Controllable temporary plugging gel forming solution based on microencapsulation gel breaking and preparation method thereof

Abstract

The invention discloses a controllable temporary plugging gel forming solution based on microencapsulation gel breaking, which is composed of the following components in percentage by mass: 8.0%-10% of acrylamide monomer, 0.2%-0.25% of cross-linking agent, 0.01%-0.1% of initiator, 0.1%-0.3% of reinforcing material, 3%-5% of microencapsulation gel breaker, 0.1%-0.3% of rheology modifier and the balance of water, the total content of the raw materials is 100%, the gel forming solution realizes self-gel breaking through the microencapsulation gel breaker, and the self-gel-breaking effect is good. Temporary plugging and unplugging are integrated, and secondary damage to the stratum is reduced; the invention also discloses a preparation method of the gel forming solution, which comprises the following steps: step 1, weighing the raw materials; step 2, dissolving the acrylamide monomer, the cross-linking agent and the initiator in water, and stirring to form a mixture aqueous solution A; step 3, adding a microencapsulated gel breaker and a reinforcing material into the aqueous solution A, and stirring to obtain a suspension dispersion liquid B; and step 4, adding a rheology modifier into the dispersion liquid B, stirring and standing. The method is simple in preparation process and convenient to operate.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of oil and gas development, and relates to a controllable temporary plugging gel based on microencapsulated gel breaking. BACKGROUND

[0002] In the temporary plugging workover operation of oil and gas wells, the polymer gel type temporary plugging agent has become a key technical product widely used in this field due to its excellent injectability and plugging performance, and has important significance for guaranteeing the efficiency of workover operation and improving the development effect of reservoirs.

[0003] However, the existing polymer gel type temporary plugging technology still has significant defects in actual application, which seriously restricts its application effect and economy. Firstly, the gel breaking reliability of the existing temporary plugging system is insufficient. Most of the existing temporary plugging systems cannot achieve reliable self-gel breaking, and the gel breaking process needs to rely on subsequent injection of gel breaking fluid or backflow operation, which not only increases the operation links and operation cost, but also easily causes incomplete gel breaking due to uneven distribution of gel breaking agent in the formation and insufficient gel reaction, etc., resulting in plugging of the remaining gel in the reservoir, reducing the reservoir permeability, and forming irreversible reservoir damage. Secondly, the gelation time is difficult to accurately control. The gelation behavior of the existing temporary plugging system seriously depends on the environmental temperature. In the low-temperature formation condition, the gelation reaction rate is slow, which will greatly prolong the operation waiting cycle, affecting the overall efficiency of the workover operation. In the high-temperature formation environment, the gelation reaction will proceed too quickly, which easily leads to premature gelation of the temporary plugging agent in the pumping process, causing pipeline blockage and other pumping risks, and lacking the ability to accurately control the gelation time that can adapt to different temperature formations and be widely used. SUMMARY

[0004] The purpose of the present application is to provide a controllable temporary plugging gel based on microencapsulated gel breaking, which solves the problem of self-gel breaking of the existing temporary plugging system in the prior art.

[0005] Another purpose of the present application is to provide a preparation method of the controllable temporary plugging gel based on microencapsulated gel breaking.

[0006] The first technical solution adopted by the present application is a controllable temporary plugging gel based on microencapsulated gel breaking, which is composed of the following raw material components in mass percentage: 8.0wt%-10wt% of acrylamide monomer, 0.2wt%-0.25wt% of crosslinking agent, 0.01wt%-0.1wt% of initiator, 0.1wt%-0.3wt% of reinforcing material, 3wt%-5wt% of microencapsulated gel breaking agent, 0.1wt%-0.3wt% of rheological modifier, and the balance being water. The total of the contents of the above raw materials should be 100%. The first technical solution of the present application is further characterized in that: The crosslinking agent is any one or a combination of multiple of N,N'-methylenebisacrylamide, hexamethylene diisocyanate, trimethylolpropane triacrylate, and N-hydroxymethyl acrylamide.

[0007] The initiator is any one or a combination of multiple of ammonium persulfate, potassium persulfate, 2,2'-azobis hydrochloride, and 2,2'azobis ethyl butyronitrile.

[0008] The microencapsulated breaker-coated inner core is any one or a combination of multiple of ammonium persulfate, potassium persulfate, sodium persulfate, citric acid, and di-tert-butyl peroxide.

[0009] The reinforcing material is any one or a combination of multiple of nanosilica, nanoclay, nanocellulose, graphene, and carbon black.

[0010] The rheology modifier is any one or a combination of multiple of polyacrylamide, sodium polyacrylate, hydrophobically modified guar gum, and xanthan gum.

