Toughening agent for oil well cement as well as preparation method and application of toughening agent

Abstract

The invention relates to the technical field of additives for oil well cement, in particular to a flexibilizer for oil well cement and a preparation method and application thereof.The flexibilizer adopts a low-modulus and high-elasticity rubbery polymer as an inner core and adopts a high-modulus rigid polymer capable of being chemically bonded with an oil well cement matrix as a shell; the prepared polymer-based toughening agent with the core-shell structure can enhance the toughness of oil well cement.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of oil well cement admixtures, in particular to a toughening agent for oil well cement and a preparation method and application thereof. BACKGROUND

[0002] In the cementing of oil and gas wells, the brittle cracking of the cement sheath is the main cause of the failure of interlayer isolation, gas channeling and loss of wellbore integrity. In order to improve the toughness of the cement stone, the following methods are usually used in the prior art:

[0003] Direct addition of fibers: such as polypropylene fiber, glass fiber, carbon fiber, etc. Invention patent CN110937857A by Gao Yuan et al. mentions that the anti-high-temperature toughening material is selected from at least one of polypropylene fiber, PVA fiber, polyacrylonitrile fiber, glass fiber, carbon fiber, polycrystalline fiber, basalt fiber or inorganic fiber. Invention patent CN112939527B by Ding Zhiwei et al. mentions that the fiber includes one or more of aluminum silicate fiber, sepiolite fiber, brucite fiber and carbon fiber. Both of these two patents mention the use of fiber materials as cement stone toughness materials. This method mainly improves the impact resistance and post-cracking toughness, but has limited contribution to improving the elastic deformation capacity of the cement stone (reducing the elastic modulus), and may affect the fluidity of the slurry.

[0004] Direct addition of modified rubber particles or polymer emulsion or powder: such as SBR butadiene emulsion, CR chloroprene rubber emulsion, etc. Invention patent CN112830723A by Shu Feisong et al. mentions modified rubber powder, and invention patent CN110937857A mentions that the anti-high-temperature organic anti-channeling emulsion is selected from at least one of styrene-butadiene anti-channeling emulsion and epoxy resin anti-channeling emulsion. Invention patent CN107699216A by Shi Zhongnan et al. mentions that a kind of toughness cement slurry for gas storage well uses an oxygen resin powder. These materials can improve toughness to some extent, but have obvious defects: ① poor compatibility with the cement matrix, weak interface bonding; ② prone to degradation and failure at high temperatures; ③ in order to achieve the effect, a large amount of addition is often required, which seriously sacrifices the compressive strength of the cement stone.

[0005] Physical blending of multiple materials: such as fiber, particle and emulsion compounding. This is an improvement, but in essence it is still a physical mixture, the functions of each component are independent, the synergistic effect is limited, and the system is complex, which is not convenient for on-site preparation.

[0006] The aforementioned methods all share a common bottleneck: the toughening material and the rigid cement matrix are incompatible in terms of physical and chemical properties, resulting in a weak interface where stress cannot be effectively transferred, leading to low toughening efficiency and often at the expense of strength. Furthermore, the cement ring is subjected to high temperatures, and the composition of the oil well cement used differs from that of the silicate cement used in construction engineering, with significant differences in their hydration products at high temperatures. Therefore, developing a specialized elastic-toughness material that is compatible with the oil well cement matrix, can significantly improve the toughness and elasticity of the cement stone simultaneously, and has minimal negative impact on strength has become an urgent need in this field. Summary of the Invention

[0007] To address the problems existing in the prior art, this invention provides a toughening agent for oil well cement. Specifically, this invention uses a low-modulus, high-elasticity rubbery polymer as the core and a high-modulus, rigid polymer that can chemically bond with the oil well cement matrix as the shell, thus preparing a polymer-based toughening agent with a core-shell structure, which can enhance the toughness of oil well cement.

[0008] Specifically, the toughening agent for oil well cement of the present invention is composed of a highly elastic core and a rigid polymer shell covering the highly elastic core. The highly elastic core is polymerized from 95-99 parts by weight of acrylate and 1-5 parts by weight of divinylbenzene, and the rigid polymer shell is polymerized from 20-35 parts by weight of methyl methacrylate and / or styrene, 1-3 parts by weight of methacrylic acid, 1-3 parts by weight of allyl glycidyl ether and 1-3 parts by weight of 2-acrylamide-2-methylpropanesulfonic acid.

