Fracturing fluid assisted carbon dioxide huff-puff oil extraction method

Abstract

The invention discloses a fracturing fluid assisted carbon dioxide huff and puff oil extraction method, and belongs to the technical field of oil and gas extraction. The fracturing fluid is prepared from the following raw materials in percentage by weight: 0.3 to 0.7 weight percent of silicon-containing tackifier, 0.1 to 0.5 weight percent of fluorine-containing tackifier, 0.8 to 1.2 weight percent of cosolvent, 6 to 23 weight percent of proppant, 0.01 to 0.1 weight percent of gel breaker and the balance of water, the silicon-containing tackifier is one or more of polydimethylsiloxane, polymethylsilsesquioxane, benzyl polysiloxane and methyl silicone oil; the silicon-containing tackifier is one or more of polydimethylsiloxane, polymethylsilsesquioxane, benzyl polysiloxane and methyl silicone oil; the fluorine-containing tackifier is a terpolymer of fluorinated acrylate, a styrene compound and maleic anhydride, and the molecular weight of the fluorine-containing tackifier is 1000 to 1500. The fracturing fluid can be used for tackifying CO2, the sand-carrying capacity of the fracturing fluid is improved, and the oil recovery rate is increased.

Description

TECHNICAL FIELD

[0001] The application relates to a fracturing fluid assisted carbon dioxide huff and puff oil production method and belongs to the technical field of oil and gas exploitation. BACKGROUND

[0002] In unconventional oil and gas exploitation operations, a large amount of fresh water is needed to exploit shale oil by adopting horizontal well and staged fracturing technology, and the large consumption of fresh water resources and the resulting environmental pollution problems have caused widespread concern of the government and the public. In addition, the tight oil reservoirs in China have the characteristics of super-low permeability, low rock brittleness, low development degree of natural fractures, low pressure coefficient, high oil viscosity and poor flowability. These characteristics bring greater challenges to drilling, hydraulic fracturing and oil production.

[0003] CO2 has great application potential in fracturing operations. As a fracturing fluid, it needs to have good sand carrying capacity, however, the viscosity of pure CO2 is still low even under supercritical conditions, and the viscosity of supercritical CO2 is 0.03-0.10 cp, and the viscosity of crude oil is 0.1-50 cp, and the viscosity of supercritical CO2 is more than one order of magnitude lower than that of crude oil. The viscosity ratio of the displacement fluid (supercritical CO2) to the displaced fluid (crude oil) results in poor mobility ratio, which can cause CO2 viscous fingering and early breakthrough of CO2, and reduces the oil recovery. Therefore, effective thickening of CO2 is very important for promoting the application of CO2 in oilfield development. SUMMARY

[0004] In order to solve the above problems, a fracturing fluid assisted carbon dioxide huff and puff oil production method is provided, which can thicken CO2, improve the sand carrying capacity of the fracturing fluid and improve the oil recovery.

[0005] The application adopts the following technical scheme: According to one aspect of the application, a fracturing fluid is provided, which comprises the following raw materials by weight fraction: 0.3-0.7wt% of a silicon-containing thickening agent, 0.1-0.5wt% of a fluorine-containing thickening agent, 0.8-1.2wt% of a cosolvent, 6-23wt% of a proppant, 0.01-0.1wt% of a gel breaker, and the balance being water. The silicon-containing thickening agent is one or more of polydimethylsiloxane, polymethylsilsesquioxane, phenylmethyl polysiloxane and methyl silicone oil. The fluorine-containing thickening agent is a terpolymer of fluorinated acrylate, styrene compound and maleic anhydride, and the molecular weight of the fluorine-containing thickening agent is 10000-15000.

[0006] Optionally, the silicon-containing thickening agent is polydimethylsiloxane, polymethylsilsesquioxane and methyl silicone oil in a weight ratio of (1-3):1:(0.8-1.5).

[0007] Optionally, the proppant is glass beads, quartz sand or ceramic particles. The breaker is ammonium persulfate, potassium persulfate or hydrogen peroxide. The cosolvent is methanol, diethyl ether, kerosene, ethanol, ethylene glycol or acetone.

