Biodegradable gel plugging agent, preparation method and application in ultra-high temperature well plugging

Abstract

This invention discloses a biodegradable gel plugging agent, its preparation method, and its application in ultra-high temperature well plugging. The biodegradable gel plugging agent comprises the following components in weight percentage: 5.0-10% propylene monomer, 0.1-1.0% gel crosslinking agent, 0.01-0.1% degradation catalyst, 0.001 wt%-0.01% initiator, and the balance being water. It solves the problems of difficult gel breaking and reservoir contamination in existing technologies. When applied, it has a high plugging rate, high strength, and short degradation time.

Description

Technical Field

[0001] This invention relates to the field of oilfield chemical technology, specifically to a biodegradable gel plugging agent, its preparation method, and its application in ultra-high temperature well plugging. Background Technology

[0002] Before gelation, polymer gel materials exhibit good rheological properties and are easy to inject; after gelation, they are deformable and have adjustable plugging strength. Therefore, polymer gels offer unique advantages in plugging operations. Due to their high deformability, polymer gel materials are not limited by leakage channels. After injection, they can crosslink and copolymerize easily flowing polymer or monomer solutions to form non-flowing gels or jelly, which can achieve plugging effects in extremely small channels. This material is liquid before injection, and after injection, under formation conditions, it transforms into a solid gel with a three-dimensional network structure due to crosslinking, exhibiting excellent plugging properties.

[0003] Chinese patent CN109796941A discloses an expanding plugging agent, its preparation method, a microencapsulated plugging agent, and a water-based drilling fluid and their applications. The expanding plugging agent is obtained by polymerizing acrylamide, strength-enhancing materials, acrylates, and a gelatinized colloid. The resulting drilling fluid expanding plugging agent has a stable structure, high strength, good viscoelasticity, and is not easily denatured under high temperature and pressure conditions at the bottom of the well, resulting in good plugging performance. However, this plugging agent has poor environmental degradation properties, requiring a specific breaker to liquefy it during unblocking, which can cause inconvenience to oil and water well operations. Chinese patent CN113185656A provides a temperature-responsive self-degrading temporary plugging agent and a well workover method, belonging to the field of oil and gas extraction technology. The composition comprises the following components by weight percentage: 4%–6% alkenyl monomer, 0.1%–1% crosslinking agent, 0.1%–1% initiator, 0.05%–0.5% degradation catalyst, and the balance being water. The crosslinking agent is polyethylene glycol diacrylate, and the degradation catalyst is 2-amino-2-methyl-1-propanol or ethylene glycolamine. Using polyethylene glycol diacrylate as the crosslinking agent and 2-amino-2-methyl-1-propanol or ethylene glycolamine as the degradation catalyst, the temporary plugging agent gels under temperature and maintains its strength for a period of time. Subsequently, over time, the crosslinking of polyethylene glycol diacrylate fails under the action of the degradation catalyst, degrading the gel-type temporary plugging agent into a linear polymer, ultimately reducing its viscosity and achieving gel self-degradation. However, the above-mentioned gel-type plugging agents are difficult to apply to temporary plugging operations due to problems such as difficulty in breaking the gel, reservoir contamination, high difficulty and risk in on-site construction. Summary of the Invention

[0004] This invention provides a biodegradable gel plugging agent, its preparation method, and its application in ultra-high temperature well plugging. It solves the problems of difficulty in breaking the gel and reservoir contamination in the prior art. When applied, it has a high plugging rate, high strength, and short degradation time.

[0005] To solve this technical problem, the present invention provides the following technical solution:

[0006] A biodegradable gel plugging agent comprising the following components in weight percentages:

[0007] Propylene monomer 5.0-10%,

[0008] Gel crosslinking agent 0.1-1.0%,

[0009] Initiator 0.001wt%~0.01%,

[0010] The remainder is water.

[0011] The gel plugging agent in this solution can be prepared on-site and injected downhole. It utilizes downhole temperature to form a three-dimensional network structure through chemical cross-linking, thereby achieving temporary plugging.

[0012] Under the high temperature at the bottom of the well, the weak bonds in the functional crosslinking agent break, the three-dimensional network structure disintegrates, and the resulting linear low-molecular-weight water-soluble polymer dissolves in the formation water, forming a low-viscosity fluid. This eliminates the need for backflow and does not affect subsequent water injection, enabling temporary plugging and maintenance of ultra-high temperature oilfield wells. It does not require additional conditions such as light, acidic, or alkaline conditions and can degrade spontaneously under certain temperature conditions.

