofiber-reinforced foam system for foam drilling fluid includes a gas phase and a liquid phase; the gas phase is nitrogen, and the mass percentages of the raw material components in the liquid phase are as follows:

[0095] 0.5 wt% foaming agent, 0.6 wt% nanofibers, balance water;

[0096] The foaming agent is a foaming agent system formed by compounding sodium isomeric tridecyl alcohol polyoxyethylene ether carboxylate and fatty acid methyl ester ethoxylate in a mass ratio of 2:1 and introducing hydrophilic monomers and crosslinking agents, and then undergoing in-situ polymerization at 60-65℃ for 4-6 hours initiated by ammonium persulfate.

[0097] The nanofibers are prepared by mixing pulverized biomass raw materials with a 1.0-2.0% sodium hydroxide solution and a choline chloride-urea eutectic solvent (molar ratio 1:2) at a 1:1 volume ratio. This pretreatment solution is then subjected to pretreatment at 70-90℃, followed by ultrasonic-assisted hydrolysis with sulfuric acid solution at 50-70℃ to obtain nanocellulose crystals. The nanocellulose is then mixed with N-isopropylacrylamide monomer and sodium silicate in a specific ratio and reacted at 60-80℃ for 4-6 hours under nitrogen protection to complete graft copolymerization. Finally, the nanofibers are purified by dialysis and freeze-dried to obtain silica-cellulose composite nanofibers.

[0098] The preparation method includes the following steps:

[0099] Add the foaming agent to 100 mL of water according to the specified ratio, and stir on a magnetic stirrer for 15-20 min to obtain a foaming agent solution. Then add silica-cellulose nanofibers and continue stirring for 20 min to obtain a foam base solution. Take 100 mL of the prepared foam base solution and stir and foam it using the Waring Blender method under a nitrogen atmosphere at a stirring speed of 7000 r / min for 10 min to obtain a reinforced foam system. After stirring, pour the prepared reinforced foam system into a 1000 mL graduated cylinder. Record the initial volume of the foam as 290 mL and the time taken for 50 mL of foam base solution to precipitate from the foam system as 5043 s at room temperature and pressure, demonstrating good foaming and foam stability.

[0100] Example 3

[0101] A nanofiber-reinforced foam system for foam drilling fluid includes a gas phase and a liquid phase; the gas phase is nitrogen, and the mass percentages of the raw material components in the liquid phase are as follows:

[0102] 0.8 wt% foaming agent, 1.0 wt% nanofibers, balance water;

[0103] The foaming agent is a foaming agent system formed by compounding sodium isomeric tridecyl alcohol polyoxyethylene ether carboxylate and fatty acid methyl ester ethoxylate in a mass ratio of 2:1 and introducing hydrophilic monomers and crosslinking agents, and then undergoing in-situ polymerization at 60-65℃ for 4-6 hours initiated by ammonium persulfate.

[0104] The nanofibers are prepared by mixing pulverized biomass raw materials with a 1.0-2.0% sodium hydroxide solution and a choline chloride-urea eutectic solvent (molar ratio 1:2) at a 1:1 volume ratio. This pretreatment solution is then subjected to pretreatment at 70-90℃, followed by ultrasonic-assisted hydrolysis with sulfuric acid solution at 50-70℃ to obtain nanocellulose crystals. The nanocellulose is then mixed with N-isopropylacrylamide monomer and sodium silicate in a specific ratio and reacted at 60-80℃ for 4-6 hours under nitrogen protection to complete graft copolymerization. Finally, the nanofibers are purified by dialysis and freeze-dried to obtain silica-cellulose composite nanofibers.

[0105] The preparation method includes the following steps:

[0106] Add the foaming agent to 100 mL of water according to the specified ratio, and stir on a magnetic stirrer for 15-20 min to obtain a foaming agent solution. Then add silica-cellulose nanofibers and continue stirring for 20 min to obtain a foam base liquid. Take 100 mL of the prepared foam base liquid and stir and foam it using the Waring Blender method under a nitrogen atmosphere at a stirring speed of 7000 r / min for 10 min to obtain a reinforced foam system. After stirring, pour the prepared reinforced foam system into a 1000 mL graduated cylinder. Record the initial volume of the foam as 245 mL and the time taken for 50 mL of foam base liquid to precipitate from the foam system as 9066 s at room temperature and pressure, demonstrating good foaming and foam stability.