[0009] Preferably, the acrylate is at least one of butyl acrylate and ethyl acrylate.

[0010] This invention also relates to a method for preparing the above-mentioned toughening agent for oil well cement, specifically comprising the following steps:

[0011] 1) Weigh each ingredient according to its weight.

[0012] 2) Mix acrylate and divinylbenzene evenly to obtain the oil phase. Mix 1-3 parts by weight of emulsifier and 122-186 parts by weight of water evenly to obtain the aqueous phase. Slowly add the oil phase dropwise to the aqueous phase while stirring to obtain the monomer emulsion.

[0013] 3) Mix 0.5-1 parts of initiator and 10-20 parts of water thoroughly, heat and stir, and slowly add dropwise to the monomer emulsion in step 2). Maintain the reaction temperature, cool, and obtain the core emulsion.

[0014] 4) Mix methyl methacrylate and / or styrene, methacrylic acid, allyl glycidyl ether, and 2-acrylamide-2-methylpropanesulfonic acid evenly to obtain a shell monomer mixture. Mix 0.25-0.5 parts of initiator and 3-5 parts of water evenly to obtain an initiator solution.

[0015] 5) Heat the core emulsion, slowly add the shell monomer mixture and initiator solution, maintain the temperature for reaction, cool, and adjust the pH to 7.5-9 to obtain the final product.

[0016] This invention breaks through the conventional physical blending approach, starting from molecular structure design, and proposes a core-shell structured polymer microsphere as a toughening material. The core of this invention is composed of a low-modulus, high-elasticity rubbery polymer, whose main function is to absorb energy, generate large deformation, and provide elasticity. The outer shell is composed of a high-modulus, rigid polymer that can chemically bond with the oil well cement matrix, forming a strong chemical bond with the hydration products of oil well cement. During processing and stirring, it protects the core layer and effectively transfers external stress to the core layer. The toughening agent of this invention exists in the form of an aqueous dispersion (emulsion). The average particle size of the polymer microspheres is 100-500 nm, which is convenient to use and easy to disperse.

[0017] Preferably, in step 2), the emulsifier is sodium dodecyl sulfate, the stirring speed is 200-400 rpm, and the stirring time is 0.5-2 h.

[0018] Preferably, in step 3), the initiator is persulfate, the temperature is raised to 75-80°C, the stirring speed is 100-300 rpm, the monomer emulsion is added dropwise for 1-2 hours, and the reaction is maintained at this temperature for 1-2 hours. More preferably, the persulfate is potassium persulfate.

[0019] Preferably, the initiator in step 4) is a persulfate. More preferably, the persulfate is potassium persulfate.

[0020] Preferably, in step 5), the temperature is raised to 75-80℃, the dropping time is 1.5-2.5h, and the heat preservation reaction time is 1.5-2h.

[0021] This invention also relates to the application of the above-mentioned toughening agent for oil well cement in the preparation process of oil well cement slurry.

[0022] Preferably, the amount of toughening agent added to the oil well cement is 5-15% of the weight of the oil well cement.

[0023] Compared with existing toughening materials that are directly physically added, the present invention has the following technical advantages:

[0024] 1. Elasticity and Toughness: The core-shell structure achieves a combination of rigidity and flexibility. The rigid shell is strongly bonded to the oil well cement matrix, ensuring effective stress transfer; the elastic core undergoes large deformation, efficiently absorbing energy and significantly increasing the ultimate strain.

[0025] 2. Minimal strength sacrifice: Due to the strong bond between the shell and the matrix, significant toughening is achieved while avoiding the strength reduction problem caused by weak interfaces.

[0026] 3. Excellent interfacial compatibility: The active functional groups on the shell can react chemically or form strong hydrogen bonds with Ca2+ and other substances in cement hydration products, forming an organic-inorganic interpenetrating network structure, which greatly improves interfacial bonding and prevents interfacial delamination.

[0027] 4. Easy to use: Added in emulsion form, it is fully compatible with existing cementing processes and has uniform dispersion.

