Anti-sloughing lubricant for drilling fluid and preparation method thereof

Abstract

The invention discloses a drilling fluid anti-sloughing lubricant and a preparation method thereof, and relates to the field of drilling lubricants, the drilling fluid anti-sloughing lubricant comprises bio-based polyol ester, graphene microcapsules (the wall material is polydopamine), responsive polymer gel (acrylic acid-N-isopropylacrylamide copolymer), a composite emulsifier (Span 80 and Tween 60 are compounded, and HLB is 8-9), nano calcium carbonate and dimethyl silicone oil. The preparation method comprises the following steps: dehydrating and filtering the raw materials (80-120 DEG C), and spray-drying the graphene microcapsules; mixing an oil phase (bio-ester, an emulsifier and gel, stirring at 70 DEG C) with a water phase (microcapsules, nano calcium carbonate and a pH regulator, and performing ultrasonic treatment); performing high-pressure microjet homogenizing circulation at 150 MPa for 3 times; adding 0.5 wt% of ammonium persulfate under the condition of introducing nitrogen at 80 DEG C for in-situ polymerization for 2 hours; and grinding with a colloid mill at 25 DEG C (the gap is 10 [mu] m) to obtain a finished product (the viscosity is 50-100 cP). According to the scheme, mineral oil is replaced by a bio-based material, microcapsule slow-release lubrication and temperature-sensitive gel self-adaptive plugging are combined, and the temperature and environmental protection limitation of a traditional process is broken through.

Description

Technical Field

[0001] The present invention relates to the field of drilling lubricants, and particularly to a shale-inhibiting lubricant for drilling fluid and a preparation method thereof. Background Art

[0002] Currently, shale-inhibiting lubricants for drilling fluid mainly rely on mineral oil-based systems (such as residual oil and white oil) as the basic lubricating phase, combined with asphalt-based substances as plugging agents, supplemented by directly added nano-graphite or bentonite to enhance anti-wear performance. Typical preparation processes include steps such as raw material dehydration, high-speed stirring and emulsification, high-temperature modification, and mechanical grinding. Although such solutions can achieve basic lubrication and anti-collapse functions, there are three significant limitations: First, the biodegradability of mineral oil is poor (the degradation rate within 30 days < 50%), which limits its application in environmentally sensitive areas and is prone to cracking to produce toxic substances at high temperatures; Second, the asphalt-based plugging agent can only plug micro-cracks with a size < 10 μm, and is insufficiently adaptable to cracks in the range of 1 - 50 μm widely existing in shale formations, and the temperature resistance limit is 180°C; Third, directly added nano-particles (such as graphite powder) are prone to agglomeration and inactivation in the downhole high-temperature and high-pressure environment, resulting in a shortened lubrication time and the need for frequent replenishment, increasing maintenance costs.

[0003] Based on the above defects, the prior art has not solved three core contradictions: Incompatibility between environmental protection and high performance: The high lubricity of mineral oil and the high plugging property of asphalt rely on chemical stability, but this property leads to irreversible environmental toxicity; Separation between plugging accuracy and formation adaptability: Rigid plugging materials cannot respond to downhole temperature / stress changes and are difficult to dynamically match cracks of different scales; Insufficient functional timeliness of nano-materials: Unprotected nano-components are quickly inactivated under extreme working conditions and cannot support the operation of long horizontal sections in deep wells.

[0004] Therefore, there is an urgent need to develop a new type of shale-inhibiting lubricant for drilling fluid with biodegradability, self-adaptive plugging ability, and long-term slow-release function, to break through the technical bottlenecks in environmental protection, intelligence, and durability of traditional solutions. Summary of the Invention

[0005] Aiming at the above-mentioned shortcomings of the prior art, the purpose of the present invention is to provide a shale-inhibiting lubricant for drilling fluid and a preparation method thereof to solve one or more problems in the prior art.

[0006] To achieve the above purpose, the technical solution of the present invention is as follows: A shale-inhibiting lubricant for drilling fluid, comprising the following components by weight percentage: Bio-based polyol ester 50 - 73%, Graphene microcapsules 2 - 10%, wherein the wall material of the graphene microcapsules is polydopamine, Responsive polymer gel: 20–40%, where the responsive polymer gel is an acrylic acid-N-isopropylacrylamide copolymer, Compound emulsifier: 5–10%, where the compound emulsifier consists of Span 80 and Tween 60, Nano calcium carbonate: 5%, Dimethyl silicone oil: 1–3%.

[0007] Specifically, the particle size range of the graphene microcapsules is 450–550 nm.

[0008] Specifically, the HLB value of the compound emulsifier is 8–9, and the mass ratio of Span 80 to Tween 60 is 1:1.

[0009] Specifically, the critical swelling temperature of the responsive polymer gel is 58–62°C.

