A biodegradable gel plugging agent, its preparation method, and its application in high-temperature well plugging.

Abstract

This invention discloses a biodegradable gel plugging agent, its preparation method, and its application in high-temperature well plugging. The biodegradable gel plugging agent comprises the following components by mass percentage: 10.0 wt% to 15 wt% propylene monomer, 1.0 wt% to 2 wt% crosslinking agent for gelation, 0.01 wt% to 0.001 wt% initiator, and the balance being water. It solves the problems of poor degradation and salt resistance in existing technologies. When applied, because the crosslinking agent contains a conjugated aromatic system, it does not require additional conditions such as light, acidic conditions, or alkaline conditions, and can degrade spontaneously under certain temperature conditions. It has the characteristics of controllable gelation time, spontaneous degradation under certain temperature conditions, and low viscosity of the degraded product. Moreover, the gel can degrade without the need for an additional gel-breaking agent.

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 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] However, existing domestically available gel-based plugging agents are difficult to apply for temporary sealing operations due to problems such as difficulty in breaking down the gel, reservoir contamination, and high risks and difficulties in on-site construction. Chinese patent application number CN2019101862751 provides a high-temperature resistant gel plugging agent that uses a novel solid-phase organic macromolecular crosslinking agent and particle toughening agent, activated diatomaceous earth, significantly improving the high-temperature resistance, strength, and toughness of the gel. Chinese patent application number CN 2021110956647 provides a high-temperature resistant biodegradable gel plugging system for reservoir protection, as well as its preparation and application. The gel plugging system comprises the following raw materials in the following mass percentages: 8-25% vinyl polymer monomer, 0.4-1.2% hypercrosslinked heat-resistant polymer, 0.3-1% organic crosslinking agent, 0.05-0.4% first initiator, 1-7% high-temperature stabilizer, 0.5-5% fiber toughening agent, and the balance being water; the hypercrosslinked heat-resistant polymer is a hypercrosslinked polymer with amide groups on its surface; however, after the above plugging agent gels, the gel breaking mechanism at high temperatures is complex, and the timing of gel breaking is difficult to control, which is not conducive to the recovery of production capacity and the protection of the reservoir, and it also has poor salt resistance. Summary of the Invention

[0004] This invention provides a biodegradable gel plugging agent, its preparation method, and its application in high-temperature well plugging. It solves the problems of poor degradation and salt resistance in existing technologies. When applied, because the crosslinking agent contains a conjugated aromatic system, it can degrade spontaneously under certain temperature conditions without additional conditions such as light, acidic or alkaline conditions. It has the characteristics of controllable gelation time, spontaneous degradation under certain temperature conditions, and low viscosity of the degraded product. Moreover, the gel can degrade without the need for additional breaker agents.

[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 monomers 10.0wt%~15wt%

[0008] Crosslinking agent for gels: 1.0% wt% ~ 2% wt%

[0009] The initiator is 0.01wt%~0.001wt%, with the balance being water;

[0010] The general structural formula of the crosslinking agent for the gel is shown in Formula I: Equation 1, where R1 = ;

[0011] m=6~18; n=6~18; z=1~18;

[0012] X = F, Cl, Br, or I.

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

[0014] Preferably, the initiator is selected from ammonium persulfate or azobisisobutyramidine hydrochloride.

[0015] Preferably, n = m = 6~18; x = 1~18.

[0016] Preferably, R1 is selected from... .

[0017] The sulfonate ions in the crosslinking agent are hydrophilic, while the benzene ring is lipophilic. The amphiphilic structure results in better blocking performance when used in blocking agents.

[0018] Preferably, the components include the following components in weight percentage:

[0019] 12% propylene monomer

[0020] The gel uses a 1.5% cross-linking agent.

[0021] The initiator is 0.005%, and the remainder is water.

[0022] This solution also provides a method for preparing the above-mentioned biodegradable gel plugging agent, comprising the following steps:

[0023] (1) Add water and propylene monomer to the reaction vessel and mix well;

[0024] (2) Add a gel crosslinking agent and an initiator to the solution obtained in step (1) and stir until homogeneous; let stand and cool to obtain the biodegradable gel plugging agent.

[0025] The above-mentioned biodegradable gel plugging agent is used in the plugging of ultra-high temperature wells in oil fields.

