Modified carboxymethyl cellulose, drilling fluid base fluid as well as preparation method and application of modified carboxymethyl cellulose and drilling fluid base fluid

Abstract

The invention discloses modified carboxymethyl cellulose, drilling fluid base fluid and a preparation method and application thereof, and belongs to the technical field of drilling fluid. The preparation method of the modified carboxymethyl cellulose comprises the following steps: mixing a carboxymethyl cellulose solution and NVP, adding an initiator, reacting at 60-80 DEG C, and introducing nitrogen to obtain the modified carboxymethyl cellulose. In addition, the invention also provides application of the modified carboxymethyl cellulose in preparation of drilling fluid base fluid. In addition, the invention also provides a preparation method of the drilling fluid base fluid, which comprises the following steps: mixing bentonite, sodium carbonate and water, curing to obtain base slurry, adding the modified carboxymethyl cellulose into the base slurry, stirring, and aging at 55-60 DEG C to obtain the drilling fluid base fluid. The modified carboxymethyl cellulose prepared by the preparation method provided by the invention is an environment-friendly filtrate reducer with relatively high temperature resistance, salt resistance and high coalescence stability.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of drilling fluid, in particular to a modified carboxymethyl cellulose, a drilling fluid base fluid, and a preparation method and application thereof. BACKGROUND

[0002] With the depletion of near-surface oil and gas reservoirs, the depth of wellbore is continuously increasing, and the development of environmentally friendly, temperature-resistant, salt-resistant, and high-coalescence-stability drilling fluid filtrate reducers has become an inevitable trend. There are many types of filtrate reducers, among which carboxymethyl cellulose (CMC) has the advantages of environmental protection and wide application range. However, CMC has problems such as easy degradation at high temperature (≥120℃), easy electrostatic shielding at high salinity (≥10wt%), and poor coalescence stability. Therefore, it is of great significance to develop temperature-resistant, salt-resistant, and high-stability CMC.

[0003] Currently, the research and development of CMC filtrate reducers mainly focuses on cross-linking modification, sulfonic acid group synergistic modification, and composite modification. However, the performance of the products is not significantly improved, and the environmental protection does not meet the standards. Ahmed and Yang tried to synthesize artificial CMC, but the performance of the product is unstable and toxic monomers are left. According to the research, researchers use acrylic acid (AA) and acrylamide (AM) monomers to graft copolymerize on CMC and use the product as a base slurry treatment agent and a thickening agent. However, AA series grafted CMC has problems such as poor solubility and insufficient salt resistance, and AM series grafted CMC has problems such as residual toxic monomers, insufficient salt resistance, and insufficient shear resistance.

[0004] How to prepare CMC with high temperature resistance, salt resistance, and high stability is a problem to be solved in the prior art. SUMMARY

[0005] The present application aims to overcome the above technical deficiencies and provide a modified carboxymethyl cellulose, a drilling fluid base fluid, and a preparation method and application thereof, which solve the technical problem of how to prepare CMC with high temperature resistance, salt resistance, and high stability in the prior art.

[0006] From the perspective of microstructure, grafting modification can reduce the regularity of CMC molecules, reduce the crystallinity of CMC, and increase the specific surface area, which is beneficial to the contact with soil particles and better play the effect of reducing filtration loss. Compared with AA and AM, N-vinylpyrrolidone (NVP) has good biocompatibility, its -CO-NH- is an electrically neutral polar group, which is resistant to ion interference and has strong hydrophilicity. In addition, the rigid five-membered ring structure of NVP can increase the molecular motion potential barrier, avoid the problem of excessive curling of AA and AM grafting chains wrapping hydrophilic groups, and reduce the solubility of CMC. Combined with the above Figure 1Therefore, the application selects natural cotton with high cellulose content (about 94%) and complete biodegradability as raw material, and prepares carboxymethyl cellulose CMC-Na through modification reactions such as alkalization and etherification, and prepares grafted and modified carboxymethyl cellulose g-CMC by graft polymerization of NPV on CMC-Na.

[0007] The technical scheme of the application provides a preparation method of modified carboxymethyl cellulose, comprising the following steps: mixing a carboxymethyl cellulose solution and NVP, then adding an initiator, and then reacting at 60-80 DEG C and passing nitrogen to obtain the modified carboxymethyl cellulose.

[0008] In any embodiment, the mass ratio of the NVP to the carboxymethyl cellulose in the carboxymethyl cellulose solution is (1-5):1.

[0009] In any embodiment, the carboxymethyl cellulose solution is prepared by dissolving carboxymethyl cellulose in water; and the mass concentration of the carboxymethyl cellulose solution is 1-5%.

[0010] In any embodiment, the initiator is cerium ammonium nitrate.

[0011] In any embodiment, the reaction at 60-80 DEG C is performed for 2-6 hours; and / or, after the reaction at 60-80 DEG C, cooling is further included, then ethanol is added to precipitate the product, and the product is washed with water and ethanol, and then dried.

[0012] In any embodiment, the carboxymethyl cellulose in the carboxymethyl cellulose solution is prepared by the following steps: The NaOH solution, isopropyl alcohol, urea and cotton are mixed and stirred, then the chloroacetic acid solution is added dropwise, then the temperature is gradually increased to 50-55 DEG C for reaction, then the temperature is further increased to 65-75 DEG C for reaction, then the system is adjusted to neutral by glacial acetic acid, and then the carboxymethyl cellulose is obtained by washing and drying.

[0013] In addition, the application further provides a modified carboxymethyl cellulose prepared by the above preparation method.

