A low-temperature activated gel breaker for fracturing and its application

Abstract

The present invention relates to the technical field of fracturing fluid debonding, and specifically discloses a low-temperature activated debonding agent for fracturing and its application. The low-temperature activated debonding agent for fracturing comprises the following raw materials in weight percentage: a debonding agent matrix 0.05-0.1%, a low-temperature activator 0.157-0.372%, and the remainder is a solvent; its application method comprises the following preparation steps: a debonding agent matrix, a low-temperature activator and a solvent are mixed in a specific proportion to obtain a low-temperature activated debonding agent for fracturing; the low-temperature activated debonding agent for fracturing is activated under a temperature condition of 0°C to 50°C, and the debonding reaction is promoted by stirring; the application method of the present invention controls the exothermic reaction speed to slowly heat the fracturing fluid system, so as to gradually increase the temperature of the fracturing fluid, and the whole process can achieve the initial viscosity of the fracturing fluid unchanged within 5 minutes, and achieve the complete debonding viscosity within 10 hours according to the technical requirements of SYT 7627-2021 water-based fracturing fluid.

Description

Technical Field

[0001] The invention relates to the technical field of fracturing fluid degelling, and more specifically to a low-temperature activated degelling agent for fracturing and application thereof. Background Art

[0002] Fracturing fluid breakers are indispensable chemical additives in the process of oil and gas extraction, and are mainly used in hydraulic fracturing operations. During the fracturing process, in order to create and maintain the extension of fractures in oil and gas wells, a fracturing fluid with high viscosity is required. After the operation is completed, in order to restore the fluidity of the liquid in the fractures and facilitate its return to the ground, a breaker needs to be added to reduce the viscosity of the fracturing fluid and reduce potential damage to the oil and gas layer. However, due to the low formation temperature (≤50℃) of shallow reservoirs (<2000m), the problem of the difficulty of completely breaking the fracturing fluid after fracturing has not been solved, which has seriously affected the oil and gas production of a single well.

[0003] The types of existing breakers include oxidative breakers, bio-enzyme breakers and composite breakers. Ammonium persulfate is a commonly used oxidant. It has attracted widespread attention due to its low price and convenient application. In acidic media, the decomposition reaction of ammonium persulfate can produce sulfate radicals (SO 4- ·), oxidatively breaking the main bonds of plant gums, water-soluble polymers and their derivatives, destroying the gel structure and degrading the gel, thus achieving gel breaking. However, the decomposition reaction of persulfate is affected by temperature, and the temperature must be above 50°C to effectively decompose the free radicals. The higher the temperature, the stronger the reactivity of the persulfate and the more thorough the gel breaking. Under conditions below 50°C, due to the lack of sufficient thermal energy to generate free radicals, the reaction rate will become slow, resulting in a significant decrease in the gel breaking effect. The inability to completely break the gel will have a serious impact on the output and economic benefits of oil field exploitation. Incomplete gel breaking will produce a large amount of residues, which may form blockages in the cracks, affecting the flow of oil and gas and reducing production. If the fracturing fluid cannot be effectively returned after the operation, it will be retained in the formation, affecting the permeability and output of oil and gas. In addition, the retention of fracturing fluid may also cause formation hydration and expansion, further damaging the formation.

[0004] Therefore, in order to achieve effective gel breaking of fracturing fluid by persulfate breaker under low temperature conditions, it is usually necessary to introduce an auxiliary agent that can effectively activate persulfate. Such an activator can promote the decomposition of persulfate to produce free radicals, thereby maintaining the activity and speed of the gel breaking reaction at a lower temperature, ensuring the smooth return of the fracturing fluid.

