A heat-resistant and salt-resistant fracturing oil displacement agent and its preparation method and application

Abstract

The present invention belongs to the field of oil and gas field development, and in particular to a heat-resistant and salt-resistant fracturing oil-displacing agent and its preparation method and application. The fracturing oil-displacing agent includes the following components by mass percentage: 20%-30% of fatty alcohol polyoxyethylene hydroxypropyl dimethyl carboxy betaine, 20%-30% of fatty alcohol polyoxyethylene hydroxypropyl dimethyl hydroxypropyl sulfobetaine, 25%-30% of composite initiator, 0.01%-0.15% of bactericide, 0.1%-0.8% of tackifier, 0.01%-0.12% of heat stabilizer, 0.01%-0.3% of pH regulator, and the rest is water. The fracturing oil-displacing agent in the present invention has the characteristics of high imbibition efficiency, good oil washing effect, good salt resistance, strong acid and alkali resistance, low interfacial tension and improved wettability, and is suitable for use in dense conglomerate reservoirs below 120°C to improve recovery.

Description

Technical Field

[0001] The invention belongs to the field of oil and gas field development, and particularly relates to a temperature-resistant and salt-resistant fracturing oil displacement agent, a preparation method and an application thereof. Background Art

[0002] Due to the extremely low permeability, poor physical properties, and complex pore-throat structure of the Mahu tight conglomerate reservoir, conventional fracturing methods result in rapid production decline and high injection pressures, resulting in low ultimate recovery rates. The flowback fluid produced by large-scale volume fracturing has also become a significant source of pollution in oil fields, and the proper handling and effective application of this fluid are currently under investigation. By adding a fracturing agent formulated with the flowback fluid to the conventional fracturing fluid, the fracturing fluid is transformed into a complex three-dimensional artificial fracture network through three-dimensional transformation of the oil and gas reservoir, maximizing the volume of the fractures within the reservoir and significantly increasing the effective permeability of the reservoir. By reducing interfacial tension, improving wettability, and emulsifying and dispersing the fluid, the fracturing agent displaces oil from the matrix, thereby increasing the recovery rate of tight conglomerate reservoirs.

[0003] Chinese invention patent application CN112961663A discloses an oil-displacement fracturing fluid and its preparation method, belonging to the field of oilfield chemistry. The oil-displacement fracturing fluid is composed of the following components, measured by mass percentage: 0.25-0.3% myocolloid, 0.5-0.8% ultra-low interfacial tension surfactant, 1.0-3.0% potassium chloride, 0.1%-0.5% bactericide, and the balance is water. The oil-displacement fracturing fluid is targeted at oil wells developed by water injection. During repeated reforming, the oil-displacement fracturing fluid is diffused into the water flooding channel, and during flowback, it has certain flooding (washing) characteristics, thereby improving the oil-washing efficiency of the fracturing fluid during repeated fracturing of water-flooded oil reservoirs. The preparation method comprises the following steps: mixing myocolloid, ultra-low interfacial tension surfactant, potassium chloride, bactericide, and water, and stirring evenly to obtain the oil-displacement fracturing fluid. The preparation method is simple, easy to prepare quickly on-site, convenient to use, and fracturing and oil displacement are synergistic. However, the compatibility of the fracturing agent and the oil displacement agent in this solution is insufficient.

[0004] Chinese invention patent application CN106350048A discloses an oil wash agent for oil well fracturing using a sulfonate as the main agent, comprising a sulfonate-type anionic surfactant, a cationic Gemini surfactant, a polyoxyethylene ether-type nonionic surfactant, and water. The agent has an interfacial tension greater than 1 mN / m and poor temperature and salt resistance, making it unsuitable for the dense conglomerate reservoir in Mahu, Xinjiang.

[0005] Chinese invention patent application CN106520105A discloses an oil-displacing agent formulated with fracturing fluid flowback. This method uses on-site flowback fluid that requires natural sedimentation, primary filtration, and secondary filtration, increasing the processing cost of the flowback fluid. In addition, the oil-displacing agent is suitable for low-permeability reservoirs above 1 mD and cannot perform an oil-washing function in the dense, low-permeability conglomerate reservoir of Mahu.

[0006] Chinese invention patent application CN107338037A discloses an oil-displacing agent for low-permeability oilfields, its preparation method, and its application. This invention provides a novel, broad-spectrum oil-displacing agent with high oil-washing efficiency, suitable for improving crude oil recovery from low-permeability, ultra-low-permeability, and ultra-low-permeability reservoirs in the Ordos Basin. However, the significant differences in physical properties between the Ordos Basin reservoirs and the Mahu tight conglomerate reservoirs preclude the application of this formulation in Xinjiang oilfields.

