Degradable nanomaterial and preparation method therefor and use thereof, and fracturing fluid

Abstract

A degradable nanomaterial and a preparation method therefor and the use thereof, and a fracturing fluid. The molecular aggregate hydrodynamic particle size D10 of the degradable nanomaterial in a liquid polyethylene glycol having a molecular weight of 380-430 is less than 30 μm, D50 is equal to 50-120 μm, and D90 is equal to 150-250 μm. The preparation method for the degradable nanomaterial comprises: subjecting a nanomicrosphere lactide raw material to a hydroxylation treatment and an activation treatment, and then mixing and bringing same into contact with a fluorocarbon-chain-containing surfactant. The degradable nanomaterial has excellent degradation performance at relatively low temperatures, which satisfies low-temperature construction requirements, and can effectively block pores having various sizes when used in a fracturing fluid system.

Description

Degradable nanomaterial, preparation method and application thereof, and fracturing fluid

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of Chinese patent application 202410153876.3, filed on February 2, 2024, the contents of which are incorporated herein by reference. Technical Field

[0003] The present invention relates to petrochemical technology, in particular to a degradable nanomaterial, a preparation method and application thereof, and a fracturing fluid containing the degradable nanomaterial. Background Art

[0004] Low-permeability, tight sandstone reservoirs typically have a porosity of less than 10% and a permeability of less than 0.1 millidarcy. This results in low natural productivity per well, necessitating fracturing. During fracturing, significant amounts of fracturing fluid can leak into the formation, causing damage to the liquid phase, such as water sensitivity and water locking, as well as solid phase damage from residual adsorption and retention. Reservoir matrix damage can exceed 30%. Both domestic and international approaches typically mitigate this damage by adding additives such as plugging agents and water-blocking agents to the fracturing fluid.

[0005] The fracturing plugging agents currently used in oil fields mainly include three categories: water-soluble plugging agents, acid-soluble plugging agents, and oil-soluble plugging agents. Acid-soluble plugging agents are mainly CaCO3 products, which can only bridge and plug pore throats or fractures. After plugging, high-concentration acid is required to dissolve and flow back. Oil-soluble plugging agents are mainly plugging agents that dissolve in oil, but most oil fields are currently in the high-water-cut development stage, making it difficult to flow back after fracturing, which pollutes the formation. Water-soluble plugging agents dissolve too quickly and incompletely within the effective time, resulting in serious adhesion problems. Therefore, in oilfield chemistry research, new biodegradable plugging agents have become the development focus. Among them, high-molecular-weight biodegradable materials such as polylactide and copolymers of lactide and other monomers are used in the production of various plugging agents or fracturing diversion agents.

[0006] However, while materials like polylactide and copolymers of lactide and other monomers are biodegradable, they require high temperatures and a slow degradation rate. Under low-temperature construction conditions (60-90°C), their degradation performance cannot meet the requirements for degradation and flowback after fracturing and plugging. Furthermore, existing materials like polylactide and copolymers of lactide and other monomers can only plug micron-sized pores and are unable to effectively plug the nanoscale pores formed in low-permeability, tight sandstone oil and gas reservoirs.

[0007] Summary of the Invention

[0008] The purpose of the present invention is to overcome the problems existing in the prior art and provide a degradable nanomaterial, a preparation method and application thereof, and a fracturing fluid. The degradable nanomaterial not only has excellent degradation performance at lower temperatures, meeting the requirements of low-temperature construction, but also can effectively block pores of various sizes when applied to the fracturing fluid system.

[0009] In order to achieve the above object, the first aspect of the present invention provides a degradable nanomaterial, wherein the hydrodynamic particle size D of the molecular aggregate of the degradable nanomaterial in liquid polyethylene glycol with a molecular weight of 380-430 is 10 Less than 30μm, D 50 =50-120μm, D 90 =150-250μm.

[0010] The second aspect of the present invention provides a method for preparing a degradable nanomaterial, which comprises: subjecting a nano-microsphere lactide raw material to hydroxylation and activation treatment, and then contacting the raw material with a fluorine-containing carbon chain surfactant.

[0011] The third aspect of the present invention provides a degradable nanomaterial composition, which contains the degradable nanomaterial as described above or the degradable nanomaterial prepared according to the method as described above.

[0012] The fourth aspect of the present invention provides the use of the aforementioned degradable nanomaterial, the degradable nanomaterial prepared according to the aforementioned method, or the aforementioned degradable nanomaterial composition in oil and gas reservoir reconstruction working fluid, preferably as a plugging agent for fracturing fluid.

[0013] A fifth aspect of the present invention provides a fracturing fluid containing the above-mentioned degradable nanomaterial composition.

[0014] Through the above technical scheme, the beneficial effects of the present invention are as follows: the degradable nanomaterial provided by the present invention is based on a specific molecular aggregate hydrodynamic particle size in liquid polyethylene glycol. When applied to a fracturing fluid system, combined with the nanoscale size of the degradable material itself, it can achieve multi-scale plugging of pores of different sizes in the reservoir, with a high plugging rate for cracks and pore throats of different sizes, a high degree of matching with the cracks and pore throats of tight sandstone reservoirs, and can adapt to the fracturing transformation technology requirements of more low-permeability tight oil and gas reservoirs, and effectively reduce the filtration loss of the working fluid; and the degradable nanomaterial has a faster degradation rate at a lower temperature (60-90°C), effectively reducing the residual content of the plugging agent, reducing damage to the reservoir matrix, and can achieve a higher return efficiency without the aid of a drainage agent, promoting the rapid flow of the working fluid back out of the reservoir, and improving the return efficiency of the working fluid. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] FIG1 is a microscopic structural representation of lactide particles in the reaction solution before purification in Example 1;

[0016] FIG2 is an infrared spectrum of the modified nanolactide material after purification in Example 1. DETAILED DESCRIPTION

[0017] The endpoints of the ranges and any values ​​disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein.

