Tackifying fluid loss agent for oil well cement as well as preparation method and application of tackifying fluid loss agent

Abstract

The invention discloses a tackifying fluid loss agent for oil well cement as well as a preparation method and application thereof, and belongs to the technical field of fluid loss agents, the tackifying fluid loss agent for oil well cement is prepared by taking 2-acrylamide-2-methylpropanesulfonic acid (AMPS), N-vinyl pyrrolidone (NVP), dimethyl diallyl ammonium chloride (DMDAAC) and isopentenol polyoxyethylene ether (TPEG) as comonomers, and mixing the comonomers, the N-vinyl pyrrolidone (NVP), the dimethyl diallyl ammonium chloride (DMDAAC) and the isopentenol polyoxyethylene ether (TPEG) to prepare the tackifying fluid loss agent for oil well cement. The quadripolymer is prepared through an aqueous solution free radical polymerization reaction. The tackifying fluid loss agent for oil well cement provided by the invention has excellent fluid loss performance and remarkable tackifying effect, can keep stable performance under extreme conditions of high temperature, high salt and the like, and has important practical significance and application value for improving the well cementation quality under complex well conditions and promoting the development of a well cementation technology.

Description

Technical Field

[0001] This invention relates to the field of fluid loss reducing agents. Specifically, it relates to a viscosity-enhancing and fluid loss-reducing agent for oil well cement, its preparation method, and its application. Background Technology

[0002] Cementing oil wells is a crucial step in oilfield development, requiring the use of cement slurry to bond the casing to the formation, thereby isolating formation fluids and protecting the casing. As oil and gas field development moves into deeper and more complex formations, more stringent requirements are being placed on the performance of oil well cement slurry under complex geological conditions such as high temperature and high salinity.

[0003] Currently, some oilfields in China (such as Changqing and Daqing) have low formation pressure, requiring the use of low-density cement slurry systems. "Viscosity enhancement" ensures good suspension of the cement slurry during long-distance pumping (preventing sedimentation of weighting agents like barite), while "water loss reduction" reduces water penetration into the formation (preventing formation damage and avoiding cement slurry shrinkage and channeling). Existing technologies commonly use water loss reduction agents for oil well cement, mostly binary copolymers (such as AMPS-AA and NVP-AMPS), which have the following shortcomings: First, poor high-temperature stability; they are prone to thermo-oxidative degradation above 120℃, leading to a significant decrease in viscosity enhancement and water loss reduction performance. Second, limited functionality; most products only meet water loss reduction requirements, necessitating the addition of viscosity enhancers, increasing construction costs and formulation complexity. Third, weak salt resistance; they are prone to salt-sensitive flocculation in high-salinity formation water (e.g., salt content ≥5%), affecting the rheological properties of the cement slurry. Summary of the Invention

[0004] Therefore, the present invention provides a thickening and dehydration reducing agent for oil well cement, which has both excellent dehydration reducing performance and significant thickening effect, and can maintain stable performance under extreme conditions such as high temperature and high salinity.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] A thickening and water loss reducing agent for oil well cement, wherein the thickening and water loss reducing agent for oil well cement is a quaternary copolymer prepared by aqueous free radical polymerization reaction using 2-acrylamide-2-methylpropanesulfonic acid (AMPS), N-vinylpyrrolidone (NVP), dimethyl diallyl ammonium chloride (DMDAAC) and isopentenyl polyoxyethylene ether (TPEG) as comonomers.

[0007] Furthermore, the molar ratio of each monomer in the comonomer is: 2-acrylamido-2-methylpropanesulfonic acid: N-vinylpyrrolidone: dimethyl diallyl ammonium chloride: isopentenyl polyoxyethylene ether = 35-55: 20-30: 15-25: 5-10.

[0008] Furthermore, the number-average molecular weight of the quaternary copolymer is 80,000-150,000, and the intrinsic viscosity is 12-18 mL / g (measured at 30°C in 0.1 mol / L NaCl solution).

[0009] This invention also provides a method for preparing a viscosity-enhancing and fluid-loss-reducing agent for oil well cement, used to prepare the viscosity-enhancing and fluid-loss-reducing agent for oil well cement described in the above scheme, comprising the following steps:

[0010] S1. Monomer solution preparation: Add the comonomers 2-acrylamide-2-methylpropanesulfonic acid, N-vinylpyrrolidone, dimethyl diallyl ammonium chloride and isopentenyl polyoxyethylene ether to deionized water and stir until completely dissolved to obtain a mixed monomer solution. Adjust the pH of the mixed monomer solution to 6.5-7.0 with alkaline solution.