[0014] In addition, the application further provides the use of the modified carboxymethyl cellulose prepared by the above preparation method or the above modified carboxymethyl cellulose in preparing a drilling fluid base fluid.

[0015] Further, the drilling fluid base fluid is prepared by the following steps: the bentonite, the sodium carbonate and the water are mixed, then the base fluid is obtained by curing, the modified carboxymethyl cellulose is added into the base fluid and stirred, then the drilling fluid base fluid is obtained by aging at 55-60 DEG C.

[0016] Further, the drilling fluid base fluid is prepared by the following steps: the bentonite, the sodium carbonate and the water are mixed, then the base fluid is obtained by curing, the modified carboxymethyl cellulose is added into the base fluid and stirred, then the drilling fluid base fluid is obtained by aging at 55-60 DEG C.

[0017] Compared with the prior art, the beneficial effects of the present application include: the preparation method of the modified carboxymethyl cellulose of the present application mixes the carboxymethyl cellulose solution and the NVP, then adds the initiator, then reacts at 60 DEG C-80 DEG C and introduces the nitrogen to obtain the modified carboxymethyl cellulose, the grafted modified carboxymethyl cellulose g-CMC is prepared by selecting the NPV to graft polymerize on the CMC-Na, the -OH, -COOH, -CO-NH- etc. on the g-CMC macromolecule can better interact with the -Si-O-, -Al-O- etc. on the clay particle through the hydrogen bond, the electrostatic attraction and the chelation operation etc. to form the relatively stable complex structure, and then form the thin and dense filter cake to play the role of the filtration loss reduction, the modified carboxymethyl cellulose is the environment-friendly filtration loss reducer with the high temperature resistance, the salt resistance and the high coalescence stability. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 is the filtration loss reduction mechanism diagram of the g-CMC prepared by the present application.

[0019] Figure 2 is the g-CMC preparation flow chart of the present application.

[0020] Figure 3 is the IR diagram of the cotton of example 1, the CMC-Na prepared by example 1 and the g-CMC prepared by example 2.

[0021] Figure 4 is the SEM diagram of the cotton of example 1, the CMC-Na prepared by example 1 and the g-CMC prepared by example 2.

[0022] Figure 5 is the POM picture of the cotton of example 1, the CMC-Na prepared by example 1 and the g-CMC prepared by example 2.

[0023] Figure 6 is the influence of the CMC-Na prepared by different urea addition amounts and water-cotton ratios of example 7 and example 8 on the substitution degree and the filtration loss.

[0024] Figure 7 The fluid loss of CMC-Na prepared in Example 1 and g-CMC prepared in Example 2 aged at different temperatures and for different times.

[0025] Figure 8 The results of TG-DTG analysis of g-CMC prepared in Example 2.

[0026] Figure 9 The corresponding filter cake and POM map of CMC-Na prepared in Example 1 and g-CMC prepared in Example 2.

[0027] Figure 10 The results of Zeta potential analysis of the drilling fluid system prepared by adding 1.5% of CMC-Na to the drilling fluid of Example 5 and the drilling fluid of Comparative Example 1.

[0028] Figure 11 The particle size distribution curve of the drilling fluid of Example 5. DETAILED DESCRIPTION

[0029] The ranges disclosed herein are defined by the lower and upper limits of the range, and the ranges are defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundaries of the particular range. The ranges defined in this manner can include the end values or not, and can be arbitrarily combined, i.e., any lower limit can be combined with any upper limit to form a range. For example, if the ranges of 60~120 and 80~110 are listed for a particular parameter, it is understood that the ranges of 60~110 and 80~120 are also contemplated. In addition, if the minimum range values of 1 and 2 are listed, and if the maximum range values of 3, 4 and 5 are listed, the following ranges are all contemplated: 1~3, 1~4, 1~5, 2~3, 2~4 and 2~5. In this application, unless otherwise stated, the numerical range "a~b" is a shorthand notation that refers to all of the real combinations of the numbers between a and b, where a and b are real numbers. For example, the numerical range "0~5" means that all of the real numbers between "0~5" have been listed herein, and "0~5" is just a shorthand notation for these numerical combinations. In addition, when it is stated that a parameter is an integer ≥2, it is equivalent to disclose that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0030] If not otherwise specified, the "comprising" and "including" mentioned in this application mean open-ended, and can also mean closed-ended. For example, the "comprising" and "including" can mean that other components not listed can also be included, or only the listed components can be included.

[0031] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0032] Combination Figure 2 This specific embodiment provides a method for preparing modified carboxymethyl cellulose (i.e., g-CMC), comprising the following steps: mixing a carboxymethyl cellulose solution and NVP, then adding an initiator, reacting at 60℃~80℃ for 2~6 hours while purging with nitrogen, then cooling, then adding ethanol to precipitate the product, washing with water and ethanol, and then drying to obtain the modified carboxymethyl cellulose; the mass ratio of NVP to carboxymethyl cellulose in the carboxymethyl cellulose solution is (1-5):1; the carboxymethyl cellulose solution is prepared by dissolving carboxymethyl cellulose in water; the mass concentration of the carboxymethyl cellulose solution is 1~5%; and the initiator is cerium ammonium nitrate.

[0033] In some embodiments, combined with Figure 2 The carboxymethyl cellulose (CMC-Na) in the carboxymethyl cellulose solution is obtained by the following steps: NaOH solution, isopropanol, urea and cotton were mixed and stirred. Then chloroacetic acid solution was added dropwise. The temperature was gradually increased to 50-55°C for etherification reaction. The temperature was then increased to 65-75°C for further reaction. The system was then adjusted to neutral with glacial acetic acid. After washing and drying, the carboxymethyl cellulose was obtained.

