Hydroxyl polymer filtrate reducer for high-temperature-resistant and high-salt-resistant drilling fluid and preparation method of hydroxyl polymer filtrate reducer

Abstract

The invention provides a high-temperature-resistant and high-salt-resistant hydroxyl polymer filtrate reducer for drilling fluid and a preparation method of the hydroxyl polymer filtrate reducer, and belongs to the technical field of petroleum drilling fluid chemical additives. During preparation, firstly, hydroxyl polymer monomers (containing acrylamide, 2-acrylamide-2-methylpropanesulfonic acid and the like) and a solvent in a specific proportion are mixed and stirred to be dissolved at the temperature of 30-40 DEG C, the pH is adjusted to 6.0-9.0, and then the hydroxyl polymer filtrate reducer is prepared; and adding a cross-linking agent N, N '-methylene bisacrylamide, adding an initiator under the protection of nitrogen at 50-80 DEG C, polymerizing for 3-5 hours, subsequently drying at 80-100 DEG C (the water content is less than or equal to 12.0%), crushing, and sieving with a 80-120-mesh sieve to obtain the product. The product is free-flowing powder or particles, has excellent high-temperature and high-salt resistance, can effectively control the filter loss of the drilling fluid, is environment-friendly, has small damage to oil and gas reservoirs, and is suitable for complex drilling working conditions such as deep wells and the like.

Description

Technical Field

[0001] This invention relates to the field of petroleum drilling fluid chemical additives, specifically to a high-temperature and high-salt resistant hydroxyl polymer filtration reducer for drilling fluids and its preparation method. Background Technology

[0002] In oil drilling engineering, the filtration performance of drilling fluids directly affects drilling safety, construction efficiency, and the protection effect of oil and gas reservoirs. When drilling encounters deep wells, ultra-deep wells (bottom hole temperature ≥150℃), or high-salt formations (formation water salinity ≥30000mg / L), traditional drilling fluid filtration reducers often face the following technical bottlenecks:

[0003] Insufficient high-temperature resistance: Traditional hydroxyl polymer filtration reducers are prone to thermal and oxidative aging at temperatures above 150°C, leading to molecular chain breakage and decreased hydration capacity, which in turn causes a sharp increase in drilling fluid filtration loss (e.g., API filtration loss > 20 mL), failing to meet the requirements for controlling drilling fluid water loss.

[0004] Poor salt resistance: In high-salt environments (such as salt water with a concentration of 4% or higher), salt ions will damage the hydration membrane of polymer molecules, leading to polymer flocculation, weakened adsorption capacity, increased filter cake porosity, increased permeability, thickened filter cake (>3mm) and poor toughness, making it easy for filter cake to stick and get stuck in the drill.

[0005] Reservoir damage and environmental issues: Some filtration loss reducers (such as compound products containing heavy metals such as chromium and lead) or non-biodegradable synthetic polymers can clog the pores of oil and gas reservoirs and pollute the environment after discharge, which does not meet the industry requirements of green drilling.

[0006] To address this, a hydroxyl polymer filtration reducer for drilling fluids resistant to high temperatures and high salinity is proposed, along with its preparation method. Summary of the Invention

[0007] The present invention aims to solve the problems mentioned in the background art by providing a high-temperature and high-salt resistant hydroxyl polymer filtration reducer for drilling fluids and its preparation method.

[0008] The specific technical solution is as follows:

[0009] A method for preparing a high-temperature, high-salt resistant hydroxyl polymer filtration reducer for drilling fluids includes the following steps:

[0010] (1) Mixing and dissolving raw materials: Weigh the hydroxyl polymer monomer and solvent and add them to the reaction vessel. Stir at 30-40℃ for 20-30 min until completely dissolved to obtain a monomer solution. The hydroxyl polymer monomer is composed of the following components in the indicated mass percentages: Acrylamide (AM): 42%-48%; 2-Acrylamide-2-methylpropanesulfonic acid (AMPS): 28%-33%; Acrylic acid (AA): 9%-12%; N-vinylpyrrolidone (NVP): 7%-10%; Hydroxyethyl acrylate (HEA): 4%-7%.

[0011] (2) pH adjustment: Add an acid or base adjuster to the monomer solution to adjust the pH value of the solution to 6.0-9.0;

[0012] (3) Add crosslinking agent: Add crosslinking agent to the monomer solution after pH adjustment and stir to disperse it evenly; the crosslinking agent is N,N'-methylenebisacrylamide, and the amount added is 0.08% to 0.6% of the total mass of the hydroxyl polymer monomer;

[0013] (4) Polymerization reaction: Add an initiator to the solution and carry out the polymerization reaction at 50-80℃ under nitrogen protection for 3-5 hours to obtain a gel-like hydroxy polymer; the initiator is a water-soluble initiator selected from at least one of ammonium persulfate and potassium persulfate, and the amount added is 0.5%-2.0% of the total mass of the hydroxy polymer monomers;

[0014] (5) Drying treatment: The gel-like hydroxy polymer is placed in a drying device and dried at 80-100℃ for 4-6 hours, and the moisture content of the dried product is controlled to be ≤12.0%.

[0015] (6) Crushing and molding: The dried product is crushed by crushing equipment and passed through an 80-120 mesh sieve to obtain free-flowing powder or granular products.

[0016] The technical advantage of this preparation method lies in the synergistic achievement of superior overall performance of the final product through precisely controlled monomer combinations and ordered chemical reaction steps. Specific hydroxyl monomers provide strong adsorption and hydration groups; sulfonic acid monomers ensure the stretching stability of the polymer chains in the electrolyte environment; and lactam monomers endow the molecular chains with excellent resistance to thermal degradation. By first dissolving and adjusting the pH before adding the crosslinking agent, the reaction system is ensured to crosslink under optimal conditions, thereby generating a polymer gel with a moderate molecular weight and a stable three-dimensional network structure. The entire process design is scientific and highly reproducible, providing a fundamental guarantee for producing filtration loss reduction agents with consistent performance.

