Cross-linking agent and preparation method thereof, self-degradable polymer gel composition, self-degradable polymer gel and application

Abstract

The invention relates to the technical field of oil and gas field leakage prevention and temporary plugging, and discloses a cross-linking agent and a preparation method thereof, a self-degradable polymer gel composition, self-degradable polymer gel and application. The cross-linking agent comprises one or more of structures as shown in formulas (1) to (3); R is at least one of H and C1-C2 alkyl; n is 1-10, and m is 1-10; after being prepared, the self-degradable polymer gel disclosed by the invention is not easy to quickly form gel on the ground, can be easily pumped into a shaft and can be self-degraded;

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of oil and gas field leak-proof temporary plugging, and particularly relates to a crosslinking agent, a preparation method thereof, a self-degradable polymer gel composition, a self-degradable polymer gel and application thereof. BACKGROUND

[0002] For drilling and completion, workover and well repair operations in low-pressure or fracture, cave development easy leakage formation, the wellbore working fluid leakage is often serious, and these liquids may even penetrate into the reservoir and cause reservoir damage and pollution. Leak-proof temporary plugging technology is usually used to complete the operation.

[0003] In recent decades, polymer gel has been widely used in the field of chemical plugging and leak-proofing of oil and gas wells. The polymer gel plugging technology has the following three advantages: (1) good flexibility makes it have excellent self-adaptability, wide range of action, and convenient construction; (2) not easy to be miscible with formation water, resistant to erosion; (3) low cost, easy to clean and unblock. At present, the crosslinked polymer gel system is mostly used for leak-proof and plugging in well completion and workover. The raw materials for preparing the crosslinked polymer gel system are crosslinking agent and polymer. The crosslinking agent can convert linear or lightly branched macromolecular polymer into gel with three-dimensional network structure, thereby improving the strength and elasticity of the gel. The swelling properties of the gel help to fill the crack space and achieve complete plugging, and finally avoid pollution of the reservoir through controllable gel breaking and degradation technology. However, the existing crosslinked polymer temporary plugging technology has the problems of limited gel strength, easy to form gel on the ground after preparation, and difficult to pump into the wellbore.

[0004] In order to solve the above problems, monomer polymerization method can be selected to directly synthesize polymer gel by using two small molecular monomers and crosslinking agent. In addition, the gel breaking technology process of polymer gel is complex. If the gel breaking is not complete, it will not only affect the effect of leak-proof temporary plugging, but also affect the subsequent normal production operation. The conventional gel breaking method is to pump a strong oxidizing agent solution such as ammonium persulfate into the formation as a gel breaker. However, the gel breaking effect of strong oxidizing gel breaker is greatly affected by temperature and the gel breaking time is not easy to control, so for the gel breaking process of leak-proof temporary plugging gel, injecting chemical oxidizing agent is not the best choice.

[0005] CN108130062A discloses a kind of quick self-degradation water-soluble liquid rubber plug and preparation method thereof, adopts konjac glucomannan and brunei gum as raw material, adds crosslinking agent, crosslinking accelerator, solidification enhancer, rubber plug degradation agent, rubber plug degradation accelerator, forms the rubber plug that can be cured in 1-2h, after curing, can automatically degrade, but the system composition is complex.

[0006] Therefore, it is of great significance to research and develop a leak-proof temporary plugging. SUMMARY

[0007] The purpose of this invention is to overcome the problems of limited gel strength and rapid gelation on the surface after preparation, which makes pumping into the wellbore difficult, in existing cross-linked polymer temporary plugging technology. This invention provides a cross-linking agent and its preparation method, a self-degradable polymer gel composition, and the self-degradable polymer gel and its application. The self-degradable polymer gel of this invention does not easily gel rapidly on the surface after preparation, can be easily pumped into the wellbore, and has good adaptability to formation temperature. Furthermore, it can self-degrade after maintaining high strength (pressure resistance up to 10 MPa or more) for a period of time, without the need for external chemical degrading agents, thus better meeting the needs of construction in formations at 60-100℃.