[0034] In addition, this specific embodiment also proposes a modified carboxymethyl cellulose, which is prepared by the above preparation method.

[0035] Furthermore, this specific embodiment also proposes the application of the modified carboxymethyl cellulose prepared by the above preparation method or the above modified carboxymethyl cellulose in the preparation of drilling fluid base fluid.

[0036] This specific embodiment also proposes a drilling fluid base fluid, including a base slurry (BT) and the above-mentioned modified carboxymethyl cellulose; the modified carboxymethyl cellulose is 0.5%-2.5% of the mass of the base slurry; the base slurry, calculated by mass parts, includes 40-45 parts bentonite, 2-4 parts sodium carbonate and 1000-1100 parts water.

[0037] Furthermore, this specific embodiment also proposes a method for preparing the above-mentioned drilling fluid base fluid, including the following steps: mixing bentonite, sodium carbonate and water, then curing to obtain a base slurry, adding modified carboxymethyl cellulose to the base slurry and stirring, and then aging at 55-60°C to obtain the drilling fluid base fluid.

[0038] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0039] In this invention, the terms "some embodiments," "this embodiment," and examples are used to describe a subset of all possible embodiments. However, it is understood that "some embodiments" can be the same subset or different subsets of all possible embodiments and can be combined with each other without conflict.

[0040] If the application documents contain similar descriptions such as "first / second", the following explanation shall be added: In the following description, the terms "first / second / third" are used only to distinguish similar objects and do not represent a specific ordering of objects. It is understood that "first / second / third" may be interchanged in a specific order or sequence where permitted, so that the embodiments described herein can be implemented in an order other than that illustrated or described herein.

[0041] In this embodiment, the term "and / or" is merely a description of the relationship between related objects, indicating that there can be three relationships. For example, object A and / or object B can represent three situations: object A exists alone, object A and object B exist simultaneously, and object B exists alone.

[0042] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0043] Experimental reagents: Cotton, Hubei Jinhanjiang Refined Cotton Co., Ltd.; N-vinylpyrrolidone, Maclean's; Chloroacetic acid, Maclean's; Isopropanol, Tianjin Yongda Chemical Reagent Co., Ltd.; Sodium hydroxide, Tianjin Yongda Chemical Reagent Co., Ltd.; Urea, Tianjin Beilian Fine Chemicals Development Co., Ltd.; Potassium chloride, Tianjin Yongda Chemical Reagent Co., Ltd.; Sodium chloride, Tianjin Bodi Technology Development Co., Ltd.; Anhydrous ethanol, Tianjin Baishi Chemical Co., Ltd.; Glacial acetic acid, Tianjin Yongda Chemical Reagent Co., Ltd.; Sodium bicarbonate, Hubei Jiufenglong Chemical Co., Ltd.

[0044] Experimental instruments: Water bath, HH-2, Shanghai Lichen Bangxi Instrument Technology Co., Ltd.; Drying oven, DZF-6020, Shanghai Lichen Bangxi Instrument Technology Co., Ltd.; Electronic balance, BSA124S, Sartorius Scientific Instruments (Beijing) Co., Ltd.; Electric furnace, DL-1, Nanbei Instrument Co., Ltd.; High-temperature roller furnace, XGRL-4A, Qingdao Hengtaida; Precision power-boosting electric stirrer, JJ-1, Changzhou Aohua Instrument Co., Ltd.; Muffle furnace, KSY-D-16, Shanghai Shuoguang Electronic Technology Co., Ltd.; Variable frequency high-speed stirrer, GJS-B12K, Qingdao Bairuida Petroleum Machinery Manufacturing Co., Ltd.; Heat-collecting magnetic stirrer, DF-101S, Shanghai Lichen Bangxi Instrument Technology Co., Ltd.

[0045] Characterization and performance testing IR testing The product was ground and mixed with potassium bromide powder at a mass ratio of approximately 1:100 on a Nicolai 6700 instrument from the United States, pressed into a transparent sheet, and subjected to infrared spectroscopy to identify the chemical groups of the material.

[0046] TGA Test Thermogravimetric analysis (TGA) was performed using a simultaneous thermal analyzer (NETZSCH TG 209F1 Libra TGA209F1D-0302-L) to test the change in sample mass in an N2 atmosphere at a temperature ranging from 30°C to 900°C and a heating rate of 10°C / min.

[0047] Scanning electron microscopy analysis Prepare a 1% product aqueous solution, dissolve it completely, and drop it onto a silicon wafer. After drying naturally at room temperature, test its morphology using a scanning electron microscope (SEM) from TESCAN at a test temperature of 25 ℃ and a voltage of 5.0 kV.

[0048] Polarizing microscope test Place the sample in the center of a clean glass slide and spread it out as much as possible, then cover it with a coverslip. Turn on the light source of the polarizing microscope (XP-550C), place the prepared glass slide on the stage, adjust the eyepiece and objective lens to make the image clear, and then take a picture.

[0049] Substitutability test The product's degree of substitution was tested according to the test method in "Drilling Fluid Materials Specification ISO 13500:2006". The specific operating steps are as follows: After performing infrared spectroscopy analysis on the product, it was placed in a porcelain crucible and ashed. Then, it was kept at 750℃ in a muffle furnace for 30 minutes. After removal, it was titrated with 0.05mol / L sulfuric acid standard solution and 0.1mol / L sodium hydroxide standard solution, respectively. The degree of substitution DS1 was calculated according to the relevant methods in the standard. Using this infrared spectrum and DS1 value as the standard, subsequent tests were conducted based on the 1605 cm⁻¹ value in the product's infrared spectrum.-1 and 1060cm -1 The absorption peak at that point is compared with the standard spectrum, and the absorbance DS2 of different products is calculated according to the formula.