[0018] The first aspect of the present invention provides a degradable nanomaterial, wherein the hydrodynamic particle size D of the molecular aggregate of the degradable nanomaterial in liquid polyethylene glycol with a molecular weight of 380-430 is 10 Less than 30μm, D 50 =50-120μm, D 90 =150-250μm.

[0019] During the research and development process, the inventors of the present invention unexpectedly discovered that the degradable nanomaterials formed by chemically modifying the degradable nanoparticle raw materials have a specific molecular aggregate hydrodynamic particle size in liquid polyethylene glycol. Not only can they retain their own excellent degradation performance, but when applied to the fracturing fluid system, they can achieve multi-scale plugging of cracks and pore throats of different sizes in the reservoir, and have a high degree of matching with the cracks and pore throats of tight sandstone reservoirs. They can adapt to the fracturing transformation technology requirements of more low-permeability tight oil and gas reservoirs, effectively reduce the filtration loss of the working fluid, and reduce damage to the reservoir. After the operation, a higher return efficiency can be achieved without the aid of a drainage agent, thereby promoting the rapid flow of the working fluid back out of the reservoir and improving the return efficiency of the working fluid.

[0020] In the present invention, the hydrodynamic particle size of molecular aggregates refers to the apparent particle size of molecular aggregates formed by the aggregation of degradable nanomaterials in liquid polyethylene glycol with a molecular weight of 380-430. The testing method is as follows: after mixing the degradable nanomaterials with liquid polyethylene glycol with a molecular weight of 380-430 at a weight ratio of 1:1-3, a wet method test is performed using a Fritsch 22 laser particle size analyzer with reference to the liquid medium dispersion and measurement method in the standard GB / T 19077-2016 "Particle Size Analysis by Laser Diffraction Method"; D 10 、D 50 and D 90They respectively represent the particle sizes corresponding to when the cumulative particle size distribution of the sample reaches 10%, 50% and 90% (manually accumulate the percentages of all particle sizes before or after this particle size); its physical meaning is that the number of particles with a size smaller than this particle size accounts for 10%, 50% and 90% of the total number of particles.

[0021] According to the present invention, the degradation rate of the degradable nanomaterial at a temperature of 90°C is preferably 15-30% in 1 hour, 32-50% in 2 hours, 52-70% in 4 hours, and 95% or more in 8 hours. The inventors have discovered that under this preferred embodiment, the degradable nanomaterial not only better promotes the rapid flow of the working fluid back out of the reservoir after operation, improving the return efficiency of the working fluid, but also meets the time requirements of on-site construction operations in low-permeability and tight oil and gas reservoirs.

[0022] In the present invention, the specific detection process of the degradation rate is: testing the initial weight M0 of the degradable nanomaterial, placing the degradable nanomaterial at a temperature of 90°C for 1h, 2h, 4h, and 8h respectively, then testing the weight M of the degradable nanomaterial, and calculating the degradation rate of the degradable nanomaterial at a temperature of 90°C for 1h, 2h, 4h, and 8h by degradation rate = (M0-M) / M0×100%.

[0023] In the present invention, the degradable nanomaterial can be any nano-scale degradable material that can form the above-mentioned specific molecular aggregate hydrodynamic particle size in liquid polyethylene glycol with a molecular weight of 380-430. Preferably, the degradable nanomaterial is a modified nanolactide material, which contains lactide particles and active groups containing fluorine-containing carbon chains adsorbed on the surface of the lactide particles; the molecular aggregate hydrodynamic particle size D of the degradable nanomaterial in liquid polyethylene glycol with a molecular weight of 380-430 is 10 =15-25μm, D 50 =60-90μm, D 90 =160-190μm.

[0024] The inventors of the present invention need to explain that although the prior art has carried out research on the application of polylactide and copolymers of lactide and other monomers in fracturing fluids, there are few applications of lactide in fracturing fluids. This is mainly because although lactide can be degraded at low temperatures, the characteristics of the material itself make it inconvenient to pump it on site. The lactide nanoparticle raw material is chemically modified to form a modified nanolactide material, which has a specific molecular aggregate hydrodynamic particle size in liquid polyethylene glycol. In addition to retaining its excellent degradation performance at relatively low temperatures (60-90°C), it is easy to pump it on site, thus realizing the application of lactide particles in fracturing fluids. When applied to a fracturing fluid system, it can achieve multi-scale plugging of different-sized fractures and pore throats in the reservoir, has a high degree of compatibility with the fractures and pore throats of tight sandstone reservoirs, and can meet the fracturing transformation technology needs of more low-permeability tight oil and gas reservoirs.

[0025] According to the present invention, the content of fluorocarbon chains in the degradable nanomaterial is preferably 2-7% by weight. The present invention effectively adsorbs the active groups containing fluorocarbon chains onto the surface of lactide particles (see the microscopic characterization diagram shown in FIG1 , which shows that the surface of the lactide particles of the modified nanolactide material is coated with adsorbed active groups). Furthermore, the content of fluorocarbon chains in the degradable nanomaterial is controlled within a specific range, so that the nanomaterial has a desired specific molecular aggregate hydrodynamic particle size in liquid polyethylene glycol.

[0026] In the present invention, the content of fluorocarbon chains can be obtained by nuclear magnetic hydrogen spectrum, nuclear magnetic carbon spectrum, infrared detection combined with fluorine element determination method.

[0027] According to the present invention, the degradable nanomaterial can be obtained by modifying various types of nano-microsphere lactide raw materials. Preferably, the lactide particles are C2-C8 lactides, such as glycolide, lactide, butylide, etc.; more preferably, they are at least one of glycolide, lactide and butylide.

[0028] According to the present invention, the active group of the fluorinated carbon chain is preferably a C4-C10 perfluoroalkyl group, a C4-C10 perfluoroalkoxy group, a substituted aromatic group containing a C4-C10 perfluoroalkyl group, or a substituted aromatic group containing a C4-C10 perfluoroalkoxy group; more preferably, it is a perfluorononenyloxyphenyl group and / or a perfluorooctyl group. The inventors have discovered that this preferred embodiment not only facilitates the formation of molecular aggregates of a specific size of the degradable nanomaterial in liquid polyethylene glycol, but also reduces the contact angle of the working liquid system, thereby improving the flowback efficiency.