[0008] To achieve the above objectives, a first aspect of the present invention provides a crosslinking agent, wherein the crosslinking agent comprises one or more of the structures shown in formulas (1) to (3):

[0009]

[0010]

[0011] In formulas (1) to (3), R is at least one of H and C1-C2 alkyl groups; n is 1-10, and m is 1-10.

[0012] A second aspect of the present invention provides a method for preparing the aforementioned crosslinking agent, wherein the preparation method includes:

[0013] (1) In the presence of a catalyst and a N2 atmosphere, the 4-arm PEG and one or more esters of the structures shown in formulas (4) to (6) are brought into contact for a first reaction.

[0014] (2) The product after step (1), acryloyl chloride as shown in formula (7) and triethylamine are brought together for a second reaction to obtain a crosslinking agent;

[0015]

[0016] In equation (7), R is one or more of H, CH3 and CH2CH3.

[0017] A third aspect of the present invention provides a self-degradable polymer gel composition, wherein the composition comprises a monomer, an initiator, a crosslinking agent and water, wherein the crosslinking agent is the aforementioned crosslinking agent.

[0018] A fourth aspect of the present invention provides a method for preparing a self-degrading polymer gel using the aforementioned composition, wherein the method comprises: mixing a monomer, a crosslinking agent, an initiator and water to obtain a self-degrading polymer gel base liquid, and then gelling it to obtain a self-degrading polymer gel; wherein the crosslinking agent is the aforementioned crosslinking agent.

[0019] The fifth aspect of the present invention provides a self-degradable polymer gel prepared by the method described above.

[0020] The sixth aspect of the present invention provides an application of the aforementioned self-degradable polymer gel as a temporary plugging agent in oil and gas field reservoirs.

[0021] Through the above technical solution, the technical solution of the present invention has the following beneficial effects:

[0022] (1) The self-degradable polymer gel provided by the present invention gels under the action of formation temperature (i.e., downhole temperature 60-100℃), becomes a solid-like structure with a three-dimensional network structure, and maintains its strength for a period of time (before degradation begins), thus better meeting the needs of formation construction at 60-100℃.

[0023] (2) The self-degradable polymer gel provided by the present invention maintains its strength for a period of time under the influence of formation temperature. As time goes by, the cross-linking agent is hydrolyzed, causing the cross-linking points inside the gel to break. The three-dimensional network structure begins to collapse, the gel's body structure is disintegrated, and it is eventually completely degraded into a small molecule linear structure, thus realizing the self-degradation of the temporary plugging gel and restoring the permeability of the formation.

[0024] (3) The present invention can select different self-degradable polymer gel formulations according to different construction conditions and progress requirements. By designing the formulation, the degradation time of the polymer gel can be changed, thereby meeting the specific needs of the oil and gas field leak prevention and temporary plugging construction site, and has good adaptability.

[0025] (4) The self-degradable polymer gel of the present invention degrades on its own after maintaining high strength (pressure resistance up to 10 MPa or more) for a period of time without the need for external chemical degrading agents. It can achieve self-degradation over time. The system composition is simple and saves economic costs.

[0026] (5) The self-degradable polymer gel of the present invention is not easy to form a gel quickly on the ground after preparation. It can be easily pumped into the wellbore and has good adaptability to formation temperature. It solves the problems of complex composition of existing anti-leakage temporary plugging agent system and rapid gelation which is not conducive to pumping. It can achieve safe operation and has little damage to the formation. Attached Figure Description

[0027] Figure 1 This is the infrared spectrum of the crosslinking agent prepared in Preparation Example 1 of the present invention. Detailed Implementation

[0028] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0029] As previously stated, a first aspect of the present invention provides a crosslinking agent, wherein the crosslinking agent comprises one or more of the structures shown in formulas (1) to (3):

[0030]

[0031] In formulas (1) to (3), R is at least one of H and C1-C2 alkyl groups; n is 1-10, and m is 1-10.

[0032] In this invention, the alkyl groups of C1-C2 can be CH3 and / or CH2CH3.

[0033] According to the present invention, in a preferred embodiment, in formula (1), R is H and / or CH3, n is 4-6, and m is 4-6.

[0034] According to the present invention, in a preferred embodiment, in formula (2), R is H and / or CH3, n is 4-6, and m is 4-6.

