Salt-tolerant anti-swelling and anti-slipping water and application thereof

Abstract

The application belongs to the technical field of oil and gas field hydraulic fracturing, and particularly provides a salt-tolerant anti-swelling slick water and application thereof. The slick water of the application is obtained by directly dissolving different concentrations of resistance reducing agents in water, and is a self-contained system. The application solves the problems of on-site rapid liquid preparation and real-time viscosity variation of the slick water system, and achieves the purposes of saving fresh water resources and environmental protection by directly preparing liquid with high salinity formation water or flowback fluid. Meanwhile, the system has anti-swelling performance, and does not need to add anti-swelling agents, thereby simplifying the formula and reducing the cost.

Description

Technical Field

[0001] This invention relates to the field of hydraulic fracturing technology in oil and gas fields, specifically to a salt-resistant, anti-swelling, and slippery surface and its application. Background Technology

[0002] With the depletion of conventional oil and gas resources, low-pressure, low-permeability unconventional oil and gas resources have become a key area and hot resource for exploration and development. Currently, unconventional oil and gas extraction mainly employs multi-stage, multi-cluster close-cut volumetric fracturing technology. This technology requires high-flow-rate pumping of low-friction fracturing fluid systems in the early stages to achieve large-scale fracture creation, followed by the use of high-viscosity gel fluid carrying a large amount of proppant to fill the fractures and ensure their long-term conductivity. Therefore, achieving continuous mixing and real-time viscosity reduction of the slickwater system at the fracturing site, directly transitioning from the slickwater system to a proppant-carrying gel fluid system, can ensure the smooth implementation of close-cut volumetric fracturing technology and also solve the inconvenience caused by limited space at mountainous construction sites. The fracturing fluid used in a single layer of this technology typically exceeds 2000 m³. 3 Construction discharge volume is usually greater than 10m³. 3 The construction scale of the project consumed precious freshwater resources excessively, significantly increasing construction costs and consequences.

[0003] In addition, current slickwater systems mainly rely on additives such as anti-swelling agents to suppress clay swelling, which has drawbacks such as difficulty in ensuring compatibility, complex solution preparation, and high cost. Furthermore, powdered drag-reducing agents have poor solubility, making it difficult to achieve online mixing, and common emulsion drag-reducing agents generally contain an oil phase, which is expensive and causes significant damage to the reservoir.

[0004] Therefore, in the current fracturing technology for unconventional oil and gas reservoirs, the main problems that need to be solved for the slickwater system include: (1) rapid on-site fluid preparation and real-time viscosity adjustment to ensure construction needs; (2) direct preparation of high-salinity formation water or flowback fluid to avoid large-scale use of freshwater resources. Direct preparation of high-salinity formation water or flowback fluid can save freshwater resources and avoid pollution of the natural environment by the discharge of formation flowback fluid; (3) drag-reducing agents have multiple effects, simplifying the formula and reducing costs and increasing efficiency; (4) water-in-water emulsion fracturing fluid can be mixed online and does not contain oil phase, protecting the reservoir. Summary of the Invention

[0005] This invention addresses the shortcomings of current slickwater systems by providing a salt-resistant and anti-swelling slickwater that enables rapid on-site preparation and real-time viscosity adjustment. It allows for the use of high-mineralization on-site water or backflow water for preparation, saving freshwater resources. It also provides anti-swelling effects, simplifying the formulation, reducing costs and increasing efficiency. Furthermore, it uses a water-in-water emulsion without an oil phase, effectively addressing environmental protection objectives.

[0006] To solve the above-mentioned technical problems, the first aspect of the present invention provides a salt-resistant, anti-swelling, and anti-slip water-reducing agent, comprising a drag-reducing agent, wherein the drag-reducing agent is an aqueous dispersion of polyacrylamide; the synthesis method of the aqueous dispersion of polyacrylamide comprises reacting a reaction system of acrylamide I, cationic monomer I, inorganic salt, stabilizer and initiator I to obtain the aqueous dispersion of polyacrylamide; wherein the stabilizer is a binary mixture of a cationic copolymer containing polyacrylamide segments and polyoxyethylene.

[0007] According to some embodiments of the present invention, based on the total mass of the salt-resistant, anti-swelling, and anti-slipping agent as 100%, the mass percentage of the drag-reducing agent is 0.1% to 6.7%, and the remainder is water.

[0008] According to some embodiments of the present invention, the mass ratio of acrylamide I, cationic monomer I, inorganic salt and stabilizer is 36:(4.32-5.76); 10:(270-275).

[0009] According to some embodiments of the present invention, the amount of initiator I added is 0.1% to 0.5% of the mass of acrylamide I.

[0010] According to some embodiments of the present invention, the cationic monomer I is selected from one or more of acryloyloxyethyltrimethylammonium chloride, methacryloyloxyethyltrimethylammonium chloride, dimethyldiallylammonium chloride, acryloyloxyethyldimethylbenzylammonium chloride, methacryloyloxyethyldimethylbenzylammonium chloride, and 2-acrylamido-2-methylpropyltrimethylammonium chloride.

[0011] According to some embodiments of the present invention, the inorganic salt is selected from ammonium salts; preferably, the ammonium salt is selected from at least one of ammonium sulfate and ammonium persulfate.

[0012] According to some embodiments of the present invention, the initiator I is selected from aqueous initiator I and / or thermal initiator I; preferably, the aqueous initiator I is selected from at least one of V-50 and VA-044; the thermal initiator I is selected from at least two of ammonium persulfate, sodium bisulfite, and potassium persulfate.