[0029] The second aspect of the present invention provides a method for preparing a degradable nanomaterial, which comprises: subjecting a nano-microsphere lactide raw material to hydroxylation and activation treatment, and then contacting the raw material with a fluorine-containing carbon chain surfactant.

[0030] The preparation method of the degradable nanomaterial provided by the present invention comprises the following steps: subjecting a nano-microsphere lactide raw material to hydroxylation and activation treatments in sequence, and then subjecting it to a contact reaction with a fluorine-containing carbon chain surfactant in a specific ratio. The obtained degradable nanomaterial has excellent degradability at a relatively low temperature, can be applied to a working fluid system for oil and natural gas reservoir reconstruction, acts as a plugging agent during on-site construction, and significantly reduces the filtration loss of the fracturing fluid. After the construction is completed, the degradable nanomaterial, due to its own degradability, not only does not leave any residue, but also promotes the rapid return of the working fluid from the reservoir, thereby improving the return efficiency of the working fluid and reducing damage to the reservoir matrix.

[0031] According to the present invention, the preparation process can be carried out in a suitable alcohol solvent. Preferably, the alcohol solvent is a polyethylene glycol liquid with a molecular weight of 380-430.

[0032] According to the present invention, preferably, the hydroxylation treatment process includes: mixing the nano-microsphere lactide raw material with water in the presence of a reducing agent to carry out reaction I. In this process, under the action of the reducing agent, the carbon-oxygen double bonds on the surface of the aggregate particles of the nano-microsphere lactide raw material are hydroxylated, and the formation of hydroxyl groups on the surface of the nano-microsphere lactide raw material can be detected using hydroxyl detection test paper or freshly prepared copper hydroxide solution.

[0033] According to the present invention, preferably, the reducing agent is an inorganic reducing agent, preferably sodium borohydride and / or lithium aluminum hydride. The inventors have found that under this preferred embodiment, the reduction process is promoted and the efficiency of hydroxylation on the surface of the lactide particles is improved.

[0034] According to the present invention, preferably, the weight ratio of the nano-microsphere lactide raw material, water and reducing agent is 3-5:2-4:1.

[0035] According to the present invention, preferably, the conditions of Reaction I include: a temperature of -5 to 5°C, specifically -5°C, -3°C, -1°C, 0°C, 1°C, 3°C, 5°C, or any value therebetween; and a reaction time of 4 to 8 hours, specifically 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, or any value therebetween. These conditions are conducive to improving the efficiency of hydroxylation on the surface of the lactide particles.

[0036] According to the present invention, preferably, the activation treatment process includes: mixing the hydroxylated product with an activating agent to carry out reaction II. The inventors have found that under this preferred embodiment, it is beneficial to promote the adsorption of the fluorinated carbon chain surfactant on the surface of the lactide particles, thereby improving the overall structural stability of the degradable nanomaterial.

[0037] In the present invention, the intermediate product obtained after activation treatment and purification can be used to perform photoquantitative analysis of amino groups on the surface of nanolactide particles using fluorescent amine and o-phthalaldehyde (OPA); three different amines, n-butylamine, 3-aminopropyltriethoxysilane (APTES) and aminodextran, are selected as standard amines for drawing a standard curve, and the effects of different standard amines on fluorescence intensity are analyzed; the results show that due to the porous structure on the surface of the nanolactide particles, a hydrophobic environment conducive to fluorescence is generated, and the chemical environment of the amino groups in the macromolecular amine is similar to that of the amino groups on the surface of the nanolactide particles. Therefore, when the standard curve is measured using the macromolecular amine as the standard amine, the number of amino groups on the surface of the nanolactide particles calculated according to the standard curve is closer to the actual number of amino groups on the surface of the nanoparticles than the result obtained using the small molecular amine as the standard amine.

[0038] Further preferably, the activator is a nitrogen-based activator, more preferably urea. The inventors have discovered that this preferred embodiment effectively promotes the adsorption and encapsulation of the modifier having a fluorinated alkyl group on the surface of the lactide particles. When the activator is urea, the activation reaction process can also be characterized by detecting the generation of ammonia gas to indicate the progress of Reaction II.

[0039] According to the present invention, preferably, the weight ratio of the activator to the nano-microsphere lactide raw material is 0.5-1.5:1.

[0040] According to the present invention, preferably, the conditions of reaction II include: a temperature of 10-40°C, specifically 10°C, 15°C, 20°C, 25°C, 30°C, 35°C, 40°C, or any value therebetween; and a reaction time of 2-8 hours, specifically 2 hours, 4 hours, 6 hours, 8 hours, or any value therebetween. These conditions are conducive to improving the efficiency of modification by reaction with an activator.

[0041] According to the present invention, preferably, the molar ratio of fluorine element to carbon element in the fluorine-containing carbon chain surfactant is 1-3:1.

[0042] According to the present invention, preferably, the fluorinated carbon chain surfactant has an active group containing a fluorinated carbon chain, and the active group containing the fluorinated carbon chain is a C4-C10 perfluoroalkyl group or a C4-C10 perfluoroalkoxy group, a substituted aromatic group containing a C4-C10 perfluoroalkyl group, or a substituted aromatic group containing a C4-C10 perfluoroalkoxy group. More preferably, the fluorinated carbon chain surfactant is perfluorononenyloxybenzenesulfonate and / or perfluorooctanesulfonate. Wherein, perfluorononenyloxybenzenesulfonate can be sodium perfluorononenyloxybenzenesulfonate, potassium perfluorononenyloxybenzenesulfonate, etc., and perfluorooctanesulfonate can be sodium perfluorooctanesulfonate, potassium perfluorooctanesulfonate, etc. The inventors have found that under this preferred embodiment, it is beneficial to improve the adsorption effect of the fluorinated group on the surface of the lactide particles.

