Safe and environment-friendly anti-freezing and anti-collapse mud for drilling in high-altitude frozen soil area and preparation method thereof

Abstract

This invention discloses a safe and environmentally friendly antifreeze and anti-collapse drilling mud for drilling in high-altitude permafrost areas and its preparation method, relating to the field of drilling engineering technology; comprising: 65-75% water, 12-18% composite antifreeze system, 4-8% propylene oxide etherified modified konjac glucomannan (low-temperature stabilizer), 3-6% chitosan grafted acrylic acid copolymer (permafrost protectant), 2-4% polydimethylsiloxane modified rapeseed oil (environmentally friendly lubricant), 0.3-0.8% pH adjuster, and 0.1-0.3% defoamer; the composite antifreeze system includes propylene glycol, ethylene glycol, carbamide, calcium chloride, and sodium chloride; this invention improves the mud's fluidity stability, viscosity stability, cuttings carrying efficiency, and permafrost structural stability through the synergistic design of multiple components: "composite antifreeze system + low-temperature stabilizer + permafrost protectant + lubricant with low-temperature fluidity," and the mud components have a high biodegradability rate and low cost.

Description

Technical Field

[0001] This invention relates to the field of drilling engineering technology, specifically to a safe and environmentally friendly antifreeze and anti-collapse mud for drilling in high-altitude permafrost areas and its preparation method. Background Technology

[0002] High-altitude permafrost regions (such as the Qinghai-Tibet Plateau and the Pamir Plateau) are important oil and gas resource and geological exploration areas in my country. These regions are characterized by four core engineering features: extreme low temperatures, large diurnal temperature variations, high ice content in permafrost, and fragile ecosystems. Areas above 3000m in altitude have an average annual temperature of -5 to -15℃, with extreme winter temperatures reaching -20℃, and diurnal temperature variations often exceeding 20℃. The permafrost layer has an astonishing ice content, generally ranging from 20% to 60%, with some "ice-rich permafrost" containing over 80%. Slight temperature fluctuations cause the permafrost to either thaw and subside or freeze and bulge, posing a double challenge for drilling. Therefore, in drilling operations in these areas, drilling mud, as the "drilling fluid," must simultaneously meet four major requirements: antifreeze and anti-collapse properties, fluidity, permafrost stability, and environmental friendliness. However, existing technical solutions have significant shortcomings, as detailed below:

[0003] (1) Insufficient antifreeze properties, unable to withstand extreme low temperatures

[0004] Existing antifreeze and anti-collapse drilling muds mostly use a single antifreeze agent (such as ethylene glycol or propylene glycol), with an antifreeze addition amount typically ranging from 10% to 15%, which can only lower the freezing point of the mud to -5 to -10°C. When encountering extreme low temperatures below -20°C, water molecules in the mud easily form ice crystals, causing a sharp increase in the system viscosity (the viscosity generally exceeds 1000 mPa·s at -20°C), or even complete freezing, making drilling circulation impossible.

[0005] (2) Poor fluidity at low temperatures leads to low drilling efficiency.

[0006] Traditional mud thickeners (such as hydroxyethyl cellulose and xanthan gum) tend to shrink their molecular chains at low temperatures, reducing cuttings carrying efficiency by more than 50% and easily causing cuttings deposition at the bottom of the well. On the other hand, the large temperature difference in the plateau climate makes the viscosity easily affected by temperature and its performance changes. A sudden increase in viscosity leads to an increase in drilling pump pressure (exceeding 25 MPa), which not only increases energy consumption but also easily causes fatigue fracture of the drill string.

[0007] (3) The permafrost around the borehole wall was destabilized, which induced the well wall to collapse.

[0008] Existing mud filtrate (containing high concentrations of inorganic salts and chemical additives) easily seeps into the pores of permafrost: at low temperatures, the filtrate freezes and expands in volume, causing the permafrost to expand and crack; when the temperature rises, the permafrost melts, and the ice content decreases, causing thaw settlement. The combined effect of these two factors leads to well wall collapse. In addition, some mud contains formaldehyde-based preservatives, which, after seeping into the permafrost, damage the soil's colloidal structure, making it difficult for vegetation to recover, thus violating the ecological protection requirements of high-altitude areas.

[0009] (4) Imbalance between environmental protection and economic efficiency

[0010] To improve freeze resistance, existing solutions often involve increasing the amount of antifreeze added, which leads to a surge in mud costs. At the same time, some antifreeze agents (such as methanol) are toxic, and waste liquid treatment requires distillation recovery processes, which increases the economic burden and poses an ecological pollution risk.

[0011] In summary, existing antifreeze and anti-collapse mud cannot simultaneously meet the four core requirements of "extreme low temperature tolerance, low temperature fluidity, permafrost stability, and environmental protection and economy" in high-altitude permafrost regions. Therefore, it is urgent to develop a special antifreeze and anti-collapse mud suitable for this region. Summary of the Invention

[0012] This invention aims to address the technical problem that existing antifreeze and anti-collapse drilling mud cannot simultaneously meet the four core requirements of "extreme low temperature tolerance, low temperature fluidity, permafrost stability, and environmental friendliness and economy" in high-altitude permafrost regions. The goal is to provide a safe and environmentally friendly antifreeze and anti-collapse drilling mud for drilling in high-altitude permafrost regions and its preparation method. Through the synergistic design of multiple components, including "composite antifreeze system + low temperature stabilizer + permafrost protectant + low temperature fluidity lubricant", the mud's fluidity stability, viscosity stability, cuttings carrying efficiency, and permafrost structural stability are improved. Moreover, the mud components have a high biodegradability rate and low cost.