[0007] The Mahu tight conglomerate reservoir is currently primarily exploited using horizontal well volume fracturing technology, but this results in rapid production decline, low recovery rates, and significant difficulty maintaining stable production. Laboratory experiments have shown that fracturing oil-displacement agents can further enhance the recovery rate of tight conglomerate reservoirs. However, existing oil-displacement agents suffer from several issues, including poor temperature and salt tolerance, incompatibility with the Mahu tight conglomerate reservoir, and inability to be applied during reservoir fracturing. Consequently, they are unable to achieve the desired recovery rate from the Mahu tight conglomerate reservoir. Therefore, there is an urgent need to develop a temperature-resistant and salt-tolerant fracturing oil-displacement agent suitable for fracturing the Mahu tight conglomerate reservoir and develop a corresponding preparation method to effectively enhance crude oil recovery from tight conglomerate reservoirs in the field. Summary of the Invention

[0008] In view of the deficiencies in the prior art, the present invention solves the technical problem of providing a temperature-resistant and salt-resistant fracturing oil displacement agent and a preparation method and application thereof.

[0009] In order to achieve the above-mentioned purpose of the present invention, the specific technical solution adopted by the present invention is:

[0010] A temperature-resistant and salt-resistant fracturing oil displacement agent, the raw materials of which include fatty alcohol polyoxyethylene hydroxypropyl dimethyl carboxy betaine, fatty alcohol polyoxyethylene hydroxypropyl dimethyl hydroxypropyl sulfobetaine, a composite initiator, a foaming agent, a bactericide, a viscosity enhancer, a heat stabilizer and a pH regulator.

[0011] Preferably, the fracturing oil displacement agent includes the following components in percentage by mass:

[0012] Fatty alcohol polyoxyethylene hydroxypropyl dimethyl carboxy betaine: 20%-30%;

[0013] Fatty alcohol polyoxyethylene hydroxypropyl dimethyl hydroxypropyl sulfobetaine: 20%-30%;

[0014] Composite initiator: 25%-30%;

[0015] Foaming agent; 0.05%-0.2%;

[0016] Fungicide: 0.01%-0.15%;

[0017] Tackifier: 0.1%-0.8%;

[0018] Thermal stabilizer: 0.01%-0.12%;

[0019] pH adjuster: 0.01%-0.3%;

[0020] Water, balance.

[0021] Preferably, the carbon chain length of the fatty alcohol in the fatty alcohol polyoxyethylene hydroxypropyl dimethyl carboxy betaine is 7-18.

[0022] Preferably, the carbon chain length of the fatty alcohol in the fatty alcohol polyoxyethylene hydroxypropyl dimethyl hydroxypropyl sulfobetaine is 7-18.

[0023] Preferably, the raw materials of the composite initiator are selected from one or more of sodium sulfite, sodium persulfate, oxalic acid, potassium aluminum sulfate and diacyl peroxide.

[0024] Further preferably, the raw materials of the composite initiator include 20%-40% of sodium sulfite and 60%-80% of potassium aluminum sulfate in percentage by mass.

[0025] Preferably, the raw materials of the foaming agent are selected from one or both of sodium α-olefin sulfonate and alkanolamide 6501.

[0026] Further preferably, the raw materials of the foaming agent include 20%-50% of sodium α-olefin sulfonate and 50%-80% of alkanolamide 6501, calculated by mass percentage.

[0027] Preferably, the raw material of the fungicide is selected from one or more of dodecyldimethylbenzylammonium chloride, glutaraldehyde and acrolein.

[0028] Further preferably, the raw materials of the fungicide include 30%-50% of dodecyldimethylbenzylammonium chloride and 50%-70% of acrolein in percentage by mass.

[0029] Preferably, the raw material of the viscosity increasing agent is selected from one or more of polyacrylic acid, polyvinyl alcohol, polyacrylamide and dialdehyde starch.

[0030] More preferably, the viscosity-average molecular weights of polyacrylic acid, polyvinyl alcohol and polyacrylamide are 5,000-10,000, 5,000-25,000 and 5 million-130 million, respectively.

[0031] Further preferably, the raw materials of the viscosity enhancer include 30%-50% of polyvinyl alcohol and 50%-70% of dialdehyde starch in percentage by mass.

[0032] Preferably, the raw material of the heat stabilizer is selected from one or more of tribasic aluminum sulfate, sodium stearate and methyl tin.

[0033] Further preferably, the raw materials of the heat stabilizer include, by mass percentage, 10%-20% of tribasic aluminum sulfate, 20%-50% of sodium stearate and 30%-70% of methyl tin.

[0034] Preferably, the raw material of the pH regulator is selected from one or more of sodium citrate, sodium carbonate and sodium hydroxide.