[0043] According to the present invention, when the fluorine-containing carbon chain surfactant is perfluorononenyloxybenzenesulfonate and / or perfluorooctanesulfonate and the activator is urea, the sulfonic acid group of the fluorine-containing carbon chain surfactant can be chemically bonded to the amino group on the surface of the activation reaction product, which is beneficial to improving the adsorption efficiency of the fluorine-containing group on the surface of the lactide.

[0044] According to the present invention, preferably, the usage ratio of the nano-microsphere lactide raw material to the fluorine-containing carbon chain surfactant is 2-4:1, which is beneficial to reducing the contact angle of the degradable nanomaterial and controlling the solid phase degradation rate.

[0045] According to the present invention, preferably, the contact conditions include: a temperature of 40-60°C, specifically 40°C, 45°C, 50°C, 55°C, 60°C, or any value between the above two values; a time of 4-8 hours, specifically 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, or any value between the above two values. The inventors have found that under this preferred embodiment, it is beneficial to better adsorb the active groups of the fluorinated carbon chain on the lactide particles, thereby improving the backflow efficiency of the working fluid. The adsorption reaction of the fluorinated carbon chain surfactant on the surface of the lactide particles during the contact process can be characterized by detecting the change in pH value before and after the contact reaction.

[0046] According to the present invention, preferably, the nano-microsphere lactide particles are C2-C8 lactide, more preferably at least one of glycolide, lactide and butyride.

[0047] The preparation process of the biodegradable nanomaterial provided by the present invention further comprises: purifying the product obtained by the contact to obtain a high-purity biodegradable nanomaterial. Specifically, the purification process can be carried out by washing with water, filtering, and low-temperature drying (eg, 35-45°C).

[0048] The third aspect of the present invention provides a degradable nanomaterial composition, which contains a solvent and the degradable nanomaterial as described above or the degradable nanomaterial prepared according to the method as described above.

[0049] The degradable nanomaterial composition provided by the present invention is based on the degradable nanomaterial, is convenient for on-site construction and pumping, and can improve the flowback efficiency of the fracturing fluid and reduce the damage of the fracturing fluid when added to the fracturing fluid.

[0050] According to the present invention, the content of the degradable nanomaterial in the composition is preferably 25-50% by weight, specifically 25%, 30%, 35%, 40%, 45%, 50%, or any value in between. The inventors have found that this preferred embodiment helps reduce the initial contact angle of the composition (the contact angle of the composition is 28-33°), promotes the rapid return of the working fluid from the reservoir, and achieves a gas permeability recovery rate (flowback efficiency) greater than 75%.

[0051] In the present invention, the contact angle of the composition is measured using a contact angle meter by dropping 5 μL of the composition onto a core piece of a reservoir having a porosity and permeability of the same order of magnitude.

[0052] According to the present invention, preferably, the composition reduces the fluid loss of a fracturing fluid composed of 0.65 wt% thickener + 0.3 wt% cross-linking agent + 0.05 wt% breaker and having a fluid loss of 600 mL by more than 40%, which can further reduce the fluid loss damage of the working fluid system to the reservoir.

[0053] The fluid loss reduction rate refers to the ratio of the change in fluid loss before and after the addition of the composition provided by the present invention (the addition amount of the composition is preferably 0.1-1 weight %) to the initial fluid loss of the fracturing fluid, and the calculation formula is shown in formula (I);

[0054] In formula (I):

[0055] ΔP——fracturing fluid loss reduction rate, %;

[0056] P0——filtration loss of the fracturing fluid when the composition provided by the present invention is not added, mL;

[0057] P1 - filtration loss of the fracturing fluid after adding the composition provided by the present invention, mL;

[0058] The filtration loss of the fracturing fluid is measured using a high-temperature and high-pressure filter loss instrument, referring to the industry standard "SY / T 5107-2016 Performance Evaluation Method of Water-Based Fracturing Fluid".

[0059] In the present invention, the thickener can be any substance that can serve as a thickener in a fracturing fluid, the crosslinker can be any substance that can serve as a crosslinker in a fracturing fluid, and the breaker can be any substance that can serve as a breaker in a fracturing fluid. Exemplarily, the thickener is an acrylamide homopolymer and / or a copolymer of acrylamide and another monomer, wherein the other monomer is selected from at least one of acryloyloxyethyltrimethylammonium chloride, sodium acrylate, and acrylic acid. More preferably, the copolymer of acrylamide and another monomer is at least one of an acrylamide-acryloyloxyethyltrimethylammonium chloride copolymer, an acrylamide-sodium acrylate-acrylic acid copolymer, and an acrylamide-acryloyloxyethyltrimethylammonium chloride-sodium acrylate-acrylic acid copolymer. Furthermore, preferably, the molecular weight of the acrylamide homopolymer is greater than 18 million, and the molecular weight of the copolymer of acrylamide and another monomer is greater than 18 million.

[0060] In the present invention, the cross-linking agent is an organic zirconium cross-linking agent, and the organic zirconium cross-linking agent is preferably zirconium lactate; the breaker is a persulfate, such as ammonium persulfate, sodium persulfate, potassium persulfate, and preferably ammonium persulfate.

[0061] In the present invention, a specific formulation of a fracturing fluid comprising a thickener, a crosslinker, and a breaker with a fluid loss of 600 mL can be: 0.65 wt% acrylamide homopolymer with a relative molecular weight of 18 million + 0.3 wt% zirconium lactate + 0.05 wt% ammonium persulfate. A fracturing fluid meeting these requirements can be, for example, the SPR series of fracturing fluids produced by Dongying Shipurui Petroleum Engineering Technology Co., Ltd., for example, a fracturing fluid formed by mixing acrylamide homopolymer (thickener SPR-08), zirconium lactate (crosslinker SPR-18), and ammonium persulfate in the aforementioned proportions.

[0062] According to the present invention, the solvent is preferably an organic alcohol, which can be any aliphatic or aromatic alcohol; more preferably, liquid polyethylene glycol with a molecular weight of 380-430 is used. The inventors have discovered that this preferred embodiment further reduces the initial contact angle of the composition, thereby reducing damage to the reservoir caused by the fracturing fluid.

