Quadripolymer multifunctional oil well cement fluid loss agent and preparation method thereof

Abstract

The invention discloses a quadripolymer multifunctional oil well cement fluid loss agent, relates to the field of oil well cementation, and solves the problems that when an existing fluid loss agent is used in medium-high-temperature conventional and unconventional horizontal wells, the low-temperature well is super-retarded, the thickening time is reversed, the high-temperature well cement slurry viscosity is too high, and the well cementation quality is difficult to guarantee due to abnormal gelling. The cement fluid loss agent is composed of the following components in parts by weight: 15-42 parts of inorganic salt; 0.1-1 part of a dispersion stabilizer; 0.49 to 16 parts of an anionic monomer; 2.69 to 29 parts of a nonionic monomer; 0-9.6 parts of inorganic mineral substances or biological organic matters; 100 parts of deionized water; the preparation method comprises the following steps: weighing the inorganic salt in proportion, putting the inorganic salt into a reactor, adding the deionized water and the dispersion stabilizer, pouring the anionic monomer and the nonionic monomer, and stirring; adding an inorganic mineral substance or a biological organic matter to enable the solid content of the active monomer in the solution to be 7-42wt%; and adding an initiator for copolymerization to obtain the product.

Description

Technical Field

[0001] This invention relates to the field of oil well cementing, and in particular to a quaternary copolymer-based multifunctional oil well cement fluid loss reducing agent and its preparation method. Background Technology

[0002] With the increasing development and utilization of unconventional oil and gas resources globally, medium-to-high maturity shale oil and tight oil have become the most promising strategic replacement resources in the petroleum industry. In recent years, shale oil development has entered a phase of rapid growth. Horizontal wells combined with large-scale volumetric fracturing are effective means to increase shale oil production. To ensure the effectiveness of large-scale volumetric fracturing, the cementing quality of the horizontal section of the horizontal well is one of the key factors. These unconventional oil and gas reservoirs typically have complex geological environments such as low permeability, high stress, high temperature, and high pressure, which makes it necessary to solve more technical problems during the cementing process. Cement fluid loss control agents play a crucial role in cementing operations. During cementing, water in the cement slurry will be lost to the formation when passing through permeable formations. If the water loss of the cement slurry is not well controlled, it will lead to a lower water-cement ratio, insufficient hydration of cement particles, loose cement stone structure, and even bridging, resulting in annular flow, interlayer sealing failure, and seriously affecting cementing quality.

[0003] Currently available fluid loss control agents generally suffer from thickening and flocculation defects. Within the 80-90℃ range, they are prone to excessively high cement slurry consistency, thickening reversal, and excessively slow setting. At 100℃-120℃, differences in oil well cement hydration can also induce fluid loss control agent deterioration, causing degradation or decomposition of water-soluble and adsorbent groups in their molecular structure. This not only reduces their ability to control free water but may also affect the thickening performance of oil well cement, leading to "core-encasing" and temperature inversion phenomena, threatening construction safety and cementing quality. To ensure construction safety, their dosage in cement slurry systems is limited, making it difficult to meet the cementing requirements of horizontal wells and shale oil wells under these conditions. High-temperature resistant products have excessive performance margins, are prone to excessively slow setting and slow low-temperature strength development, and are relatively expensive. Their molecular structure design focuses on the physicochemical reaction with oil well cement at ultra-high temperatures, but these measures are not entirely effective for oil well cement in the medium-to-high temperature range.

[0004] In summary, existing oil well cement fluid loss control agents still have certain shortcomings under medium and high temperature conditions, especially when used in medium and high temperature (80-120℃) horizontal wells. Low temperature wells are prone to problems such as excessively slow setting and thickening reversal. When used in high temperature wells, the settling stability is poor. When used in combination with stabilizers, it is not easy to settle the cement, the slurry is viscous, and there is a problem of low temperature viscosity and high temperature dilution, which is not conducive to the stability of cement slurry performance and the improvement of cementing quality. Summary of the Invention

[0005] This invention addresses the problems of existing fluid loss control agents in conventional and unconventional horizontal wells at medium and high temperatures, such as excessively slowed setting in low-temperature wells, reversal of thickening time, and excessively high cement slurry viscosity and abnormal gelation in high-temperature wells, which make it difficult to ensure cementing quality. It provides a quaternary copolymer-based multifunctional oil well cement fluid loss control agent. This quaternary copolymer-based multifunctional oil well cement fluid loss control agent has a wide applicable temperature range. In addition to good temperature resistance, time delay, and fluid loss control effects, it also has weak slowing and dispersing effects. It can meet the thickening, rheological, and other performance requirements of cement slurry in horizontal wells at 80-120℃ without the addition of retarders or dispersants, achieving multiple effects with a single agent and effectively reducing costs. This invention also provides a method for preparing the quaternary copolymer-based multifunctional oil well cement fluid loss control agent.