[0050] Rheological performance testing The viscosity of drilling fluids was tested at room temperature and atmospheric pressure using a six-speed rotational viscometer according to American Petroleum Institute (API) standards. The rheological parameters of the drilling fluids, namely apparent viscosity (AV), plastic viscosity (PV), and yield point (YP), were calculated based on the readings of the six-speed rotational viscometer at 600 and 300 rpm.

[0051] Filterability API Testing According to the American Petroleum Institute (API) standard, a pressure of 0.69 ± 0.03 MPa was applied at room temperature using a medium-pressure fluid loss meter (ZNS-2A type, China). Timing started the moment the pressure stabilized, and the collected filtrate volume (FLAPI) was read and recorded after 30 minutes.

[0052] Filterability HTHP test According to the American Petroleum Institute (API) standard, high-temperature high-pressure filtration volume (FLHTHP) is measured using a high-temperature high-pressure filtration device (GGS42, Qingdao Jiaonan Tongchun Machinery Petroleum Instruments, China) at a pressure of 3.5 MPa and a set temperature.

[0053] Particle size distribution measurement The prepared drilling fluid was fully dispersed using a laser particle size analyzer (S3500, Malvern, UK) to form a uniform suspension with appropriate concentration. The instrument was started to measure the background of the dispersion medium. The sample suspension was then smoothly introduced into the sample cell for laser scattering measurement. After the results stabilized, the data was saved, and the sample cell and pipeline were thoroughly cleaned for future use.

[0054] Zeta potential measurement The stability of drilling fluid was studied using a Zeta potential analyzer (S3500, Malvern Instruments, UK). The drilling fluid was diluted 10 times and injected into a dedicated sample cell. Electrodes were inserted, parameters were set, and the instrument was started to measure the Zeta potential three times. The average value was then used for further analysis.

[0055] Example 1 The CMC-Na of this embodiment is prepared by the following steps: Measure 140 mL of isopropanol and 20 mL of distilled water into a 250 mL three-necked flask as solvents. Add 10 mL of 27.5 wt% NaOH solution (27.5 wt% is the percentage relative to the total mass of NaOH solution, chloroacetic acid, and cotton) as an alkalizing agent, and then add 6 wt% urea (6 wt% is the percentage relative to the total mass of NaOH solution, chloroacetic acid solution, and cotton). While stirring, add 5 g of cotton and react for 2 h at 20 °C. After alkalization, slowly add 12 mL of 35% chloroacetic acid solution, then gradually raise the temperature to the etherification reaction temperature. After raising the temperature to 50 °C, react for 1 h, then continue to raise the temperature to 65 °C and react for another 1 h. After etherification, adjust the system to neutral with glacial acetic acid, filter to remove the solvent, and wash with 80% ethanol aqueous solution in a 250 mL flat-bottomed beaker with stirring. Filter again. Repeat three times to remove chloride ions. Then dry in a 105 °C oven for 2 h, pulverize after drying, and pass through an 80 mesh sieve to obtain CMC-Na.

[0056] Example 2 This embodiment proposes a g-CMC, prepared by the following steps: CMC-Na obtained in Example 1 is dissolved in distilled water to prepare a 3% (w / w) CMC-Na solution. NVP is added at a mass ratio of CMC-Na:NVP = 1:3, and the mixture is stirred. 0.05% (w / w) of cerium ammonium nitrate (by mass of NVP) is added as an initiator, and the mixture is reacted at 70°C for 6 hours while nitrogen gas is introduced. After cooling, ethanol is added to precipitate the product. Unreacted NVP is washed with water and ethanol, and the product is dried to obtain the grafted product. The g-CMC preparation flowchart is shown below. Figure 2 As shown.

[0057] Example 3 This embodiment proposes a g-CMC, prepared by the following steps: CMC-Na obtained in Example 1 is dissolved in water to prepare a 1% (w / w) CMC-Na solution. NVP is added at a mass ratio of CMC-Na:NVP = 1:5, and the mixture is stirred. 0.05% (w / w) of cerium ammonium nitrate (by mass of NVP) is added as an initiator, and the mixture is reacted at 80°C for 2 hours while nitrogen gas is introduced. After cooling, ethanol is added to precipitate the product. Unreacted NVP is washed with water and ethanol, and the product is dried to obtain the grafted product. The g-CMC preparation flow chart is shown below. Figure 2 As shown.

[0058] Example 4 This embodiment proposes a g-CMC, prepared by the following steps: CMC-Na obtained in Example 1 is dissolved in water to prepare a 5% (w / w) CMC-Na solution. NVP is added at a mass ratio of CMC-Na:NVP = 1:1, and the mixture is stirred. 0.05% (w / w) of cerium ammonium nitrate (by mass of NVP) is added as an initiator, and the mixture is reacted at 60°C for 4 hours while nitrogen gas is introduced. After cooling, ethanol is added to precipitate the product. Unreacted NVP is washed with water and ethanol, and the product is dried to obtain the grafted product. The g-CMC preparation flowchart is shown below. Figure 2 As shown.

[0059] Example 5 This embodiment proposes a drilling fluid base fluid, prepared by the following steps: Add 40g of bentonite and 2g of sodium carbonate to 1000mL of water, stir at 11000r / min for 20min (this speed is used for all subsequent stirring), and cure at room temperature for 24h to obtain the base slurry. Take an appropriate amount of the base slurry and add 1.5% by weight of the filtration loss reducer g-CMC prepared in Example 2 above, stir at high speed until the filtration loss reducer is uniformly dispersed, then place it in an aging tank and age it in an aging furnace at 60℃ for 16h, then remove it for later use.

