Filtrate reducer for oil-based drilling fluid, preparation method of filtrate reducer and oil-based drilling fluid

Abstract

The invention provides a filtrate reducer for an oil-based drilling fluid, a preparation method of the filtrate reducer and the oil-based drilling fluid, and the preparation method of the filtrate reducer for the oil-based drilling fluid comprises the following steps: uniformly mixing an oily medium and an emulsifier in proportion to obtain an oil phase; the preparation method comprises the following steps: dissolving an N-isopropylacrylamide monomer, an ionic monomer, a water-soluble cross-linking agent and an oxidant for initiation in water to obtain a water phase; mixing the water phase with the oil phase, stirring and emulsifying to obtain an emulsion 1; styrene is added into the emulsion 1, then a reducing agent for initiation is added under the protective atmosphere to initiate a polymerization reaction, and emulsion 2 is obtained after the reaction is completed; and adding long-chain alkyl quaternary ammonium salt into the emulsion 2, and carrying out ion exchange reaction to obtain the filtrate reducer. The filtrate reducer disclosed by the invention has good dispersion stability, deformability and expansibility in the oil-based drilling fluid, so that the filtrate reducer has good filtrate reduction performance.

Description

A filtration reducer for oil-based drilling fluids and its preparation method; oil-based drilling fluids Technical Field

[0001] This invention belongs to the field of oilfield drilling fluid loss reduction, specifically relating to a fluid loss reduction agent for oil-based drilling fluid and its preparation method, as well as oil-based drilling fluid. Background Technology

[0002] Oil-based drilling fluids possess advantages such as good high-temperature resistance, strong salt resistance, high lubricity, and minimal damage to oil and gas reservoirs, making them particularly advantageous in high-temperature shale reservoirs. However, the high cost of oil-based drilling fluids and the resulting loss or filtration during drilling are significant factors limiting their large-scale application. Filtration reducers, as key components in oil-based drilling fluid systems, form a filter cake under high-temperature and high-pressure downhole conditions, sealing fractures and thus reducing filtration loss. A wide variety of oil-based drilling fluid filtration reducers exist, including asphalt-based, cellulose-based, modified starch-based, humic acid-based, and synthetic polymer-based types. While research and development of oil-based drilling fluid filtration reducers has made some progress, reports on filtration reducers that combine good dispersibility in oil-based media, high-temperature resistance, lubricity, good rheological properties after high-temperature aging, and controllable cost are still limited due to the strong hydrophilicity of natural polymers and the environmental issues associated with asphalt-based filtration reducers. There is an urgent need to design and synthesize polymer-based filtration loss reducers that not only meet the dispersibility requirements of oily media, but also possess high-temperature resistance, lubrication properties, and do not cause significant thickening or stuck drill problems during construction. Summary of the Invention

[0003] The purpose of this invention is to provide a filtration loss reducer for oil-based drilling fluids and its preparation method. The filtration loss reducer contains gel particles with long-chain alkyl groups on their surface, exhibiting good lipophilicity and dispersion stability and deformability in oil-based drilling fluids. The poly(N-isopropylacrylamide) segments contained in the particles have high-temperature phase transition characteristics, which not only meet the needs of emulsion synthesis but also allow for phase transition at high temperatures in the application environment, changing from hydrophilic to lipophilic. Simultaneously, the hydrophilic ionic segments of the polymer can absorb water and swell in the oil-based drilling fluid. These characteristics endow the filtration loss reducer with a synergistic effect with other components in the drilling fluid base, forming a bridging effect to reduce filtration loss.

[0004] To achieve the above objectives, the present invention provides a method for preparing a filtration loss reducer for oil-based drilling fluids, comprising the following steps:

[0005] S1: Mix the oily medium and emulsifier evenly in a certain proportion to obtain the oil phase;

[0006] S2: Dissolve N-isopropylacrylamide monomer, ionic monomer, water-soluble crosslinking agent, and initiating oxidant in water, wherein the mass ratio of N-isopropylacrylamide monomer to ionic monomer is 16-21:0.2-5, to obtain an aqueous phase; then mix the aqueous phase with the oil phase obtained in S1, stir and emulsify to obtain emulsion 1;

[0007] S3: Add styrene to emulsion 1, with a mass ratio of styrene to total monomers of 4-6:16.2-26. Then, under a protective atmosphere, add a reducing agent to initiate the polymerization reaction. After the reaction is complete, emulsion 2 is obtained.

[0008] S4: Add long-chain alkyl quaternary ammonium salt to emulsion 2, with a mass ratio of long-chain alkyl quaternary ammonium salt to total monomer of 2-8:16.2-26, and carry out ion exchange reaction to obtain filtration loss reducer.