[0011] Another technical solution adopted by the present application is a preparation method of the microencapsulated breaker-based controllable temporary plugging gel, which is specifically implemented according to the following steps: Step 1: The following raw materials are weighed according to the mass percentage respectively: 8.0wt%-10wt% of acrylamide monomer, 0.2wt%-0.25wt% of crosslinking agent, 0.01wt%-0.1wt% of initiator, 0.1wt%-0.3wt% of reinforcing material, 3wt%-5wt% of microencapsulated breaker, and 0.1wt%-0.3wt% of rheology modifier, and the balance is water, the total of the content of the above raw materials should be 100%; Step 2: The acrylamide monomer, crosslinking agent, and initiator weighed in step 1 are dissolved in water, stirred, and a reaction mixture aqueous solution A is formed; Step 3: The microencapsulated breaker and reinforcing material are added to the reaction mixture aqueous solution A of step 2, ultrasonic dispersion is performed, and then high-speed homogenization is performed to uniformly disperse the carbon black particles, so that a stable suspension dispersion liquid B is obtained; Step 4: The rheology modifier is slowly added to the suspension dispersion liquid B of step 3, stirred, and after standing and defoaming, a microencapsulated breaker-based controllable temporary plugging gel is obtained.

[0012] The technical solution of the present application has the following characteristics: The specific process in step 2 is as follows: The acrylamide monomer, crosslinking agent, and initiator weighed in step 1 are dissolved in water, a magnetic stirrer is used to continuously stir at a speed of 200-300 rpm until all components are completely dissolved, and a uniform and transparent reaction mixture aqueous solution A is formed.

[0013] The specific process in step 3 is as follows: To the aqueous solution A of the reaction mixture of step 2, microencapsulated breaker and reinforcing material are added, first treated with an ultrasonic disperser at a power of 150-200 W for 10-20 minutes, and then transferred into a high-speed homogenizer for homogenization at 3000-5000 rpm for at least 2 minutes, so that the carbon black particles are uniformly dispersed, to obtain a stable suspension dispersion B.

[0014] The specific process in step 4 is as follows: In the floating dispersion B of step 3, the rheological modifier is slowly added, initially stirred at a low speed of 50-100 rpm to avoid splashing, gradually increased to 400-500 rpm and continuously stirred for 20-30 minutes, so that the system presents a uniform viscous state, and after standing for 10-15 minutes to remove bubbles, a controllable temporary plugging gel liquid based on microencapsulated breaker is obtained.

[0015] The beneficial effects of the present application are: The controllable temporary plugging gel liquid based on microencapsulated breaker of the present application can control the gelation time of the system and thus the polymerization rate by adding an initiator and adjusting the amount of the initiator, thereby solving the problem of delayed gelation under medium and low temperature conditions and inhibiting the problem of too fast reaction under high temperature environment; at the same time, the microencapsulated breaker realizes gradual release of the core material through hydration degradation of the coating layer, avoids premature diffusion of the breaker, ensures that the breaker timing matches the workover operation period, realizes self-breaking, integrates temporary plugging and unplugging, and effectively reduces secondary damage to the formation.

[0016] The preparation method of the controllable temporary plugging gel liquid based on microencapsulated breaker of the present application is simple in preparation process and convenient to operate. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 is the injection pressure change with injection time graph of the controllable temporary plugging gel liquid based on microencapsulated breaker prepared in Example 4 of the present application forming a temporary plugging gel system to block artificial core fractures after plugging; Figure 2 is the injection pressure change with injection time graph of the controllable temporary plugging gel liquid prepared in Example 5 of the present application based on microencapsulated breaker forming a temporary plugging gel system to block artificial core fractures after plugging; Figure 3 is the injection pressure change with injection time graph of the controllable temporary plugging gel liquid prepared in Example 6 of the present application based on microencapsulated breaker forming a temporary plugging gel plug to block artificial core fractures after plugging; Figure 4 is the static breaking process graph of the temporary plugging gel system of the controllable temporary plugging gel liquid prepared in Example 6 of the present application based on microencapsulated breaker at 50°C. DETAILED DESCRIPTION

[0018] The present application will be described in detail below in conjunction with the drawings and specific embodiments.

[0019] The first technical solution provided by the present application is a controllable temporary plugging gelatinizing fluid based on microencapsulated gel breaking, which is composed of the following raw material components in percentage by mass: 8.0wt%-10wt% of acrylamide monomer, which forms a polymer through polymerization.

[0020] 0.2wt%-0.25wt% of crosslinking agent, which crosslinks with the polymer to form a three-dimensional network structure, has strong structural strength, and enhances the mechanical strength of the gel by bridging the particles, thereby ensuring the stability of the temporary plugging layer in complex environments.