[0107] Example 4

[0108] A nanofiber-reinforced foam system for foam drilling fluid includes a gas phase and a liquid phase; the gas phase is nitrogen, and the mass percentages of the raw material components in the liquid phase are as follows:

[0109] 0.8 wt% foaming agent, 1.0 wt% nanofibers, balance water;

[0110] The foaming agent is a foaming agent system formed by compounding sodium isomeric tridecyl alcohol polyoxyethylene ether carboxylate and fatty acid methyl ester ethoxylate in a mass ratio of 2:1 and introducing hydrophilic monomers and crosslinking agents, and then undergoing in-situ polymerization at 50-55℃ for 4-6 hours initiated by ammonium persulfate.

[0111] The nanofibers are prepared by mixing pulverized biomass raw materials with a 1.0-2.0% sodium hydroxide solution and a choline chloride-urea eutectic solvent (molar ratio 1:2) at a 1:1 volume ratio. This pretreatment solution is then subjected to pretreatment at 70-90°C, followed by ultrasonic-assisted hydrolysis with sulfuric acid solution at 50-70°C to obtain nanocellulose crystals. The nanocellulose is then mixed with N-isopropylacrylamide monomer and sodium silicate in a specific ratio and reacted at 50-70°C for 4-6 hours under nitrogen protection to complete graft copolymerization. Finally, the nanofibers are purified by dialysis and freeze-dried to obtain silica-cellulose composite nanofibers.

[0112] The preparation method includes the following steps:

[0113] Add the foaming agent to 100 mL of water according to the specified ratio, and stir on a magnetic stirrer for 15-20 min to obtain a foaming agent solution. Then add silica-cellulose nanofibers and continue stirring for 20 min to obtain a foam base liquid. Take 100 mL of the prepared foam base liquid and stir and foam it using the Waring Blender method under a nitrogen atmosphere at a stirring speed of 7000 r / min for 10 min to obtain a reinforced foam system. After stirring, pour the prepared reinforced foam system into a 1000 mL graduated cylinder. Record the initial volume of the foam as 289 mL and the time taken for 50 mL of foam base liquid to precipitate from the foam system as 7441 s at room temperature and pressure, demonstrating good foaming and foam stability.

[0114] Example 5

[0115] A nanofiber-reinforced foam system for foam drilling fluid includes a gas phase and a liquid phase; the gas phase is nitrogen, and the mass percentages of the raw material components in the liquid phase are as follows:

[0116] 0.8 wt% foaming agent, 1.0 wt% nanofibers, balance water;

[0117] The foaming agent is a foaming agent system formed by compounding sodium isomeric tridecyl alcohol polyoxyethylene ether carboxylate and fatty acid methyl ester ethoxylate in a mass ratio of 2:1 and introducing hydrophilic monomers and crosslinking agents, and then undergoing in-situ polymerization at 70-75°C for 4-6 hours initiated by ammonium persulfate.

[0118] The nanofibers are prepared by mixing pulverized biomass raw materials with a 1.0-2.0% sodium hydroxide solution and a choline chloride-urea eutectic solvent (molar ratio 1:2) at a 1:1 volume ratio. This pretreatment solution is then subjected to pretreatment at 70-90°C, followed by ultrasonic-assisted hydrolysis with sulfuric acid solution at 50-70°C to obtain nanocellulose crystals. The nanocellulose is then mixed with N-isopropylacrylamide monomer and sodium silicate in a specific ratio and reacted at 90-110°C for 4-6 hours under nitrogen protection to complete graft copolymerization. Finally, the nanofibers are purified by dialysis and freeze-dried to obtain silica-cellulose composite nanofibers.

[0119] The preparation method includes the following steps:

[0120] Add the foaming agent to 100 mL of water according to the specified ratio, and stir on a magnetic stirrer for 15-20 min to obtain a foaming agent solution. Then add silica-cellulose nanofibers and continue stirring for 20 min to obtain a foam base liquid. Take 100 mL of the prepared foam base liquid and stir and foam it using the Waring Blender method under a nitrogen atmosphere at a stirring speed of 7000 r / min for 10 min to obtain a reinforced foam system. After stirring, pour the prepared reinforced foam system into a 1000 mL graduated cylinder. Record the initial volume of the foam as 260 mL and the time taken for 50 mL of foam base liquid to precipitate from the foam system as 8580 s at room temperature and pressure, demonstrating good foaming and foam stability.

