Preparation and application method of a supramolecular fracturing fluid system with both percolation and oil displacement capabilities

Abstract

This invention relates to the field of oil and gas field fracturing technology, and discloses a supramolecular fracturing fluid system and application method with both percolation and oil displacement capabilities. Its components include 0.3%-0.8% by mass of a supramolecular hydrophobic associating polymer, 0.2%-0.5% of a nano-microcapsule oil displacement agent, 0.05%-0.1% of a pH adjuster, and 0.1%-0.3% of a co-solvent, with the balance being a base fluid. The supramolecular hydrophobic associating polymer forms a dynamic three-dimensional network through self-assembly of hydrophobic side chains. The nano-microcapsule oil displacement agent uses a biodegradable polymer as a wall material to embed surfactants, achieving controlled release triggered by the reservoir environment. This system requires no crosslinking agent, has low residue content to reduce reservoir damage, and combines low friction with strong proppant carrying capacity. The controlled release of the nano-microcapsule improves the utilization rate of the oil displacement agent, realizing integrated fracturing and percolation oil displacement, and is suitable for the fracturing needs of various low-permeability to tight reservoirs.

Description

Technical Field

[0001] This invention belongs to the field of oil and gas field fracturing technology, and in particular to a method for preparing and applying a supramolecular fracturing fluid system with both percolation and oil displacement capabilities. Background Technology

[0002] Low-permeability tight oil and gas reservoirs have become a core development area for increasing oil and gas reserves and production in my country. These reservoirs are generally characterized by low permeability, complex pore structure, and dispersed crude oil occurrence. They require fracturing to create an artificial fracture network for economical development. Fracturing fluid, as the core working medium in fracturing operations, determines the fracturing effect and ultimate recovery rate. Currently, the mainstream fracturing fluid systems used in the industry are mainly divided into two categories: guar gum fracturing fluid and slickwater fracturing fluid. Guar gum fracturing fluid relies on the cross-linking of natural guar gum polysaccharide molecules to form a high-viscosity system, possessing strong proppant carrying capacity and supporting the effective placement of large-diameter proppant within fractures. It is widely used in the fracturing of medium-to-high permeability reservoirs. Its advantages lie in its mature system, simple preparation process, and excellent temperature resistance, adapting to the needs of high-temperature reservoir stimulation above 120℃. Another mainstream system is polyacrylamide-based slickwater fracturing fluid, which achieves high-volume pumping through the drag reduction effect of modified polyacrylamide molecules. It can form a complex volumetric fracture network in the reservoir, and the system has a low residue content, causing less damage to the reservoir. It has now become the preferred technology for volumetric fracturing of tight oil and gas reservoirs.

[0003] Existing fracturing fluid systems still face significant technical bottlenecks in practical applications. Guar gum fracturing fluids require the addition of boron-based and zirconium-based crosslinking agents to form a high-viscosity structure. The crosslinking reaction is highly sensitive to conditions such as pH and temperature, and strict precision is required for on-site preparation. Furthermore, incomplete degradation of guar gum molecules easily generates a large amount of residue, clogging reservoir pore throats and fracture flow channels, resulting in reservoir damage rates generally exceeding 30%. At the same time, conventional guar gum fracturing fluids do not have the function of percolation oil displacement; after fracturing, oil displacement relies solely on natural energy, and the residual crude oil in the matrix pores is difficult to effectively utilize, resulting in limited improvement in single-well recovery. To achieve low-friction, high-volume pumping, slickwater fracturing fluids typically have a low viscosity, resulting in insufficient proppant carrying capacity, rapid ceramsite settling, and a high risk of sand blockage during operation. To improve adsorption-driven oil displacement, oil displacement agents are often directly mixed into the fracturing fluid. However, in these mixed systems, the oil displacement agent cannot be controlled-released, and a large amount is consumed prematurely with the filtrate during pumping, resulting in a low content of effective oil displacement agent entering the matrix pores and a minimal improvement in adsorption-driven oil displacement efficiency. Furthermore, both existing fracturing fluid systems suffer from limited functionality, failing to simultaneously achieve excellent proppant carrying capacity and efficient adsorption-driven oil displacement, thus hindering the integrated development of low-permeability, tight reservoirs requiring fracturing stimulation and enhanced oil recovery.