[0017] The above-mentioned method for preparing a high-temperature and high-salt resistant drilling fluid hydroxy polymer filtration reducer, wherein the solvent in step (1) is deionized water, and the mass ratio of the total mass of the hydroxy polymer monomer to the mass of deionized water is (30-50):(50-70).

[0018] This method optimizes the system concentration for the polymerization reaction by limiting the specific ratio of monomer to water. This ratio ensures that the monomer is fully dissolved in water, possessing sufficient fluidity, while maintaining a sufficiently high concentration. This allows the polymerization reaction to proceed efficiently, facilitating smooth molecular chain growth and ultimately yielding a polymer with the desired molecular weight. Concentrations that are too high or too low will affect the kinetics of the polymerization reaction and the properties of the product; this ratio is a critical process window for achieving efficient polymerization and the desired product form.

[0019] The above-mentioned method for preparing a high-temperature and high-salt resistant hydroxyl polymer filtration reducer for drilling fluids, wherein the nitrogen purity of the nitrogen gas used for nitrogen protection in step (4) is ≥99.9%, and the protection time extends throughout the entire polymerization reaction stage.

[0020] This method emphasizes that the polymerization reaction is carried out under an inert gas atmosphere. Its technical advantage lies in completely eliminating the inhibitory and chain-terminating effects of oxygen on free radical polymerization. Oxygen is a major inhibitor of free radical reactions, consuming initiators and causing premature chain termination, resulting in low-molecular-weight products and affecting product performance. Using high-purity nitrogen gas throughout the entire process creates an oxygen-free, inert environment for the polymerization reaction, ensuring initiation efficiency and allowing the polymerization reaction to proceed more completely and thoroughly, ultimately yielding high-molecular-weight, high-performance polymers.

[0021] The above-mentioned method for preparing a high-temperature and high-salt resistant drilling fluid hydroxy polymer filtration reducer, wherein the acid regulator in step (2) is a 5% hydrochloric acid solution and the alkali regulator is a 5% sodium hydroxide solution.

[0022] This method specifies the types and concentrations of acids and bases used for pH adjustment. Its technical advantage lies in providing a gentle yet precise means of pH control. Using low-concentration acid and base solutions avoids problems such as monomer (e.g., acrylamide) hydrolysis, crosslinking agent failure, or molecular chain breakage caused by localized over-acidity or over-alkaliness. This gentle adjustment method can smoothly and precisely control the system pH within the preset optimal range, creating a stable and reliable reaction environment for the subsequent addition of crosslinking agents and initiators, thus ensuring the quality stability of the polymerization product.

[0023] The present invention also provides a high-temperature and high-salt resistant hydroxyl polymer filtration reducer for drilling fluid, which is prepared by the above-mentioned preparation method of the high-temperature and high-salt resistant hydroxyl polymer filtration reducer for drilling fluid; the main finished product of the filtration reducer is a hydroxyl polymer, which appears as a free-flowing powder or granules, has a moisture content ≤12.0%, and a pH value of 6.0-9.0.

[0024] This scheme defines the product itself and its basic physical properties prepared by the method. Its technical advantage lies in directly reflecting the excellent physical state and intrinsic quality of the final product. The product is a free-flowing powder or granules, indicating good solubility and ease of field application. Strictly controlled low moisture content ensures product stability during storage, preventing clumping and degradation. A neutral pH range ensures good compatibility with various drilling fluid systems, without drastically affecting the overall acidity or alkalinity of the drilling fluid system.

[0025] The aforementioned high-temperature and high-salt resistant hydroxyl polymer filtration reducer for drilling fluids has an API filtration loss of ≤12.0 mL in freshwater drilling fluid and ≤12.0 mL in 4% saline drilling fluid.

[0026] This solution describes the product's conventional performance in both freshwater and brine drilling fluids. Its technical effectiveness lies in demonstrating that this filtration loss reducer possesses broad-spectrum and highly efficient filtration loss control capabilities. It not only effectively seals filter cake pores in freshwater through hydration and adsorption bridging, but also maintains polymer chain extension and sealing efficiency in high-ionic-strength brine environments thanks to the strong anti-salting properties of its anionic sulfonic acid groups, exhibiting excellent resistance to salt precipitation and making it suitable for various water quality preparation environments.

[0027] The aforementioned high-temperature and high-salt resistant hydroxyl polymer filtration reducer for drilling fluids, wherein after being aged at 180°C for 16 hours in saturated brine drilling fluid, the API filtration loss can still be controlled below 12.0 mL.

[0028] This scheme describes the product's performance under extremely harsh conditions. Its technical effectiveness lies in highlighting the excellent synergistic stability of the filtration loss reducer against high temperatures and salt. Under the dual severe tests of extremely high concentrations of brine and prolonged high-temperature aging, the rigid ring structure and strong hydration groups in the product's molecular chain effectively inhibit the coiling, breakage, and degradation of the molecular chain, thereby maintaining its core filtration loss reduction function. This demonstrates its suitability for high-temperature and high-salinity formations in deep and ultra-deep well drilling.

[0029] Because of its excellent salt resistance (regulated by the salt-resistant components in the monomer), the product can still function stably in saturated brine drilling fluid; and its excellent thermal stability means that the molecular structure of the hydroxyl polymer is not easily damaged after high-temperature aging, and it can still effectively control the filtration loss of drilling fluid. It is suitable for drilling scenarios with high salt, high temperature and long-term operation, and ensures the continuous stability of drilling fluid filtration performance.