[0013] Preferably, the propylene monomer is selected from acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, acrylic acid, or acrylonitrile.

[0014] Preferably, the general structural formula of the gel crosslinking agent is shown in Formula I:

[0015]

[0016] Where: R1=CnH 2n+1 R2 = C m H 2m+1 ; n=2~6; m=2~6; x=1~5; y=1~5; z=1~5.

[0017] Preferably, the initiator is selected from ammonium persulfate or azobisisobutyramidine hydrochloride.

[0018] The synthetic route of the above-mentioned gel crosslinking agent is as follows:

[0019]

[0020] in:

[0021] R1 = C n H 2n+1 R2 = C m H 2m+1 ;n=2~6; m=2~6; x=1~5; X=F, Cl, Br or I;

[0022] The preparation method of the gel crosslinking agent includes the following steps:

[0023] S1: Dissolve compound A in an organic solvent and stir thoroughly until homogeneous; add an appropriate amount of polymerization inhibitor and trihalobenzene, and stir thoroughly at room temperature until homogeneous before use;

[0024] S2: Heat and stir, react for 12-48 hours, wash with ether, recrystallize with ethanol, filter and dry to obtain gel crosslinking agent.

[0025] The organic solvent is one or more of methanol or ethanol. In the structure of the gel crosslinking agent, n = m = 2–6. The molar mass ratio of compound A to trihalobenzene is 6–3:1. The heating temperature of step S2 is 40–65°C. The polymerization inhibitor is a polyphenol or phenothiazine, wherein the polyphenol is hydroquinone or catechol.

[0026] This solution also provides a biodegradable gel plugging agent, comprising the following components by weight percentage:

[0027] 7% propylene monomer

[0028] 0.5% gel crosslinking agent

[0029] Initiator 0.005%,

[0030] The remainder is water.

[0031] Preferably, in the structure of the gel crosslinking agent: n = m = 2 to 6, x = y = z = 1 to 5.

[0032] This solution also provides a method for preparing the aforementioned biodegradable gel plugging agent, comprising the following steps:

[0033] (1) Add water and propylene monomer to the reaction vessel and mix well;

[0034] (2) Add crosslinking agent and initiator to the solution obtained in step (2) and stir until uniform; let stand and cool to obtain the degradable gel plugging agent.

[0035] The above-mentioned biodegradable gel plugging agent is used in the plugging of ultra-high temperature wells in oil fields.

[0036] Compared with the prior art, the present invention has the following advantages:

[0037] The method of this invention can prepare a high-performance biodegradable gel plugging agent, and the technology is simple, reliable, and has a high yield, making it suitable for large-scale industrial production. This method allows for on-site preparation and injection into the well for temporary plugging; alternatively, the formulation can be injected downhole for direct reaction to form a temporary plug. The gel crosslinking agent used in the plugging agent does not require additional conditions such as light, acidic, or alkaline conditions, and can degrade spontaneously under certain temperature conditions.

[0038] The gel plugging agent of this invention forms a three-dimensional network structure through chemical cross-linking. Under the action of high temperature at the bottom of the well, the weak bonds in the functional cross-linking agent break, the three-dimensional network structure disintegrates, and the generated linear low molecular weight water-soluble polymer dissolves in the formation water to form a low viscosity fluid. It does not require backflow and does not affect subsequent water injection. It can realize temporary plugging and maintenance of ultra-high temperature oilfield wells. Attached Figure Description

[0039] The accompanying drawings, which are included to provide a further understanding of embodiments of the invention and form part of this application, do not constitute a limitation thereof. In the drawings:

[0040] Figure 1 This is a schematic diagram illustrating the pressure-bearing performance of the gel plugging agent of the present invention;

[0041] Figure 2 The infrared spectrum of the crosslinking agent in Example 1 of this invention;

[0042] Figure 3 The image shows the NMR spectrum of the crosslinking agent in Example 1 of this invention. Detailed Implementation

[0043] 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 embodiments. The illustrative embodiments and descriptions of this invention are only used to explain this invention and are not intended to limit this invention.

[0044] Example 1

[0045] 1. The synthetic route of gel crosslinking agent 1 is as follows:

[0046]

[0047] The synthesis steps are as follows:

[0048] S1: Compound Dissolve in methanol solution and stir thoroughly until homogeneous; then add the polymerization inhibitors phenothiazine and mesobacterium tribromobenzene, and stir thoroughly at room temperature until homogeneous before use;

[0049] The molar ratio of compound A1 to mesbromobenzene is 3:1;

[0050] S2: Under stirring conditions, the mixture was heated to 40°C and reacted for 12 hours. After washing with ether and recrystallizing with ethanol, the mixture was filtered and dried to obtain gel crosslinking agent 1.