[0004] As the development of low-permeability tight oil and gas reservoirs continues to deepen, the industry's requirements for the comprehensive performance of fracturing fluids are constantly increasing. There is an urgent need to develop a new type of fracturing fluid system that does not require additional crosslinking agents, causes low reservoir damage, and has excellent sand-carrying capacity and efficient percolation oil displacement function. This system will solve the core problems of existing technologies, such as the difficulty in balancing sand-carrying performance and oil displacement performance, low utilization rate of oil displacement agents, and significant reservoir damage, and provide technical support for the efficient development of low-permeability tight oil and gas reservoirs. Summary of the Invention

[0005] To address the shortcomings of existing fracturing fluids, such as their inability to simultaneously achieve proppant carrying and oil displacement capabilities, significant reservoir damage, and low oil displacement agent utilization, this invention provides a method for preparing and applying a supramolecular fracturing fluid system that combines proppant displacement capabilities.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A method for preparing a supramolecular fracturing fluid system with both percolation and oil displacement capabilities includes the following steps: S1. Anionic acrylamide with a molecular weight of 12 million, 2-acrylamido-2-methylpropanesulfonic acid with a sulfonation degree of 90%, and perfluoroalkyl betaine monomer with 12 carbon atoms are added to a reaction vessel in a mass ratio of 65~75:15~20:10~15. Deionized water with a mineralization degree not exceeding 500 mg / L is added, and the mixture is stirred continuously at a rate of 300 r / min for 30~40 min until the monomers are completely dissolved, resulting in a monomer mixture with a total mass concentration of 20%~30%. The pH of the monomer mixture is slowly adjusted to a weakly alkaline range of 7.5~8.5 using a 20% sodium hydroxide solution. During the adjustment process, the stirring rate is kept not less than 200 r / min to avoid local pH being too high, which could lead to monomer hydrolysis side reactions. S2. High-purity nitrogen is continuously introduced into the adjusted monomer mixture for 20-30 minutes to remove oxygen. The nitrogen introduction rate is controlled at 1L / min to ensure that the residual oxygen in the reactor is below 0.1mg / L. Then, a composite initiation system composed of potassium persulfate-sodium bisulfite redox initiator and azobisisobutylamidine hydrochloride azo initiator is added. The total amount of the composite initiation system added is 0.05%-0.2% of the total monomer mass, and the mass ratio of redox initiator to azo initiator is 1:1-1:2. After stirring evenly, the reactor is sealed and the constant temperature water bath temperature is controlled at 10-30℃ for adiabatic polymerization reaction for 6-8 hours. No additional stirring is required during the reaction. The reaction process is maintained by the exothermic reaction of the system itself to obtain an amphoteric hydrophobic associative polymer thickener colloid with an apparent viscosity of 20000-30000mPa·s. S3. Cetyltrimethylammonium bromide, fatty alcohol polyoxyethylene ether with a degree of polymerization of 10, and nonionic fluorocarbon surfactant with a fluorocarbon chain length of 6 are added to a high-speed mixer in a mass ratio of 40~50:30~35:15~30. The mixture is heated to 60~70℃ to melt all components. The mixture is stirred at a rate of 300~500 r / min for 15~20 min to ensure that all components are fully miscible. The molten mixture is then fed into a twin-screw extruder and granulator. The extrusion temperature is controlled at 55℃ and the pelletizing speed is 100 r / min. After cooling, modified penetrant oil displacement agent solid particles with a particle size of 0.5~1 mm are obtained. The surface of these particles forms abundant hydrophobic association sites, which can interact with the polymer thickener molecular chain through non-covalent bonds. S4. The polymer thickener colloid obtained by polymerization is fed into a spiral shear granulator and cut into colloid particles with a particle size of 2-3 cm. The colloid particles are evenly spread on the conveyor belt of a mesh belt dryer. The hot air temperature is controlled at 60-80℃ and the drying time is 2-3 hours. After drying, the moisture content of the polymer thickener is less than 8%. Then, the dried colloid particles are fed into a grinder to be crushed. After grinding, they are passed through an 80-100 mesh standard sieve to obtain polymer thickener powder. The polymer thickener powder and modified permeation displacement agent particles are fed into a twin spiral mixer at a mass ratio of 80-90:10-20 and mixed at a rate of 150 r / min for 30 minutes to obtain a uniformly composed supramolecular fracturing fluid dry powder base material. S5. Add the supramolecular fracturing fluid dry powder base material to the preparation water at a ratio of 0.1% to 0.5% of the total mass. The preparation water can be oilfield produced water with a salinity not exceeding 20,000 mg / L. Stir at a rate of 200 to 300 r / min for 3 to 5 min at room temperature. The amide groups and sulfonic acid groups on the polymer thickener molecular chain and the hydrophobic groups on the surface of the modified permeation displacement agent particles self-assemble through hydrogen bonding and hydrophobic association to form a dynamic and reversible three-dimensional supramolecular network structure, resulting in a supramolecular fracturing fluid system with an adjustable apparent viscosity of 30 to 120 mPa·s at 25℃.

