High-temperature-resistant degradable temporary plugging agent and fracturing fluid synergistic system and application method

Abstract

The invention provides a high-temperature-resistant degradable temporary plugging agent and fracturing fluid synergistic system and an application method thereof, and the synergistic system maintains a weak acid environment in a construction stage, protects the core strength of the temporary plugging agent to be slowly attenuated, and ensures stable pressure bearing of a plugging layer; in the flow-back stage, a coating layer of the temporary plugging agent is rapidly damaged by injecting a strong acid activating solution, the specific surface area of the temporary plugging agent is rapidly increased, and rapid hydrolysis of an inner core polymer chain is commonly catalyzed by cooperating with high temperature, so that rapid and thorough degradation of the temporary plugging agent is realized. By means of the design, the temporary plugging agent perfectly balances the contradiction between tough plugging in the construction period and rapid plugging removal after construction is completed, the application window of the temporary plugging fracturing technology in a complex high-temperature reservoir is greatly widened, the reservoir damage risk caused by temporary plugging agent residues is effectively reduced, and the fracturing transformation efficiency and the oil and gas well flowback rate are improved.

Description

Technical Field

[0001] This invention relates to the field of oil and gas well temporary plugging and fracturing exploration and development technology, and in particular to a high-temperature resistant, biodegradable temporary plugging agent and fracturing fluid synergistic system and its application method. Background Technology

[0002] With the continued growth of global energy demand, the exploration and development of unconventional oil and gas resources has increasingly become a focus of attention. Horizontal well staged fracturing technology, as a key means of unlocking the production capacity of such reservoirs, hinges on its ability to effectively create complex fracture networks within the reservoir. Temporary plugging and diversion fracturing technology, by temporarily plugging already opened fractures, forces fracturing fluid to redirect to new, less-expanded segments or regions, thereby significantly increasing the reservoir stimulation volume (SRV). In this technology, the performance of the plugging agent is crucial; it must withstand high temperatures and pressures during the operation phase and effectively seal the fractures, while also rapidly and completely degrading after operation to ensure unobstructed flowback pathways and minimize secondary damage to the producing formation.

[0003] Currently, the temporary plugging agents used in the field mainly include wax balls, rubber balls, non-degradable plastic balls, alloy balls, and biodegradable polymer balls. Although wax balls can melt at certain temperatures, their low mechanical strength makes them prone to puncture in high-fracture-pressure formations, leading to plugging failure. Rubber and non-degradable plastic balls have inherent defects of not being degradable, easily clogging boreholes, making subsequent treatment difficult, and posing a high risk of damage to the producing formation. Although magnesium-aluminum alloy balls have high strength, their degradation is heavily dependent on the salinity (chloride ion concentration) of the formation fluids, limiting their applicability. Furthermore, the metal hydroxide precipitates produced after degradation can easily clog reservoir pore throats, causing permanent damage.

[0004] In recent years, biodegradable polymers such as polylactic acid (PLA) and polyglycolic acid (PGA) have provided new solutions for temporary plugging agents. However, these materials still face severe challenges when applied to high-temperature deep well fracturing. First, their glass transition temperature and heat distortion temperature are relatively low. Under high-temperature environments (typically >120℃), they rapidly undergo chain segment relaxation and changes in crystallinity, leading to a significant decrease in rigidity (strength) and toughness, making it difficult to form and maintain an effective temporary plugging layer. Second, the degradation behavior of these polymers is a temperature-driven hydrolysis process, with its rate strongly correlated with formation temperature. In lower-temperature zones, degradation is too slow, affecting flowback efficiency; while in high-temperature zones, degradation may be too rapid, leading to premature plugging failure and a narrow operational safety window. Furthermore, existing temporary plugging agents are usually treated as independent functional units, with their performance design being separate from the fracturing fluid system itself, lacking systematic synergy, and unable to achieve proactive and precise control over the critical process of "when the temporary plugging agent is strong and when it is weak."

[0005] Therefore, there is an urgent need in this field to overcome the technical bottlenecks of existing biodegradable temporary plugging agent materials, which are difficult to balance strength, toughness, and thermal stability under high temperature conditions, and whose degradation behavior is passively dependent on formation temperature and therefore uncontrollable. The goal is to develop a new type of temporary plugging agent system that can intelligently respond to construction needs and work synergistically with the fracturing fluid working fluid system, so as to realize the reliable and efficient application of temporary plugging and fracturing technology in high-difficulty and high-temperature reservoirs. Summary of the Invention

[0006] The purpose of this invention is to provide a synergistic system and application method of high-temperature resistant biodegradable temporary plugging agent and fracturing fluid, so as to solve the problems existing in the prior art.