[0008] Optionally, the preparation method of the fluorine-containing tackifier comprises the following steps: (1) Put maleic anhydride into a reaction vessel filled with inert gas, dissolve it with water, then add auxiliary agent and mix uniformly; (2) Increase the temperature of the reaction system to 50-80℃, then add styrene compound, initiator and fluorinated acrylate successively, and drop fluorinated acrylate for 0.8-1.2h, after the reaction is completed, cool to room temperature to obtain a polymer solution, wash, filter and dry to obtain the fluorine-containing tackifier.

[0009] Optionally, the molar ratio of the styrene compound, maleic anhydride and fluorinated acrylate is 1: (3-5): (2-3). The amount of the initiator is 0.5-3wt% of the sum of the styrene compound, maleic anhydride and fluorinated acrylate. The amount of the auxiliary agent is 0.1-2wt% of the sum of the styrene compound, maleic anhydride and fluorinated acrylate.

[0010] Optionally, the fluorinated acrylate is trifluoroethyl acrylate, hexafluorobutyl acrylate or perfluoroalkyl ethyl methacrylate.

[0011] Optionally, the styrene compound is styrene, methylstyrene or chlorostyrene.

[0012] Optionally, the initiator is benzoyl peroxide, azobisisobutylonitrile, azobisisopentyl nitrile or azobisisoheptyl nitrile.

[0013] Optionally, the auxiliary agent is isopropyl alcohol, isobutyl alcohol or tert-butyl alcohol.

[0014] According to another aspect of the present application, a fracturing fluid assisted carbon dioxide huff and puff oil production method is provided, which comprises the following steps: S1, inject CO2 and the fracturing fluid of any one of the above into a core holder containing a rock sample, open the fracturing fluid injection end after 10-15h of soaking to produce, and complete one round of huff and puff; S2, repeat the operation in step S1, and perform 2-3 rounds of huff and puff to complete the production.

[0015] Optionally, the injection pressure of CO2 and fracturing fluid is 28-32MPa.

[0016] In the present application, "room temperature" refers to 20-30℃.

[0017] The beneficial effects of the present application include but are not limited to: 1. The fracturing fluid assisted carbon dioxide huff and puff oil recovery method of the present application, CO2 as the displacing agent, fracturing fluid as the huffing agent, the imbibition of fracturing fluid and the displacement of CO2 are in a good combination, which can fully exert the advantages of imbibition of liquid in dense shale reservoir rock and displacement of CO2, to exploit the crude oil in various levels of pores in shale reservoir and realize continuous energy supplement of shale oil reservoir, and maximize the recovery of shale oil reservoir; wherein, the synergistic effect of the silicon-containing tackifier and the fluorine-containing tackifier can enhance the stability of the fracturing fluid under high temperature and high pressure conditions, reduce the degradation risk under complex geological conditions, thereby greatly improving the sand carrying capacity and recovery of the fracturing fluid; the addition of the cosolvent can help reduce the dissolution pressure of the silicon-containing tackifier, thereby increasing its solubility in carbon dioxide; the addition of the proppant can keep the fracture open when CO2 is injected, forming a high-permeability channel to ensure that CO2 can effectively penetrate into the deep part of the reservoir; after the gel breaker is used to quickly break the gel, the fracturing fluid can easily flow back from the fracture, reducing the damage to the reservoir, and at the same time, providing space for CO2 seepage; the components in the fracturing fluid work together to change the microstructure and physicochemical properties of the shale reservoir, thereby achieving the purpose of improving imbibition and oil displacement.

[0018] 2. The fracturing fluid assisted carbon dioxide huff and puff oil recovery method of the present application, the viscosity of CO2 is mainly relied on the complex spatial structure formed by the tackifier molecules in the system to hinder the diffusion movement of CO2, increase the viscosity of the system, and improve the sand carrying capacity of the fracturing fluid system; wherein, the fluorocarbon functional group (CO2-philic group) in the fluorine-containing tackifier can destroy the interaction of the electric quadrupole moment between CO2 molecules, and occur dipole-quadrupole interaction with CO2 molecules. According to the Lewis acid-base theory, the hydrogen atoms and fluorine atoms on the main chain of the semi-fluorinated copolymer molecule can be used as Lewis acid and Lewis base respectively to interact with CO2 through H—O and F—C, thus having good CO2-philic property; the π-π stacking between the styrene side chain groups (CO2-phobic groups) provides driving force for the polymer molecules to form a spatial network structure, thereby increasing the viscosity of the whole system; the introduction of the carbonyl functional group in maleic anhydride enhances the interaction between the polymer and CO2, and reduces the interaction between the polymer and the polymer; therefore, the tackifier can be well dissolved in CO2, and has good tackifying effect on the fracturing fluid. DETAILED DESCRIPTION