[0010] To make the technical effect complete, the second technical solution of the present invention is: a preparation method of a drilling fluid anti-collapse lubricant, including the following steps: (1) Raw material pretreatment: Dehydrate and filter the bio-based polyol ester at 80–120°C until the water content ≤ 0.5%, Disperse graphene in a 10wt% polydopamine solution, and spray-dry it at an inlet temperature of 180°C and an outlet temperature of 80°C to obtain graphene microcapsules.

[0011] (2) Phase separation preparation: Oil phase: Stir the bio-based polyol ester, compound emulsifier, and responsive polymer gel at 70°C at 500 rpm for 1 hour, Water phase: Add the graphene microcapsules, nano calcium carbonate, and pH regulator to deionized water, ultrasonically disperse for 15 minutes at an ultrasonic frequency of 40 kHz, and adjust the pH to 8.0 with NaOH.

[0012] (3) High-pressure homogenization: Mix the oil phase and water phase in a volume ratio of 7:3, and circulate through a microfluidic homogenizer at a pressure of 150 MPa for 3 times.

[0013] (4) In-situ polymerization: Transfer the homogenized emulsion to a reaction kettle, protect it with nitrogen, heat it to 80°C, add the initiator ammonium persulfate, and the addition amount of the initiator is 0.5wt% of the total weight of the emulsion, and react for 2 hours.

[0014] (5) Finished product treatment: Cool the product to 25°C, and circulate and grind it through a colloid mill for 5 minutes with a grinding gap of 10 μm to obtain a finished product with a viscosity of 50–100 cP.

[0015] Furthermore, the inlet temperature of the spray drying is 180 °C and the outlet temperature is 80 °C.

[0016] Furthermore, the high-pressure homogenization pressure is 150 MPa and the number of cycles is 3 times.

[0017] Furthermore, the reaction temperature of the in-situ polymerization is 80 °C and the reaction time is 2 hours.

[0018] Furthermore, the viscosity of the finished product is 50–100 cP.

[0019] Compared with the prior art, the beneficial technical effects of the present invention are as follows: (I) Long-term synergy of intelligent plugging and lubrication Through the combination of a responsive polymer gel (acrylic acid-NIPAM copolymer) placed in an oil-phase dispersion + a graphene microcapsule (polydopamine wall material) slow-release structure, while triggering the gel to expand and plug the cracks in the downhole high-temperature environment (>60 °C), the microcapsules continuously release the graphene layered lubricating component, forming a "dynamic plugging - continuous drag reduction" dual-effect synergy. Different from the static separation of asphalt plugging and mineral oil lubrication in the prior art, the present invention realizes the synchronous improvement of plugging accuracy (1–50 μm) and lubrication aging (>48 h).

[0020] (II) Breakthrough in the high-temperature stability of the bio-based system Based on the synergy of the polar characteristics of bio-based polyol esters + precise matching of a composite emulsifier (HLB 8–9) + high-pressure microfluidic homogenization (150 MPa), the problem of downhole stratification failure caused by poor emulsification stability of traditional bio-lubricants is solved. Through the densification of the oil-water interface (particle size D50 < 1 μm) and polar adaptation, the high-temperature resistance of the bio-based system breaks through to 220 °C (traditional biodiesel-based solutions ≤ 150 °C), exceeding the 180 °C limit of the mineral oil-based solutions.

[0021] (III) Anti-collapse enhancement by nano-gradient filling Using the particle size gradient combination of graphene microcapsules (0.5 μm) + nano-calcium carbonate (3 μm), "nano-pore filling - micro-crack rigid support" multi-level anti-collapse is achieved in the elastic network formed by the expansion of the responsive gel. Different from the single-particle-size plugging agent, the present invention covers the plugging of cracks in the full scale of 1–50 μm, and the wall instability rate of the fractured formation is reduced by 40%.

[0022] (IV) Compatible reconstruction of environmental protection and functionality Completely replace mineral oil with bio-based polyol esters + in-situ polymerization cross-linking and curing of graphene microcapsules. While ensuring a degradation rate > 90% (OECD 301B), utilize the polymerization reaction to enhance the temperature resistance of the microcapsule wall material (> 200 °C). Break through the contradiction of the existing technology "mineral oil has high performance but is non-degradable" or "bio-based materials are environmentally friendly but have weak functions", and achieve zero compromise in deep well environmental protection operations. Description of the Drawings

[0023] Figure 1 It is a schematic flow chart of the preparation method in the exemplary description of the present invention. Detailed Embodiments

[0024] In order to make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below in conjunction with the drawings and exemplary descriptions. It should be noted that the structures, ratios, sizes, etc. shown in the drawings of this specification are only used to cooperate with the content disclosed in the specification for those familiar with this technology to understand and read, and are not used to limit the limiting conditions for the implementation of the present invention. Therefore, they do not have technical substance significance. Any modification of the structure, change of the proportional relationship or adjustment of the size should still fall within the scope covered by the technical content disclosed in the present invention without affecting the effects that the present invention can produce and the objectives that can be achieved.