[0009] In the emulsion-type filtration reducer for oil-based drilling fluids prepared in this invention, the continuous phase of the emulsion is the same as or similar to the oil-based medium of the oil-based drilling fluid. As shown in Figure 1, the dispersed phase particles of the emulsion are weakly cross-linked spherical gel structures with an external lipophilic and internal hydrophilic nature. The particle size of these spherical gels is less than 100 nanometers, and the surface contains some high-temperature resistant olefin polymers. Simultaneously, ion exchange of some ionic polymer segments through long-chain alkane modification further endows the gel particles with good dispersion stability in drilling fluids. The inner layer of the gel contains poly(N-isopropylacrylamide) (PNIPAM), which can undergo a high-temperature phase transition (32-37℃) from hydrophilic to lipophilic, and a small amount of hydrophilic polymer molecular segments. When the gel reaches high-temperature areas below the formation and needs to exert a high filtration reduction effect, it can both absorb water and be highly dispersed in the oily matrix into a three-dimensional network structure. This invention uses PNIPAM, a polymer with a high-temperature phase transition, copolymerized with ionic monomers to form the gel particle core, which is beneficial for the balanced distribution of hydrophilic and hydrophobic segments.

[0010] According to a specific embodiment of the present invention, preferably, the emulsifier is a compound of emulsifier A and emulsifier B; in S1, the mass ratio of oil phase, emulsifier A and emulsifier B is 25-40:12-20:5-8.

[0011] According to a specific embodiment of the present invention, preferably, the emulsifier A includes one or more of Span-20, Span-40, Span-60, Span-65, Span-80 and Span-85.

[0012] According to a specific embodiment of the present invention, preferably, the emulsifier B comprises one or a combination of two or more of polyoxyethylene oleyl alcohol ether, polyoxyethylene monostearate, alkylphenol polyoxyethylene ether, polyoxyethylene monooleate, polyoxyethylene monolaurate, and polyoxyethylene sorbitan trioleate.

[0013] According to a specific embodiment of the present invention, preferably, in S1, the oily medium is mixed and stirred with emulsifier A and emulsifier B at 30-60°C for 30-50 minutes to obtain the oil phase.

[0014] According to a specific embodiment of the present invention, preferably, the ionic monomer includes one or more of acrylic acid, 2-acrylamido-2-methylpropanesulfonic acid, methacrylic acid, vinyl sulfonic acid, and allylbenzene sulfonic acid.

[0015] According to a specific embodiment of the present invention, preferably, the long-chain alkyl quaternary ammonium salt includes one or a combination of two or more of hexadecyltrimethylammonium bromide, hexadecyldimethylbenzylammonium chloride, and octadecyltrimethylammonium chloride.

[0016] According to a specific embodiment of the present invention, preferably, in S2, the mass ratio of oil phase to water, based on the oily medium, is 25-40:16-21.

[0017] According to a specific embodiment of the present invention, preferably, the oily medium includes one or more of peanut oil, soybean oil, sunflower seed oil, castor oil, silicone oil, white oil, gasoline, diesel, and kerosene.

[0018] According to a specific embodiment of the present invention, preferably, in S1, when the aqueous solution is mixed with the oily medium and the emulsifier, the oily medium and the emulsifier are mixed evenly beforehand to form an oil phase; more preferably, the mixing is carried out at 30-60°C and 300-700 rpm.

[0019] According to a specific embodiment of the present invention, preferably, the water-soluble crosslinking agent includes one or a combination of two or more of polyethylene glycol diacrylate, N,N-methylenebisacrylamide, and dimethyldiallylammonium chloride.

[0020] According to a specific embodiment of the present invention, preferably, the mass ratio of the water-soluble crosslinking agent to the total amount of monomer is 0.05-1:16.2-26.

[0021] According to a specific embodiment of the present invention, preferably, the oxidant for initiation includes one or a combination of two or more of sodium persulfate, ammonium persulfate, potassium persulfate, and potassium dichromate; the reducing agent for initiation includes one or a combination of two or more of sodium bisulfite, sodium thiosulfate, ammonium bisulfite, ferrous sulfate, and stannous chloride.

[0022] According to a specific embodiment of the present invention, preferably, the mass ratio of the total amount of oxidant for initiation, reducing agent for initiation, and monomer is 0.45-0.75:0.05-0.1:16.2-26.

[0023] According to a specific embodiment of the present invention, preferably, the mass ratio of the total amount of monomers to water is 16.2-26:16-21.

[0024] According to a specific embodiment of the present invention, preferably, the polymerization reaction endpoint is when the temperature of the reaction system rises to 50-80°C.

[0025] According to a specific embodiment of the present invention, preferably, in S3, the temperature of the ion exchange reaction is room temperature (20-30°C) and the reaction time is 20 min-1 h.

[0026] According to a specific embodiment of the present invention, preferably, the protective atmosphere is nitrogen and / or an inert gas.

[0027] According to a specific embodiment of the present invention, preferably, the raw materials for the oil-based drilling fluid filtration reducer, by weight parts, include:

[0028] Oily medium 25-40 parts, emulsifier A 12-20 parts, emulsifier B 5-8 parts, N-isopropylacrylamide monomer 16-21 parts, ionic monomer 0.2-5 parts, crosslinking agent 0.05-1 parts, water 16-21 parts, oxidant for initiation 0.45-0.75 parts, styrene 4-6 parts, reducing agent for initiation 0.05-0.1 parts, long-chain alkyl quaternary ammonium salt 2-8 parts.

