CN109611070B - Gel breaking degradation method for polyacrylamide polymer fracturing fluid - Google Patents
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- 230000015556 catabolic process Effects 0.000 title claims description 58
- 238000006731 degradation reaction Methods 0.000 title claims description 58
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- ROOXNKNUYICQNP-UHFFFAOYSA-N ammonium persulfate Chemical compound [NH4+].[NH4+].[O-]S(=O)(=O)OOS([O-])(=O)=O ROOXNKNUYICQNP-UHFFFAOYSA-N 0.000 claims description 12
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- MHAJPDPJQMAIIY-UHFFFAOYSA-N Hydrogen peroxide Chemical compound OO MHAJPDPJQMAIIY-UHFFFAOYSA-N 0.000 claims description 6
- CHJJGSNFBQVOTG-UHFFFAOYSA-N N-methyl-guanidine Natural products CNC(N)=N CHJJGSNFBQVOTG-UHFFFAOYSA-N 0.000 claims description 6
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 claims description 6
- WQDUMFSSJAZKTM-UHFFFAOYSA-N Sodium methoxide Chemical compound [Na+].[O-]C WQDUMFSSJAZKTM-UHFFFAOYSA-N 0.000 claims description 6
- SWSQBOPZIKWTGO-UHFFFAOYSA-N dimethylaminoamidine Natural products CN(C)C(N)=N SWSQBOPZIKWTGO-UHFFFAOYSA-N 0.000 claims description 6
- 238000006073 displacement reaction Methods 0.000 claims description 6
- UMPKMCDVBZFQOK-UHFFFAOYSA-N potassium;iron(3+);oxygen(2-) Chemical compound [O-2].[O-2].[K+].[Fe+3] UMPKMCDVBZFQOK-UHFFFAOYSA-N 0.000 claims description 6
- MFRIHAYPQRLWNB-UHFFFAOYSA-N sodium tert-butoxide Chemical compound [Na+].CC(C)(C)[O-] MFRIHAYPQRLWNB-UHFFFAOYSA-N 0.000 claims description 6
- 239000003513 alkali Substances 0.000 claims description 5
- 239000012752 auxiliary agent Substances 0.000 claims description 4
- 230000009467 reduction Effects 0.000 claims description 4
- ZZZCUOFIHGPKAK-UHFFFAOYSA-N D-erythro-ascorbic acid Natural products OCC1OC(=O)C(O)=C1O ZZZCUOFIHGPKAK-UHFFFAOYSA-N 0.000 claims description 3
- 229930003268 Vitamin C Natural products 0.000 claims description 3
- 239000011790 ferrous sulphate Substances 0.000 claims description 3
- 235000003891 ferrous sulphate Nutrition 0.000 claims description 3
- BAUYGSIQEAFULO-UHFFFAOYSA-L iron(2+) sulfate (anhydrous) Chemical compound [Fe+2].[O-]S([O-])(=O)=O BAUYGSIQEAFULO-UHFFFAOYSA-L 0.000 claims description 3
- 229910000359 iron(II) sulfate Inorganic materials 0.000 claims description 3
- 239000005543 nano-size silicon particle Substances 0.000 claims description 3
- RPDAUEIUDPHABB-UHFFFAOYSA-N potassium ethoxide Chemical compound [K+].CC[O-] RPDAUEIUDPHABB-UHFFFAOYSA-N 0.000 claims description 3
- 239000012286 potassium permanganate Substances 0.000 claims description 3
- USHAGKDGDHPEEY-UHFFFAOYSA-L potassium persulfate Chemical compound [K+].[K+].[O-]S(=O)(=O)OOS([O-])(=O)=O USHAGKDGDHPEEY-UHFFFAOYSA-L 0.000 claims description 3
- 125000001453 quaternary ammonium group Chemical group 0.000 claims description 3
- 235000012239 silicon dioxide Nutrition 0.000 claims description 3
- QDRKDTQENPPHOJ-UHFFFAOYSA-N sodium ethoxide Chemical compound [Na+].CC[O-] QDRKDTQENPPHOJ-UHFFFAOYSA-N 0.000 claims description 3
- 235000019154 vitamin C Nutrition 0.000 claims description 3
- 239000011718 vitamin C Substances 0.000 claims description 3
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- HEMHJVSKTPXQMS-UHFFFAOYSA-M Sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 description 3
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Classifications
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- E—FIXED CONSTRUCTIONS
- E21—EARTH OR ROCK DRILLING; MINING
- E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
- E21B43/00—Methods or apparatus for obtaining oil, gas, water, soluble or meltable materials or a slurry of minerals from wells
- E21B43/25—Methods for stimulating production
- E21B43/26—Methods for stimulating production by forming crevices or fractures