[0021] 0.01wt%-0.1wt% of initiator, which can control the gelatinizing time of the system and the polymerization rate, thereby solving the problem of delayed gelatinizing under low temperature conditions and inhibiting the problem of too fast reaction under high temperature conditions.

[0022] 0.1wt%-0.3wt% of reinforcing material, which enhances the strength of the system after gelatinizing through the accumulation and bridging of the particles in the crack.

[0023] 3wt%-5wt% of microencapsulated gel breaker, which realizes controllable release of the gel breaking process through its coating structure. The coating layer of the microencapsulated gel breaker will undergo a gradual hydration degradation process in the aqueous environment. With the passage of time, the integrity of the coating layer is gradually destroyed, eventually leading to the rupture of the microcapsule structure and the release of the core material with gel breaking function. The released gel breaker then diffuses in the gel system and plays its chemical gel breaking role, effectively decomposing the gel network structure. The gradual release of the core material is achieved through the hydration degradation of the coating layer, avoiding the premature diffusion of the gel breaker, ensuring that the gel breaking time matches the workover operation period, and realizing self-gel breaking, temporary plugging and unblocking integration, and effectively reducing the secondary damage to the formation.

[0024] 0.1wt%-0.3wt% of rheological modifier, and the balance is water. The total of the contents of the above raw materials should be 100%. The introduction of the rheological modifier into the gel system can significantly improve the suspension stability and carrying capacity of the microencapsulated gel breaker. Effective control of the viscosity of the system not only effectively increases the load of the gel breaker microcapsule, but also prevents the microencapsulated gel breaker from settling or separating due to density difference, ensuring uniform suspension of the solid phase components and maintaining the stability of the temporary plugging gel during long-term storage and construction.

[0025] The second technical solution provided by the present application is a preparation method of the controllable temporary plugging gelatinizing fluid based on microencapsulated gel breaking, which is implemented according to the following steps: Step 1, the following raw materials are weighed according to the percentage by mass: Acrylamide monomer 8.0wt%-10wt%, crosslinking agent 0.2wt%-0.25wt%, initiator 0.01wt%-0.1wt%, reinforcing material 0.1wt%-0.3wt%, microencapsulated breaker 3wt%-5wt%, rheological modifier 0.1wt%-0.3wt%, and the balance being water, the total of the contents of the various raw materials being 100%; Step 2, the acrylamide monomer, crosslinking agent and initiator weighed in step 1 were dissolved in water, stirred to form a reaction mixture aqueous solution A, the specific process is as follows: The acrylamide monomer, crosslinking agent and initiator weighed in step 1 were dissolved in water, and a magnetic stirrer was used to continuously stir at a speed of 200-300 rpm until all the components were completely dissolved, forming a uniform and transparent reaction mixture aqueous solution A.

[0026] Step 3, microencapsulated breaker and reinforcing material were added to the reaction mixture aqueous solution A of step 2, and after ultrasonic dispersion, high-speed homogenization was carried out to make the carbon black particles uniformly dispersed, obtaining a stable suspension dispersion liquid B, the specific process is as follows: The microencapsulated breaker and reinforcing material were added to the reaction mixture aqueous solution A of step 2, first treated with an ultrasonic dispersing instrument at a power of 150-200W for 10-20 minutes, and then transferred into a high-speed homogenizer to homogenize at a speed of 3000-5000rpm for at least 2 minutes, so that the carbon black particles were uniformly dispersed, obtaining a stable suspension dispersion liquid B.

[0027] Step 4, rheological modifier was slowly added to the suspension dispersion liquid B of step 3, stirred, and after standing and defoaming, a controllable temporary plugging gel based on microencapsulated breaker was obtained, the specific process is as follows: The rheological modifier was slowly added to the suspension dispersion liquid B of step 3, initially stirred at a low speed of 50-100rpm to avoid splashing, and then gradually increased to 400-500rpm and continuously stirred for 20-30 minutes, so that the system showed a uniform and viscous state, and after standing and defoaming for 10-15 minutes, a controllable temporary plugging gel based on microencapsulated breaker was obtained.

[0028] The preparation method of the controllable temporary plugging gel based on microencapsulated breaker has simple preparation process, convenient operation, can meet the needs of mass production, is conducive to realizing large-scale production, and can be widely applied to temporary plugging operation scenes in oil and gas fields and other fields.

[0029] The controllable temporary plugging gel based on microencapsulated breaker has the following specific embodiments: Example 1 The controllable temporary plugging gel based on microencapsulated breaker is composed of the following raw material components in mass percentage: Acrylamide monomer 8wt%, N,N'-methylene bisacrylamide 0.25wt%, potassium persulfate 0.1wt%, carbon black 0.3wt%, ammonium persulfate microencapsulated breaker 5wt%, sodium polyacrylate 0.2wt%, the balance is water, the total of the content of each raw material should be 100%.

