CN114456793B - Self-viscosity-reduction fracturing fluid for low-permeability heavy oil reservoir and preparation method thereof - Google Patents

Self-viscosity-reduction fracturing fluid for low-permeability heavy oil reservoir and preparation method thereof Download PDF

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CN114456793B
CN114456793B CN202011135506.5A CN202011135506A CN114456793B CN 114456793 B CN114456793 B CN 114456793B CN 202011135506 A CN202011135506 A CN 202011135506A CN 114456793 B CN114456793 B CN 114456793B
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杜勇
姜涛
滕学伟
贾耀勤
隋清国
侯洪涛
李积祥
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China Petroleum And Chemical Corp Shengli Youtian Branch Zhuangxi Oil Rec Overy Fac
China Petroleum and Chemical Corp
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Abstract

The invention belongs to the technical field of petroleum engineering, and relates to a self-viscosity-reducing fracturing fluid for a low-permeability heavy oil reservoir and a preparation method thereof. The self-viscosity reduction fracturing fluid comprises the following components in percentage by weight: 0.3 to 1.5 percent of hydrophobic association polymer, 0.5 to 2.5 percent of viscoelasticity surfactant and 0.01 to 0.15 percent of pH regulator; 0.01 to 0.1 percent of gel breaker, 0.2 to 0.8 percent of cleanup additive and 0.2 to 1.0 percent of clay stabilizer. The hydrophobic association polymer is polymerized by acrylamide, acrylic acid, gemini type cationic Gemini surfactant functional monomer and 2-acrylamide alkyl sulfonic acid functional monomer. After the self-viscosity reduction fracturing fluid is used for construction of the low-permeability heavy oil reservoir, viscosity reduction construction is not needed in a certain time, so that the yield of crude oil can be greatly increased, and the self-viscosity reduction fracturing fluid has a good application prospect.

Description

Self-viscosity-reduction fracturing fluid for low-permeability heavy oil reservoir and preparation method thereof
Technical Field
The invention belongs to the technical field of petroleum engineering, and relates to a self-viscosity-reducing fracturing fluid for a low-permeability heavy oil reservoir and a preparation method thereof.
Background
The heavy oil reservoir has the characteristics of high viscosity, high density, high solidifying point, high non-hydrocarbon content, high wax content and the like, and because the heavy oil has poor fluidity under the reservoir condition, crude oil in the reservoir is not easy to flow into a shaft, so that the exploitation difficulty is great, the exploitation of the low-permeability heavy oil reservoir mostly adopts a steam huff-puff method at present, and the exploitation of the oil field usually needs to carry out oil reservoir reconstruction to obtain a certain yield, so the adaptability problem of the applied reconstruction technology to the oil reservoir needs to be considered.
For low-permeability and ultra-low permeability reservoirs, a hydraulic fracturing stimulation technique is generally used, and the air permeability is generally applicable to low-permeability reservoirs under the condition that the air permeability is less than 50md. The fracturing enables the low-permeability heavy oil reservoir to be effectively developed and used, the pore throats of the medium-low-permeability oil reservoir are smaller, and the low-permeability heavy oil reservoir is more sensitive to blocking injury of clay in the reservoir, reaction sediment and mechanical residues carried by stratum liquid, or more serious injury is more easily caused by foreign substances to the low-permeability stratum. In order to realize the maximum utilization degree of the oil reservoir, a reasonable modification method and mode are researched aiming at the oil reservoir characteristics, so that the purposes of improving the oil reservoir recovery ratio and increasing the oil well yield are achieved, and a new way is opened up for the modification measure of the low-permeability heavy oil sensitive oil reservoir steam huff and puff in the later period.
However, the fracturing can only improve the flow channel of the crude oil, but cannot improve the flow state of the crude oil, if the fluidity of the crude oil is poor, the crude oil yield is difficult to be greatly improved by only fracturing the reservoir, and the viscosity of the thick oil is often required to be reduced by continuously using the viscosity reducer, so that the fluidity of the crude oil is improved, and the purpose of increasing the crude oil yield is achieved.
Chinese patent application CN110791271a discloses a viscosity-reducing sand-carrying fluid and its preparation method. The viscosity-reducing sand-carrying fluid comprises the following components in parts by mass: 0.25-0.30 part of thickener; 0.5-1.0 part of anti-swelling agent; 0.20-0.30 parts of a cleanup additive; 1.5-2.5 parts of demulsifier; 3.0-5.0 parts of viscosity reducer; 90-100 parts of water. The sand-carrying fluid smoothly brings propping agent into stratum, fills pore canal and cavity, the carried anti-swelling agent can prevent clay from hydration migration, the demulsifier can separate oil from water, after the oil-water emulsion is demulsified in a short time, the viscosity reducer plays a role in reducing the viscosity of crude oil, and after construction is finished, the sand-carrying fluid is broken and discharged back under the actions of stratum temperature, pressure and cleanup additive. The patent only adds the viscosity reducer component on the basis of the traditional sand-carrying fluid to realize the viscosity reduction effect of the sand-carrying fluid.