[0013] According to some embodiments of the present invention, the conditions for reaction I include: a temperature of 25°C to 45°C and a time of 1 hour to 6 hours.

[0014] According to some embodiments of the present invention, the preparation of the stabilizer includes: mixing cationic monomer II, acrylamide II, and polyoxyethylene in water to obtain a mixed solution under the conditions of initiator II and inactive atmosphere, and reacting II to obtain the stabilizer.

[0015] In this invention, polyoxyethylene does not participate in the polymerization reaction during the preparation of the stabilizer. That is, the cationic copolymer and polyoxyethylene do not react with each other in the binary mixture containing the cationic copolymer of polyacrylamide segments. The role of polyoxyethylene is to stabilize the cationic copolymer.

[0016] According to some embodiments of the present invention, the mass ratio of the cationic monomer II, acrylamide II, polyoxyethylene and water is 72:60:(30-100):(160-260).

[0017] According to some embodiments of the present invention, the amount of initiator II added is 0.1% to 0.5% of the mass of cationic monomer II.

[0018] According to some embodiments of the present invention, the cationic monomer II is selected from one or more of acryloyloxyethyltrimethylammonium chloride, methacryloyloxyethyltrimethylammonium chloride, dimethyldiallylammonium chloride, acryloyloxyethyldimethylbenzylammonium chloride, methacryloyloxyethyldimethylbenzylammonium chloride, and 2-acrylamido-2-methylpropyltrimethylammonium chloride.

[0019] According to some embodiments of the present invention, the polyoxyethylene is selected from polyoxyethylene with or without end capping; preferably, the molecular weight of the polyoxyethylene is 2000 Da to 200000 Da; more preferably, the polyoxyethylene with end capping includes single-end capped polyoxyethylene and double-end capped polyoxyethylene; even more preferably, the single-end capped polyoxyethylene is selected from polyoxyethylene monomethyl ether; the double-end capped polyoxyethylene is selected from polyoxyethylene dimethyl ether; and the polyoxyethylene without end capping is polyethylene glycol.

[0020] According to some embodiments of the present invention, the initiator II is selected from aqueous initiator II and / or thermal initiator II; preferably, the aqueous initiator II is selected from at least one of V-50 and VA-044; the thermal initiator II is selected from at least two of ammonium persulfate, sodium bisulfite, and potassium persulfate.

[0021] According to some embodiments of the present invention, the non-active atmosphere is selected from at least one of nitrogen and argon.

[0022] According to some embodiments of the present invention, the conditions for reaction II include: a temperature of 30°C to 80°C and a reaction time of 5 hours to 10 hours.

[0023] According to some embodiments of the present invention, the reaction II is further followed by dilution; preferably, the stabilizer is cooled to room temperature, and then a certain amount of water is added to dilute the stabilizer to a mass concentration of 5wt% to 10wt%, to obtain an aqueous solution of a binary mixture containing a cationic copolymer of polyacrylamide segments and polyoxyethylene.

[0024] The second aspect of this invention provides the application of the above-mentioned salt-resistant, anti-swelling, and slippery water-cooling method in hydraulic fracturing in oil and gas fields.

[0025] Beneficial effects:

[0026] This invention provides a salt-resistant and anti-swelling slippery water system. The system has a simple formulation, and the drag-reducing agent (aqueous polyacrylamide dispersion) has both drag-reducing and anti-swelling functions. It can be completely dissolved in brine or backflow solution with a mineralization of 0 to 300,000 mg / L within 5 to 30 seconds. The drag reduction rate can reach more than 71% in the laboratory and more than 85% in the field.

[0027] This invention can simultaneously achieve real-time viscosity adjustment of the slickwater system by changing the amount of drag-reducing agent (aqueous polyacrylamide dispersion). An addition of 0.1%–1.0% produces a low-viscosity slickwater system with a viscosity of 1 mPa·s–10 mPa·s; an addition of 1.0%–2.0% produces a medium-viscosity slickwater system with a viscosity of 10 mPa·s–25 mPa·s; and an addition of more than 2.0% produces a high-viscosity slickwater system with a rapidly increasing viscosity, suitable for use as an adhesive. The slickwater system exhibits good temperature and shear resistance at 120°C. In the laboratory, using saline solution with a mineralization of 300,000 mg / L, the viscosity of the slickwater showed almost no decrease compared to the solution prepared with clean water. In the field, high-mineralization backflow solution was continuously mixed with the drag-reducing agent described in this invention, resulting in real-time viscosity adjustment after crack formation, allowing sand to enter the crack with a sand addition compliance rate as high as 97%.

[0028] This invention solves the problems of rapid on-site preparation and real-time viscosity change required for slickwater systems. It also enables the direct preparation of solutions using high-mineralization formation water or flowback fluid, thereby saving freshwater resources and protecting the environment. Furthermore, with an addition amount of ≥1.0%, the anti-swelling rate of the slickwater system is greater than or equal to 75%, meeting the on-site anti-swelling requirements. This invention simplifies the formulation and reduces costs while increasing efficiency. Attached Figure Description

[0029] Figure 1 The apparent viscosity of slippery water of different concentrations prepared from clean water and 300,000 mg / L saline solution varies with the amount added.

[0030] Figure 2 Different concentrations of slick water systems prepared for use with clean water were tested at 120℃ for 170 seconds. -1 Rheological test results under shear conditions.

[0031] Figure 3 Different concentrations of slickwater systems prepared for 300,000 mg / L saline solution were tested at 120℃ for 170 seconds. -1 Rheological test results under shear conditions.

[0032] Figure 4 This is a construction curve for a section of a well on a shale gas platform that features ultra-salt tolerance and anti-swelling properties in slickwater.