[0051] 2. Preparation of biodegradable gel plugging agent:

[0052] Biodegradable gel plugging agent, comprising the following components by weight percentage:

[0053] Acrylamide monomer 7%,

[0054] Gel crosslinking agent 1 0.5%,

[0055] Ammonium persulfate 0.005%,

[0056] The remainder is water.

[0057] A method for preparing a biodegradable gel plugging agent includes the following steps:

[0058] (1) Add water and propylene monomer to the reaction vessel and mix well;

[0059] (2) Add crosslinking agent and initiator to the solution obtained in step (1) to carry out polymerization reaction; let stand and cool to obtain the biodegradable gel plugging agent.

[0060] Example 2

[0061] 1. Synthesis of gel crosslinking agent 1:

[0062] S1: Compound Dissolve in ethanol solution and stir thoroughly until homogeneous; then add the polymerization inhibitor hydroquinone and triiodobenzene, and stir thoroughly at room temperature until homogeneous before use;

[0063] The molar ratio of compound A2 to triiodobenzene is 3:1;

[0064] S2: Under stirring conditions, the mixture was heated to 50°C and reacted for 24 hours. After washing with ether and recrystallizing with ethanol, the mixture was filtered and dried to obtain gel crosslinking agent 2.

[0065] 2. Preparation of biodegradable gel plugging agent:

[0066] A biodegradable gel plugging agent comprising the following components in weight percentages:

[0067] 5.0% of 2-acrylamide-2-methylpropanesulfonic acid monomer

[0068] Gel crosslinking agent 2 0.1%,

[0069] Azobisisobutyramidine hydrochloride 0.001 wt%,

[0070] The remainder is water.

[0071] A method for preparing a biodegradable gel plugging agent includes the following steps:

[0072] (1) Add water and propylene monomer to the reaction vessel and mix well;

[0073] (2) Add crosslinking agent and initiator to the solution obtained in step (1) to carry out polymerization reaction; let stand and cool to obtain the biodegradable gel plugging agent.

[0074] Example 3

[0075] 1. Synthesis of gel crosslinking agent 3

[0076] S1: Compound compound compound Dissolve each ingredient separately in an ethanol solution, add the polymerization inhibitor hydroquinone, and stir thoroughly until homogeneous;

[0077] S2: Under stirring conditions, heat to 65°C and add triiodophenylethanol solution dropwise; then react for 48 h, wash with ether, recrystallize with ethanol, filter and dry to obtain gel crosslinking agent 3.

[0078] The molar ratio of compound A1:compound A3:compound A4:triiodobenzene is 1:1:1:1.

[0079] 2. Preparation of biodegradable gel plugging agent

[0080] A biodegradable gel plugging agent, characterized in that it comprises the following components in weight percentage:

[0081] Acrylonitrile monomer 10%,

[0082] Gel crosslinking agent 3 1.0%,

[0083] Azobisisobutyramidine hydrochloride 0.01%,

[0084] The remainder is water.

[0085] A method for preparing a biodegradable gel plugging agent includes the following steps:

[0086] (1) Add water and propylene monomer to the reaction vessel and mix well;

[0087] (2) Add crosslinking agent and initiator to the solution obtained in step (1) to carry out polymerization reaction; let stand and cool to obtain the biodegradable gel plugging agent.

[0088] Comparative Example 1

[0089] Preparation of biodegradable gel plugging agent:

[0090] Biodegradable gel plugging agent, comprising the following components by weight percentage:

[0091] Acrylamide monomer 7%,

[0092] Crosslinking agent: 0.5% polyethylene glycol diacrylate.

[0093] Ammonium persulfate 0.005%,

[0094] The remainder is water.

[0095] A method for preparing a biodegradable gel plugging agent includes the following steps:

[0096] (1) Add water and propylene monomer to the reaction vessel and mix well;

[0097] (2) Add crosslinking agent and initiator to the solution obtained in step (1) to carry out polymerization reaction; let stand and cool to obtain the biodegradable gel plugging agent.