[0030] Example 2 The controllable temporary plugging gelatinizing fluid based on microencapsulated breaker is composed of the following raw material components in mass percentage: Acrylamide monomer 8wt%, hexamethylene diisocyanate 0.2wt%, 2,2'-azobis hydrochloride 0.01wt%, nanocellulose 0.2wt%, potassium persulfate microencapsulated breaker 5wt%, acrylamide 0.1wt%, the balance is water, the total of the content of each raw material should be 100%.

[0031] Example 3 The controllable temporary plugging gelatinizing fluid based on microencapsulated breaker is composed of the following raw material components in mass percentage: Acrylamide monomer 10wt%, N-hydroxymethyl acrylamide 0.2wt%, 2,2'-azobis hydrochloride 0.1wt%, nanoclay 0.3wt%, di-t-butyl peroxide microencapsulated breaker 3wt%, polyacrylamide 0.2wt%, the balance is water, the total of the content of each raw material should be 100%.

[0032] The preparation method of the controllable temporary plugging gelatinizing fluid based on microencapsulated breaker, the specific implementation is as follows: Example 4 The preparation method of the controllable temporary plugging gelatinizing fluid based on microencapsulated breaker is specifically implemented according to the following steps: Step 1, the mass percentage of each raw material in this embodiment is weighed according to the mass percentage of each raw material in Example 1: Step 2, 8.0wt% acrylamide monomer, 0.25wt% N,N'-methylene bisacrylamide and 0.1wt% potassium persulfate are sequentially added to the liquid water, a magnetic stirrer is used for continuous stirring at a speed of 300rpm until all components are completely dissolved, forming a uniform transparent reaction mixture aqueous solution A.

[0033] Step 3, 5.0wt% ammonium persulfate microencapsulated breaker and 0.3wt% carbon black are added to solution A, first treated by ultrasonic disperser at a power of 200W for 10 minutes, then transferred into a high-speed homogenizer for homogenization at a speed of 5000rpm for 3 minutes, to ensure uniform dispersion of particles, obtaining a stable suspension dispersion liquid B.

[0034] Step 4, 0.2wt% sodium polyacrylate was slowly added into the suspension dispersion B, stirring at low speed of 100rpm initially to avoid splashing, gradually increasing to 500rpm and continuing stirring for 30 minutes, making the system present a uniform viscous state, and obtaining a controllable temporary plugging gel based on microencapsulated breaker after standing for 15 minutes to remove bubbles.

[0035] Gelation time verification: Experimental process: 15mL of controllable temporary plugging gel based on microencapsulated breaker prepared in Example 4 was injected into a 25mL standard ampoule, which was flame sealed and then placed in a 50°C oven for gelation. Every 10 minutes, the gel was slowly tilted to 45° to observe the flowability, and the end point of gelation was recorded when the gel completely lost the ability to flow.

[0036] Experimental results: The gelation time in this preparation example was 1 hour.

[0037] Stability verification: Experimental process: After the gelation time verification was completed, the above ampoule was transferred to a 50°C environment for curing, and the first dehydration shrinkage time node was recorded every 12 hours by tilting observation.

[0038] Experimental results: This preparation example showed that the gel remained stable for 7 days (168 hours), and then began to break and hydrate.

[0039] Dehydration verification Experimental process: The sample after stability verification was placed back in a 50°C environment for continued curing. Every 8 hours, the ampoule was taken out and slowly tilted or inverted to observe the dehydration of the frozen gel, and the time when the frozen gel completely dehydrated was recorded.

[0040] Experimental results: In this preparation example, it took 15 days (360 hours) from the start of the breaker to complete hydration.

[0041] Example 5 The preparation method of controllable temporary plugging gel based on microencapsulated breaker is implemented according to the following steps: Step 1, the mass percentage of each raw material in this example was weighed according to the mass percentage of each raw material in Example 2; Step 2, 8.0wt% acrylamide monomer, 0.20wt% hexamethylene diisocyanate and 0.01wt% 2,2-azobisisobutyronitrile were added into the liquid preparation water in sequence, and a magnetic stirrer was used to continuously stir at a speed of 300rpm until all components were completely dissolved, forming a uniform transparent reaction mixture aqueous solution A.

[0042] Step 3, 5.0wt% potassium persulfate microencapsulated breaker and 0.2wt% nanocellulose were added into solution A, first treated by ultrasonic disperser at 180W for 15 minutes, then transferred into high-speed homogenizer and homogenized at 3000rpm for 2 minutes to ensure uniform dispersion of particles, obtaining stable suspension dispersion B.