[0006] The present invention solves its problems through the following technical solution: This quaternary copolymer multifunctional oil well cement fluid loss reducing agent is composed of the following components in parts by weight:

[0007] Inorganic salts 15-42 parts; dispersant stabilizer 0.1-1 parts; anionic monomers 0.49-16 parts; nonionic monomers 2.69-29 parts; inorganic minerals or biological organic matter 0-9.6 parts; deionized water 100 parts.

[0008] Preferably, the inorganic salt is at least one selected from potassium chloride, sodium chloride, ammonium chloride, potassium sulfate, sodium sulfate, and ammonium sulfate.

[0009] Preferably, the dispersant stabilizer is a cationic polymer or a nonionic polymer with a molecular weight of 100,000 to 1,500,000;

[0010] Preferably, the cationic polymer is at least one of poly(dimethyldiallylammonium chloride), poly(acryloyloxyethyltrimethylammonium chloride), and poly(methacryloyloxyethyltrimethylammonium chloride);

[0011] The nonionic polymer is at least one of polyvinyl alcohol and polyvinylpyrrolidone.

[0012] Preferably, the anionic monomer is at least one selected from AMPS (2-acrylamide-2-methylpropanesulfonic acid), acrylic acid, styrene sulfonate, vinyl sulfonate, methacrylic acid, fumaric acid, and itaconic acid.

[0013] The nonionic monomer is at least one of acrylamide, N,N-dimethylacrylamide, and NVP (N-vinylpyrrolidone).

[0014] Preferably, the inorganic mineral is a common mineral or a partially hydrophobically modified mineral, with a median particle size ranging from 0.1 to 300 micrometers;

[0015] The biological organic matter is at least one of lignin sulfonate, cellulose derivative, starch derivative, and xanthan gum derivative.

[0016] Preferably, the hydrophobic modified mineral is hydrophobic modified fly ash;

[0017] The preparation method of the hydrophobic modified fly ash is as follows: fly ash is pretreated by sieving with an 80-mesh sieve to remove impurities and obtain fly ash with a particle size of less than 150 µm; the pretreated fly ash is then dried in an oven at 105 ℃ for 4 h; the fly ash is hydrophobically modified by esterification using long-chain acyl chloride as a hydrophobic agent and anhydrous ethanol as a solvent; after the reaction is completed, the fly ash is centrifuged, the lower precipitate is dispersed and centrifuged again with anhydrous ethanol, and this process is repeated 2-3 times; the lower precipitate is then dried for later use.

[0018] The long-chain acyl chloride is at least one of lauroyl chloride, myristoyl chloride, palmitoyl chloride, and stearoyl chloride; the amount of long-chain acyl chloride used is 5-50 wt% of the fly ash; the esterification reaction temperature is 60-80℃; and the esterification reaction time is 12-24h.

[0019] This invention also provides a method for preparing a quaternary copolymer-based multifunctional oil well cement fluid loss reducing agent, comprising the following steps:

[0020] Weigh out 15-42 parts of inorganic salt according to the mass ratio and put them into the reactor. Add 100 parts of deionized water and stir well.

[0021] Weigh 0.1-1 part of a cationic or nonionic polymer with a molecular weight of 100,000 to 1,500,000 as a dispersing stabilizer and add it to the reactor, stirring until homogeneous;

[0022] Weigh 0.49-16 parts of anionic monomer and 2.69-29 parts of nonionic monomer and pour them into the reactor, then stir until homogeneous;

[0023] Weigh out 0-9.6 parts of inorganic minerals or biological organic matter and pour them into the reactor, then stir until homogeneous; adjust the pH value to 6-7.

[0024] A certain amount of deionized water is added to make the solid content of the active monomer in the solution 7-42wt%; then 0.1-5% of the active monomer mass of initiator is added to carry out free radical copolymerization, and the resulting product is a fluid loss reducing agent for cementing slurry.