[0035] According to the present invention, in a preferred embodiment, in formula (3), R is H and / or CH3, n is 4-6, and m is 4-6.

[0036] The inventors of this invention have discovered that a self-degradable crosslinking agent was synthesized, and a self-degradable polymer gel was prepared via free radical polymerization based on this agent. On one hand, because the crosslinking agent contains double bonds, it can participate in the addition reaction of at least two polymer chains; on the other hand, the crosslinking agent connects long-chain polymers, transforming linear polymer molecular chains into a three-dimensional structure, thus enhancing the gel's strength. After a period of time, under the combined effects of temperature and water, the ester groups in the unstable crosslinking agent gradually hydrolyze, causing the crosslinking points inside the gel to break, the polymer network structure to be destroyed, and the gel gradually loses its strength, eventually completely degrading into low-molecular-weight polymers and returning to the ground.

[0037] The self-degradable polymer gel of this invention is a liquid before injection into the formation, making it difficult to gel rapidly on the surface. It can be easily pumped into the wellbore and exhibits good adaptability to formation temperatures. After injection, it undergoes free radical polymerization at formation temperatures (i.e., downhole temperatures of 60-100°C) to form a high-strength gel (withstanding pressures up to 10 MPa or more). After maintaining its strength for a period, it self-degrades for temporary leak sealing. The gel formation and degradation times are controllable and adjustable, exhibiting excellent pressure resistance and degradation performance. After the leak sealing operation is completed, the cross-linking agent inside the self-degradable polymer gel hydrolyzes, resulting in the self-degradation of the polymer gel into a low-viscosity solution. The self-degradable polymer gel does not require additional injection of a gel-breaking agent after the leak sealing operation, saving economic costs and minimizing formation damage.

[0038] In addition, the composition of self-degradable polymer gels is simple, and the degradation time of polymer gels can be changed by designing the formula, thereby meeting the specific needs of oil and gas field leak prevention and temporary plugging construction sites.

[0039] A second aspect of the present invention provides a method for preparing the aforementioned crosslinking agent, wherein the preparation method includes:

[0040] (1) In the presence of a catalyst and a N2 atmosphere, the 4-arm PEG and one or more esters of the structures shown in formulas (4) to (6) are brought into contact for a first reaction.

[0041] (2) The product after step (1), acryloyl chloride as shown in formula (7) and triethylamine are brought together for a second reaction to obtain a crosslinking agent;

[0042]

[0043] In equation (7), R is one or more of H, CH3 and CH2CH3.

[0044] According to the present invention, the ester represented by formula (2) can be one or more of ε-caprolactone, lactide and glycolide.

[0045] According to the present invention, the acryloyl chloride represented by formula (3) can be one or more of acryloyl chloride, methacryloyl chloride and 2-ethylacryloyl chloride.

[0046] According to the present invention, the preparation method further includes: separating and purifying the product after the first reaction and / or the product after the second reaction: specifically, in step (1), the product after the first reaction is dissolved in hexane to remove unreacted monomers and catalysts, and the obtained product is dissolved in dichloromethane and separated and purified by azeotropic distillation with toluene; and in step (2), the product after the second reaction is removed by rotary evaporation to remove the solvent, then dissolved in ethyl acetate to precipitate triethylamine hydrochloride, and then the product is dried and precipitated in diethyl ether for separation and purification.

[0047] According to the present invention, the catalyst is tin isooctanoate.

[0048] According to the present invention, the molar ratio of 4-arm-PEG and the ester shown in formula (2) is 1:(5-10), preferably 1:(8-10).

[0049] According to the present invention, the conditions for the first reaction include: a temperature of 120-150°C and a time of 10-18 hours.

[0050] According to the present invention, the conditions for the second reaction include: a temperature of 20-30°C and a time of 6-24 hours.

