A method for evaluating and optimizing the performance of drilling fluid for open hole freezing

Abstract

This invention discloses a method for evaluating and optimizing the performance of drilling fluids used in open-hole freezing, relating to the field of mining tunnel engineering technology. The method includes determining the required temperature range for the drilling fluid based on the formation temperature environment during open-hole freezing construction, and selecting multiple temperature test points, including at least 36℃, 10℃, -4℃, -10℃, -15℃, -20℃, and -25℃. By constructing a multi-point performance evaluation system covering all temperature conditions of open-hole freezing, and setting clear qualification standards based on the dual functional requirements of drilling wall protection and refrigerant freezing, a scientific quantitative evaluation and targeted optimization of the performance of low-temperature solids-free drilling fluids is achieved. This not only effectively solves the problems of rheological degradation, uncontrolled filtration loss, and high freezing point of traditional drilling fluids at low temperatures, but also improves the wellbore stability and freezing efficiency of drilling fluids in complex formations such as water-sensitive mudstone and loose sand layers, avoiding the risk of freezing pipe breakage or freezing wall failure due to performance mismatch.

Description

Technical Field

[0001] This invention relates to the field of mining tunnel engineering technology, and in particular to a method for evaluating and optimizing the performance of solid-free drilling fluids used for open-hole freezing. Background Technology

[0002] Mining tunnel engineering technology is a core branch of mining engineering. It primarily studies the planning, design, construction, and maintenance of various underground passages (such as vertical shafts, inclined shafts, horizontal tunnels, and chambers) used to establish a safe and efficient production system during underground mineral deposit mining. This field comprehensively applies rock mechanics, geology, and blasting and support theories to solve key technical challenges such as underground space excavation under complex geological conditions, surrounding rock stability control, ventilation and drainage, and ground pressure management. It is a fundamental engineering technology for ensuring safe mine production, efficient resource extraction, and the long-term stable operation of underground engineering projects.

[0003] In open-hole freezing operations, the formation temperature range is extremely wide. Conventional drilling fluids have high filtration loss and poor wall protection at high temperatures, while they are prone to solidification or rapid deterioration of rheological properties at low temperatures. They cannot simultaneously meet the requirements of wellbore stability during the drilling stage and effective flow of the coolant during the freezing stage. In addition, ordinary solid-free drilling fluids have a high freezing point and are prone to phase change or viscosity runaway at -25°C, leading to circulation interruption, uneven freezing, and even downhole accidents. At the same time, they lack the ability to maintain sufficient dynamic shear force and plastic viscosity at extremely low temperatures, making it difficult to suspend rock cuttings or maintain the fluidity of the coolant. Summary of the Invention

[0004] In view of the aforementioned existing problems, the present invention is proposed.

[0005] Therefore, this invention provides a method for evaluating and optimizing the performance of solid-free drilling fluids for open hole freezing. This solves the problems of ordinary solid-free drilling fluids having a high freezing point, being prone to phase change or viscosity runaway at -25℃, leading to circulation interruption, uneven freezing, and even downhole accidents; and lacking the ability to maintain sufficient dynamic shear force and plastic viscosity at extremely low temperatures, making it difficult to suspend cuttings or maintain the fluidity of the coolant.

[0006] To solve the above-mentioned technical problems, the present invention provides the following technical solution:

[0007] In a first aspect, the present invention provides a method for evaluating and optimizing the performance of drilling fluids used for open hole freezing, comprising:

[0008] Based on the formation temperature environment during open-hole freezing construction, the required temperature range for the drilling fluid is determined, and multiple temperature test points are selected, including at least 36℃, 10℃, -4℃, -10℃, -15℃, -20℃, and -25℃.

[0009] At each of the aforementioned temperature test points, the funnel viscosity, apparent viscosity, plastic viscosity, dynamic shear force of the candidate drilling fluid samples were measured, and the API filtration loss at the highest and lowest temperatures was also measured.

[0010] Based on the technical requirements of the open hole freezing process for maintaining wellbore stability during the drilling stage and maintaining effective coolant flow during the freezing stage, performance qualification standards are set, including API filtration loss not exceeding 20 mL at 36℃, API filtration loss not exceeding 10 mL at -25℃, funnel viscosity not exceeding 91 seconds, and dynamic shear force not less than 4 Pa.