[0025] Preferably, the mass ratio of the anionic monomer to the nonionic monomer is 1:1 to 1:10;

[0026] The initiator is at least one of persulfate, hydrogen peroxide, or water-soluble azo initiators.

[0027] Preferably, the pH value is adjusted to 6-7 by adding sodium hydroxide.

[0028] Preferably, the free radical copolymerization reaction temperature is 30–60°C, and the polymerization reaction time is 4–16 hours.

[0029] In this invention, there is a significant synergistic effect among the components of the dehydration agent molecule:

[0030] Anionic monomers , The ionic monomers form a hydration film through electrostatic adsorption and hydration to stabilize cement particles and enhance the adsorption capacity of polymer chains. The large side groups of nonionic monomers provide steric hindrance, and the two work synergistically to inhibit cement particle agglomeration and abnormal gelation, while enhancing temperature resistance and shear resistance. Anionic / nonionic monomers and cationic polymer stabilizers enhance intermolecular interactions through charge attraction, accelerating the formation of weakly cross-linked colloids. Combined with the thickening effect of nonionic polymer stabilizers, this optimizes the rheology of cement slurry and improves the stability of colloid embedding in mud cake to enhance the water loss reduction effect. Organic monomers combined with inorganic minerals or biological organic matter not only improve compatibility through the adsorption and complexation properties of organic segments, but also enhance the toughness of cement stone by relying on the rigidity of inorganic / biological components. Furthermore, the salt resistance and environmental friendliness of both are superimposed, further improving performance and reducing costs. In addition, the weak retarding properties of nonionic monomers, the retardation effect of anionic monomers on hydration, and the regulation effect of cationic stabilizers on thickening time work synergistically to meet the requirements of 80-120℃ horizontal wells without the need for additional retarder, achieving multi-functional synergistic effects.

[0031] Compared with the above-mentioned background technology, the present invention has the following beneficial effects:

[0032] This invention discloses a quaternary copolymer-based multifunctional oil well cement fluid loss reducer. By selecting monomers with specific functionalities and employing graft copolymerization, these monomers are introduced into the molecular chain as modular carriers. Nonionic and anionic monomers serve as temperature-resistant, adsorption, and dispersion modules. Graft copolymerization forms a branched structure, reducing molecular chain deflection and increasing spatial distance. The hydrophilic-hydrophobic balance of the nonionic monomers imparts a weak retarding effect to the fluid loss reducer, while the charge repulsion of the anionic monomers enhances dispersion performance. Simultaneously, the rigid structure of inorganic minerals or biological organic matter participates in molecular chain construction, improving the overall strength of the copolymer combined with the cement system. The anionic monomers adsorb cement particles, and the ionic environment provided by the inorganic salts promotes molecular chain aggregation; the two synergistically form a weakly cross-linked colloid. The dispersant stabilizer regulates the colloidal dispersion state, allowing it to stably embed into the filter cake pores, significantly reducing filter cake permeability and thus enhancing fluid loss reduction performance. During water-dispersion polymerization, the dispersant stabilizer regulates the monomer dispersion state throughout the process. Combined with the stepwise addition of monomers, this avoids excessively high local concentrations. High concentrations initiate a synergistic effect of the ionic strength of the system and inorganic salts, precisely controlling the molecular weight distribution and ensuring the product possesses both suitable molecular weight and rapid dissolution and dispersion capabilities. Furthermore, the salt tolerance of each monomer in the water-dispersion system (especially the inorganic salts and dispersant stabilizer) is superimposed, enhancing the overall salt tolerance of the product while avoiding the use of organic solvents, thus improving environmental friendliness. The weak retarding effect of the nonionic monomers synergizes with the performance of other monomers, meeting the thickening time requirements of horizontal wells at 80-120℃ without the need for additional retarder. A single product achieves multiple functions, including reducing water loss, dispersion, and weak retarding, realizing multi-effects with cost control.