[0035] Further preferably, the raw materials of the pH regulator include, by mass percentage, 20%-50% of sodium citrate, 20%-30% of sodium carbonate and 20%-60% of sodium hydroxide.

[0036] The present invention also relates to a method for preparing a fracturing oil displacement agent, comprising the following steps:

[0037] (1) dissolving fatty alcohol polyoxyethylene hydroxypropyl dimethyl carboxy betaine, fatty alcohol polyoxyethylene hydroxypropyl dimethyl hydroxypropyl sulfobetaine and a composite initiator in water and stirring to obtain a mixed solution;

[0038] (2) Adding a foaming agent, a fungicide, a viscosity enhancer, a heat stabilizer and a pH adjuster into the above solution and stirring to obtain a fracturing oil displacement agent solution.

[0039] Preferably, in step (2), the stirring speed is 600 r / min, the reaction temperature is 25-50° C., and the stirring time is 4-6 h.

[0040] The present invention also relates to the application of the above-mentioned fracturing oil displacement agent or the preparation method of the fracturing oil displacement agent in the field of oil and gas field development.

[0041] Compared with the prior art, the present invention has the following beneficial effects:

[0042] (1) The fracturing oil displacement agent has high permeation efficiency (30%-50%), good oil washing effect (40%-70%), good salt resistance (mineralization below 100000 mg / L), strong acid and alkali resistance (pH between 6-12), low interfacial tension (maintained at 10 -2 -10 - 5 mN / m) and improved wettability, and is suitable for use in tight conglomerate reservoirs below 100°C to enhance oil recovery.

[0043] (2) The preparation method is simple and can be directly used to prepare on-site fracturing flowback fluid, and can be used to recover crude oil from the Mahu tight conglomerate reservoir. DETAILED DESCRIPTION

[0044] The technical solutions in the embodiments of the present invention are further clearly described. The described embodiments are only a part of the present invention and are used to explain the present invention, but not to limit the present invention. Therefore, other embodiments obtained by other technicians in this field without creative work all fall within the scope of protection of the present invention.

[0045] The reagents not otherwise specified in the following examples are all conventional reagents in the art and are commercially available.

[0046] Example 1

[0047] A temperature-resistant and salt-resistant fracturing oil displacement agent comprises the following components, calculated by mass percentage: 20% fatty alcohol polyoxyethylene hydroxypropyl dimethyl carboxy betaine; 30% fatty alcohol polyoxyethylene hydroxypropyl dimethyl hydroxypropyl sulfobetaine; 30% composite initiator; 0.2% foaming agent; 0.15% bactericide; 0.8% viscosity enhancer; 0.12% heat stabilizer; 0.3% pH regulator; and 18.43% water.

[0048] Among them, the carbon chain length of the fatty alcohol in fatty alcohol polyoxyethylene hydroxypropyl dimethyl carboxy betaine is 15, which is purchased from Shandong Xinquansheng Chemical Technology Co., Ltd.; the carbon chain length of the fatty alcohol in fatty alcohol polyoxyethylene hydroxypropyl dimethyl hydroxypropyl sulfobetaine is 9, which is purchased from Shandong Xinquansheng Chemical Technology Co., Ltd.

[0049] The composite initiator is a mixture of 20% sodium sulfite and 80% potassium aluminum sulfate, calculated by mass percentage;

[0050] The foaming agent is a mixture of 20% sodium α-olefin sulfonate and 80% alkanolamide 6501;

[0051] The fungicide is a mixture of 30% dodecyldimethylbenzyl ammonium chloride and 70% acrolein;

[0052] The viscosity enhancer is a mixture of 30% polyvinyl alcohol (PVA2699, purchased from Zibo Shengda Chemical Technology Co., Ltd.) and 70% dialdehyde starch (9047-50-1, purchased from Hubei Hengjingrui Chemical Co., Ltd.);

[0053] The heat stabilizer is a mixture of 10% tribasic aluminum sulfate, 20% sodium stearate and 70% methyl tin;

[0054] The pH adjuster is a mixture of 20% sodium citrate, 20% sodium carbonate and 60% sodium hydroxide.

[0055] A method for preparing a temperature-resistant and salt-resistant fracturing oil displacement agent comprises the following steps:

[0056] (1) Dissolving fatty alcohol polyoxyethylene hydroxypropyl dimethyl carboxy betaine, fatty alcohol polyoxyethylene hydroxypropyl dimethyl hydroxypropyl sulfobetaine, and a composite initiator in water, adding the mixture into a reaction vessel, controlling the temperature at 50° C., the rotation speed at 600 r / min, and stirring for 3 h to obtain a mixed solution;

[0057] (2) Add a foaming agent, a fungicide, a viscosity enhancer, a heat stabilizer, and a pH adjuster to the above solution, and continue stirring for 6 hours to obtain a fracturing oil displacement agent solution.