[0011] The measured performance parameters are compared with the qualified standards. If any parameter is not met at any temperature point, the candidate drilling fluid is determined to be unsuitable.

[0012] Adjust the drilling fluid composition ratio according to the type of performance defect, and return to the measurement step for iterative verification until all qualification criteria are met to obtain an optimized formula.

[0013] As a preferred embodiment of the drilling fluid performance evaluation and optimization method for open hole freezing described in this invention, the candidate drilling fluid is a water-based solid-free system comprising water, calcium chloride, sodium chloride, polyacrylamide, thickener, filtration reducer, and lubricant.

[0014] As a preferred embodiment of the drilling fluid performance evaluation and optimization method for open hole freezing described in this invention, the polyacrylamide is a cationic polyacrylamide or anionic partially hydrolyzed polyacrylamide, and the lubricant is polyether polyol PPG-400.

[0015] As a preferred embodiment of the drilling fluid performance evaluation and optimization method for open hole freezing described in this invention, the adjustment of the drilling fluid composition ratio includes:

[0016] When the filtration loss exceeds the standard at high temperature, increase the dosage of the filtration loss reducing agent;

[0017] When the rheological properties are insufficient at low temperatures, increase the total amount of calcium chloride and sodium chloride.

[0018] When the viscosity is low at room temperature, increase the amount of thickener.

[0019] As a preferred embodiment of the drilling fluid performance evaluation and optimization method for open hole freezing described in this invention, the freezing point of the drilling fluid should not be higher than -28℃. If the measured freezing point is higher than -28℃, the amount of calcium chloride or a mixture of calcium chloride and sodium chloride should be increased when adjusting the component ratio.

[0020] As a preferred embodiment of the drilling fluid performance evaluation and optimization method for open hole freezing described in this invention, the API filtration loss is determined according to GB / T16783.1 standard, the funnel viscosity is determined according to SY / T5677 standard, and the apparent viscosity, plastic viscosity, and dynamic shear force are determined according to SY / T5621 standard.

[0021] As a preferred embodiment of the drilling fluid performance evaluation and optimization method for open hole freezing described in this invention, the method is applied to open hole freezing construction in mine shaft and tunnel construction projects, and the construction does not require the lowering of freezing pipes.

[0022] As a preferred embodiment of the drilling fluid performance evaluation and optimization method for open hole freezing described in this invention, the strata traversed by the mine shaft construction project include water-sensitive mudstone, shallow loose sand layers, or fractured rock layers.

[0023] As a preferred embodiment of the drilling fluid performance evaluation and optimization method for open hole freezing described in this invention, wherein: at -25℃, the apparent viscosity of the drilling fluid is not less than 23 mPas and the plastic viscosity is not less than 19 mPas.

[0024] As a preferred embodiment of the drilling fluid performance evaluation and optimization method for open hole freezing described in this invention, the optimized formula maintains non-Newtonian fluid characteristics at all temperature test points, and has a funnel viscosity of 2022 seconds at 36°C and a funnel viscosity of 6091 seconds at -25°C.

[0025] The beneficial effects of this invention are as follows: By constructing a multi-point performance evaluation system covering all temperature conditions of open hole freezing, and setting clear qualification standards based on the dual functional requirements of drilling wall protection and refrigerant freezing, a scientific quantitative evaluation and directional optimization of the performance of low-temperature solids-free drilling fluid is achieved. This not only effectively solves the problems of rheological degradation, uncontrolled filtration loss, and high freezing point of traditional drilling fluids at low temperatures, but also improves the wellbore stability and freezing efficiency of drilling fluids in complex formations such as water-sensitive mudstone and loose sand layers. It avoids the risk of freezing pipe breakage or freezing wall failure caused by performance mismatch, thereby ensuring the safety, reliability, and economy of open hole freezing construction. Attached Figure Description

[0026] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0027] Figure 1This is a flowchart of the drilling fluid performance evaluation and optimization method for open hole freezing in Example 1. Detailed Implementation

[0028] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0029] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0030] Secondly, the term "one embodiment" or "example" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the invention. The appearance of an embodiment in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that mutually excludes other embodiments.