[0028] 5. Stable performance: Suitable for high-temperature oil well cement slurry construction, does not affect the rheological properties and other properties of cement slurry, and the core-shell structure also improves the stability of the polymer itself. Detailed Implementation

[0029] To characterize the technical effects of this invention, a toughening agent was prepared and added to the oil well cement slurry at a dosage of 10% of the weight of the oil well cement. Specimens were molded and cured at 50℃ and 0.1MPa for 48 hours. The performance of the specimens was tested using an RTR-1000 triaxial rock mechanics testing system according to the mechanical testing standard GB / T 50266-2013 "Standard for Test Methods of Engineering Rock Mass". The oil well cement slurry mix consisted of 100 parts of Grade G oil well cement, 10 parts of toughening agent, 1.5 parts of fluid loss reducer, 0.5 parts of retarder, 0.01 parts of defoamer, and 44 parts of water.

[0030] Example 1

[0031] The toughening agent is prepared by the following steps:

[0032] 1) Weigh each ingredient according to its weight.

[0033] 2) Mix 98 parts ethyl acrylate and 2 parts divinylbenzene evenly to obtain the oil phase. Mix 2 parts by weight of sodium dodecyl sulfate and 175 parts by weight of water evenly to obtain the aqueous phase. Slowly add the oil phase dropwise to the aqueous phase while stirring to obtain the monomer emulsion.

[0034] 3) Mix 0.6 parts potassium persulfate and 15 parts water thoroughly, heat to 75°C while stirring, and slowly add dropwise to the monomer emulsion from step 2). Maintain the reaction temperature for 1.5 hours, then cool to obtain the core emulsion.

[0035] 4) Mix 31 parts methyl methacrylate, 2 parts methacrylic acid, 1 part allyl glycidyl ether, and 4 parts 2-acrylamide-2-methylpropanesulfonic acid evenly to obtain a shell monomer mixture. Mix 0.4 parts potassium persulfate and 5 parts water evenly to obtain an initiator solution.

[0036] 5) Heat the core emulsion to 75°C, slowly add the shell monomer mixture and initiator solution, keep the reaction at this temperature for 2 hours, cool, and adjust the pH to 8 to obtain the final product.

[0037] The specimen was tested and found to have a compressive strength of 28.9 MPa and an elastic modulus of 5.33 GPa.

[0038] Example 2

[0039] The toughening agent is prepared by the following steps:

[0040] 1) Weigh each ingredient according to its weight.

[0041] 2) Mix 96 parts butyl acrylate and 4 parts divinylbenzene evenly to obtain the oil phase. Mix 1.5 parts by weight of sodium dodecyl sulfate and 180 parts by weight of water evenly to obtain the aqueous phase. Slowly add the oil phase dropwise to the aqueous phase while stirring to obtain the monomer emulsion.

[0042] 3) Mix 0.7 parts potassium persulfate and 12 parts water thoroughly, heat to 80°C while stirring, and slowly add dropwise to the monomer emulsion from step 2). Maintain the reaction temperature for 1.5 hours, then cool to obtain the core emulsion.

[0043] 4) Mix 90 parts methyl methacrylate, 5 parts styrene, 1 part methacrylic acid, 3 parts allyl glycidyl ether, and 1 part 2-acrylamide-2-methylpropanesulfonic acid evenly to obtain a shell monomer mixture. Mix 0.4 parts potassium persulfate and 5 parts water evenly to obtain an initiator solution.

[0044] 5) Heat the core emulsion to 80°C, slowly add the shell monomer mixture and initiator solution, keep the reaction at this temperature for 2 hours, cool, and adjust the pH to 8 to obtain the final product.

[0045] The specimen was tested and found to have a compressive strength of 29.6 MPa and an elastic modulus of 5.77 GPa.

[0046] Example 3

[0047] The toughening agent is prepared by the following steps:

[0048] 1) Weigh each ingredient according to its weight.

[0049] 2) Mix 97 parts of acrylate and 3 parts of divinylbenzene evenly to obtain the oil phase. Mix 2.5 parts by weight of sodium dodecyl sulfate and 170 parts by weight of water evenly to obtain the aqueous phase. Slowly add the oil phase dropwise to the aqueous phase while stirring to obtain the monomer emulsion.