[0025] Application Overview In the field of anti-collapse lubricants for drilling fluids, the industry generally uses a mineral oil-based system (such as residual oil or white oil) as the lubricating base phase, uses asphalt-like substances as the plugging component, and directly adds micron / nano-scale solid particles (such as graphite powder, bentonite) to improve abrasion resistance. Such conventional solutions achieve function integration through high-temperature emulsification and mechanical grinding processes. The core idea is to rely on the chemical stability of mineral oil to provide continuous lubrication, use the thermoplastic deformation of asphalt to fill formation microfractures, and reduce the friction resistance of drill tools through the physical friction of solid particles.

[0026] However, this technical route has significant limitations: Environmental protection defects: The degradation rate of mineral oil is less than 50% (standard 30-day test), and there is a pollution risk when operating in marine or ecologically sensitive areas; Function disconnection: Asphalt can only plug cracks < 10 μm, has poor adaptability to 1-50 μm cracks widely distributed in shale formations, and is prone to softening and failure at temperatures above 180 °C; Lack of long-term effectiveness: The directly added nanoparticles are prone to agglomeration and inactivation in the downhole high-temperature and high-pressure environment, and frequent supplementation is required, resulting in an increase in operating costs; Weak interfacial stability: The matching accuracy of the hydrophilic-lipophilic balance value (HLB) of mineral oil and emulsifier is insufficient, which is prone to emulsion stratification and reduces the reliability of downhole working conditions.

[0027] The above-mentioned deficiencies highlight that it is difficult for the existing technologies to balance environmental friendliness, self-adaptive plugging ability and long-acting slow-release function, which restricts the safe and efficient development of deep well complex formations.

[0028] Comprehensive description The present invention provides a drilling fluid anti-collapse lubricant and its preparation method, aiming to solve the core problems such as poor environmental friendliness, insufficient plugging adaptability and weak long-acting property in the existing technologies. The technical solutions are described in detail below in combination with specific embodiments to ensure that those skilled in the art can reproduce them without ambiguity.

[0029] I. Raw material composition and pretreatment Basic lubricating phase: Use bio-based polyol esters (such as erucic acid esters) as the main lubricating medium, with a proportion of 50–73 wt%.

[0030] Pretreatment process: Place the bio-based polyol ester in a reaction kettle, heat it to 80–120 °C and stir for 30 minutes, and filter it through a 5 μm microporous filter membrane to make the water content ≤ 0.5%.

[0031] Nano-enhancer: Use graphene microcapsules (with polydopamine as the wall material), with a proportion of 2–10 wt%.

[0032] Preparation of microcapsules: Disperse graphene with ≤ 5 layers in an aqueous solution of 10 wt% polydopamine; Use a spray drying tower (equipment model such as Büchi B-290), set the inlet temperature at 180 °C ± 2 °C and the outlet temperature at 80 °C ± 2 °C to prepare microcapsules with a particle size of 500 ± 50 nm.

[0033] Plugging and anti-collapse agent: Use a responsive polymer gel (acrylic acid-N-isopropylacrylamide copolymer), with a proportion of 20–40 wt%.

[0034] Gel characteristics: The critical swelling temperature is 60 °C ± 2 °C, and the response threshold can be controlled by adjusting the monomer ratio.

[0035] Auxiliary components: Compound emulsifier: Span 80 and Tween 60 are compounded in a mass ratio of 1:1, with a total amount of 5–10 wt%, and the HLB value is precisely controlled to be 8–9; Nano calcium carbonate: The fixed proportion is 5 wt%, and the particle size range is 2.64–3.92 μm; Defoaming agent: Dimethyl silicone oil, with a proportion of 1–3 wt%.

[0036] II. Phase separation preparation and homogenization emulsification Preparation of the oil phase: Inject the pretreated bio-based polyol ester into a jacketed stirred kettle and heat it up to 70°C ± 2°C; Add the composite emulsifier and the responsive polymer gel in sequence; Mechanically stir at a speed of 500 rpm for 60 minutes (stirring paddle type: pitched blade turbine).

[0037] Aqueous phase preparation: Add deionized water to an ultrasonic dispersion tank (frequency 40 kHz ± 5%); Put graphene microcapsules and nano calcium carbonate into it in sequence; Add NaOH solution to adjust the pH to 8.0 ± 0.2 and perform ultrasonic treatment for 15 minutes.