[0031] Example 1, referring to Figure 1 This is the first embodiment of the present invention, which provides a method for evaluating and optimizing drilling fluid performance for open hole freezing, comprising the following steps:

[0032] S1. Based on the formation temperature environment during open-hole freezing construction, determine the temperature range that the drilling fluid needs to adapt to, and select multiple temperature test points, including at least 36℃, 10℃, -4℃, -10℃, -15℃, -20℃ and -25℃.

[0033] Furthermore, the freezing point of the drilling fluid should not be higher than -28℃. If the measured freezing point is higher than -28℃, the amount of calcium chloride should be increased when adjusting the composition ratio. At -25℃, the apparent viscosity of the drilling fluid should not be lower than 23 mPas and the plastic viscosity should not be lower than 19 mPas.

[0034] It should be noted that by controlling the freezing point of the drilling fluid to a sufficiently low level and ensuring that it still has sufficient rheological properties at the lowest operating temperature, it is possible to effectively prevent the drilling fluid from undergoing phase change or loss of fluidity during the freezing stage, thereby ensuring the continuous operation of the refrigerant circulation system and the uniformity of the formation freezing effect.

[0035] S2. At each temperature test point, determine the funnel viscosity, apparent viscosity, plastic viscosity, dynamic shear force of the candidate drilling fluid sample, and measure its API filtration loss at the highest and lowest temperatures.

[0036] Furthermore, the candidate drilling fluid is a water-based solids-free system containing water, calcium chloride, sodium chloride, polyacrylamide, thickener, filtration reducer, and lubricant; the polyacrylamide is cationic polyacrylamide or anionic partially hydrolyzed polyacrylamide, and the lubricant is polyether polyol PPG-400.

[0037] It should be noted that the use of a water-based solid-free system with a specific composition not only avoids contamination of the formation and pore blockage by solid particles, but also improves the stability, lubricity and cuttings carrying capacity of the drilling fluid in a wide temperature range by optimizing the polymer type and lubricating components, thus providing a basic guarantee for safe drilling in open hole environments.

[0038] S3. Based on the technical requirements of the open hole freezing process for maintaining wellbore stability during the drilling stage and maintaining effective refrigerant flowability during the freezing stage, set performance qualification standards, including API filtration loss not exceeding 20 mL at 36℃, API filtration loss not exceeding 10 mL at -25℃, funnel viscosity not exceeding 91 seconds, and dynamic shear force not less than 4 Pa.

[0039] Furthermore, the API filtration loss was determined according to GB / T16783.1 standard, the funnel viscosity was determined according to SY / T5677 standard, and the apparent viscosity, plastic viscosity, and dynamic shear force were determined according to SY / T5621 standard.

[0040] It should be noted that by uniformly measuring key performance parameters according to industry standards, the repeatability, comparability, and engineering applicability of the evaluation results are ensured, avoiding misjudgments caused by inconsistent testing methods, and providing a reliable basis for the objective screening and process adaptation of different formulations.

[0041] S4. Compare the measured performance parameters with the qualified standards. If any parameter at any temperature point is not met, the candidate drilling fluid is deemed unsuitable.

[0042] It should be noted that the judgment logic of rejecting the entire product if any temperature point fails to meet the standard can comprehensively identify the performance shortcomings of the drilling fluid in the entire operating temperature range, prevent the assumption that only local conditions are met while ignoring the risks of extreme operating conditions, and thus improve the reliability of the formula in actual complex construction environments.

[0043] S5. Adjust the drilling fluid composition ratio according to the type of performance defect, and return to the measurement step for iterative verification until all qualified standards are met to obtain the optimized formula.

[0044] Furthermore, when the filtration loss exceeds the standard at high temperatures, the amount of filtration loss reducing agent is increased; when the rheological properties are insufficient at low temperatures, the amount of calcium chloride alone or a mixture of calcium chloride and sodium chloride is increased; when the viscosity at room temperature is too low, the amount of thickener is increased; the optimized formula maintains non-Newtonian fluid characteristics at all temperature test points, and the funnel viscosity is 2022 seconds at 36℃ and 6091 seconds at -25℃.