[0050] 3) Mix 0.5 parts potassium persulfate and 15 parts water thoroughly, heat to 75°C while stirring, and slowly add dropwise to the monomer emulsion from step 2). Maintain the reaction temperature for 1.5 hours, then cool to obtain the core emulsion.

[0051] 4) Mix 30 parts styrene, 2 parts methacrylic acid, 2 parts allyl glycidyl ether, and 4 parts 2-acrylamide-2-methylpropanesulfonic acid evenly to obtain a shell monomer mixture. Mix 0.4 parts potassium persulfate and 5 parts water evenly to obtain an initiator solution.

[0052] 5) Heat the core emulsion to 75°C, slowly add the shell monomer mixture and initiator solution, keep the reaction at this temperature for 2 hours, cool, and adjust the pH to 8 to obtain the final product.

[0053] The specimen was tested and found to have a compressive strength of 29.2 MPa and an elastic modulus of 5.23 GPa.

[0054] Comparative Example 1

[0055] This comparative example does not contain any toughening agent and serves as a control group.

[0056] The specimen was tested and found to have a compressive strength of 30.6 MPa and an elastic modulus of 9.46 GPa.

[0057] Comparative Example 2

[0058] This comparative example uses 8 parts styrene-butadiene emulsion and 2 parts PVA fiber as toughening agents.

[0059] The specimen was tested and found to have a compressive strength of 20.6 MPa and an elastic modulus of 7.12 GPa.

[0060] Comparative Example 3

[0061] The toughening agent is prepared by the following steps:

[0062] 1) Weigh each ingredient according to its weight.

[0063] 2) Take 100 parts of butyl acrylate to obtain the oil phase. Mix 1.5 parts by weight of sodium dodecyl sulfate and 180 parts by weight of water evenly to obtain the aqueous phase. Slowly add the oil phase dropwise to the aqueous phase while stirring to obtain the monomer emulsion.

[0064] 3) Mix 0.7 parts potassium persulfate and 12 parts water thoroughly, heat to 80°C while stirring, and slowly add dropwise to the monomer emulsion from step 2). Maintain the reaction temperature for 1.5 hours, then cool to obtain the core emulsion.

[0065] 4) Mix 90 parts methyl methacrylate, 5 parts styrene, 1 part methacrylic acid, 3 parts allyl glycidyl ether, and 1 part 2-acrylamide-2-methylpropanesulfonic acid evenly to obtain a shell monomer mixture. Mix 0.4 parts potassium persulfate and 5 parts water evenly to obtain an initiator solution.

[0066] 5) Heat the core emulsion to 80°C, slowly add the shell monomer mixture and initiator solution, keep the reaction at this temperature for 2 hours, cool, and adjust the pH to 8 to obtain the final product.

[0067] The specimen was tested and found to have a compressive strength of 26.0 MPa and an elastic modulus of 6.25 GPa.

[0068] Comparative Example 4

[0069] The toughening agent is prepared by the following steps:

[0070] 1) Weigh each ingredient according to its weight.

[0071] 2) Take 100 parts of divinylbenzene to obtain the oil phase. Mix 1.5 parts by weight of sodium dodecyl sulfate and 180 parts by weight of water evenly to obtain the aqueous phase. Slowly add the oil phase dropwise to the aqueous phase while stirring to obtain the monomer emulsion.

[0072] 3) Mix 0.7 parts potassium persulfate and 12 parts water thoroughly, heat to 80°C while stirring, and slowly add dropwise to the monomer emulsion from step 2). Maintain the reaction temperature for 1.5 hours, then cool to obtain the core emulsion.

[0073] 4) Mix 90 parts methyl methacrylate, 5 parts styrene, 1 part methacrylic acid, 3 parts allyl glycidyl ether, and 1 part 2-acrylamide-2-methylpropanesulfonic acid evenly to obtain a shell monomer mixture. Mix 0.4 parts potassium persulfate and 5 parts water evenly to obtain an initiator solution.

[0074] 5) Heat the core emulsion to 80°C, slowly add the shell monomer mixture and initiator solution, keep the reaction at this temperature for 2 hours, cool, and adjust the pH to 8 to obtain the final product.

[0075] The specimen was tested and found to have a compressive strength of 26.8 MPa and an elastic modulus of 7.26 GPa.

[0076] Comparative Example 5

[0077] The toughening agent is prepared by the following steps:

[0078] 1) Weigh each ingredient according to its weight.