[0019] The endpoints of the ranges and any values disclosed herein are not limited to the precise values recited as the exact dimensions are not critical to the properties. The endpoints of the ranges and any values are provided as approximations only, and are understood to be open-ended. Thus, the endpoints of the ranges and any values are not to be understood as being stated to be the only values that can be used to define the range or the value. The range and any value are understood to include values approximating the value, in addition to the exact value.

[0020] Unless otherwise indicated, conventional conditions or manufacturer's recommended conditions are employed in the examples. Unless otherwise indicated, the materials used are conventional materials available from commercial vendors.

[0021] Example 1 A method for preparing a fracturing fluid, comprising the following steps: 0.3wt% benzyl polysiloxane is dissolved in 0.8wt% methanol to obtain a mixed solution A, 0.1wt% fluorine-containing tackifier is dissolved in water to obtain a mixed solution B, the mixed solution A and the mixed solution B are uniformly mixed, 6wt% glass beads (20 mesh) are added, stirring for 5 min, and then 0.01wt% ammonium sulfate is added to obtain the fracturing fluid; The method for preparing the fluorine-containing tackifier comprises the following steps: (1) Maleic anhydride is placed in a nitrogen-filled reaction vessel, dissolved in water, and then 0.1wt% isobutyl alcohol is added and mixed uniformly; (2) The temperature of the reaction system is raised to 50℃, styrene, 0.5wt% azobisisobutyronitrile and trifluoroethyl acrylate are sequentially added, and the trifluoroethyl acrylate is dropped for 0.8h, the molar ratio of styrene, maleic anhydride and trifluoroethyl acrylate is 1:3:2, after the reaction is completed, it is cooled to room temperature to obtain a polymer solution, which is washed, suction filtered and dried to obtain a fluorine-containing tackifier with a molecular weight of 10000.

[0022] Example 2 A method for preparing a fracturing fluid, comprising the following steps: 0.25wt% polydimethylsiloxane, 0.1wt% polymethylsilsesquioxane and 0.15wt% methyl silicone oil are dissolved in 1wt% ethanol to obtain a mixed solution A, 0.3wt% fluorine-containing tackifier is dissolved in water to obtain a mixed solution B, the mixed solution A and the mixed solution B are uniformly mixed, 15wt% quartz sand (40 mesh) is added, stirring for 8 min, and then 0.05wt% potassium persulfate is added to obtain the fracturing fluid; The method for preparing the fluorine-containing tackifier comprises the following steps: (1) Maleic anhydride is placed in a nitrogen-filled reaction vessel, dissolved in water, and then 1wt% isopropyl alcohol is added and mixed uniformly; (2) The temperature of the reaction system is raised to 65℃, methylstyrene, 1.8wt% benzoyl peroxide and hexafluorobutyl acrylate are added in turn, and the dropping of hexafluorobutyl acrylate is completed in 1h, the molar ratio of methylstyrene, maleic anhydride and hexafluorobutyl acrylate is 1:4:2.5, after the reaction is completed, it is cooled to room temperature to obtain a polymer solution, which is washed, suction filtered and oven dried to obtain a fluorine-containing tackifier with a molecular weight of 12500.