[0005] The low-temperature activation technology of persulfate mainly includes the following methods: First, physical activation: including thermal activation, photoactivation, ultrasonic activation, microwave activation and electrical activation. For example, ultrasonic activation and microwave activation can also effectively activate persulfate at low temperature through physical means to promote the degradation of organic pollutants. The second is chemical activation: using transition metals (such as Fe, Co, Cu, etc.), alkali activation, carbon material activation and organic matter activation. These chemicals react chemically with persulfate to promote its decomposition and produce free radicals. For example, transition metal ions can act as a medium for electron transfer, activate persulfate and produce free radicals, but adding them to the fracturing fluid will significantly reduce the viscosity of the fracturing fluid, fail to guarantee the initial viscosity and increase the residue content; studies have shown that carbon-containing materials can activate persulfate at low temperatures through their surface defects and functional groups. These materials include biochar, activated carbon, carbon nanotubes, graphene and its derivatives, but after adding them to the fracturing fluid, a high residue content will be formed, so it is difficult to apply them in special environments.

[0006] Although methods such as electroactivation can effectively promote the activation of persulfate under low temperature conditions, these technologies often require professional operators and specific large-scale equipment support, and it is difficult to accurately meet the viscosity change requirements during dynamic displacement construction, making it difficult to promote and apply. In addition, redox activation methods, including but not limited to ferrous ions, are difficult to accurately control the reaction rate, resulting in a significant reduction in the initial viscosity of the fracturing fluid within 5 minutes, which cannot meet the requirements of forming effective pre-fractures and ensuring efficient sand carrying performance. In addition, the gel-breaking reaction is too intense, which will affect the safety of the fracturing operation, the corrosion resistance of the wellbore, and the integrity of the reservoir properties. On the other hand, excessive use of metal ions may cause water pollution and have adverse effects on the environment. In addition, some activators have high biological toxicity and high cost, which will increase the economic burden of oil and gas development and poison the ecological environment and surface water, and are not suitable for use in actual oilfield development work. In addition, after fracturing, the fluid must be quickly discharged. According to the fracturing fluid breaking standard, the fracturing fluid must be completely broken within 10 hours to reach a viscosity of less than or equal to 5mPa·s. Regardless of whether it is a physical or chemical effect, the initial viscosity of the fracturing fluid must not decrease during the construction process, and the requirement of completely breaking the fracturing fluid within 10 hours after fracturing must be met. Based on the above statement, the present invention proposes a low-temperature activated breaker for fracturing and its application. Summary of the invention

[0007] In order to solve the problems that the gel breaking effect of the prior art under low temperature environment cannot meet the construction technical standards, the low temperature activation means have great toxicity and safety hazards, and the application conditions are harsh, etc., the present invention provides a low temperature activated gel breaker for fracturing and its application, aiming to develop an activation method that can effectively activate persulfate under low temperature conditions and is easy to operate and control. The method of the present invention is safe and efficient, does not require the addition of any additional equipment, is non-toxic and harmless, and can maintain the initial viscosity of the fracturing fluid, ensuring smooth seam creation and sand carrying, meets the current dual requirements for environmental protection and efficiency, and is of great significance for improving the gel breaking effect of the fracturing fluid under low temperature conditions and reducing the complexity of the operation.

[0008] In the first aspect, the present invention provides a low-temperature activated breaker for fracturing, which adopts the following technical solution:

[0009] A low-temperature activated breaker for fracturing comprises the following raw materials in weight percentage: 0.05-0.1% of a breaker matrix, 0.157-0.372% of a low-temperature activator, and the remainder being a solvent.

[0010] Preferably, the low-temperature activated breaker for fracturing comprises the following raw materials in weight percentage: the following raw materials in weight percentage: 0.06-0.08% of breaker matrix, 0.2-0.3% of low-temperature activator, and the balance being solvent.

[0011] Preferably, the low-temperature activated breaker for fracturing comprises the following raw materials in weight percentage: 0.05% of breaker base, 0.274% of low-temperature activator, and the balance being solvent.

[0012] Preferably, the breaker matrix comprises persulfate.

[0013] Preferably, the persulfate is ammonium persulfate and / or potassium persulfate.

[0014] Preferably, the low temperature activator comprises urea, sodium nitrite and a regulator in a molar ratio of 0.5-1:1-2:0.3-0.9.