[0060] Example 6 This embodiment proposes a drilling fluid base fluid, prepared by the following steps: Add 40g of bentonite and 2g of sodium carbonate to 1000mL of water, stir at 11000r / min for 20min (this speed is used for all subsequent stirring), and cure at room temperature for 24h to obtain the base slurry. Take an appropriate amount of base slurry and add 0%, 0.5%, 1.0%, 1.5%, 2.0%, and 2.5% of g-CMC prepared in Example 2 according to the proportions of the base slurry mass, respectively. Stir at high speed until the filtration loss reducer is evenly dispersed, then put it into an aging tank and age it in an aging furnace at 60℃ for 16h. Take it out for later use to obtain 6 different drilling fluid base fluids.

[0061] Example 7 The CMC-Na of this embodiment is prepared by the following steps: Measure 10 mL of 27.5 wt% NaOH solution (27.5 wt% is the percentage relative to the total mass of NaOH solution, chloroacetic acid solution, and cotton) into a 250 mL three-necked flask. Add 140 mL of isopropanol and 20 mL of distilled water as solvents. Then add 0 wt%, 2 wt%, 4 wt%, 6 wt%, and 8 wt% urea (0 wt%, 2 wt%, 4 wt%, 6 wt%, and 8 wt% are the percentages relative to the total mass of NaOH solution, chloroacetic acid solution, and cotton) respectively. While stirring at 20 °C, add 5 g of cotton and react for 2 h. After alkalization, slowly add 12 mL of 35% chloroacetic acid solution. Then gradually raise the temperature to the etherification reaction temperature. After raising the temperature to 50 °C, react for 1 h. Continue to raise the temperature to 65 °C and react for 1 h. After etherification, adjust the system to neutral with glacial acetic acid, filter to remove the solvent, wash with 80% ethanol aqueous solution in a 250 mL flat-bottomed beaker, and filter. Repeat the process three times to remove chloride ions; then dry in an oven at 105℃ for 2 hours, pulverize after drying, and pass through an 80-mesh sieve to obtain five kinds of CMC-Na.

[0062] This embodiment proposes a g-CMC, which is prepared by the following steps: The five types of CMC-Na obtained above are dissolved in distilled water to prepare a 3% (w / w) CMC-Na solution. NVP is added at a mass ratio of CMC-Na:NVP = 1:3, and the mixture is stirred. 0.05% (w / w) of cerium ammonium nitrate (by mass of NVP) is added as an initiator, and the mixture is reacted at 70°C for 6 hours while nitrogen gas is introduced. After cooling, ethanol is added to precipitate the product. Unreacted NVP is washed with water and ethanol, and the mixture is dried to obtain the five grafted products, g-CMC.

[0063] This embodiment proposes a drilling fluid base fluid, prepared by the following steps: Add 40g of bentonite and 2g of sodium carbonate to 1000mL of water, stir at 11000r / min for 20min (this speed is used for all subsequent stirring), and cure at room temperature for 24h to obtain the base slurry. Take an appropriate amount of the base slurry and add 1.5% of the above five filtration loss reducers g-CMC by weight of the base slurry, stir at high speed until the filtration loss reducers are evenly dispersed, then put it into an aging tank and age it in an aging furnace at 60℃ for 16h, then remove it for later use.

[0064] Example 8 The CMC-Na of this embodiment is prepared by the following steps: Measure 10 mL of 27.5 wt% NaOH (27.5 wt% is the percentage relative to the total mass of NaOH solution, chloroacetic acid solution, and cotton) into a 250 mL three-necked flask. Add 140 mL of isopropanol and 5 mL, 10 mL, 15 mL, 20 mL, 25 mL, or 30 mL of distilled water as solvents. Then add 6 wt% urea (6 wt% is the percentage relative to the total mass of NaOH solution, chloroacetic acid solution, and cotton). While stirring at 20 °C, add 5 g of cotton and react for 2 h. After alkalization, slowly add 12 mL of 35% chloroacetic acid solution. Then gradually raise the temperature to the etherification reaction temperature. After raising the temperature to 50 °C, react for 1 h, and then continue to raise the temperature to 65 °C and react for 1 h. After etherification, adjust the system to neutral with glacial acetic acid, filter to remove the solvent, wash with 80% ethanol aqueous solution in a 250 mL flat-bottomed beaker, and filter. Repeat the process three times to remove chloride ions; then dry in an oven at 105℃ for 2 hours, pulverize after drying, and pass through an 80-mesh sieve to obtain six kinds of CMC-Na.

[0065] This embodiment proposes a g-CMC, which is prepared by the following steps: The six CMC-Na types prepared above are dissolved in distilled water to prepare a 3% (w / w) CMC-Na solution. NVP is added at a mass ratio of CMC-Na:NVP = 1:3, and the mixture is stirred. 0.05% (w / w) of cerium ammonium nitrate (by mass of NVP) is added as an initiator, and the mixture is reacted at 70°C for 6 hours while nitrogen gas is introduced. After cooling, ethanol is added to precipitate the product. Unreacted NVP is washed with water and ethanol, and the mixture is dried to obtain the six grafted products, g-CMC.

[0066] This embodiment proposes a drilling fluid base fluid, prepared by the following steps: Add 40g of bentonite and 2g of sodium carbonate to 1000mL of water, stir at 11000r / min for 20min (this speed is used for all subsequent stirring), and cure at room temperature for 24h to obtain the base slurry. Take an appropriate amount of the base slurry and add 1.5% of the above six filtration loss reducers g-CMC by weight of the base slurry, stir at high speed until the filtration loss reducers are evenly dispersed, then put it into an aging tank and age it in an aging furnace at 60℃ for 16h, then remove it for later use.

