A betaine surfactant for high-temperature resistant clean fracturing fluid and preparation and application thereof

Abstract

The present application relates to a kind of betaine surfactant for high-temperature resistant clean fracturing fluid.The main problem to be solved is that the sand-carrying performance and shear resistance of traditional clean fracturing fluid are poor when well temperature is greater than 90℃, which greatly limits its application in high-temperature reservoirs.The preparation method comprises the following steps: (1) using fatty acid methyl ester and disubstituted urea as raw materials, N,N-dialkyl-1-alkanamide urea intermediate (I) is obtained through condensation reaction; (2) N,N-dialkyl-1-alkanamide urea intermediate I is quaternized with 3-chloro-2-hydroxypropanesulfonic acid sodium to prepare propyl hydroxyl sulfobetaine (II).The betaine surfactant has excellent shear resistance, interfacial properties and oil-washing efficiency under high-temperature conditions, and can be applied to clean fracturing fluid for high-temperature low-permeability sandstone reservoirs, tight oil reservoirs and shale reservoirs.

Description

TECHNICAL FIELD

[0001] The present application relates to a fracturing fluid system used in oil exploitation, in particular to a betaine surfactant for high-temperature-resistant clean fracturing fluid and preparation and application thereof. BACKGROUND

[0002] Hydraulic fracturing is an important means for developing low-pressure and low-permeability oil reservoirs and liberating production capacity. Through fracturing construction, the fracturing fluid with certain viscosity can greatly improve the fracturing construction efficiency, reduce the filtration loss to the formation, produce a wider fracture and good sand-carrying effect, and reduce the process risk of fracturing construction, thereby becoming a key factor for improving the success of fracturing construction. At present, the plant polymer fracturing fluid system is still widely used in China, and the thickening agent used is mainly natural plant gum, which has the characteristics of strong sand-carrying capacity, shear resistance and good salt resistance, and has become the thickening agent of 90% water-based fracturing fluid for fracturing construction in China. With the improvement of fracturing process requirements and the in-depth exploration and development of oil and gas reservoirs, in particular, the development of ultra-low permeability and unconventional oil and gas reservoirs has become the main direction of future development in China. The fracturing target layer is buried deep, the well temperature is high, and the effective permeability is lower than millidarcy. The use of traditional water-based fracturing fluid cannot meet the requirements. At the same time, the water-insoluble substances after the gel breaking of the traditional water-based fracturing fluid system block the rock fracture pores, causing pollution to the formation. The clean fracturing fluid (VES) was first introduced from the United States to China. It mainly relies on the plasticity and structure of the liquid to carry the proppant, rather than the viscosity of the liquid. Its unique fluid properties can also reduce the friction resistance. The clean fracturing fluid is simple to prepare, has little damage to the formation, and can form a fracture with high conductivity. Due to its advantages such as almost no residue, strong sand-carrying capacity, and no pollution, it is widely accepted and recognized.

[0003] In the high-temperature-resistant clean fracturing fluid system, the surfactant is one of the key factors, and different molecular structures have important influences on the performance of the fracturing fluid. The traditional cationic quaternary ammonium salt type, anionic type and non-ionic type clean fracturing fluid has poor sand-carrying performance and shear resistance at well temperatures higher than 90℃, and is greatly limited in the application in high-temperature deep reservoirs. SUMMARY

[0004] The present application aims to overcome the problems in the background art that the traditional fracturing fluid has poor sand-carrying performance and shear resistance at well temperatures higher than 90℃, and is greatly limited in the application in high-temperature deep reservoirs, and to provide a betaine surfactant for high-temperature-resistant clean fracturing fluid. The betaine surfactant has excellent shear resistance, interfacial performance and oil-washing performance under high-temperature conditions. The present application also provides a preparation and application of the betaine surfactant for high-temperature-resistant clean fracturing fluid.