[0013] The present invention is achieved through the following technical solution.

[0014] The first objective of this invention is to provide a safe, environmentally friendly, antifreeze, and anti-collapse drilling mud for drilling in high-altitude permafrost regions, comprising the following components by weight percentage:

[0015] Water 65-75%, composite antifreeze system 12-18%, propylene oxide etherified modified konjac glucomannan (low temperature stabilizer) 4-8%, chitosan grafted acrylic acid copolymer (frozen soil protectant) 3-6%, polydimethylsiloxane modified rapeseed oil (environmentally friendly lubricant) 2-4%, pH adjuster 0.3-0.8%, and defoamer 0.1-0.3%;

[0016] The composite antifreeze system includes propylene glycol, ethylene glycol, carbamide, calcium chloride, and sodium chloride.

[0017] The water used in the formula of this invention is glacial meltwater or shallow groundwater from plateaus (after sedimentation and filtration, with suspended solids content ≤5mg / L and mineralization ≤300mg / L).

[0018] The technical principle of this invention is as follows:

[0019] The composite antifreeze system of this invention utilizes the fluidity of propylene glycol, the freezing point reduction efficiency of ethylene glycol, and the hydrogen bond breaking effect of carbamide, along with the ionic effect of sodium chloride to synergistically lower the freezing point of the system. This multi-component synergy enhances the fluidity and stability of the drilling mud in ultra-low temperature environments, disrupts the ice crystal formation structure, and lowers the freezing point to below -25°C, achieving antifreeze and anti-collapse effects below -25°C. This ensures that the drilling mud can maintain its rheological properties suitable for drilling operations even under extreme low temperature conditions.

[0020] The mud of this invention incorporates propylene oxide-modified konjac glucomannan as a low-temperature stabilizer. The hydroxyl groups on the glucose / mannose residues of the konjac glucomannan backbone undergo an etherification reaction with propylene oxide, introducing -O-CH2-CH(OH)-CH3 ether bonds. This can inhibit the coiling of molecular chains at low temperatures, maintain the three-dimensional network structure, and thus improve the stability of molecular chains at low temperatures. When the diurnal temperature fluctuation is 20°C, the molecular chains can adjust the viscosity through stretching and contraction, avoiding sudden increases and decreases, so that the mud still has a stable viscosity (80-120 mPa·s) below -20°C. Through long-term research and comparative experiments, the inventors have demonstrated that, compared to hydroxypropyl modification, propylene oxide etherification-modified konjac glucomannan exhibits superior molecular chain elasticity, with a viscosity retention rate of 90% at -20℃, compared to only 75% for hydroxypropyl modification. Furthermore, the main chain structure of konjac glucomannan is more prone to forming a dense network structure, resulting in a suspension capacity that is more than 30% better than other polysaccharides such as guar gum modification.

[0021] The present invention incorporates chitosan-grafted acrylic acid copolymer as a permafrost protectant in the drilling mud. This copolymer forms a dense adsorption film on the wellbore, preventing the seepage of drilling mud filtrate. Simultaneously, the amino groups of chitosan form hydrogen bonds with permafrost clay particles, enhancing the structural stability of the permafrost and preventing its destruction. The colloidal particles (1-5 μm) of the permafrost protectant enhance the suspension capacity of the drilling mud, maintaining a dynamic shear force / plastic viscosity ratio of 0.4-0.6 and a cuttings carrying efficiency ≥90%. This protectant combines filtrate reduction and permafrost stabilization functions, avoiding the component conflicts associated with traditional solutions that combine filtrate reduction agents and permafrost stabilizers. Furthermore, the inventors have discovered through long-term research that ungrafted chitosan-based acrylic acid copolymers have poor water solubility and cannot form a uniform adsorption film, resulting in a permafrost thaw sedimentation rate as high as 8%-10%, while grafting reduces this rate to below 3%.

[0022] This invention also incorporates polydimethylsiloxane-modified rapeseed oil as an environmentally friendly lubricant. The fatty acid esters in the rapeseed oil undergo transesterification with the polydimethylsiloxane, introducing -Si(CH3)2-O-siloxane segments into the rapeseed oil molecular chain. This combines the lubricity of rapeseed oil with the low-temperature fluidity of polydimethylsiloxane. The lubricant encapsulates chitosan-grafted acrylic acid copolymer colloidal particles, forming a "suspension-lubrication" synergistic layer, reducing friction between the drill string and the wellbore, and preventing mechanical disturbance from causing frozen soil cracking.