[0033] This invention relates to a quaternary copolymer-based multifunctional oil well cement fluid loss reducer. It has a wide applicable temperature range and, in addition to excellent temperature resistance, time delay, and fluid loss control, also possesses weak retarding and dispersing properties. It can meet the thickening and rheological performance requirements of cement slurry in horizontal wells at 80-120℃ without the addition of retarder or dispersant, achieving multiple effects with a single agent and effectively reducing costs. Furthermore, it can effectively suppress thickening reversal and abrupt thickening linear changes such as "bulging" and "steps" that are prone to occur with polycarboxylate additives in the medium- and high-temperature range. Simultaneously, the cement slurry has low initial thickness, adjustable thickening time, and low dosage sensitivity, providing strong technical support for the exploration, development, and transformation of oil and gas resources. Attached Figure Description

[0034] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present invention and, together with the specification, serve to explain the technical solutions of the present invention.

[0035] Figure 1 This is a thickening curve of the temperature drop dehydration agent in an embodiment of the present invention at 80℃ × 43.4MPa;

[0036] Figure 2This is a thickening curve of the temperature drop dehydration agent in an embodiment of the present invention at 90℃ × 53.3MPa;

[0037] Figure 3 This is a thickening curve of the temperature drop dehydration agent in Example 100 of the present invention at 60.2 MPa.

[0038] Figure 4 This is a thickening curve of the temperature drop dehydration agent in Example 1 of the present invention at 110℃ × 67.0MPa;

[0039] Figure 5 This is a thickening curve of the temperature drop dehydration agent in Example 1 of the present invention at 120℃ × 73.9MPa;

[0040] Figure 6 This is a graph showing the relationship between the amount of material added and the amount of filtration loss in Embodiment 1 of the present invention;

[0041] Figure 7 This is a flowchart of the preparation method of the quaternary copolymer multifunctional oil well cement dehydration reducer of the present invention. Detailed Implementation

[0042] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0043] Unless otherwise specified, the experimental methods used in the following examples are conventional methods; the materials and reagents used in the following examples are commercially available unless otherwise specified.

[0044] This invention is not limited to the specific embodiments listed below. Those skilled in the art can implement this invention using various other specific embodiments based on the content disclosed herein. Any modifications or alterations made to the design structure and concept of this invention fall within the protection scope of this invention. It should be noted that, unless otherwise specified, the embodiments and features described in this invention can be combined with each other.

[0045] A quaternary copolymer multifunctional oil well cement fluid loss reducer, comprising the following components in parts by weight:

[0046] Inorganic salts 15-42 parts; dispersant stabilizer 0.1-1 parts; anionic monomers 0.49-16 parts; nonionic monomers 2.69-29 parts; inorganic minerals or biological organic matter 0-9.6 parts; deionized water 100 parts.

[0047] The inorganic salt is at least one of potassium chloride, sodium chloride, ammonium chloride, potassium sulfate, sodium sulfate, and ammonium sulfate.

[0048] The dispersant stabilizer is a cationic polymer or a nonionic polymer with a molecular weight of 100,000 to 1,500,000.

[0049] The cationic polymer is at least one of poly(dimethyldiallylammonium chloride), poly(acryloyloxyethyltrimethylammonium chloride), and poly(methacryloyloxyethyltrimethylammonium chloride);

[0050] The nonionic polymer is at least one of polyvinyl alcohol and polyvinylpyrrolidone.

[0051] The anionic monomer is at least one selected from AMPS (2-acrylamide-2-methylpropanesulfonic acid), acrylic acid, styrene sulfonate, vinyl sulfonate, methacrylic acid, fumaric acid, and itaconic acid.

[0052] The nonionic monomer is at least one of acrylamide, N,N-dimethylacrylamide, and NVP (N-vinylpyrrolidone).

[0053] The inorganic minerals are ordinary minerals or partially hydrophobically modified minerals, with a median particle size ranging from 0.1 to 300 micrometers.

[0054] The biological organic matter is at least one of lignin sulfonate, cellulose derivative, starch derivative and xanthan gum derivative;

[0055] Preferably, the hydrophobic modified mineral is hydrophobic modified fly ash;

[0056] The preparation method of the hydrophobic modified fly ash is as follows:

[0057] Fly ash was pretreated by sieving through an 80-mesh sieve to remove impurities, resulting in fly ash with a particle size of less than 150 µm. The pretreated fly ash was then dried in an oven at 105 ℃ for 4 h. The fly ash was then modified by esterification using long-chain acyl chloride as a hydrophobic agent and anhydrous ethanol as a solvent. After the reaction, the fly ash was centrifuged, and the lower precipitate was dispersed and centrifuged again with anhydrous ethanol. This process was repeated 2-3 times, and the lower precipitate was dried for later use.