[0005] In order to achieve the above-mentioned purpose, the first aspect of the present application provides a betaine surfactant for high-temperature-resistant clean fracturing fluid, which has the following chemical structure:

[0006] ;

[0007] wherein: R = C 12 -C 24 fatty alkyl; R1= R2= CH3, C2H5, C3H7, C4H9 or C5H 11 ;

[0008] The second aspect of the present application provides a preparation method of the betaine surfactant for high-temperature-resistant clean fracturing fluid, which comprises the following steps:

[0009] (1) taking fatty acid methyl ester and disubstituted urea as raw materials, and obtaining N,N-dialkyl-1-alkylamide urea intermediate (I) through condensation reaction;

[0010]

[0011] (2) preparing propyl hydroxyl sulfobetaine (II) by quaternization reaction of N,N-dialkyl-1-alkylamide urea intermediate I and 3-chloro-2-hydroxypropane sulfonic acid sodium.

[0012] ;

[0013] Preferably, the molar ratio of the fatty acid methyl ester and the disubstituted urea is 1:1.1.

[0014] Preferably, the molar ratio of the N,N-dialkyl-1-alkylamide urea intermediate I and the 3-chloro-2-hydroxypropane sulfonic acid sodium is 1:1.

[0015] Preferably, the preparation method of the N,N-dialkyl-1-alkylamide urea intermediate (I) in step 1 is:

[0016] The sodium hydroxide and the disubstituted urea are added at one time, and gradually heated and stirred until dissolved; the temperature is raised to 110°C, the feeding device is added dropwise, after the dropwise addition is completed, the stirring reaction is carried out at 110°C under normal pressure for 3 h until no methanol is refluxed and separated; the temperature is lowered to 70°C, the vacuum is about -0.03 MPa, the vacuum is about 2 h, until no methanol is refluxed and separated, and then the temperature is lowered to room temperature, to obtain the yellow solid N,N-dialkyl-1-alkylamide urea (I);

[0017] Preferably, the mass ratio of the disubstituted urea and the fatty acid methyl ester is 1.1:1, and the sodium hydroxide is added at 1% of the mass of the fatty acid methyl ester.

[0018] Preferably, the preparation method of the propyl hydroxyl sulfobetaine (II) in step 2 is:

[0019] In a 250 mL four-necked flask equipped with a reflux condenser and a stirrer, a certain amount of 3-chloro 2-hydroxy sodium propyl sulfonate was added, the pH value of the system was adjusted to 9-10; the same amount of N, N-dialkyl-1-alkylamide urea (I) was added, and after the addition was completed, rapid heating and stirring were carried out, and the temperature was maintained at 90 DEG C for 8-12 h; the product was neutralized to be neutral with hydrochloric acid, and then evaporated to dryness, and then dissolved with petroleum ether and anhydrous ethanol repeatedly, and then evaporated to dryness to obtain a light yellow solid propyl hydroxy sulfobetaine (II).

[0020] The third aspect of the present application provides a betaine surfactant for a high-temperature-resistant clean fracturing fluid, which is applied to a clean fracturing fluid in a high-temperature low-permeability sandstone reservoir, a tight oil reservoir and a shale reservoir.

[0021] Preferably, the components of the clean fracturing fluid are matched according to the following mass percentage: 1%-5% of propyl hydroxy sulfobetaine surfactant, 0.1%-1.0% of sodium dodecyl benzene sulfonate, 1%-6% of glycerol, 0.5%-3% of potassium chloride, and the rest is water.

[0022] Preferably, the propyl hydroxy sulfobetaine surfactant is 2%-4%, the sodium dodecyl benzene sulfonate is 0.4%-0.8%, the glycerol is 2%-5%, and the potassium chloride is 1%-2%.