[0067] Comparative Example 1 The difference between this comparative example and Example 6 is that the g-CMC in the drilling fluid base fluid is replaced with an equal amount of CMC-Na prepared in Example 1. Specifically, this comparative example proposes a drilling fluid base fluid prepared by the following steps: 40g of bentonite and 2g of sodium carbonate are added to 1000mL of water, and the mixture is stirred at 11000r / min for 20min (this speed is used for all subsequent stirring). After curing at room temperature for 24h, it is used as the base slurry. An appropriate amount of base slurry is taken, and 0, 0.5%, 1.0%, 1.5%, 2.0%, and 2.5% of the CMC-Na prepared in Example 1 are added according to the proportions. The mixture is stirred at high speed until the filtration loss reducer is evenly dispersed, then it is placed in an aging tank and aged in an aging furnace at 60℃ for 16h. The resulting six different drilling fluid base fluids are then ready for use.

[0068] Results and Discussion Figure 3 The IR spectra of cotton from Example 1, the prepared CMC-Na, and g-CMC from Example 2 are shown at 3467 cm⁻¹. -1 The stronger absorption peak nearby is the hydroxyl (OH) absorption peak, 1013 cm⁻¹. -1 The area near the COC bond shows absorption peaks. The -COOH of CMC-Na, the -COOH of g-CMC, and the -C=O peak are at 1619 cm⁻¹. -1 The absorption peak is generated by the nearby asymmetric stretching vibration, at 1421 cm⁻¹. -1 The peak at this point represents the CN bond absorption peak of g-CMC. Infrared testing results confirm that CMC-Na and g-CMC are the target products.

[0069] Figure 4 SEM images of cotton from Example 1, the prepared CMC-Na, and g-CMC from Example 2 are shown. Cotton fibers are long, flat, ribbon-like, with a naturally twisted spiral shape along the axial direction. The cross-section is kidney-shaped, shriveled in the middle, and while the fiber surface has shallow fine lines along the axial direction, it is generally smooth. Modified CMC-Na fibers become fuller after radial expansion, with a circular cross-section. The surface roughness increases, some protrusions appear, the specific surface area increases, and axial breakage is more pronounced. The overall morphology of g-CMC fibers is similar to CMC-Na, but the surface roughness further increases, with numerous pores appearing, and the specific surface area further increases. Furthermore, the axial breakage of g-CMC fibers is slightly increased compared to CMC-Na. SEM analysis confirmed that both carboxymethyl modification and grafting modification altered the morphology of cellulose, increasing surface roughness and specific surface area. It is believed that this morphological change in cellulose is beneficial for its better contact with water, clay, and inorganic salts when used as a drilling fluid filtration reducer, thus enhancing its filtration reduction effect.

[0070] Figure 5The POM images of the cotton from Example 1, the prepared CMC-Na, and the g-CMC from Example 2 show no obvious light-dark variations in the dry cotton. This is not because the dry cotton lacks a crystalline structure; in fact, the dry cotton has a high crystallinity (approximately 70%). This phenomenon occurs because the crystalline structure of cotton fibers typically exists in the form of microfibrils, which are tightly packed and relatively disordered, resulting in minimal birefringence and thus no light-dark variations observed in the POM image. The dried CMC-Na and g-CMC products exhibit a brownish luminescence in their POM images, but this luminescence is discontinuous, the boundaries of light-dark variations are unclear, and there is a distinct brown interference color. Since brown interference colors appear in POM images when the crystallinity of cellulose is low, it can be determined that the crystallinity of CMC-Na and g-CMC is low. The cotton after absorbing water exhibits a more continuous luminescence along its axis. This is because water molecules enter the cotton fibers, forming hydrated crystals. Furthermore, the water molecules alter the arrangement of the cellulose macromolecules, enhancing anisotropy. The POM images of CMC-Na and g-CMC dissolved in water show discontinuous axial luminescence, with g-CMC exhibiting a further enhanced discontinuous luminescence phenomenon compared to CMC-Na. This indicates that the carboxymethylation and grafting modifications of cotton alter the microstructure of cotton fiber macromolecules, reducing crystallinity. Analysis suggests that the reduced crystallinity of cellulose and the increased intermolecular distances facilitate better penetration and contact of water molecules, thereby improving filtration efficiency.

[0071] Depend on Figure 6 It can be seen that DS first increases and then decreases with the increase of water-to-cotton ratio and urea dosage. Filtration loss is related to DS; the larger the DS, the smaller the filtration loss. When the water-to-cotton ratio is 4 and the urea dosage is 6 wt%, the DS is at its maximum of 1.12. Analysis suggests that a low water-to-cotton ratio and insufficient water dosage reduce the swelling capacity of the alkali solution, while excessive water dosage increases side reactions such as hydrolysis. Urea can activate cellulose, allowing -OH groups to react better with the etherifying agent; however, excessive urea will form a large number of hydrogen bonds with -OH groups, affecting the formation and uniform distribution of sodium cellulose salts, thus affecting DS and filtration loss.

[0072] Rheology and filtration loss are two important indicators for evaluating drilling fluid performance. Therefore, the effects of g-CMC and CMC-Na addition on the rheology and filtration loss of the drilling fluid base fluid in Example 6 and Comparative Example 1 were analyzed, and the results are shown in Table 1.