[0030] It is worth noting that in saturated brine drilling fluid systems (mineralization ≥ 300,000 mg / L, saturated solution containing NaCl), this filtration loss reducer exhibits excellent salt resistance, with specific parameters as follows:

[0031] Under normal temperature (25℃) conditions, the API filtration loss of saturated salt cement slurry prepared with a 2% addition is ≤10mL (30min, 0.7MPa);

[0032] After being aged at 180℃ for 16 hours, the API filtration loss of saturated salt cement slurry can still be controlled at ≤12mL, with an increase in filtration loss of ≤15% (compared to data before aging).

[0033] Significant resistance to calcium contamination, even in environments containing 5000 ppm Ca. 2+ In saturated brine, the API filtration loss is ≤12mL, demonstrating good multi-ion stability.

[0034] The aforementioned high-temperature and high-salt resistant hydroxyl polymer filtration reducer for drilling fluids is characterized by its ability to adhere to the surface of clay particles in the drilling fluid and form a hydration film to improve the dispersion of clay particles. The resulting filter cake has the characteristics of low porosity, low permeability, and low friction coefficient.

[0035] This solution reveals the product's mechanism of action. Its technical effect lies in demonstrating that this filtration reducer optimizes filter cake quality by improving the colloidal stability of drilling fluid. Polymer molecules encapsulate clay particles through adsorption, forming a dense hydration layer. This increases the electrostatic repulsion and steric hindrance between particles, thereby preventing particle aggregation and maintaining excellent dispersion in the drilling fluid. These highly dispersed fine particles ultimately form an extremely thin, dense, tough, and very low-permeability filter cake, effectively sealing formation pores, reducing filtrate intrusion, and exhibiting a low coefficient of friction due to its smooth surface.

[0036] The aforementioned high-temperature and high-salt resistant hydroxyl polymer filtration reducer for drilling fluids has minimal damage to oil and gas reservoirs and is environmentally friendly, containing no harmful heavy metals or recalcitrant components.

[0037] This solution emphasizes the product's environmental compatibility. Its technical effectiveness demonstrates that the filtration reducer is environmentally friendly and causes minimal damage to oil and gas reservoirs. Its components do not contain any toxic heavy metals or persistent pollutants that are difficult to degrade naturally; it is readily biodegradable and meets increasingly stringent environmental regulations. Simultaneously, its highly effective plugging properties reduce the intrusion of filtrate into the producing formation, and its polymer molecules do not adversely react with formation fluids, thereby maximizing the protection of oil and gas reservoir permeability and improving well productivity.

[0038] The product manufacturing process does not introduce environmentally harmful heavy metals or recalcitrant components, and the hydroxyl polymer itself has a small blocking effect on oil and gas reservoirs, which can reduce damage to oil and gas reservoirs and ensure reservoir production capacity. At the same time, its characteristic of not containing harmful components makes it meet environmental protection requirements, avoids pollution to the environment after drilling fluid discharge, and takes into account both drilling function and environmental protection and reservoir protection needs.

[0039] Furthermore, the damage control effect of this filtration loss reducer on oil and gas reservoirs was quantitatively evaluated using the core permeability recovery rate. Experimental verification was conducted according to SY / T5358-2010 "Evaluation Method for Reservoir Sensitivity Flow Experiments": Under simulated formation temperature (150-180℃) and pressure conditions, displacement experiments were performed using natural core samples with a diameter of 2.5cm and a length of 4-6cm. The core permeability recovery rate was measured to be ≥90%, corresponding to a permeability damage rate ≤10%. This indicator is significantly superior to traditional sulfonated phenolic resin filtration loss reducers (permeability recovery rate is typically ≤60%), indicating that it can effectively reduce the blockage of reservoir pores by drilling fluid filtrate and solid particles, thus reducing damage to oil and gas migration pathways.

[0040] The aforementioned high-temperature and high-salt resistant drilling fluid hydroxyl polymer filtration reducer has an intrinsic viscosity of 8.5-12.5 dL / g (measured in 1 mol / L NaCl aqueous solution at 30 ± 0.5 °C).

[0041] This method indirectly defines the molecular weight range of the polymer by limiting its intrinsic viscosity. The technical advantage lies in ensuring that the product has optimal hydrodynamic volume and viscosity-enhancing and pore-clogging efficiency. An intrinsic viscosity within this specific range indicates that the polymer has sufficiently long molecular chains to effectively bridge multiple clay particles and form a stable spatial network structure, thereby significantly improving the viscosity and shear strength of the drilling fluid and enhancing its ability to seal the filter cake. If the molecular weight is too low, the clogging effect will be insufficient; if it is too high, it may lead to dissolution difficulties or excessive viscosity enhancement. This range is the ideal range for achieving the best application results.

[0042] The aforementioned high-temperature and high-salt resistant hydroxyl polymer filtration reducer for drilling fluids, wherein the filtration reducer, after being subjected to hot rolling aging at 180°C for 16 hours in a 4% brine slurry containing 1.5% by weight of the product, exhibits a high-temperature and high-pressure filtration loss of ≤25.0 mL under conditions of 3.5 MPa and 150°C.

[0043] This method simulates extreme downhole conditions (high temperature, high pressure, brine) to test product performance. Its technical effectiveness lies in fully verifying the reliability and practicality of the filtration loss reducer under real drilling environments. High-temperature, high-pressure filtration loss is one of the most critical indicators for evaluating the performance of a filtration loss reducer. Even after prolonged high-temperature aging, this product can still effectively control filtration loss under the combined effects of high temperature and high pressure, demonstrating its exceptional thermal and mechanical stability of its molecular structure. This provides crucial technical support for safe and efficient drilling in deep, complex formations, significantly reducing the risks associated with complex downhole conditions.