[0058] Example 2

[0059] A temperature-resistant and salt-resistant fracturing oil displacement agent comprises the following components, calculated by mass percentage: 30% fatty alcohol polyoxyethylene hydroxypropyl dimethyl carboxy betaine; 20% fatty alcohol polyoxyethylene hydroxypropyl dimethyl hydroxypropyl sulfobetaine; 25% composite initiator; 0.05% foaming agent; 0.15% bactericide; 0.1% viscosity enhancer; 0.01% heat stabilizer; 0.01% pH regulator; and 24.68% water.

[0060] Among them, the carbon chain length of the fatty alcohol in fatty alcohol polyoxyethylene hydroxypropyl dimethyl carboxy betaine is 8, which was purchased from Shandong Xinquansheng Chemical Technology Co., Ltd.; the carbon chain length of the fatty alcohol in fatty alcohol polyoxyethylene hydroxypropyl dimethyl hydroxypropyl sulfobetaine is 11, which was purchased from Shandong Xinquansheng Chemical Technology Co., Ltd.

[0061] The composite initiator is a mixture of 30% sodium sulfite and 70% potassium aluminum sulfate;

[0062] The foaming agent is a mixture of 30% sodium α-olefin sulfonate and 70% alkanolamide 6501;

[0063] The fungicide is a mixture of 40% dodecyldimethylbenzyl ammonium chloride and 60% acrolein;

[0064] The thickener is a mixture of 40% polyvinyl alcohol (PVA, purchased from Wuhan Jiyesheng Chemical Co., Ltd.) and 60% dialdehyde starch (9047-50-1, purchased from Tai'an Jinshan Modified Starch Co., Ltd.);

[0065] The heat stabilizer is a mixture of 20% tribasic aluminum sulfate, 50% sodium stearate and 30% methyl tin;

[0066] The pH adjuster is a mixture of 50% sodium citrate, 30% sodium carbonate and 20% sodium hydroxide.

[0067] A method for preparing a temperature-resistant and salt-resistant fracturing oil displacement agent comprises the following steps:

[0068] (1) Dissolving fatty alcohol polyoxyethylene hydroxypropyl dimethyl carboxybetaine, fatty alcohol polyoxyethylene hydroxypropyl dimethyl hydroxypropyl sulfobetaine, and a composite initiator in water, adding the mixture into a reaction vessel, controlling the temperature at 45° C., the rotation speed at 400 r / min, and stirring for 3 h to obtain a mixed solution;

[0069] (2) Add a foaming agent, a fungicide, an oxygen scavenger, a viscosity enhancer, a heat stabilizer, and a pH adjuster to the above solution, and continue stirring for 6 hours to obtain a fracturing oil displacement agent solution.

[0070] Example 3

[0071] A temperature-resistant and salt-resistant fracturing oil displacement agent comprises the following components, calculated by mass percentage: 25% fatty alcohol polyoxyethylene hydroxypropyl dimethyl carboxy betaine; 25% fatty alcohol polyoxyethylene hydroxypropyl dimethyl hydroxypropyl sulfobetaine; 28% composite initiator; 0.1% foaming agent; 0.1% bactericide; 0.5% viscosity enhancer; 0.09% heat stabilizer; 0.2% pH regulator; and 21.01% water.

[0072] Among them, the carbon chain length of the fatty alcohol in fatty alcohol polyoxyethylene hydroxypropyl dimethyl carboxy betaine is 17, which was purchased from Shandong Xinquansheng Chemical Technology Co., Ltd.; the carbon chain length of the fatty alcohol in fatty alcohol polyoxyethylene hydroxypropyl dimethyl hydroxypropyl sulfobetaine is 13, which was purchased from Shandong Xinquansheng Chemical Technology Co., Ltd.

[0073] The composite initiator is a mixture of 35% sodium sulfite and 65% potassium aluminum sulfate;

[0074] The foaming agent is a mixture of 20% sodium α-olefin sulfonate and 80% alkanolamide 6501;

[0075] The fungicide is a mixture of 50% dodecyldimethylbenzyl ammonium chloride and 50% acrolein;

[0076] The viscosity enhancer is a mixture of 50% polyvinyl alcohol (PVA100-86, purchased from Anhui Wanwei High-tech Materials Co., Ltd.) and 50% dialdehyde starch (9047-50-1, purchased from Shandong Baihong New Materials Co., Ltd.);

[0077] The heat stabilizer is a mixture of 20% tribasic aluminum sulfate, 20% sodium stearate and 60% methyl tin;

[0078] The pH adjuster is a mixture of 40% sodium citrate, 30% sodium carbonate and 30% sodium hydroxide.