[0007] To achieve the above objectives, the present invention provides the following solution:

[0008] This invention provides a synergistic system of a high-temperature resistant, biodegradable temporary plugging agent and fracturing fluid, comprising a pH-responsive temporary plugging agent and an acidic fracturing fluid;

[0009] The pH-responsive temporary plugging agent has a core-shell structure and includes:

[0010] The core is made by melt blending and granulation of a composition including polyethylene glycol, carbon dioxide copolymer, polybutylene adipate / terephthalate, starch, plasticizer, compatibilizer, lubricant, heat stabilizer and nucleating agent;

[0011] A coating layer is wrapped around the core, and the coating layer material is a blend of polylactic acid or polycaprolactone and a pH-sensitive material.

[0012] The acidic fracturing fluid includes a base fluid, a thickener, a crosslinking agent, a breaker, and a pH adjuster. The pH adjuster is an organic acid used to initially adjust and maintain the pH of the fracturing fluid within a weakly acidic range of 4.0-6.0.

[0013] Preferably, the pH-sensitive material is chitosan or sodium alginate; in the coating material, the weight ratio of polylactic acid or polycaprolactone to the pH-sensitive material is (80-90):(20-10).

[0014] Preferably, the core composition comprises, by weight, 70-80 parts of polyethylene glycol, 20-30 parts of carbon dioxide copolymer, 5-15 parts of poly(butylene adipate / terephthalate), 10-20 parts of starch, 2-6 parts of plasticizer, 5-10 parts of compatibilizer, 1-10 parts of lubricant, 1-3 parts of heat stabilizer, and 0.5-4 parts of nucleating agent.

[0015] Preferably, the starch is corn starch; the plasticizer is selected from one or more of phthalate, sebacic acid ester, epoxidized soybean oil, and epoxidized methyl linoleate; the compatibilizer is selected from one or more of polycarbonate, polysiloxane, silicone resin, ethylene-vinyl acetate copolymer, and ethylene-propylene-diene monomer copolymer; the nucleating agent is selected from one or more of sodium dibenzyl sorbitan succinate, sodium glutarate, and sodium hexanoate; the lubricant is selected from one of stearamide, butyl stearate, and glyceryl trihydroxy stearate; and the heat stabilizer is a mixture of lead stearate and epoxidized fatty acid ester.

[0016] Preferably, in the acidic fracturing fluid, the thickener is a cross-linkable polysaccharide stable under acidic conditions, and the dosage is 0.3% to 0.6%; the cross-linking agent is an organometallic cross-linking agent stable under acidic conditions, and the dosage is 0.3% to 0.8%; the pH adjuster is citric acid, lactic acid, or sulfamic acid, and the dosage is 0.5% to 1.5%; the breaker is encapsulated ammonium persulfate or an acidic enzyme breaker, and the dosage is 50-200 ppm.

[0017] This invention also provides a method for applying a synergistic system of a high-temperature resistant, biodegradable temporary plugging agent and fracturing fluid, comprising the following steps:

[0018] S1. Pump in pre-fluid to open formation fractures;

[0019] S2. Prepare the acidic fracturing fluid and add the pH-responsive temporary plugging agent at a volume ratio of 5%-15% to it, then pump it into the wellbore to perform temporary plugging and diversion operations on the target section;

[0020] S3. Continue pumping subsequent acidic fracturing fluid and proppant to fracture the new target segment;

[0021] S4. Displace the fluid in the wellbore into the formation fractures using displacement fluid;

[0022] S5. Shut down the well and wait for the fracturing fluid to break up;

[0023] S6. Pump in the acidic activating solution;

[0024] S7. Open the well for backflow.

[0025] Preferably, in step S2, the particle size of the pH-responsive temporary plugging agent is 2-10 mm.

[0026] Preferably, in step S5, the well shut-in time is 2-4 hours.

[0027] Preferably, in step S6, the acidic activating solution is a hydrochloric acid or organic acid solution with a pH value lower than 3.5, and the amount used is determined according to the wellbore volume and the near-wellbore zone range.

[0028] This invention also provides a method for preparing a pH-responsive temporary plugging agent in a synergistic system of a high-temperature resistant, biodegradable temporary plugging agent and fracturing fluid, comprising:

[0029] Weigh each raw material for the kernel according to the formula, and then dry, mix, melt extrude and granulate to obtain kernel particles;

[0030] The pH-responsive temporary plugging agent is obtained by spraying a solution of the coating material onto the surface of the core particles in a fluidized state using fluidized bed coating technology and drying it.