[0015] The exothermic method of the redox reaction of urea and sodium nitrite under acidic conditions is used to increase the system temperature of the gel breaking system, thereby activating the gel breaker to release free radicals, providing an efficient, safe and environmentally friendly system for achieving low-temperature gel breaking. The exothermic mechanism of the reaction is:

[0016] NaNO2→NO2 - +Na +

[0017] NO2 - +H + →HNO2

[0018] CO(NH2)2+2HNO2+→CO2↑+2N2↑+3H2O

[0019] The above-mentioned urea is an environmentally friendly compound, and its decomposition products are ammonia and carbon dioxide, which have little impact on the environment and are relatively cheap. The binary mixture formed by urea and sodium nitrite can be used as a phase change material. The melting temperature of the mixture is 85°C and the melting enthalpy is 172J / g. These characteristics make it suitable for heating and domestic hot water applications, such as solar thermal systems and cogeneration equipment, and it has good thermal properties and is a potential heat generating agent.

[0020] Urea and sodium nitrite act as redox agents in the reaction, urea acts as a reducing agent, and sodium nitrite acts as an oxidizing agent. During the reaction, urea is oxidized and sodium nitrite is reduced, while releasing heat.

[0021] Preferably, the regulator is amino acid and / or citric acid.

[0022] Preferably, the regulator comprises glycine, lysine and citric acid in a mass ratio of 1-3:1-3:7-9.

[0023] Preferably, the solvent is water or a water-based solution.

[0024] In a second aspect, the present invention provides an application of a low-temperature activated breaker for fracturing, using the following technical solution:

[0025] A method for applying a low-temperature activated gel breaker for fracturing comprises the following preparation steps:

[0026] The breaker base, the low temperature activator and the solvent are mixed in a specific ratio to form a low temperature activated breaker for fracturing;

[0027] The low-temperature activated breaker for fracturing is activated at a temperature of 0°C to 50°C, and the breaking reaction is promoted to completion by stirring.

[0028] Preferably, the activation reaction time is at least 4-6 hours.

[0029] Preferably, the activation reaction time is at least 5 hours.

[0030] After the gel-breaking system is injected into the formation, the temperature difference between the heated gel-breaking fluid and the original temperature of the deep formation will cause heat to be transferred from the high-temperature fracturing fluid area to the low-temperature deep formation area. This heat transfer process will consume the heat in the fracturing fluid, which will in turn affect the complete gel-breaking of the fracturing fluid, resulting in low post-fracturing production. This process is also the reason why the current conventional heating system cannot completely break the gel. In order to ensure that the fracturing fluid maintains a temperature level that completely breaks the gel after being injected into the formation, the gel-breaking system needs to scientifically supplement the heat dissipated during the conduction process (conduction heat). In order to achieve scientific dosage and ensure that the breaker can decompose free radicals at normal temperatures, a simulation system for scientifically calculating dosage is designed:

[0031] The above conduction heat can be calculated using Fourier's law:

[0032]

[0033] ΔΤ=T-Ts

[0034] Q represents the heat of conduction, k represents the thermal conductivity, A represents the heat transfer area, Δx represents the heat transfer distance, T represents the temperature of the fracturing fluid system, and Ts represents the original formation temperature

[0035] Meyer three-dimensional fracturing software is used to model hydraulic fractures. The fracture area and length can be calculated through the MFrac module, which are equivalent to the heat transfer area and heat transfer distance of the above equation.

[0036] After finding the conduction heat Q, the required amount of low-temperature activator can be calculated according to the formula:

[0037] Q+Q1=Cm1ΔT

[0038] The specific heat capacity of the fracturing fluid is C, the mass of the fracturing fluid after scientific calculation is m1, the temperature change in the experiment is ΔΤ, and Q1 is the heat of the fracturing fluid without scientific calculation.

[0039] According to the above formula, the scientifically calculated mass of the fracturing fluid is m1. By adding an additional amount of activator, the gel breaker is ensured to be completely broken.