[0058] The long-chain acyl chloride is at least one of lauroyl chloride, myristoyl chloride, palmitoyl chloride, and stearoyl chloride; the amount of long-chain acyl chloride used is 5-50 wt% of the fly ash; the esterification reaction temperature is 60-80℃; and the esterification reaction time is 12-24h.

[0059] like Figure 7 As shown, the preparation method of the quaternary copolymer multifunctional oil well cement fluid loss reducing agent includes the following steps:

[0060] S1. Weigh 15-42 parts of inorganic salt according to the mass ratio and put them into the reactor. Add 100 parts of deionized water and stir evenly.

[0061] S2. Weigh 0.1-1 part of a cationic or nonionic polymer with a molecular weight of 100,000 to 1,500,000 as a dispersing stabilizer and add it to the reactor, stirring until homogeneous.

[0062] S3. Weigh 0.49-16 parts of anionic monomer and 2.69-29 parts of nonionic monomer and pour them into the reactor, then stir until homogeneous.

[0063] S4. Weigh 0-9.6 parts of inorganic minerals or biological organic matter and pour them into the reactor, stirring evenly; adjust the pH value to 6-7 by adding sodium hydroxide;

[0064] S5. Add a certain amount of deionized water to make the solid content of the active monomer in the solution 7-42wt%; add 0.1-5% of the active monomer mass of initiator to carry out free radical copolymerization. The free radical copolymerization reaction temperature is 30-60℃ and the polymerization reaction time is 4-16 hours. The product obtained is a water loss reducing agent for cementing slurry.

[0065] The mass ratio of the anionic monomer to the nonionic monomer is 1:1 to 1:10;

[0066] The initiator is at least one of persulfate, hydrogen peroxide, or water-soluble azo initiators.

[0067] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail through the following embodiments.

[0068] Example 1:

[0069] Weigh 384g of a 25% sodium chloride aqueous solution and add 3.0g of poly(dimethyldiallylammonium chloride) with a molecular weight of 250,000 as a dispersant and stabilizer. Add 10.92g of acrylic acid, 21.83g of AMPS, 49.13g of N,N-dimethylacrylamide and 16.38g of NVP to a reactor, add 14.25g of sodium lignosulfonate and adjust its mass concentration to 22.6%. Add sodium hydroxide to adjust the pH value to 6-7. Then add 0.98g of ammonium persulfate and carry out free radical copolymerization at 50℃ for 12 hours to obtain brown emulsion dispersion No. 1.

[0070] Example 2:

[0071] Weigh 393g of a 25% sodium sulfate aqueous solution and add 3.0g of poly(dimethyldiallyl ammonium chloride) with a molecular weight of 250,000 as a dispersant and stabilizer. Add 9.94g of acrylic acid, 29.84g of AMPS, 35.37g of N,N-dimethylacrylamide and 17.69g of NVP to a reactor, add 11.14g of sodium lignosulfonate and adjust its mass concentration to 20.8%. Add sodium hydroxide to adjust the pH value to 6-7. Then, 0.74g of ammonium persulfate is subjected to free radical copolymerization at 50℃ for 12 hours to obtain brown emulsion dispersion No. 2.

[0072] Example 3:

[0073] Weigh 398g of a 25% sodium chloride aqueous solution, add 3.0g of poly(dimethyldiallyl ammonium chloride) with a molecular weight of 250,000 as a dispersant and stabilizer, and add 10.28g of acrylic acid, 15.43g of AMPS, 48.22g of N,N-dimethylacrylamide and 16.07g of NVP to a reactor. Add 9g of hydrophobically modified fly ash and adjust its mass concentration to 19.8%. Add sodium hydroxide to adjust the pH value to 6-7. Then add a mixture of 0.225g of ammonium persulfate and 0.225g of sodium bisulfite, and carry out free radical copolymerization at 50℃ for 10 hours to obtain brown emulsion dispersion No. 3.