[0033] Figure 5 Construction curve of a section of a well on a shale gas platform with ultra-salt-resistant and anti-swelling properties in slickwater. Detailed Implementation

[0034] The present invention will be further described below with reference to embodiments. However, the present invention is not limited to these embodiments.

[0035] Unless otherwise specified, the three-necked flasks and three-necked bottles used in the embodiments of this invention are all commercially available products.

[0036] Unless otherwise specified, the methacryloyloxyethyltrimethylammonium chloride, acryloyloxyethyltrimethylammonium chloride, acrylamide, polyethylene glycol, VA-044 initiator, ammonium sulfate, ammonium persulfate, and sodium bisulfite in this invention are all commercially available reagents.

[0037] Unless otherwise specified, the room temperature mentioned in the embodiments of the present invention is 25°C.

[0038] Preparation Example 1

[0039] This preparation example provides a binary mixture containing a cationic copolymer and polyoxyethylene.

[0040] In a three-necked flask, 60g of an 80% aqueous solution of methacryloyloxyethyltrimethylammonium chloride, 30g of an 80% aqueous solution of acryloyloxyethyltrimethylammonium chloride, 60g of acrylamide, 30g of polyethylene glycol (PEG20000, molecular weight 20000 Da), 0.10g of VA-044 initiator, and 160g of water were added sequentially. After degassing and deoxygenation, nitrogen gas was introduced, and the reaction was carried out at 45℃ for 7 hours. Then, the mixture was cooled to room temperature, and 2900g of water was added to dilute it into a 5% aqueous solution containing a mixture of cationic copolymer and polyoxyethylene, i.e., stabilizer A1.

[0041] This preparation example further provides an aqueous dispersion of polyacrylamide.

[0042] At room temperature, 36g of acrylamide, 5.4g of 80% aqueous solution of methacryloyloxyethyltrimethylammonium chloride, 270g of the above stabilizer A1 (a 5% aqueous solution containing a cationic copolymer and a binary mixture of polyoxyethylene) and 10g of ammonium sulfate were added to a three-necked flask equipped with a stirrer. The mixture was stirred until all the additives were completely dissolved. Then, after degassing and deoxygenation, nitrogen gas was introduced and the temperature was raised to 45°C. 1mL of degassed and deoxygenated VA-044 aqueous solution (the concentration of VA-044 aqueous solution was 40mg / mL) was added, and the reaction was continued for 6 hours. The heating source was removed, and the reaction was stopped to obtain polyacrylamide aqueous dispersion B1.

[0043] Preparation Example 2

[0044] This preparation example provides a binary mixture containing a cationic copolymer and polyoxyethylene.

[0045] In a three-necked flask, 60g of an 80% aqueous solution of methacryloyloxyethyltrimethylammonium chloride, 30g of an 80% aqueous solution of acryloyloxyethyltrimethylammonium chloride, 60g of acrylamide, 30g of polyethylene glycol (PEG20000, molecular weight 20000 Da), 0.10g of VA-044 initiator, and 160g of water were added sequentially. After degassing and deoxygenation, nitrogen gas was introduced, and the reaction was carried out at 45℃ for 7 hours. After cooling to room temperature, 2900g of water was added to dilute the solution into a 5% aqueous solution containing a binary mixture of cationic copolymer and polyoxyethylene, i.e., stabilizer A1.

[0046] This preparation example further provides an aqueous dispersion of polyacrylamide.

[0047] At room temperature, 36 g of acrylamide, 5.4 g of 80% aqueous solution of methacryloyloxyethyltrimethylammonium chloride, 270 g of stabilizer A1 (a 5% aqueous solution containing a cationic copolymer and a binary mixture of polyoxyethylene) and 10 g of ammonium sulfate were added to a three-necked flask equipped with a stirrer. The mixture was stirred until all the added substances were completely dissolved. Then, after degassing and deoxygenation, nitrogen gas was introduced, and the temperature was raised to 30°C. 0.60 mL of degassed and deoxygenated aqueous solution of ammonium persulfate (concentration of ammonium persulfate was 40 mg / mL) and 0.40 mL of aqueous solution of sodium bisulfite (concentration of sodium bisulfite was 40 mg / mL) were added respectively. The reaction was continued for 6 hours, the heating source was removed, and the reaction was stopped to obtain aqueous dispersion of polyacrylamide B2.

[0048] Preparation Example 3

[0049] This preparation example provides a binary mixture containing a cationic copolymer and polyoxyethylene.

[0050] In a three-necked flask, 90g of an 80% aqueous solution of methacryloyloxyethyltrimethylammonium chloride, 60g of acrylamide, 100g of polyethylene glycol (PEG20000, molecular weight 20000 Da), 0.10g of VA-044 initiator, and 260g of water were added sequentially. After degassing and deoxygenation, nitrogen gas was introduced, and the mixture was reacted at 45°C for 7 hours. After cooling to room temperature, 4130g of water was added to dilute the mixture into a 5% aqueous solution containing a binary mixture of cationic copolymer and polyoxyethylene, i.e., stabilizer A2.

[0051] This preparation example further provides an aqueous dispersion of polyacrylamide.