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- Environmental & Geological Engineering (AREA)
- Fluid Mechanics (AREA)
- General Life Sciences & Earth Sciences (AREA)
- Geochemistry & Mineralogy (AREA)
- Biological Depolymerization Polymers (AREA)
- Processes Of Treating Macromolecular Substances (AREA)
Abstract
The invention belongs to the technical field of oil field production, and particularly relates to a gel breaking and degrading method of polyacrylamide polymer fracturing fluid. The invention reduces the viscosity of the polymer flowback fluid to be below 2mPa.s, degrades the molecular weight to be below 20000, has the molecular particle size within 80nm, has the formation damage rate of less than 5 percent and improves the flowback rate by more than 10 percent by four steps of adding the energizer, adding the adjuvant, adding CO2 and releasing pressure, and meets the requirement of reservoir transformation of low-permeability oil-gas fields, thereby ensuring the fracturing construction effect.
Description
Technical Field
The invention belongs to the technical field of oil field production, and particularly relates to a gel breaking and degrading method of polyacrylamide polymer fracturing fluid.
Background
Fracturing has been rapidly developed and widely used as a primary means of increasing production and injection in hydrocarbon reservoirs. Fracturing is a stimulation and stimulation measure that uses pressure to fracture a formation and uses proppant to prop it up to reduce the resistance to fluid flow. The purpose of fracturing is to form a crack with flow conductivity in a stratum, the adopted fracturing fluid determines the fracturing effect to a great extent, and meanwhile, certain requirements are placed on the viscosity of the fracturing fluid, so that the fracturing fluid can be called low-viscosity fluid to be easy to flow back after fracturing, and the damage to an oil-gas layer in the stratum is avoided.
The most common fracturing fluid at home and abroad is a water-based fracturing fluid mainly taking guanidine gum and a modified substance thereof as a thickening agent, is widely applied to various oil fields at present, and obtains a good yield-increasing effect. However, with the changing of the fracturing operation mode of the compact oil and gas reservoir of the oil and gas field and the increasing trend of environmental protection, the water-based fracturing fluid is required to have the characteristics of low damage, low friction, low cost, easy flowback and easy continuous mixing, easy recovery and high recycling rate, so as to reduce the pollution of the flowback fluid to the environment and soil after the fracturing and simultaneously reduce the quantity of industrial water. Guanidine gum and its modified substance have the inherent defect that vegetable gum is easy to decay, and the fracturing liquid system has complex components, jelly formation depends on chemical crosslinking, and the treatment difficulty of flowback liquid after gum breaking is large, the cost is high, and the recycling feasibility is poor, so that the plant gum fracturing liquid such as guanidine gum can not relieve the environmental protection pressure and can not meet the field construction requirements.
The currently used acrylamide polymer thickener has more varieties, generally has the problems of incomplete gel breaking, easy gel returning, high content of gel breaking liquid residues and the like, is easy to form blocking damage, causes the reduction of matrix permeability and crack conductivity, and influences the fracturing modification effect, so a degradation method of the polymer needs to be formed, the polymer is rapidly degraded into small molecules, and then the small molecules are rapidly returned to reduce the damage to the stratum, so that the requirement of the current compact oil and gas reservoir modification is met.