[0051] According to a preferred embodiment of the present invention, the preparation process of the crosslinking agent is as follows:

[0052]

[0053] Specifically, according to a preferred embodiment of the present invention, the method for preparing the crosslinking agent includes:

[0054] Four-arm PEG and ε-caprolactone (lactide, glycolide) were added to a three-necked flask in a 1:10 molar ratio, followed by a small amount of tin isooctanoate as a catalyst. The mixture was heated to 140°C under N2 atmosphere and reacted for 12 h. After the reaction was complete, the product was added to ice-cold hexane to precipitate and remove unreacted monomers and catalyst. The resulting product was dissolved in dichloromethane and dried by azeotropic distillation with toluene. After drying, the flask was placed in an ice-water bath, and equimolar amounts of acryloyl chloride (methacryloyl chloride, 2-ethylacryloyl chloride) and triethylamine were added. The mixture was reacted under N2 atmosphere for 12 h. The solvent was removed by rotary evaporation, and the product was then dissolved in ethyl acetate to precipitate triethylamine hydrochloride. The product was then dried and precipitated twice in ice-cold diethyl ether to obtain the unstable crosslinking agent.

[0055] A third aspect of the present invention provides a self-degradable polymer gel composition, wherein the composition comprises a monomer, an initiator, the aforementioned crosslinking agent, and water.

[0056] In this invention, the crosslinking agent can be used to crosslink linear polymer chains to form a three-dimensional structure, thereby improving the strength and compressive strength of the gel.

[0057] According to the present invention, the monomer content is 10-20% by weight, the initiator content is 0.01-0.04% by weight, the crosslinking agent content is 0.6-1% by weight, and the balance is water, based on the total weight of the composition.

[0058] Preferably, based on the total weight of the composition, the content of the monomer is 10-15% by weight, the content of the initiator is 0.02-0.03% by weight, the content of the crosslinking agent is 0.8-1% by weight, and the balance is water.

[0059] According to the present invention, the monomer is acrylamide.

[0060] According to the present invention, the initiator is ammonium persulfate.

[0061] A fourth aspect of the present invention provides a method for preparing a self-degrading polymer gel using the aforementioned composition, wherein the method comprises: mixing a monomer, a crosslinking agent, an initiator and water to obtain a self-degrading polymer gel base liquid, and then gelling it to obtain a self-degrading polymer gel; wherein the crosslinking agent is the aforementioned crosslinking agent.

[0062] According to the present invention, monomers, initiators, crosslinking agents and water are mixed, preferably under stirring conditions. The present invention does not have special limitations on the stirring time and speed, and the materials can be mixed evenly according to the actual situation.

[0063] The self-degradable polymer of this invention exhibits excellent overall performance in terms of gelation and complete degradation time. Within the gelation time range, the self-degradable polymer gel reaction solution can be delivered downhole, allowing sufficient time for the delivery of raw materials for the self-degradable polymer gel, thus facilitating operations. If the gelation time is too short, the gel may not reach the temporary plugging location during pumping, potentially causing wellbore blockage. The degradation time of the self-degradable polymer of this invention is more conducive to construction, allowing sufficient plugging time before degradation begins. If the complete degradation time is too short, the gel may degrade before the operation is completed, leading to leakage of subsequent working fluids. An excessively long complete degradation time results in low efficiency of the temporary plugging operation.

[0064] According to the present invention, the conditions for gel formation include: a temperature of 60-100°C; and a time of 0.9-2.5 h, preferably 1-2 h, more preferably 1-1.5 h.

[0065] In this invention, according to the synthesis raw materials and proportions of the self-degradable polymer gel, raw materials including the monomer, (unstable) crosslinking agent, initiator and water are mixed evenly to obtain a self-degradable polymer gel reaction solution; the self-degradable polymer gel reaction solution is pumped into the target temporary plugging formation, and the reaction solution gels at the formation temperature to form a self-degradable polymer gel, that is, the reaction solution gels at the target temporary plugging formation temperature to seal the cracks in the formation.

[0066] The fifth aspect of the present invention provides a self-degradable polymer gel prepared by the method described above.

[0067] According to the present invention, in a preferred embodiment, the self-degrading polymer gel has at least one of the structures shown in formulas (8) to (10):

[0068]

[0069]

[0070]

[0071] Wherein, R is at least one of H and C1-C2 alkyl groups; n is 1-10, m is 1-10; p is 50-70.

[0072] According to the present invention, preferably, the self-degradable polymer gel of the present invention has a sealing pressure of 10 MPa or higher, more preferably 20 MPa or higher, and has good pressure-bearing performance.