[0052] At room temperature, 36 g of acrylamide, 5.4 g of 80% aqueous solution of methacryloyloxyethyltrimethylammonium chloride, 270 g of stabilizer A2 (a 5% aqueous solution containing a cationic copolymer and a binary mixture of polyoxyethylene) and 10 g of ammonium sulfate were added to a three-necked flask equipped with a stirrer. The mixture was stirred until all the additives were completely dissolved. Then, after degassing and deoxygenation, nitrogen gas was introduced, and the temperature was raised to 45°C. 1 mL of degassed and deoxygenated VA-044 aqueous solution (the concentration of VA-044 aqueous solution was 40 mg / mL) was added, and the reaction was continued for 6 hours. The heating source was removed, and the reaction was stopped to obtain polyacrylamide aqueous dispersion B3.

[0053] Preparation Example 4

[0054] This preparation example provides a binary mixture containing a cationic copolymer and polyoxyethylene.

[0055] In a three-necked flask, 90g of an 80% aqueous solution of methacryloyloxyethyltrimethylammonium chloride, 60g of acrylamide, 100g of polyethylene glycol (PEG20000, molecular weight 20000 Da), 0.10g of VA-044 initiator, and 260g of water were added sequentially. After degassing and deoxygenation, nitrogen gas was introduced, and the mixture was reacted at 45°C for 7 hours. After cooling to room temperature, 4130g of water was added to dilute the mixture into a 5% aqueous solution containing a binary mixture of cationic copolymer and polyoxyethylene, i.e., stabilizer A2.

[0056] This preparation example further provides an aqueous dispersion of polyacrylamide.

[0057] At room temperature, 36 g of acrylamide, 7.2 g of 80% aqueous solution of methacryloyloxyethyltrimethylammonium chloride, 275 g of stabilizer A2 (a 5% aqueous solution containing a cationic copolymer and a binary mixture of polyoxyethylene) and 10 g of ammonium sulfate were added to a three-necked flask equipped with a stirrer. The mixture was stirred until all the added substances were completely dissolved. Then, after degassing and deoxygenation, nitrogen gas was introduced, and the temperature was raised to 30°C. 0.60 mL of degassed aqueous solution of ammonium persulfate (concentration of ammonium persulfate was 40 mg / mL) and 0.40 mL of aqueous solution of sodium bisulfite (concentration of sodium bisulfite was 40 mg / mL) were added respectively. The reaction was continued for 6 hours, the heating source was removed, and the reaction was stopped to obtain aqueous dispersion of polyacrylamide B4.

[0058] Preparation Example 5

[0059] This preparation example provides a binary mixture containing a cationic copolymer and polyoxyethylene.

[0060] In a three-necked flask, 90g of an 80% aqueous solution of methacryloyloxyethyltrimethylammonium chloride, 60g of acrylamide, 200g of polyethylene glycol (PEG20000, molecular weight 20000 Da), 0.10g of VA-044 initiator, and 260g of water were added sequentially. After degassing and deoxygenation, nitrogen gas was introduced, and the reaction was carried out at 45°C for 7 hours. After cooling to room temperature, 6362g of water was added to dilute the solution into a 5% aqueous solution containing a mixture of cationic copolymer and polyoxyethylene, i.e., stabilizer A3.

[0061] This preparation example further provides an aqueous dispersion of polyacrylamide.

[0062] At room temperature, 36 g of acrylamide, 5.4 g of 80% aqueous solution of methacryloyloxyethyltrimethylammonium chloride, 270 g of stabilizer A3 (a 5% aqueous solution containing a cationic copolymer and a binary mixture of polyoxyethylene) and 10 g of ammonium sulfate were added to a three-necked flask equipped with a stirrer. The mixture was stirred until all the additives were completely dissolved. Then, after degassing and deoxygenation, nitrogen gas was introduced, and the temperature was raised to 45°C. 1 mL of degassed and deoxygenated VA-044 aqueous solution (the concentration of VA-044 aqueous solution was 40 mg / mL) was added, and the reaction was continued for 6 hours. The heating source was removed, and the reaction was stopped to obtain polyacrylamide aqueous dispersion B5.

[0063] Preparation Example 6

[0064] This preparation example provides a binary mixture containing a cationic copolymer and polyoxyethylene.

[0065] In a three-necked flask, 90g of an 80% aqueous solution of methacryloyloxyethyltrimethylammonium chloride, 60g of acrylamide, 200g of polyethylene glycol (PEG20000, molecular weight 20000 Da), 0.10g of VA-044 initiator, and 260g of water were added sequentially. After degassing and deoxygenation, nitrogen gas was introduced, and the reaction was carried out at 45°C for 7 hours. After cooling to room temperature, 6362g of water was added to dilute the solution into a 5% aqueous solution containing a mixture of cationic copolymer and polyoxyethylene, i.e., stabilizer A3.

[0066] This preparation example further provides an aqueous dispersion of polyacrylamide.

[0067] At room temperature, 36 g of acrylamide, 7.2 g of 80% aqueous solution of methacryloyloxyethyltrimethylammonium chloride, 275 g of stabilizer A3 (a 5% aqueous solution containing a cationic copolymer and a binary mixture of polyoxyethylene) and 10 g of ammonium sulfate were added to a three-necked flask equipped with a stirrer. The mixture was stirred until all the added substances were completely dissolved. Then, after degassing and deoxygenation, nitrogen gas was introduced, and the temperature was raised to 30°C. 0.60 mL of degassed aqueous solution of ammonium persulfate (concentration of ammonium persulfate was 40 mg / mL) and 0.40 mL of aqueous solution of sodium bisulfite (concentration of sodium bisulfite was 40 mg / mL) were added respectively. The reaction was continued for 6 hours, the heating source was removed, and the reaction was stopped to obtain aqueous dispersion of polyacrylamide B6.

[0068] Comparative Preparation Example 1

[0069] This comparative preparation example provides a cationic copolymer.