[0074] Preparation of the hydrophobically modified fly ash:

[0075] Fly ash was pretreated by sieving through an 80-mesh sieve to remove impurities, resulting in fly ash with a particle size of less than 150 µm. The pretreated fly ash was then dried in an oven at 105 ℃ for 4 h. 50 g of the dried fly ash and 100 g of anhydrous ethanol were weighed into a three-necked flask and stirred at 150 rpm for 1 h at room temperature to ensure uniform dispersion of the fly ash. The temperature was then raised to 70 ℃, and 5 g of palmitoyl chloride was added. The mixture was stirred and reacted for another 20 h. After the reaction was completed, the mixture was centrifuged, and the lower precipitate was dispersed and centrifuged again with anhydrous ethanol. This process was repeated 2-3 times. The lower precipitate was then dried and stored for use as hydrophobically modified fly ash.

[0076] Example 4:

[0077] Weigh 397g of a 25% sodium chloride aqueous solution, add 3.0g of polyvinylpyrrolidone (molecular weight 150,000) as a dispersant and stabilizer, and add 8.93g of acrylic acid, 26.78g of AMPS, 31.75g ​​of N,N-dimethylacrylamide and 15.87g of NVP to a reactor. Add 16.67g of sodium lignosulfonate to adjust its mass concentration to 20%. Add sodium hydroxide to adjust the pH value to 6-7. Then add 0.25g of potassium persulfate as an initiator and carry out free radical copolymerization at 50℃ for 10 hours to obtain brown emulsion dispersion No. 4.

[0078] Comparative Example 1:

[0079] Weigh 397g of a 25% sodium chloride aqueous solution, add 3g of poly(dimethyldiallyl ammonium chloride) with a molecular weight of 250,000 as a dispersant and stabilizer to the reactor and stir until homogeneous; add 13.88g of acrylic acid, 41.56g of AMPS, 18.51g of N,N-dimethylacrylamide and 9.26g of NVP, and stir until homogeneous; add 16.67g of sodium lignosulfonate to adjust its mass concentration to 20%; add sodium hydroxide to adjust the pH value to 6-7; then add 0.25g of potassium persulfate and carry out free radical copolymerization at 50℃ for 10 hours to obtain brown emulsion dispersion No. 5.

[0080] Comparative Example 2:

[0081] Weigh 384g of a 25% sodium chloride aqueous solution, add 3g of poly(dimethyldiallyl ammonium chloride) with a molecular weight of 250,000 as a dispersant and stabilizer to the reactor and stir until homogeneous; add 6.55g of acrylic acid, 26.2g of AMPS and 65.51g of N,N-dimethylacrylamide, and stir until homogeneous; add 14.74g of sodium lignosulfonate to adjust its mass concentration to 22.6%; add sodium hydroxide to adjust the pH value to 6-7; then add 0.1g of ammonium persulfate and carry out free radical copolymerization at 50℃ for 12 hours to obtain brown emulsion dispersion No. 6.

[0082] Comparative Example 3:

[0083] Weigh 384g of a 25% sodium chloride aqueous solution, add 3g of poly(dimethyldiallyl ammonium chloride) with a molecular weight of 250,000 as a dispersant and stabilizer to the reactor and stir until homogeneous; add 6.55g of acrylic acid, 26.2g of AMPS and 65.51g of NVP, and stir until homogeneous; add 14.74g of sodium lignosulfonate to adjust its mass concentration to 22.6%; add sodium hydroxide to adjust the pH value to 6-7; then add 0.1g of ammonium persulfate and carry out free radical copolymerization at 50℃ for 12 hours to obtain brown emulsion dispersion No. 7.

[0084] Comparative Example 4:

[0085] Weigh 384g of a 25% sodium chloride aqueous solution, add 3g of poly(dimethyldiallyl ammonium chloride) with a molecular weight of 250,000 as a dispersant and stabilizer into the reactor and stir until homogeneous; add 7.53g of acrylic acid, 30.13g of AMPS, 56.5g of N,N-dimethylacrylamide and 18.83g of NVP, stir until homogeneous, and adjust the mass concentration to 22.6%; add sodium hydroxide to adjust the pH to 6-7; then add 0.11g of ammonium persulfate and carry out free radical copolymerization at 50℃ for 12 hours to obtain colorless and transparent dispersion No. 8.

[0086] The filtration loss reduction performance and overall performance of the present invention were tested.

[0087] To verify the filtration loss reduction performance and overall performance of the present invention, the filtration loss reduction agent in the above embodiments was evaluated for filtration loss performance, thickening performance, free fluid properties, and rheological properties in accordance with GB / T 19139-2012 Oil Well Cement Test Methods and industry standard SY / T 5504.2-2013 Oil Well Cement Fluid Loss Reduction Agent Evaluation Methods.