[0121] Example 6

[0122] A nanofiber-reinforced foam system for foam drilling fluid includes a gas phase and a liquid phase; the gas phase is nitrogen, and the mass percentages of the raw material components in the liquid phase are as follows:

[0123] 0.8 wt% foaming agent, 1.0 wt% nanofibers, balance water;

[0124] The foaming agent is a foaming agent system formed by compounding sodium isomeric tridecyl alcohol polyoxyethylene ether carboxylate and fatty acid methyl ester ethoxylate in a mass ratio of 2:1 and introducing hydrophilic monomers and crosslinking agents, and then undergoing in-situ polymerization at 60-65℃ for 4-6 hours initiated by ammonium persulfate.

[0125] The nanofibers are prepared by mixing pulverized biomass raw materials with a 1.0-2.0% sodium hydroxide solution and a choline chloride-urea eutectic solvent (molar ratio 1:2) at a 1:1 volume ratio. This pretreatment solution is then subjected to pretreatment at 70-90℃, followed by ultrasonic-assisted hydrolysis with sulfuric acid solution at 50-70℃ to obtain nanocellulose crystals. The nanocellulose is then mixed with N-isopropylacrylamide monomer and sodium silicate in a specific ratio and reacted at 60-80℃ for 1-3 hours under nitrogen protection to complete graft copolymerization. Finally, the nanofibers are purified by dialysis and freeze-dried to obtain silica-cellulose composite nanofibers.

[0126] The preparation method includes the following steps:

[0127] Add the foaming agent to 100 mL of water according to the specified ratio, and stir on a magnetic stirrer for 15-20 min to obtain a foaming agent solution. Then add silica-cellulose nanofibers and continue stirring for 20 min to obtain a foam base liquid. Take 100 mL of the prepared foam base liquid and stir and foam it using the Waring Blender method under a nitrogen atmosphere at a stirring speed of 7000 r / min for 10 min to obtain a reinforced foam system. After stirring, pour the prepared reinforced foam system into a 1000 mL graduated cylinder. Record the initial volume of the foam as 237 mL and the time taken for 50 mL of foam base liquid to precipitate from the foam system as 6360 s at room temperature and pressure, demonstrating good foaming and foam stability.

[0128] Example 7

[0129] A nanofiber-reinforced foam system for foam drilling fluid includes a gas phase and a liquid phase; the gas phase is nitrogen, and the mass percentages of the raw material components in the liquid phase are as follows:

[0130] 0.8 wt% foaming agent, 1.0 wt% nanofibers, balance water;

[0131] The foaming agent is a foaming agent system formed by compounding sodium isomeric tridecyl alcohol polyoxyethylene ether carboxylate and fatty acid methyl ester ethoxylate in a mass ratio of 2:1 and introducing hydrophilic monomers and crosslinking agents, and then undergoing in-situ polymerization at 60-65℃ for 4-6 hours initiated by ammonium persulfate.

[0132] The nanofibers are prepared by mixing pulverized biomass raw materials with a 1.0-2.0% sodium hydroxide solution and a choline chloride-urea eutectic solvent (molar ratio 1:2) at a 1:1 volume ratio. This pretreatment solution is then subjected to pretreatment at 70-90°C, followed by ultrasonic-assisted hydrolysis with sulfuric acid solution at 50-70°C to obtain nanocellulose crystals. The nanocellulose is then mixed with N-isopropylacrylamide monomer and sodium silicate in a specific ratio and reacted at 60-80°C for 7-9 hours under nitrogen protection to complete graft copolymerization. Finally, the nanofibers are purified by dialysis and freeze-dried to obtain silica-cellulose composite nanofibers.

[0133] The preparation method includes the following steps:

[0134] Add the foaming agent to 100 mL of water according to the specified ratio, and stir on a magnetic stirrer for 15-20 min to obtain a foaming agent solution. Then add silica-cellulose nanofibers and continue stirring for 20 min to obtain a foam base solution. Take 100 mL of the prepared foam base solution and stir and foam it using the Waring Blender method under a nitrogen atmosphere at a stirring speed of 7000 r / min for 10 min to obtain a reinforced foam system. After stirring, pour the prepared reinforced foam system into a 1000 mL graduated cylinder. Record the initial volume of the foam as 252 mL and the time taken for 50 mL of foam base solution to precipitate from the foam system as 7625 s at room temperature and pressure, demonstrating good foaming and foam stability.