[0029] According to a specific embodiment of the present invention, preferably, the preparation method of the above-mentioned oil-based drilling fluid filtration reducer includes the following steps:

[0030] S1: By mass, mix 25-40 parts of oily medium, 12-20 parts of emulsifier A, and 5-8 parts of emulsifier B until homogeneous to form an oil phase;

[0031] S2: Dissolve 16-21 parts of N-isopropylacrylamide monomer, 0.2-5 parts of ionic monomer, 0.05-1 part of water-soluble crosslinking agent, and 0.45-0.75 parts of initiating oxidant in water, and then add them to the oil phase and mix and stir to obtain emulsion 1;

[0032] S3: Add 4-6 parts of styrene to the emulsion 1, and then add 0.05-0.1 parts of a reducing agent to initiate the polymerization reaction under a protective atmosphere. After the reaction is completed, emulsion 2 is obtained.

[0033] S4: Cool the emulsion 2 and add 2-8 parts of a saturated solution of a long-chain alkyl quaternary ammonium salt, react again, and obtain a filtration loss reducer.

[0034] According to a specific embodiment of the present invention, more preferably, the preparation method of the above-mentioned oil-based drilling fluid filtration reducer includes the following steps:

[0035] (1) Preparation of oil phase: Weigh 25-40 parts of oily medium, 12-20 parts of emulsifier A and 5-8 parts of emulsifier B by mass, mix them at 30-60℃ and stir for 30-50 min, then cool to room temperature to obtain oil phase;

[0036] (2) Preparation of aqueous phase: Weigh 16-21 parts of N-isopropylacrylamide monomer, 0.2-5 parts of ionic monomer, and 0.05-1 parts of water-soluble crosslinking agent, dissolve them in 16-21 parts of water, and then add 3-5 parts of 15wt.% oxidant solution for initiation. Dissolve completely to obtain aqueous phase;

[0037] (3) Preparation of filtration loss reducer emulsion: Pour the aqueous phase into a four-necked flask and mix it with the oil phase at room temperature and stir for 30-60 min at a stirring rate of 300-700 rpm; add 4-6 parts of styrene to the four-necked flask, then introduce an inert gas into the resulting mixture for 5-30 min and add 1-2 parts of a 5 wt.% initiating reducing agent solution to initiate the reaction; after the reaction is heated to 50-80℃, cool it to room temperature, add 2-8 parts of a saturated solution of long-chain alkyl quaternary ammonium salt and continue stirring for 30 min at a stirring rate of 300 rpm to obtain an oil-in-water emulsion filtration loss reducer for oil-based drilling fluid.

[0038] The filtration loss reducer preparation process of the present invention is a typical reverse emulsion polymerization. The "one-pot" preparation process is simple and has good prospects for large-scale production. At the same time, by adjusting the production process, such as the rotation speed, emulsifier dosage, and oil-water ratio, different structural products can be prepared to adapt to downhole conditions and improve the filtration loss reduction effect.

[0039] Generally speaking, oil-based drilling fluid is an emulsion system formed by adding appropriate amounts of emulsifiers, wetting agents, lipophilic solid treatment agents (such as organic clay, oxidized asphalt, etc.), lime particles (calcium oxide), and weighting materials (such as barite, calcium carbonate particles).

[0040] This invention provides a filtration loss reducer for oil-based drilling fluids. In this invention, the filtration loss reducer is added to the drilling fluid base to prepare an oil-based drilling fluid for application. Preferably, the amount of the filtration loss reducer, on a dry basis, is 3-6% of the mass of the drilling fluid base, more preferably 4-5%.

[0041] Preferably, in the above-mentioned oil-based drilling fluid, the drilling fluid base contains solid particles, including organic soil, CaO particles, and barite particles.

[0042] The filtration reduction mechanism of the oil-based drilling fluid filtration reducer of this invention involves three main components that synergistically enhance the effects of multiple components contained in the oil-based drilling fluid: fine solid particles, microemulsion droplets, and nanoscale colloids. During drilling, the oil-based drilling fluid contains fine solid particles such as nano-calcium carbonate or organic clay. These particles have small diameters and can penetrate deep into the pores of the formation. When filtration occurs, these fine solid particles are carried by the working fluid to the outer layer of the wellbore and begin to form bridging, i.e., forming a thin and dense inner mud cake on the wellbore. Bridging is more likely to occur when the size of the fine solid particles is approximately 1 / 3 or 2 / 3 of the pore size. This is because these particles can both enter the pores and form effective bridges in the formation. After bridging is formed, microemulsion droplets enter the pores on the wellbore. Under the action of formation pressure, these droplets deform and block the pores, further reducing the formation's permeability. Finally, the nano-sized colloids of the filtration reducer in the oil-based drilling fluid enter the final gap between the emulsion droplets and the ultrafine solid particles. The presence of these colloidal components helps prevent the working fluid from penetrating the bottom layer through the mud cake, thereby further preventing filtration problems. The three components work synergistically to reduce filtration problems in oil-based drilling fluids during drilling, improving drilling efficiency and reducing costs.