[0063] The fourth aspect of the present invention provides the use of the aforementioned degradable nanomaterial, the degradable nanomaterial prepared according to the aforementioned method, or the aforementioned degradable nanomaterial composition in a working fluid for oil and gas reservoir reconstruction.

[0064] In the present invention, the working fluid for oil and gas reservoir reconstruction can be a fracturing fluid, drilling fluid, completion fluid, or any other working fluid. Preferably, the aforementioned degradable nanomaterial or degradable nanomaterial composition is used as a plugging agent for the fracturing fluid. During on-site construction, the plugging agent acts to temporarily reduce formation permeability or temporarily plug high-permeability oil reservoirs, significantly reducing fluid loss from the fracturing fluid. After completion of the construction, the degradable nanomaterial, due to its inherent degradability, not only effectively reduces the residual content of the plugging agent itself, minimizing damage to the reservoir matrix, but also promotes the rapid return of the fracturing fluid from the reservoir, improving the return efficiency of the working fluid.

[0065] A fifth aspect of the present invention provides a fracturing fluid containing the above-mentioned degradable nanomaterial composition.

[0066] According to the present invention, preferably, the content of the degradable nanomaterial composition is 0.1-1% by weight based on the total amount of the fracturing fluid. The inventors have found that under this preferred embodiment, it is beneficial to better reduce the filtration loss of the fracturing fluid, promote the rapid return of the fracturing fluid to the reservoir, and reduce the damage of the liquid to the reservoir.

[0067] According to the present invention, the fracturing fluid preferably also contains, based on the total amount of the fracturing fluid, 0.1-1.2% by weight of a thickener, 0-0.6% by weight of a cross-linking agent, and 0.01-0.1% of a breaker. The fracturing fluid provided by the present invention, by incorporating the aforementioned degradable nanomaterial composition into an existing conventional fracturing fluid system, significantly reduces solid and liquid phase damage caused by fluid loss compared to the initial fracturing fluid system, while also improving the flowback efficiency of the working fluid.

[0068] According to the present invention, preferably, the thickener is an acrylamide homopolymer and / or a copolymer of acrylamide and other monomers, and the other monomers are selected from at least one of acryloyloxyethyltrimethylammonium chloride, sodium acrylate and acrylic acid; further preferably, the copolymer of acrylamide and other monomers is at least one of acrylamide-acryloyloxyethyltrimethylammonium chloride copolymer, acrylamide-sodium acrylate-acrylic acid copolymer and acrylamide-acryloyloxyethyltrimethylammonium chloride-sodium acrylate-acrylic acid copolymer; the cross-linking agent is an organic zirconium cross-linking agent, and the breaker is a persulfate.

[0069] The present invention will be described in detail below through examples.

[0070] In the following examples, nano-microsphere glycolide was used as nano-microsphere lactide raw material I, purchased from Suzhou Guren Nanomaterial Technology Co., Ltd., with a CAS number of 502-97-6 and a particle size of 100-120 nm. Nano-microsphere lactide was used as nano-microsphere lactide raw material II, purchased from Suzhou Guren Nanomaterial Technology Co., Ltd., with a CAS number of 95-96-5 and a particle size of 200-250 nm. Sodium perfluorononenyloxybenzenesulfonate had a CAS number of 87-56-8; potassium perfluorooctanesulfonate had a CAS number of 2795-39-3. Liquid polyethylene glycol was purchased from Chengdu Kelong Chemical Co., Ltd., with the product specification of polyethylene glycol 400, an average molecular weight of 400, and a molecular weight of 380-430. Unless otherwise specified, all other reagents were conventional commercial products.

[0071] In the following examples, the content of fluorocarbon chains in the biodegradable nanomaterials was determined by H-NMR spectroscopy, C-NMR spectroscopy, and IR detection; elemental analysis was performed using a FP2012114 scanning electron microscope, and the peripheral coating structure of the lactide particles was characterized using an OLYMPUS200 microscope.

[0072] The specific detection process of the degradation rate is as follows: test the initial weight M0 of the degradable nanomaterial, place the degradable nanomaterial at a temperature of 90°C for 1h, 2h, 4h, and 8h respectively, then test the weight M of the degradable nanomaterial, and calculate the degradation rate of the degradable nanomaterial at a temperature of 90°C for 1h, 2h, 4h, and 8h through degradation rate = (M0-M) / M0×100%.

[0073] The hydrodynamic particle size detection process of molecular aggregates of degradable nanomaterials in liquid polyethylene glycol with a molecular weight of 380-430 is as follows: the degradable nanomaterials and liquid polyethylene glycol with a molecular weight of 380-430 are mixed in a weight ratio of 35:65 to obtain a dispersed sample, and the Fritsch 22 laser particle size analyzer is used to perform the test at room temperature of 20-25°C and normal pressure with reference to the measurement method in the standard GB / T 19077-2016 "Particle Size Analysis by Laser Diffraction Method", wherein the frequency of the laser particle size analyzer is 50-60 Hz and the pump speed is 40 L / min.

[0074] The contact angle is tested by using a contact angle meter and dropping 5 μL of the composition onto a core piece of a reservoir having a porosity and a permeability of the same order of magnitude.

[0075] The filtration loss P of the fracturing fluid with or without the composition is measured using a high-temperature and high-pressure filter loss instrument, with reference to the industry standard "SYT 5107-2016 Water-based Fracturing Fluid Performance Evaluation Method"; the filtration loss reduction rate of the fracturing fluid after adding the composition is calculated according to formula (I):

[0076] In formula (I):

[0077] ΔP——fracturing fluid loss reduction rate, %;

[0078] P0——filtration loss of the fracturing fluid when the composition provided by the present invention is not added, mL;

[0079] P1 - the filtration loss of the fracturing fluid after adding the composition provided by the present invention, mL.