[0070] The preparation was carried out according to the method described in Example 2, except that PEG20000 was not added to the raw materials; the details are as follows:

[0071] In a three-necked flask, 90g of an 80% aqueous solution of methacryloyloxyethyltrimethylammonium chloride, 60g of acrylamide, 0.10g of VA-044 initiator, and 160g of water were added sequentially. After degassing and deoxygenation, nitrogen gas was introduced, and the reaction was carried out at 45°C for 7 hours. After cooling to room temperature, 2330g of water was added to dilute the solution into an aqueous solution of a 5% cationic copolymer, i.e., stabilizer A4.

[0072] This comparative preparation example further provides an aqueous dispersion of polyacrylamide.

[0073] At room temperature, 36 g of acrylamide, 5.4 g of 80% aqueous solution of methacryloyloxyethyltrimethylammonium chloride, 270 g of stabilizer A4 (5% aqueous solution of cationic copolymer) and 10 g of ammonium sulfate were added to a three-necked flask equipped with a stirrer. The mixture was stirred until all the additives were completely dissolved. Then, after degassing and deoxygenation, nitrogen gas was introduced and the temperature was raised to 45°C. 1 mL of degassed and deoxygenated VA-044 aqueous solution (concentration of VA-044 aqueous solution was 40 mg / mL) was added, and the reaction was continued for 6 hours. The heating source was removed, and the reaction was stopped to obtain polyacrylamide aqueous dispersion B7.

[0074] Comparative Preparation Example 2

[0075] This comparative preparation example provides a cationic copolymer.

[0076] The preparation was carried out according to the method described in Example 2, except that PEG20000 was not added to the raw materials; the details are as follows:

[0077] In a three-necked flask, 90g of an 80% aqueous solution of methacryloyloxyethyltrimethylammonium chloride, 60g of acrylamide, 0.10g of VA-044 initiator, and 160g of water were added sequentially. After degassing and deoxygenation, nitrogen gas was introduced, and the reaction was carried out at 45°C for 7 hours. After cooling to room temperature, 2330g of water was added to dilute the solution into a 5% aqueous solution of the cationic copolymer, i.e., stabilizer A4.

[0078] This comparative preparation example further provides an aqueous dispersion of polyacrylamide.

[0079] At room temperature, 36 g of acrylamide, 7.2 g of 80% aqueous solution of methacryloyloxyethyltrimethylammonium chloride, 280 g of stabilizer A4 (5% aqueous solution of cationic copolymer), and 10 g of ammonium sulfate were added to a three-necked flask equipped with a stirrer. The mixture was stirred until all the additives were completely dissolved. Then, after degassing and deoxygenation, nitrogen gas was introduced, and the temperature was raised to 30°C. 0.60 mL of degassed and deoxygenated aqueous solution of ammonium persulfate (concentration of ammonium persulfate was 40 mg / mL) and 0.40 mL of aqueous solution of sodium bisulfite (concentration of sodium bisulfite was 40 mg / mL) were added respectively. The reaction was continued for 6 hours, the heating source was removed, and the reaction was stopped to obtain aqueous dispersion B8 of polyacrylamide.

[0080] Comparative preparation example 3

[0081] In this comparative preparation example, a 5% (w / w) aqueous solution of polyoxyethylene (PEG20000) was used as stabilizer A5.

[0082] This comparative preparation example further provides an aqueous dispersion of polyacrylamide.

[0083] At room temperature, 36 g of acrylamide, 5.4 g of 80% aqueous solution of methacryloyloxyethyltrimethylammonium chloride, 270 g of stabilizer A5 (5% aqueous solution of polyoxyethylene), and 10 g of ammonium sulfate were added to a three-necked flask equipped with a stirrer. The mixture was stirred until all the additives were completely dissolved. Then, after degassing and deoxygenation, nitrogen gas was introduced, and the temperature was raised to 45°C. 1 mL of degassed and deoxygenated VA-044 aqueous solution (concentration of VA-044 aqueous solution was 40 mg / mL) was added, and the reaction was continued for 6 hours. The heating source was removed, and the reaction was stopped to obtain polyacrylamide aqueous dispersion B9.

[0084] Test (I) Stabilizer Parameters

[0085] The basic parameters of stabilizers A1-A3 prepared in Examples 1-6 of this invention are shown in Table 1.

[0086] In Preparation Examples 1-6, the binary mixtures containing cationic copolymers and polyethylene oxide, namely stabilizers A1, A2, and A3, were prepared and used. The weight ratio of cationic copolymers to polyethylene oxide varied. In A1, the ratio was 4.4 / 1 ((mass of cationic monomer II in the raw material + mass of acrylamide) / mass of PEG20000), indicating that the cationic copolymer was the main component. In A2, the content of polyethylene oxide increased, and the ratio was 1.3 / 1. In A3, the content of polyethylene oxide further increased, and the ratio was 0.66 / 1, indicating that PEG20000 was the main component.

[0087] Comparative preparation examples 1-3 show the preparation and use of a single cationic copolymer aqueous solution or PEG20000 aqueous solution as a stabilizer.

[0088] In Table 1, the appearance, solid content, and viscosity of stabilizers A1-A3 were tested in accordance with GB / T 11175-2002.

[0089] The viscosity testing instrument was a Brookfield DV1 viscometer, and the viscosity was measured directly at a temperature of 25°C.

[0090] Table 1. Comparison of basic parameters of the stabilizers prepared in Preparation Examples 1-6 and the stabilizers described in Comparative Preparation Examples 1-2

[0091]

[0092] In Table 1, the PEG content (taking Example 1 as an example) is: 30g / (60g+30g+60g+30g+160g+2900g)×100%=0.92%.