Patent CN105967306A describes a water-soluble polymer solution degradation agent and a preparation method and application thereof, which only considers the aspects of apparent viscosity of a polymer solution and filter element replacement frequency during recovery treatment, improves the recovery utilization rate of produced water as much as possible, does not disclose the damage of the molecular weight and the particle size of the polymer to the radius of a formation throat, does not further analyze and research the degradation degree of a main chain and a branch chain of the polymer molecule, and simultaneously has longer degradation time and fundamentally does not solve the problem of the damage of polymer retention to the formation.
Disclosure of Invention
The invention provides a gel breaking and degrading method of polyacrylamide polymer fracturing fluid, and aims to provide a fracturing fluid gel breaking and degrading method which is convenient for later flowback and has small damage to a reservoir; the invention also aims to provide a fracturing fluid gel breaking degradation method which has low cost and rapid degradation and reduces the pollution of the discharged fluid after pressing on the environment and soil.
In order to achieve the purpose, the invention adopts the technical scheme that:
a gel breaking degradation method of polyacrylamide polymer fracturing fluid comprises the following steps:
the method comprises the following steps: adding an energizer
In the process of fracturing construction, an energizer accounting for 0.01-0.03 percent of the total mass of the fracturing fluid is added;
step two: adding auxiliary agent
At the final stage of the fracturing construction after the first step is finished, sequentially adding 0.05-0.15% of regulator, 0.01-0.02% of catalyst and 0.02-0.05% of degradation agent by mass of a fracturing fluid system;
step three: adding CO2
After the second step is finished and before the displacement liquid is filled, 15-30m of the displacement liquid is injected3CO of2；
Step four: pressure reduction by open flow
And after the third construction step is completed, closing the well for at least half an hour, then open-blowing by adopting a first nozzle until the pressure is reduced to 8-12MPa, then open-blowing by adopting a second nozzle with the caliber smaller than that of the first nozzle until the pressure is reduced to 3-7MPa, and finally removing the nozzle to open-blow until the pressure is zero, thus finishing the degradation of the fracturing flow-back fluid.
The first nozzle in the fourth step is a nozzle with the diameter of 8-12mm, and the second nozzle is a nozzle with the diameter of 4-8 mm.
In the second step, a regulator accounting for 0.10 percent of the mass percentage of the fracturing fluid system, a catalyst accounting for 0.015 percent of the mass percentage of the fracturing fluid system and a degradation agent accounting for 0.035 percent of the mass percentage of the fracturing fluid system are sequentially added; step three injected is 20m3 of CO 2.
The energizer in the first step is one of ammonium persulfate, hydrogen peroxide, potassium persulfate or potassium permanganate.
The regulator in the second step is strong alkali.
The alkali is one or two of sodium methoxide, sodium ethoxide, potassium ethoxide, sodium tert-butoxide, guanidine and quaternary ammonium hydroxide according to the mass ratio of 3-8: 1-2, and mixing.
The catalyst in the second step is prepared from potassium ferrate and ammonium persulfate according to the mass ratio of 1: 2-9, and mixing.
The degrading agent in the second step is vitamin C and ferrous sulfate according to the mass ratio of 3-5: 1-2, and simultaneously adding nano silicon dioxide with the total mass volume ratio of 5-8 percent.
And in the fourth step, the first nozzle is adopted for open blowing until the pressure is reduced to 10MPa, then the second nozzle with the caliber smaller than that of the first nozzle is adopted for open blowing until the pressure is reduced to 5MPa, and finally the nozzle is taken off for open blowing until the pressure is zero.
Has the advantages that:
the invention adds energizer, adjuvant and CO2And releasing and depressurizing, namely rapidly decomposing polymer molecules into inorganic small molecules within 30 minutes at the low temperature of 30 ℃, so that the viscosity of the polymer flowback fluid is reduced to be below 2mPa.s, the molecular weight is reduced to be below 20000, the molecular particle size is within 80nm, the formation damage rate is less than 5%, and the flowback rate is improved by more than 10%, thereby reducing the damage to the polymer fracturing fluid formation, meeting the requirement of reservoir transformation of a low-permeability oil and gas field, and ensuring the fracturing construction effect.