[0023] Furthermore, all components of this invention, including propylene glycol, ethylene glycol, carbamide, calcium chloride, sodium chloride, modified konjac glucomannan, and lubricant, are biodegradable materials (biodegradation rate ≥92%, conforming to GB / T 19277.1-2011 "Determination of Final Aerobic Biodegradation Capacity of Materials under Controlled Composting Conditions"); the composite antifreeze system is added at only 12%-18% (lower than the traditional scheme by 20%-25%), and the base liquid uses local glacial meltwater (no desalination treatment required), keeping the mud cost at 800-1000 yuan / ton (reduced by 30%-40% compared to the traditional scheme); the waste liquid can be treated through a sedimentation-adsorption process (using montmorillonite adsorbent), reducing the treatment cost to 120-150 yuan / ton (reduced by more than 50%). After treatment, the COD of the experimental well waste liquid is ≤80mg / L, meeting the Class III standard of the "Surface Water Environmental Quality Standard", and can be directly discharged into the surrounding streams without affecting vegetation growth.

[0024] In summary, this invention, through the synergistic design of multiple components including a composite antifreeze system, a low-temperature stabilizer, a permafrost protectant, and a lubricant with low-temperature fluidity, achieves the following: the mud does not freeze at -25°C, maintains stable fluidity, exhibits a mud viscosity change rate of ≤15% under a diurnal temperature fluctuation of 20°C, and a cuttings carrying efficiency of ≥90%. It also effectively protects permafrost stability, reduces mud filtrate infiltration, and ensures a permafrost thaw settlement rate of ≤3%, a frost heave rate of ≤3%, and a wellbore enlargement rate of ≤8%, thus improving wellbore stability. Furthermore, the mud components exhibit a biodegradability rate of ≥90%, resulting in high utilization efficiency and reduced wastewater treatment costs. Therefore, this invention overcomes the limitations of extreme low temperatures, achieving antifreeze, anti-collapse, and stable performance of mud in high-altitude permafrost regions.

[0025] Furthermore, in the composite antifreeze system, the weight ratio of propylene glycol, ethylene glycol, carbamide, calcium chloride, and sodium chloride is (2-3):2:1:1:1. Experiments have shown that the optimal balance between viscosity and antifreeze / collapse prevention is achieved when the ratio of propylene glycol, ethylene glycol, and carbamide is within the range of (2:2:1) to (3:2:1). Deviations from this range result in either insufficient antifreeze / collapse prevention or excessive viscosity.

[0026] Furthermore, the propylene oxide etherified modified konjac glucomannan is obtained by mixing konjac glucomannan as raw material with propylene oxide at a molar ratio of 1:(0.5-0.8) under alkaline conditions and at a temperature of 55-65℃, and then performing an etherification reaction for 4-5 hours.

[0027] Furthermore, the degree of substitution of the propylene oxide etherified modified konjac glucomannan is 0.4-0.6.

[0028] Furthermore, the chitosan-grafted acrylic acid copolymer has a grafting rate of ≥80% and a molecular weight of 5×10⁻⁶. 5 -8×10 5 Da.

[0029] Furthermore, the preparation method of the polydimethylsiloxane-modified rapeseed oil is as follows:

[0030] Rapeseed oil and polydimethylsiloxane were mixed at a mass ratio of (5-6):1, and potassium hydroxide (0.5% by weight of rapeseed oil) was added as a catalyst. The mixture was reacted under nitrogen protection at a temperature of 110-125℃ for 3-4 hours to obtain polydimethylsiloxane-modified rapeseed oil.

[0031] Furthermore, the hydroxyl value of the polydimethylsiloxane-modified rapeseed oil is ≤40mgKOH / g.

[0032] Furthermore, the pH adjuster is a mixture of sodium bicarbonate and sodium carbonate in a weight ratio of 2:1.

[0033] Furthermore, the defoamer is a polyether-modified silicone defoamer. BYK-024 (a commercially available polyether-modified silicone defoamer) can be used, with an effective ingredient content ≥30%, a defoaming speed ≤5s, and suitability for water-based systems. The main component of this defoamer is a polydimethylsiloxane-polyoxyethylene-polyoxypropylene block copolymer. By grafting polyether segments (polyoxyethylene / polyoxypropylene) onto the silicone backbone, a balance between water solubility and defoaming properties is achieved, with an effective ingredient content ≥30% and a defoaming speed ≤5s.

[0034] The second objective of this invention is to provide a method for preparing safe and environmentally friendly antifreeze and anti-collapse drilling mud for drilling in high-altitude permafrost regions, comprising the following steps:

[0035] According to the formula ratio, a pH adjuster is added to the water to adjust the pH to 7.5-8.5. Then, the composite antifreeze system, propylene oxide etherified modified konjac glucomannan, chitosan grafted acrylic acid copolymer, polydimethylsiloxane modified rapeseed oil and defoamer are added in sequence and mixed evenly to obtain antifreeze and anti-collapse mud for drilling in high-altitude permafrost areas.

[0036] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0037] This invention achieves stable mud flow at -25℃ through the synergistic design of multiple components, including a composite antifreeze system, a low-temperature stabilizer, a permafrost protectant, and a lubricant with low-temperature fluidity. Under a diurnal temperature fluctuation of 20℃, the mud viscosity change rate is ≤15%, and the cuttings carrying efficiency is ≥90%. It also effectively protects permafrost stability, reduces mud filtrate infiltration, and ensures a permafrost thaw settlement rate of ≤3%, a frost heave rate of ≤3%, and a wellbore enlargement rate of ≤8%, thus improving wellbore stability. Furthermore, the biodegradability rate of the mud components is ≥90%, resulting in high utilization efficiency and reduced wastewater treatment costs. Therefore, this invention overcomes the limitations of extreme low temperatures and achieves antifreeze, anti-collapse, and stable performance of mud in high-altitude permafrost regions. Detailed Implementation

[0038] To make the objectives, technical solutions, and advantages of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the illustrative embodiments and descriptions of the present invention are only used to explain the present invention and are not intended to limit the present invention.