[0093] The results in Table 1 show that, compared with the cationic copolymer stabilizer A4 prepared in Comparative Preparation Example 1-2, the stabilizers A1, A2, and A3 prepared in Preparation Examples 1-6 have slightly lower viscosity due to the presence of the nonionic polymer PEG. The viscosity of stabilizers A1, A2, and A3 prepared in Preparation Examples 1-6 decreases with increasing PEG20000 content.

[0094] Test (II) Parameters of Aqueous Polyacrylamide Dispersion

[0095] The basic parameters of the polyacrylamide aqueous dispersions prepared in Examples 1-6 and Comparative Examples 1-3 of this invention are shown in Table 2.

[0096] The polymer concentration measurement method is as follows: the weight of C1 of the polyacrylamide aqueous dispersion is diluted with water to a concentration of 1% of the polyacrylamide aqueous dispersion, placed in a dialysis bag (molecular weight cutoff: 1000 Da) and dialyzed in water for three days. Then the sample is freeze-dried to obtain the weight of the dried sample C2. The polymer concentration is the percentage of the ratio of C2 to C1.

[0097] The apparent viscosity is the viscosity of the polyacrylamide aqueous dispersions prepared in Preparation Examples 1-6 and Comparative Preparation Examples 1-3, which are tested directly without dilution with water; the viscosity of the polymer solution with a mass concentration of 1% refers to the viscosity of the solution when the polyacrylamide aqueous dispersion is diluted with water to a mass concentration of 1% for polyacrylamide and its copolymers.

[0098] Among them, the stability of the polyacrylamide aqueous dispersions prepared in Examples 1-6 and Comparative Examples 1-3 at room temperature was determined by visual observation. If the dispersion did not separate into layers, it was considered stable; if it separated into layers, it was considered unstable.

[0099] Freeze-thaw stability: 50 mL of polyacrylamide dispersion was placed in a low-temperature chamber at -5±2℃. After 18 hours, it was taken out and placed at 23±2℃ for 6 hours. The operation was repeated to observe whether there was any precipitation.

[0100] Table 2. Parameters of the polyacrylamide aqueous dispersions described in Examples 1-6 and Comparative Examples 1-3 of this invention.

[0101]

[0102]

[0103] The results in Table 2 show that the aqueous polyacrylamide dispersions prepared in Examples 1-6 have suitable apparent viscosity and high viscosity of a 1% polymer solution, with stability exceeding 6 months, even reaching 1 year. In contrast, the aqueous polyacrylamide dispersions prepared in Examples 1-3 have significantly lower viscosity of a 1% polymer solution, and their stability is less than 1 month. This indicates that the present invention, using cationic copolymers and polyoxyethylene binary polymers as stabilizers in dispersion polymerization, is an effective method for preparing highly stable, high-viscosity aqueous polyacrylamide dispersions.

[0104] Example 1

[0105] This embodiment provides a salt-resistant, anti-swelling, and slippery water-resistant solution.

[0106] Based on a total mass of 100% for salt-resistant, anti-swelling, and slippery materials, the mass percentage of drag-reducing agent (the aqueous dispersion of polyacrylamide prepared in Preparation Example 2) is 1.0%, with the remainder being water.

[0107] Example 2

[0108] This embodiment provides a salt-resistant, anti-swelling, and slippery water-resistant solution.

[0109] Based on a total mass of 100% for salt-resistant, anti-swelling, and slippery materials, the drag-reducing agent (the aqueous dispersion of polyacrylamide prepared in Preparation Example 2) has a mass percentage of 2.0%, with the remainder being water.

[0110] Example 3

[0111] This embodiment provides a salt-resistant, anti-swelling, and slippery water-resistant solution.

[0112] Based on a total mass of 100% for salt-resistant, anti-swelling, and slippery materials, the mass percentage of drag-reducing agent (the aqueous dispersion of polyacrylamide prepared in Preparation Example 2) is 3.0%, with the remainder being water.

[0113] Example 4

[0114] This embodiment provides a salt-resistant, anti-swelling, and slippery water-resistant solution.

[0115] Based on a total mass of 100% for salt-resistant, anti-swelling, and slippery materials, the drag-reducing agent (the aqueous dispersion of polyacrylamide prepared in Preparation Example 2) has a mass percentage of 4.0%, with the remainder being water.

[0116] Example 5

[0117] This embodiment provides a salt-resistant, anti-swelling, and slippery water-resistant solution.

[0118] Based on a total mass of 100% for salt-resistant, anti-swelling, and slippery materials, the drag-reducing agent (the aqueous dispersion of polyacrylamide prepared in Preparation Example 2) has a mass percentage of 5.0%, with the remainder being water.

[0119] Example 6

[0120] This embodiment provides a salt-resistant, anti-swelling, and slippery water-resistant solution.

[0121] Based on a total mass of 100% for salt-resistant, anti-swelling, and slippery materials, the drag-reducing agent (the aqueous dispersion of polyacrylamide prepared in Preparation Example 2) has a mass percentage of 0.1%, with the remainder being water.

[0122] Comparative Example 1

[0123] This comparative example provides a slippery water.

[0124] Based on a total mass of 100% for salt-resistant, anti-swelling, and slippery materials, the mass percentage of conventional drag-reducing agent (SFFRE-3, an integrated emulsion drag-reducing agent independently developed by the Sinopec Petroleum Engineering Technology Research Institute) is 1.0%, with the remainder being water.