[0044] The present invention has the following beneficial effects:

[0045] (I) Significantly improved resistance to high temperature and high salinity

[0046] High-temperature resistance: Based on the thermally stable structure of NVP monomers and the complete polymerization reaction under nitrogen protection, the product can maintain molecular chain stability in extreme high-temperature environments (such as high-temperature formations in ultra-deep wells), avoid thermal and oxygen aging, and still maintain the core filtration loss reduction function after long-term high-temperature aging, meeting the high-temperature working conditions of deep wells, ultra-deep wells and geothermal wells.

[0047] Salt resistance: Relying on the anti-salting ability of the sulfonic acid groups of AMPS monomers and the stability of the three-dimensional network structure, the product can still maintain the extension of molecular chains and the dispersibility of clay particles in high-salt (such as saturated brine) and high calcium and magnesium ion environments, avoiding polymer flocculation and filter cake porosity. It is suitable for drilling in complex salt environments such as salt gypsum layers and saline water layers.

[0048] (ii) Stable and reliable filtration loss control performance

[0049] Broad-spectrum filtration loss control: Through the formation of dense filter cake and the stabilization mechanism of clay particles, the product can effectively control filtration loss in fresh water, salt water and saturated salt water drilling fluids. The filter cake is thin and tough with low permeability, which can reduce the intrusion of filtrate into the formation, ensure the stability of drilling fluid performance, and reduce the risks of wellbore instability and reservoir damage caused by excessive filtration loss.

[0050] Extreme operating conditions ensure filtration loss control: Under the combined effects of high temperature and high pressure (such as high temperature aging followed by high pressure environment), the three-dimensional network structure and hydration film can still maintain stability, ensuring the filtration loss control effect and providing safety assurance for drilling in deep and complex formations.

[0051] (III) Outstanding environmental protection and reservoir protection characteristics

[0052] Green and environmentally friendly: The preparation process does not introduce heavy metals or difficult-to-biodegrade components. The product itself is easy to biodegrade, which meets the requirements of the green drilling industry, avoids pollution to the environment after drilling fluid is discharged, and reduces environmental treatment costs.

[0053] Minimal reservoir damage: On the one hand, efficient filtration control reduces the intrusion of filtrate into the oil and gas reservoir; on the other hand, polymer molecules do not react adversely with formation fluids and have a weak effect on blocking reservoir pores, which can effectively protect the permeability of oil and gas reservoirs and improve the productivity of oil and gas wells, which is superior to the reservoir protection effect of traditional sulfonated phenolic resin filtration reducers.

[0054] (iv) Product usability and process reliability

[0055] Ease of use: Free-flowing powder / granule form, good solubility and broad compatibility reduce the difficulty of on-site use, reduce drilling fluid system adjustment steps, and improve construction efficiency; low moisture content ensures product storage stability, avoids clumping and degradation, and extends the storage period.

[0056] Process controllability: The preparation process ensures batch-to-batch performance consistency by precisely controlling monomer ratio, polymerization temperature (50-80℃), reaction time (3-5h), and drying conditions (80-100℃, 4-6h); mild pH adjustment and nitrogen protection processes reduce reaction risks and improve the stability and safety of industrial production, providing a guarantee for large-scale applications. Attached Figure Description

[0057] Figure 1 A flowchart illustrating the preparation method of a high-temperature and high-salt resistant hydroxyl polymer filtration reducer for drilling fluids provided in this embodiment of the invention;

[0058] Figure 2 This is a graph comparing the API filtering loss of different embodiments of the present invention. Detailed Implementation

[0059] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0060] The accompanying drawings are for illustrative purposes only and are schematic diagrams, not actual images. They should not be construed as limiting the scope of this application. To better illustrate the embodiments of the present invention, some parts in the drawings may be omitted, enlarged, or reduced, and do not represent the actual dimensions of the product. It is understandable to those skilled in the art that some well-known structures and their descriptions may be omitted in the drawings.

[0061] In the accompanying drawings of the embodiments of the present invention, the same or similar reference numerals correspond to the same or similar components. In the description of the present invention, it should be understood that if terms such as "upper," "lower," "left," "right," "inner," and "outer" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, they are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, the terms used to describe positional relationships in the drawings are only for illustrative purposes and should not be construed as limiting the present application. For those skilled in the art, the specific meaning of the above terms can be understood according to the specific circumstances.

[0062] In the description of this invention, unless otherwise explicitly specified and limited, the term "connection" or similar designation indicating a connection between components should be interpreted broadly. For example, it can refer to a fixed connection, a detachable connection, or an integral part; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium; it can refer to the internal communication between two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0063] Example 1: Standard Formulation Example

[0064] 1. Preparation steps (refer to...) Figure 1 ):

[0065] The monomers are weighed according to their mass percentages: AM (45%), AMPS (30%), AA (10%), NVP (8%), and HEA (7%). The total mass of the monomers is 50% of the mass of the deionized water.

[0066] The monomer and deionized water were added to the reaction vessel and stirred at 35°C to dissolve.

[0067] Adjust the pH of the system to 7.0 using a 5% NaOH solution.

[0068] Add 0.1% N,N'-methylenebisacrylamide by mass of the total monomers and stir to dissolve.

[0069] High-purity nitrogen gas was introduced to remove oxygen for 30 minutes, and protection was maintained.

[0070] Add 1.0% of ammonium persulfate by mass of the monomers, heat to 65°C and react for 4 hours to obtain an elastic gel.

[0071] The gel was dried at 95°C for 5 hours, then pulverized and passed through a 100-mesh sieve to obtain a white powder product.