[0039] The embodiments of the present invention will be described in detail below, but unnecessary details may be omitted. For example, detailed descriptions of well-known matters and repeated descriptions may be omitted. This is to avoid making the following description unnecessarily lengthy and to facilitate understanding by those skilled in the art.

[0040] The "scope" disclosed in this invention is defined in the form of a lower limit and an upper limit. A given scope is defined by selecting a lower limit and an upper limit, which define the boundaries of the specific scope. The scope defined in this way can include or exclude end values, and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a scope.

[0041] Unless otherwise specified, all embodiments and optional embodiments of the present invention can be combined with each other to form new technical solutions.

[0042] Unless otherwise specified, all technical features and optional technical features of this invention can be combined to form new technical solutions.

[0043] Unless otherwise specified, the terms "comprising" and "including" as used in this invention can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other substances not listed may also be included, or that only the listed substances may be included.

[0044] Unless otherwise specified, all steps of the present invention may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0045] The technical solution of the present invention will be further described in detail below with reference to the embodiments.

[0046] It should be noted that, unless otherwise specified, the experimental methods used in the embodiments are conventional methods. Unless otherwise specified, the materials, reagents, methods, and instruments used are all conventional materials, reagents, methods, and instruments in the art, and can be obtained commercially by those skilled in the art.

[0047] Example 1

[0048] Preparation method of propylene oxide etherification modified konjac glucomannan:

[0049] Konjac glucomannan was dissolved in water to prepare a 5% (w / w) solution. 10% (w / w) of NaOH was added to the solution, and the mixture was stirred and activated for 30 min. Propylene oxide (molar ratio of konjac glucomannan to propylene oxide was 1:0.6) was slowly added dropwise, and the reaction was carried out at 60 °C for 4 h. After the reaction was completed, the solution was neutralized with hydrochloric acid to pH=7, filtered, washed, and dried to obtain propylene oxide etherified modified konjac glucomannan with a degree of substitution of 0.6 and a viscosity of 250 mPa·s at -20 °C.

[0050] Example 2

[0051] Preparation method of polydimethylsiloxane modified rapeseed oil:

[0052] Rapeseed oil and polydimethylsiloxane (containing silane groups, molecular weight 1000-2000) were mixed at a mass ratio of 5:1, and 0.5% potassium hydroxide by weight of rapeseed oil was added as a catalyst. The mixture was reacted at 120℃ for 3 hours, during which nitrogen gas was introduced for protection. After the reaction was completed, unreacted polydimethylsiloxane was removed by vacuum distillation to obtain polydimethylsiloxane-modified rapeseed oil with a hydroxyl value of 35 mgKOH / g and a viscosity of 45 mPa·s at -20℃.

[0053] Example 3

[0054] (1) A safe and environmentally friendly antifreeze and anti-collapse mud for drilling in high-altitude permafrost areas, comprising the following components by weight percentage: 70% glacial meltwater, 16% composite antifreeze system (propylene glycol, ethylene glycol, carbamide, calcium chloride, sodium chloride in a weight ratio of 3:2:1:1:1), 6% propylene oxide etherified modified konjac glucomannan, 4% chitosan grafted acrylic acid copolymer (grafting rate 85%), 3% polydimethylsiloxane modified rapeseed oil, 0.7% pH adjuster (sodium bicarbonate-sodium carbonate 2:1), and 0.3% defoamer.

[0055] (2) The preparation method of the antifreeze and anti-collapse mud for drilling in the above-mentioned high-altitude permafrost areas includes the following steps:

[0056] Step 1: Base Liquid Pretreatment

[0057] Using glacial meltwater as the base solution, a pH adjuster (sodium bicarbonate and sodium carbonate in a weight ratio of 2:1) was added. The mixture was stirred at 350 rpm for 7 minutes, and the pH value of the system was monitored in real time using a pH meter until it stabilized at 8. At the same time, the base solution was filtered a second time using a filter (filtration accuracy of 5 μm) to ensure that the suspended solids content was 3 mg / L, so as to avoid impurities affecting the dispersion of subsequent components.

[0058] Step 2: Adding the composite antifreeze system

[0059] Mix propylene glycol, ethylene glycol, carbamide, calcium chloride, and sodium chloride in the specified proportions. Start stirring at 220 rpm and control the stirring temperature at 6°C (controlled by a water bath). Stir for 12 minutes until a homogeneous and transparent antifreeze solution is formed (no stratification or precipitation). Then, slowly inject the antifreeze solution into the mixture obtained in step 1 using a metering pump (injection rate 6 L / min). Maintain the stirring speed at 300 rpm and continue stirring for 18 minutes to ensure that the antifreeze system is fully mixed with the base liquid.