[0073] According to the present invention, the degradation time of the self-degrading polymer gel refers to the time from when the gel strength reaches level H until complete degradation. Before degradation, the strength of the gel remains basically stable.

[0074] According to the present invention, the self-degradable polymer gel is capable of automatic degradation, wherein the conditions for the self-degradable polymer gel to degrade (i.e., degradation performance) include: a temperature of 60-100°C and a degradation time of 5-13 days, preferably 5-10 days, more preferably 7-10 days, and even more preferably 7-8 days.

[0075] In this invention, it should be noted that the degradation time refers to the time when the gel is completely degraded, at which point the gel degrades into a low-viscosity solution.

[0076] According to the present invention, when the self-degrading polymer gel reaches its degradation time, the strength of the self-degrading polymer gel decreases until it loses its strength and becomes a low-viscosity liquid that is discharged back to the ground. That is, construction is carried out during the time when the self-degrading polymer gel has not degraded. After the construction is completed, the unstable crosslinking agent inside the self-degrading polymer gel undergoes hydrolysis, causing the gel to lose its strength, and the resulting degradation residue is discharged back to the ground.

[0077] The sixth aspect of the present invention provides an application of the aforementioned self-degradable polymer gel as a temporary plugging agent in oil and gas field reservoirs.

[0078] According to the present invention, the temperature of the reservoir section is 60-100°C.

[0079] The present invention preferably achieves controllable adjustment of the gelation time and degradation time of the self-degrading polymer gel by adjusting the amount of unstable crosslinking agent, without the need for subsequent injection of a breaker.

[0080] According to the present invention, the self-degradable polymer gel has a low viscosity in the reaction solution before gelation, which is beneficial for pumping. After injection into the formation fracture, the initiator ammonium persulfate decomposes at a certain temperature to release free radicals, which initiate the free radical polymerization reaction of the monomer acrylamide to form linear molecular chains. Since the unstable crosslinking agent contains double bonds, it can participate in the addition reaction of two polymer chains. The crosslinking agent connects the long-chain polymers, transforming the linear polymer molecular chains into a three-dimensional structure, thus enhancing the strength of the gel. After a period of time, under the combined action of temperature and water, the ester groups in the unstable crosslinking agent gradually hydrolyze, causing the crosslinking points inside the gel to break, the polymer network structure to be destroyed, the gel gradually loses its strength, and finally completely degrades into low molecular weight polymers, which are then returned to the ground.

[0081] As previously described, the self-degradable polymer gel provided by this invention gels under formation temperature (60-100℃, i.e., downhole temperature), becoming a solid-like substance with a three-dimensional network structure, and maintains its strength for a period of time (before degradation begins). Over time, the unstable cross-linking agent hydrolyzes, causing the cross-linking points inside the gel to break, the three-dimensional network structure to collapse, and the gel's bulk structure to disintegrate, ultimately degrading completely into a small molecule linear structure. This achieves the self-degradation of the temporary plugging gel, restoring formation permeability. This invention allows for control of the gel degradation time by changing the amount of cross-linking agent added, enabling regulation of gelation and degradation times within the 60-100℃ range (gelation time is 0.9-2.5h, preferably 1.0-2.0h, more preferably 1.0-1.5h; degradation time is 5-13d, preferably 7-10d, more preferably 7-8d). Different self-degradable polymer gel formulations can be selected according to different construction conditions and schedule requirements, demonstrating good adaptability. The self-degradable polymer gel of the present invention degrades on its own after maintaining high strength for a period of time, without the need for external chemical breaker to degrade the gel. This better meets the needs of construction in formations at 60-100℃, and solves the problems of complex composition and rapid gelation that are not conducive to pumping in existing anti-leakage and temporary plugging agent systems. It enables safe operation and causes little damage to the formation.

[0082] The present invention will be described in detail below through embodiments.

[0083] In the following examples and comparative examples:

[0084] Detection method:

[0085] 1. Methods for detecting gelation time and degradation time:

[0086] The Syndansk gel coding method (see Table 1) was used to quickly determine the gel formation and degradation times of the gel. During evaluation, the blue-capped bottle was inverted; the gel formation time was defined as when the gel strength reached grade H or higher; the degradation time was defined as when the gel strength decreased to grade B after gel formation.