[0079] A method for preparing a temperature-resistant and salt-resistant fracturing oil displacement agent comprises the following steps:

[0080] (1) Dissolving fatty alcohol polyoxyethylene hydroxypropyl dimethyl carboxybetaine, fatty alcohol polyoxyethylene hydroxypropyl dimethyl hydroxypropyl sulfobetaine, and a composite initiator in water, adding the mixture into a reaction vessel, controlling the temperature at 35° C., the rotation speed at 600 r / min, and stirring for 3 h to obtain a mixed solution;

[0081] (2) Add a foaming agent, a fungicide, an oxygen scavenger, a viscosity enhancer, a heat stabilizer, and a pH adjuster to the above solution, and continue stirring for 5 hours to obtain a fracturing oil displacement agent solution.

[0082] Example 4

[0083] A temperature-resistant and salt-resistant fracturing oil displacement agent comprises the following components, calculated by mass percentage: 20% fatty alcohol polyoxyethylene hydroxypropyl dimethyl carboxy betaine; 30% fatty alcohol polyoxyethylene hydroxypropyl dimethyl hydroxypropyl sulfobetaine; 25% composite initiator; 0.15% foaming agent; 0.01% bactericide; 0.8% viscosity enhancer; 0.01% heat stabilizer; 0.2% pH regulator; and 23.83% water.

[0084] Among them, the carbon chain length of the fatty alcohol in fatty alcohol polyoxyethylene hydroxypropyl dimethyl carboxy betaine is 11, which is purchased from Shandong Xinquansheng Chemical Technology Co., Ltd.; the carbon chain length of the fatty alcohol in fatty alcohol polyoxyethylene hydroxypropyl dimethyl hydroxypropyl sulfobetaine is 16, which is purchased from Shandong Xinquansheng Chemical Technology Co., Ltd.

[0085] The composite initiator is a mixture of 40% sodium sulfite and 60% potassium aluminum sulfate;

[0086] The foaming agent is a mixture of 50% sodium α-olefin sulfonate and 50% alkanolamide 6501;

[0087] The fungicide is a mixture of 45% dodecyldimethylbenzyl ammonium chloride and 55% acrolein;

[0088] The viscosity enhancer is a mixture of 30% polyvinyl alcohol (PVA1788, purchased from Shandong Tianfeng Chemical Technology Co., Ltd.) and 70% dialdehyde starch (9047-50-1, purchased from Shandong Baihong New Materials Co., Ltd.);

[0089] The heat stabilizer is a mixture of 20% tribasic aluminum sulfate, 40% sodium stearate and 40% methyl tin;

[0090] The pH adjuster is a mixture of 20% sodium citrate, 20% sodium carbonate and 60% sodium hydroxide.

[0091] A method for preparing a temperature-resistant and salt-resistant fracturing oil displacement agent comprises the following steps:

[0092] (1) Dissolving fatty alcohol polyoxyethylene hydroxypropyl dimethyl carboxy betaine, fatty alcohol polyoxyethylene hydroxypropyl dimethyl hydroxypropyl sulfobetaine, and a composite initiator in water, adding the mixture into a reaction vessel, controlling the temperature at 30° C., the rotation speed at 800 r / min, and stirring for 3 h to obtain a mixed solution;

[0093] (2) Add a foaming agent, a fungicide, an oxygen scavenger, a viscosity enhancer, a heat stabilizer, and a pH adjuster to the above solution, and continue stirring for 3 hours to obtain a fracturing oil displacement agent solution.

[0094] Comparative Example 1

[0095] A temperature-resistant and salt-resistant fracturing oil displacement agent comprises the following components, calculated by mass percentage: 50% fatty alcohol polyoxyethylene hydroxypropyl dimethyl carboxy betaine; 30% composite initiator; 0.2% foaming agent; 0.15% bactericide; 0.8% viscosity enhancer; 0.12% heat stabilizer; 0.3% pH regulator; and 18.43% water.

[0096] Among them, the carbon chain length of the fatty alcohol in fatty alcohol polyoxyethylene hydroxypropyl dimethyl carboxy betaine is 15, which was purchased from Shandong Xinquansheng Chemical Technology Co., Ltd.