The energizer is added to mainly provide certain energy for polymer degradation, and can be quickly fused into the fracturing fluid to generate a large amount of heat energy, so that the temperature of the fracturing fluid is quickly increased to reach more than 90 ℃, and the temperature for quick degradation is met; at the same time, the strong oxidation can cause a certain degree of decomposition of the polymer.
The addition of the regulator can provide an alkaline environment for the degradation of the polymer, so that the pH value is more than 10; meanwhile, the regulator is added into water to release certain heat, so that the formation temperature is increased, and the rapid degradation is further promoted.
The addition of the catalyst mainly serves to accelerate the polymer degradation and pre-degradation. The potassium ferrate plays a catalytic role in the later degradation of the polymer, so that the chemical condition of degradation is achieved; the main action of the degradation agent is to rapidly react with the organic polymer through the interaction with the catalyst and the energizer and the self-body when the molecular main chain is degraded, so as to be thoroughly oxidized into inorganic small molecules, the molecular weight of the inorganic small molecules is rapidly reduced, the viscosity of the fracturing fluid is reduced to be below 2mPa.s, the molecular weight is less than 20000, the particle size is less than 80nm, and meanwhile, the introduction of the nano material can accelerate the migration of the degraded molecules, reduce the stratum detention and cause the damage of the nano material to the reservoir to be less than 5%.
CO2The injection of the degrading liquid can ensure that the degrading liquid is fully and uniformly contacted with the fracturing liquid, thereby accelerating the degradation speed; at the same time, CO2The injection of the oil is supplemented with the formation energy, so that the oil is convenient to flow back in the later period;
and in the blowout stage, blowout at different pressures is controlled, so that the damage of the flowback liquid to the stratum caused by large pressure change can be reduced.
The foregoing description is only an overview of the technical solutions of the present invention, and in order to clearly understand the technical solutions of the present invention and to implement the technical solutions according to the contents of the description, the following detailed description is given with reference to the preferred embodiments of the present invention and the accompanying drawings.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings needed in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings without creative efforts.
FIG. 1 is a flow chart of the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The first embodiment is as follows:
the gel breaking degradation method of the polyacrylamide polymer fracturing fluid shown in figure 1 comprises the following steps:
the method comprises the following steps: adding an energizer
In the process of fracturing construction, an energizer accounting for 0.01-0.03 percent of the total mass of the fracturing fluid is added;
step two: adding auxiliary agent
At the final stage of the fracturing construction after the first step is finished, sequentially adding 0.05-0.15% of regulator, 0.01-0.02% of catalyst and 0.02-0.05% of degradation agent by mass of a fracturing fluid system;
step three: adding CO2
After the second step is finished and before the displacement liquid is filled, 15-30m of the displacement liquid is injected3CO of2；
Step four: pressure reduction by open flow
And after the third construction step is completed, closing the well for at least half an hour, then open-blowing by adopting a first nozzle until the pressure is reduced to 8-12MPa, then open-blowing by adopting a second nozzle with the caliber smaller than that of the first nozzle until the pressure is reduced to 3-7MPa, and finally removing the nozzle to open-blow until the pressure is zero, thus finishing the degradation of the fracturing flow-back fluid.
The invention adds energizer, adjuvant and CO2And releasing and depressurizing, namely rapidly decomposing polymer molecules into inorganic small molecules within 30 minutes at the low temperature of 30 ℃, so that the viscosity of the polymer flowback fluid is reduced to be below 2mPa.s, the molecular weight is reduced to be below 20000, the molecular particle size is within 80nm, the formation damage rate is less than 5%, and the flowback rate is improved by more than 10%, thereby reducing the damage to the polymer fracturing fluid formation, meeting the requirement of reservoir transformation of a low-permeability oil and gas field, and ensuring the fracturing construction effect.
The energizer is added to mainly provide certain energy for polymer degradation, and can be quickly fused into the fracturing fluid to generate a large amount of heat energy, so that the temperature of the fracturing fluid is quickly increased to reach more than 90 ℃, and the temperature for quick degradation is met; at the same time, the strong oxidation can cause a certain degree of decomposition of the polymer.