[0087] Table 1

[0088]

[0089]

[0090] 2. Testing methods for the plugging performance of self-degradable polymer gels:

[0091] The pressure resistance of the self-degradable polymer gel was tested using an indoor physical model apparatus through a displacement experiment. First, a certain amount of reaction solution was prepared and injected into a sand-filled tube using a horizontal flow pump. Then, the sand-filled tube was placed in an oven to react and form a gel. The pressure resistance of the self-degradable gel was tested using a water-drive experiment, with pressure gauge readings monitored in real time. The maximum pressure gauge reading was selected as the sealing pressure of the self-degradable polymer gel.

[0092] Unless otherwise specified, the devices and raw materials used in the following embodiments are all commercially available products.

[0093] Preparation Example 1

[0094] Example 1 illustrates the crosslinking agent prepared according to the present invention.

[0095] Four-arm PEG and ε-caprolactone were added to a 25 mL three-necked flask at a molar ratio of 1:10, followed by the addition of a small amount of tin isooctanoate as a catalyst. The mixture was heated to 140 °C under a N2 atmosphere and reacted for 12 h. After the reaction was complete, the reaction product was added to ice-cold hexane to precipitate and remove unreacted monomers and catalyst.

[0096] The obtained product was dissolved in dichloromethane and dried by azeotropic distillation with toluene. After drying, the flask was placed in an ice-water bath, and equimolar amounts of acryloyl chloride and triethylamine were added. The reaction was carried out under a nitrogen atmosphere for 12 h. The solvent was removed by rotary evaporation, and then the product was dissolved in ethyl acetate to precipitate triethylamine hydrochloride. The product was then dried and precipitated twice in ice-cold diethyl ether to obtain the unstable crosslinking agent with the following structure:

[0097]

[0098] in addition, Figure 1 This is the infrared spectrum of the crosslinking agent prepared in Example 1 of this invention. Figure 1 It can be seen that: 3577cm -1 The absorption peak is for the stretching vibration of the OH bond, at 2871 cm⁻¹. -1 The absorption peak for the stretching vibration of methylene (CH) is 1722 cm⁻¹. -1 The absorption peak is the stretching vibration of C=O, at 1635 cm⁻¹. -1 The absorption peak is the C=C stretching vibration, at 1460 cm⁻¹. -1 The absorption peak for the deformation vibration of -CH2 is 1409 cm⁻¹. -1 The absorption peak is the stretching vibration of C=O, at 1103 cm⁻¹. -1 The absorption peak represents the stretching vibration of CO. The presence of characteristic peaks from carbon-carbon double bonds in the infrared spectrum confirms the successful preparation of the target crosslinking agent.

[0099] Preparation Example 2

[0100] Example 1 illustrates the crosslinking agent prepared according to the present invention.

[0101] The crosslinking agent was prepared using the same method as in Preparation Example 1, except that the "molar ratio of 4-arm-PEG and ε-caprolactone in Preparation Example 1 was changed to "molar ratio of 4-arm-PEG and lactide in Preparation Example 1 was 1:10", and the rest was the same as in Preparation Example 1.

[0102] The resulting crosslinking agent has the following structure:

[0103]

[0104] Preparation Example 3

[0105] Example 1 illustrates the crosslinking agent prepared according to the present invention.

[0106] The crosslinking agent was prepared in the same manner as in Preparation Example 1, except that the "molar ratio of 4-arm-PEG and ε-caprolactone in Preparation Example 1 was changed to "molar ratio of 4-arm-PEG and hexyl alcohol in Preparation Example 1 was 1:5".

[0107] And the "acryloyl chloride" in Preparation Example 1 was changed to "methacryloyl chloride";

[0108] The rest is the same as the preparation example.

[0109] The resulting crosslinking agent has the following structure:

[0110]

[0111] Examples 1-5

[0112] Examples 1-5 illustrate the self-degradable polymer gel prepared according to the present invention.