[0040] In summary, the present invention has the following beneficial effects:

[0041] 1. The low-temperature activated breaker for fracturing of the present invention has a more efficient and safer breaking effect than the existing breakers. The present invention introduces a low-temperature activator to enable the breaker to quickly and stably break the gel in a low-temperature environment of 0°C to 50°C, and the breaking system used has higher safety, avoiding the difficulties and problems such as toxicity and environmental risks existing in the existing low-temperature activation technology.

[0042] 2. The application method of the present invention controls the heating reaction speed to slowly heat the fracturing fluid system, so as to gradually increase the temperature of the fracturing fluid. The entire process can keep the initial viscosity of the fracturing fluid unchanged within 5 minutes, and achieve complete gel-breaking viscosity within 10 hours in accordance with the technical requirements of SYT 7627-2021 water-based fracturing fluid. And by combining the design simulation calculation, the energy consumed by the diffusion of the fracturing fluid from the high temperature zone to the low temperature zone during actual use can be calculated, so as to more scientifically achieve the effect of heating to activate the gel breaker. By controlling the temperature rising speed, the persulfate can be activated to different degrees according to the degelling time to effectively decompose free radicals, ensuring the smooth return of the fracturing fluid in the oil and gas wells and avoiding residue, thereby improving the fracturing efficiency and the production effect of the oil and gas wells; and the exothermic reaction material has good compatibility with the fracturing fluid and can be smoothly used in oil field exploitation; it is simple to operate and has high safety, and is suitable for a variety of complex operation scenarios; in addition, the present invention also realizes that the final reactant of the degelling system will not cause secondary pollution to the reservoir, and can produce a large amount of gas to increase energy and assist in the displacement of oil and gas, which is particularly beneficial to the exploitation of low-permeability, low-porosity, low-pressure and difficult-to-use reserves and the increase of energy and production of reservoirs. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 Schematic diagram of the temperature rise of Examples 1-3 of the present invention at 25°C using different low-temperature activators.

[0044] Figure 2 The sulfate radical concentrations of Examples 1-4 of the present invention at different low-temperature activators and different breaker usages.

[0045] Figure 3 The viscosity of the fracturing fluid in Examples 1-3 of the present invention at different low temperature activator usage amounts. DETAILED DESCRIPTION

[0046] The present invention is further described in detail below with reference to the embodiments.

[0047] Unless otherwise specified, the materials, reagents, etc. used in the present invention can be obtained from commercial sources.

[0048] Embodiment 1-3 provides a low-temperature activated breaker for fracturing and its application.

[0049] Example 1

[0050] A low-temperature activated breaker for fracturing comprises the following raw materials in weight percentage: 0.05% of a breaker matrix, 0.274% of a low-temperature activator, and the balance is water; wherein the breaker matrix is ​​ammonium persulfate, and the low-temperature activator comprises urea, sodium nitrite and a regulator in a molar ratio of 0.8:1.5:0.6; and the regulator is citric acid.

[0051] A method for applying a low-temperature activated gel breaker for fracturing comprises the following steps: first, at a room temperature of 25°C, urea is added to water, and stirred continuously for 30 minutes to ensure that it is completely dissolved. After the urea is completely dissolved, sodium nitrite is added, and stirring is continued for 25 minutes, and a mixed solution of citric acid is added. Ammonium persulfate is added to the mixed solution, and stirred to dissolve, thereby obtaining a low-temperature activated gel breaker for fracturing.

[0052] The low-temperature activated breaker for fracturing of this embodiment is applied to the fracturing fluid to perform an activation reaction, and the breaking reaction is accelerated by stirring.

[0053] The fracturing fluid formula in this embodiment is to prepare 400mL of slippery water, and the formula also includes the following: 0.3% drag reducing agent (polyacrylamide (PAM) with a weight average molecular weight of 3 million) + 0.5% potassium chloride + 0.279% low-temperature activated breaker for fracturing. After the reaction starts, the system temperature is recorded with a thermometer, and the system viscosity is measured with a rotational viscometer. The results are shown in Table 1 below:

[0054] Table 1 Rotational viscosity of fracturing fluid system at different system temperatures

[0055]

[0056] According to the data in Table 1, it can be concluded that within 5 minutes, the system temperature hardly changed and the viscosity of the fracturing fluid did not decrease, which met the sand carrying standard. After 30 minutes, the system temperature rose to 89°C, at which time the viscosity of the fracturing fluid dropped to 5.7 mPa·s, and finally at 60 minutes, the viscosity dropped to 3.5 mPa·s, which met the gel breaking standard.