[0135] Example 8

[0136] A nanofiber-reinforced foam system for foam drilling fluid includes a gas phase and a liquid phase; the gas phase is nitrogen, and the mass percentages of the raw material components in the liquid phase are as follows:

[0137] 0.3 wt% foaming agent, 0.3 wt% nanofibers, balance water;

[0138] The foaming agent is a foaming agent system formed by compounding sodium isomeric tridecyl alcohol polyoxyethylene ether carboxylate and fatty acid methyl ester ethoxylate in a mass ratio of 2:1 and introducing hydrophilic monomers and crosslinking agents, and then undergoing in-situ polymerization at 60-65℃ for 4-6 hours initiated by ammonium persulfate.

[0139] The nanofibers are prepared by mixing pulverized biomass raw materials with a 1.0-2.0% sodium hydroxide solution and a choline chloride-urea eutectic solvent (molar ratio 1:2) at a 1:1 volume ratio. This pretreatment solution is then subjected to pretreatment at 70-90℃, followed by ultrasonic-assisted hydrolysis with sulfuric acid solution at 50-70℃ to obtain nanocellulose crystals. The nanocellulose is then mixed with N-isopropylacrylamide monomer and sodium silicate in a specific ratio and reacted at 60-80℃ for 4-6 hours under nitrogen protection to complete graft copolymerization. Finally, the nanofibers are purified by dialysis and freeze-dried to obtain silica-cellulose composite nanofibers.

[0140] The preparation method of reinforced foam system for use in drilling site operations includes the following steps:

[0141] Empty and rinse the ground circulation tank. Add water and foaming agent to the mixing tank according to the specified ratio, stir for 1-3 minutes, then add nanofibers and stir for 5-10 minutes to ensure uniform mixing and prepare the foam base liquid. Pump the foam base liquid into the foam generator and mix it with nitrogen according to the formation adaptive foaming process to obtain the reinforced foam system.

[0142] Example 9

[0143] A nanofiber-reinforced foam system for foam drilling fluid includes a gas phase and a liquid phase; the gas phase is nitrogen, and the mass percentages of the raw material components in the liquid phase are as follows:

[0144] 0.5 wt% foaming agent, 0.6 wt% nanofibers, balance water;

[0145] The foaming agent is a foaming agent system formed by compounding sodium isomeric tridecyl alcohol polyoxyethylene ether carboxylate and fatty acid methyl ester ethoxylate in a mass ratio of 2:1 and introducing hydrophilic monomers and crosslinking agents, and then undergoing in-situ polymerization at 60-65℃ for 4-6 hours initiated by ammonium persulfate.

[0146] The nanofibers are prepared by mixing pulverized biomass raw materials with a 1.0-2.0% sodium hydroxide solution and a choline chloride-urea eutectic solvent (molar ratio 1:2) at a 1:1 volume ratio. This pretreatment solution is then subjected to pretreatment at 70-90℃, followed by ultrasonic-assisted hydrolysis with sulfuric acid solution at 50-70℃ to obtain nanocellulose crystals. The nanocellulose is then mixed with N-isopropylacrylamide monomer and sodium silicate in a specific ratio and reacted at 60-80℃ for 4-6 hours under nitrogen protection to complete graft copolymerization. Finally, the nanofibers are purified by dialysis and freeze-dried to obtain silica-cellulose composite nanofibers.

[0147] The preparation method of reinforced foam system for use in drilling site operations includes the following steps:

[0148] Empty and rinse the ground circulation tank. Add water and foaming agent to the mixing tank according to the specified ratio, stir for 1-3 minutes, then add nanofibers and stir for 5-10 minutes to ensure uniform mixing and prepare the foam base liquid. Pump the foam base liquid into the foam generator and mix it with nitrogen according to the formation adaptive foaming process to obtain the reinforced foam system.