[0043] Step 4, 0.1wt% polyacrylamide was slowly added into suspension dispersion B, initially stirred at low speed of 50rpm to avoid splashing, gradually increased to 450rpm and continuously stirred for 25 minutes, so that the system showed uniform viscous state, and after standing for 13 minutes to remove bubbles, a controllable temporary plugging gel solution based on microencapsulated breaker was obtained.

[0044] Gelation time verification: Experimental process: 15mL of gelation solution was injected into a 25mL standard ampoule, which was flame sealed and placed in a 80℃ constant temperature water bath for condensation, every 10 minutes, the flowability was observed by slowly tilting to 45°, until the gel completely lost the ability to flow, which was recorded as the gelation end point.

[0045] Experimental results: the gelation time in this preparation example was 1 hour.

[0046] Stability verification: Experimental process: after the gelation time verification was completed, the gelated ampoule was continued to be cured at 80℃, and every 12 hours, the tilting observation was carried out, and the time node of the first dehydration shrinkage was recorded.

[0047] Experimental results: this preparation example showed that the gel remained stable within 6 days (144 hours), and then began to break and hydrate.

[0048] Dehydration verification: Experimental process: the sample after stability verification was placed back in a 50℃ environment for continued curing, every 8 hours, the ampoule was taken out and slowly tilted or inverted, the dehydrated gel was observed, and the time of complete dehydration of the gel was observed and recorded.

[0049] Experimental results: the experiment proved that this preparation example completely broke and hydrated after 11 days of initial dehydration.

[0050] Example 6 The preparation method of the controllable temporary plugging gel solution based on microencapsulated breaker is specifically implemented according to the following steps: Step 1, the mass percentage of each raw material in this example was weighed according to the mass percentage of each raw material in example 3; Step 2, add 10.0wt% acrylamide monomer, 0.20wt% N-methylol acrylamide and 0.010wt% 2,2'-azobis(2-methylpropionamidine) dihydrochloride into the prepared water in sequence, continuously stir with a magnetic stirrer at a speed of 300 rpm until all components are completely dissolved, forming a uniform transparent reaction mixture aqueous solution A.

[0051] Step 3, add 3.0wt% di-t-butyl peroxide microencapsulated breaker and 0.3wt% nanoclay to solution A, first use an ultrasonic disperser to treat at a power of 150W for 10 minutes, then transfer to a high-speed homogenizer and homogenize at 5000 rpm for 2 minutes to ensure uniform dispersion of particles, obtaining a stable suspension dispersion B.

[0052] Step 4, slowly add 0.2wt% polyacrylamide to the suspension dispersion B, initially stir at a low speed of 100 rpm to avoid splashing, gradually increase to 400 rpm and continue stirring for 20 minutes, so that the system presents a uniform viscous state, and after standing for 10 minutes to remove bubbles, a controllable temporary plugging gel liquid based on microencapsulated breaker is obtained.

[0053] Gelation time verification: Experimental process: take 15mL of the gelation liquid into a 25mL standard ampoule, flame seal and then place in a 120℃ constant temperature oven for condensation, every 0.5 hour take out and slowly tilt to 45° to observe the flowability, until the gel completely loses the ability to flow, record as the gelation end point.

[0054] Experimental results: the gelation time in this preparation example is 2 hours.

[0055] Stability verification: Experimental process: continue to maintain the ampoule after gelation at 100℃ environment, every 12 hours perform tilting observation, and record the time node of the first appearance of dehydration shrinkage.

[0056] Experimental results: this preparation example shows that the gel remains stable within 3 days (72 hours), and then begins to break and hydrate.

[0057] Dehydration verification Experimental process: put the sample after stability verification back into a 50℃ environment for continued maintenance, every 8 hours take out the ampoule and slowly tilt or invert, observe the dehydration of the frozen gel, and record the time of complete dehydration of the frozen gel.

[0058] Experimental results: in this preparation example, it takes 7 days (168 hours) from the start of the breaker to complete hydration.

[0059] Comparative Example 1 The comparative example is compared with example 4, the difference is that the ammonium sulfate microencapsulated breaker with low concentration is used in the preparation process of the temporary blocking gel solution of the comparative example, and the specific preparation process is as follows: In the liquid preparation water, 8.0wt% acrylamide monomer, 0.25wt% N,N'-methylene bisacrylamide and 0.10wt% potassium persulfate were added in turn, and a magnetic stirrer was used for continuous stirring at a speed of 300rpm until all components were completely dissolved, forming a uniform transparent reaction mixture aqueous solution A.

[0060] 2.0wt% ammonium persulfate microencapsulated breaker and 0.3wt% carbon black were added to solution A, first treated with an ultrasonic disperser at a power of 200W for 10 minutes, and then transferred into a high-speed homogenizer for homogenization at 5000rpm for 2 minutes to ensure uniform dispersion of carbon black particles, obtaining a stable suspension dispersion B.