[0007] Furthermore, the 2-acrylamide-2-methylpropanesulfonic acid selected in step S1 needs to be pre-recrystallized and purified, with a purity of not less than 99.5% after purification. The effective content of the fluoroalkyl betaine monomer is not less than 98%. The deionized water used to prepare the monomer mixture needs to be sterilized by ultraviolet light to avoid the negative impact of microorganisms on the subsequent polymerization reaction. After adjusting the pH, it needs to stand for 10 minutes. The pH value of the mixture is measured at multiple points using a pH meter to ensure that the pH deviation at different locations does not exceed 0.2.

[0008] Furthermore, in step S2, the mass ratio of potassium persulfate to sodium bisulfite is 1:1.2. Before adding the initiator, the initiator needs to be prepared as a 1% aqueous solution and added to the reactor in three equal parts with a 2-minute interval between each addition. After the addition is completed, continue stirring for 5 minutes to ensure that the initiator is evenly dispersed in the system. During the polymerization reaction, the temperature change inside the reactor is monitored in real time. When the temperature rises to 45°C, the cooling water in the reactor jacket is turned on to control the maximum reaction temperature to not exceed 70°C and avoid degradation of the polymer molecular chain.

[0009] Furthermore, in step S3, the fatty alcohol polyoxyethylene ether selected has a hydroxyl value of 110~120 mgKOH / g, and the surface tension of the nonionic fluorocarbon surfactant is 18~20 mN / m. During the mixing process, nitrogen gas is introduced into the high-speed mixer for protection to prevent the surfactant from oxidizing and deteriorating at high temperatures. After granulation, the modified penetrant oil displacement agent particles need to be cooled to room temperature in a fluidized bed, with the air volume controlled at 1000 m³ / g during the cooling process. 3 / h, to prevent particles from sticking together.

[0010] Furthermore, in step S4, the grinding process adopts a graded grinding process. First, the granules are crushed to a particle size of less than 1 mm through coarse grinding, and then fine grinding is used to obtain powder of the target particle size. The sieving process uses a vibrating sieve with an amplitude of 2 mm and a sieving time of 5 min to ensure that there are no particles larger than 100 mesh in the powder after sieving. During the mixing process, samples are taken every 10 min to check the mixing uniformity so that the mixing deviation of the polymer thickener and the oil displacement agent does not exceed 2%.

[0011] Furthermore, in step S5, the liquid preparation process uses a jet mixing device. The dry powder base material is initially mixed with the liquid preparation water through a negative pressure suction device, and then enters the mixing tank for full dissolution. During the mixing process, the liquid flow rate is controlled at 2m / s to avoid the dry powder base material from clumping and producing "fish eyes". After dissolution, a six-speed rotational viscometer is used to detect the viscosity of the system. When the viscosity deviation exceeds 5%, the amount of dry powder base material added is appropriately adjusted so that the fracturing fluid performance meets the reservoir stimulation requirements.

[0012] Furthermore, its application to fracturing and stimulation of low-permeability, tight oil and gas reservoirs with porosity of 5%–15% includes the following steps: S1. Based on the porosity, permeability, formation temperature, and crude oil viscosity parameters of the target reservoir, adjust the addition ratio of supramolecular fracturing fluid dry powder base. For tight reservoirs with porosity below 10% and permeability below 0.1 mD, adjust the viscosity of the supramolecular fracturing fluid system to 30~50 mPa·s; for low-permeability reservoirs with porosity of 10%~15% and permeability of 0.1~1 mD, adjust the viscosity of the supramolecular fracturing fluid system to 50~120 mPa·s. After preparation, test the temperature and shear resistance of the fracturing fluid to ensure that the viscosity retention rate is not less than 70% after shearing at the reservoir temperature for 1 hour. S2. Add proppant to the prepared supramolecular fracturing fluid system. The proppant should be a high-strength ceramic proppant with a mesh size of 30-50 or 40-70 mesh and a bulk density of 1.5-1.7 g / cm³. 3 The volume ratio of the proppant is 10%~30%, and it is stirred at a rate of 200~300r / min for 2~3min. The settling velocity of the ceramsite is tested to be no higher than 0.01cm / min, which meets the requirement that the proppant does not settle during long-distance pumping. S3. Using fracturing pumping equipment, pre-flush fluid, proppant-carrying fluid, and displacement fluid are sequentially injected into the reservoir, with the pumping rate controlled at 4~8m³. 3 / min, the amount of pre-flush fluid is 20%~30% of the total fluid volume, used to create fractures in the reservoir and reduce formation filtration loss, the amount of proppant-carrying fluid is 50%~60% of the total fluid volume, which carries the proppant into the fracture to achieve effective placement, and the amount of displacement fluid is 10%~20% of the total fluid volume, which displaces the proppant-carrying fluid in the wellbore into the fracture to avoid sand blockage in the wellbore; S4. After the pumping operation is completed, the well is shut in and left to simmer for 2 to 7 days. During the simmering period, the supramolecular network structure slowly desorbs under the action of formation temperature and shear, and continuously releases the permeation displacement agent. The released permeation displacement agent is spontaneously permeated into the reservoir matrix pores through capillary force, reducing the interfacial tension between crude oil and rock surface, and peeling off the residual oil and gas attached to the pore wall. The permeation displacement efficiency is more than 1.5 times higher than that of conventional single displacement agent. S5. After the well is shut off, when reopening the well, gradually increase the flowback rate from low to high, controlling the initial flowback rate to not exceed 0.5m. 3 The flow rate is gradually increased after the sand content of the flowback fluid is lower than 0.1% per hour. The flowback operation is completed when the viscosity of the flowback fluid is lower than 5 mPa·s, and then the oil and gas production stage begins.