[0057] Example 2

[0058] A low-temperature activated breaker for fracturing comprises the following raw materials in weight percentage: 0.05% of a breaker matrix, 0.372% of a low-temperature activator, and the balance is water; wherein the breaker matrix is ​​ammonium persulfate, and the low-temperature activator comprises urea, sodium nitrite, and a regulator in a molar ratio of 1:2:0.9; and the regulator is citric acid.

[0059] A method for applying a low-temperature activated gel breaker for fracturing comprises the following steps: first, at a temperature of 14°C, urea is added to water, and stirred continuously for 40 minutes to ensure that it is completely dissolved. After the urea is completely dissolved, sodium nitrite is added, and stirring is continued for 30 minutes, and a mixed solution of citric acid is added. Ammonium persulfate is added to the mixed solution, and stirred to dissolve, thereby obtaining a low-temperature activated gel breaker for fracturing.

[0060] The low-temperature activated breaker for fracturing of this embodiment is applied to the fracturing fluid to perform an activation reaction, and the breaking reaction is accelerated by stirring.

[0061] The fracturing fluid formula in this embodiment is to prepare 400mL of slippery water, and the formula also includes the following: 0.3% drag reducing agent (polyacrylamide (PAM) with a weight average molecular weight of 3 million) + 0.5% potassium chloride + 0.377% low-temperature activated breaker for fracturing. After the reaction starts, the system temperature is recorded with a thermometer, and the system viscosity is measured with a rotational viscometer. The results are shown in Table 2 below:

[0062] Table 2 Rotational viscosity of fracturing fluid system at different system temperatures

[0063]

[0064] According to the data in Table 2, it can be concluded that within 5 minutes, the system temperature hardly changed, and the viscosity of the fracturing fluid did not drop much, which met the sand carrying standard. After 20 minutes, the system temperature rose to 89°C, at which time the viscosity of the fracturing fluid dropped to 6.4 mPa·s, and finally at 40 minutes, the viscosity dropped to 3.9 mPa·s, which met the gel breaking standard.

[0065] Example 3

[0066] A low-temperature activated breaker for fracturing comprises the following raw materials in weight percentage: 0.05% of a breaker matrix, 0.157% of a low-temperature activator, and the balance is water; wherein the breaker matrix is ​​ammonium persulfate, and the low-temperature activator comprises urea, sodium nitrite and a regulator in a molar ratio of 0.5:1:0.3; and the regulator is citric acid.

[0067] A method for applying a low-temperature activated gel breaker for fracturing comprises the following steps: first, at a temperature of 38°C, urea is added to water, and stirred for 25 minutes to ensure that it is completely dissolved. After the urea is completely dissolved, sodium nitrite is added, and stirring is continued for 15 minutes, and a mixed solution of citric acid is added. Ammonium persulfate is added to the mixed solution, and stirred to dissolve, thereby obtaining a low-temperature activated gel breaker for fracturing.

[0068] The low-temperature activated breaker for fracturing of this embodiment is applied to the fracturing fluid to perform an activation reaction, and the breaking reaction is accelerated by stirring.

[0069] The fracturing fluid formula in this embodiment is to prepare 400mL of slippery water, and the formula also includes the following: 0.3% drag reducing agent (polyacrylamide (PAM) with a weight average molecular weight of 3 million) + 0.5% potassium chloride + 0.162% low-temperature activated breaker for fracturing. After the reaction starts, the system temperature is recorded with a thermometer, and the system viscosity is measured with a rotational viscometer. The results are shown in Table 3 below:

[0070] Table 3 Rotational viscosity of fracturing fluid system at different system temperatures

[0071]

[0072] According to the data in Table 3, it can be concluded that within 5 minutes, the system temperature hardly changed, and the viscosity of the fracturing fluid did not decrease, which met the sand carrying standard. After 20 minutes, the system temperature rose to 83°C, at which time the viscosity of the fracturing fluid dropped to 7.8 mPa·s, and finally at 50 minutes, the viscosity dropped to 3.6 mPa·s, which met the gel breaking standard.