[0080] The evaluation experiment of the gas permeability recovery rate (flowback efficiency) of the fracturing fluid is as follows:

[0081] A natural core of tight sandstone with a gas permeability of the same order of magnitude in the range of 0.001-0.1 millidarcy (core length 3.8 cm, diameter 2.54 cm) was selected, and an initial water saturation of 40 wt% was established using 20,000 mg / L standard brine (2 wt% KCl + 5.5 wt% NaCl + 0.45 wt% MgCl2 + 0.55 wt% CaCl2), and the initial permeability of the gas-measured core was measured;

[0082] 0.08 wt% ammonium persulfate was added to the fracturing fluid for 8 hours to obtain a breaking fluid. The breaking fluid was heated to 80°C and then added to an intermediate container. The fluid was pressurized to 3.5 MPa by a pressure source and then squeezed into the core from the other end of the core holder. The damage was displaced by the breaking fluid for 180 minutes. The permeability of the core was measured 24 hours after the damage by the breaking fluid. The ratio of the permeability of the core 24 hours after the damage to the initial permeability before the damage was calculated according to formula (II) to obtain the permeability recovery rate k (24-hour flowback efficiency) of the fracturing fluid.

[0083] Gas permeability formula:

[0084] Where: K—core permeability, μm 2 ;

[0085] Q0—Volume flow rate of gas at atmospheric pressure p0 (0.1MPa), mL / s;

[0086] μ—viscosity of the gas passing through the core, 0.01795 MPa·s;

[0087] L—core length, cm;

[0088] A—core cross-sectional area, cm 2 ;

[0089] p1—core inlet pressure (displacement pressure + 0.0955), MPa;

[0090] p2—core outlet pressure, 0.0955 MPa.

[0091] The 24-hour permeability recovery rate was calculated according to formula (III):

[0092] Core permeability recovery rate

[0093] Where: K fi —Permeability of core damage flowback 24 hours later, mD;

[0094] K0—initial permeability of core, mD.

[0095] Example 1

[0096] 1) Mix 30 g of the nanosphere lactide raw material I, 7.5 g of sodium borohydride, and 20 g of water, react in an ice-water bath for 6 h, and detect the completion of the reaction using a hydroxyl test paper to obtain a first mixture;

[0097] 2) mixing the first mixture with 30 g of urea and reacting at 25° C. for 5 h to obtain a second mixture;

[0098] 3) mixing the second mixture with 7.5 g of sodium perfluorononenyloxybenzenesulfonate, reacting at 50° C. for 6 h (the progress of the reaction can be characterized by measuring absorbance by colorimetry), washing with water, filtering, and low-temperature drying to purify the modified nanolactide material as a degradable nanomaterial;

[0099] In the reaction solution before purification of Example 1, the microscopic structure characterization diagram of the lactide particles is shown in FIG1 , which shows that the periphery of the lactide particles is wrapped with adsorption groups; the elemental analysis of the modified nanolactide material after purification shows that fluorine is introduced into the peripheral adsorption groups of the modified nanolactide material in the composition; the infrared spectrum of the modified nanolactide material after purification is shown in FIG2 , which shows that the modified nanolactide material contains a peak at 1641 cm -1 Nearby carbon-oxygen double bonds, 2800-3000 cm -1 Nearby are long-chain alkanes, 1749 cm -1 Nearby is the sulfur-oxygen double bond, 947 cm -1 Nearby is the benzene ring, 1352-1460cm -1 Nearby is the fluorine-carbon bond, 3300cm -1 There is an amino group nearby.

[0100] Example 2

[0101] 1) Mix 40 g of the nano-microsphere lactide raw material II, 10 g of lithium aluminum hydride, and 20 g of water, react at 5° C. for 4 h, and detect the completion of the reaction using a hydroxyl test paper to obtain a first mixture;

[0102] 2) mixing the first mixture with 55 g of urea and reacting at 40° C. for 3 h to obtain a second mixture;

[0103] 3) The second mixture was mixed with 15 g of sodium perfluorononenyloxybenzenesulfonate, reacted at 40° C. for 8 h, and then washed with water, filtered, and dried at low temperature for purification to obtain a modified nanolactide material as a degradable nanomaterial.

[0104] Example 3

[0105] 1) Mixing 20 g of a nano-microsphere lactide raw material (composed of 10 g of a nano-microsphere lactide raw material I and 10 g of a nano-microsphere lactide raw material II), 5 g of sodium borohydride, and 20 g of water, reacting at -5°C for 8 h, and detecting the completion of the reaction using a hydroxyl test paper to obtain a first mixture;

[0106] 2) mixing the first mixture with 15 g of urea and reacting at 10° C. for 8 h to obtain a second mixture;

[0107] 3) The second mixture was mixed with 5 g of potassium perfluorooctane sulfonate, reacted at 60° C. for 4 h, and then washed with water, filtered, and dried at low temperature for purification to obtain a modified nanolactide material as a degradable nanomaterial.

[0108] Example 4

[0109] The degradable nanomaterial was prepared according to the method of Example 1, except that 20 g of water in step 1) was replaced by 10 g of water.

[0110] Example 5

[0111] The degradable nanomaterial was prepared according to the method of Example 1, except that the amount of sodium perfluorononenyloxybenzenesulfonate in step 3) was replaced with 3 g.

[0112] Example 6

[0113] The degradable nanomaterial was prepared according to the method of Example 1, except that the amount of the nano-microsphere lactide raw material I in step 2) was replaced by 20 g and the amount of urea was replaced by 50 g.

[0114] Example 7

[0115] The degradable nanomaterial was prepared according to the method of Example 1, except that the reaction temperature in step 1) was replaced with 10°C.

[0116] Example 8

[0117] The degradable nanomaterial was prepared according to the method of Example 1, except that the reaction temperature in step 2) was replaced with 50°C.

[0118] Example 9

[0119] The degradable nanomaterial was prepared according to the method of Example 1, except that the reaction temperature in step 3) was replaced with 70°C.

[0120] Comparative Example 1

[0121] 30 g of the nano-microsphere lactide raw material I and 7.5 g of sodium perfluorononenyloxybenzenesulfonate were physically mixed, washed with water, filtered, and dried at low temperature to obtain a modified nano-lactide material as a degradable nano-material.