[0149] Example 10

[0150] A nanofiber-reinforced foam system for foam drilling fluid includes a gas phase and a liquid phase; the gas phase is nitrogen, and the mass percentages of the raw material components in the liquid phase are as follows:

[0151] 0.8 wt% foaming agent, 1.0 wt% nanofibers, balance water;

[0152] The foaming agent is a foaming agent system formed by compounding sodium isomeric tridecyl alcohol polyoxyethylene ether carboxylate and fatty acid methyl ester ethoxylate in a mass ratio of 2:1 and introducing hydrophilic monomers and crosslinking agents, and then undergoing in-situ polymerization at 60-65℃ for 4-6 hours initiated by ammonium persulfate.

[0153] The nanofibers are prepared by mixing pulverized biomass raw materials with a 1.0-2.0% sodium hydroxide solution and a choline chloride-urea eutectic solvent (molar ratio 1:2) at a 1:1 volume ratio. This pretreatment solution is then subjected to pretreatment at 70-90℃, followed by ultrasonic-assisted hydrolysis with sulfuric acid solution at 50-70℃ to obtain nanocellulose crystals. The nanocellulose is then mixed with N-isopropylacrylamide monomer and sodium silicate in a specific ratio and reacted at 60-80℃ for 4-6 hours under nitrogen protection to complete graft copolymerization. Finally, the nanofibers are purified by dialysis and freeze-dried to obtain silica-cellulose composite nanofibers.

[0154] The preparation method of reinforced foam system for use in drilling site operations includes the following steps:

[0155] Empty and rinse the ground circulation tank. Add water and foaming agent to the mixing tank according to the specified ratio, stir for 1-3 minutes, then add nanofibers and stir for 5-10 minutes to ensure uniform mixing and prepare the foam base liquid. Pump the foam base liquid into the foam generator and mix it with nitrogen according to the formation adaptive foaming process to obtain the reinforced foam system.

[0156] Comparative Examples 1-7

[0157] The reinforced foam systems obtained in Examples 1-7 were compared with the foam system without silica-cellulose nanofibers, and the results are as follows: Figure 4 As shown, they are respectively:

[0158] Comparative Example 1: A foaming agent of 0.3 wt%, with the balance being water. The foaming agent was a system prepared by in-situ polymerization of sodium isomeric tridecyl alcohol polyoxyethylene ether carboxylate and fatty acid methyl ester ethoxylate in a 2:1 mass ratio, with the introduction of a hydrophilic monomer (acrylamide) and a crosslinking agent (N,N-methylenebisacrylamide) initiated by ammonium persulfate at 60-65°C for 4-6 hours. The initial foam volume was recorded as 415 mL at room temperature and pressure, and the time taken for 50 mL of foam base liquid to precipitate from the foam system was recorded as 365 s.

[0159] Comparative Example 2: 0.5 wt% foaming agent, with the balance being water. The foaming agent is a system prepared by in-situ polymerization of sodium isomeric tridecyl alcohol polyoxyethylene ether carboxylate and fatty acid methyl ester ethoxylate in a 2:1 mass ratio, with the introduction of a hydrophilic monomer (N-hydroxymethylacrylamide) and a crosslinking agent (divinylbenzene). The polymerization reaction was initiated by ammonium persulfate at 60-65°C and proceeded for 4-6 hours. At room temperature and pressure, the initial foam volume was recorded as 525 mL, and the time taken for 50 mL of foam base liquid to precipitate from the foam system was approximately 440 s.

[0160] Comparative Example 3: 0.8 wt% foaming agent, with the balance being water. The foaming agent was a system prepared by in-situ polymerization of sodium isomeric tridecyl alcohol polyoxyethylene ether carboxylate and fatty acid methyl ester ethoxylate in a 2:1 mass ratio, with the introduction of hydrophilic monomers (acrylamide and N-ethylacrylamide mixed in a 1:1 mass ratio) and a crosslinking agent (N,N-methylenebisacrylamide and divinylbenzene mixed in a 1:1 mass ratio) initiated by ammonium persulfate at 60-65°C for 6 hours. The initial foam volume was recorded as 612 mL at room temperature and pressure, and the time taken for 50 mL of foam base liquid to precipitate from the foam system was recorded as 550 s.

[0161] Comparative Example 4: 0.8 wt% foaming agent, with the balance being water. The foaming agent is a system prepared by in-situ polymerization of sodium isomeric tridecyl alcohol polyoxyethylene ether carboxylate and fatty acid methyl ester ethoxylate in a 2:1 mass ratio, with the introduction of a hydrophilic monomer (acrylamide) and a crosslinking agent (N,N-methylenebisacrylamide) initiated by ammonium persulfate at 50-55°C for 4-6 hours. The initial foam volume was recorded as 486 mL at room temperature and pressure, and the time taken for 50 mL of foam base liquid to precipitate from the foam system was recorded as 493 s.