[0045] The method is applied to the open-hole freezing construction in mine shaft and tunnel construction projects, which does not require the lowering of freezing pipes; the strata traversed by the mine shaft and tunnel construction projects include water-sensitive mudstone, shallow loose sand layers or fractured rock layers.

[0046] It should be noted that by implementing targeted component adjustments based on the type of performance defect and combining them with the requirement to maintain the characteristics of non-Newtonian fluids, a shift from experience-based trial and error to targeted optimization has been achieved, shortening the R&D cycle. At the same time, it ensures that the optimized drilling fluid can perform both wall protection and freeze transfer functions in various typical adverse formations.

[0047] In summary, this invention constructs a multi-point performance evaluation system covering all temperature conditions of open-hole freezing and sets clear qualification standards based on the dual functional requirements of drilling wall protection and refrigerant freezing. This enables scientific quantitative evaluation and targeted optimization of the performance of low-temperature solids-free drilling fluid. It not only effectively solves the problems of rheological degradation, uncontrolled filtration loss, and high freezing point of traditional drilling fluids at low temperatures, but also improves the wellbore stability and freezing efficiency of drilling fluids in complex formations such as water-sensitive mudstone and loose sand layers. It avoids the risk of freezing pipe breakage or freezing wall failure caused by performance mismatch, thereby ensuring the safety, reliability, and economy of open-hole freezing construction.

[0048] Example 2, the second embodiment of the present invention, provides a water-based solids-free drilling fluid for open-hole freezing. Its formulation, by weight, includes: 700 parts water, 150 parts calcium chloride, 80 parts sodium chloride, 0.2 parts polyacrylamide, 1.0-1.2 parts thickener, 8 parts filtration loss reducer, and 18 parts lubricant. This drilling fluid has a funnel viscosity of 22 seconds, a pH of 7.6, and a specific gravity of 1.24 at room temperature. At 36°C, the API filtration loss is 18.2 mL, decreasing to 7.8 mL at -25°C. Tested across the entire temperature gradient (36°C to -25°C), its rheological properties steadily improve with decreasing temperature, maintaining good dynamic shear strength and apparent viscosity at -25°C, meeting the requirements for low-temperature refrigerant circulation and wellbore stability.

[0049] Example 3, the third embodiment of the present invention, provides a water-based solids-free drilling fluid for open-hole freezing. Its formulation, by weight, includes: 700 parts water, 150 parts calcium chloride, 80 parts sodium chloride, 0.2 parts polyacrylamide, 1.0-1.2 parts viscosifier, 0.7 parts filtration loss reducer, and 18 parts lubricant. This drilling fluid has a pH of 7.0 and a specific gravity of 1.22; at 36°C, its funnel viscosity is 20 seconds, and its filtration loss is 12.6 mL; at -25°C, its filtration loss is 9.8 mL. It exhibits moderate rheological growth in the low-temperature range, and its dynamic shear force reaches over 4 Pa ​​at -25°C, demonstrating basic low-temperature cuttings carrying and wall protection capabilities.

[0050] Example 4, the fourth embodiment of the present invention, provides a water-based solids-free drilling fluid for open-hole freezing. Its formulation, by weight, includes: 700 parts water, 150 parts calcium chloride, 80 parts sodium chloride, 0.2 parts polyacrylamide, 1.0-1.2 parts thickener, 1.5 parts filtration loss reducer, and 18 parts lubricant. This drilling fluid has a pH of 7.1 and a specific gravity of 1.21; its funnel viscosity at room temperature is 21 seconds; its filtration loss at 36°C is 12.2 mL; and its filtration loss at -25°C is further reduced to 7.7 mL. Its low-temperature rheological properties are superior to those of Example 2, with increased apparent viscosity and plastic viscosity at -25°C, and a dynamic shear stress of 5.11 Pa, demonstrating better low-temperature stability.