[0011] S2. Inert gas protection: Transfer the pH-adjusted mixed monomer solution into the reactor, introduce nitrogen gas (purity ≥99.9%) at a flow rate of 0.5-1.0 L / min for 30-40 min, and remove oxygen from the system;

[0012] S3. Polymerization reaction: Heat to 55-65℃, add composite initiator, which is a mixture of ammonium persulfate and sodium bisulfite, and keep the reaction at this temperature for 4-6 hours;

[0013] S4. Post-processing: After the reaction is completed, the product is cooled to room temperature, precipitated with ethanol, and filtered to obtain a solid product. The solid product is dried in a vacuum drying oven at 60-70℃ for 8-10 hours, and then pulverized to obtain a thickening and dehydration reducing agent for oil well cement.

[0014] Furthermore, in step S1, the mass fraction of the comonomer in the mixed monomer solution is 30%.

[0015] Furthermore, in step S3, the molar ratio of ammonium persulfate to sodium bisulfite in the composite initiator is 1:1.

[0016] Furthermore, the amount of composite initiator added in step S3 is 0.1-0.3% of the total mass of the comonomer.

[0017] Furthermore, in step S3, the amount of composite initiator added is 0.2% of the total mass of the comonomer.

[0018] The present invention also provides an application of a thickening and dehydration reducing agent for oil well cement, wherein the thickening and dehydration reducing agent for oil well cement described in the above scheme is used in oil well cement, the amount of the thickening and dehydration reducing agent for oil well cement added is 0.5-1.5% of the mass of oil well cement, and the water-cement ratio of the oil well cement slurry used in the oil well cement is 0.44.

[0019] The technical solution of the present invention achieves the following beneficial technical effects:

[0020] 1. This invention employs aqueous solution polymerization under mild reaction conditions (55-65℃), requiring no special equipment and facilitating industrial production. Utilizing the salt and heat resistance of AMPS, the water loss reduction assistance of NVP, the high adhesion and thickening properties of TPEG, and the cationic thickening effect of DMDAAC, under specific reaction conditions (pH 6.5-7.0) and the combined action of the composite initiator, the four monomers work synergistically within the molecular chain segments, endowing the copolymer with excellent comprehensive properties. Ultimately, a multifunctional thickening and water loss reducing agent with both high-temperature stability and salt resistance is obtained. In cement slurry applications, no additional thickening or water loss reducing agents are required, simplifying cement slurry formulations and reducing construction costs and formulation compatibility risks.

[0021] 2. Among the four comonomers, AMPS contains a strong hydrophilic sulfonic acid group (-SO3H), which can improve the polymer's salt resistance and thermal stability. NVP has a rigid five-membered ring structure, which can enhance the polymer's high-temperature resistance. Its amide group can be adsorbed onto the surface of cement particles through hydrogen bonding, which helps reduce water loss. TPEG can provide steric hindrance and dispersion properties. DMDAAC is a cationic monomer that can electrostatically adsorb onto cement particles (which have a negatively charged surface), thus enhancing the thickening effect. Strictly controlling the reaction environment (pH 6.5-7.0) can improve the polymerization activity and structural stability of DMDAAC and TPEG, and avoid hydrolysis and molecular chain breakage of macromonomer molecules. In the composite initiator, the combined use of ammonium persulfate and sodium bisulfite constitutes a redox initiation system, which can significantly reduce the activation energy required for dimethyl diallyl ammonium chloride and isopentenyl polyoxyethylene ether to participate in the polymerization reaction, enabling them to rapidly initiate polymerization at low temperatures and avoid explosive polymerization. Therefore, the four monomers work synergistically under the action of the composite initiator to obtain a thickening and water-loss-reducing agent with controllable molecular weight and excellent performance. Detailed Implementation

[0022] Example 1

[0023] A viscosity-enhancing and fluid-loss-reducing agent for oil well cement is prepared by the following steps:

[0024] S1. Monomer solution preparation: Add 0.4 mol AMPS, 0.3 mol NVP, 0.2 mol DMDAAC and 0.1 mol TPEG-2400 to deionized water and stir until completely dissolved to obtain a mixed monomer solution. The mass fraction of the copolymer in the mixed monomer solution is 30%. Adjust the pH of the mixed monomer solution to 6.5-7.0 with a 30% NaOH solution.

[0025] S2. Inert gas protection: Transfer the mixed monomer solution after pH adjustment in step 1 into a 2L four-necked flask, and purge with nitrogen gas (purity ≥99.9%) at a flow rate of 0.8L / min for 35min.

[0026] S3. Polymerization reaction: Heat to 60℃, add composite initiator, which is a mixture of ammonium persulfate and sodium bisulfite in a 1:1 molar ratio, and the amount of composite initiator added is 0.2% of the total mass of the comonomer. Keep the reaction at this temperature for 5 hours.