[0162] Comparative Example 5: 0.8 wt% foaming agent, with the balance being water. The foaming agent is a system prepared by in-situ polymerization of sodium isomeric tridecyl alcohol polyoxyethylene ether carboxylate and fatty acid methyl ester ethoxylate in a 2:1 mass ratio, with the introduction of a hydrophilic monomer (N-hydroxymethylacrylamide) and a crosslinking agent (divinylbenzene), initiated by ammonium persulfate at 70-75°C for 4-6 hours. The initial foam volume was recorded as 524 mL at room temperature and pressure, and the time taken for 50 mL of foam base liquid to precipitate from the foam system was recorded as 490 s.

[0163] Comparative Example 6: 0.8 wt% foaming agent, with the balance being water. The foaming agent is a system prepared by in-situ polymerization of sodium isomeric tridecyl alcohol polyoxyethylene ether carboxylate and fatty acid methyl ester ethoxylate in a 2:1 mass ratio, with the introduction of hydrophilic monomers (acrylamide and N-ethylacrylamide mixed in a 1:1 mass ratio) and a crosslinking agent (N,N-methylenebisacrylamide and divinylbenzene mixed in a 1:1 mass ratio) initiated by ammonium persulfate at 60-65°C for 5 hours. The initial foam volume was recorded as 615 mL at room temperature and pressure, and the time taken for 50 mL of foam base liquid to precipitate from the foam system was recorded as 578 s.

[0164] Comparative Example 7: 0.8 wt% foaming agent, with the balance being water. The foaming agent is a system prepared by in-situ polymerization of sodium isomeric tridecyl alcohol polyoxyethylene ether carboxylate and fatty acid methyl ester ethoxylate in a 2:1 mass ratio, with the introduction of a hydrophilic monomer (acrylamide) and a crosslinking agent (N,N-methylenebisacrylamide) initiated by ammonium persulfate at 60-65°C for 4 hours. The initial foam volume was recorded as approximately 598 mL at room temperature and pressure, and the time taken for 50 mL of foam base liquid to precipitate from the foam system was approximately 541 s.

[0165] By comparing the examples and comparative examples, it can be seen that the foam drilling fluid system with added silica-cellulose nanofibers in this invention, although the initial foam volume is slightly reduced, the time required for 50 mL of liquid to be released from the foam (i.e., the foam half-life) is significantly extended, and the overall foam value is also significantly improved (see Figure 5). This shows that the foam stability of the system of this invention is significantly better than that of the system without added nanofibers, verifying the superiority of this invention.

[0166] The above embodiments are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Any technical solutions obtained by means of equivalent substitution or equivalent transformation should be covered within the protection scope of the present invention.

Claims

1. A nanofiber-reinforced foam system for foam drilling fluid, characterized in that, It includes a gas phase and a liquid phase; the liquid phase contains the following raw material components by mass percentage: 0.3~0.8wt% foaming agent, 0.3~1.0wt% nanofiber, and the balance being water; the foaming agent is prepared by in-situ polymerization of sodium isomeric tridecyl alcohol polyoxyethylene ether carboxylate and fatty acid methyl ester ethoxylate, followed by the introduction of hydrophilic monomers and crosslinking agents, with ammonium persulfate as the initiator. The mass ratio of sodium isotridecyl alcohol polyoxyethylene ether carboxylate to fatty acid methyl ester ethoxylate is 2:

1. The nanofibers are silica-cellulose composite nanofibers prepared from biomass as raw material through multi-stage pretreatment, ultrasonic-assisted acid hydrolysis, graft copolymerization, and purification. The total mass of silica and cellulose accounts for ≥80 wt% of the total mass of the silica-cellulose composite nanofibers, with a particle size ≤500 nm, a cluster particle size ≤500 μm, and a specific surface area ≥100 m². 2 / g; The hydrophilic monomer is selected from one or a mixture of two or more of acrylamide, N-hydroxymethylacrylamide, and N-ethylacrylamide; The crosslinking agent is selected from one or two of N,N-methylenebisacrylamide and divinylbenzene; The method for preparing the nanofibers includes the following steps: S1. Multi-stage pretreatment: The alkaline solution is mixed with a eutectic solvent to form a pretreatment solution; the biomass raw material and the pretreatment solution are then mixed according to a preset solid-liquid ratio, and after stirring and reacting for a period of time, the product is filtered, washed and dried to obtain refined cellulose. S2. Ultrasonic-assisted acid hydrolysis: The refined cellulose is mixed with sulfuric acid solution and then ultrasonically dispersed. After centrifugation, dialysis and drying, nanofiber crystals are obtained. S3. Graft copolymerization: The nanofiber crystals, N-isopropylacrylamide, and sodium silicate are mixed, and deionized water is added to control the solid content. The mixture is then stirred and reacted under nitrogen protection. The reaction product is neutralized and washed by centrifugation. The mass ratio of the nanofiber crystals, N-isopropylacrylamide, and sodium silicate is 1:(0.1~0.3):(0.2~0.5); the solid content is 3~8%. S4. The product after centrifugation and washing is placed into a dialysis bag, dialyzed in deionized water, and then freeze-dried to obtain silica-cellulose composite nanofibers.

2. The nanofiber-reinforced foam system for foam drilling fluid according to claim 1, characterized in that, The gas phase is selected from nitrogen, carbon dioxide, or air.

3. The nanofiber-reinforced foam system for foam drilling fluid according to claim 1, characterized in that, When the gas phase is nitrogen, the foam mass of the foam system is 45%–90%; when the gas phase is carbon dioxide, the foam mass is 55%–90%; when the gas phase is air, the foam mass is 42%–90%; the foam mass is the percentage of the gas volume in the foam to the total foam volume.

4. The nanofiber-reinforced foam system for foam drilling fluid according to claim 1, characterized in that, In step S1, the alkaline solution is a sodium hydroxide solution with a mass fraction of 1.0~2.0%; the eutectic solvent is a choline chloride-urea eutectic solvent, and the molar ratio of choline chloride to urea is 1:2; the volume ratio of the alkaline solution to the eutectic solvent is 1:1; the biomass raw material is wood, cotton or agricultural waste; the solid-liquid ratio of the biomass raw material to the pretreatment liquid is 1:(12-18) g / mL; the stirring reaction conditions are: temperature 70~90℃, stirring rate 200~400rpm, time 1.5-2.5h; washing until the filtrate is neutral, and drying at 75~85℃ for 10~14h.

5. The nanofiber-reinforced foam system for foam drilling fluid according to claim 1, characterized in that, In step S2, the sulfuric acid solution has a mass concentration of 60%; the solid-liquid ratio of the refined cellulose to the sulfuric acid solution is 1:15 g / mL; the ultrasonic dispersion power is 400 W and the frequency is 20 kHz; and / or, in step S3, the stirring reaction conditions are: reaction temperature 60~80℃, stirring speed 200~400 rpm, time 4~6 h; the neutralization alkaline solution is a 10% sodium hydroxide solution, and the pH of the system after neutralization is 6.5~7.0; the centrifugation conditions are: centrifugation speed 8000~10000 rpm, centrifugation time 15~20 min, and centrifugation washing 3~5 times; and / or, in step S4, dialysis is performed in flowing deionized water, and dialysis is performed until the pH of the system stabilizes at 6.5~7.0; the molecular weight cutoff of the dialysis bag is 8000~14000, the dialysis time is 48-72 h, the freeze-drying temperature is -50℃, and the drying time is 24~48 h.

6. A method for preparing a nanofiber-reinforced foam system for foam drilling fluid as described in any one of claims 1-5, characterized in that, The process includes the following steps: mixing water and foaming agent according to a certain ratio, adding nanofibers and stirring evenly to obtain a foam base liquid; then foaming the foam base liquid to obtain the nanofiber reinforced foam system for foam drilling fluid.

7. A method for preparing a foaming agent in a nanofiber-reinforced foam system for foam drilling fluid as described in any one of claims 1-5, characterized in that, Includes the following steps: Sodium isomeric tridecyl alcohol polyoxyethylene ether carboxylate and fatty acid methyl ester ethoxylate were mixed at a mass ratio of 2:1, and hydrophilic monomers and crosslinking agents were added. The mixture was then subjected to in-situ polymerization at 60-65°C for 4-6 hours using ammonium persulfate as an initiator to obtain the foaming agent.

Images