The addition of the regulator can provide an alkaline environment for the degradation of the polymer, so that the pH value is more than 10; meanwhile, the regulator is added into water to release certain heat, so that the formation temperature is increased, and the rapid degradation is further promoted.
The addition of the catalyst mainly serves to accelerate the polymer degradation and pre-degradation. The potassium ferrate plays a catalytic role in the later degradation of the polymer, so that the chemical condition of degradation is achieved; the ammonium persulfate is mainly used for breaking a main molecular chain of a polymer of the ammonium persulfate, and the specific process is as follows:
the oxidative degradation of macromolecules comprises two main processes: autoxidation processes and chain cleavage processes. P-H represents a high molecular polymer, and POOH represents a peroxide. The oxidation reaction process is as follows:
POOH→PO•+•OH
P-H+•OH→P•+H2O
P•+O2→POO•
POO•→POOH+P•
subsequently, the free radicals on the polymer initiate the α -cleavage reaction and the β -cleavage reaction, breaking the backbone as follows:
the main function of the degradation agent is to degrade the main chain of the molecule, and simultaneously, the degradation agent can generate a large amount of OH with strong oxidation capability through the interaction with the catalyst and the energizer and the self interaction, the oxidation potential of the OH is as high as 2.80V, the electronegativity is extremely high, and the OH has the characteristic of strong addition reaction. The nano-material can quickly react with an organic polymer, H atoms in the polymer are captured to form organic free radicals, unsaturated C-C bonds are filled to quickly degrade the polymer, and the polymer is thoroughly oxidized into inorganic small molecules, so that the molecular weight of the inorganic small molecules is quickly reduced, the viscosity of the fracturing fluid is reduced to be below 2mPa.s, the molecular weight is less than 20000, the particle size is less than 80nm, meanwhile, the migration of the degraded molecules can be accelerated by introducing the nano-material, the stratum detention is reduced, and the damage to a reservoir stratum is less than 5%.
CO2The injection of the degrading liquid can ensure that the degrading liquid is fully and uniformly contacted with the fracturing liquid, thereby accelerating the degradation speed; at the same time, CO2The injection of the oil is supplemented with the formation energy, so that the oil is convenient to flow back in the later period;
and in the blowout stage, blowout at different pressures is controlled, so that the damage of the flowback liquid to the stratum caused by large pressure change can be reduced.
According to the technical scheme, polymer molecules can be rapidly decomposed at a low temperature of 30 ℃ and are decomposed into inorganic small molecules within 30 minutes, so that the viscosity of a polymer flowback liquid is reduced to be below 2mPa.s, the molecular weight is degraded to be below 20000, the molecular particle size is within 80nm, the formation damage rate is less than 5%, and the flowback rate is improved by more than 10%.
Example two:
fig. 1 shows a gel breaking degradation method of a polyacrylamide polymer fracturing fluid, which is different from the first embodiment in that: the first nozzle in the fourth step is a nozzle with the diameter of 8-12mm, and the second nozzle is a nozzle with the diameter of 4-8 mm.
In actual use, the first nozzle is a nozzle with the diameter of 8-12mm, and the second nozzle is a nozzle with the diameter of 4-8mm, so that the open-flow depressurization process can be stably carried out, and good effects are achieved.
Example three:
fig. 1 shows a gel breaking degradation method of a polyacrylamide polymer fracturing fluid, which is different from the first embodiment in that: in the second step, a regulator accounting for 0.10 percent of the mass percentage of the fracturing fluid system, a catalyst accounting for 0.015 percent of the mass percentage of the fracturing fluid system and a degradation agent accounting for 0.035 percent of the mass percentage of the fracturing fluid system are sequentially added; step three implant 20m3CO of2。
In practical application, the technical scheme has high gel breaking speed and thorough gel breaking, thereby reducing the damage to the polymer fracturing fluid stratum, ensuring that the flowback fluid is rapidly degraded, and having important significance on low-permeability oil and gas fields adopting a polymer fracturing fluid system to perform reservoir transformation.
Example four:
fig. 1 shows a gel breaking degradation method of a polyacrylamide polymer fracturing fluid, which is different from the first embodiment in that: the energizer in the first step is one of ammonium persulfate, hydrogen peroxide, potassium persulfate or potassium permanganate.