[0073] Example 4

[0074] A low-temperature activated breaker for fracturing comprises the following raw materials in weight percentage: 0.1% of a breaker matrix, 0.274% of a low-temperature activator, and the balance is water; wherein the breaker matrix is ​​ammonium persulfate, and the low-temperature activator comprises urea, sodium nitrite, and a regulator in a molar ratio of 0.8:1.5:0.6; and the regulator is citric acid.

[0075] A method for applying a low-temperature activated gel breaker for fracturing comprises the following steps: first, at a room temperature of 25°C, urea is added to water, and stirred continuously for 30 minutes to ensure that it is completely dissolved. After the urea is completely dissolved, sodium nitrite is added, and stirring is continued for 25 minutes, and a mixed solution of citric acid is added. Ammonium persulfate is added to the mixed solution, and stirred to dissolve, thereby obtaining a low-temperature activated gel breaker for fracturing.

[0076] The low-temperature activated breaker for fracturing of this embodiment is applied to the fracturing fluid to perform an activation reaction, and the breaking reaction is accelerated by stirring.

[0077] The fracturing fluid formula in this embodiment is to prepare 400mL of slick water, and the formula also includes the following: 0.3% drag reducing agent (polyacrylamide (PAM) with a weight average molecular weight of 3 million) + 0.5% potassium chloride + 0.279% low-temperature activated breaker for fracturing. After the reaction starts, the system temperature is recorded with a thermometer, and the system viscosity is measured with a rotational viscometer. The results are shown in Table 4 below:

[0078] Table 4 Rotational viscosity of fracturing fluid system at different system temperatures

[0079]

[0080]

[0081] According to the data in Table 4, it can be concluded that within 5 minutes, the system temperature hardly changed and the viscosity of the fracturing fluid did not decrease, which met the sand carrying standard. After 20 minutes, the system temperature rose to 89°C, at which time the viscosity of the fracturing fluid dropped to 7.2 mPa·s, and finally at 40 minutes, the viscosity dropped to 3.7 mPa·s, which met the gel breaking standard.

[0082] Example 5

[0083] A low-temperature activated breaker for fracturing comprises the following raw materials in weight percentage: 0.05% of a breaker matrix, 0.274% of a low-temperature activator, and the balance being water; wherein the breaker matrix is ​​ammonium persulfate, the low-temperature activator comprises urea, sodium nitrite and a regulator in a molar ratio of 0.8:1.5:0.6; and the regulator comprises glycine, lysine and citric acid in a mass ratio of 1:1:4.

[0084] A method for applying a low-temperature activated gel breaker for fracturing comprises the following steps: first, at a temperature of 5°C, urea is added to water, and stirred continuously for 30 minutes to ensure that it is completely dissolved. After the urea is completely dissolved, sodium nitrite is added, and stirring is continued for 25 minutes, and a mixed solution of citric acid is added. Ammonium persulfate is added to the mixed solution, and stirred to dissolve, thereby obtaining a low-temperature activated gel breaker for fracturing.

[0085] The low-temperature activated breaker for fracturing of this embodiment is applied to the fracturing fluid to perform an activation reaction, and the breaking reaction is accelerated by stirring.