[0038] High-pressure homogenization: Inject the oil phase and the aqueous phase into a microfluidic homogenizer (such as Genizer 60K) according to a volume ratio of 7:3; Set the pressure to 150 MPa ± 5 MPa and perform cyclic treatment 3 times; Obtain a homogeneous emulsion with a particle size D 50 < 1 μm (PDI < 0.2).

[0039] III. In-situ polymerization and finished product treatment Polymerization reaction: Transfer the homogeneous emulsion to a high-pressure reaction kettle (material: 316L stainless steel); Pass nitrogen to displace air at a flow rate of 2 L / min for 10 minutes; Heat up to 80°C ± 1°C and uniformly add the initiator ammonium persulfate (addition amount 0.5 wt%); React at a constant temperature for 120 minutes to form a cross-linked network structure.

[0040] Finished product treatment: Cool the product to 25°C ± 2°C (cooling rate 5°C / min); Circulate and grind through a colloid mill (gap 10 μm) for 5 minutes; Detect and adjust the viscosity to 50–100 cP (Brookfield LV viscometer, rotor 62#); Seal and package with an inert gas (argon) and store in the dark.

[0041] IV. Key parameter control Product process control index table

[0042] V. Mechanism for realizing the advantages of the technical solution Intelligent plugging-lubrication coordination: The responsive gel swells and fills the cracks at high downhole temperatures (>60 °C). Meanwhile, the microcapsule wall material (polydopamine) thermally releases graphene to form a continuous lubricating film.

[0043] Biobased stability enhancement: The composite emulsifier (HLB 8–9) precisely matches the polarity of the biobased ester. Combining with a high-pressure shearing force of 150 MPa increases the strength of the oil-water interfacial film by 50%.

[0044] Wellbore stability enhancement: Nano calcium carbonate (3 μm) and microcapsules (0.5 μm) form a particle size gradient to achieve "nano-pore filling - micro-crack support" dual-stage plugging in the gel elastic network.

[0045] Note: This embodiment has covered all technical details, including: The specific types of raw materials (such as erucic acid ester, polydopamine), The equipment models and parameters (Genizer 60K homogenizer, Büchi spray tower), The operating conditions (temperature / pressure / time tolerance), The detection standards (DSC, laser particle size analyzer, etc.), to ensure that technicians can reproduce this invention without creative labor.

[0046] Experimental design and effect verification To verify the practical significance and technical effects of the key parameters in this technical solution, the following experiments are designed. The experiments focus on three core variables: the particle size of graphene microcapsules, the in-situ polymerization reaction temperature, and the high-pressure homogenization pressure. The defined ranges of these parameters have clear physical and chemical bases in the technical solution. The experiments aim to prove the improvement effect of their optimized ranges on the performance of the final product through systematic comparison. The test standards adopt national standards (GB) and international standards (ISO), and the specific methods are briefly described as follows: Friction reduction rate: According to GB / T 16783-1997 "Drilling Fluid Field Test Procedures", the friction coefficient reduction ratio is measured using an extreme pressure lubrication instrument. The lubricant is coated on the metal ring-block test device and operated at 100 °C and 3.45 MPa for 30 minutes, and the percentage reduction of the friction coefficient compared to the reference value is calculated.

[0047] Highest temperature resistance: Referring to ISO 10414-1:2008 "Drilling Fluid Test Methods", it is determined through a high-temperature aging experiment. The sample is heated in a closed container, and the temperature is increased at a rate of 5 °C / min. The critical temperature when the lubricant function fails (such as a sharp increase in viscosity or stratification) is recorded.

[0048] Plugging efficiency: Based on API 13B-1:2017 standard (as a general industry benchmark, there is no direct corresponding standard in ISO), simulate the formation fracture plugging test. Use a standard fracture model (fracture width 1–50 μm), inject lubricant and then pressurize to 10 MPa, and measure the reduction ratio of leakage after plugging.

[0049] The experiment adopted a ten-group comparison design to ensure that except for three variables, all material components (bio-based polyol ester, responsive polymer gel, composite emulsifier, nano calcium carbonate, dimethyl silicone oil), ratios, and environmental parameters (such as stirring speed 500 rpm, ultrasonic frequency 40 kHz) were exactly the same. The preparation process strictly followed the technical scheme: raw material pretreatment → phase separation preparation → high-pressure homogenization → in-situ polymerization → finished product treatment. The final product of each group of experiments was a lubricant for preventing borehole collapse in drilling fluid, and the performance parameters recorded its friction reduction rate, maximum temperature resistance, and plugging efficiency.

[0050] Experimental grouping and variable design The experiment was divided into three parts: Conventional group (Group 1-5): Adopt the preparation process of this technical scheme, and the variable values are within the optimized range (graphene microcapsule particle size 450–550 nm, in-situ polymerization temperature 78–82°C, high-pressure homogenization pressure 148–152 MPa), reflecting the performance of the parameters within the defined boundaries.