When the polymer fracturing fluid is actually used, the energizer is added to mainly provide certain energy for polymer degradation, and the polymer fracturing fluid can be quickly fused into the fracturing fluid to generate a large amount of heat energy, so that the temperature of the fracturing fluid is quickly increased to be more than 90 ℃, and the temperature for quick degradation is met; at the same time, the strong oxidation can cause a certain degree of decomposition of the polymer.
Example five:
fig. 1 shows a gel breaking degradation method of a polyacrylamide polymer fracturing fluid, which is different from the first embodiment in that: the regulator in the second step is strong alkali.
Preferably, the strong base is one or two of sodium methoxide, sodium ethoxide, potassium ethoxide, sodium tert-butoxide, guanidine and quaternary ammonium base and sodium hydroxide according to the mass ratio of 3-8: 1-2, and mixing.
In actual use, the addition of the regulator in the technical scheme can provide an alkaline environment for the degradation of the polymer, so that the pH value is more than 10; meanwhile, the regulator is added into water to release certain heat, so that the formation temperature is increased, and the rapid degradation is further promoted.
Example six:
fig. 1 shows a gel breaking degradation method of a polyacrylamide polymer fracturing fluid, which is different from the first embodiment in that: the catalyst in the second step is prepared from potassium ferrate and ammonium persulfate according to the mass ratio of 1: 2-9, and mixing.
In practical use, the potassium ferrate in the technical scheme plays a catalytic role in the later degradation of the polymer, so that the chemical condition of degradation is achieved; ammonium persulfate is mainly the main molecular chain of the polymer of the ammonium persulfate is broken.
Example seven:
fig. 1 shows a gel breaking degradation method of a polyacrylamide polymer fracturing fluid, which is different from the first embodiment in that: the degrading agent in the second step is vitamin C and ferrous sulfate according to the mass ratio of 3-5: 1-2, and simultaneously adding nano silicon dioxide with the total mass volume ratio of 5-8 percent.
In practical use, the degradation agent adopted in the technical scheme mainly plays a role in degrading a molecular main chain, and simultaneously can generate a large amount of OH with strong oxidizing capability through the interaction with a catalyst, an energizer and the degradation agent, wherein the oxidation potential of the OH is as high as 2.80V, the electronegativity is extremely high, and the OH has the characteristic of strong addition reaction. The nano-material can quickly react with an organic polymer, H atoms in the polymer are captured to form organic free radicals, unsaturated C-C bonds are filled to quickly degrade the polymer, and the polymer is thoroughly oxidized into inorganic small molecules, so that the molecular weight of the inorganic small molecules is quickly reduced, the viscosity of the fracturing fluid is reduced to be below 2mPa.s, the molecular weight is less than 20000, the particle size is less than 80nm, meanwhile, the migration of the degraded molecules can be accelerated by introducing the nano-material, the stratum detention is reduced, and the damage to a reservoir stratum is less than 5%.
CO2The injection of the degrading liquid can ensure that the degrading liquid is fully and uniformly contacted with the fracturing liquid, thereby accelerating the degradation speed; at the same time, CO2The injection of the oil is supplemented with the formation energy, and the later-stage flowback is convenient.
Example eight:
fig. 1 shows a gel breaking degradation method of a polyacrylamide polymer fracturing fluid, which is different from the first embodiment in that: and in the fourth step, the first nozzle is adopted for open blowing until the pressure is reduced to 10MPa, then the second nozzle with the caliber smaller than that of the first nozzle is adopted for open blowing until the pressure is reduced to 5MPa, and finally the nozzle is taken off for open blowing until the pressure is zero.
When in actual use, the blowout stage in the technical scheme controls different pressures for blowout, so that the damage of the flowback liquid to the stratum caused by large pressure change can be reduced.
The polymer fracturing fluid degradation method is mainly suitable for fracturing fluid systems taking polyacrylamide and derivatives thereof as main thickening agents, and has a certain degradation effect on other polymer fluids.