[0023] By studying the mechanism of the viscoelastic surfactant as a thickening agent for the fracturing fluid, the betaine surfactant has the advantages of temperature resistance and good interfacial performance of anionic and cationic surfactants, improves the technical problems existing in the traditional surfactant, has the characteristics of good viscoelasticity and low critical micelle concentration, and is more temperature-resistant than the traditional VES clean fracturing fluid. According to the characteristics of the aggregation and winding of the surfactant, a new type of propyl hydroxy sulfobetaine betaine surfactant is designed and synthesized as a thickening agent for the high-temperature-resistant clean fracturing fluid, the matched additives are selected, and a high-temperature-resistant viscoelastic surfactant fracturing fluid system suitable for 120 DEG C is developed according to the fracturing fluid evaluation standard. This new type of high-temperature-resistant fracturing fluid system inherits the low damage characteristics of the previous VES system, and can also be constructed at a high sand ratio, a low friction and a high temperature, and becomes a new type of clean fracturing fluid system which can be applied to high-temperature low-permeability sandstone reservoirs, tight oil reservoirs and shale reservoirs.

[0024] Compared with the above background art, the present application can have the following beneficial effects:

[0025] The propyl hydroxyl sulfobetaine surfactant provided by the application is suitable for being used as a clean fracturing fluid under high temperature conditions, relies on the hydrophobic interaction between surfactant molecules to gather to form worm-like micelles, the micelles can be intertwined to form a viscoelastic colloid, the charge shielding effect of counterion salt is used to promote the formation of micelles and improve the stability of the micelle system, and is suitable for being applied in high-temperature low-permeability sandstone reservoirs, tight oil reservoirs and shale oil reservoirs.

[0026] Meanwhile, the novel propyl hydroxyl sulfobetaine surfactant provided by the application not only greatly reduces the oil-water interfacial tension, but also can generate a middle-phase microemulsion in a certain salt concentration range, the microemulsion has a good matching relationship with the void radius of a shale core due to the small micro-nano size, can effectively penetrate into a shale matrix to absorb oil, improves the absorption recovery rate, is suitable for being used as a clean fracturing fluid for low-permeability sandstone reservoirs, tight oil reservoirs and shale reservoirs, and is applied to fracturing construction of high-temperature reservoirs. BRIEF DESCRIPTION OF DRAWINGS

[0027] ATTACHMENT Figure 1 The viscosity test result of the propyl hydroxyl sulfobetaine surfactant clean fracturing fluid system in the embodiment of the application;

[0028] ATTACHMENT Figure 2 The interfacial tension performance of the propyl hydroxyl sulfobetaine surfactant system in the embodiment of the application;

[0029] ATTACHMENT Figure 3 The emulsification performance of the propyl hydroxyl sulfobetaine surfactant system in the embodiment of the application;

[0030] ATTACHMENT Figure 4 The oil absorption performance of the propyl hydroxyl sulfobetaine surfactant system in the embodiment of the application. DETAILED DESCRIPTION

[0031] The application will be further described below in combination with the drawings and embodiments:

[0032] Embodiment 1

[0033] The preparation method of the propyl hydroxyl sulfobetaine surfactant provided by the application comprises the following steps:

[0034] (1) Preparation of N,N-dialkyl-1-alkylamide urea intermediate (I)

[0035] A 250 mL four-necked flask equipped with a thermometer and a stirrer was purged with nitrogen for 15 minutes, and then 1,1-dimethylurea and fatty acid methyl ester were added according to a molar ratio of 1.1:1, and sodium hydroxide was added according to 1% of the mass of the fatty acid methyl ester. Sodium hydroxide and 1,1-dimethylurea were added at one time, and the temperature was gradually increased to dissolve. The temperature was increased to 110°C, and the fatty acid methyl ester was added dropwise through an equilibrated dropping funnel. The addition was completed in about 2 hours, and the reaction was stirred at 110°C under normal pressure for 3 hours until no methanol was refluxed and separated. The temperature was decreased to 70°C, and the pressure was reduced to about -0.03 MPa. Vacuum was applied for about 2 hours until no methanol was refluxed and separated, and then the temperature was decreased to room temperature to obtain a light yellow solid N,N-dialkyl-1-alkanamide urea (I).