[0097] The composite initiator is a mixture of 20% sodium sulfite and 80% potassium aluminum sulfate;

[0098] The foaming agent is a mixture of 20% sodium α-olefin sulfonate and 80% alkanolamide 6501;

[0099] The fungicide is a mixture of 30% dodecyldimethylbenzyl ammonium chloride and 70% acrolein;

[0100] The viscosity enhancer is a mixture of 30% polyvinyl alcohol (PVA2699, purchased from Zibo Shengda Chemical Technology Co., Ltd.) and 70% dialdehyde starch (9047-50-1, purchased from Hubei Hengjingrui Chemical Co., Ltd.);

[0101] The heat stabilizer is a mixture of 10% tribasic aluminum sulfate, 20% sodium stearate and 70% methyl tin;

[0102] The pH adjuster is a mixture of 20% sodium citrate, 20% sodium carbonate and 60% sodium hydroxide.

[0103] A method for preparing a temperature-resistant and salt-resistant fracturing oil displacement agent comprises the following steps:

[0104] (1) Dissolving fatty alcohol polyoxyethylene hydroxypropyl dimethyl carboxybetaine and a composite initiator in water, adding the mixture into a reaction vessel, controlling the temperature at 50° C. and the rotation speed at 600 r / min, and stirring for 3 h to obtain a mixed solution;

[0105] (2) Add a foaming agent, a fungicide, a viscosity enhancer, a heat stabilizer, and a pH adjuster to the above solution, and continue stirring for 6 hours to obtain a fracturing oil displacement agent solution.

[0106] Comparative Example 2

[0107] A temperature-resistant and salt-resistant fracturing oil displacement agent comprises the following components, calculated by mass percentage: 50% fatty alcohol polyoxyethylene hydroxypropyl dimethyl hydroxypropyl sulfobetaine; 30% composite initiator; 0.2% foaming agent; 0.15% bactericide; 0.8% viscosity enhancer; 0.12% heat stabilizer; 0.3% pH regulator; and 18.43% water.

[0108] Among them, the carbon chain length of the fatty alcohol in fatty alcohol polyoxyethylene hydroxypropyl dimethyl hydroxypropyl sulfobetaine is 9, which was purchased from Shandong Xinquansheng Chemical Technology Co., Ltd.

[0109] The composite initiator is a mixture of 20% sodium sulfite and 80% potassium aluminum sulfate;

[0110] The foaming agent is a mixture of 20% sodium α-olefin sulfonate and 80% alkanolamide 6501;

[0111] The fungicide is a mixture of 30% dodecyldimethylbenzyl ammonium chloride and 70% acrolein;

[0112] The viscosity enhancer is a mixture of 30% polyvinyl alcohol (PVA2699, purchased from Zibo Shengda Chemical Technology Co., Ltd.) and 70% dialdehyde starch (9047-50-1, purchased from Hubei Hengjingrui Chemical Co., Ltd.);

[0113] The heat stabilizer is a mixture of 10% tribasic aluminum sulfate, 20% sodium stearate and 70% methyl tin;

[0114] The pH adjuster is a mixture of 20% sodium citrate, 20% sodium carbonate and 60% sodium hydroxide.

[0115] A method for preparing a temperature-resistant and salt-resistant fracturing oil displacement agent comprises the following steps:

[0116] (1) Dissolving fatty alcohol polyoxyethylene hydroxypropyl dimethyl hydroxypropyl sulfobetaine and a composite initiator in water, adding the mixture into a reaction vessel, controlling the temperature at 50° C. and the rotation speed at 600 r / min, and stirring for 3 h to obtain a mixed solution;

[0117] (2) Add a foaming agent, a fungicide, a viscosity enhancer, a heat stabilizer, and a pH adjuster to the above solution, and continue stirring for 6 hours to obtain a fracturing oil displacement agent solution.

[0118] Comparative Example 3

[0119] A temperature-resistant and salt-resistant fracturing oil displacement agent comprises the following components, calculated by mass percentage: 20% fatty alcohol polyoxyethylene hydroxypropyl dimethyl carboxy betaine; 30% fatty alcohol polyoxyethylene hydroxypropyl dimethyl hydroxypropyl sulfobetaine; 30% initiator; 0.2% foaming agent; 0.15% bactericide; 0.8% viscosity enhancer; 0.12% heat stabilizer; 0.3% pH regulator; and 18.43% water.

[0120] Among them, the carbon chain length of the fatty alcohol in fatty alcohol polyoxyethylene hydroxypropyl dimethyl carboxy betaine is 15; the carbon chain length of the fatty alcohol in fatty alcohol polyoxyethylene hydroxypropyl dimethyl hydroxypropyl sulfo betaine is 9, both of which were purchased from Shandong Xinquansheng Chemical Technology Co., Ltd.