[0125] To further illustrate the advancements of the salt-resistant and anti-swelling slipper prepared in Examples 1-6 of this invention, performance tests were conducted on the salt-resistant and anti-swelling slipper prepared in Examples 1-6 and the slipper prepared in Comparative Example 1. The results are summarized in Table 3. The anti-swelling rate evaluation method was performed according to the standard SY / T 5971-2016, "Performance Evaluation Method of Clay Stabilizer for Fracturing, Acidizing and Water Injection in Oil and Gas Fields".

[0126] Table 3

[0127]

[0128]

[0129] In Table 3 above, the anti-swelling rate (B) is calculated using the following formula:

[0130] Where B is the swelling rate, expressed as a percentage; V0 is the volume of bentonite after swelling in kerosene, in milliliters (mL); V1 is the volume of bentonite after swelling in slickwater, in milliliters (mL); and V2 is the volume of bentonite after swelling in distilled water, in milliliters (mL).

[0131] Application Example 1:

[0132] In this application example, temperature-resistant, anti-swelling slippery water containing different concentrations (0.1%–5.0%) of drag-reducing agent (the polyacrylamide aqueous dispersion prepared in Preparation Example 2) was prepared using clean water and brine with a mineralization of 300,000 mg / L. No anti-swelling agent was added. The viscosity change was tested and shown in [the table below]. Figure 1 ;

[0133] The test results are as follows: When the amount of drag-reducing agent (aqueous polyacrylamide dispersion prepared in Preparation Example 2) is in the range of 0.1% to 1.0%, it belongs to a low-viscosity slickwater system and can be used as a slickwater system for high-volume close-cutting fracture creation in shale gas reservoirs and tight gas reservoirs; when the amount of drag-reducing agent (aqueous polyacrylamide dispersion prepared in Preparation Example 2) is increased to the range of 1.0% to 2.0%, it belongs to a medium-viscosity slickwater system and is suitable for sand carrying operations; when the amount of drag-reducing agent (aqueous polyacrylamide dispersion prepared in Preparation Example 2) is increased to more than 2.0%, the apparent viscosity of the slickwater system increases significantly, and it belongs to a high-viscosity slickwater system, which can be used as a glue-to-sand mixture.

[0134] Depend on Figure 1 It can also be seen that the temperature-resistant, anti-swelling, and slippery water prepared with brine of 300,000 mg / L maintains the same viscosity as the temperature-resistant, anti-swelling, and slippery water prepared with clean water, indicating that it has good salt resistance and meets the needs of on-site backflow preparation.

[0135] In this application example, clean water and brine with a mineralization of 300,000 mg / L were used to prepare temperature-resistant, anti-swelling, and slippery water containing different concentrations (0.1%–5.0%) of drag-reducing agent (the aqueous dispersion of polyacrylamide prepared in Preparation Example 2). The temperature resistance and shear resistance of this temperature-resistant, anti-swelling, and slippery water system were tested using a high-temperature, high-pressure rotational rheometer. The test temperature was maintained at 120°C and the shear rate at 170 s. -1 Shearing for 2 hours; test results are shown below. Figure 2 , Figure 3 ;

[0136] Figure 2 , Figure 3 The results show that both water-based and salt-based heat-resistant, anti-swelling, and slippery water-repellent systems can withstand temperatures up to 120℃ and 170 seconds. -1 Under the condition of shearing for 2 hours, the viscosity is maintained above 50 mPa·s, demonstrating that the temperature-resistant and anti-swelling slipper can maintain good sand-carrying capacity in high-temperature reservoirs at 120℃.

[0137] Application Example 2:

[0138] This application example uses the salt-resistant, swelling-resistant, and slip-resistant fracturing material prepared according to this invention for hydraulic fracturing operations. The construction curve is shown in [Figure 1]. Figure 4 The specific operation is as follows: In this application example, the salt-resistant and anti-swelling slippery water prepared by the present invention is used to mix and prepare a variable viscosity slippery water system in a well of a shale gas platform in the Sichuan-Chongqing area. The water used for preparing the solution is a flowback fluid with a total mineralization of 38475 mg / L.

[0139] In this application example, during fracturing operations in a certain section of the well, hydrochloric acid acidification was used from the start of fracturing until 50 minutes. From 55 minutes onwards, high-viscosity slickwater was used for fracturing, and the drag-reducing agent (aqueous polyacrylamide dispersion prepared in Preparation Example 2) was added at a dosage of 5%. Up to 75 minutes, 148m of the gel solution was used.3 Then, low-viscosity slickwater was used, with a drag-reducing agent (the aqueous dispersion of polyacrylamide prepared in Preparation Example 2) added at a rate of 0.6%, and the process was continued for 165 minutes. The amount of low-viscosity slickwater used was 1352 mg / L. 3 Subsequently, the drag-reducing agent (the aqueous dispersion of polyacrylamide prepared in Preparation Example 2) in the slick water was increased to 2.0% to form a medium-viscosity slick water, and this process continued for 275 minutes. The amount of medium-viscosity slick water used was 1320 ml. 3 It carries a total of 37.9m of 80 / 120 mesh proppant. 3 .

[0140] The sand addition compliance rate in this section reached 97.4%, and the on-site resistance reduction rate reached 83%. This slickwater system demonstrated excellent performance in construction and application.

[0141] Application Example 3:

[0142] This application example uses the salt-resistant, swelling-resistant, and slip-resistant fracturing material prepared according to this invention for hydraulic fracturing operations. The construction curve is shown in [Figure 1]. Figure 5 The specific operation is as follows: In this application example, the salt-resistant and anti-swelling slickwater prepared by the present invention is used to mix and prepare a variable viscosity slickwater system in a well of a shale gas platform. The water used for preparing the solution is a flowback fluid with a total mineralization of 36984 mg / L.