[0086] The fracturing fluid formula in this embodiment is to prepare 400mL of slick water, and the formula also includes the following: 0.3% drag reducing agent (polyacrylamide (PAM) with a weight average molecular weight of 3 million) + 0.5% potassium chloride + 0.279% low-temperature activated breaker for fracturing. After the reaction starts, the system temperature is recorded with a thermometer, and the system viscosity is measured with a rotational viscometer. The results are shown in Table 5 below:

[0087] Table 5 Rotational viscosity of fracturing fluid system at different system temperatures

[0088]

[0089]

[0090] According to the data in Table 5, it can be concluded that within 5 minutes, the system temperature hardly changed and the viscosity of the fracturing fluid did not decrease, which met the sand carrying standard. After 30 minutes, the system temperature rose to 89°C, at which time the viscosity of the fracturing fluid dropped to 6.3 mPa·s, and finally at 60 minutes, the viscosity dropped to 3.7 mPa·s, which met the gel breaking standard.

[0091] By combining Examples 1-5 with the attached Figure 1-3 It can be seen that the application method of the present invention controls the exothermic reaction rate to slowly heat the fracturing fluid system, so as to gradually increase the temperature of the fracturing fluid. The whole process can maintain the initial viscosity of the fracturing fluid unchanged within 5 minutes, and reach the complete gel-breaking viscosity within 10 hours according to the technical requirements of SYT 7627-2021 water-based fracturing fluid.

[0092] Further, according to Figure 2 As shown in the figure, when the addition amount of ammonium persulfate is set to 0.05%, the corresponding addition amounts of the low-temperature activator system are 0.157%, 0.274% and 0.372% respectively. After 1 hour of reaction, the measured sulfate radical (SO 4- ·) concentrations reached 0.11mmol / L, 0.16mmol / L, and 0.2mmol / L, respectively. When the amount of ammonium persulfate added was increased to 0.1%, and the amount of the low-temperature activator system added was maintained at 0.274%, after 1 hour, the concentration of sulfate radicals was measured to be 0.31mmol / L. The experimental data show that adjusting the amount of ammonium persulfate and the low-temperature activator system can effectively adjust the breaking performance of the breaking system to meet the needs of different breaking environments.

[0093] This specific embodiment is merely an explanation of the present invention and is not a limitation of the present invention. After reading this specification, those skilled in the art may make non-creative modifications to the present embodiment as needed. However, as long as they are within the scope of the claims of the present invention, they are protected by the patent law.

Claims

1. A low temperature activated gel breaker for fracturing, characterized in that: The invention comprises the following raw materials in weight percentage: 0.05-0.1% of a breaker matrix, 0.157-0.372% of a low-temperature activator, and the balance being a solvent.

2. The low temperature activated gel breaker for fracturing according to claim 1, characterized in that: The invention comprises the following raw materials in weight percentage: 0.05% of a breaker matrix, 0.274% of a low-temperature activator, and the balance of solvent.

3. The low temperature activated gel breaker for fracturing according to claim 1, characterized in that: The breaker matrix includes persulfate.

4. The low temperature activated gel breaker for fracturing according to claim 1, characterized in that: The persulfate is ammonium persulfate and / or potassium persulfate.

5. The low temperature activated gel breaker for fracturing according to claim 1, characterized in that: The low-temperature activator comprises urea, sodium nitrite and a regulator in a molar ratio of 0.5-1:1-2:0.3-0.

9.

6. The low temperature activated gel breaker for fracturing according to claim 5, characterized in that: The regulator is amino acid and / or citric acid.

7. The low temperature activated gel breaker for fracturing according to claim 6, characterized in that: The regulator comprises glycine, lysine and citric acid in a mass ratio of 1-3:1-3:7-9.

8. The low temperature activated gel breaker for fracturing according to claim 1, characterized in that: The solvent is water or a water-based solution.

9. A method for using the low temperature activated gel breaker for fracturing according to any one of claims 1 to 8, characterized in that: The method comprises the following preparation steps: The breaker base, the low temperature activator and the solvent are mixed in a specific ratio to form a low temperature activated breaker for fracturing; The low-temperature activated breaker for fracturing is activated at a temperature of 0°C to 50°C, and the breaking reaction is promoted to completion by stirring.

10. The method for applying the low temperature activated gel breaker for fracturing according to claim 9, characterized in that: The activation reaction time is at least 4-6 hours.

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