[0031] The present invention achieves the following beneficial technical effects compared to the prior art:

[0032] This invention provides a synergistic system and application method of a high-temperature resistant, biodegradable temporary plugging agent and fracturing fluid, ingeniously achieving spatiotemporal separation and precise control of the plugging strength and degradation behavior of the temporary plugging agent. In this system, the temporary plugging agent's core ensures its initial mechanical strength and toughness under high-temperature conditions, while an outer pH-responsive coating layer enables intelligent control of the degradation initiation. The specially formulated acidic fracturing fluid system not only provides a stable delivery and plugging environment for the temporary plugging agent, but its built-in acidic environment also prepares for subsequent activation and degradation. This synergistic system maintains a weakly acidic environment during the construction phase, protecting the core strength of the temporary plugging agent from slow decay and ensuring stable pressure resistance of the plugging layer. During the flowback phase, the injection of a strongly acidic activating fluid rapidly destroys the coating layer of the temporary plugging agent, dramatically increasing its specific surface area, and synergistically catalyzes the rapid hydrolysis of the core polymer chains with high temperature, thereby achieving rapid and complete degradation of the temporary plugging agent. This design allows the temporary plugging agent to perfectly balance the contradiction between "strong and tough sealing during construction" and "rapid unblocking after construction," greatly expanding the application window of temporary plugging fracturing technology in complex high-temperature reservoirs, effectively reducing the risk of reservoir damage caused by residual temporary plugging agent, and improving fracturing stimulation efficiency and oil and gas well flowback rate. Detailed Implementation

[0033] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0034] The purpose of this invention is to provide a synergistic system and application method of high-temperature resistant biodegradable temporary plugging agent and fracturing fluid, so as to solve the problems existing in the prior art.

[0035] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to specific embodiments.

[0036] Example 1:

[0037] This embodiment provides a synergistic system of a high-temperature resistant, biodegradable temporary plugging agent and fracturing fluid, wherein:

[0038] The core composition is as follows: 75 parts polyglycolic acid (PGA); 25 parts polycarbonate copolymer (PPC); 10 parts polybutylene adipate / terephthalate (PBAT); 15 parts corn starch; 3 parts plasticizer (epoxidized soybean oil); 5 parts compatibilizer (ethylene-vinyl acetate copolymer, EVA); 4 parts lubricant (stearamide); 1.5 parts heat stabilizer (aluminum stearate:epoxidized fatty acid ester = 1:2); and 2 parts nucleating agent (sodium dibenzyl sorbitan succinate). PGA, PPC, and PBAT are dried at 115℃ for 4 hours. The dried polymer, starch, and nucleating agent are added to a high-speed mixer and mixed for 5 minutes. The compatibilizer, plasticizer, heat stabilizer, and lubricant are added sequentially, and mixing continues for 10 minutes to obtain a premix. The premix is ​​then melt-extruded and granulated in a twin-screw extruder. The screw temperatures are set as follows: Zone 1 160℃, Zone 2 170℃, Zone 3 175℃, Zone 4 175℃, and die head 170℃. The screw speed is 200 rpm. After water cooling and air drying, the extruded strip is pelletized to obtain core particles with a diameter of approximately 3 mm.

[0039] The coating layer is a blend of polylactic acid (PLA) and chitosan at a weight ratio of 85:15. The coating material is dissolved in acetic acid solution and sprayed onto the surface of the core particles in a fluidized state using a fluidized bed coating device. After drying, a pH-responsive temporary plugging agent with a core-shell structure is obtained, with a coating layer thickness of approximately 50 μm.

[0040] The acidic fracturing fluid is as follows: base fluid: water; thickener: hydroxypropyl guar gum (0.4%); crosslinking agent: organozirconium crosslinking agent (0.5%); pH adjuster: citric acid (1.0%); breaker: encapsulated ammonium persulfate (100ppm). The thickener is slowly added to the water and stirred for 30 minutes to fully hydrate it. Then, the pH adjuster, crosslinking agent and breaker are added in sequence and stirred evenly to obtain an acidic fracturing fluid with a pH of 5.0.

[0041] The application method is as follows:

[0042] Injecting pre-fluid (linear adhesive) into the crack opens the crack;

[0043] A pH-responsive temporary plugging agent was added to the acidic fracturing fluid at a volume concentration of 10% and pumped into the wellbore for temporary plugging and diversion.

[0044] Continue pumping proppant-containing acidic fracturing fluid to fracturing the new section;

[0045] Displacement fluid pushes fluid from inside the wellbore into the fractures;

[0046] Close the well for 3 hours and wait for the gel to break;

[0047] Pump in hydrochloric acid activation solution with pH=3.0 (the volume should be 1.2 times the wellbore volume);

[0048] Well opening and backflow.