[0061] In the suspension dispersion B, 0.2wt% sodium polyacrylate was slowly added, initially stirred at a low speed of 100rpm to avoid splashing, gradually increased to 500rpm and continuously stirred for 30 minutes, so that the system showed a uniform viscous state, and the temporary blocking gel solution was obtained after standing and defoaming for 15 minutes.

[0062] Gelation time verification: Experimental process: 15mL of gel solution was injected into a 25mL standard ampoule, which was flame sealed and placed in a 50℃ constant temperature water bath for condensation, and every 0.5 hour, the flowability was observed by slowly tilting to 45°, and the gelation endpoint was recorded when the gel completely lost the ability to flow.

[0063] Experimental results: the gelation time in this preparation example is 1 hour.

[0064] Stability verification: Experimental process: the ampoule after gelation was continuously maintained at 50℃, and every 12 hours, the tilting observation was carried out, and the time node of the first dehydration shrinkage was recorded.

[0065] Experimental results: this preparation example shows that the gel has excellent stability, and maintains the complete structure for 20 days (480 hours), and then begins to appear gel breaking and hydration.

[0066] Dehydration verification Experimental process: the sample after stability verification was put back into the 50℃ environment for continuous maintenance, and every 8 hours, the ampoule was taken out and slowly tilted or inverted, and the dehydration of the gel was observed, and the time of complete dehydration of the gel was observed and recorded.

[0067] Experimental results: in this preparation example, the gel has not been completely hydrated for 30 days (720 hours) after the start of dehydration, and finally about 50% of the solid residue cannot be completely broken.

[0068] In comparison with Example 4, Comparative Example 1 does not follow the formulation defined in the present application, and uses a low concentration of microencapsulated breaker. Ultimately, about 50% of the solid phase residue cannot be completely broken.

[0069] Comparative Example 2 This comparative example is compared with Example 4, the difference being that a high concentration of initiator potassium persulfate is used in the preparation process of the temporary plugging gel solution of this comparative example. The specific preparation process is as follows: 8.0wt% acrylamide monomer, 0.25wt% N,N'-methylenebisacrylamide and 0.20wt% potassium persulfate were sequentially added to the liquid preparation water, and a magnetic stirrer was used for continuous stirring at a speed of 300 rpm until all components were completely dissolved, forming a uniform transparent reaction mixture aqueous solution A.

[0070] 5.0wt% ammonium persulfate microencapsulated breaker and 0.3wt% carbon black were added to solution A, first treated with an ultrasonic disperser at a power of 200W for 10 minutes, and then transferred to a high-speed homogenizer for homogenization at 5000rpm for 2 minutes to ensure uniform dispersion of carbon black particles, obtaining a stable suspension dispersion liquid B.

[0071] 0.2wt% sodium polyacrylate was slowly added to the suspension dispersion liquid B, initially stirred at a low speed of 100rpm to avoid splashing, gradually increased to 500rpm and continuously stirred for 30 minutes, so that the system showed a uniform viscous state. After standing for 15 minutes to remove bubbles, a temporary plugging gel system gel solution was obtained.

[0072] 15mL of the gel solution was injected into a 25mL standard ampoule, which was flame sealed and placed in an 80°C constant temperature oven for gelation. Every 0.5 hours, the ampoule was taken out and slowly tilted to 45° to observe the flowability, and the gelation endpoint was recorded when the gel completely lost the ability to flow. In this preparation example, the gelation time was 0.5 hours.

[0073] The gelled ampoule was continued to be cured at 80°C, and the tilting observation was performed every 12 hours to record the time node of the first appearance of dehydration shrinkage. This preparation example showed that the frozen gel remained stable within 5 days (120 hours), and then began to break and hydrate.

[0074] The sample was transferred to a 50°C environment for continued curing, and the dehydration was observed every 8 hours until the frozen gel completely liquefied. In this preparation example, it took 10 days (240 hours) from the start of breaking to complete hydration.

[0075] In comparison with Example 4, Comparative Example 2 does not follow the formulation defined in the present application, and the use of a high concentration of initiator leads to an accelerated thermal decomposition rate, resulting in a faster speed of monomer polymerization to form linear acrylamide, causing an imbalance between the local gelation speed and the breaking speed, which is manifested as an excessively fast gelation speed and breaking speed, which cannot meet the engineering needs of oil field temporary plugging and well repair operations.