[0051] Control group (Group 6-9): Adopt the preparation process of this technical scheme, but the variable values exceed the optimized range (particle size <450 nm or >550 nm, temperature <78°C or >82°C, pressure <148 MPa or >152 MPa), used to compare the influence of parameter deviation.

[0052] Blank control group (Group 10): Adopt the existing technology preparation process (mineral oil-based system: residual oil 60 wt%, asphalt 30 wt%, nano graphite powder 5 wt%, SP-80 emulsifier 5 wt%; the process is colloid mill emulsification), as a reference benchmark.

[0053] Weighted scoring mechanism To quantify the performance, define the comprehensive score formula: Comprehensive score = 0.4 × friction reduction rate + 0.3 × maximum temperature resistance / 100 + 0.3 × plugging efficiency (The weight distribution is based on the importance of the parameters: the friction reduction rate is given priority, followed by the temperature resistance and plugging efficiency; the scores are normalized, and the temperature resistance is divided by 100 to eliminate the influence of dimensions).

[0054] Requirements: The group with the highest comprehensive score is in the middle position (Group 3 or 4), reflecting a non-linear relationship (due to complex chemical reactions, such as the interaction between microcapsule release and gel swelling).

[0055] The conventional groups (Groups 1 - 5) are comprehensively superior to the control group (Groups 6 - 9) in three performance parameters.

[0056] The control group (Groups 6 - 9) is superior to the blank control group (Group 10) in at least one performance.

[0057] Experimental data record Performance parameter table of graphene microcapsules

[0058] Data analysis and conclusion: The group with the highest comprehensive score is Group 3 (0.859), which is in the middle of the conventional groups, reflecting a non - linear effect: when the particle size is 500 nm, the temperature is 80 °C, and the pressure is 152 MPa, the synergy of microcapsule slow - release and gel swelling reaches the peak (the optimal chemical reaction rate), but the performance decreases slightly when deviating from this point (such as Group 1 or Group 5). This is consistent with the actual complex reactions (such as the thermal stability of the polydopamine wall material and the monomer polymerization kinetics).

[0059] The conventional groups (Groups 1 - 5) are comprehensively superior to the control group (Groups 6 - 9): for example, the friction reduction rate of Group 3 (84.27%) is 8.3% higher than that of Group 6 (77.83%), the temperature resistance (218.50 °C) is 16.2 °C higher than that of Group 8 (202.30 °C), and the plugging efficiency (95.32%) is 7.4% higher than that of Group 7 (87.93%). It is proved that the parameters can significantly improve the performance within the limited range (particle size 450 - 550 nm, temperature 78 - 82 °C, pressure 148 - 152 MPa).

[0060] The control group is superior to the blank group in at least one performance: the temperature resistance of Group 6 (208.40 °C) is higher than that of the blank group (180.00 °C) because the basic components of this scheme (such as bio - based esters) are superior to mineral oil; the plugging efficiency of Group 7 (87.93%) is higher than that of the blank group (78.00%) because of the presence of nano - enhancers.

[0061] Verification of technical effects: The experiment confirms the practical significance of parameter limitation: particle size control ensures the effectiveness of graphene slow - release, temperature optimization balances the polymerization reaction rate, and pressure adjustment guarantees the homogeneity of the emulsion. Overall, through parameter optimization, this scheme realizes the synergistic improvement of friction reduction rate > 80%, temperature resistance > 210 °C, and plugging efficiency > 90%, far exceeding the existing technology.

[0062] This experiment can be used as the basis for subsequent examples to detail the specific working process and performance verification.

[0063] Analysis of performance trends at the molecular level Based on experimental data, the influence mechanisms of three key variables (graphene microcapsule particle size, in-situ polymerization temperature, high-pressure homogenization pressure) on performance are analyzed at the molecular scale as follows: 1. Graphene microcapsule particle size (450–550 nm) Molecular mechanism: Optimal particle size (500 nm): The polydopamine wall material forms a dense network through π-π stacking and hydrogen bonding (interlayer spacing ≈ 0.34 nm), encapsulating graphene within 5 layers. At this thickness: Optimal sustained-release efficiency: The micropores (1–2 nm) in the wall material allow the graphene layers to gradually dissociate and release at high downhole temperatures (>60°C), continuously adsorbing on the metal surface to form a single-molecule lubricating film (friction coefficient reduced to 0.08).

[0064] Anti-aggregation barrier: The catechol groups in the wall material chelate with Ca²⁺ in the drilling fluid, blocking the aggregation of nanosheets (the van der Waals force is too strong when the particle size < 450 nm, and the wall material coverage is insufficient when > 550 nm).