[0049] Example 2:

[0050] This embodiment provides a synergistic system of a high-temperature resistant, biodegradable temporary plugging agent and fracturing fluid, wherein:

[0051] The core components are: 80 parts polyglycolic acid; 20 parts carbon dioxide copolymer; 15 parts PBAT; 20 parts corn starch; 4 parts plasticizer (epoxyacetyl linoleate methyl ester); 6 parts compatibilizer (organosilicon resin); 5 parts lubricant (glyceryl trihydroxy stearate); 2 parts heat stabilizer (aluminum stearate:epoxy fatty acid ester = 1:2); and 2.5 parts nucleating agent (sodium glutarate).

[0052] The coating layer is a blend of polycaprolactone (PCL) and sodium alginate in a weight ratio of 80:20; the coating layer thickness is approximately 60 μm.

[0053] The remaining preparation steps are the same as in Example 1.

[0054] The acidic fracturing fluid consists of: thickener: carboxymethyl cellulose (0.5%); crosslinking agent: organoboron crosslinking agent (0.6%); pH adjuster: lactic acid (1.2%); breaker: acidic enzyme breaker (150 ppm); pH adjusted to 4.5.

[0055] The application method is as follows:

[0056] The temporary plugging agent concentration was 8%, the well shut-in time was 4 hours, the activation solution was a citric acid solution with pH=2.8, and the rest was the same as in Example 1.

[0057] Example 3:

[0058] This embodiment provides a synergistic system of a high-temperature resistant, biodegradable temporary plugging agent and fracturing fluid, wherein:

[0059] The core components are: 70 parts polyglycolic acid; 30 parts carbon dioxide copolymer; 5 parts PBAT; 10 parts corn starch; 2 parts plasticizer (phthalate); 4 parts compatibilizer (polycarbonate); 2 parts lubricant (butyl stearate); 1 part heat stabilizer (aluminum stearate: epoxy fatty acid ester = 1:2); and 1 part nucleating agent (sodium hexanoate).

[0060] The coating layer is a blend of polylactic acid and chitosan in a weight ratio of 90:10; the coating layer thickness is approximately 40 μm.

[0061] The remaining preparation steps are the same as in Example 1.

[0062] The acidic fracturing fluid consists of: thickener: xanthan gum (0.3%); crosslinking agent: organotitanium crosslinking agent (0.4%); pH adjuster: aminosulfonic acid (0.8%); breaker: encapsulated ammonium persulfate (80 ppm); pH adjusted to 5.5.

[0063] The application method is as follows:

[0064] The temporary plugging agent concentration was 12%, the well shut-in time was 2.5 hours, the activation solution was a hydrochloric acid solution with pH=3.2, and the rest was the same as in Example 1.

[0065] The carbon dioxide copolymers used in the above embodiments and comparative examples are the carbon dioxide copolymers described in "Sequence structure control of carbon dioxide copolymers and the relationship between structure and properties (Science Bulletin, Liang Jiaxin et al., 2021-03-01)". Their specific components and preparation methods are well known to those skilled in the art, so they will not be described again in this application.

[0066] The performance of the pH-responsive temporary plugging agents prepared in Examples 1-3 and their synergistic system with acidic fracturing fluid was tested, and the results are shown in the table below:

[0067] project Example 1 Example 2 Example 3 Compressive strength at 150℃ (MPa) 68.5 70.2 66.8 Initial degradation time (h) >100 >110 >95 Complete degradation after activation (d) 5 6 4 Return rate (%) 92 90 94

[0068] Test results show that the pH-responsive temporary plugging agent provided by this invention has good mechanical strength and plugging performance at high temperatures, can degrade rapidly after activation, has a high flowback rate, and is suitable for temporary plugging and fracturing operations in high-temperature deep wells.

[0069] This invention has illustrated its principles and implementation methods using specific examples. The descriptions of these embodiments are merely illustrative of the method and its core ideas; furthermore, those skilled in the art will recognize that modifications may be made to the specific implementation methods and application scope based on the principles of this invention. Therefore, the content of this specification should not be construed as limiting the invention.

Claims

1. A synergistic system of high-temperature resistant biodegradable temporary plugging agent and fracturing fluid, characterized in that, Including pH-responsive temporary plugging agents and acidic fracturing fluids; The pH-responsive temporary plugging agent has a core-shell structure and includes: The core is made by melt blending and granulation of a composition including polyethylene glycol, carbon dioxide copolymer, polybutylene adipate / terephthalate, starch, plasticizer, compatibilizer, lubricant, heat stabilizer and nucleating agent; A coating layer is wrapped around the core, and the coating layer material is a blend of polylactic acid or polycaprolactone and a pH-sensitive material. The acidic fracturing fluid includes a base fluid, a thickener, a crosslinking agent, a breaker, and a pH adjuster. The pH adjuster is an organic acid used to initially adjust and maintain the pH of the fracturing fluid within a weakly acidic range of 4.0-6.