In conclusion, the fracturing fluid gel breaking degradation method has the advantages that the gel breaking degradation method is low in cost and rapid in degradation through four steps of adding the energizer, adding the auxiliary agent, adding CO2 and discharging and reducing pressure, and pollution of the return fluid after pressing to the environment and soil is reduced. The invention provides a fracturing fluid gel breaking degradation method which is convenient for later-stage flowback and has small damage to a reservoir.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.
In addition, the descriptions related to "first", "second", etc. in the present invention are for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one such feature.
In the case of no conflict, a person skilled in the art may combine the related technical features in the above examples according to actual situations to achieve corresponding technical effects, and details of various combining situations are not described herein.
The foregoing is illustrative of the preferred embodiments of the present invention, and the present invention is not to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein. Any simple modification, equivalent change and modification of the above embodiments according to the technical spirit of the present invention still fall within the scope of the technical solution of the present invention.
Claims (6)
1. A gel breaking degradation method of polyacrylamide polymer fracturing fluid is characterized by comprising the following steps: the method comprises the following steps:
the method comprises the following steps: adding an energizer
In the process of fracturing construction, an energizer accounting for 0.01-0.03 percent of the total mass of the fracturing fluid is added;
step two: adding auxiliary agent
At the final stage of the fracturing construction after the first step is finished, sequentially adding 0.05-0.15% of regulator, 0.01-0.02% of catalyst and 0.02-0.05% of degradation agent by mass of a fracturing fluid system;
step three: adding CO2
After the second step is finished and before the displacement liquid is filled, 15-30m of the displacement liquid is injected3CO of2；
Step four: pressure reduction by open flow
After the third construction step is completed, closing the well for at least half an hour, then open-blowing by adopting a first nozzle until the pressure is reduced to 8-12MPa, then open-blowing by adopting a second nozzle with the caliber smaller than that of the first nozzle until the pressure is reduced to 3-7MPa, and finally removing the nozzle to open-blow until the pressure is zero, thus finishing the degradation of the fracturing flow-back fluid;
the energizer in the first step is one of ammonium persulfate, hydrogen peroxide, potassium persulfate or potassium permanganate;
the regulator in the second step is strong alkali;
the catalyst in the second step is prepared from potassium ferrate and ammonium persulfate according to the mass ratio of 1: 2-9, and mixing.
2. The method for breaking gel and degrading the polyacrylamide polymer fracturing fluid of claim 1, wherein the method comprises the following steps: the first nozzle in the fourth step is a nozzle with the diameter of 8-12mm, and the second nozzle is a nozzle with the diameter of 4-8 mm.
3. The method for breaking gel and degrading the polyacrylamide polymer fracturing fluid of claim 1, wherein the method comprises the following steps: in the second step, a regulator accounting for 0.10 percent of the mass percentage of the fracturing fluid system, a catalyst accounting for 0.015 percent of the mass percentage of the fracturing fluid system and a degradation agent accounting for 0.035 percent of the mass percentage of the fracturing fluid system are sequentially added; step three implant 20m3CO of2。
4. The method for breaking gel and degrading the polyacrylamide polymer fracturing fluid of claim 1, wherein the method comprises the following steps: the alkali is one or two of sodium methoxide, sodium ethoxide, potassium ethoxide, sodium tert-butoxide, guanidine and quaternary ammonium hydroxide according to the mass ratio of 3-8: 1-2, and mixing.
5. The method for breaking gel and degrading the polyacrylamide polymer fracturing fluid of claim 1, wherein the method comprises the following steps: the degrading agent in the second step is vitamin C and ferrous sulfate according to the mass ratio of 3-5: 1-2, and simultaneously adding nano silicon dioxide with the total mass volume ratio of 5-8 percent.
6. The method for breaking gel and degrading the polyacrylamide polymer fracturing fluid of claim 1, wherein the method comprises the following steps: and in the fourth step, the first nozzle is adopted for open blowing until the pressure is reduced to 10MPa, then the second nozzle with the caliber smaller than that of the first nozzle is adopted for open blowing until the pressure is reduced to 5MPa, and finally the nozzle is taken off for open blowing until the pressure is zero.
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