[0013] Furthermore, in step S1, for reservoirs with formation temperatures above 90°C, thiourea at a mass concentration of 0.05% can be added as an antioxidant stabilizer when preparing the fracturing fluid to improve the temperature resistance and degradation resistance of the polymer molecular chain. The prepared fracturing fluid must be pumped within 4 hours to avoid premature desorption of the supramolecular network structure, which would lead to a decline in performance.

[0014] Furthermore, in step S2, the proppant must be screened and dust removed before being added to ensure that the roundness and sphericity of the proppant are not less than 0.8 and the breakage rate is not higher than 5%. During the stirring process, the uniformity of the sand-carrying liquid is monitored in real time, and samples are taken every 5 minutes to test the proppant concentration deviation between the upper and lower liquid layers to ensure that the deviation does not exceed 5%.

[0015] Furthermore, in step S3, the wellhead pressure changes are monitored in real time during the pumping process. When the pressure fluctuation exceeds 5MPa, the pumping rate is adjusted appropriately to ensure that the fracture propagation morphology meets the design requirements. A drag-reducing agent with a mass concentration of 0.1% can be added to the pre-fluid to reduce pipeline friction during the pumping process and reduce construction energy consumption.

[0016] The present invention has the following beneficial effects: This invention constructs a dynamic three-dimensional network structure through the self-assembly of supramolecular hydrophobic associating polymers. It achieves high viscosity without the need for additional crosslinking agents such as boron-based or zirconium-based ones. Simultaneously, the polymer molecules are easily degraded by breaker agents, resulting in extremely low residue generation. This effectively solves the defects of existing guar gum fracturing fluids, such as demanding crosslinking conditions and high reservoir damage rates due to residue clogging of reservoir pore throats. The supramolecular system constructed in this invention possesses excellent viscoelasticity and dynamic reversibility. Under high shear conditions, the molecular network temporarily dissociates to achieve low friction, meeting the requirements of high-volume pumping. After entering the reservoir, the shear force decreases, and the molecular network quickly recovers to achieve high viscosity, stably carrying proppant and uniformly distributing it within the fracture. Furthermore, the nano-encapsulated oil displacement agent loaded within the system is slowly released after the fracturing fluid enters the reservoir pores, triggered by reservoir temperature and pH conditions, improving the effective utilization rate of the oil displacement agent. This effectively solves the defects of existing slickwater fracturing fluids, such as insufficient sand-carrying capacity and premature consumption of oil displacement agents leading to low percolation oil displacement efficiency. Without the need for separate configuration of proppant-carrying fluid and oil displacement plug, a single system can simultaneously achieve multiple functions such as fracture creation, proppant delivery, and matrix infiltration and oil displacement. This simplifies the on-site preparation process, reduces construction complexity, and effectively solves the shortcomings of existing fracturing fluid systems that are single-function and unable to simultaneously achieve proppant-carrying and oil displacement performance.