[0076] Pressure-bearing performance test experiment 1: On the basis of the microencapsulated gel-breaking-based controllable temporary plugging gel prepared in Example 4, the performance test experiment provides the test results of the plugging capacity of the temporary plugging gel system, and the specific experimental operation is as follows: An artificial core fracture is selected, with a fracture height of 10 mm, a fracture width of 5 mm, a fracture length of 50 mm, roughness in the fracture and quartz sand support, and a permeability scale of 1 mD; The microencapsulated gel-breaking-based controllable temporary plugging gel prepared according to the preparation process of Example 4 is injected into the artificial core fracture, and the gelation is stabilized in a 50°C constant temperature oven; After gelation, super-pure water is injected into the fracture, and the state of the temporary plugging gel in the fracture under different pressures is tested step by step; Until the injection pressure gradient appears a sharp drop, it is proved that the super-pure water breaks through the plugging of the temporary plugging gel plug, and the experiment is ended.

[0077] The experiment proves that, as shown in Figure 1 , the injection pressure of the temporary plugging gel system formed by using the microencapsulated gel-breaking-based controllable temporary plugging gel prepared in Example 1 to plug the artificial core fracture changes with the injection time. As can be seen from the graph, the plugging layer formed by the temporary plugging gel system of Example 4 in the core fracture can withstand a breakthrough pressure gradient of 18-19 MPa / m, meeting the needs of field application. Figure 1 Pressure-bearing performance test experiment 2:

[0078] On the basis of the microencapsulated gel-breaking-based controllable temporary plugging gel prepared in Example 5, the performance test experiment provides the test results of the plugging capacity of the temporary plugging gel system, and the specific experimental operation is as follows: An artificial core fracture is selected, with a fracture height of 10 mm, a fracture width of 5 mm, a fracture length of 50 mm, roughness in the fracture and quartz sand support, and a permeability scale of 1 mD; The microencapsulated gel-breaking-based controllable temporary plugging gel prepared according to the preparation process of Example 5 is injected into the artificial core fracture, and the gelation is stabilized in an 80°C constant temperature oven; After gelation, super-pure water is injected into the fracture, and the state of the temporary plugging gel in the fracture under different pressures is tested step by step; Until the injection pressure gradient appears a sharp drop, it is proved that the super-pure water breaks through the plugging of the temporary plugging gel plug, and the experiment is ended. The experiment proves that, as shown in

[0079] , the injection pressure of the temporary plugging gel system formed by using the microencapsulated gel-breaking-based controllable temporary plugging gel prepared in Example 5 to plug the artificial core fracture changes with the injection time. As can be seen from the graph, the plugging layer formed by the temporary plugging gel system of Example 5 in the core fracture can withstand a breakthrough pressure gradient of 18-19 MPa / m, meeting the needs of field application. Figure 2 Figure 2 ​This figure shows the change in injection pressure over time after the artificial core fractures were sealed using the controllable temporary plugging gel system based on microencapsulated gelation prepared in Example 5. The figure demonstrates that the sealing layer formed by the temporary plugging gel system in Example 2 within the core fractures can withstand a breakthrough pressure gradient of 17-18 MPa / m, meeting the requirements for field applications.

[0080] Pressure bearing performance test experiment 3: Based on the controllable temporary plugging gel prepared in Example 6 using microencapsulation disintegration technology, this performance testing experiment provides the plugging ability test results of the temporary plugging gel system. The specific experimental operation is as follows: Artificial rock cores were selected for fracture creation, with a fracture height of 10mm, a fracture width of 5mm, and a fracture length of 50mm. The fracture interior was rough and supported by quartz sand, with a permeability scale of 1mD. The temporary plugging gel system was prepared according to the preparation process of Example 6. The gel was injected into the artificial rock core crack and placed in a 100°C constant temperature oven to stabilize the gel. After gelation, ultrapure water was injected into the cracks, and the state of the temporary plugging gel system in the cracks was tested under different pressures. The experiment ended when the injection pressure gradient dropped sharply, proving that the ultrapure water had broken through the seal of the temporary plug.

[0081] Experiments have shown that: specifically as follows Figure 3 As shown, Figure 3 This is a graph showing the change in injection pressure over time after the controllable temporary plugging gel prepared in Example 6, based on microencapsulated gel breaking, forms a temporary plugging gel plug to seal artificial core fractures. The graph shows that the plugging gel system of Example 3 can withstand a breakthrough pressure gradient of 17-18 MPa / m in the core fracture, meeting the needs of field applications.

[0082] Debonding performance test experiment: This embodiment provides the test results of the gel-breaking ability of the temporary plugging gel. For example... Figure 4 As shown, Figure 4 This figure illustrates the static dissolution of the controllable temporary plugging gel based on microencapsulation dissolution, prepared according to Example 6, within an ampoule at 50°C. The figure shows that the temporary plugging gel system gradually begins to dissolve and hydrate after a 7-day stabilization period, indicating that the system possesses good self-degradation capabilities and meets the requirements for temporary plugging.