[0072] 2. Working principle:

[0073] This formulation features a balanced design. AM serves as the foundation of the main chain; AMPS provides strong hydrophilicity and sulfonic acid groups to resist calcium and magnesium ion contamination; AA is partially ionized at neutral pH, providing electrostatic repulsion and hydration capabilities; the rigid ring structure of NVP is embedded in the polymer chain, effectively enhancing chain rigidity and resisting molecular chain curling and breakage caused by thermal motion; the hydroxyl groups of HEA further enhance the overall hydration capability of the molecule. A moderate degree of crosslinking forms a three-dimensional network structure that can fully extend in solution, encapsulating and bridging solid particles in the drilling fluid.

[0074] 3. Technical effects:

[0075] This product dissolves rapidly in both freshwater and saltwater drilling fluids and significantly reduces filtration loss.

[0076] The resulting filter cake is thin, tough, and highly dense, effectively sealing micropores in the formation.

[0077] The product exhibits excellent thermal stability, maintaining its network structure and hydration layer even after high-temperature aging, with minimal performance degradation.

[0078] Its overall performance is well-balanced, making it suitable for most medium- and high-temperature complex geological environments.

[0079] 4. Experimental Data Table:

[0080]

[0081] Example 2: High Salt Resistance Focus Example

[0082] 1. Preparation steps:

[0083] Adjusted monomer ratio: AM (42%), AMPS (33%), AA (12%), NVP (8%), HEA (5%).

[0084] The process parameters are the same as in Example 1, but the amount of crosslinking agent is increased to 0.2% of the total monomer mass.

[0085] 2. Working principle:

[0086] This formulation significantly increases the ratio of AMPS to AA. The sulfonic acid groups (-SO3H) of AMPS are completely ionized in high-concentration brine and have strong hydration capabilities; the ions are not easily compressed, allowing the polymer chains to remain extended rather than coiled up in a high-ionic-strength environment. The increase in AA further enhances the polymer's hydration capabilities and anionic properties. A slightly increased degree of crosslinking makes the network structure more robust, resisting the damage to the spatial network caused by the charge neutralization effect of salt ions.

[0087] 3. Technical effects:

[0088] The product's resistance to salt and calcium and magnesium ion contamination has been greatly enhanced.

[0089] In drilling fluid systems with ultra-high salinity, its retention rate of filtration loss reduction performance is far superior to that of ordinary products.

[0090] It is particularly suitable for drilling salt deposits, brackish water layers, or operating environments where seawater or brine is used to prepare the slurry.

[0091] 4. Experimental Data Table:

[0092]

[0093] Example 3: Ultra-high temperature focused example

[0094] 1. Preparation steps:

[0095] Adjusted monomer ratio: AM (48%), AMPS (28%), AA (9%), NVP (10%), HEA (5%).

[0096] The initiator was replaced with potassium persulfate, at a dosage of 1.5% of the total monomer mass.

[0097] The polymerization reaction temperature was increased to 75°C.

[0098] The other steps are the same as in Example 1.

[0099] 2. Working principle:

[0100] This formulation significantly increases the NVP content. The lactam ring of NVP exhibits extremely high thermal stability, and its large steric hindrance effect physically hinders molecular chain movement and protects the main chain C-C bonds from thermal attack. Increasing the polymerization temperature helps to generate polymers with higher molecular weights and greater stability. Potassium persulfate decomposes more smoothly at higher temperatures, which is beneficial for forming a well-ordered polymer network. This makes the entire molecular chain less prone to depolymerization and degradation under ultra-high temperature conditions.

[0101] 3. Technical effects:

[0102] The product's high-temperature resistance has been significantly improved, and its thermal stability window is wider.

[0103] It can work effectively for a long time in the extremely high temperature environment encountered in ultra-deep well drilling, and has a long performance life.

[0104] It is suitable for extreme high-temperature conditions such as geothermal wells and ultra-deep oil and gas wells.

[0105] 4. Experimental Data Table:

[0106] Performance indicators Test conditions result API filtration loss (mL) In freshwater-based slurry, aged at 200℃ for 16 hours. ≤12.0 API filtration loss (mL) The mixture was aged at 200°C for 16 hours in a 4% brine slurry. ≤12.5 HTHP filtration loss (mL) In 4% saline slurry, at 180℃ and 3.5MPa ≤25.0

[0107] Example 4: Low crosslinking degree thickening example

[0108] 1. Preparation steps:

[0109] The monomer ratio is the same as in Example 1.

[0110] Reduce the amount of crosslinking agent to 0.08% of the total monomer mass.

[0111] The other steps are the same as in Example 1.

[0112] 2. Working principle:

[0113] Extremely low crosslinking agent dosage means a reduced tendency for intramolecular crosslinking between polymer chains, making it easier to generate polymers with higher linearity and larger molecular weight. These polymers have a larger hydrodynamic volume in solution, which can more effectively improve the viscosity and dynamic shear force of drilling fluid through bridging and coating effects, while sealing filter cake pores by forming a denser network structure.

[0114] 3. Technical effects:

[0115] While effectively reducing filtration loss, the product also possesses excellent thickening and rock-carrying capabilities.

[0116] One agent has multiple effects, which can reduce the amount of viscosifier used in drilling fluid systems and simplify the formulation.

[0117] It is suitable for loose formations that require a strong colloidal system and helps stabilize the wellbore.

[0118] 4. Experimental Data Table:

[0119] Performance indicators Test conditions result API filtration loss (mL) In freshwater-based slurry ≤9.0 Apparent viscosity (mPa·s) Add 1.0% to the freshwater-based slurry. greatly improve Dynamic shear force (Pa) Add 1.0% to the freshwater-based slurry. greatly improve

[0120] Example 5: Low-Temperature Oxidation-Reduction Initiation Example

[0121] 1. Preparation steps:

[0122] The monomer ratio is the same as in Example 1.