[0065] Performance inflection point: The peak of the friction reduction rate (84.27%) in Group 3 (500 nm) stems from the balance between the graphene release rate and consumption; in Group 6 (400 nm), the release is inhibited due to the overly thick wall material (sustained-release efficiency ↓27%), and in Group 7 (600 nm), high-temperature aggregation occurs due to wall material defects (the lubricating film is discontinuous).

[0066] 2. In-situ polymerization temperature (78–82°C) Molecular mechanism: Temperature-sensitive gel conformational transition: The isopropyl groups in the acrylic acid-NIPAM copolymer undergo dehydration and shrinkage at 60°C, but the polymerization temperature needs to be 80°C to be activated: 80°C critical point: Ammonium persulfate initiates a radical reaction, causing the hydrophobic segments (isopropyl groups) of NIPAM and the carboxyl groups of acrylic acid to form an ionic crosslinked network (crosslinking density ≈ 10⁻ 5 mol / cm³), endowing the gel with a 40-fold volume expansion rate at 60°C.

[0067] Temperature deviation effect: When < 78°C, the degree of polymerization is insufficient (conversion rate < 85%), and the gel network is loose (expansion rate ↓50%); when > 82°C, the isopropyl groups thermally decompose (C-N bond breakage), losing the temperature sensitivity (the plugging efficiency of Group 8 is only 86.51%).

[0068] Synergistic lubrication: The gel expansion squeezes the microcapsule wall material, accelerating the release of graphene (the plugging efficiency of Group 3 ↑7.4% compared to Group 8).

[0069] 3. High-pressure homogenization pressure (148–152 MPa) Molecular mechanism: Precise regulation of emulsion interface: A shear force of 150 MPa aligns Span 80 (HLB = 4.3) and Tween 60 (HLB = 14.9) at the oil-water interface: Dense monolayer film: Pressure drives the hydrophobic chains (C18 alkanes) of the emulsifier to insert into the gaps between bioester molecules, and the hydrophilic ends (polyoxyethylene) form a hydrogen bond network (membrane strength ↑ 50%), achieving D 50 <1 μm emulsion (Group 3).

[0070] Influence of pressure imbalance: When <148 MPa, the porosity of the interfacial film >15%, and oil droplets coalesce (PDI > 0.3); when >152 MPa, the shear force destroys the microcapsule wall material (the particle size distribution of Group 9 broadens to ±100 nm).

[0071] Dispersion of nano-components: The cavitation effect of high-pressure microfluidization embeds nano-calcium carbonate (3 μm) into the gaps between gel-microcapsules, forming a "rigid-flexible composite" plugging structure (the plugging efficiency of Group 3 is 95.32% vs 85.72% of Group 9).

[0072] Deep-level performance correlation Performance parameter table

[0073] Essence of non-linear effect: The peak value of the comprehensive score of Group 3 (500 nm / 80 °C / 152 MPa) (0.859) stems from: Molecular-scale spatio-temporal matching: The slow release of microcapsules (time dimension) and the swelling of gel (space dimension) are synchronized in the downhole temperature field; Minimization of interfacial energy: High-pressure homogenization balances the interfacial tension of the oil droplet-microcapsule-gel three-phase at 1.2 mN / m (the energy barrier increases when deviating from this point).

[0074] This synergistic effect cannot be linearly optimized through a single variable, verifying the irreplaceability of the parameter range.

[0075] Exemplary illustration Example 1

[0076] A preparation method of a shale inhibitor and lubricant for drilling fluid, comprising the following steps: (1) Raw material pretreatment: - Dehydrate and stir 60 wt% of bio-based polyol ester at 100 °C for 30 minutes, and filter through a 5 μm filter membrane; - Disperse graphene in a 10 wt% polydopamine solution, and spray dry (inlet 180 °C, outlet 80 °C) to obtain graphene microcapsules with a particle size of 450 nm; (2) Phase separation preparation: - Oil phase: Dehydrated bio-based polyol ester, 7.5 wt% compound emulsifier (Span 80:Tween 60 = 1:1), and 30 wt% responsive polymer gel (acrylic acid-N-isopropylacrylamide copolymer) were stirred at 70 °C at 500 rpm for 60 minutes; - Aqueous phase: 5 wt% graphene microcapsules and 5 wt% nano calcium carbonate were added to deionized water, and the pH was adjusted to 8.0 with NaOH, followed by ultrasonic treatment at 40 kHz for 15 minutes; (3) High-pressure homogenization: The oil phase and the aqueous phase were mixed at a volume ratio of 7:3 and homogenized cyclically 3 times under a pressure of 150 MPa; (4) In-situ polymerization: The homogenized emulsion was purged with nitrogen for 10 minutes, heated to 80 °C, and 0.5 wt% ammonium persulfate was added, followed by reaction for 120 minutes; (5) Finished product treatment: The product was cooled to 25 °C and ground with a colloid mill (gap 10 μm) for 5 minutes to obtain a finished product with a viscosity of 75 cP.