[0023] Example 3 A preparation method of a fracturing fluid, comprising the following steps: 0.3wt% polymethylsilsesquioxane and 0.4wt% phenylmethylsilicone are dissolved in 1.2wt% kerosene to obtain a mixed solution A, 0.5wt% fluorine-containing tackifier is dissolved in water to obtain a mixed solution B, the mixed solution A and the mixed solution B are uniformly mixed, 23wt% ceramic particles (60 mesh) are added, after stirring for 10min, 0.1wt% hydrogen peroxide is added, and a fracturing fluid is obtained. The preparation method of the fluorine-containing tackifier comprises the following steps: (1) Maleic anhydride is placed in a reaction container filled with nitrogen, dissolved in water, and then 2wt% tert-butyl alcohol is added and uniformly mixed; (2) The temperature of the reaction system is raised to 80℃, chlorostyrene, 3wt% azobis diisopropyl cyanide and perfluoroalkyl ethyl methacrylate are added in turn, and the dropping of perfluoroalkyl ethyl methacrylate is completed in 1.2h, the molar ratio of chlorostyrene, maleic anhydride and perfluoroalkyl ethyl methacrylate is 1:5:3, after the reaction is completed, it is cooled to room temperature to obtain a polymer solution, which is washed, suction filtered and oven dried to obtain a fluorine-containing tackifier with a molecular weight of 15000.

[0024] Example 4 A preparation method of a fracturing fluid, comprising the following steps: 0.25wt% polydimethylsiloxane, 0.1wt% polymethylsilsesquioxane and 0.15wt% methyl silicone oil are dissolved in 1wt% ethanol to obtain a mixed solution A, 0.3wt% hexafluorobutyl acrylate is dissolved in water to obtain a mixed solution B, the mixed solution A and the mixed solution B are uniformly mixed, 15wt% quartz sand (40 mesh) is added, after stirring for 8min, 0.05wt% potassium persulfate is added, and a fracturing fluid is obtained.

[0025] Example 5 The difference from Example 2 is that the preparation method of the fluorine-containing tackifier comprises the following steps: Methylstyrene, 1.8wt% benzoyl peroxide and hexafluorobutyl acrylate were sequentially added into a nitrogen-filled reaction vessel, and the hexafluorobutyl acrylate was dropped for 1h, the reaction temperature was 65℃, the molar ratio of methylstyrene and hexafluorobutyl acrylate was 1:2.5, after the reaction was completed, it was cooled to room temperature to obtain a polymer solution, which was washed, suction filtered and oven dried to obtain a fluorine-containing tackifier with a molecular weight of 12500.

[0026] Comparative Example 1 A method for preparing a fracturing fluid, comprising the following steps: 0.3wt% fluorine-containing tackifier was dissolved in water, 15wt% quartz sand (40 mesh) was added, stirred for 8min, and then 0.05wt% potassium persulfate was added to obtain the fracturing fluid. The method for preparing the fluorine-containing tackifier comprises the following steps: (1) Maleic anhydride was placed in a nitrogen-filled reaction vessel, dissolved in water, and then 1wt% isopropyl alcohol was added and mixed uniformly; (2) The temperature of the reaction system was increased to 65℃, methylstyrene, 1.8wt% benzoyl peroxide and hexafluorobutyl acrylate were sequentially added, and the hexafluorobutyl acrylate was dropped for 1h, the molar ratio of methylstyrene, maleic anhydride and hexafluorobutyl acrylate was 1:4:2.5, after the reaction was completed, it was cooled to room temperature to obtain a polymer solution, which was washed, suction filtered and oven dried to obtain a fluorine-containing tackifier with a molecular weight of 12500.

[0027] Comparative Example 2 A method for preparing a fracturing fluid, comprising the following steps: 0.25wt% polydimethylsiloxane, 0.1wt% polymethylsilsesquioxane and 0.15wt% methyl silicone oil were dissolved in 1wt% ethanol, 15wt% quartz sand (40 mesh) was added, stirred for 8min, and then 0.05wt% potassium persulfate was added to obtain the fracturing fluid.

[0028] Test Example 1 A method for CO2 assisted fracturing and huff and puff oil production, comprising the following steps: S1, CO2 and fracturing fluid were injected into a core holder containing rock samples (taken from shale oil reservoirs in Shengli Oilfield, with an average porosity of 15.73% and an average permeability of 0.0281mD), the fracturing fluid was obtained by Examples 1-5 and Comparative Examples 1-2, the injection pressure of CO2 and fracturing fluid was 30MPa, after 12h of soaking, the fracturing fluid injection end was opened for production, and one cycle of huff and puff was completed. S2, the operation in step S1 was repeated, and two cycles of huff and puff were carried out to complete the production.

[0029] The recovery results are shown in Table 1 below.