[0123] After adjusting the pH and adding a crosslinking agent, the system temperature was lowered to 40°C.

[0124] A redox initiation system consisting of ammonium persulfate (0.8% by mass of total monomers) and sodium bisulfite (0.8% by mass) was added.

[0125] The reaction was carried out at 40°C for 5 hours, and the subsequent steps were the same as in Example 1.

[0126] 2. Working principle:

[0127] Redox initiation systems can efficiently generate free radicals at low temperatures, thereby initiating polymerization at lower temperatures. Low-temperature polymerization helps control the reaction rate, reduces burst polymerization, and results in a more concentrated molecular weight distribution and a more regular polymer chain structure. This more uniform structure helps improve the final performance and batch stability of the product.

[0128] 3. Technical effects:

[0129] The polymerization reaction conditions are mild, energy consumption is lower, and the production process is safer and more controllable.

[0130] The resulting product has a narrower molecular weight distribution and may exhibit superior and more stable performance.

[0131] It is suitable for industrial production with high requirements for energy consumption and reaction control.

[0132] 4. Experimental Data Table:

[0133] Performance indicators Test conditions result API filtration loss (mL) In 4% saline slurry ≤9.5 API filtration loss (mL) In saturated brine slurry, aged at 180℃ for 16 hours. ≤11.0 Intrinsic viscosity (dL / g) 1 mol / L NaCl, 30℃ At a high level

[0134] It is worth noting that the filtration control performance of this high-temperature and high-salt resistant hydroxyl polymer drilling fluid filtration reducer in high-temperature and high-salt environments can be predicted by the following formula:

[0135]

[0136] in:

[0137] FL represents the predicted filtration loss (mL);

[0138] FL0 is the baseline filtration loss (mL), with a value of 12.0;

[0139] [η] is the intrinsic viscosity of the polymer (dL / g);

[0140] [η]0 is the intrinsic viscosity reference value, which is 10.0 dL / g;

[0141] S represents the mass concentration (%) of salt in the drilling fluid;

[0142] S0 is the baseline value for salt concentration, which is 4%.

[0143] T represents the ambient temperature (°C).

[0144] T0 is the temperature reference value, which is 150℃.

[0145] α, β, γ are material property constants, with values ​​of 1.2, 0.5, and 0.3, respectively.

[0146] Derivation process:

[0147] This equation is constructed based on the conformational changes, adsorption behavior, and filter cake formation mechanism of polymers under high temperature and high salt conditions, combined with Arrhenius-type temperature dependence and logarithmic salt concentration response function:

[0148] 1. Effect of intrinsic viscosity: Intrinsic viscosity [η] reflects the length of polymer molecular chains and hydrodynamic volume, and is positively correlated with filtration loss control capability. It is expressed as the normalized ratio [η] / [η]0.

[0149] 2. Effect of salt concentration: Increased salt concentration will compress the double layer and weaken the polymer's hydration ability. The nonlinear inhibition effect is simulated using the form ln(1+S / S0).

[0150] 3. Temperature effect: High temperature accelerates molecular chain movement and hydrolysis reaction, reducing polymer stability. The degree of temperature deviation from the baseline value is represented by (T-T0) / T0 and placed in the denominator to reflect its negative impact.

[0151] 4. Comprehensive effect: The three factors are coupled together, and an exponential decay form is introduced to simulate the trend of filtration loss decreasing as polymer performance improves.

[0152] Example: If the intrinsic viscosity of a certain batch of products is [η] = 11.0 dL / g, and it is used in drilling fluid with a salt concentration of S = 6%, at a temperature of T = 180℃, substituting into the equation:

[0153]

[0154] The calculated FL≈9.8mL indicates that the filtration loss under these conditions is still less than 12.0mL, which meets the product performance requirements.

[0155] Parameter description table:

[0156] parameter meaning Values ​​or ranges FL Predicted filtration loss Dynamically calculated value <![CDATA[FL0]]> Reference filtration loss 12.0mL [η] The intrinsic viscosity of polymers 8.5–12.5 dL / g <![CDATA[[η]0]]> intrinsic viscosity reference value 10.0 dL / g S Mass concentration of salt in drilling fluid 0 – Saturated salt water <![CDATA[S0]]> Salt concentration benchmark value 4％ T Ambient temperature Room temperature to above 200°C <![CDATA[T0]]> Temperature reference value 150℃ α,β,γ Material property constants 1.2,0.5,0.3

[0157] Technical effects:

[0158] This equation couples the intrinsic properties of the polymer (intrinsic viscosity) with the external environment (salt concentration, temperature), quantifying the performance of the filtration loss reducer under extreme conditions. Its technical advantages are:

[0159] Highly predictive: It can predict fluid loss under different drilling fluid systems and downhole conditions, guiding field applications;

[0160] Optimized design: provides a theoretical basis for polymer molecular weight design and formulation optimization;

[0161] Performance verification: The description of the product's resistance to high temperature and high salt content was enhanced through mathematical means.

[0162] Working principle and process:

[0163] 1. Input parameters: Obtain the current environmental salt concentration S, temperature T, and product intrinsic viscosity [η];

[0164] 2. Calculate each factor: Calculate the intrinsic viscosity factor, salt concentration factor, and temperature factor separately;

[0165] 3. Comprehensive calculation: Substitute into the equation to calculate the predicted filtration loss FL;

[0166] 4. Performance evaluation: If FL ≤ 12.0 mL, the product is considered to be qualified under this condition;

[0167] 5. Feedback optimization: If the predicted value is too high, the polymer formula or construction parameters can be adjusted.

[0168] It is worth noting that, Figure 2 The horizontal axis represents the salt concentration gradient (fresh water → 4% saline → saturated saline → saturated saline + 1% CaCl2); the vertical axis represents the API filtration loss (mL).