Disclosure of Invention
The invention mainly aims to overcome the defects in the prior art and provides a self-viscosity-reducing fracturing fluid for a low-permeability heavy oil reservoir and a preparation method thereof. After the self-viscosity reduction fracturing fluid is used for construction of low-permeability heavy oil reservoirs, the viscosity reduction construction is not needed within a certain time, the crude oil yield can be greatly increased, the fracturing fluid is clean and has no residue, the damage to stratum is small, flowback is not needed, and the self-viscosity reduction fracturing fluid has a good application prospect.
In order to achieve the above purpose, the present invention adopts the following technical scheme:
a self-viscosity-reducing fracturing fluid for low-permeability heavy oil reservoirs comprises the following components in percentage by weight: 0.3 to 1.5 percent of hydrophobic association polymer, 0.5 to 2.5 percent of viscoelasticity surfactant and 0.01 to 0.15 percent of pH regulator; 0.01 to 0.1 percent of gel breaker, 0.2 to 0.8 percent of cleanup additive, 0.2 to 1.0 percent of clay stabilizer and the balance of water.
The structural formula of the hydrophobically associating polymer is shown as follows:
Figure GDA0004122360840000031
wherein R is alkyl with 8-18 carbon atoms; r is R 1 Is an alkyl group having 6 to 16 carbon atoms.
Preferably, the molecular weight of the hydrophobically associating polymer is between 100 and 200 thousand g/mol.
Preferably, the hydrophobic association polymer is polymerized by acrylamide, acrylic acid, gemini type cationic Gemini surfactant functional monomer and 2-acrylamide alkyl sulfonic acid functional monomer;
the specific reaction comprises the following steps:
(1) Adding acrylic acid and distilled water into a reactor, neutralizing with a pH value regulator under stirring until the pH value is 5-6,
(2) Adding acrylamide under stirring, introducing nitrogen into a reactor, and after the air in the reactor is exhausted, adding Gemini cationic Gemini surfactant functional monomer and 2-acrylamidoalkylsulfonic acid functional monomer;
(3) Stirring until all the system solids are dissolved, and adding ammonium persulfate and sodium bisulfite initiator aqueous solution under the condition of introducing nitrogen; the ratio of ammonium persulfate to sodium bisulphite is 0.01-0.05% of the total material;
(4) After the materials are added, keeping the condition of introducing nitrogen, and continuously reacting for 5-12 h at 50-80 ℃;
(5) And taking out the gel block after the reaction is finished, crushing and granulating, placing the gel particles in a vacuum oven at 50 ℃ for drying for 6-8 hours, taking out and crushing by a crusher, and thus obtaining the hydrophobic association polymer product.
The Gemini type cationic Gemini surfactant functional monomer is biscationic quaternary ammonium salt acrylamide, and the specific structure is as follows:
Figure GDA0004122360840000041
the structure of the 2-acrylamidoalkylsulfonic acid is as follows:
Figure GDA0004122360840000042
preferably, the viscoelastic surfactant is selected from one or more of oleamide propyl betaine, erucic acid amide propyl hydroxysulfobetaine.
Preferably, the pH regulator is selected from one or more of sodium carbonate, sodium bicarbonate, sodium hydroxide, potassium hydroxide and triethanolamine.
Preferably, the breaker is selected from one or more of ammonium persulfate, sodium persulfate, potassium persulfate, sodium hypochlorite and sodium bromate.
Preferably, the clay stabilizer is one or a mixture aqueous solution of a plurality of choline chloride, tetramethyl ammonium chloride, trimethylamine hydrochloride, potassium chloride, sodium chloride and ammonium chloride;
preferably, the clay stabilizer consists of the following components in percentage by mass: 10% of choline chloride, 10% of tetramethyl ammonium chloride, 20% of trimethylamine hydrochloride and the balance of water;
preferably, the clay stabilizer is a choline chloride aqueous solution with a mass concentration of 40%;
preferably, the clay stabilizer is a trimethylammonium hydrochloride aqueous solution with a mass concentration of 40%;
preferably, the clay stabilizer consists of the following components: calculated by mass percent, choline chloride is 5%, tetramethyl ammonium chloride is 15%, trimethylamine hydrochloride is 20%, and the balance is water;
preferably, the clay stabilizer consists of the following components: the weight percentage is 15 percent of choline chloride, 5 percent of tetramethyl ammonium chloride, 20 percent of trimethylamine hydrochloride and the balance of water.