[0017] This invention is suitable for fracturing and stimulation needs in various low-permeability to tight sandstone and shale oil and gas reservoirs. It exhibits good tolerance to high-salinity formation water and reservoir temperatures up to 120°C. It can be directly adapted to existing continuous mixing processes in fracturing operations without requiring additional equipment investment. It can be applied in various operational scenarios, including conventional volumetric fracturing, repeated fracturing, and deep reservoir stimulation, demonstrating excellent industry promotion value. This invention improves fracturing and stimulation effects while simultaneously increasing the utilization rate of matrix crude oil, achieving integrated fracturing and enhanced oil recovery operations, thus facilitating the efficient development of low-permeability to tight oil and gas reservoirs. Attached Figure Description

[0018] Figure 1The present invention provides a flowchart of a method for preparing a supramolecular fracturing fluid system with both percolation and oil displacement capabilities; Figure 2 A flowchart illustrating the application of a supramolecular fracturing fluid system with both percolation and oil displacement capabilities; Figure 3 This is a bar chart comparing the core performance of different fracturing fluid systems proposed in this invention; Figure 4 This is a line graph showing the viscosity variation of fracturing fluid under different shear rates, as proposed in this invention. Figure 5 This is a radar image of the multi-dimensional performance of the fracturing fluid proposed in this invention. Detailed Implementation

[0019] The following will refer to the appendices in the embodiments of the present invention. Figure 1-5 The technical solutions in the embodiments of the present invention are clearly and completely described herein. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the 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.

[0020] Scenario Example 1: Volumetric Fracturing of Tight Sandstone Reservoirs Application Scenario Description: This scenario is applicable to horizontal well staged fracturing operations in tight sandstone reservoirs in the Ordos Basin. The reservoir depth is 3200m, the formation temperature is 95℃, the total formation water salinity is 65000mg / L, the porosity is 8.2%, the permeability is 0.18mD, the reservoir pore structure is complex, the throat radius is generally less than 1μm, the daily oil production of a single well after conventional fracturing fluid stimulation is less than 5t, and the production declines rapidly, with the utilization rate of matrix crude oil less than 20%.

[0021] Technical Adaptation Details: During construction, the supramolecular fracturing fluid system of this invention is used. The mass ratio of each component is set as follows: supramolecular hydrophobic associative polymer 0.5%, nano-microcapsule oil displacement agent 0.3%, pH adjuster 0.08%, and co-solvent 0.2%. The base fluid is formation produced water treated on-site. The apparent viscosity of the system is controlled at 120 mPa·s, and the frictional resistance is reduced by 45% compared to clean water. A 10m... 3 High-volume pump injection at / min, single-stage fracturing injection volume 1200m³ 3The proppant used is 40 / 70 mesh ceramsite, with the sand ratio gradually increased to 25%. Under high shear in the wellbore, the viscosity of the fracturing fluid temporarily decreases to 30 mPa·s, reducing pumping friction. After entering the formation fracture, the shear effect disappears, and the viscosity recovers to over 110 mPa·s within 30 seconds, stably carrying the proppant and spreading it evenly within the fracture. The nano-microcapsule oil displacement agent is filtered out with the fracturing fluid and enters the matrix pores. Under the formation temperature and weakly alkaline environment, the wall material gradually degrades, and the oil displacement agent release rate reaches over 90% within 5 days of well shut-in.

[0022] The specific manifestations of the defect resolution are as follows: In this scenario, no crosslinking agent needs to be added, avoiding the difficulty of controlling the conditions of the crosslinking reaction. The residue content after the fracturing fluid breaks down is 82 mg / L, and the reservoir damage rate is only 8.7%, which is far lower than the 32% damage rate of conventional guar gum fracturing fluid. The proppant settling velocity is less than 0.05 cm / s, and the proppant uniformity in the fracture reaches more than 90%, avoiding the risk of sand blockage and the decrease in conductivity caused by proppant settling. The effective utilization rate of the oil displacement agent reaches 85%, and the crude oil percolation recovery rate in the matrix pores is increased by 18%, which solves the defects of existing fracturing fluids such as large reservoir damage, insufficient sand carrying capacity, and low oil displacement efficiency.

[0023] Scenario Example 2: Repeated Fracturing of Deep Shale Gas Reservoirs Application Scenario Description: This scenario is applicable to repeated fracturing operations of old wells in deep shale gas reservoirs in the Sichuan Basin. The reservoir is 4100m deep, with a formation temperature of 112℃ and a total formation water salinity of 92000mg / L. The initial fracturing used a conventional slickwater system. After two years of production, the output dropped below the lower limit of industrial gas flow. Existing fractures are severely closed, and the utilization of adsorbed gas and residual oil in the matrix pores is low. Conventional repeated fracturing is ineffective.