[0121] The initiator is potassium aluminum sulfate;

[0122] The foaming agent is a mixture of 20% sodium α-olefin sulfonate and 80% alkanolamide 6501;

[0123] The fungicide is a mixture of 30% dodecyldimethylbenzyl ammonium chloride and 70% acrolein;

[0124] The viscosity enhancer is a mixture of 30% polyvinyl alcohol (PVA2699, purchased from Zibo Shengda Chemical Technology Co., Ltd.) and 70% dialdehyde starch (9047-50-1, purchased from Hubei Hengjingrui Chemical Co., Ltd.);

[0125] The heat stabilizer is a mixture of 10% tribasic aluminum sulfate, 20% sodium stearate and 70% methyl tin;

[0126] The pH adjuster is a mixture of 20% sodium citrate, 20% sodium carbonate and 60% sodium hydroxide.

[0127] A method for preparing a temperature-resistant and salt-resistant fracturing oil displacement agent comprises the following steps:

[0128] (1) Dissolving fatty alcohol polyoxyethylene hydroxypropyl dimethyl carboxybetaine, fatty alcohol polyoxyethylene hydroxypropyl dimethyl hydroxypropyl sulfobetaine, and an initiator in water, adding the mixture into a reaction vessel, controlling the temperature at 50° C., the rotation speed at 600 r / min, and stirring for 3 h to obtain a mixed solution;

[0129] (2) Add a foaming agent, a fungicide, a viscosity enhancer, a heat stabilizer, and a pH adjuster to the above solution, and continue stirring for 6 hours to obtain a fracturing oil displacement agent solution.

[0130] Example 5 Effect Test

[0131] Compatibility of fracturing oil displacement agents and flowback fluids

[0132] Use oilfield fracturing flowback fluid (mineralization of 10000mg / L-100000mg / L, Ca 2+ and Mg 2+ The total concentration is 300-20000 mg / L) The fracturing oil displacement agent in the embodiment is diluted to a concentration of 0.02wt%-0.5wt%, placed in an oven at 85-110°C, and the sample is observed after one week for precipitation and flocculation.

[0133] Interfacial tension of fracturing oil displacement agents

[0134] Referring to the Chinese petroleum and natural gas industry standard "Surface and interfacial tension determination method", the interfacial tension between the fracturing oil displacement agent in the example and the dehydrated crude oil in the reservoir was measured at 80°C using a rotary interfacial tension meter TX500C.

[0135] Fracturing oil displacement agent to improve wettability

[0136] The quartz plate was aged with dimethyl silicone oil, and the change in the contact angle of the quartz plate surface before and after the action of the fracturing oil displacement agent system in the example was measured using a DSA30 contact angle meter using a static contact angle method.

[0137] Oil washing efficiency of fracturing oil displacement agents

[0138] The measurement steps are as follows: ① Mix degassed and dehydrated crude oil from the formation with quartz sand at a mass ratio of 7:1 and age the mixture at the target formation temperature of 80°C for at least 48 hours. ② Add 15g of oil sand to a 100mL oil wash bottle, then add 30mL of a fracturing oil displacement agent solution. Place the bottle in a constant temperature shaking water bath and shake it at the target formation temperature of 80°C for 2 hours. After the mixture is placed in an oven at the target formation temperature of 80°C for 5 hours, the wash oil volume is read and the oil washing efficiency of the fracturing oil displacement agent is calculated.

[0139] Imbibition efficiency of fracturing oil displacement agents

[0140] The imbibition efficiency of the fracturing oil-displacing agent system in the examples was determined using a method described in the literature. The determination steps were as follows: a dense conglomerate sample saturated with formation crude oil was aged for at least one week. The aged sample and the fracturing oil-displacing agent solution were then placed in an imbibition bottle at the target formation temperature until the amount of oil imbibed by the sample remained constant. The imbibition efficiency of the fracturing oil-displacing agent was calculated by comparing the ratio of the imbibition oil volume to the saturated oil volume of the sample.

[0141] Acid and alkali resistance

[0142] Use acetic acid or sodium hydroxide to prepare solutions with different pH values ​​(6-12) for later use. Add 30 mL of solutions with different pH values ​​to a 100 mL beaker, add 30 mL of the fracturing oil displacement agent solution, stir for 5 minutes, and then let it stand. After 2 hours, observe whether precipitation and flocculation occur.

[0143] Salt resistance

[0144] Prepare simulated water with a mineralization of 10000mg / L-100000mg / L, of which Ca 2+ and Mg 2+ The total concentration is 300-20000 mg / L, the fracturing oil displacement agent in the embodiment is diluted to a concentration of 0.02wt%-0.5wt%, and placed at room temperature. After one week, the sample is observed for precipitation and flocculation.

[0145] Field application effect of fracturing oil displacement agent

[0146] The fracturing oil recovery system prepared in Example 1 is mainly used in the fracturing process of the Mahu tight conglomerate oil reservoir in the Xinjiang Oilfield. After the system is mixed with the fracturing fluid, it is used in the fracturing process of the shut-down vertical wells, achieving a significant oil-increasing effect. The cumulative oil-increasing effect of 12 test wells is 21,820 tons.