[0122] Comparative Example 2

[0123] 30 g of nano-microsphere lactide raw material I, 7.5 g of sodium borohydride, 60 g of water, 30 g of urea, and 7.5 g of sodium perfluorononenyloxybenzenesulfonate were physically mixed, washed with water, filtered, and dried at low temperature to obtain a modified nano-lactide material as a degradable nanomaterial.

[0124] Comparative Example 3

[0125] 1) Mix 30 g of polyglycolide (purchased from Wuhan Haishan Technology Co., Ltd., with a particle size of 200-250 nm), 7.5 g of sodium borohydride, and 20 g of water, and react in an ice-water bath for 6 h. The reaction is complete using a hydroxyl group test strip to obtain a first mixture;

[0126] 2) mixing the first mixture with 30 g of urea and reacting at 25° C. for 5 h to obtain a second mixture;

[0127] 3) The second mixture was mixed with 7.5 g of sodium perfluorononenyloxybenzenesulfonate, reacted at 50° C. for 6 h, and then washed with water, filtered, and dried at low temperature to purify the modified polylactide material as a degradable nanomaterial.

[0128] Comparative Example 4

[0129] The commercially available fracturing aid SPR-201 (oleylamine polyoxyethylene ether) produced by Dongying Shipurui Petroleum Engineering Technology Co., Ltd. was used as comparative example 4.

[0130] Test Example 1

[0131] The materials prepared in Examples 1 to 9 and Comparative Examples 1 to 3 were tested, as well as the solid phase degradation rates at 90° C. for 1 h, 2 h, 4 h, and 8 h. The results are shown in Table 1.

[0132] Table 1

[0133] Test Example 2

[0134] The materials prepared in Examples 1 to 9 and Comparative Examples 1 to 3, and the fracturing aid in Comparative Example 4 were mixed with liquid polyethylene glycol at a weight ratio of 1:1-3 to obtain a composition. The material prepared in Example 1 was mixed with ethanol at a weight ratio of 35:65 to obtain a composition. The compositions of nano-microsphere lactide raw material I and nano-microsphere lactide raw material II and liquid polyethylene glycol were used as controls to test the initial contact angle, molecular aggregate hydrodynamic particle size D of each composition. 10 、D 50 、D 90 , the results are shown in Table 2.

[0135] Table 2

[0136] Test Example 3

[0137] Step 1) Add 0.65g of acrylamide homopolymer with a weight average molecular weight of 18 million (purchased from Dongying Shipurui Petroleum Engineering Technology Co., Ltd., product model: thickener SPR-08) to 99g of clean water. During the addition process, control the addition speed to prevent the formation of fish eyes, and adjust the speed at all times to ensure a vortex state until it is fully dissolved to form a uniform solution;

[0138] Step 2) While maintaining the stirring state, 0.5 g of the various compositions prepared in Test Example 2, 0.3 g of a zirconium lactate crosslinker (purchased from Dongying Shipurui Petroleum Engineering Technology Co., Ltd., product model crosslinker SPR-18) and 0.05 g of ammonium persulfate were added to the solution obtained in step 1), and the mixture was stirred to obtain a fracturing fluid.

[0139] Test Example 4

[0140] Step 1) Add 0.1 g of acrylamide-acryloyloxyethyltrimethylammonium chloride copolymer (purchased from Dongying Shipurui Petroleum Engineering Technology Co., Ltd., product model: thickener SPR-06) with a weight average molecular weight of 18 million to 99.79 g of clean water. During the addition process, control the addition speed to prevent the formation of fish eyes, and constantly adjust the speed to ensure a vortex state until it is fully dissolved to form a uniform solution;

[0141] Step 2) While maintaining the stirring state, 0.1 g of the composition corresponding to the material obtained in Example 1 and 0.01 g of ammonium persulfate were added to the solution obtained in step 1), and the mixture was stirred to obtain the fracturing fluid.

[0142] Test Example 5

[0143] Step 1) Add 1.2 g of polyacrylamide with a weight average molecular weight of 18 million (purchased from Dongying Shipurui Petroleum Engineering Technology Co., Ltd., product model: thickener SPR-08) to 98.1 g of clean water. During the addition process, control the addition speed to prevent the formation of fish eyes, and adjust the speed at all times to ensure a vortex state until it is fully dissolved to form a uniform solution;

[0144] Step 2) Keep stirring, add 1g of the composition corresponding to the material prepared in Example 1, 0.6g of zirconium lactate crosslinker (purchased from Dongying Shipurui Petroleum Engineering Technology Co., Ltd., product model crosslinker SPR-18) and 0.1g of ammonium persulfate to the solution obtained in step 1), and stir to obtain a fracturing fluid.

[0145] Test Example 6

[0146] The fracturing fluid was prepared according to the method of Test Example 5, except that the amount of the composition corresponding to the material prepared in Example 1 in step 2) was replaced with 1.5 g.

[0147] Comparative test example

[0148] Fracturing fluids were prepared according to the method of Test Example 3, except that 0.5 g of the various compositions prepared in Test Example 2 was added in step 2).

[0149] The fracturing fluid prepared in the comparative test example is used as the original fracturing fluid.

[0150] The fluid loss and fluid loss reduction rate of each fracturing fluid prepared in Test Examples 3 to 6 and the comparative test example were measured, and a permeability recovery rate (flowback efficiency) evaluation experiment was conducted. The results are shown in Table 3.

[0151] Table 3

[0152] The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, various simple variations of the technical solution of the present invention may be made, including combining the various technical features in any other appropriate manner. These simple variations and combinations should also be regarded as disclosed in the present invention and fall within the scope of protection of the present invention.

Claims

1. A degradable nanomaterial, characterized in that: The hydrodynamic particle size D of the molecular aggregate of the degradable nanomaterial in liquid polyethylene glycol with a molecular weight of 380-430 is 10 Less than 30μm, D 50 =50-120μm, D 90 =150-250μm.