[0036] (2) Preparation of propyl hydroxyl sulfobetaine (II)

[0037] A 250 mL four-necked flask equipped with a reflux condenser and a stirrer was added with 5 g of 3-chloro-2-hydroxypropanesulfonic acid sodium, and then 30% sodium hydroxide aqueous solution was slowly added to make the pH value of the system 9-10. N,N-dialkyl-1-alkanamide urea (I) was added in an amount equal to that of 3-chloro-2-hydroxypropanesulfonic acid sodium. After the addition was completed, the temperature was quickly increased and stirred, and the temperature was maintained at 90°C for 8-12 hours. The product was neutralized to be neutral with hydrochloric acid, and then evaporated to dryness. The product was repeatedly dissolved in petroleum ether and anhydrous ethanol, and then filtered and evaporated to dryness to obtain a light yellow solid propyl hydroxyl sulfobetaine (II).

[0038] The performance evaluation of the propyl hydroxyl sulfobetaine surfactant prepared in the application is as follows:

[0039] I. Temperature resistance

[0040] The shear resistance was measured by using an Anton Paar MCR-302 high temperature and high pressure rheometer, and the water used in the experiment was the GuLong shale field water of Daqing Oilfield. Different mass fractions (1%-4%) of propyl hydroxyl sulfobetaine (R=16, R1=R2=C2H5) were used as surfactants, and 1% of potassium chloride, 1% of sodium dodecyl benzene sulfonate and 2% of glycerol were used to prepare an aqueous solution, which was stirred to be viscous at room temperature. The temperature was increased from 60°C to 120°C at a gradient, and the viscosity of the solution was measured under a constant shear condition. -1 When the mass fraction of propyl hydroxyl sulfobetaine (R=16, R1=R2=C2H5) was ≥2%, the viscosity of the system was higher than 30 mPa·s under a constant shear condition at 120°C and 170 s -1 , which met the viscosity requirements of the fracturing technology, as shown in Figure 1 .

[0041] II. Interfacial performance

[0042] The interfacial tension was measured by TX-500C rotating drop interfacial tension meter. The oil used in the experiment was GY-3HC shale oil from Daqing Oilfield, and the water used in the experiment was GuLong shale field water from Daqing Oilfield. The propyl hydroxyl sulfobetaine (R=16, R1=R2=C2H5) with a mass fraction of 0.1%-0.4% was used as a surfactant, and the potassium chloride with a mass fraction of 0.4%-1.4% was dissolved in the GuLong shale field water from Daqing Oilfield to prepare an aqueous solution. The oil-water interfacial tension of the system was tested at 85°C. The interfacial tension of the Daqing Oilfield shale oil / field water can be reduced to 10 -3 mN / m order of magnitude, as shown in Figure 2 .

[0043] III. Emulsifying performance

[0044] The propyl hydroxyl sulfobetaine (R=16, R1=R2=C2H5) was used as a surfactant and dissolved in the GuLong shale field water from Daqing Oilfield to prepare an aqueous solution. The mass fraction of the surfactant was 0.3%, and the mass fraction of the potassium chloride was 0.3-0.9%. In a 5ml pipette, 2.5ml of the surfactant / potassium chloride aqueous solution and 2.5ml of the Daqing Oilfield GY-3HC shale oil were added, and the two sections of the pipette were fused and sealed. The pipette was inverted and shaken 200 times, and then placed vertically and statically in an 85°C constant temperature oven. After 12 hours, the emulsification state of the binary system and the shale oil was observed. When the mass fraction of the surfactant was 0.3% and the mass fraction of the potassium chloride was 0.5%, 0.6%, and 0.7% respectively, the solution in the pipette formed three phases, the middle phase was obvious, and the phase state characteristics were good, reaching the best hydrophilic-lipophilic balance, as shown in Figure 3 .