[0051] Example 5, the fifth embodiment of the present invention, provides a water-based solids-free drilling fluid for open-hole freezing. Its formulation, by weight, includes: 700 parts water, 150 parts calcium chloride, 80 parts sodium chloride, 0.2 parts polyacrylamide, 1.0-1.2 parts thickener, 2 parts filtration loss reducer (composed of polyanionic cellulose and modified starch in a 1:1 weight ratio), and 18 parts lubricant. This drilling fluid has a pH of 7.0 and a specific gravity of 1.20; at 36°C, its funnel viscosity is 22 seconds, and its filtration loss is 9.2 mL; at -25°C, the filtration loss is only 5.6 mL, the lowest among all embodiments. Its rheological parameters steadily increase across the entire temperature range, and the dynamic shear force exceeds 5.6 Pa at -25°C, indicating that the composite filtration loss reducer system effectively improves high-temperature sealing performance and low-temperature structural strength.

[0052] Example 6, the sixth embodiment of the present invention, provides a water-based solids-free drilling fluid for open-hole freezing. Its formulation, by weight, includes: 700 parts water, 150 parts calcium chloride, 80 parts sodium chloride, 0.2 parts polyacrylamide, 1.0-1.2 parts thickener, 4 parts filtration loss reducer (composed of hydroxyethyl cellulose and modified starch in a 1:3 weight ratio), and 18 parts lubricant. This drilling fluid has a pH of 7.0 and a specific gravity of 1.21; at 36°C, its funnel viscosity is 21 seconds, and its filtration loss is 11 mL; at -25°C, its filtration loss is 6.2 mL. It exhibits excellent low-temperature rheological properties, with an apparent viscosity of 35 mPas at -25°C, a plastic viscosity of 30 mPas, and a dynamic shear stress of 5.11 Pa. Its overall performance is well-balanced, making it suitable for open-hole freezing operations under complex formation conditions.

[0053] Comparative Example 1: This comparative example uses a conventional low-temperature drilling fluid (without sufficient filtration reducer and optimized viscosity-enhancing system), the specific components of which are not fully disclosed. Within the test temperature range, this drilling fluid has an apparent viscosity of 18 mPas, a plastic viscosity of 11 mPas, and a filtration loss of 5.4 mL at 30°C. As the temperature decreases to -25°C, the apparent viscosity increases to 48 mPas, and the plastic viscosity reaches 22 mPas, but the filtration loss decreases to 3.0 mL. However, this system lacks effective filtration loss control at high temperatures (such as around 36°C) and does not demonstrate the wide-temperature-range rheological stability design required for open-hole freezing processes. In particular, it lacks dynamic shear strength in the room temperature to medium-low temperature range, making it difficult to simultaneously achieve the dual functions of drilling wall protection and coolant flow.

[0054] Comparative Example 2 uses another existing low-temperature drilling fluid formulation (also not including the composite filtration loss reduction system and specific electrolyte ratio of this invention), and its component details are not disclosed. Test results show that the drilling fluid has an apparent viscosity of 16 mPas and a plastic viscosity of 10 mPas at 30°C, with a filtration loss of 5.2 mL; when cooled to -25°C, the apparent viscosity increases to 44 mPas, the plastic viscosity is 18 mPas, and the filtration loss is 2.4 mL. Although its low-temperature filtration loss is low, the overall rheological parameters increase too slowly, and the dynamic shear force is significantly low at -25°C, failing to form effective suspension and cuttings carrying capacity. Furthermore, the high-temperature filtration loss control is not specifically optimized according to the open hole freezing requirements, making it difficult to meet the requirements for consistent performance across all temperature conditions in actual engineering.

[0055] The details are shown in the table below:

[0056]

[0057] Table 1. Variation of drilling fluid parameters under various temperature gradients.

[0058] Analysis of the data from Examples 2-6 and Comparative Examples 1-2 reveals that existing low-temperature solids-free drilling fluids have shortcomings in their performance values, failing to meet the performance requirements of drilling fluids for open-hole freezing technology. In particular, the lack of data on funnel viscosity makes it impossible to provide a reference for formation drilling. Furthermore, compared to existing drilling fluid formulations, the developed low-temperature solids-free drilling fluid for open-hole freezing exhibits higher viscosity characteristics and a higher dynamic-plasticity ratio, resulting in better shear-thinning ability. This means that the viscosity decreases further under high shear conditions while maintaining sufficient shear force in the annulus. Additionally, the low-temperature resistant base fluid used in the examples is simple, consisting of only two salt mixtures, while the low-temperature resistant base fluid used in the comparative examples comprises three complex alcohols and salts. Therefore, the examples demonstrate stronger engineering applicability.