[0026] Compared with the prior art, the present invention has the following advantages:

[0027] The gel sealing system of the present invention is formed by cross-linking reaction of propylene monomer and specific cross-linking agent. Compared with the traditional temperature-resistant gel system formed by cross-linking of propylene monomer and organic cross-linking agent, the gel formed after curing has better high-temperature stability, higher strength and better viscoelastic properties, and has a better sealing effect on leakage channels.

[0028] The crosslinking agent for gels designed in this invention contains a conjugated aromatic system in its structure, so it can degrade on its own under certain temperature conditions without additional conditions such as light, acidic conditions or alkaline conditions.

[0029] The application of the gel crosslinking agent of the present invention in high-temperature biodegradable gel plugging agent forms a three-dimensional network structure through chemical crosslinking. Under the action of 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 generated linear low molecular weight water-soluble polymer dissolves in the formation water to form a low viscosity fluid. No backflow is required, and it does not affect subsequent water injection. It can realize temporary plugging and maintenance of oilfield wells. Attached Figure Description

[0030] 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:

[0031] Figure 1 This is a schematic diagram of the structure for testing the salt resistance of the gel plugging agent of the present invention;

[0032] Figure 2 The infrared spectrum of compound A1 of this invention;

[0033] Figure 3 The NMR spectrum of compound A1 of this invention;

[0034] Figure 4 The infrared spectrum of compound B3 of this invention;

[0035] Figure 5 The NMR spectrum of compound B3 of this invention;

[0036] Figure 6 The infrared spectrum of the product of Example 1 of this invention;

[0037] Figure 7The NMR spectrum of the product of Example 1 of this invention; Detailed Implementation

[0038] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the embodiments. The illustrative embodiments and descriptions of this invention are only used to explain this invention and are not intended to limit this invention.

[0039] Example 1

[0040] 1. The synthetic route of gel crosslinking agent 1 is shown in the following formula: Synthesis of compound A1:

[0041] An appropriate amount of n-heptylamine and activated carbon were added to a reaction vessel, and the mixture was stirred under suitable conditions. After stirring for a certain period of time, ethyl acrylate was slowly added dropwise to the reactants. After the reaction was completed, the reaction mixture was extracted and separated with ethanol. Finally, the obtained product was purified and dried to obtain compound A1. This synthetic method is existing technology.

[0042] Synthesis of crosslinking agents:

[0043] S1: Dissolve compound A1 in methanol solution and stir thoroughly until homogeneous; then add the polymerization inhibitor phenothiazine and compound B1, and stir thoroughly at room temperature until homogeneous before use;

[0044] The molar ratio of compound A1 to compound B1 is 2:1;

[0045] S2: Under stirring conditions, the mixture was heated to 40°C and reacted for 48 h. After washing with ether, recrystallization with ethanol, filtration and drying, the crosslinking agent compound 1 for gelation was obtained.

[0046] 2. Preparation of biodegradable gel plugging agent:

[0047] The prepared gel crosslinking agent is used to prepare a high-temperature degradable gel plugging agent. The components of the high-temperature degradable gel plugging agent are composed of the following raw material formulation:

[0048] 10% propylene monomer

[0049] 1% cross-linking agent for gel

[0050] Initiator 0.001%, balance water.

[0051] A method for preparing a biodegradable gel plugging agent includes the following steps:

[0052] (1) Add water and acrylamide monomer to the reaction vessel and mix well;

[0053] (2) Add a gel crosslinking agent and an initiator to the solution obtained in step (1) to carry out a polymerization reaction; let it stand and cool to obtain the biodegradable gel plugging agent.

[0054] Example 2

[0055] 1. The synthetic route of the crosslinking agent is shown in the following formula:

[0056] S1: Dissolve compound A2 in methanol solution and stir thoroughly until homogeneous; then add the polymerization inhibitor phenothiazine and compound B2, and stir thoroughly at room temperature until homogeneous before use;

[0057] The molar ratio of compound A2 to compound B2 is 3:1;

[0058] S2: Under stirring conditions, the mixture was heated to 50°C and reacted for 12 h. The product was then washed with ether, recrystallized with ethanol, filtered, and dried to obtain the crosslinking agent compound for gelation.

[0059] 2. Preparation of biodegradable gel plugging agent:

[0060] The prepared gel was used as a crosslinking agent to prepare a high-temperature degradable gel plugging agent. The components of the high-temperature degradable gel plugging agent were formulated as follows: 12% wt% 2-acrylamide-2-methylpropanesulfonic acid monomer.

[0061] 1.5wt% gel crosslinking agent

[0062] The initiator is 0.005 wt%, with the balance being water.