Preferably, the cleanup additive consists of the following components in parts by mass: 5% of cocamidopropyl betaine, 3% of sodium perfluorononenoxybenzenesulfonate, 10% of ethanol, 2% of isopropanol and the balance of water.
The invention also provides a preparation method of the self-viscosity reduction fracturing fluid, which comprises the following steps: mixing the hydrophobic association polymer with water, stirring until the hydrophobic association polymer is completely dissolved, adding the viscoelastic surfactant, the pH regulator, the cleanup additive and the clay stabilizer, and stirring uniformly to obtain the modified hydrophobic association polymer.
Compared with the prior art, the invention has the beneficial effects that:
(1) Clean and residue-free, and has little damage to stratum: the hydrophobic association polymer and the viscoelasticity surfactant have synergistic thickening effect to form the high viscoelasticity fracturing fluid, so that the consumption is low, and the damage to a low-permeability reservoir is small.
(2) Self-viscosity reduction: the small molecular surfactant containing Gemini cationic Gemini type and 2-acrylamide tetradecyl sulfonic acid is formed after the gel breaking of the hydrophobic association polymer, has good emulsifying effect on thick oil, can emulsify crude oil in a reservoir into an oil-in-water emulsion, reduces the viscosity of the crude oil, improves the mobility of the crude oil in a stratum, and improves the crude oil extraction rate.
(3) No flowback is needed: because the system is mainly thickened and carried with sand by molecular association, the hydrophobic association is degraded after gel breaking, the synergistic tackifying effect with the viscoelasticity surfactant is lost, and the viscosity-reducing and oil-increasing functions are exerted.
(4) The Gemini type cationic Gemini surfactant and 2-acrylamidoalkylsulfonic acid functional monomers are added to serve as hydrophobic monomers and emulsifying agent precursors, and meanwhile the molecular weight regulating function is exerted, so that the obtained polymer is small in molecular weight, and the small molecular surfactant emulsifying agent is easily released by oxidative gel breaking.
Drawings
The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the invention.
FIG. 1 is a graph of the rheology of a self-viscosity reducing fracturing fluid-1 according to the present invention.
Detailed Description
It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the invention. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.
It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of exemplary embodiments according to the present invention. As used herein, the singular forms also are intended to include the plural forms unless the context clearly indicates otherwise, and furthermore, it should be understood that when the terms "comprises" and/or "comprising" are used in this specification, they specify the presence of stated features, steps, operations, and/or combinations thereof.
In order to enable those skilled in the art to more clearly understand the technical scheme of the present invention, the technical scheme of the present invention will be described in detail with reference to specific embodiments.
The cleanup additive in the following examples comprises the following components in parts by mass: 5% of cocamidopropyl betaine, 3% of sodium perfluorononenoxybenzenesulfonate, 10% of ethanol, 2% of isopropanol and the balance of water.
Example 1
A method of synthesizing a hydrophobically associating polymer, the method comprising the steps of:
(1) Adding 10 parts of acrylic acid and 20 parts of distilled water into a reactor, and neutralizing with a pH value regulator under stirring until the pH value is 7;
(2) 10 parts of acrylamide is added under stirring, nitrogen is introduced into a reactor, and after the air in the reactor is exhausted, 5 parts of Gemini cationic Gemini surfactant functional monomer is added, wherein the structural formula is shown as the following formula, and R=C 16 And 2 parts of 2-acrylamido tetradecyl sulfonic acid;
Figure GDA0004122360840000071
(3) Stirring until all the system solids are dissolved, and adding ammonium persulfate and sodium bisulfite initiator aqueous solution under the condition of introducing nitrogen; the ratio of ammonium persulfate to sodium bisulphite is 0.05% of the total material;
(4) After the materials are added, keeping the condition of introducing nitrogen, and continuing to react for 8 hours at 60 ℃;
(5) Taking out the gel blocks after the reaction is finished, crushing and granulating, placing the gel particles in a vacuum oven at 50 ℃ for drying for 6-8 hours, taking out and crushing by a crusher to obtain a hydrophobic association polymer product; the molecular weight was found to be 200 ten thousand g/mol.