[0059] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for evaluating and optimizing drilling fluid performance for open hole freezing, characterized in that: include: Based on the formation temperature environment during open-hole freezing construction, the required temperature range for the drilling fluid is determined, and multiple temperature test points are selected, including at least 36℃, 10℃, -4℃, -10℃, -15℃, -20℃, and -25℃. At each of the aforementioned temperature test points, the funnel viscosity, apparent viscosity, plastic viscosity, dynamic shear force of the candidate drilling fluid samples were measured, and the API filtration loss at the highest and lowest temperatures was also measured. Based on the technical requirements of the open hole freezing process for maintaining wellbore stability during the drilling stage and maintaining effective coolant flow during the freezing stage, performance qualification standards are set, including API filtration loss not exceeding 20 mL at 36℃, API filtration loss not exceeding 10 mL at -25℃, funnel viscosity not exceeding 91 seconds, and dynamic shear force not less than 4 Pa. The measured performance parameters are compared with the qualified standards. If any parameter is not met at any temperature point, the candidate drilling fluid is determined to be unsuitable. Adjust the drilling fluid composition ratio according to the type of performance defect, and return to the measurement step for iterative verification until all qualification criteria are met to obtain an optimized formula.

2. The method for evaluating and optimizing drilling fluid performance for open hole freezing as described in claim 1, characterized in that: The candidate drilling fluid is a water-based, solids-free system containing water, calcium chloride, sodium chloride, polyacrylamide, thickener, filtration reducer, and lubricant.

3. The method for evaluating and optimizing drilling fluid performance for open hole freezing as described in claim 2, characterized in that: The polyacrylamide is a cationic polyacrylamide or anionic partially hydrolyzed polyacrylamide, and the lubricant is polyether polyol PPG-400.

4. The method for evaluating and optimizing drilling fluid performance for open hole freezing as described in claim 1, characterized in that: The adjustment of the drilling fluid composition ratio includes: When the filtration loss exceeds the standard at high temperature, increase the dosage of the filtration loss reducing agent; When the rheological properties are insufficient at low temperatures, increase the total amount of calcium chloride and sodium chloride. When the viscosity is low at room temperature, increase the amount of thickener.

5. The method for evaluating and optimizing drilling fluid performance for open hole freezing as described in claim 1, characterized in that: The freezing point of the drilling fluid should not be higher than -28℃. If the actual freezing point is higher than -28℃, the amount of calcium chloride or a mixture of calcium chloride and sodium chloride should be increased when adjusting the composition ratio.

6. The method for evaluating and optimizing drilling fluid performance for open hole freezing as described in claim 1, characterized in that: The API filtration loss was determined according to GB / T16783.1 standard, the funnel viscosity was determined according to SY / T5677 standard, and the apparent viscosity, plastic viscosity and dynamic shear force were determined according to SY / T5621 standard.

7. The method for evaluating and optimizing drilling fluid performance for open hole freezing as described in claim 1, characterized in that: The method is applied to the open-hole freezing construction in mine shaft and tunnel construction projects, and the construction does not require the lowering of freezing pipes.

8. The method for evaluating and optimizing drilling fluid performance for open hole freezing as described in claim 1, characterized in that: The geological formations traversed by the mine shaft and tunnel construction project include water-sensitive mudstone, shallow loose sand layers or fractured rock layers, and hard rock formations.

9. The method for evaluating and optimizing drilling fluid performance for open hole freezing as described in claim 1, characterized in that: At -25°C, the apparent viscosity of the drilling fluid is not less than 23 mPas, and the plastic viscosity is not less than 19 mPas.

10. The method for evaluating and optimizing drilling fluid performance for open hole freezing as described in claim 1, characterized in that: The optimized formulation maintained non-Newtonian fluid properties at all temperature test points, with a funnel viscosity of 2022 seconds at 36°C and 6091 seconds at -25°C.

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