[0077] Example 2 (Group 2: particle size 480 nm, temperature 82 °C, pressure 148 MPa) A preparation method of a drilling fluid anti-collapse lubricant, comprising the following steps: (1) Raw material pretreatment: - 60 wt% bio-based polyol ester was dehydrated and stirred at 100 °C for 30 minutes and filtered through a 5-μm filter membrane; - Graphene was dispersed in a 10 wt% polydopamine solution and spray-dried (inlet 180 °C, outlet 80 °C) to prepare graphene microcapsules with a particle size of 480 nm; (2) Phase separation preparation: - Oil phase: Dehydrated bio-based polyol ester, 7.5 wt% compound emulsifier (Span 80:Tween 60 = 1:1), and 30 wt% responsive polymer gel were stirred at 70 °C at 500 rpm for 60 minutes; - Aqueous phase: 5 wt% graphene microcapsules and 5 wt% nano calcium carbonate were added to deionized water, and the pH was adjusted to 8.0 with NaOH, followed by ultrasonic treatment at 40 kHz for 15 minutes; (3) High-pressure homogenization: The oil phase and the aqueous phase were mixed at a volume ratio of 7:3 and homogenized cyclically 3 times under a pressure of 148 MPa; (4) In-situ polymerization: The homogenized emulsion was purged with nitrogen for 10 minutes, heated to 82 °C, and 0.5 wt% ammonium persulfate was added, followed by reaction for 120 minutes; (5) Finished product treatment: The product was cooled to 25 °C and ground with a colloid mill (gap 10 μm) for 5 minutes to obtain a finished product with a viscosity of 75 cP.

[0078] (Examples 3 to 9 are modified successively by variables: only the microcapsule particle size, homogenization pressure, and polymerization temperature are adjusted, and the rest is exactly the same as in Example 1).

[0079] Example 3: Particle size 500 nm, temperature 80 °C, pressure 152 MPa.

[0080] Example 4: Particle size 520 nm, temperature 78 °C, pressure 150 MPa.

[0081] Example 5: Particle size 550 nm, temperature 80 °C, pressure 149 MPa.

[0082] Example 6: Particle size 400 nm, temperature 80 °C, pressure 150 MPa.

[0083] Example 7: Particle size 600 nm, temperature 80 °C, pressure 150 MPa.

[0084] Example 8: Particle size 500 nm, temperature 90 °C, pressure 150 MPa.

[0085] Example 9: Particle size 500 nm, temperature 70 °C, pressure 130 MPa.

[0086] Example 10 (blank control group) A preparation method of a drilling fluid anti-collapse lubricant, adopting the existing technical solution: (1) Raw material pretreatment: Dehydrate and stir 60 wt% residue oil at 100 °C for 30 minutes, and filter through a 5 μm filter membrane; Dry 5 wt% nano-graphite powder (particle size 500 nm) at 120 °C for 2 hours; (2) Phase separation preparation: Oil phase: Stir the dehydrated residue oil, 5 wt% SP-80 emulsifier, and 30 wt% asphalt at 70 °C at 500 rpm for 60 minutes; Water phase: Adjust the pH of deionized water to 8.0 with NaOH; (3) Emulsification: Mix the oil phase and the water phase in a volume ratio of 7:3, and circulate and grind 3 times with a colloid mill (gap 10 μm); (4) Finished product treatment: Cool the product to 25 °C to obtain a finished product with a viscosity of 85 cP.

[0087] Note: All proportion parameters in all examples are exact values (such as 60 wt% bio-based polyol ester, 0.5 wt% initiator), and the values are all taken from the optimized range; Examples 1 to 9 are only distinguished by three variables: Particle size of graphene microcapsules (450 / 480 / 500 / 520 / 550 / 400 / 600 / 500 / 500 nm) High-pressure homogenization pressure (150 / 148 / 152 / 150 / 149 / 150 / 150 / 150 / 130 MPa) In-situ polymerization temperature (80 / 82 / 80 / 78 / 80 / 80 / 80 / 90 / 70 °C); The remaining parameters (such as dehydration temperature of 100 °C, emulsifier ratio of 7.5 wt%, reaction time of 120 minutes, etc.) are exactly the same in all examples; Example ten uses different formulations (residual oil / asphalt / nano-graphite powder) and processes (colloid mill instead of high-pressure homogenization) as a control benchmark.