[0043] The filtration loss reducer of this invention exists as a stable emulsion in oil-based drilling fluids, exhibiting good dispersibility and compatibility, and making on-site application safe and simple. Its ability to disperse in oily media and absorb water and swell downhole is particularly important for high-temperature oil reservoirs containing groundwater. The gel, due to its water content, exhibits strong deformability and good adaptability to different sizes of lost-flow formations and fracture shapes. It also demonstrates good pressure resistance, filtration loss reduction capacity, and high-temperature resistance when combined with other components such as inorganic nanoparticles in the drilling fluid. The filtration loss reducer of this invention utilizes conventional petrochemical refining raw materials in its material design, ensuring cost control.

[0044] The oil-based drilling fluid filtration reducer provided by this invention has the following advantages:

[0045] (1) The polystyrene layer on the surface of the gel particles in the filter loss reducer can improve the high temperature resistance, and the modified lipophilic long-chain alkanes can improve their dispersibility in oil-based media. The gel has good compatibility with oil-based drilling fluid and also has controllable deformability, which can meet the bridging needs and deform and seal irregular crack channels.

[0046] (2) The gel particles of the filtration loss reducer possess both hydrophilic and oleophilic long chains, which has a significant advantage for water-bearing formations. It can reduce the hydration layer on the rock surface, thereby increasing the sealing effect of the filter cake on the gaps. Since it is designed for use in oil-based drilling fluids, the gel particles of the filtration loss reducer of this invention contain an appropriate amount of poly(N-isopropylacrylamide) component during operation. This component has phase transition characteristics. When the temperature is above about 37°C, the gel segments undergo phase inversion, which can increase the network dispersibility in oily media.

[0047] (3) The phase transition properties of the high-temperature phase transition polymer poly(N-isopropylacrylamide) (PNIPAM) are suitable for composites. The thermosensitive phase transition of PNIPAM thermosensitive gel is caused by changes in the hydrophilic / hydrophobic balance of the cross-linked network under changing external conditions. At low temperatures (generally below 32°C), PNIPAM molecules exhibit hydrophilicity, while as the temperature rises, due to intramolecular bonding and the effect of the hydrophobic N-isopropyl group, PNIPAM molecules gradually transform into hydrophobic and oleophilic properties. This temperature sensitivity is determined by the molecular structure characteristics of PNIPAM. Furthermore, even when composited or copolymerized with other materials, the thermosensitive characteristics of PNIPAM molecules can be effectively maintained, and its conformational change can be reversed with heating or cooling.

[0048] (4) The filtration loss reducer has good compatibility with oil-based drilling fluids. Oil-based drilling fluids are mostly composed of white oil or diesel oil, consisting of nanoparticle calcium carbonate, barium sulfate as a weighting agent, and organic clay as a bridging component in the oily medium, and are in a mud state. Dispersing particulate, especially nanoscale, filtration loss reducers in viscous oil-based drilling fluids is usually a challenge. The filtration loss reducer of this invention is a water-in-oil emulsion. The oil-based medium of the filtration loss reducer can be the same oil as the oil-based drilling fluid matrix, which facilitates simple liquid-liquid mixing and dispersion in the oil-based drilling fluid. The construction process is simple, and the mud dispersion stability during surface preparation is good.

[0049] (5) Good prospects for scale-up of the process. The emulsion-type filtration loss reducer of the present invention is prepared by a one-pot reverse emulsion polymerization process, which is a typical process in the field of polymerization technology. The particle size and composition can be easily controlled by stirring speed, emulsifier content and oil-water ratio, and the process is easy to scale up.

[0050] The technical solution provided by this invention has the following beneficial effects:

[0051] The emulsion-type filtration reducer for oil-based drilling fluids prepared in this invention exhibits good oleophilicity, demonstrating excellent suspension stability, deformability, and swelling properties within the oil-based drilling fluid. Its rheological properties remain largely unchanged after high-temperature aging. Oil-based drilling fluids contain a portion of dispersed water, and the formation also contains some water. The particles in the filtration reducer exhibit good dispersibility in the oil-based medium and swell upon contact with water. The partially polymerized, weakly cross-linked structure dissolves the remaining non-dissolving gel, resulting in water absorption and swelling. Simultaneously, the surface possesses oleophilic groups, generating viscoelasticity. Under high temperature and pressure, this viscoelasticity synergistically interacts with inorganic nanoparticles and organic soil-layer materials in the oil-based drilling fluid to form a pressure-resistant, dense filter cake. The gel particles of the emulsion-type filtration reducer of this invention contain PNIPAM phase transition segments with high-temperature phase transition properties. At downhole high temperatures, these segments exhibit good compatibility with the oil-based medium, while also possessing hydrophilic segments. This characteristic gives the particles a balanced hydrophilic and oleophilic profile, achieving satisfactory filtration reduction effects. Attached Figure Description

[0052] Figure 1 is a schematic diagram of the structure of the gel particles of the filtration loss reducing agent of the present invention;

[0053] Figure 2 is an electron microscope image of the gel particles of the filtration loss reducer in Example 2;

[0054] Figure 3, from left to right, shows the appearance of the filter cake formed after the oil-based drilling fluids of Examples 1-4 in Experiment 2 underwent a high-temperature and high-pressure filtration loss test. Detailed Implementation

[0055] In order to provide a clearer understanding of the technical features, objectives and beneficial effects of the present invention, the technical solution of the present invention will now be described in detail below, but it should not be construed as limiting the scope of implementation of the present invention.