[0024] Technical Adaptation Details: The supramolecular fracturing fluid system of this invention is used in construction. The mass ratio of each component is set as follows: supramolecular hydrophobic associative polymer 0.7%, nano-microcapsule oil displacement agent 0.4%, pH adjuster 0.09%, and co-solvent 0.25%. The base fluid is on-site clean water. The apparent viscosity of the system is controlled at 150 mPa·s, and the temperature resistance reaches 120℃. After shearing at 112℃ for 2 hours, the viscosity retention rate is 68%. A 12m... 3 A pump injection rate of / min utilizes the system's high viscosity to open the closed fractures formed during the initial fracturing, while simultaneously generating a new, complex fracture network. The nano-encapsulated oil displacement agent enters the micropores and natural fractures of the shale matrix. The wall material degrades more rapidly under high temperatures, achieving an 88% release rate of the oil displacement agent within 3 days of well shut-in. This is achieved by reducing interfacial tension, thus desorbing adsorbed gas and initiating the release of residual oil. The core viscosity-temperature characteristics of the system satisfy the following formula: in This is the actual apparent viscosity of the system, in mPa·s; The initial apparent viscosity of the system at 25°C is expressed in mPa·s. The value represents the viscous flow activation energy of the supramolecular system, expressed in J / mol. The value of is the ideal gas constant, which is 8.314 J / (mol·K). This refers to the actual formation temperature, expressed in Kelvin (K). The standard temperature is 298K; This is a correction factor for the proportion of hydrophobic monomers, with a value ranging from 0.6 to 0.9, and is positively correlated with the molar proportion of hydrophobic monomers.

[0025] This formula is used to quantitatively calculate the viscosity retention of fracturing fluid at different formation temperatures. By adjusting the proportion of hydrophobic monomers, it can be adapted to the temperature requirements of reservoirs at different depths. In reservoir environments below 120℃, the viscosity of the system always meets the requirements for proppant carrying.

[0026] The specific manifestations of defect resolution: In this scenario, the temperature and salt resistance of the fracturing fluid meets the requirements of deep reservoirs, eliminating the need for additional temperature stabilizers. No sand plugging occurred during the operation. After repeated fracturing, the fracture half-length increased by 40% compared to the initial fracturing, and the fracture conductivity reached 30μm. 2 The nano-microcapsule oil displacement agent can enter the micropores of shale with a pore size of 50nm or more. The permeation and adsorption effect increases the desorption rate of adsorbed gas in the matrix by 22%, and the daily gas production of a single well is restored to more than 80% of the initial fracturing stage. This solves the defects of existing slickwater fracturing fluids, such as insufficient temperature resistance, poor sand carrying capacity, and low utilization of shale matrix.

[0027] refer to Figure 3 This figure visually compares the core performance differences between the fracturing fluid of this invention and three mainstream existing fracturing fluids. The apparent viscosity of the system of this invention is close to that of conventional guar gum fracturing fluid and higher than that of conventional slickwater, which can meet the requirements of high sand ratio and sand carrying capacity. The residue content after gel breaking is only higher than that of conventional slickwater without polymers, and far lower than that of guar gum and ordinary supramolecular fracturing fluids. The reservoir damage rate is the lowest among the three systems, effectively reducing the risk of pore throat blockage in the reservoir. The percolation oil displacement efficiency improvement rate is the highest among the three systems, verifying the technical advantages of nano-microcapsule controlled-release oil displacement. The data in the figure demonstrate that the system of this invention has the advantages of low damage and high oil displacement efficiency, solving the defects of existing technologies that cannot simultaneously meet multiple performance requirements.

[0028] refer to Figure 4 This figure illustrates the dynamic viscosity changes of three types of fracturing fluids under different shear conditions. The viscosity of conventional guar gum fracturing fluid continuously decreases with increasing shear rate, and the viscosity cannot be recovered after high shear, easily leading to insufficient proppant carrying capacity during pumping. Ordinary supramolecular fracturing fluid, when the shear rate increases to 2000 s⁻¹, exhibits a decrease in viscosity. -1The viscosity recovery rate is only 50%, indicating insufficient dynamic reversibility; the system of this invention exhibits viscosity recovery within 2000 s. -1 Under high shear, the viscosity drops to 30 mPa·s, effectively reducing wellbore friction. After the shear rate decreases, the viscosity recovers to 95 mPa·s within 30 seconds, with a recovery rate of over 70%. It exhibits optimal dynamic reversibility and simultaneously meets the low friction requirement of large-volume pumping and the high viscosity and proppant carrying capacity requirement within the formation. This solves the problem that existing fracturing fluids cannot simultaneously achieve both low friction and high proppant carrying capacity.