[0063] A method for preparing a biodegradable gel plugging agent includes the following steps:

[0064] (1) Add water and 2-acrylamide-2-methylpropanesulfonic acid monomer to the reaction vessel and mix well;

[0065] (2) Add a gel crosslinking agent and an initiator to the solution obtained in step (1) to carry out a polymerization reaction; let it stand and cool to obtain the biodegradable gel plugging agent.

[0066] Example 3

[0067] 1. The synthetic route of gel crosslinking agent 3 is shown in the following formula: Synthesis of compound B3:

[0068] This compound was synthesized using propanesulfonic acid and 2,5-diiodo-1,4-benzenediol as raw materials. Propanesulfonic acid and 2,5-diiodo-1,4-benzenediol were added sequentially in a three-necked flask purged with nitrogen (N2). After reacting for 24 hours under heating and stirring, the product was separated from the reaction mixture through extraction, washing, and drying. The product was then neutralized with sodium hydroxide solution to obtain the compound. This synthetic method is existing technology.

[0069] Synthesis of crosslinking agents:

[0070] S1: Dissolve compound A3 in methanol solution and stir thoroughly until homogeneous; then add the polymerization inhibitor phenothiazine and compound B3, and stir thoroughly at room temperature until homogeneous before use;

[0071] The molar ratio of compound A3 to compound B3 is 2:1;

[0072] S2: Under stirring conditions, the mixture was heated to 40°C and reacted for 48 h. After washing with ether, recrystallization with ethanol, filtration and drying, the crosslinking agent compound 3 for gelation was obtained.

[0073] 2. Preparation of biodegradable gel plugging agent:

[0074] The prepared gel crosslinking agent is used to prepare a high-temperature degradable gel plugging agent. The components of the high-temperature degradable gel plugging agent are composed of the following raw material formulation:

[0075] 10% propylene monomer

[0076] 1% cross-linking agent for gel

[0077] Initiator 0.001%, balance water.

[0078] A method for preparing a biodegradable gel plugging agent includes the following steps:

[0079] (1) Add water and acrylamide monomer to the reaction vessel and mix well;

[0080] (2) Add a gel crosslinking agent and an initiator to the solution obtained in step (1) to carry out a polymerization reaction; let it stand and cool to obtain the biodegradable gel plugging agent.

[0081] Comparative Example 1

[0082] Commercially available polyethylene glycol o-phenyl ether acrylate was used instead of the crosslinking agent in Example 1 to prepare a high-temperature degradable gel plugging agent.

[0083] The infrared spectrum of compound A1 (A2 / A3) is as follows: Figure 2 As shown. Figure 2 2985 cm -1 The peak at 2817 cm⁻¹ represents the stretching vibration of CH in the double bond.-1 and 2767 cm -1 Absorption at saturated CH stretching vibration, 1725cm -1 The peak at 1297 cm⁻¹ represents the stretching vibration of the C=O group in the ester group. -1 The absorption vibration peak of NH is at 1193 cm⁻¹. -1 The absorption peak at position 1 is the symmetric vibration of C—O. Based on the above analysis, it can be found that the absorption peaks of carbon-carbon double bonds, ester groups, and carbon-nitrogen bonds appear in the spectrum, which indicates that the synthesized substance conforms to the structure of the compound.

[0084] The NMR spectrum of compound A1 (A2 / A3) is as follows: Figure 3 As shown. By Figure 3 It can be seen that the chemical shifts of the protons at positions 6.57, 6.38, and 5.97 are the chemical shifts of the protons on the carbon-carbon double bond, position 4.19 is the chemical shift of the proton on the carbon atom adjacent to the ester group, position 3.09 is the chemical shift of the proton on the carbon atom connected to the nitrogen atom, and positions 1.81, 0.80, and 0.71 are the chemical shifts of the protons on the octyl carbon atom connected to the nitrogen atom. It can be found that the chemical shifts of all the protons of this compound appear in the spectrum, indicating that the synthesized substance conforms to the structure of this compound.

[0085] The infrared spectrum of compound B3 is shown in [reference needed]. Figure 4 , Figure 4 2904cm -1 and 2858 cm -1 Absorption occurs at saturated CH stretching vibration, 1400 cm⁻¹ -1 The peak at 1328 cm⁻¹ represents the stretching vibration of the benzene ring. -1 The peak at 1164 cm⁻¹ represents the absorption vibration of the S=O group in sulfonic acid. -1 The peak at this position represents the symmetric vibration absorption peak of the ether bond COC. Based on the above analysis, it can be found that the spectrum contains absorption peaks for the ether bond, sulfonic acid group, and benzene ring, indicating that the synthesized substance conforms to the structure of the compound.