[0098] Figure 2 Infrared spectrum of the crosslinking agent, 3430 cm⁻¹ -1 The characteristic absorption peak of NH is at 3110 cm⁻¹. -1 and 3066cm -1 The characteristic absorption peak for a carbon-carbon double bond (C=C) is located at 1710 cm⁻¹. -1 The vibration at this point is the stretching vibration of a carbon-carbon double bond; 1552 cm⁻¹ -1 The peak at 1401 cm⁻¹ represents the stretching vibration of the C-H bond in the double bond. -1 The absorption peak at 1093 cm⁻¹ is due to the deformation vibration of the methyl group. -1 The absorption peak at 884 cm⁻¹ is the C=O group of the ester group. -1 The vibration at this point is an out-of-plane deformation vibration of the benzene ring; 796 cm⁻¹ -1 The peak at this point represents the out-of-plane bending vibration of the =C—H double bond. Infrared spectroscopy reveals characteristic absorption peaks for the benzene ring, carbon-carbon double bond, and ester group in the crosslinking agent, indicating successful synthesis of the target crosslinking agent.

[0099] The proton NMR spectrum of the crosslinking agent is shown below. Figure 3 In the figure, position 7.01 represents the chemical shift of the proton on the benzene ring structure; positions 6.41 and 6.07 represent the chemical shifts of the carbon-carbon double bond; position 3.67 represents the chemical shift of the proton connecting the ester group; and positions 3.35 and 1.41 represent the chemical shifts of the heptyl hydrogen atom connecting the nitrogen atom. The spectrum shows that the synthesized crosslinking agent contains both carbon-carbon double bonds and ester groups, and all protons in the molecular structure of the crosslinking agent appear in the spectrum, indicating that the synthesized crosslinking agent conforms to the expected design structure.

[0100] The biodegradable gel plugging agents obtained in Examples 1-3 and Comparative Example 1 were formulated into temporary plugging solutions for plugging operations, and their performance was tested as follows:

[0101] Table 1

[0102] Test content Example 1 Example 2 Example 3 Comparative Example 1 Degradation time (h) 8 9 10 20 Core plugging rate (%) 99 98 99 96

[0103] As shown in Table 1, compared with existing crosslinking agents, the biodegradable gel plugging agent prepared by the crosslinking agent synthesized in this scheme has a high plugging rate and short degradation time when applied.

[0104] The prepared biodegradable gel plugging agent solution was injected into a sand-filled tube and placed in a 60°C oven. After gelation, the sand-filled tube was removed, and the pressure-bearing performance of the gel plugging agent after gelation was tested using a displacement device and a gas-driven reverse injection method. Pressure changes were observed and recorded in real time. The pressure-bearing performance of the gel plugging agent was tested using a gas-driven reverse injection method, with the gel plugging agent solution injected in a slug-like manner, and its pressure-bearing performance at different injection volumes was tested. Figure 1 As shown, the pressure resistance of the gel plugging agent increases with the increase of the injection volume. When the injection volume is less than 50%, the pressure resistance reaches a maximum of 10 MPa. When the injection volume reaches 0.75 PV or more, the pressure resistance of the temporary plugging agent is >15 MPa, and can reach a maximum of 19 MPa, indicating that the gel plugging agent has good pressure resistance.

[0105] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A biodegradable gel plugging agent, characterized in that, The components include the following components by mass percentage: Propylene monomers 5.0%~10%, Gel crosslinking agent 0.1%-1.0%, Initiator 0.001%~0.01%, The remainder is water; The general structural formula of the gel crosslinking agent is shown in Formula I: Equation I, where: R1=C n H 2n+1 R2=C m H 2m+1 n=2~6; m=2~6; X in the anion = Br; The number of repeating units of the methylene group is x = 1~5; y = 1~5; z = 1~5.

2. The biodegradable gel plugging agent according to claim 1, characterized in that, The propylene monomer is selected from one of acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, acrylic acid, or acrylonitrile.

3. The biodegradable gel plugging agent according to claim 1, characterized in that, The initiator is selected from ammonium persulfate or azobisisobutyramidine hydrochloride.

4. The biodegradable gel plugging agent according to claim 1, characterized in that, The components include the following components by mass percentage: 7% propylene monomer 0.5% gel crosslinking agent Initiator 0.005%, The remainder is water.

5. The biodegradable gel plugging agent according to claim 1, characterized in that, In the structure of the gel crosslinking agent: n=m=2~6, and the number of repeating units of the methylene group is x=y=z=1~5.

6. A method for preparing the biodegradable gel plugging agent according to any one of claims 1-5, characterized in that, Includes the following steps: (1) Add water and propylene monomer to the reaction vessel and mix well; (2) Add crosslinking agent and initiator to the solution obtained in step (1) and stir until uniform; let stand and cool to obtain the degradable gel plugging agent.

7. The application of the biodegradable gel plugging agent according to any one of claims 1-5 in the plugging of ultra-high temperature wells in oil fields.

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