[0169] Comparison of Examples:

[0170] Example 1 (Standard Formulation): Filtration loss increased steadily with increasing salt concentration.

[0171] Example 2 (High salt resistance): It still maintains ≤15mL in CaCl2 environment.

[0172] Example 3 (High Temperature Focus): The filtration loss at 200℃ is slightly higher than that in Example 1.

[0173] Example 4 (low crosslinking): The fresh water-based slurry performed best (≤9 mL).

[0174] Example 5 (low temperature initiation): showed equilibrium in 4% saline and saturated saline.

[0175] Technical effectiveness verification:

[0176] Example 2 showed a 50% increase in filtration loss in a complex salt environment (CaCl2), but still met industry standards.

[0177] Example 3 demonstrates that controllable filtration loss (≤12.5 mL) is maintained even at a high temperature of 200°C.

[0178] Example 4 achieves increased viscosity by reducing the degree of crosslinking, but sacrifices some salt resistance.

[0179] In summary, the working principle of the high-temperature and high-salt resistant hydroxyl polymer filtration reducer for drilling fluids provided in this embodiment is as follows:

[0180] (I) Functional Synergy of Monomer Components

[0181] 1. Main chain support and basic adsorption: Acrylamide (AM) serves as the core monomer, forming the polymer main chain and providing a stable molecular skeleton. At the same time, its amino groups have strong adsorption capacity, laying the foundation for subsequent bonding with clay particles.

[0182] 2. Enhanced salt resistance: The sulfonic acid groups contained in 2-acrylamide-2-methylpropanesulfonic acid (AMPS) can stably ionize in high-salt environments, and have strong hydration capabilities and are not easily compressed. This can effectively maintain the extended state of polymer molecular chains in high ionic strength environments, avoid molecular chain curling failure, and thus resist the damage of salt ions to polymer properties.

[0183] 3. Enhanced hydration and electrostatic repulsion: Acrylic acid (AA) is partially ionized under neutral pH conditions, which enhances the hydration capacity of the polymer on the one hand, and provides electrostatic repulsion on the other hand, reducing the aggregation of clay particles and maintaining the colloidal stability of drilling fluid.

[0184] 4. Core guarantee of high temperature resistance: The lactam ring structure of N-vinylpyrrolidone (NVP) has extremely high thermal stability. Its huge side group steric hindrance effect can physically hinder the thermal motion of molecular chains, protect the main chain C-C bonds from high temperature attack, inhibit molecular chain curling and breakage, and improve the overall high temperature resistance of the product.

[0185] 5. Enhanced hydration capacity: The hydroxyl groups in hydroxyethyl acrylate (HEA) further enhance the overall hydration capacity of the polymer molecules, helping to maintain the stable morphology of the molecular chains in complex environments.

[0186] (II) Stability Optimization of Polymer Structure

[0187] 1. Construction of a three-dimensional network structure: By adding N,N'-methylenebisacrylamide as a crosslinking agent, a stable three-dimensional network structure is formed during polymerization. This structure can fully extend in drilling fluid, enhancing the polymer's ability to encapsulate and bridge clay particles, and reducing filtrate permeation through the network pores.

[0188] 2. Precise control of the polymerization environment: Nitrogen protection (purity ≥99.9%, throughout the entire polymerization process) is used to eliminate the inhibition and chain termination effects of oxygen on free radical polymerization, ensuring a complete and thorough polymerization reaction and generating high molecular weight polymers with regular structures; pH is gently adjusted to 6.0-9.0 with 5% hydrochloric acid / sodium hydroxide solution to avoid monomer hydrolysis, crosslinking agent failure or molecular chain breakage, providing a stable environment for the polymerization reaction and ensuring product structural consistency.

[0189] (III) Mechanism of Filter Loss Control

[0190] 1. Clay particle dispersion and stabilization: Polymer molecules adhere to the surface of clay particles in the drilling fluid through adsorption, forming a dense hydration film, which improves the dispersion of clay particles and reduces particle aggregation. At the same time, the hydration film and electrostatic repulsion work together to maintain the stable suspension of clay particles in the drilling fluid, avoiding the increase of filter cake porosity due to particle sedimentation.

[0191] 2. Dense Filter Cake Formation: Highly dispersed clay particles and an extended polymer three-dimensional network work synergistically to form a thin, tough filter cake with low porosity and low permeability on the wellbore. This filter cake effectively seals formation pores, reduces drilling fluid filtrate intrusion into the formation, and the low friction coefficient of the filter cake surface reduces frictional resistance during drilling, minimizing downhole complications.

[0192] How to use

[0193] The fluid loss reducer of this invention is used as a chemical additive for drilling fluids. Its application method is designed based on the product's performance characteristics and drilling conditions, as detailed below:

[0194] (I) Applicable drilling fluid systems

[0195] Broad compatibility: It can be directly applied to freshwater drilling fluids, brine drilling fluids (such as 4% brine) and saturated brine drilling fluids without the need for formula adjustments for different water quality systems, and is suitable for a variety of slurry preparation environments.

[0196] Extreme working condition adaptation: Due to its excellent resistance to high temperature and high salinity, it is particularly suitable for drilling operations in deep wells, ultra-deep wells (high temperature environment at the bottom of the well), salt gypsum layers, saline water layers, and drilling operations using seawater / brine for mud preparation. It can cope with complex working conditions such as high formation water salinity and long-term high temperature aging.

[0197] (II) Method of addition and dosage

[0198] Addition method: The product is a free-flowing powder or granules (passing through an 80-120 mesh sieve). It has good solubility and can be directly mixed with drilling fluid-based slurry. No special pretreatment is required. It is easy to operate and suitable for on-site construction needs.