[0147] The test data of the fracturing oil displacement agents prepared in Examples 1-4 and Comparative Examples 1-3 are shown in Table 1.

[0148] Table 1 Test results

[0149]

[0150]

[0151] The experimental results show that the oil-water interfacial tension in the valve can reach 10 at a concentration of 0.02wt%-0.5wt%. -4 -10 - 3 The ultra-low magnitude of mN / m demonstrates excellent ability to reduce oil-water interfacial tension. This system exhibits a wettability reversal effect on quartz wafers. At an effective concentration of 0.2% fracturing oil displacement agent, the contact angle of the quartz wafer in Example 1 changes from 170° to 35°. At a concentration of 0.2wt% fracturing oil displacement agent, the oil washing efficiency of Example 1 reaches 66.3%. At a concentration of 0.2wt%, the imbibition efficiency of Example 1 reaches 45.97%.

[0152] The fracturing oil displacement agent has high permeation efficiency (30%-50%), good oil washing effect (40%-70%), good salt resistance (mineralization below 100000 mg / L), strong acid and alkali resistance (pH between 6-12), low interfacial tension (maintained at 10 -2 -10 - 5 mN / m) and improved wettability, and is suitable for use in tight conglomerate reservoirs below 100°C to enhance oil recovery.

[0153] The above detailed description is a specific description of one feasible embodiment of the present invention. This embodiment is not intended to limit the patent scope of the present invention. Any equivalent implementation or modification that does not depart from the present invention should be included in the scope of the technical solution of the present invention.

Claims

1. A temperature-resistant and salt-resistant fracturing oil displacement agent, characterized in that: The raw materials of the fracturing oil displacement agent include the following components in percentage by mass: Fatty alcohol polyoxyethylene hydroxypropyl dimethyl carboxy betaine: 20%-30%; Fatty alcohol polyoxyethylene hydroxypropyl dimethyl hydroxypropyl sulfobetaine: 20%-30%; Composite initiator: 25%-30%; Foaming agent; 0.05%-0.2%; Fungicide: 0.01%-0.15%; Tackifier: 0.1%-0.8%; Heat stabilizer: 0.01%-0.12%; pH adjuster: 0.01%-0.3%; water, balance; The carbon chain length of the fatty alcohol in the fatty alcohol polyoxyethylene hydroxypropyl dimethyl carboxy betaine is 7-18; The carbon chain length of the fatty alcohol in the fatty alcohol polyoxyethylene hydroxypropyl dimethyl hydroxypropyl sulfobetaine is 7-18; Calculated by mass percentage, the raw materials of the composite initiator include 20%-40% sodium sulfite and 60%-80% potassium aluminum sulfate; Calculated by mass percentage, the raw materials of the foaming agent include 20%-50% of sodium α-olefin sulfonate and 50%-80% of alkanolamide 6501; Calculated by mass percentage, the raw materials of the fungicide include 30%-50% of dodecyldimethylbenzylammonium chloride and 50%-70% of acrolein; Calculated by mass percentage, the raw materials of the viscosity enhancer include 30%-50% polyvinyl alcohol and 50%-70% dialdehyde starch; Calculated by mass percentage, the raw materials of the heat stabilizer include 10%-20% tribasic aluminum sulfate, 20%-50% sodium stearate and 30%-70% methyl tin; Calculated by mass percentage, the raw materials of the pH regulator include 20%-50% sodium citrate, 20%-30% sodium carbonate and 20%-60% sodium hydroxide.

2. The fracturing oil displacement agent according to claim 1, characterized in that The viscosity average molecular weight of the polyvinyl alcohol is 5000-25000.

3. A method for preparing the fracturing oil displacement agent according to any one of claims 1 to 2, characterized in that: The following steps are involved: (1) Dissolve fatty alcohol polyoxyethylene hydroxypropyl dimethyl carboxy betaine, fatty alcohol polyoxyethylene hydroxypropyl dimethyl hydroxypropyl sulfobetaine and a composite initiator in water and stir to obtain a mixed solution; (2) Add a foaming agent, a fungicide, a viscosity enhancer, a heat stabilizer and a pH adjuster to the above solution and stir to obtain a fracturing oil displacement agent solution.

4. The preparation method according to claim 3, characterized in that The stirring speed in steps (1) and (2) is 400-800 r / min, the temperature of the solution system is 25-50° C., and the stirring time is 3-6 h.

5. Use of the fracturing oil displacement agent according to any one of claims 1 to 2 or the fracturing oil displacement agent prepared by the preparation method according to any one of claims 3 to 4 in the field of oil and gas field development.

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