[0079] 2) Mix 96 parts butyl acrylate and 4 parts divinylbenzene evenly to obtain the oil phase. Mix 1.5 parts by weight of sodium dodecyl sulfate and 180 parts by weight of water evenly to obtain the aqueous phase. Slowly add the oil phase dropwise to the aqueous phase while stirring to obtain the monomer emulsion.

[0080] 3) Mix 0.7 parts potassium persulfate and 12 parts water thoroughly, heat to 80°C while stirring, and slowly add dropwise to the monomer emulsion from step 2). Maintain the reaction temperature for 1.5 hours, then cool to obtain the core emulsion.

[0081] 4) Mix 90 parts methyl methacrylate, 8 parts styrene, and 2 parts methacrylic acid evenly to obtain a shell monomer mixture. Mix 0.4 parts potassium persulfate and 5 parts water evenly to obtain an initiator solution.

[0082] 5) Heat the core emulsion to 80°C, slowly add the shell monomer mixture and initiator solution, keep the reaction at this temperature for 2 hours, cool, and adjust the pH to 8 to obtain the final product.

[0083] The specimen was tested and found to have a compressive strength of 23.7 MPa and an elastic modulus of 6.81 GPa.

[0084] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A toughening agent for oil well cement, characterized in that... It consists of a highly elastic core and a rigid polymer shell covering the highly elastic core. The highly elastic core is polymerized from 95-99 parts by weight of acrylate and 1-5 parts by weight of divinylbenzene. The rigid polymer shell is polymerized from 20-35 parts by weight of methyl methacrylate and / or styrene, 1-3 parts by weight of methacrylic acid, 1-3 parts by weight of allyl glycidyl ether, and 1-3 parts by weight of 2-acrylamide-2-methylpropanesulfonic acid.

2. The toughening agent for oil well cement according to claim 1, characterized in that... The acrylate is at least one of butyl acrylate and ethyl acrylate.

3. The method for preparing the toughening agent for oil well cement according to any one of claims 1-2, characterized in that... It includes the following steps: 1) Weigh each ingredient according to its weight. 2) Mix acrylate and divinylbenzene evenly to obtain the oil phase. Mix 1-3 parts by weight of emulsifier and 122-186 parts by weight of water evenly to obtain the aqueous phase. Slowly add the oil phase dropwise to the aqueous phase while stirring to obtain the monomer emulsion. 3) Mix 0.5-1 parts of initiator and 10-20 parts of water thoroughly, heat and stir, and slowly add dropwise to the monomer emulsion in step 2). Maintain the reaction temperature, cool, and obtain the core emulsion. 4) Mix methyl methacrylate, styrene, methacrylic acid, allyl glycidyl ether, and 2-acrylamide-2-methylpropanesulfonic acid evenly to obtain a shell monomer mixture. Mix 0.25-0.5 parts of initiator and 3-5 parts of water evenly to obtain an initiator solution. 5) Heat the core emulsion, slowly add the shell monomer mixture and initiator solution, maintain the temperature for reaction, cool, and adjust the pH to 7.5-9 to obtain the final product.

4. The preparation method according to claim 3, characterized in that, In step 2), the emulsifier is sodium dodecyl sulfate, the stirring speed is 200-400 rpm, and the stirring time is 0.5-2 h.

5. The preparation method according to claim 3, characterized in that, In step 3), the initiator is persulfate, the temperature is heated to 75-80℃, the stirring speed is 100-300rpm, the monomer emulsion is added dropwise for 1-2 hours, and the reaction is kept at the temperature for 1-2 hours.

6. The preparation method according to claim 3, characterized in that, Step 4) The initiator is persulfate.

7. The preparation method according to any one of claims 5-6, characterized in that, The persulfate is potassium persulfate.

8. The preparation method according to claim 3, characterized in that, In step 5), the temperature is raised to 75-80℃, the dropping time is 1.5-2.5h, and the reaction time is kept at this temperature for 1.5-2h.

9. The application of the toughening agent for oil well cement according to any one of claims 1-2 in the preparation process of oil well cement slurry.

10. The application according to claim 9, characterized in that, The amount of toughening agent added to the oil well cement is 5-15% of the weight of the oil well cement.