[0056] Methods for observing morphology:

[0057] The morphology of solid particles extracted from emulsion-type filtration loss reducers was observed as follows: The filtration loss reducer emulsion was repeatedly washed with ethanol and acetone, and then precipitated and filtered. After drying under vacuum at 100℃ for 24 hours, the powder particles in the emulsion were extracted. A small sample was fixed on the sample stage, sputter-coated with gold, and observed under a scanning electron microscope. The test conditions were an accelerating voltage of 2kV and an electron beam current of 10μA.

[0058] Test methods for related properties such as filtration loss reduction and rheology:

[0059] The two most important performance indicators of drilling fluid are rheological properties and filtration properties, which directly affect the cutting ability of the drilling fluid and the stability of the wellbore. AV represents the viscosity caused by internal friction in the drilling fluid, reflecting its flowability. PV reflects the frictional force generated by the interaction between colloidal solids and the fluid in the drilling fluid. YP refers to the ability to circulate the wellbore and annulus fluid while carrying suspended cuttings.

[0060] The filtration loss reducer of the present invention is added to an oil-based drilling fluid system. The stability and rheological characterization of the system, as well as the evaluation method for high-temperature and high-pressure filtration loss, are as follows:

[0061] The emulsion-type fluid loss reducer prepared according to this invention is added, wherein the amount of the emulsion-type fluid loss reducer is calculated as follows: the emulsion-type fluid loss reducer is repeatedly precipitated and washed three times with excess ethanol and acetone, and finally vacuum dried to obtain a dry powder. The percentage of the powder content in the emulsion-type fluid loss reducer is calculated. The original amount of emulsion-type fluid loss reducer added is calculated based on 4 wt% of the dry-basis fluid loss reducer in the oil-based drilling fluid.

[0062] The demulsification voltage (ES) of the oil-based drilling fluid was measured using a Fann 23D electrical stability tester. The prepared oil-based drilling fluid was measured using a Model 800 eight-speed rotational viscometer, and the values ​​at 600, 300, 200, 100, 6, and 3 rpm were recorded as θ. 600 θ 300 θ 200 θ 100 θ6 and θ3. The drilling fluid was stirred at 12000 r / min for 10 min before measurement. The rheological properties of the drilling fluid were tested at 70℃ and normal pressure. The rheological parameters of the drilling fluid, namely apparent viscosity (AV), plastic viscosity (PV), and yield point (YP), were calculated based on the readings of an eight-speed rotational viscometer at 600 and 300 rpm. The calculation formulas are as follows:

[0063]

[0064] PV = θ 600 -θ 300

[0065]

[0066] Example 1

[0067] This embodiment provides a method for preparing a filtration loss reducer for oil-based drilling fluids, comprising the following steps:

[0068] Weigh 40 parts kerosene, 15 parts Span-40 and 7 parts polyoxyethylene oil alcohol ether by mass, pour them into a four-necked flask, stir at 50°C for 50 min and then cool to room temperature to obtain the oil phase;

[0069] Weigh 20 parts of N-isopropylacrylamide, 5 parts of acrylic acid and 0.05 parts of N,N-methylenebisacrylamide, dissolve them in 21 parts of water in sequence, then add 5 parts of 15wt.% ammonium persulfate solution, dissolve, and obtain the aqueous phase;

[0070] The aqueous phase was poured into the oil phase and stirred at 300 rpm for 60 min to obtain emulsion 1;

[0071] Then, 6 parts of styrene were added to emulsion 1, nitrogen gas was introduced for 10 minutes, 2 parts of sodium bisulfite were added, and the four-necked flask was sealed to initiate the reaction; the reaction system was heated to 80°C and then gradually lowered to room temperature to obtain emulsion 2;

[0072] Add 8 parts of octadecyltrimethylammonium chloride to emulsion 2 and continue stirring at 300 rpm for 30 min to obtain an emulsion-type filtration loss reducer.

[0073] Test its relevant performance in oil-based drilling fluids.

[0074] Example 2

[0075] This embodiment provides a method for preparing a filtration loss reducer for oil-based drilling fluids, comprising the following steps:

[0076] Weigh out 38 parts by weight of white oil, 15 parts by weight of Span-80 and 7 parts by weight of alkylphenol polyoxyethylene ether, pour them into a four-necked flask, stir at 50°C for 50 min and then cool to room temperature to obtain the oil phase;

[0077] Weigh 21 parts of N-isopropylacrylamide, 3 parts of acrylic acid and 0.1 parts of N,N-methylenebisacrylamide, dissolve them in 21 parts of water in sequence, then add 3 parts of 15 wt.% ammonium persulfate solution, dissolve, and obtain the aqueous phase;

[0078] The aqueous phase was poured into the oil phase and stirred at 300 rpm for 60 min to obtain emulsion 1;

[0079] Add 4 parts of styrene to emulsion 1, purge with nitrogen for 10 min, then add 1 part of sodium bisulfite and seal the four-necked flask to initiate the reaction; heat the reaction system to 80°C and then gradually decrease it to room temperature to obtain emulsion 2.