[0113] Add 5g of acrylamide, 0.01g of ammonium persulfate, and (0.3-0.5)g of the unstable crosslinking agent prepared in Preparation Example 1 to a 100mL reagent bottle in sequence. Then add deionized water to prepare a 50g mixed solution. Place the reagent bottle in a 90℃ water bath and react for a period of time to obtain a self-degrading polymer gel. In addition, record the degradation time of the gel. The experimental results are shown in Table 2.

[0114] Table 2

[0115]

[0116] Examples 6-10

[0117] Examples 6-10 illustrate the self-degradable polymer gel prepared according to the present invention.

[0118] Add (5-10)g acrylamide, 0.01g ammonium persulfate, and 0.4g of the unstable crosslinking agent prepared in Preparation Example 2 to a 100mL reagent bottle in sequence. Then add deionized water to prepare a 50g mixed solution. Place the reagent bottle in a 90℃ water bath and react for a period of time to obtain a self-degradable polymer gel. In addition, record the degradation time of the gel. The experimental results are shown in Table 3.

[0119] Table 3

[0120]

[0121] Examples 11-15

[0122] Examples 11-14 illustrate the self-degradable polymer gel prepared according to the present invention.

[0123] Add 5g of acrylamide, (0.01-0.04)g of ammonium persulfate, and 0.4g of the unstable crosslinking agent prepared in Preparation Example 3 to a 100mL reagent bottle in sequence. Then add deionized water to prepare a 50g mixed solution. Place the reagent bottle in a 90℃ water bath and react for a period of time to obtain a self-degradable polymer gel. In addition, record the degradation time of the gel. The experimental results are shown in Table 4.

[0124] Table 4

[0125]

[0126] The experimental results above show that the amounts of monomer, initiator, and unstable crosslinking agent all affect the gelation and degradation times of the gel; the greater the amount of each, the shorter the overall gelation time. The residual liquid after complete degradation of the self-degradable polymer gel has low viscosity, which facilitates drainage from fissures and reduces formation contamination. The gelation and degradation times of the self-degradable gel can be controlled by changing the amounts of monomer, initiator, and crosslinking agent.

[0127] Comparative Example 1

[0128] The self-degrading polymer gel was prepared using the same method as in Example 1, except that 1g of the unstable crosslinking agent prepared in Example 1 was used. The result was a self-degrading polymer gel with a degradation time of 17 days (17d), which was too long.

[0129] Comparative Example 2

[0130] The self-degrading polymer gel was prepared using the same method as in Example 1, except that 0.1 g of the unstable crosslinking agent prepared in Example 1 was used. As a result, the self-degrading polymer gel was degraded in 2 days, which was too short.

[0131] Comparative Example 3

[0132] The self-degradable polymer gel was prepared using the same method as in Example 1, except that "the unstable crosslinking agent prepared in Example 1" was changed to "0.3 g N,N-methylenebisacrylamide". As a result, the gel could not self-degrade within 20 days.

[0133] Test Example 1

[0134] According to the formula: 10% monomer + 0.02% initiator + 0.8% unstable crosslinking agent + balance deionized water, wherein the unstable crosslinking agent is the crosslinking agent prepared in Examples 1-15 and Comparative Examples 1-3. The reaction solution was prepared and injected into sand-filled tubes with different permeabilities for testing. After injecting 2PV of the reaction solution into the sand-filled tube, both ends of the sand-filled tube were sealed with plastic wrap and placed in a 90℃ oven to solidify. Then, the sealing performance of the self-degrading gel was tested using water-driven methods, and pressure changes were monitored and recorded in real time. The results of the sealing performance of the self-degrading polymer gel on sand-filled tubes with different permeabilities are shown in Table 5.

[0135] Table 5

[0136]

[0137] Test Example 2

[0138] According to the formula: 10% monomer + 0.02% initiator + 0.8% unstable crosslinking agent + balance deionized water, wherein the unstable crosslinking agent is the crosslinking agent prepared in Examples 1-15 and Comparative Examples 1-3. The reaction solution was prepared and injected into sand-filled tubes with different permeabilities for testing. After injecting 2PV of the reaction solution into the sand-filled tube, both ends of the sand-filled tube were sealed with plastic wrap and placed in a 90℃ oven for gelation and aging. The permeability of the sand-filled tube was measured before gel injection and half a month later, and the core damage rate was calculated. The results of the core damage experiment are shown in Table 6.