[0199] Dosage principle: Adjust the dosage according to the type of drilling fluid system and the requirements of the working conditions. The regular dosage can be controlled between 1.0% and 2.0% (by weight). For extreme high-salt (such as saturated brine) or high-temperature (such as ≥180℃) working conditions, the dosage can be adjusted appropriately to maintain the best filtration loss reduction effect. The specific dosage can be optimized based on the results of on-site drilling fluid performance monitoring.

[0200] (III) Precautions for use

[0201] Compatibility Guarantee: The product has a pH value of 6.0-9.0 and is well compatible with various conventional drilling fluid systems (such as water-based drilling fluids). Its addition will not cause drastic disturbance to the overall pH of the drilling fluid, and no additional pH adjustment is required.

[0202] Storage and pretreatment: The product moisture content is ≤12.0%, and it should be stored in a dry and ventilated environment to avoid moisture and clumping. If slight clumping occurs, it can be crushed and used normally without affecting the product performance.

[0203] Performance monitoring: During use, the effect can be evaluated in real time through conventional drilling fluid performance tests (such as filtration loss monitoring). If special formations are encountered (such as formations with high calcium and magnesium ions), the dosage can be finely adjusted in combination with the formation water composition to ensure stable filtration loss control.

[0204] The above are merely preferred embodiments of the present invention and are not intended to limit the implementation methods and protection scope of the present invention. Those skilled in the art should recognize that any equivalent substitutions and obvious changes made based on the description and illustrations of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a high-temperature, high-salt resistant hydroxyl polymer filtration reducer for drilling fluids, characterized in that, Includes the following steps: (1) Mixing and dissolving raw materials: Weigh the hydroxyl polymer monomer and solvent and add them to the reaction vessel. Stir at 30-40℃ for 20-30 min until completely dissolved to obtain a monomer solution. The hydroxyl polymer monomer is composed of the following components by mass percentage: acrylamide: 42%-48%; 2-acrylamide-2-methylpropanesulfonic acid: 28%-33%; acrylic acid: 9%-12%; N-vinylpyrrolidone: 7%-10%; hydroxyethyl acrylate: 4%-7%. (2) pH adjustment: Add an acid or base adjuster to the monomer solution to adjust the pH value of the solution to 6.0-9.0; (3) Add crosslinking agent: Add crosslinking agent to the monomer solution after pH adjustment and stir to disperse it evenly; the crosslinking agent is N,N'-methylenebisacrylamide, and the amount added is 0.08% to 0.6% of the total mass of the hydroxyl polymer monomer; (4) Polymerization reaction: Add an initiator to the solution and carry out the polymerization reaction at 50-80℃ under nitrogen protection for 3-5 hours to obtain a gel-like hydroxy polymer; the initiator is a water-soluble initiator selected from at least one of ammonium persulfate and potassium persulfate, and the amount added is 0.5%-2.0% of the total mass of the hydroxy polymer monomers; (5) Drying treatment: The gel-like hydroxy polymer is placed in a drying device and dried at 80-100℃ for 4-6 hours, and the moisture content of the dried product is controlled to be ≤12.0%. (6) Crushing and molding: The dried product is crushed by crushing equipment and passed through an 80-120 mesh sieve to obtain free-flowing powder or granular products.

2. The preparation method of the high-temperature and high-salt resistant hydroxyl polymer filtration reducer for drilling fluid according to claim 1, characterized in that, The solvent in step (1) is deionized water, and the mass ratio of the total mass of the hydroxyl polymer monomer to the mass of deionized water is (30-50):(50-70).

3. The preparation method of the high-temperature and high-salt resistant hydroxyl polymer filtration reducer for drilling fluids according to claim 1, characterized in that, The nitrogen purity of the nitrogen gas used for protection in step (4) is ≥99.9%, and the protection time lasts throughout the entire polymerization reaction stage.

4. The preparation method of the high-temperature and high-salt resistant hydroxyl polymer filtration reducer for drilling fluid according to claim 1, characterized in that, The acid regulator in step (2) is a 5% hydrochloric acid solution and the alkali regulator is a 5% sodium hydroxide solution.

5. A hydroxyl polymer filtration reducer for drilling fluids resistant to high temperatures and high salinity, characterized in that, The filtration loss reducer for drilling fluid with high temperature and high salt resistance is prepared by any one of the preparation methods of claims 1-4; the main finished product of the filtration loss reducer is a hydroxy polymer, which appears as a free-flowing powder or granules, has a moisture content of ≤12.0%, and a pH value of 6.0-9.

0.

6. The high-temperature and high-salt resistant hydroxyl polymer filtration reducer for drilling fluids according to claim 5, characterized in that, The API filtration loss of the filtration reducer is ≤12.0 mL in freshwater drilling fluid and ≤12.0 mL in 4% saline drilling fluid.

7. The high-temperature and high-salt resistant hydroxyl polymer filtration reducer for drilling fluids according to claim 5, characterized in that, Even after the filter loss reducer is aged at 180°C for 16 hours in saturated brine drilling fluid, the API filter loss can still be controlled below 12.0 mL.

8. The high-temperature and high-salt resistant hydroxyl polymer filtration reducer for drilling fluids according to claim 5, characterized in that, The filtration loss reducer can adhere to the surface of clay particles in the drilling fluid and form a hydration film to improve the dispersion of clay particles.

9. The high-temperature and high-salt resistant hydroxyl polymer filtration reducer for drilling fluids according to claim 5, characterized in that, The intrinsic viscosity of the hydroxyl polymer is 8.5-12.5 dL / g.

10. The high-temperature and high-salt resistant hydroxyl polymer filtration reducer for drilling fluids according to claim 5, characterized in that, The filtration loss reducer is prepared in a 4% brine slurry containing 1.5% by weight of the product at 180°C.

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