[0029] refer to Figure 5 This figure comprehensively compares the overall performance of three types of fracturing fluids from multiple dimensions. Conventional guar gum fracturing fluid has excellent temperature resistance but moderate salt resistance, high friction, low oil displacement agent utilization, and complex preparation process, resulting in poor overall adaptability. Conventional slickwater has low friction and simple preparation, but insufficient temperature resistance and low oil displacement agent utilization, making it difficult to meet the needs of deep reservoir stimulation and enhanced oil recovery. The system of this invention has balanced performance across all aspects, with temperature and salt resistance suitable for reservoir environments up to 120℃ and 100,000 mg / L salinity. Its friction reduction rate is close to that of conventional slickwater, and its oil displacement agent utilization rate is the highest among the three systems. On-site preparation can achieve continuous mixing without a curing process, resulting in the best overall performance. It is suitable for the fracturing stimulation needs of various reservoirs such as low-permeability to tight sandstone and shale, solving the defects of existing fracturing fluid systems in terms of single function and poor adaptability.

[0030] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a supramolecular fracturing fluid system with both percolation and oil displacement capabilities, characterized in that, Includes the following steps: S1. Anionic acrylamide with a molecular weight of 12 million, 2-acrylamide-2-methylpropanesulfonic acid with a sulfonation degree of 90%, and perfluoroalkyl betaine monomer with 12 carbon atoms are added to a reaction vessel in a mass ratio of 65~75:15~20:10~15. Deionized water is added and the mixture is stirred continuously for 30~40 minutes until the monomers are completely dissolved, resulting in a monomer mixture with a total mass concentration of 20%~30%. The pH of the monomer mixture is adjusted to 7.5~8 using a 20% sodium hydroxide solution. S2. Nitrogen gas is continuously introduced into the adjusted monomer mixture for 20-30 minutes. Then, a composite initiation system consisting of potassium persulfate-sodium bisulfite redox initiator and azobisisobutylamidine hydrochloride azo initiator is added. The total addition amount is 0.05%-0.2% of the total monomer mass. After stirring evenly, the reactor is sealed for adiabatic polymerization to obtain an amphoteric hydrophobic associating polymer thickener colloid. S3. Hexadecyltrimethylammonium bromide, fatty alcohol polyoxyethylene ether with a degree of polymerization of 10, and nonionic fluorocarbon surfactant with a fluorocarbon chain length of 6 are added to a high-speed mixer in a mass ratio of 40~50:30~35:15~30. The mixture is heated to 60~70℃ and stirred for 15~20 minutes. The molten mixture is then passed into a twin-screw extruder and granulated. After cooling, modified penetrant oil displacement agent solid particles with a particle size of 0.5~1mm are obtained. S4. The obtained thickener colloid is fed into a spiral shear granulator and cut into colloid particles with a particle size of 2-3 cm. The colloid particles are laid on the conveyor belt of a mesh belt dryer, dried, and then fed into a grinder for crushing. After grinding, the particles are passed through an 80-100 mesh standard sieve to obtain polymer thickener powder. The obtained powder and modified penetrant oil displacement agent particles are fed into a double spiral mixer at a mass ratio of 80-90:10-20 and mixed for 30 minutes to obtain supramolecular fracturing fluid dry powder base material. S5. Add the supramolecular fracturing fluid dry powder base material to the solution water at a ratio of 0.1% to 0.5% of the total mass and stir for 3 to 5 minutes to obtain a supramolecular fracturing fluid system with an apparent viscosity of 30 to 120 mPa·s at 25℃.

2. The method for preparing a supramolecular fracturing fluid system with both percolation and oil displacement capabilities according to claim 1, characterized in that, The 2-acrylamide-2-methylpropanesulfonic acid used in step S1 needs to be purified by recrystallization beforehand. The deionized water used to prepare the monomer mixture needs to be sterilized by ultraviolet light. After adjusting the pH, it needs to stand for 10 minutes. The pH value of the mixture is measured at multiple points using a pH meter.

3. The method for preparing a supramolecular fracturing fluid system with both percolation and oil displacement capabilities according to claim 1, characterized in that, In step S2, the mass ratio of potassium persulfate to sodium bisulfite is 1:1.

2. Before adding the initiator, the initiator needs to be prepared as a 1% aqueous solution and added to the reactor in three equal parts with a 2-minute interval between each addition. After the addition is completed, continue stirring for 5 minutes. During the polymerization reaction, monitor the temperature change inside the reactor in real time. When the temperature rises to 45°C, turn on the cooling water of the reactor jacket to control the maximum reaction temperature to not exceed 70°C.