[0139] Table 6

[0140]

[0141] In industry standards, a core damage rate of less than 5% is defined as no impact on the reservoir. The results above show that the self-degrading gels all achieve self-degradation after gelation in the sand-packed tubes, and the core damage rate after complete degradation is almost always less than 5%. Comparative Example 1, due to an excessive amount of unstable crosslinking agent, resulted in a longer degradation time; within half a month, the core damage rate was higher than that of the Example. Comparative Example 3, due to the stable crosslinking agent, did not undergo self-degradation, and its core damage rate was significantly higher than that of the Example.

[0142] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A crosslinking agent, characterized in that, The crosslinking agent includes one or more of the structures shown in formulas (1) to (3): In formulas (1) to (3), R is at least one of H and C1-C2 alkyl groups; n is 1-10, and m is 1-10.

2. The crosslinking agent according to claim 1, wherein, In equations (1) to (3), R is H and / or CH3, n is 4-6, and m is 4-6.

3. A method for preparing the crosslinking agent according to claim 1 or 2, characterized in that, The preparation method includes: (1) In the presence of a catalyst and a N2 atmosphere, the 4-arm PEG and one or more esters of the structures shown in formulas (4) to (6) are brought into contact for a first reaction. (2) The product after step (1), acryloyl chloride as shown in formula (7) and triethylamine are brought together for a second reaction to obtain a crosslinking agent; In equation (7), R is one or more of H, CH3 and CH2CH3.

4. The preparation method according to claim 3, wherein, The preparation method further includes: separating and purifying the product after the first reaction and / or the product after the second reaction.

5. The preparation method according to claim 3, wherein, The molar ratio of 4-arm-PEG and the ester shown in formula (2) is 1:(5-10), preferably 1:(8-10); And / or, the conditions for the first reaction include: a temperature of 120-150°C and a time of 10-18 hours; And / or, the conditions for the second reaction include: a temperature of 20-30°C and a time of 6-24 hours.

6. A self-degradable polymer gel composition, characterized in that, The composition comprises a monomer, an initiator, a crosslinking agent, and water, wherein the crosslinking agent is the crosslinking agent according to claim 1 or 2.

7. The composition according to claim 6, wherein, Based on the total weight of the composition, the monomer content is 10-20% by weight, the initiator content is 0.01-0.04% by weight, the crosslinking agent content is 0.6-1% by weight, and the balance is water; Preferably, based on the total weight of the composition, the content of the monomer is 10-15% by weight, the content of the initiator is 0.02-0.03% by weight, the content of the crosslinking agent is 0.8-1% by weight, and the balance is water.

8. The composition according to claim 6 or 7, wherein, The monomer is acrylamide; And / or, the initiator is ammonium persulfate.

9. A method for preparing a self-degradable polymer gel using the composition according to any one of claims 6-8, characterized in that, The method includes: mixing monomers, crosslinking agents, initiators and water to obtain a self-degradable polymer gel base liquid, and then gelling it to obtain a self-degradable polymer gel; wherein the crosslinking agent is the crosslinking agent according to claim 1 or 2.

10. The method according to claim 9, wherein, The conditions for gel formation include: a temperature of 60-100℃; and a time of 0.9-2.5h, preferably 1-2h, and more preferably 1-1.5h.

11. A self-degradable polymer gel prepared by the method of claim 9 or 10.

12. The self-degrading polymer gel according to claim 11, wherein, The self-degradable polymer gel has at least one of the structures shown in formula (8) to formula (10); Wherein, R is at least one of H and C1-C2 alkyl groups; n is 1-10, m is 1-10; p is 50-70.

13. The self-degrading polymer gel according to claim 12, wherein, The self-degrading conditions of the self-degrading polymer gel include: a degradation temperature of 60-100℃; and a degradation time of 5-13 days, preferably 5-10 days, more preferably 7-10 days, and even more preferably 7-8 days.

14. The application of the self-degradable polymer gel according to any one of claims 11-13 as a leak-proof temporary plugging agent in oil and gas field reservoirs.

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