[0073] Table 1. Effects of g-CMC and CMC-Na addition on drilling fluid properties in Example 6 and Comparative Example 1 Table 1 shows that the addition of CMC-Na and g-CMC significantly reduced FLAPI and FLHTHP levels. Furthermore, with increasing concentration, the rheological properties continuously increased, while the filtration loss continuously decreased. Comparison revealed that the filtration loss and rheological properties of g-CMC were consistently lower than those of CMC-Na at the same concentration. Since excessively high rheological properties such as AV in drilling fluids are detrimental to safe operation, and the decreasing trend in filtration loss slows down after the product dosage exceeds 1.5 wt%, the optimal dosage of g-CMC for this product was determined to be 1.5 wt%.

[0074] Drilling fluids may be exposed to high-temperature environments for extended periods, therefore, filtration loss reducers are required to have good temperature resistance. Figure 7 The changes in filtration loss after aging at different temperatures for 16 hours were analyzed, revealing a significant inflection point in the filtration loss curve above 160℃. To further clarify the product's temperature resistance at 160℃, the effect of aging time on filtration loss was analyzed. It was found that after 96 hours of aging, the filtration loss of g-CMC did not increase significantly, remaining less than 10 ml, while the filtration loss of CMC-Na increased significantly with aging time. Combined with TG-DTG analysis results, it is believed that temperatures above 160℃ cause partial decomposition of carboxymethyl groups, leading to a decrease in DS (dissolved solids) and affecting filtration loss. Furthermore, the macromolecular backbone -CC- is prone to aging and chain breakage under prolonged high-temperature conditions, resulting in a decrease in molecular weight, which also affects filtration loss. The introduction of the rigid five-membered ring structure of NVP in the g-CMC molecule increases the molecular motion barrier. In addition, its grafting structure can alleviate the damage to the overall macromolecular structure caused by -CC- chain breakage. Therefore, g-CMC exhibits better temperature resistance than CMC-Na.

[0075] The TG-DTG analysis results of the g-CMC obtained in Example 2 are as follows: Figure 8 As shown, its thermal weight loss can be divided into four stages. The mass loss is approximately 6.45% between 30°C and 234°C, approximately 33.05% between 234°C and 314°C, with the largest heat loss occurring at 285°C. Above 100°C, intramolecularly bound water and other molecules volatilize, resulting in mass loss. As the temperature continues to rise, less thermally stable molecules such as hydroxyl and carboxymethyl groups decompose, causing further mass loss, although the amount is relatively small. At 285°C, a large number of functional groups decompose, severely damaging the molecular structure and resulting in a significant mass loss.

[0076] Filter cake morphology analysis: The filter cake formed on the wellbore during drilling is thin and dense, resulting in wellbore stability, low water loss, and minimal formation damage from the drilling fluid. Filter cakes obtained from API tests of different drilling fluid systems were compared, and samples were taken from the filter cakes and observed under a polarizing microscope. The results are as follows: Figure 10 As shown.

[0077] Depend on Figure 9It can be seen that adding sodium chloride to the base slurry increases the filter cake thickness. Further addition of CMC-Na or g-CMC reduces the filter cake thickness and significantly improves its density. The filter cake thickness and density of the g-CMC drilling fluid system are superior to those of CMC-Na. The presence of luminescence in the POM image indicates the presence of crystalline structures in the filter cake. Without cellulose, the crystals are fine and dispersed. Further addition of CMC-Na or g-CMC significantly increases the crystal size, and the crystallization ratio of the g-CMC system is higher than that of CMC-Na. Both the filter cake and POM comparisons demonstrate that cellulose effectively adsorbs clay and sodium chloride particles, forming a stable structure. Furthermore, it indicates that the adsorption stability of g-CMC is superior to that of CMC-Na.

[0078] Zeta potential analysis: The zeta potential is a key parameter for measuring drilling fluid stability, and its absolute value reflects the strength of the repulsive force between particles. A low absolute value of zeta potential (<30mV) indicates that particles such as clay aggregate too quickly, easily forming loose mud cakes and increasing the risk of filtration loss. A high absolute value of zeta potential indicates enhanced electrostatic repulsion between particles, resulting in system stability and improved filtration loss reduction.

[0079] The zeta potential of different drilling fluid systems was analyzed, and the results are as follows: Figure 10 As shown, the zeta potential of the base slurry is -33.44 mV, close to the critical value for drilling fluid stability. Adding NaCl to the base slurry reduces the absolute value of the zeta potential to -20.44 mV. However, adding the filtration loss reducer CMC-Na or g-CMC to the base slurry increases the absolute value of the zeta potential to over -50.44 mV. Further addition of sodium chloride slightly decreases the absolute value of the zeta potential. The addition of NaCl may induce double-layer compression, electrostatic shielding, and thinning of the hydration film, reducing the dispersion stability of clay particles and thus decreasing the absolute value of the zeta potential. Adding the filtration loss reducer increases the thickness of the diffuse double layer and hydration film on the particle surface, improving stability and increasing the absolute value of the zeta potential. Further addition of NaCl does not significantly reduce the absolute value of the zeta potential, indicating that g-CMC can effectively adsorb NaCl, reducing the adverse effects of NaCl on the stability of bentonite particles.

[0080] Particle size distribution analysis: A reasonable particle size distribution is conducive to the formation of a thin and dense filter cake, thus improving the filtration loss reduction effect. Combined with... Figure 11 The study found that adding NaCl to the base slurry increased the D50 from 13.08 μm to 15.55 μm, while adding g-CMC decreased the D50 from 13.08 μm to 7.78 μm. Further addition of sodium chloride increased the D50 to 9.25 μm. These results indicate that g-CMC is beneficial for the formation of a hydration film on the surface of clay particles and reduces the D50. + To mitigate the adverse effects on the dispersion stability of clay particles and prevent excessive aggregation of clay particles.