2. The degradable nanomaterial according to claim 1, wherein The degradation rate of the degradable nano material at a temperature of 90° C. is 15-30% in 1 hour, 32-50% in 2 hours, 52-70% in 4 hours and more than 95% in 8 hours.

3. The degradable nanomaterial according to claim 1 or 2, wherein: The degradable nanomaterial contains lactide particles and active groups containing fluorine-containing carbon chains adsorbed on the surface of the lactide particles; The hydrodynamic particle size D of the molecular aggregate of the degradable nanomaterial in liquid polyethylene glycol with a molecular weight of 380-430 is 10 =15-25μm, D 50 =60-90μm, D 90 =160-190μm.

4. The degradable nanomaterial according to claim 3, wherein: The content of fluorocarbon chains in the degradable nanomaterial is 2-7% by weight.

5. The degradable nanomaterial according to claim 3, wherein: The lactide particles are C2-C8 lactide, more preferably at least one of glycolide, lactide and butyride; Preferably, the active group of the fluorine-containing carbon chain is a C4-C10 perfluoroalkyl group, a C4-C10 perfluoroalkoxy group, a substituted aromatic group containing a C4-C10 perfluoroalkyl group, or a substituted aromatic group containing a C4-C10 perfluoroalkoxy group; preferably, perfluorononenyloxyphenyl and / or perfluorooctyl group.

6. A method for preparing a degradable nanomaterial, characterized in that: The method comprises the following steps: subjecting a nanometer microsphere lactide raw material to hydroxylation and activation treatment, and then mixing and contacting the raw material with a fluorine-containing carbon chain surfactant.

7. The preparation method according to claim 6, characterized in that The hydroxylation treatment process includes: mixing the nano-microsphere lactide raw material with water in the presence of a reducing agent to perform reaction I; Preferably, the reducing agent is an inorganic reducing agent, more preferably sodium borohydride and / or lithium aluminum hydride; Preferably, the weight ratio of the nano-microsphere lactide raw material, water and reducing agent is 3-5:2-4:1; Preferably, the conditions of the reaction I include: temperature of -5 to 5°C, and time of 4-8 hours.

8. The preparation method according to claim 6 or 7, characterized in that The activation treatment process includes: mixing the hydroxylation product with an activating agent to perform reaction II; Preferably, the activator is a nitrogen-based activator, more preferably urea; Preferably, the weight ratio of the activator to the nano-microsphere lactide raw material is 0.5-1.5:1; Preferably, the conditions of reaction II include: temperature of 10-40° C. and time of 2-8 h.

9. The preparation method according to any one of claims 6 to 8, characterized in that The molar ratio of fluorine element to carbon element in the fluorine-containing carbon chain surfactant is 1-3:1; Preferably, the fluorinated carbon chain surfactant has a fluorinated carbon chain active group, and the fluorinated carbon chain active group is a C4-C10 perfluoroalkyl group or a C4-C10 perfluoroalkoxy group, a substituted aromatic group containing a C4-C10 perfluoroalkyl group, or a substituted aromatic group containing a C4-C10 perfluoroalkoxy group; Preferably, the fluorine-containing carbon chain surfactant is perfluorononenyloxybenzenesulfonate and / or perfluorooctanesulfonate.

10. The preparation method according to any one of claims 6 to 9, characterized in that: The ratio of the nano-microsphere lactide raw material to the fluorine-containing carbon chain surfactant is 2-4:1; The mixing contact conditions include: temperature of 40-60° C. and time of 4-8 hours.

11. The preparation method according to any one of claims 6 to 10, characterized in that: The lactide raw material of the nano-microspheres is C2-C8 lactide, more preferably at least one of glycolide, lactide and butyride.

12. A degradable nanomaterial composition, characterized in that: The composition contains a solvent and the degradable nanomaterial according to any one of claims 1 to 5 or the degradable nanomaterial prepared by the method according to any one of claims 6 to 11.

13. The degradable nanomaterial composition according to claim 12, characterized in that: The content of the degradable nano material in the composition is 25-50% by weight.

14. The degradable nanomaterial composition according to claim 12 or 13, characterized in that: The composition has a fluid loss reduction rate of more than 40% for a fracturing fluid having a composition of 0.65 wt% of a thickener, 0.3 wt% of a cross-linking agent, and 0.05 wt% of a breaker and a fluid loss of 600 mL.

15. The degradable nanomaterial composition according to any one of claims 12 to 14, characterized in that: The solvent is an organic alcohol, preferably liquid polyethylene glycol with a molecular weight of 380-430.

16. Use of the degradable nanomaterial according to any one of claims 1 to 5, the degradable nanomaterial prepared according to the method according to any one of claims 6 to 11, or the degradable nanomaterial composition according to any one of claims 12 to 15 in oil and gas reservoir reconstruction working fluid, preferably as a plugging agent in fracturing fluid.

17. A fracturing fluid comprising the degradable nanomaterial composition according to any one of claims 12 to 15.

18. The fracturing fluid according to claim 17, wherein: Based on the total amount of the fracturing fluid, the content of the degradable nanomaterial composition is 0.1-1% by weight; Preferably, the fracturing fluid further contains, based on the total amount of the fracturing fluid, 0.1-1.2 wt% of a thickener, 0-0.6 wt% of a cross-linking agent, and 0.01-0.1% of a breaker; Preferably, the thickener is an acrylamide homopolymer and / or a copolymer of acrylamide and other monomers, wherein the other monomers are selected from at least one of acryloyloxyethyltrimethylammonium chloride, sodium acrylate, and acrylic acid; further preferably, the copolymer of acrylamide and other monomers is at least one of acrylamide-acryloyloxyethyltrimethylammonium chloride copolymer, acrylamide-sodium acrylate-acrylic acid copolymer, and acrylamide-acryloyloxyethyltrimethylammonium chloride-sodium acrylate-acrylic acid copolymer; Preferably, the cross-linking agent is an organic zirconium cross-linking agent, and the breaker is a persulfate.

Images