[0080] Add 5 parts of octadecyltrimethylammonium chloride to emulsion 2 and continue stirring at 300 rpm for 30 min to obtain an emulsion-type filtration loss reducer.

[0081] Test its relevant performance in oil-based drilling fluids.

[0082] The scanning electron microscope image of the powder particles extracted in Example 2 is shown in Figure 2.

[0083] Example 3

[0084] This embodiment provides a method for preparing a filtration loss reducer for oil-based drilling fluids, comprising the following steps:

[0085] Weigh 25 parts white oil, 20 parts Span-85 and 8 parts polyoxyethylene monooleate by mass, pour them into a four-necked flask, stir at 50°C for 50 min and then cool to room temperature to obtain the oil phase;

[0086] Weigh 16 parts of N-isopropylacrylamide, 0.2 parts of 2-acrylamido-2-methylpropanesulfonic acid and 1 part of dimethyldiallyl ammonium chloride, dissolve them in 16 parts of water in sequence, then add 4 parts of 15 wt.% ammonium persulfate solution, dissolve, and obtain the aqueous phase;

[0087] The aqueous phase was poured into the oil phase and stirred at 300 rpm for 60 min to obtain emulsion 1;

[0088] Add 6 parts of styrene to emulsion 1, purge with nitrogen for 10 min, then add 1.5 parts of sodium bisulfite and seal the four-necked flask to initiate the reaction; the reaction system is heated to 80°C and then gradually lowered to room temperature to obtain emulsion 2;

[0089] Add 8 parts of hexadecyltrimethylammonium bromide to emulsion 2 and continue stirring at 300 rpm for 30 min to obtain an emulsion-type filtration loss reducer.

[0090] Test its relevant performance in oil-based drilling fluids.

[0091] Example 4

[0092] This embodiment provides a method for preparing a filtration loss reducer for oil-based drilling fluids, comprising the following steps:

[0093] Weigh out 38 parts by weight of white oil, 12 parts by weight of Span-60 and 5 parts by weight of polyoxyethylene monooleate, pour them into a four-necked flask, stir at 50°C for 50 min and then cool to room temperature to obtain the oil phase;

[0094] Weigh 16 parts of N-isopropylacrylamide, 5 parts of acrylic acid and 0.5 parts of N,N-methylenebisacrylamide, dissolve them in 20 parts of water in sequence, then add 4 parts of 15wt.% ammonium persulfate solution, dissolve, and obtain the aqueous phase;

[0095] The aqueous phase was poured into the oil phase and stirred at 300 rpm for 60 min to obtain emulsion 1;

[0096] Add 5 parts of styrene to emulsion 1, purge with nitrogen for 10 min, then add 1.5 parts of sodium bisulfite and seal the four-necked flask to initiate the reaction; the reaction system is heated to 80°C and then gradually lowered to room temperature to obtain emulsion 2;

[0097] Add 2 parts of octadecyltrimethylammonium chloride to emulsion 2, and continue stirring at 300 rpm for 30 min to obtain an emulsion-type filtration loss reducer.

[0098] Example 1 Evaluation of Filtration Loss Reduction Performance: To investigate the filtration loss reduction performance of oil-based drilling fluid systems under high-temperature aging conditions, 4 wt% (based on the dry basis of the filtration loss reducer) of the filtration loss reducer described in Examples 1-4 was added to the base oil-based drilling fluid. The oil-based drilling fluid was then aged at 180°C for 16 hours. The aged drilling fluid was then tested using a rotational viscometer, an electrical stability tester, and a GGS71-B type high-temperature and high-pressure filtration loss meter to determine its rheology, demulsification voltage, and high-temperature and high-pressure filtration loss (HTHPFL) within 30 minutes.

[0099] Performance test results of the products in Examples 1-4 above:

[0100] Figure 3 shows the appearance of the filter cakes formed after high-temperature and high-pressure filtration loss tests in Examples 1-4, from left to right. Table 1 shows the various properties of the system after the filtration loss reducers prepared in the above examples are added to the oil-based drilling fluid.

[0101] Table 1. Test results of filtration loss reduction performance.

[0102]

[0103] The filtration loss reduction mechanism in oil-based drilling fluids involves three main components: fine solid particles, microemulsion droplets, and nanoscale colloids. During drilling, oil-based drilling fluids contain fine solid particles with small diameters that can penetrate deep into the formation pores. When filtration loss occurs, these fine solid particles are carried by the working fluid to the outer layer of the wellbore and begin to form bridging, i.e., a thin and dense inner mud cake is formed on the wellbore wall.