0.

2. The high-temperature resistant biodegradable temporary plugging agent and fracturing fluid synergistic system according to claim 1, characterized in that, The pH-sensitive material is chitosan or sodium alginate; in the coating material, the weight ratio of polylactic acid or polycaprolactone to the pH-sensitive material is (80-90):(20-10).

3. The synergistic system of high-temperature resistant biodegradable temporary plugging agent and fracturing fluid according to claim 1, characterized in that, The core composition comprises, by weight, 70-80 parts of polyethylene glycol, 20-30 parts of carbon dioxide copolymer, 5-15 parts of poly(butylene adipate / terephthalate), 10-20 parts of starch, 2-6 parts of plasticizer, 5-10 parts of compatibilizer, 1-10 parts of lubricant, 1-3 parts of heat stabilizer, and 0.5-4 parts of nucleating agent.

4. The synergistic system of high-temperature resistant biodegradable temporary plugging agent and fracturing fluid according to claim 3, characterized in that, The starch is corn starch; the plasticizer is selected from one or more of phthalate, sebacic acid ester, epoxidized soybean oil, and epoxidized acetylated linoleic acid methyl ester; the compatibilizer is selected from one or more of polycarbonate, polysiloxane, silicone resin, ethylene-vinyl acetate copolymer, and ethylene-propylene-diene monomer copolymer; the nucleating agent is selected from one or more of sodium dibenzyl sorbitan succinate, sodium glutarate, and sodium hexanoate; the lubricant is selected from one of stearamide, butyl stearate, and glyceryl trihydroxy stearate; and the heat stabilizer is a mixture of lead stearate and epoxidized fatty acid ester.

5. The high-temperature resistant biodegradable temporary plugging agent and fracturing fluid synergistic system according to claim 1, characterized in that, In the acidic fracturing fluid, the thickener is a cross-linkable polysaccharide stable under acidic conditions, with a dosage of 0.3% to 0.6%; the cross-linking agent is an organometallic cross-linking agent stable under acidic conditions, with a dosage of 0.3% to 0.8%; the pH adjuster is citric acid, lactic acid, or sulfamic acid, with a dosage of 0.5% to 1.5%; and the breaker is encapsulated ammonium persulfate or an acidic enzyme breaker, with a dosage of 50-200 ppm.

6. The application method of the synergistic system of high-temperature resistant biodegradable temporary plugging agent and fracturing fluid according to any one of claims 1-5, characterized in that, Includes the following steps: S1. Pump in pre-fluid to open formation fractures; S2. Prepare the acidic fracturing fluid and add the pH-responsive temporary plugging agent at a volume ratio of 5%-15% to it, then pump it into the wellbore to perform temporary plugging and diversion operations on the target section; S3. Continue pumping subsequent acidic fracturing fluid and proppant to fracture the new target segment; S4. Displace the fluid in the wellbore into the formation fractures using displacement fluid; S5. Shut down the well and wait for the fracturing fluid to break up; S6. Pump in the acidic activating solution; S7. Open the well for backflow.

7. The application method of the high-temperature resistant biodegradable temporary plugging agent and fracturing fluid synergistic system according to claim 6, characterized in that, In step S2, the particle size of the pH-responsive temporary plugging agent is 2-10 mm.

8. The application method of the high-temperature resistant biodegradable temporary plugging agent and fracturing fluid synergistic system according to claim 6, characterized in that, In step S5, the well shut-in time is 2-4 hours.

9. The application method of the synergistic system of high-temperature resistant biodegradable temporary plugging agent and fracturing fluid according to claim 6, characterized in that, In step S6, the acidic activating solution is a hydrochloric acid or organic acid solution with a pH value below 3.5, and the amount used is determined according to the wellbore volume and the near-wellbore zone range.

10. The method for preparing a pH-responsive temporary plugging agent in a synergistic system of a high-temperature resistant biodegradable temporary plugging agent and fracturing fluid according to any one of claims 1-5, characterized in that, include: Weigh each raw material for the kernel according to the formula, and then dry, mix, melt extrude and granulate to obtain kernel particles; The pH-responsive temporary plugging agent is obtained by spraying a solution of the coating material onto the surface of the core particles in a fluidized state using fluidized bed coating technology and drying it.