[0086] NMR analysis of compound B3 as follows Figure 5 As shown, by Figure 5 It can be seen that the chemical shift of the proton on the benzene ring is at position 7.03, the chemical shift of the proton on the carbon atom connected to the ether bond is at position 3.96, the chemical shift of the proton on the carbon atom connected to the sulfonic acid group is at position 3.09, and the chemical shift of the proton on the carbon atom adjacent to the sulfonic acid group is at position 2.06. It can be found that the chemical shifts of all protons of this compound appear in the spectrum, indicating that the synthesized substance conforms to the structure of this compound.

[0087] Figure 6 The infrared spectrum of the crosslinking agent in Example 1 is shown. In the infrared spectrum, 3417 cm⁻¹ -1The characteristic absorption peak of NH is at 1583 cm⁻¹. -1 The peak at 1471 cm⁻¹ represents the stretching vibration of the C-H bond in the double bond. -1 and 1382 cm -1 The absorption peaks at 1062 cm⁻¹ are the deformation vibration absorption peaks of the methylene and methyl groups, respectively. -1 The absorption peak at 995 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; 804 cm -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.

[0088] The proton NMR spectrum of the crosslinking agent in Example 1 is shown below. Figure 7 . Figure 7 The chemical shifts at 7.23 on the benzene ring, 6.30 and 5.08 on the carbon-carbon double bond, and 3.09, 1.72 and 1.34 on the heptyl hydrogen atom connecting the nitrogen atom, are shown in the spectrum. The spectrum shows that the synthesized crosslinking agent contains both carbon-carbon double bonds and ester groups, and all the protons in the molecular structure of the crosslinking agent appear in the spectrum, indicating that the synthesized crosslinking agent conforms to the expected structure of the designed crosslinking agent.

[0089] The crosslinking agents of Examples 1-2 were used in the blocking agents of Examples 3-4, and compared with the blocking agent of Comparative Example 1. The results are shown in Table 1.

[0090] Table 1 Biodegradable Gel Blocking Agents

[0091]

[0092] As shown in Table 1, the compound in this scheme, used as a gel crosslinking agent and propylene monomer, along with the initiator as a formulation, is applicable to the biodegradable gel plugging agent. The system has an applicable temperature range of 90–120°C, an adjustable gelation time of 1.5–3 h, a controllable degradation time of 5–10 days, and a viscosity ≤10 mPa·s after degradation. In contrast, the system of the control compound 1 is insoluble in water, making it unsuitable for plugging operations in water-injection development oilfields. Furthermore, its degradation requires acid or light conditions and may damage the environment. Therefore, the gel crosslinking agent designed in this invention, containing a conjugated aromatic system in its structure, can self-degrade under certain temperature conditions without additional conditions such as light, acidic, or alkaline conditions. It features controllable gelation time, spontaneous degradation under certain temperature conditions, and low viscosity of the degraded product. Moreover, this gel degrades without the need for an additional gel-breaking agent.

[0093] Salt resistance tests were conducted on the gel plugging agent of Example 1. The gel plugging agent was prepared using mineralized water with a salinity of 10,000–100,000 mg / L prepared with NaCl. The results are as follows: Figure 1 As shown, the results indicate that the gelation time of the gel plugging agent remained at about 3 hours under different salt concentrations. When the concentration was below 70,000 mg / L, the gel degradation time started at 7 days. At 70,000 mg / L, the degradation time was shortened to about 6.5 days. The gel degradation time remained basically stable under different concentrations, indicating that the temporary plugging agent has good salt resistance.

[0094] 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 10.0wt%~15wt% Crosslinking agent for gels: 1.0% wt% ~ 2% wt% Initiator 0.01wt%~0.001wt% The remainder is water; The general structural formula of the crosslinking agent for the gel is shown in Formula I: Equation 1, where R1 is selected from... one; m=6~18; n=6~18; z=1~18; X = F, Cl, Br, or I.

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, n = m = 6~18; z = 1~18.

5. The biodegradable gel plugging agent according to claim 1, characterized in that, The components include the following components by mass percentage: 12% propylene monomer The gel uses a 1.5% cross-linking agent. Initiator 0.005%, The remainder is water.

6. The 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 a gel crosslinking agent and an initiator to the solution obtained in step (1) and stir until homogeneous; let stand and cool to obtain the biodegradable 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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