[0060] Step 3: Dispersion of propylene oxide etherified modified konjac glucomannan

[0061] The propylene oxide etherified modified konjac glucomannan (pre-crushed to a particle size ≤100μm to avoid clumping) was slowly added to the mixture obtained in step 2 (addition rate 0.8kg / min). The stirring speed was increased to 550rpm and the stirring time was 28min. During this period, samples were taken every 5min and the viscosity of the system was monitored by a viscometer (NDJ-5S type, test temperature 5℃) until the viscosity stabilized at 180mPa·s (5℃) to ensure that the stabilizer molecular chains were fully extended and formed a three-dimensional network suspension structure.

[0062] Step 4: Blending and adding chitosan-grafted acrylic acid copolymer with polydimethylsiloxane-modified rapeseed oil

[0063] Add the chitosan-grafted acrylic acid copolymer to the mixture obtained in step 3 at a rate of 0.4 kg / min, maintain a stirring speed of 500 rpm, and stir for 18 min to form uniformly dispersed colloidal particles in the slurry (monitor the particle size distribution using a laser particle size analyzer to ensure that 90% of the particles are within the 1-5 μm range); then add polydimethylsiloxane-modified rapeseed oil, reduce the stirring speed to 400 rpm, and stir for 12 min to ensure that the lubricant is uniformly coated on the surface of the colloidal particles, forming a "suspension-lubrication" synergistic layer.

[0064] Step 5: Defoaming and Performance Testing

[0065] Finally, add the defoamer according to the ratio, reduce the stirring speed to 200 rpm, stir for 4 min, and visually confirm that there are no obvious bubbles in the system (the number of bubbles with a diameter ≤0.5 mm ≤5 / L); take samples for testing, and the freezing point (using differential scanning calorimeter DSC-200F3), low temperature viscosity (Brookfield DV3T viscometer) and filtration loss (API filtration meter, room temperature 30 min) results are shown in Table 1.

[0066] Table 1. Performance test results of the mud prepared in Example 3

[0067]

[0068] (3) On-site application effect

[0069] Geological and mineral exploration wells at an altitude of 4500m and an extreme low temperature of -20℃

[0070] The well was drilled to a depth of 1200m. At night, when the temperature dropped to -22℃, the mud circulation system (pump pressure 16MPa) operated continuously for 48 hours without freezing. Cuttings carrying efficiency was 92%, and there was no sediment at the bottom of the well. 24 hours after drilling, the wellbore enlargement rate was 6.2%, and the frozen soil thawing settlement rate was 1.8%. After montmorillonite adsorption treatment, the COD of the waste liquid was 75mg / L, and it was directly discharged into the surrounding stream. After 30 days, the surrounding vegetation (Kobresia and Sedge) grew normally. The results are shown in Table 2.

[0071] Table 2. Application effect data of the mud prepared in Example 3

[0072]

[0073] Example 4

[0074] (1) A safe and environmentally friendly antifreeze and anti-collapse mud for drilling in high-altitude permafrost areas, comprising the following components by weight percentage: 75% shallow groundwater in the plateau, 15.3% composite antifreeze system (propylene glycol, ethylene glycol, carbamide, calcium chloride, sodium chloride in a weight ratio of 2.5:2:1:1:1), 4% propylene oxide etherified modified konjac glucomannan, 3% chitosan grafted acrylic acid copolymer (grafting rate 85%), 2% polydimethylsiloxane modified rapeseed oil, 0.5% pH adjuster (sodium bicarbonate-sodium carbonate 2:1), and 0.2% defoamer.

[0075] (2) The preparation method of the antifreeze and anti-collapse mud for drilling in the above-mentioned high-altitude permafrost areas includes the following steps:

[0076] Step 1: Base Liquid Pretreatment

[0077] Using shallow groundwater from the plateau as the base solution, a pH adjuster (sodium bicarbonate and sodium carbonate in a weight ratio of 2:1) was added. The mixture was stirred at 300 rpm for 5 minutes, and the pH value of the system was monitored in real time with a pH meter until it stabilized at 7.5. At the same time, the base solution was filtered a second time using a filter (filtration accuracy of 5 μm) to ensure that the suspended solids content was 4 mg / L, so as to avoid impurities affecting the dispersion of subsequent components.

[0078] Step 2: Adding the composite antifreeze system

[0079] Mix propylene glycol, ethylene glycol, carbamide, calcium chloride, and sodium chloride in the specified proportions. Start stirring at 200 rpm and control the stirring temperature at 5°C (controlled by a water bath). Stir for 10 minutes until a homogeneous and transparent antifreeze solution is formed (no stratification or precipitation). Then, slowly inject the antifreeze solution into the mixture obtained in step 1 using a metering pump (injection rate 5 L / min). Maintain the stirring speed at 300 rpm and continue stirring for 15 minutes to ensure that the antifreeze system is fully mixed with the base liquid.

[0080] Step 3: Dispersion of propylene oxide etherified modified konjac glucomannan

[0081] The propylene oxide etherified modified konjac glucomannan (pre-crushed to a particle size ≤100μm to avoid clumping) was slowly added to the mixture obtained in step 2 (addition rate 0.5kg / min), and the stirring speed was increased to 500rpm for 25min. During this period, samples were taken every 5min, and the viscosity of the system was monitored by a viscometer (NDJ-5S type, test temperature 5℃) until the viscosity stabilized at 150mPa·s (5℃) to ensure that the stabilizer molecular chains were fully extended and formed a three-dimensional network suspension structure.