[0045] IV. Oil-washing performance

[0046] 1. Saturated oil of shale core

[0047] The drilled 3HC well shale core was vacuumed and heated to 80°C by using a high temperature and high pressure core saturated oil device. The GuLong shale oil was saturated at low pressure and low speed, and the pressure was increased by 2.0MPa gradient every time, and each time the pressure was maintained for more than 6 hours, until the core inlet pressure reached 10.0MPa, and the oil output at the outlet end of the core reached more than 3.0ml. The device was cooled to room temperature and normal pressure, and the core was taken out and weighed to calculate the saturated oil amount.

[0048] 2. High temperature imbibition experiment

[0049] The propyl hydroxyl sulfobetaine (R=16, R1=R2=C2H5) is dissolved in the potassium chloride in the Gulong shale field water of Daqing oil field as a surfactant to prepare an aqueous solution, the mass fraction of the surfactant is 0.3%, and the mass fraction of the potassium chloride is 0.6%. The saturated oil shale core is pre-placed in a 250ml osmotic bottle, and then the aqueous solution of the surfactant and the potassium chloride is moved in. The osmotic oil washing effect is observed in a high-temperature oven at 85℃, the oil output is recorded every 2 hours, and the osmotic recovery rate is calculated according to the saturated oil amount. The experimental results show that the osmotic recovery rate of the new propyl hydroxyl sulfobetaine surfactant (II) and the potassium chloride brine system of the application to the shale core can reach 61.7%, which is 32.1% and 12.7% higher than that of the comparative experiments of using water and conventional slick water as soaking liquid respectively (see Figure 4 ].

[0050] In summary of the above examples and experimental evaluation results, it is shown that the propyl hydroxyl sulfobetaine surfactant provided by the application can exhibit dipole characteristics in a wide PH range due to the presence of quaternary ammonium salt and sulfonic acid groups in the molecular structure, and has good chemical stability in acidic and alkaline media. After being compounded with anionic surfactants, strong mutual interaction is generated between the molecules to form worm-like micelles, the viscosity-increasing effect of which is significantly increased, and the viscosity stability is also good under high temperature and high shear conditions. Meanwhile, the new propyl hydroxyl sulfobetaine surfactant of the application not only greatly reduces the oil-water interfacial tension, but also can generate a middle-phase microemulsion in a certain salt concentration range. The micro-nano-sized particle size of the microemulsion is small and has a good matching relationship with the void radius of the shale core, which can effectively penetrate into the shale matrix to osmotic wash oil and improve the osmotic recovery rate, and is suitable for being used as a clean fracturing fluid for low-permeability reservoirs, tight reservoirs and shale reservoirs, and applied to the fracturing construction of high-temperature reservoirs.

[0051] It should be noted that the above examples are only used to explain the application and do not constitute any limitation on the application. The application is described by referring to typical examples, but it should be understood that the words used therein are descriptive and explanatory words rather than limiting words. The application can be modified as specified within the scope of the claims of the application, and the application can be revised without departing from the scope and spirit of the application. Although the application described therein relates to specific methods, materials and examples, it does not mean that the application is limited to the specific examples disclosed therein, on the contrary, the application can be extended to all other methods and applications with the same function. Therefore, the content of the application is not limited to the examples listed, and any equivalent transformation of the technical solutions of the application made by a person skilled in the art by reading the specification of the application is covered by the claims of the application.

Claims

1. Use of a betaine surfactant in a clean fracturing fluid for high-temperature, low-permeability sandstone, tight oil, or shale reservoirs, characterized in that: The chemical structural formula of the betaine surfactant is as follows: ； wherein: R = C 12 -C 24 aliphatic hydrocarbon radical; R1= R2= CH3, C2H5, C3H7, C4H9or C5H 11 ; The components of the cleaning fracturing fluid are proportioned as follows in percentage by mass: the betaine surfactant 1%-5%, sodium dodecyl benzene sulfonate 0.1%-1.0%, glycerol 1%-6%, potassium chloride 0.5%-3%, and the balance being water.

2. Use according to claim 1, characterized in that: The betaine surfactant 2%-4%, sodium dodecyl benzene sulfonate 0.4%-0.8%, glycerol 2%-5%, potassium chloride 1%-2%, and the balance being water.

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