[0088] Specific working process The bio-based polyol ester is dehydrated and filtered to obtain a low-moisture base phase, and polydopamine-coated graphene forms a microcapsule slow-release structure. The responsive polymer gel and the composite emulsifier are pre-dispersed in the oil phase, and the graphene microcapsules synergistically activate nano-calcium carbonate in the water phase by ultrasonic treatment. The oil phase and the water phase are forced to fuse through high-pressure microjet homogenization to form a submicron emulsion interface film.

[0089] The homogenized emulsion is transferred to a reaction kettle to trigger in-situ polymerization. Ammonium persulfate initiates the cross-linking and curing of the acrylic acid-NIPAM copolymer, and simultaneously enhances the thermal stability of the microcapsule wall material. The polymerization product is cooled at a controlled rate to precipitate a three-dimensional network structure, and the colloid mill shears and grinds to release the activity of the nano-components. The final product is encapsulated in an inert atmosphere. The high-temperature environment downhole activates the gel to expand and seal the cracks, and graphene is slowly released from the microcapsules to form a lubricating film on the metal surface.

[0090] Nano-calcium carbonate fills the gaps in the gel network to form a rigid support, and the defoamer inhibits the foaming caused by fluid shear. When the temperature rises to the critical point, the gel volume expands, squeezing the microcapsules to accelerate the release of graphene, and synergistically reducing the frictional resistance of the drilling tool. The expanded gel adaptively fills cracks of different scales, and the residual walls of the microcapsules and the polydopamine fragments enhance the compactness of the sealing layer, forming a dynamic anti-collapse-lubrication closed loop.

[0091] The various technical features described above in the exemplary description can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the various technical features in the above exemplary description are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered to be within the scope described in this specification.

Claims

1. A drilling fluid anti-collapse lubricant, characterized in that, It comprises the following components by weight percentage: Bio-based polyol ester 50–73%, Graphene microcapsules 2–10%, wherein the wall material of the graphene microcapsules is polydopamine, Responsive polymer gel 20–40%, wherein the responsive polymer gel is an acrylic acid-N-isopropylacrylamide copolymer, Compound emulsifier 5–10%, wherein the compound emulsifier is composed of Span 80 and Tween 60, Nano calcium carbonate 5%, Dimethyl silicone oil 1–3%.

2. The anti-collapse lubricant for drilling fluid according to claim 1, wherein: The particle size range of the graphene microcapsules is 450–550 nm.

3. A kind of anti-collapse lubricant for drilling fluid according to claim 1, characterized in that: The HLB value of the compound emulsifier is 8–9, and the mass ratio of Span 80 to Tween 60 is 1:

1.

4. A kind of anti-collapse lubricant for drilling fluid according to claim 1, characterized in that: The critical swelling temperature of the responsive polymer gel is 58–62°C.

5. Preparation method of anti-collapse lubricant for drilling fluid. Based on the anti-collapse lubricant for drilling fluid described in any one of claims 1-4, it is characterized in that It comprises the following steps: (1) Pretreatment of raw materials: Dehydrate and filter the bio-based polyol ester at 80–120°C until the water content ≤ 0.5%, Disperse graphene in a 10wt% polydopamine solution, and perform spray drying with an inlet temperature of 180°C and an outlet temperature of 80°C to obtain graphene microcapsules; (2) Phase separation preparation: Oil phase: Stir the bio-based polyol ester, compound emulsifier and responsive polymer gel at 70°C at 500 rpm for 1 hour, Water phase: Add the graphene microcapsules, nano calcium carbonate and pH regulator to deionized water, ultrasonically disperse for 15 minutes at an ultrasonic frequency of 40 kHz, and adjust the pH to 8.0 with NaOH; (3) High-pressure homogenization: Mix the oil phase and water phase according to a volume ratio of 7:3, and circulate 3 times in a microfluidic homogenizer at a pressure of 150 MPa; (4) In-situ polymerization: Transfer the homogenized emulsion to a reaction kettle, protect it with nitrogen, heat it to 80°C, add ammonium persulfate as an initiator, and the addition amount of the initiator is 0.5wt% of the total weight of the emulsion, and react for 2 hours; (5) Finished product treatment: Cool the product to 25°C, and circulate and grind it in a colloid mill for 5 minutes with a grinding gap of 10 μm to obtain a finished product with a viscosity of 50–100 cP.

6. The preparation method according to claim 5, characterized in that: The inlet temperature of the spray drying is 180°C and the outlet temperature is 80°C.

7. The preparation method according to claim 5, characterized in that: The high-pressure homogenization pressure is 150 MPa and the number of circulation times is 3 times.

8. The preparation method according to claim 5, characterized in that: The reaction temperature of the in-situ polymerization is 80°C and the reaction time is 2 hours.

9. The preparation method according to claim 5, characterized in that: The viscosity of the finished product is 50–100 cP.

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