[0143] In this application example, during fracturing operations on a certain section of the well, hydrochloric acid acidification was used from the start of fracturing until 30 minutes. From 30 minutes onwards, low-viscosity slickwater was used for fracturing, and the drag-reducing agent (aqueous polyacrylamide dispersion prepared in Preparation Example 2) was added at a rate of 0.6%. Up to 210 minutes, the low-viscosity slickwater dosage was 2225 m³. 3 Subsequently, the drag-reducing agent (the aqueous dispersion of polyacrylamide prepared in Preparation Example 2) in the slick water was increased to 2.0% to form a medium-viscosity slick water, and this process continued for 270 minutes. The amount of medium-viscosity slick water used was 640 ml. 3 It carries a total of 56m of 80 / 120 mesh proppant. 3 .

[0144] The drag reduction rate on site reached 80%, and the sand addition compliance rate was 97.1%. This slickwater system demonstrated excellent performance in construction and application.

[0145] It should be noted that the embodiments described above are only for explaining the present invention and do not constitute any limitation on the present invention. The present invention has been described with reference to typical embodiments, but it should be understood that the words used therein are descriptive and explanatory terms, not limiting terms. Modifications can be made to the present invention within the scope of the claims, and revisions can be made to the present invention without departing from the scope and spirit of the present invention. Although the present invention described herein relates to specific methods, materials, and embodiments, it does not mean that the present invention is limited to the specific examples disclosed herein; on the contrary, the present invention can be extended to all other methods and applications with the same function.

Claims

1. An application of a salt-resistant, anti-swelling, slippery surface in hydraulic fracturing of oil and gas fields, characterized in that, The slippery water includes a drag-reducing agent, which is an aqueous dispersion of polyacrylamide. The method for synthesizing the aqueous polyacrylamide dispersion includes reacting a reaction system of acrylamide I, cationic monomer I, inorganic salt, stabilizer and initiator I to obtain the aqueous polyacrylamide dispersion. Wherein, the cationic monomer I is selected from one or more of acryloyloxyethyltrimethylammonium chloride, methacryloyloxyethyltrimethylammonium chloride, dimethyldiallylammonium chloride, acryloyloxyethyldimethylbenzylammonium chloride, methacryloyloxyethyldimethylbenzylammonium chloride, and 2-acrylamido-2-methylpropyltrimethylammonium chloride; the inorganic salt is ammonium sulfate; and the stabilizer is a binary mixture of a cationic copolymer containing polyacrylamide segments and polyoxyethylene. The preparation of the stabilizer includes: mixing cationic monomer II, acrylamide II, and polyoxyethylene in water under the conditions of initiator II and inactive atmosphere, and carrying out reaction II to obtain the stabilizer; The cationic monomer II is selected from one or more of acryloyloxyethyltrimethylammonium chloride, methacryloyloxyethyltrimethylammonium chloride, dimethyldiallylammonium chloride, acryloyloxyethyldimethylbenzylammonium chloride, methacryloyloxyethyldimethylbenzylammonium chloride, and 2-acrylamido-2-methylpropyltrimethylammonium chloride; the molecular weight of the polyoxyethylene is 2000 Da to 200000 Da.

2. The application according to claim 1, characterized in that, Based on the total mass of the salt-resistant, anti-swelling, and slippery material being 100%, the mass percentage of the drag-reducing agent is 0.1% to 6.7%, with the remainder being water.

3. The application according to claim 1, characterized in that, The mass ratio of acrylamide I, cationic monomer I, inorganic salt, and stabilizer is 36:(4.32–5.76). 10：（270～275）； And / or, the amount of initiator I added is 0.1% to 0.5% of the mass of acrylamide I.

4. The application according to any one of claims 1-3, characterized in that, The initiator I is selected from aqueous initiator I and / or thermal initiator I.

5. The application according to claim 4, characterized in that, The aqueous initiator I is selected from at least one of V-50 and VA-044; the thermal initiator I is selected from at least two of ammonium persulfate, sodium bisulfite, and potassium persulfate.

6. The application according to any one of claims 1-3, characterized in that, The conditions for reaction I include: a temperature of 25°C to 45°C and a time of 1 hour to 6 hours.

7. The application according to any one of claims 1-3, characterized in that, The mass ratio of the cationic monomer II, acrylamide II, polyethylene oxide and water is 72:60:(30-100):(160-260). And / or, the amount of initiator II added is 0.1% to 0.5% of the mass of cationic monomer II.

8. The application according to any one of claims 1-3, characterized in that, The polyoxyethylene is selected from polyoxyethylene with or without end capping; And / or, the initiator II is selected from aqueous initiator II and / or thermal initiator II; And / or, the inactive atmosphere is selected from at least one of nitrogen and argon.

9. The application according to claim 8, characterized in that, The terminated polyethylene oxide includes single-terminated polyethylene oxide and double-terminated polyethylene oxide; And / or, the aqueous initiator II is selected from at least one of V-50 and VA-044; the thermal initiator II is selected from at least two of ammonium persulfate, sodium bisulfite, and potassium persulfate.

10. The application according to claim 9, characterized in that, The single-end capped polyoxyethylene is selected from polyoxyethylene monomethyl ether; the double-end capped polyoxyethylene is selected from polyoxyethylene dimethyl ether.

11. The application according to any one of claims 1-3, characterized in that, The conditions for reaction II include: a temperature of 30°C to 80°C and a reaction time of 5 to 10 hours. And / or, the reaction II may be followed by dilution.

Images