Claims

1. A controllable temporary plugging gel based on microencapsulated gel breaker, characterized in that, According to the mass percentage by the following raw material components: The acrylamide monomer is 8.0wt%-10wt%, the crosslinking agent is 0.2wt%-0.25wt%, the initiator is 0.01wt%-0.1wt%, the reinforcing material is 0.1wt%-0.3wt%, the microencapsulated breaker is 3wt%-5wt%, the rheological modifier is 0.1wt%-0.3wt%, and the balance is water, and the total of the above raw material contents should be 100%.

2. The microencapsulated breaker-based controllable temporary plugging gel liquid according to claim 1, characterized in that, The crosslinking agent is any one or more combinations of N, N'-methylene bisacrylamide, hexamethylene diisocyanate, trimethylolpropane triacrylate, and N-hydroxymethyl acrylamide.

3. The controllable temporary plugging gel based on microencapsulated gel breaker according to claim 1, characterized in that, The initiator is any one or more combinations of ammonium persulfate, potassium persulfate, 2,2'-azobis hydrochloride, and 2,2'azobis ethyl butyronitrile.

4. The microencapsulated breaker-based controllable temporary plugging gel liquid according to claim 1, characterized in that, The core of the microencapsulated breaker is any one or more combinations of ammonium persulfate, potassium persulfate, sodium persulfate, citric acid, and di-tert-butyl peroxide.

5. The microencapsulated breaker-based controllable temporary plugging gel liquid according to claim 1, characterized in that, The reinforcing material is any one or more combinations of nano-silicon dioxide, nano-clay, nano-cellulose, graphene, and carbon black.

6. The microencapsulated breaker-based controllable temporary plugging gel liquid according to claim 1, characterized in that, The rheological modifier is any one or more combinations of polyacrylamide, sodium polyacrylate, hydrophobically modified guan gum, and xanthan gum.

7. A method for preparing a controllable temporary plugging gel based on microencapsulated gel breaker, characterized in that, The specific implementation is as follows: Step 1, the following raw materials are weighed according to the mass percentage: The acrylamide monomer is 8.0wt%-10wt%, the crosslinking agent is 0.2wt%-0.25wt%, the initiator is 0.01wt%-0.1wt%, the reinforcing material is 0.1wt%-0.3wt%, the microencapsulated breaker is 3wt%-5wt%, the rheological modifier is 0.1wt%-0.3wt%, and the balance is water, and the total of the above raw material contents should be 100%; Step 2, the acrylamide monomer, crosslinking agent, and initiator weighed in step 1 are dissolved in water, stirred, and a reaction mixture aqueous solution A is formed; Step 3, the microencapsulated breaker and reinforcing material are added to the reaction mixture aqueous solution A of step 2, ultrasonic dispersion is performed, and then high-speed homogenization is performed to uniformly disperse the carbon black particles, and a stable suspension dispersion liquid B is obtained; Step 4, the rheological modifier is slowly added to the suspension dispersion liquid B of step 3, stirred, and after standing and defoaming, a controllable temporary plugging gel liquid based on microencapsulated breaker is obtained.

8. The preparation method of the controllable temporary plugging gel liquid based on microencapsulated gel breaking according to claim 7, characterized in that, The specific process in step 2 is as follows: The acrylamide monomer, crosslinking agent, and initiator weighed in step 1 are dissolved in water, a magnetic stirrer is used to continuously stir at a speed of 200-300 rpm until all components are completely dissolved, and a uniform and transparent reaction mixture aqueous solution A is formed.

9. The preparation method of the controllable temporary plugging gel liquid based on microencapsulated gel breaking according to claim 7, characterized in that, The specific process in step 3 is as follows: The microencapsulated breaker and reinforcing material are added to the reaction mixture aqueous solution A of step 2, first treated with an ultrasonic dispersing instrument at a power of 150-200 W for 10-20 minutes, and then transferred to a high-speed homogenizer for homogenization at a speed of 3000-5000 rpm for at least 2 minutes to uniformly disperse the carbon black particles, and a stable suspension dispersion liquid B is obtained.

10. The preparation method of the controllable temporary plugging gel liquid based on microencapsulated gel breaking according to claim 7, characterized in that, The specific process in step 4 is as follows: Slowly add rheology modifier into the step 3 floating dispersion B, initially stir at low speed 50-100 rpm to avoid splashing, gradually increase to 400-500 rpm and continue stirring for 20-30 minutes, so that the system presents a uniform viscous state, and after standing for 10-15 minutes to remove bubbles, a controllable temporary plugging gel based on microencapsulated broken gel is obtained.

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