[0082] Step 4: Blending and adding chitosan-grafted acrylic acid copolymer with polydimethylsiloxane-modified rapeseed oil

[0083] Add the chitosan-grafted acrylic acid copolymer to the mixture obtained in step 3 at a rate of 0.3 kg / min, maintain a stirring speed of 500 rpm, and stir for 15 min to form uniformly dispersed colloidal particles in the slurry (monitor the particle size distribution using a laser particle size analyzer to ensure that 90% of the particles are within the range of 1-5 μm). Then add polydimethylsiloxane-modified rapeseed oil, reduce the stirring speed to 400 rpm, and stir for 10 min to ensure that the lubricant is uniformly coated on the surface of the colloidal particles, forming a "suspension-lubrication" synergistic layer.

[0084] Step 5: Defoaming and Performance Testing

[0085] Finally, add the defoamer according to the ratio, reduce the stirring speed to 200 rpm, stir for 3 minutes, and visually confirm that there are no obvious bubbles in the system (the number of bubbles with a diameter ≤0.5 mm ≤5 / L); take samples for testing, and the freezing point (using differential scanning calorimeter DSC-200F3), low temperature viscosity (Brookfield DV3T viscometer) and filtration loss (API filtration meter, room temperature 30 min) results are shown in Table 3.

[0086] Table 3. Performance test results of the mud prepared in Example 4

[0087]

[0088] (3) On-site application effect

[0089] Geological and mineral exploration wells at an altitude of 5100m and an extreme low temperature of -30℃

[0090] The exploration well was drilled to a depth of 1100m, with a diurnal temperature range of 20℃ (-35℃ to -15℃). The mud viscosity increased from 85mPa·s to 97mPa·s (a change rate of 14.1%). The well was continuously drilled for 180m without stopping to remove cuttings. The well diameter enlargement rate was 5.8%, and there was no collapse.

[0091] Table 4. Application effect data of the mud prepared in Example 4

[0092]

[0093] Example 5

[0094] (1) A safe and environmentally friendly antifreeze and anti-collapse mud for drilling in high-altitude permafrost areas, comprising the following components by weight percentage: 65% glacial meltwater, 16% composite antifreeze system (propylene glycol, ethylene glycol, carbamide, calcium chloride, sodium chloride in a weight ratio of 2:2:1:1:1), 8% propylene oxide etherified modified konjac glucomannan, 6% chitosan grafted acrylic acid copolymer (grafting rate 85%), 4% polydimethylsiloxane modified rapeseed oil, 0.8% pH adjuster (sodium bicarbonate-sodium carbonate 2:1), and 0.2% defoamer.

[0095] (2) The preparation method of the antifreeze and anti-collapse mud for drilling in the above-mentioned high-altitude permafrost areas includes the following steps:

[0096] Step 1: Base Liquid Pretreatment

[0097] Using glacial meltwater as the base solution, a pH adjuster (sodium bicarbonate and sodium carbonate in a weight ratio of 2:1) was added. The mixture was stirred at 400 rpm for 8 minutes, and the pH value of the system was monitored in real time using a pH meter until it stabilized at 8.5. At the same time, the base solution was filtered a second time using a filter (filtration accuracy of 5 μm) to ensure that the suspended solids content was 2 mg / L, so as to avoid impurities affecting the dispersion of subsequent components.

[0098] Step 2: Adding the composite antifreeze system

[0099] Mix propylene glycol, ethylene glycol, carbamide, calcium chloride, and sodium chloride in the specified proportions. Start stirring at 250 rpm and control the stirring temperature at 8°C (controlled by a water bath). Stir for 15 minutes until a homogeneous and transparent antifreeze solution is formed (no stratification or precipitation). Then, slowly inject the antifreeze solution into the mixture obtained in step 1 using a metering pump (injection rate 8 L / min). Maintain the stirring speed at 300 rpm and continue stirring for 20 minutes to ensure that the antifreeze system is fully mixed with the base liquid.

[0100] Step 3: Dispersion of propylene oxide etherified modified konjac glucomannan

[0101] The propylene oxide etherified modified konjac glucomannan (pre-crushed to a particle size ≤100μm to avoid clumping) was slowly added to the mixture obtained in step 2 (addition rate 1kg / min), and the stirring speed was increased to 600rpm for 30min. During this period, samples were taken every 5min, and the viscosity of the system was monitored by a viscometer (NDJ-5S type, test temperature 5℃) until the viscosity stabilized at 200mPa·s (5℃) to ensure that the stabilizer molecular chains were fully extended and formed a three-dimensional network suspension structure.

[0102] Step 4: Blending and adding chitosan-grafted acrylic acid copolymer with polydimethylsiloxane-modified rapeseed oil

[0103] Add the chitosan-grafted acrylic acid copolymer to the mixture obtained in step 3 at a rate of 0.5 kg / min, maintain a stirring speed of 500 rpm, and stir for 20 min to form uniformly dispersed colloidal particles in the slurry (monitor the particle size distribution using a laser particle size analyzer to ensure that 90% of the particles are within the range of 1-5 μm). Then add the polydimethylsiloxane-modified rapeseed oil, reduce the stirring speed to 400 rpm, and stir for 15 min to ensure that the lubricant is uniformly coated on the surface of the colloidal particles, forming a "suspension-lubrication" synergistic layer.