[0088] Experimental Example 1:

[0089] The test conditions were: ① 80℃; 1.90 g / cm³ 3 The cement slurry formula is: Grade G cement + 3.5% water loss reducer + water; the test results are shown in Table 1.

[0090] Table 1

[0091]

[0092] Experimental Example 2:

[0093] The test conditions were: ① 120℃; 1.90 g / cm³ 3 The cement slurry formula is: Grade G cement + 35% silica fume + 6% water loss reducer + water; the test results are shown in Table 2.

[0094] Table 2

[0095]

[0096] Through performance comparison of the examples and comparative examples, it was found that the mass ratio of each component in the water loss reducing agent has a certain impact on its filtration performance. The addition of inorganic / organic minerals is significant in improving dispersion performance. As can be seen from the evaluation results of Comparative Example 8, the water loss reducing agent without the introduction of inorganic / organic minerals has high initial viscosity and poor rheological properties. Example 3 uses hydrophobic modified fly ash. As can be seen from the data in Tables 1 and 2, the flow stability of the cement slurry with the addition of Example 3 is significantly improved. The cement slurry still maintains a high viscosity at high temperature and there is no problem of high-temperature dilution. At the same time, the hydrophobic modified fly ash increases the density of the filter cake through physical filling and chemical inhibition, effectively reducing the filtration loss. As can be seen from the evaluation results of Comparative Examples 6 and 7, the nonionic monomers DMAA and NVP are indispensable. The filtration performance is greatly affected by the use of a single nonionic monomer, and an abnormal "core-encased" gelation phenomenon occurs. The large steric hindrance groups can effectively reduce the degree of deflection of the molecular chain when heated and hinder the adhesion and agglomeration between cement particles, thereby inhibiting the abnormal gelation phenomenon of cement slurry.

[0097] Figures 1-5 This is a schematic diagram showing the thickening curve of cement slurry containing 6% (by weight) of the water loss reducing agent described in this application at 80℃~120℃; where, Figure 1 This is a thickening curve of the temperature drop dehydration agent in an embodiment of the present invention at 80℃ × 43.4MPa; Figure 2 This is a thickening curve of the temperature drop dehydration agent in an embodiment of the present invention at 90℃ × 53.3MPa; Figure 3 This is a thickening curve of the temperature drop dehydration agent in Example 100 of the present invention at 60.2 MPa. Figure 4 This is a thickening curve of the temperature drop dehydration agent in Example 1 of the present invention at 110℃ × 67.0MPa; Figure 5 This is a thickening curve of the temperature drop dehydration agent in Example 1 of the present invention at 120℃ × 73.9MPa; Figure 6 This is a graph showing the relationship between the amount of material added and the amount of filtration loss in Embodiment 1 of the present invention.

[0098] From Table 1 and Table 2 and Figures 1-6 As can be seen, the fluid loss reducing agents in Examples 1-4, under conditions of 80℃ and 120℃, exhibit good filtration loss reduction performance while ensuring good rheological properties, and can control API filtration loss to within 50ml. They do not have an over-retarding or over-setting effect on the cement slurry system, and there is no temperature "inversion" phenomenon. With increasing dosage, the thickening time is slightly affected, but within the acceptable range. Simultaneously, the cement slurry shows no abnormal gelation phenomena such as "bulging" or "steps," and the curve is normal. This invention has no adverse effect on the compressive strength of the cement slurry; the 24-hour compressive strength at all temperature points is >14MPa, which meets the requirements of well cementing operations. This further verifies the inventive effect of this application.

[0099] Those skilled in the art will recognize that the embodiments described herein are intended to help the reader understand the implementation methods of the present invention, and should be understood that the scope of protection of the present invention is not limited to such specific statements and embodiments. Those skilled in the art can make various other specific modifications and combinations based on the technical teachings disclosed in this invention without departing from the spirit of the invention, and these modifications and combinations are still within the scope of protection of the present invention.

Claims

1. A quaternary copolymer-based multifunctional oil well cement fluid loss reducer, characterized in that: It consists of the following components in parts by weight: Inorganic salts 15-42 parts; dispersant stabilizer 0.1-1 parts; anionic monomers 0.49-16 parts; nonionic monomers 2.69-29 parts; inorganic minerals or biological organic matter 0-9.6 parts; deionized water 100 parts.