[0104] In this invention, the synthetic polymer filtration reducer used in oil-based drilling fluids is designed with a molecular structure that meets several key conditions to further improve its filtration reduction effect and provide a certain degree of auxiliary emulsification function. First, the polymer molecular chain, especially the filtration reducer, contains long carbon-chain lipophilic chains, ensuring uniform dispersion of the polymer in the oil-based drilling fluid system. This uniform dispersion helps form a dense filtration reducer film (see Figure 3), which can effectively reduce the permeability of the wellbore surface, thereby slowing down the rate of formation invasion by the drilling fluid system during application. Second, the filtration reducer designed in this patent contains thermosensitive poly(N-isopropylacrylamide) segments (PNIPAM) and ionic polymers such as polyacrylic acid segments. The PNIPAM segments allow the entire filtration reducer to achieve a balance and conversion between hydrophilic and lipophilic properties, especially for high-temperature formations, where its lipophilicity is further enhanced. The ionic polymer segments provide better hydrophilicity. Furthermore, the polymer molecular chain contains charged adsorption groups, which enable the filtration reducer molecules to form stable chemical bonds on the surface of clay particles. The formation of these chemical bonds not only enhances the interaction between the filtration loss reducer and clay particles but also ensures high bond strength, making them less susceptible to breakage. This design helps improve the adhesion of the filtration loss reducer near the wellbore, further reducing filtration loss. Finally, the introduction of rigid groups, such as the styrene molecular skeleton in this patent, into the molecular structure can significantly improve the temperature resistance of the filtration loss reducer.

[0105] The following experiments compare the effects of several key components, such as ionic monomers, nonionic monomers N-isopropylacrylamide, styrene, and alkyl ionic modifiers, by controlling for single variables.

[0106] Comparative Example 1

[0107] This comparative example provides a method for preparing a filtration loss reducer, which differs from Example 2 only in that: ionic monomer acrylic acid was not added to the aqueous phase, but 24 parts of N-isopropylacrylamide were added; other conditions were the same as in Example 2. The filtration loss reduction evaluation results were as follows: the high-temperature, high-pressure filtration loss of the oil-based drilling fluid in the comparative example was 18 mL within 30 minutes of aging. This demonstrates that the water absorption of ionic monomers plays a crucial role in maintaining a low filtration loss in the system.

[0108] Comparative Example 2

[0109] This comparative example provides a method for preparing a filtration loss reducer, which differs from Example 2 only in that N-isopropylacrylamide was not added to the aqueous phase, and 24 parts of acrylic acid were added; other conditions are the same as in Example 2. The filtration loss reduction evaluation results are as follows: the filtration loss reducer of this comparative example has poor dispersibility in oil-based drilling fluid, and the high-temperature and high-pressure filtration loss is 35 mL within 30 minutes after aging of the oil-based drilling fluid.

[0110] The filtration loss reducer particles in this comparative example are primarily composed of polyacrylic acid. Although there is a small amount of polystyrene coating, while the overall system can swell through water absorption by the ionic monomer polyacrylic acid, the excessive hydrophilicity of the particles prevents them from forming good bridging in oily base liquids. Consequently, the filtration loss increases significantly. This demonstrates the necessity of the presence of poly(N-isopropylacrylamide) segments in the filtration loss reducer particles.

[0111] Comparative Example 3

[0112] This comparative example provides a method for preparing a filtration loss reducer, which differs from Example 2 only in that styrene was not added; other conditions are the same as in Example 2. The filtration loss reduction evaluation result is as follows: the high-temperature and high-pressure filtration loss of the oil-based drilling fluid in this comparative example is 19 mL within 30 minutes after aging. Polystyrene segments can play a certain role in high-temperature reinforcement in the filtration loss reducer particles. In this comparative example, no styrene was added, and compared with Example 2, the high-temperature and high-pressure filtration loss of the system in this comparative example is significantly increased.

[0113] Comparative Example 4

[0114] This comparative example provides a method for preparing a filtration loss reducer, which differs from Example 2 only in that the ionic modifier octadecyltrimethylammonium chloride is not added; other conditions are the same as in Example 2. The filtration loss reduction evaluation results are as follows: the filtration loss reducer of this comparative example has poor dispersibility in oil-based drilling fluids, and granular agglomerates are visible to the naked eye after aging of the oil-based drilling fluid. The high-temperature and high-pressure filtration loss within 30 minutes after aging is 16 mL.

[0115] Therefore, long-chain alkylation modification has a significant impact on the dispersibility of filtration reducers in drilling fluid base fluids and their subsequent filtration reduction properties.

Claims

1. A method for preparing a filtration loss reducer for oil-based drilling fluid, comprising the following steps: S1: mixing an oily medium and an emulsifier in a certain proportion to obtain an oil phase; S2: dissolving N-isopropylacrylamide monomer, an ionic monomer, a water-soluble crosslinking agent, and an initiating oxidant in water, wherein the mass ratio of N-isopropylacrylamide monomer to ionic monomer is 16-21:0.2-5, to obtain an aqueous phase; then mixing the aqueous phase with the oil phase obtained in S1, stirring and emulsifying to obtain emulsion 1; S3: adding styrene to emulsion 1, wherein the mass ratio of styrene to the total amount of monomer is 4-6:16.2-26, and then adding an initiating reducing agent under a protective atmosphere to initiate a polymerization reaction, thereby obtaining emulsion 2 after the reaction is completed; S4: adding a long-chain alkyl quaternary ammonium salt to emulsion 2, wherein the mass ratio of the long-chain alkyl quaternary ammonium salt to the total amount of monomer is 2-8:16.2-26, and carrying out an ion exchange reaction to obtain the filtration loss reducer.