[0081] Salt resistance analysis: Table 2 analyzes the effect of NaCl addition on filtration loss and rheological properties. Rheological parameters such as apparent viscosity and filtration loss both increase with increasing NaCl addition, but the increasing trend is not significant. NaCl reduces the electrostatic repulsion between chain segments through salting out, double-layer compression, and ion bridging, leading to molecular chain aggregation, increased solution viscosity, and increased filtration loss. However, when the NaCl addition is as high as 30 wt%, the API and AV values ​​of the drilling fluid base fluid system in Example 5 (i.e., the data corresponding to g-CMC in Table 2) are 9.97 mL and 46.2 mPa·s, respectively, meeting the relevant drilling fluid requirements. This indicates that the introduction of NVP electrically neutral grafted chains in g-CMC further improves the salt resistance of the product. In Table 2, g-CMC represents the drilling fluid base fluid of Example 5, and CMC-Na in Table 2 represents the drilling fluid base fluid prepared by adding 1.5% CMC-Na by mass of the base slurry in Comparative Example 1.

[0082] Table 2 Effect of NaCl concentration on polymer rheology and filtration properties This invention uses natural cotton as raw material, and prepares CMC-Na through alkalization and etherification reactions. NVP is then used for graft copolymerization on CMC-Na to obtain g-CMC. IR analysis confirmed the product as the target product. SEM and POM analysis showed that carboxymethylation and graft modification altered the microstructure of cellulose, reducing crystallinity and increasing specific surface area, which facilitates better contact between g-CMC and clay particles, thus reducing filtration loss. Response surface methodology was used to analyze the effect of reaction conditions on filtration loss, optimizing the optimal alkalization dosage to 27.5 wt% and the optimal etherification dosage to 35 wt%. Single-factor analysis determined that a urea dosage of 6 wt% and a water-to-cotton ratio of 4 resulted in the highest degree of substitution (1.12) for g-CMC. Rheological and filtration loss analysis determined the optimal dosage of g-CMC in drilling fluid to be 1.5 wt%. High-temperature aging experiments confirmed that the filtration loss of g-CMC remained essentially unchanged after long-term use at 160°C. Drilling fluid particle size distribution, zeta potential, filter cake morphology, and POM analysis confirmed that this filtration loss reducer effectively adsorbed and stabilized clay and sodium chloride, exhibiting good coalescence stability. Even with a sodium chloride concentration as high as 30%, the drilling fluid maintained good rheological properties and filtration loss characteristics. The results indicate that g-CMC meets the relevant performance requirements of this study and is an environmentally friendly filtration loss reducer with high temperature resistance, salt tolerance, and high coalescence stability.

[0083] The specific embodiments of the present invention described above do not constitute a limitation on the scope of protection of the present invention. Any other corresponding changes and modifications made in accordance with the technical concept of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing modified carboxymethyl cellulose, characterized in that, The process includes the following steps: mixing a carboxymethyl cellulose solution with NVP, then adding an initiator, reacting at 60°C to 80°C and purging with nitrogen to obtain the modified carboxymethyl cellulose.

2. The method for preparing modified carboxymethyl cellulose according to claim 1, characterized in that, The mass ratio of the NVP to the carboxymethyl cellulose in the carboxymethyl cellulose solution is (1-5):

1.

3. The method for preparing modified carboxymethyl cellulose according to claim 1 or 2, characterized in that, The carboxymethyl cellulose solution is prepared by dissolving carboxymethyl cellulose in water; the mass concentration of the carboxymethyl cellulose solution is 1-5%.

4. The method for preparing modified carboxymethyl cellulose according to claim 1, characterized in that, The initiator is cerium ammonium nitrate.

5. The method for preparing modified carboxymethyl cellulose according to claim 1, characterized in that, The reaction time is 2 to 6 hours at 60°C to 80°C; and / or, after the reaction at 60°C to 80°C, the product is cooled, then ethanol is added to precipitate the product, and the product is washed with water and ethanol, and then dried.

6. The method for preparing modified carboxymethyl cellulose according to claim 1, characterized in that, The carboxymethyl cellulose in the carboxymethyl cellulose solution is obtained by the following steps: NaOH solution, isopropanol, urea and cotton were mixed and stirred, and then chloroacetic acid solution was added dropwise. The temperature was then gradually raised to 50-55℃ for reaction, and then the temperature was further raised to 65-75℃ for reaction. The system was then adjusted to neutral with glacial acetic acid, and then washed and dried to obtain the carboxymethyl cellulose.

7. A modified carboxymethyl cellulose, characterized in that, It is prepared by the preparation method according to any one of claims 1-6.

8. The use of the modified carboxymethyl cellulose prepared by the preparation method according to any one of claims 1-6 or the modified carboxymethyl cellulose according to claim 7 in the preparation of drilling fluid base fluid.

9. A drilling fluid base fluid, characterized in that, Includes the base pulp and the modified carboxymethyl cellulose as described in claim 8; The modified carboxymethyl cellulose accounts for 0.5%-2.5% of the mass of the base slurry; the base slurry, calculated by mass parts, includes 40-45 parts bentonite, 2-4 parts sodium carbonate and 1000-1100 parts water.

10. A method for preparing the drilling fluid base fluid according to claim 9, characterized in that, The process includes the following steps: mixing bentonite, sodium carbonate, and water, then curing to obtain a base slurry; adding modified carboxymethyl cellulose to the base slurry and stirring; and then aging at 55-60°C to obtain the drilling fluid base fluid.

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