[0030] Table 1

[0031] Test Example 2 A carbon dioxide huff and puff oil production method, comprising the following steps: S1, injecting CO2 into a core holder containing a rock sample (taken from a shale oil reservoir of Shengli Oilfield, with an average porosity of 15.73% and an average permeability of 0.0281 mD), the CO2 injection pressure is 30 MPa, after 12 hours of soaking, the CO2 injection end is opened for production, and one round of huff and puff is completed; S2, repeating the operation in step S1, and performing two rounds of huff and puff, and completing the production.

[0032] The recovery rate of the first huff and puff round is 18.56%, the recovery rate of the second huff and puff round is 9.61%, the recovery rate of the third huff and puff round is 0.47%, and the total recovery rate is 28.64%, which is much lower than that of the fracturing fluid assisted carbon dioxide huff and puff oil production method.

[0033] The above is only an embodiment of the present application, and the protection scope of the present application is not limited by these specific embodiments, but is determined by the claims of the present application. The present application can have various changes and variations for those skilled in the art. Any modification, equivalent replacement, improvement, etc. within the technical thought and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A fracturing fluid, characterized in that, The raw materials include the following weight fractions: 0.3-0.7 wt% silicone-containing tackifier, 0.1-0.5 wt% fluorinated tackifier, 0.8-1.2 wt% co-solvent, 6-23 wt% proppant, 0.01-0.1 wt% breaker, and the balance being water; The silicone-containing thickener is one or more of polydimethylsiloxane, polymethylsilsesquioxane, benzyl polysiloxane, and methyl silicone oil; The fluorinated tackifier is a terpolymer of fluorinated acrylate, styrene compounds and maleic anhydride, and the molecular weight of the fluorinated tackifier is 10,000-15,000.

2. The fracturing fluid according to claim 1, characterized in that, The silicone-containing tackifier is polydimethylsiloxane, polymethylsilsesquioxane and methyl silicone oil in a weight ratio of (1-3):1:(0.8-1.5).

3. The fracturing fluid according to claim 1, characterized in that, The proppant is glass beads, quartz sand, or ceramsite; The degreasing agent is ammonium persulfate, potassium persulfate, or hydrogen peroxide; The co-solvent is methanol, diethyl ether, kerosene, ethanol, ethylene glycol, or acetone.

4. The fracturing fluid according to claim 1, characterized in that, The preparation method of the fluorinated thickener includes the following steps: (1) Place maleic anhydride in a reaction vessel filled with inert gas, add water to dissolve it, then add the auxiliary agent and mix well; (2) Raise the temperature of the reaction system to 50-80℃, add styrene compounds, initiators and fluorinated acrylates in sequence, and add the fluorinated acrylates dropwise over 0.8-1.2h. After the reaction is complete, cool to room temperature to obtain a polymer solution, wash, filter and dry to obtain a fluorinated thickener.

5. The fracturing fluid according to claim 4, characterized in that, The molar ratio of the styrene compound, maleic anhydride, and fluorinated acrylate is 1:(3-5):(2-3). The amount of the initiator is 0.5-3 wt% of the sum of styrene compounds, maleic anhydride, and fluorinated acrylates; The amount of the additive is 0.1-2 wt% of the sum of styrene compounds, maleic anhydride, and fluorinated acrylates.

6. The fracturing fluid according to claim 4, characterized in that, The styrene compounds are styrene, methylstyrene, or chlorostyrene.

7. The fracturing fluid according to claim 4, characterized in that, The initiator is benzoyl peroxide, azobisisobutyronitrile, azobisisovalerate, or azobisisoheptanenitrile.

8. The fracturing fluid according to claim 4, characterized in that, The additive is isopropanol, isobutanol, or tert-butanol.

9. A fracturing fluid-assisted carbon dioxide huff and puff method for oil recovery, comprising the following steps: S1. Inject CO2 and the fracturing fluid as described in any one of claims 1-8 into the core holder containing the rock sample, let it sit for 10-15 hours, then open the fracturing fluid injection end to start production, completing one round of infeed and outfeed. S2. Repeat the operation in step S1, and perform 2-3 more rounds of throughput to complete the mining.

10. The fracturing fluid-assisted carbon dioxide huff and puff method for oil recovery according to claim 9, characterized in that, The injection pressure of both CO2 and fracturing fluid is 28-32 MPa.

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