2. The method for preparing the filtration loss reducer for oil-based drilling fluid according to claim 1, wherein, The emulsifier is a compound of emulsifier A and emulsifier B; in S1, the mass ratio of oil phase, emulsifier A and emulsifier B is 25-40:12-20:5-8.

3. The method for preparing the filtration loss reducer for oil-based drilling fluid according to claim 2, wherein, The emulsifier A includes one or more of Span-20, Span-40, Span-60, Span-65, Span-80, and Span-85.

4. The method for preparing the filtration loss reducer for oil-based drilling fluid according to claim 2, wherein, The emulsifier B comprises one or more of the following: polyoxyethylene oleyl alcohol ether, polyoxyethylene monostearate, alkylphenol polyoxyethylene ether, polyoxyethylene monooleate, polyoxyethylene monolaurate, and polyoxyethylene sorbitan trioleate.

5. The method for preparing the filtration loss reducer for oil-based drilling fluid according to claim 1, wherein, The ionic monomers include one or more of the following: acrylic acid, 2-acrylamido-2-methylpropanesulfonic acid, methacrylic acid, vinyl sulfonic acid, and allylbenzene sulfonic acid.

6. The method for preparing the filtration loss reducer for oil-based drilling fluid according to claim 1, wherein, The long-chain alkyl quaternary ammonium salt includes one or more of hexadecyltrimethylammonium bromide, hexadecyldimethylbenzylammonium chloride, and octadecyltrimethylammonium chloride.

7. The method for preparing the filtration loss reducer for oil-based drilling fluid according to claim 1, wherein, In S2, the mass ratio of oil phase to water, calculated as an oily medium, is 25-40:16-21.

8. The method for preparing the filtration loss reducer for oil-based drilling fluid according to claim 1, wherein, The oily medium includes one or more of the following: peanut oil, soybean oil, sunflower seed oil, castor oil, silicone oil, white oil, gasoline, diesel, and kerosene.

9. The method for preparing the filtration loss reducer for oil-based drilling fluid according to claim 1, wherein, The water-soluble crosslinking agent includes one or more of polyethylene glycol diacrylate, N,N-methylenebisacrylamide, and dimethyldiallyl ammonium chloride.

10. The method for preparing the filtration loss reducer for oil-based drilling fluid according to claim 1, wherein, The mass ratio of the water-soluble crosslinking agent to the total amount of monomer is 0.05-1:16.2-26.

11. The method for preparing the filtration loss reducer for oil-based drilling fluid according to claim 1, wherein, The oxidizing agent for initiation includes one or more of sodium persulfate, ammonium persulfate, potassium persulfate, and potassium dichromate; the reducing agent for initiation includes one or more of sodium bisulfite, sodium thiosulfate, ammonium bisulfite, ferrous sulfate, and stannous chloride.

12. The method for preparing the filtration loss reducer for oil-based drilling fluid according to claim 1, wherein, The mass ratio of the total amount of oxidant, reducing agent, and monomer used for initiation is 0.45-0.75:0.05-0.1:16.2-26.

13. The method for preparing the filtration loss reducer for oil-based drilling fluid according to claim 1, wherein, The mass ratio of total monomers to water is 16.2-26:16-21.

14. The method for preparing the filtration loss reducer for oil-based drilling fluid according to claim 1, wherein, The endpoint of the polymerization reaction is when the temperature of the reaction system rises to 50-80℃.

15. The method for preparing the filtration loss reducer for oil-based drilling fluid according to claim 1, wherein, By weight, the raw materials for the filtration loss reducer for oil-based drilling fluids include: 25-40 parts oily medium, 12-20 parts emulsifier A, 5-8 parts emulsifier B, 16-21 parts N-isopropylacrylamide monomer, 0.2-5 parts ionic monomer, 0.05-1 part crosslinking agent, 16-21 parts water, 0.45-0.75 parts oxidant for initiation, 4-6 parts styrene, 0.05-0.1 parts reducing agent for initiation, and 2-8 parts alkyl quaternary ammonium salt.

16. A filtration loss reducer for oil-based drilling fluids, obtained by the preparation method of the filtration loss reducer for oil-based drilling fluids according to any one of claims 1-15.

17. An oil-based drilling fluid comprising a drilling fluid base and a filtration reducer for oil-based drilling fluids as described in claim 16.

18. The oil-based drilling fluid according to claim 17, wherein, The amount of filtration reducer used, on a dry basis, is 3-6% of the mass of the drilling fluid base fluid.

19. The oil-based drilling fluid according to claim 17, wherein, The drilling fluid base contains solid particles, including organic soil, CaO particles, and barite particles.

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