[0104] Step 5: Defoaming and Performance Testing

[0105] Finally, add the defoamer according to the ratio, reduce the stirring speed to 200 rpm, stir for 5 minutes, and visually confirm that there are no obvious bubbles in the system (the number of bubbles with a diameter ≤0.5 mm ≤5 / L); take samples for testing, and the freezing point (using differential scanning calorimeter DSC-200F3), low temperature viscosity (Brookfield DV3T viscometer), and filtration loss (API filtration meter, room temperature 30 min) results are shown in Table 5.

[0106] Table 5. Performance test results of the mud prepared in Example 5

[0107]

[0108] (3) On-site application effect

[0109] Drilling in permafrost regions at an altitude of 4200m and extreme low temperatures of -25℃

[0110] The well was drilled to a depth of 800m, and mud circulation remained normal (pump pressure 17MPa) at an extreme low temperature of -25℃; the frozen soil thaw settlement rate was 2.1%, and the well wall remained intact; after drilling was completed, the mud waste was treated and reused for well washing, increasing water resource utilization by 60%; the biodegradation rate was 93%, with no ecological pollution.

[0111] Table 6. Application effect data of the mud prepared in Example 5

[0112]

[0113] Comparative Example 1

[0114] The difference between this embodiment and embodiment 5 is as follows:

[0115] In the composite antifreeze system, no carbamide is added, that is, the composition of the composite antifreeze system is: propylene glycol, ethylene glycol, calcium chloride, and sodium chloride in a weight ratio of 2:2:1:1.

[0116] Table 7. Performance test results of the mud prepared in Comparative Example 1

[0117]

[0118] The data comparison in Table 7 shows that Comparative Example 1, lacking the addition of carbamide, failed to utilize its hydrogen bond-breaking effect, resulting in a significant decrease in the synergistic antifreeze effect of the composite antifreeze system. The freezing point was only -18℃, failing to meet the requirement of ≤-25℃. Simultaneously, ice crystal formation increased the system viscosity to 150 mPa·s, exceeding the standard of ≤120 mPa·s, and the filtration loss also increased to 18 mL, failing to meet technical requirements. This demonstrates that carbamide is an indispensable component in the composite antifreeze system. Its synergistic effect with propylene glycol, ethylene glycol, calcium chloride, and sodium chloride is essential to effectively disrupt the ice crystal structure and ensure the low-temperature performance of the drilling mud.

[0119] Comparative Example 2

[0120] The difference between this comparative example and Example 5 is as follows:

[0121] The compound antifreeze system has different formulation ratios, namely, propylene glycol, ethylene glycol, carbamide, calcium chloride, and sodium chloride in a weight ratio of 4:2:1:1:1.

[0122] Comparative Example 3

[0123] The difference between this comparative example and Example 5 is as follows:

[0124] The compound antifreeze system has different formulation ratios, namely propylene glycol, ethylene glycol, carbamide, calcium chloride, and sodium chloride in a weight ratio of 1:2:1:1:1.

[0125] Table 8. Performance test results of the mud prepared in Comparative Examples 2 and 3

[0126]

[0127] The data comparison in Table 8 shows that: in Comparative Example 2, the propylene glycol ratio was too high. Although the freezing point could still reach -45℃, the excessive propylene glycol caused the system viscosity to rise to 130 mPa·s, exceeding the standard, and the filtration loss increased to 16 mL, disrupting the balance between viscosity and antifreeze properties. In Comparative Example 3, the propylene glycol ratio was too low, failing to provide sufficient flowability support, resulting in a freezing point of only -22℃, which did not meet the requirement of ≤-25℃, and the filtration loss also increased to 17 mL. This proves that the components in the composite antifreeze system must be strictly controlled within the ratio range of (2-3):2:1:1:1 to achieve the optimal balance between antifreeze properties, flowability, and filtration loss.

[0128] Comparative Example 4

[0129] The difference between this comparative example and Example 5 is as follows:

[0130] Without adding propylene oxide etherified modified konjac glucomannan, and with other steps unchanged, the properties of the resulting mud are shown in Table 9.

[0131] Table 9. Performance test results of the mud prepared in Comparative Example 4

[0132]

[0133] The data comparison in Table 9 shows that the low-temperature stabilization effect of propylene oxide etherified modified konjac glucomannan is crucial. In Comparative Example 4, the absence of this component caused the slurry's molecular chains to lose stability and curl up at -25℃, resulting in a sharp increase in viscosity to 180 mPa·s, far exceeding the requirement of ≤120 mPa·s, thus failing to guarantee low-temperature fluidity. Although the freezing point was not significantly affected, the filtration loss also increased to 14 mL, and the overall performance did not meet the standards. This component, by inhibiting molecular chain curling and maintaining a three-dimensional network structure, is the core component for ensuring the low-temperature viscosity stability of the slurry.

[0134] Comparative Example 5

[0135] The difference between this comparative example and Example 5 is as follows:

[0136] The frozen soil protectant was obtained by replacing chitosan-grafted acrylic acid copolymer with polyacrylamide, while keeping other steps unchanged. The properties of the resulting mud are shown in Table 10.