[0027] S4. Post-processing: After the reaction is completed, the product is cooled to room temperature, precipitated with ethanol, and filtered to obtain a solid product. The solid product is dried in a vacuum drying oven at 65℃ for 9 hours, and then pulverized to obtain a thickening agent for oil well cement with a number average molecular weight of 120,000 and an intrinsic viscosity of 15 mL / g (determined at 30℃ in 0.1 mol / L NaCl solution).

[0028] The oil well cement prepared by the above method was added to the oil well cement slurry to obtain oil well cement. The amount of the thickening and water loss reducing agent added was 1% of the mass of the oil well cement. The water-cement ratio of the oil well cement slurry used was 0.44. The final oil well cement was subjected to performance testing, and the test results are as follows:

[0029] At room temperature (25℃): apparent viscosity 45 mPa·s, API filtration loss 32 mL;

[0030] Hot rolling at 80℃ (16h): apparent viscosity 42mPa·s, API filtration loss 38mL;

[0031] 150℃ hot rolling (16h): apparent viscosity 39mPa·s, API filtration loss 48mL;

[0032] Meanwhile, oil well cement can be stably dispersed in formation water with a salt content of over 30%, without salt-sensitive flocculation.

[0033] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of the claims of this patent application.

Claims

1. A viscosity increasing fluid loss additive for oil well cement, characterized by, The tackifying fluid loss reducer for oil well cement is a quaternary copolymer prepared by aqueous solution free radical polymerization reaction with 2-acrylamide-2-methylpropane sulfonic acid, N-vinyl pyrrolidone, dimethyl diallyl ammonium chloride and polyoxyethylene isopentenyl ether as comonomers.

2. The viscosity enhancing fluid loss additive for oil well cements according to claim 1, characterized in that, The molar ratio of each monomer in the comonomer is: 2-acrylamide-2-methylpropane sulfonic acid: N-vinyl pyrrolidone: dimethyl diallyl ammonium chloride: polyoxyethylene isopentenyl ether = 35-55: 20-30: 15-25: 5-10.

3. The viscosity enhancing fluid loss additive for oil well cements according to claim 1, characterized in that, The number average molecular weight of the quaternary copolymer is 80000-150000, and the intrinsic viscosity is 12-18 mL / g.

4. A method for preparing a viscosity increasing fluid loss additive for oil well cement, characterized by, The tackifying fluid loss reducer for oil well cement is prepared by the following steps: S1. Monomer solution preparation: add comonomers 2-acrylamide-2-methylpropane sulfonic acid, N-vinyl pyrrolidone, dimethyl diallyl ammonium chloride and polyoxyethylene isopentenyl ether into deionized water, stir until completely dissolved to obtain a mixed monomer solution, and adjust the pH of the mixed monomer solution to 6.5-7.0 with lye; S2. Inert gas protection: transfer the mixed monomer solution after adjusting the pH into a reactor, introduce nitrogen, and discharge oxygen in the system; S3. Polymerization reaction: heat to 55-65℃, add a composite initiator which is a mixture of ammonium persulfate and sodium bisulfite, and keep the temperature for 4-6h; S4. Post-treatment: after the reaction is completed, cool the product to room temperature, precipitate with ethanol, and filter to obtain a solid product, dry and crush the solid product to obtain the tackifying fluid loss reducer for oil well cement.

5. The method of preparing a viscosity enhancing fluid loss additive for oil well cements according to claim 4, characterized in that, The mass fraction of comonomers in the mixed monomer solution in step S1 is 30%.

6. The method of preparing a viscosity enhancing fluid loss additive for oil well cements according to claim 4, characterized in that, The molar ratio of ammonium persulfate to sodium bisulfite in the composite initiator in step S3 is 1:

1.

7. The method of preparing a viscosity enhancing fluid loss additive for oil well cements according to claim 4, characterized in that, The addition amount of the composite initiator in step S3 is 0.1-0.3% of the total mass of the comonomers.

8. The method of preparing a viscosity enhancing fluid loss additive for oil well cements according to claim 4, characterized in that, The addition amount of the composite initiator in step S3 is 0.2% of the total mass of the comonomers.

9. Use of a viscosity enhancing fluid loss additive for oil well cement, characterized in that, The tackifying fluid loss reducer for oil well cement as claimed in any one of claims 1-3 is used in oil well cement, and the addition amount of the tackifying fluid loss reducer for oil well cement is 0.5-1.5% of the mass of the oil well cement.

10. The use of the viscosity increasing fluid loss additive for oil well cement according to claim 9, characterized by, The tackifying fluid loss reducer for oil well cement is used in oil well cement, and the addition amount of the tackifying fluid loss reducer for oil well cement is 1.0% of the mass of the oil well cement, and the water-cement ratio of the oil well cement slurry used in the oil well cement is 0.44.