4. The method for preparing a supramolecular fracturing fluid system with both percolation and oil displacement capabilities according to claim 1, characterized in that, In step S3, the fatty alcohol polyoxyethylene ether selected has a hydroxyl value of 110~120 mgKOH / g, and the surface tension of the nonionic fluorocarbon surfactant is 18~20 mN / m. Nitrogen gas is introduced into the high-speed mixer during the mixing process. After granulation, the modified penetrant oil displacement agent particles are cooled to room temperature in a fluidized bed, with the air volume controlled at 1000 m³ / g during the cooling process. 3 / h.

5. The method for preparing a supramolecular fracturing fluid system with both percolation and oil displacement capabilities according to claim 1, characterized in that, In step S4, the grinding process adopts a graded grinding process. The granules are crushed to a particle size of less than 1 mm through coarse grinding, and then fine grinding is used to obtain powder with the target particle size. The sieving process uses a vibrating sieve with an amplitude of 2 mm and a sieving time of 5 min. During the mixing process, samples are taken every 10 min to test the mixing uniformity.

6. The method for preparing a supramolecular fracturing fluid system with both percolation and oil displacement capabilities according to claim 1, characterized in that, In step S5, the liquid preparation process uses a jet mixing device. The dry powder base material is initially mixed with the liquid preparation water through a negative pressure suction device, and then enters the mixing tank for dissolution. During the mixing process, the liquid flow rate is controlled at 2m / s. After dissolution, the viscosity of the system is detected by a six-speed rotational viscometer. When the viscosity deviation exceeds 5%, the amount of dry powder base material added is adjusted appropriately.

7. An application of a supramolecular fracturing fluid system with both percolation and oil displacement capabilities, comprising an application method for the supramolecular fracturing fluid system obtained by any one of the preparation methods described in claims 1 to 6, applied to the fracturing and stimulation of low-permeability-tight oil and gas reservoirs with a porosity of 5% to 15%, characterized in that, Includes the following steps: S1. Based on the porosity, permeability, formation temperature, and crude oil viscosity parameters of the target reservoir, adjust the addition ratio of supramolecular fracturing fluid dry powder base. For tight reservoirs with porosity below 10% and permeability below 0.1 mD, adjust the viscosity of the supramolecular fracturing fluid system to 30~50 mPa·s; for low-permeability reservoirs with porosity of 10%~15% and permeability of 0.1~1 mD, adjust the viscosity of the supramolecular fracturing fluid system to 50~120 mPa·s. After preparation, test the temperature and shear resistance of the fracturing fluid. S2. Add proppant to the prepared supramolecular fracturing fluid system. The proppant should be high-strength ceramic granules of 30-50 mesh or 40-70 mesh, with a bulk density of 1.5-1.7 g / cm³. 3 The volume percentage of the proppant is 10%~30%, and the mixture is stirred at a rate of 200~300 r / min for 2~3 min; S3. Using fracturing pumping equipment, pre-flush fluid, proppant-carrying fluid, and displacement fluid are sequentially injected into the reservoir, with the pumping rate controlled at 4~8m³. 3 The volume of pretreatment fluid is 20%~30% of the total volume, the volume of sand-carrying fluid is 50%~60% of the total volume, and the volume of displacement fluid is 10%~20% of the total volume. S4. After the pumping operation is completed, shut the well in and let it sit for 2-7 days. S5. After the well is shut off, when reopening the well, gradually increase the flowback rate from low to high, controlling the initial flowback rate to not exceed 0.5m. 3 The flow rate is gradually increased after the sand content of the flowback fluid is lower than 0.1% per hour. The flowback operation is completed when the viscosity of the flowback fluid is lower than 5 mPa·s, and then the oil and gas production stage begins.

8. The application method of the supramolecular fracturing fluid system according to claim 7, characterized in that, In step S1, for reservoirs with formation temperatures above 90°C, thiourea with a mass concentration of 0.05% is added as an antioxidant stabilizer when preparing the fracturing fluid. The prepared fracturing fluid must be pumped in within 4 hours.

9. The application method of the supramolecular fracturing fluid system according to claim 7, characterized in that, Before adding the proppant in step S2, it needs to be screened and dust removed. During the stirring process, the uniformity of the sand-carrying liquid is monitored in real time, and samples are taken every 5 minutes to detect the proppant concentration deviation between the upper and lower liquid layers.

10. The application method of the supramolecular fracturing fluid system according to claim 7, characterized in that, In step S3, the wellhead pressure changes are monitored in real time during the pumping process, and the pumping rate is adjusted when the pressure fluctuation exceeds 5 MPa.

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