[0137] Table 10. Performance test results of the mud prepared in Comparative Example 5

[0138]

[0139] The data comparison in Table 10 shows that polyacrylamide cannot replace the permafrost protection function of chitosan-grafted acrylic acid copolymer. Although the freezing point was not affected, polyacrylamide has poor water solubility and cannot form a dense adsorption film on the well wall, resulting in a large amount of mud filtrate seeping into the permafrost, increasing the filtrate loss to 20 mL, far exceeding the requirement of ≤15 mL. At the same time, it cannot form hydrogen bonds with permafrost clay particles, reducing permafrost stability and indirectly causing the system viscosity to rise to 125 mPa·s, close to the exceeding threshold. This proves that chitosan-grafted acrylic acid copolymer has both filtrate loss reduction and permafrost stabilization functions, and is a key component for ensuring the integrity of the well wall.

[0140] In summary, this invention achieves the core performance requirements for drilling in high-altitude permafrost regions, such as antifreeze, anti-collapse, stability, and environmental protection, through the synergistic effect of specific components and precise proportions of "composite antifreeze system + low-temperature stabilizer + permafrost protectant + low-temperature fluidity lubricant". The absence of any component or deviation from the set range will lead to a significant decrease in mud performance, which will not meet the actual application requirements.

[0141] Finally, it should be noted that the above specific embodiments are only used to describe the purpose, technical solution, and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation of the present invention and is not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to the foregoing specific embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions or improvements can be made to some or all of the technical features. These modifications, equivalent substitutions, and improvements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be covered within the scope of the claims and specification of the present invention.

Claims

1. A safe and environmentally friendly antifreeze and anti-collapse drilling mud for drilling in high-altitude permafrost areas, characterized in that, By weight percentage, it includes the following components: The ingredients are: 65-75% water, 12-18% composite antifreeze system, 4-8% propylene oxide etherified modified konjac glucomannan, 3-6% chitosan grafted acrylic acid copolymer, 2-4% polydimethylsiloxane modified rapeseed oil, 0.3-0.8% pH adjuster, and 0.1-0.3% defoamer. The composite antifreeze system includes propylene glycol, ethylene glycol, carbamide, calcium chloride, and sodium chloride.

2. The safe and environmentally friendly antifreeze and anti-collapse drilling mud for drilling in high-altitude permafrost areas according to claim 1, characterized in that, In the composite antifreeze system, the weight ratio of propylene glycol, ethylene glycol, carbamide, calcium chloride and sodium chloride is (2-3):2:1:1:

1.

3. The safe and environmentally friendly antifreeze and anti-collapse mud for drilling in high-altitude permafrost areas according to claim 1, characterized in that, The propylene oxide etherified modified konjac glucomannan is obtained by mixing konjac glucomannan as raw material with propylene oxide at a molar ratio of 1:(0.5-0.8) under alkaline conditions and at a temperature of 55-65℃, and then performing an etherification reaction for 4-5 hours.

4. The safe and environmentally friendly antifreeze and anti-collapse mud for drilling in high-altitude permafrost areas according to claim 3, characterized in that, The degree of substitution of the propylene oxide etherified modified konjac glucomannan is 0.4-0.

6.

5. The safe and environmentally friendly antifreeze and anti-collapse mud for drilling in high-altitude permafrost areas according to claim 1, characterized in that, The chitosan-grafted acrylic acid copolymer has a grafting rate of ≥80% and a molecular weight of 5×10⁻⁶. 5 -8×10 5 Da.

6. The safe and environmentally friendly antifreeze and anti-collapse drilling mud for drilling in high-altitude permafrost areas according to claim 1, characterized in that, The preparation method of the polydimethylsiloxane-modified rapeseed oil is as follows: Rapeseed oil and polydimethylsiloxane were mixed at a mass ratio of (5-6):1, and potassium hydroxide (0.5% by weight of rapeseed oil) was added as a catalyst. The mixture was reacted under nitrogen protection at a temperature of 110-125℃ for 3-4 hours to obtain polydimethylsiloxane-modified rapeseed oil.

7. The safe and environmentally friendly antifreeze and anti-collapse drilling mud for drilling in high-altitude permafrost areas according to claim 1, characterized in that, The hydroxyl value of the polydimethylsiloxane-modified rapeseed oil is ≤40mgKOH / g.

8. The safe and environmentally friendly antifreeze and anti-collapse mud for drilling in high-altitude permafrost areas according to claim 1, characterized in that, The pH adjuster is a mixture of sodium bicarbonate and sodium carbonate.

9. The safe and environmentally friendly antifreeze and anti-collapse drilling mud for drilling in high-altitude permafrost areas according to claim 1, characterized in that, The defoamer used is a polyether-modified silicone defoamer.

10. The method for preparing safe, environmentally friendly, antifreeze, and anti-collapse drilling mud for drilling in high-altitude permafrost areas as described in claim 1, characterized in that, Includes the following steps: According to the formula ratio, a pH adjuster is added to the water to adjust the pH to 7.5-8.

5. Then, the composite antifreeze system, propylene oxide etherified modified konjac glucomannan, chitosan grafted acrylic acid copolymer, polydimethylsiloxane modified rapeseed oil and defoamer are added in sequence and mixed evenly to obtain antifreeze and anti-collapse mud for drilling in high-altitude permafrost areas.

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