2. The quaternary copolymer multifunctional oil well cement fluid loss reducing agent according to claim 1, characterized in that: The inorganic salt is at least one of potassium chloride, sodium chloride, ammonium chloride, potassium sulfate, sodium sulfate, and ammonium sulfate.

3. The quaternary copolymer multifunctional oil well cement fluid loss reducing agent according to claim 1, characterized in that: The dispersant stabilizer is a cationic polymer or a nonionic polymer with a molecular weight of 100,000 to 1,500,000.

4. The quaternary copolymer multifunctional oil well cement fluid loss reducer according to claim 3, characterized in that: The cationic polymer is at least one of poly(dimethyldiallylammonium chloride), poly(acryloyloxyethyltrimethylammonium chloride), and poly(methacryloyloxyethyltrimethylammonium chloride); The nonionic polymer is at least one of polyvinyl alcohol and polyvinylpyrrolidone.

5. The quaternary copolymer multifunctional oil well cement fluid loss reducer according to claim 1, characterized in that: The anionic monomer is at least one selected from AMPS, acrylic acid, styrene sulfonate, vinyl sulfonate, methacrylic acid, fumaric acid, and itaconic acid. The nonionic monomer is at least one of acrylamide, N,N-dimethylacrylamide, and NVP.

6. The quaternary copolymer multifunctional oil well cement fluid loss reducer according to claim 1, characterized in that: The inorganic minerals are ordinary minerals or partially hydrophobically modified minerals, with a median particle size ranging from 0.1 to 300 micrometers; The biological organic matter is at least one of lignin sulfonate, cellulose derivative, starch derivative and xanthan gum derivative.

7. The quaternary copolymer multifunctional oil well cement fluid loss reducing agent according to claim 6, characterized in that: The hydrophobic modified mineral is hydrophobic modified fly ash; The preparation method of the hydrophobically modified fly ash is as follows: fly ash is pretreated by sieving with an 80-mesh sieve to remove impurities and obtain fly ash with a particle size of less than 150 µm; the pretreated fly ash is then dried in an oven at 105 ℃ for 4 h; the fly ash is hydrophobically modified by esterification using long-chain acyl chloride as a hydrophobic agent and anhydrous ethanol as a solvent; after the reaction, the fly ash is centrifuged, the lower precipitate is dispersed and centrifuged again with anhydrous ethanol, and this process is repeated 2-3 times; the lower precipitate is then dried for later use. The long-chain acyl chloride is at least one of lauroyl chloride, myristoyl chloride, palmitoyl chloride, and stearoyl chloride; the amount of long-chain acyl chloride used is 5-50 wt% of the fly ash; the esterification reaction temperature is 60-80℃; and the esterification reaction time is 12-24h.

8. A method for preparing a quaternary copolymer-based multifunctional oil well cement fluid loss reducing agent according to any one of claims 1-7, characterized in that: Includes the following steps: Weigh out 15-42 parts of inorganic salt according to the mass ratio and put them into the reactor. Add 100 parts of deionized water and stir well. Weigh 0.1-1 part of a cationic or nonionic polymer with a molecular weight of 100,000 to 1,500,000 as a dispersing stabilizer and add it to the reactor, stirring until homogeneous; Weigh 0.49-16 parts of anionic monomer and 2.69-29 parts of nonionic monomer and pour them into the reactor, then stir until homogeneous; Weigh out 0-9.6 parts of inorganic minerals or biological organic matter and pour them into the reactor, then stir until homogeneous; adjust the pH value to 6-7. Add deionized water to make the solid content of active monomers in the solution 7-42wt%; then add 0.1-5% of the active monomers by mass of an initiator to carry out free radical copolymerization, and the resulting product is an oil well cement fluid loss reducer.

9. The preparation method according to claim 8, characterized in that: The mass ratio of the anionic monomer to the nonionic monomer is 1:1 to 1:10; The initiator is at least one of persulfate, hydrogen peroxide, or water-soluble azo initiators.

10. The preparation method according to claim 8, characterized in that: Adjust the pH value to 6-7 by adding sodium hydroxide.

11. The preparation method according to claim 8, characterized in that: The free radical copolymerization reaction temperature is 30–60℃, and the polymerization time is 4–16 hours.

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