Example 2
A method of synthesizing a hydrophobically associating polymer, the method comprising the steps of:
(1) Adding 5 parts of acrylic acid and 52 parts of distilled water into a reactor, and stirring and neutralizing with 5% NaOH solution until the pH value is 6 under cooling;
(2) Adding 20 parts of acrylamide, heating to 45 ℃ in a water bath, and introducing nitrogen into the reactor;
(3) Weighing 6 parts of Gemini cationic Gemini surfactant monomer in a beaker, wherein the structural formula is shown as the following formula, and R=C 14 Dissolving 4 parts of 2-acrylamido hexadecyl sulfonic acid with 20 parts of distilled water, drawing a nitrogen guide pipe to a position above the liquid level after the air in the reactor is exhausted, and adding the nitrogen guide pipe into the reactor;
Figure GDA0004122360840000072
(4) Weighing the ammonium persulfate and the sodium bisulphite accounting for 0.05% of the total material in a mass ratio of 3:2, dissolving the ammonium persulfate and the sodium bisulphite in a proper amount of distilled water, and sequentially adding the distilled water into a reactor;
(5) After the materials are added, keeping the condition of introducing nitrogen, and continuing to react for 5 hours at 80 ℃;
(6) And taking out the gel block after the reaction is finished, crushing and granulating, putting the gel particles in a vacuum oven at 50 ℃ for drying for 6 hours, taking out and crushing by a crusher to obtain a hydrophobic association polymer product, and measuring the molecular weight to be 160 ten thousand g/mol.
Example 3
A method of synthesizing a hydrophobically associating polymer, the method comprising the steps of:
(1) Adding 5 parts of acrylic acid and 72 parts of distilled water into a reactor, and stirring with 5% NaOH solution under cooling to neutralize to pH value of 6;
(2) Adding 20 parts of acrylamide, heating to 45 ℃ in a water bath, and introducing nitrogen into the reactor;
(3) Weighing 6 parts of Gemini cationic Gemini surfactant monomer in a beaker, wherein the structural formula is shown as the following formula, and R=C 16 Dissolving 4 parts of 2-acrylamidodecyl sulfonic acid in 20 parts of distilled water, and after the air in the reactor is exhausted, pulling a nitrogen guide pipe to above the liquid level and adding the nitrogen guide pipe into the reactor;
Figure GDA0004122360840000081
(4) Weighing the ammonium persulfate and the sodium bisulphite accounting for 0.05% of the total material in a mass ratio of 3:2, dissolving the ammonium persulfate and the sodium bisulphite in a proper amount of distilled water, and sequentially adding the distilled water into a reactor;
(5) After the materials are added, keeping the condition of introducing nitrogen, and continuing to react for 6 hours at 70 ℃;
(6) And taking out the gel block after the reaction is finished, crushing and granulating, placing the gel particles in a vacuum oven at 50 ℃ for drying for 6 hours, taking out and crushing by a crusher to obtain a hydrophobic association polymer product, and measuring the molecular weight to be 150 ten thousand g/mol.
Example 4
A method of synthesizing a hydrophobically associating polymer, the method comprising the steps of:
(1) 7 parts of acrylic acid and 72 parts of distilled water are added into a reactor, and the mixture is stirred and neutralized to pH value of 6 by 5% NaOH solution under cooling;
(2) 15 parts of acrylamide is added, the temperature is raised to 45 ℃ in a water bath, and nitrogen is introduced into a reactor;
(3) In a beaker, 7 parts of Gemini cationic Gemini surfactant monomer are weighed, wherein the structural formula is shown as the following formula, and R=C 18 Dissolving 6 parts of 2-acrylamido dodecyl sulfonic acid in 20 parts of distilled water, and after the air in the reactor is exhausted, pulling a nitrogen guide pipe to above the liquid level and adding the nitrogen guide pipe into the reactor;
Figure GDA0004122360840000091
(4) Weighing the ammonium persulfate and the sodium bisulphite accounting for 0.05% of the total material in a mass ratio of 3:2, dissolving the ammonium persulfate and the sodium bisulphite in a proper amount of distilled water, and sequentially adding the distilled water into a reactor;
(5) After the materials are added, keeping the condition of introducing nitrogen, and continuing to react for 8 hours at 50 ℃;
(6) And taking out the gel block after the reaction is finished, crushing and granulating, placing the gel particles in a vacuum oven at 50 ℃ for drying for 6 hours, taking out and crushing by a crusher to obtain a hydrophobic association polymer product, and measuring the molecular weight to be 110 ten thousand g/mol.
Example 5
The preparation method of the self-viscosity-reducing fracturing fluid for the low-permeability heavy oil reservoir comprises the following steps: 1000ml of distilled water is added into a Wu Yin stirrer, stirring is started, the rotating speed is regulated to 1500 r/min-3000 r/min, 6.0g of hydrophobic association polymer is added under stirring, and stirring is carried out for 30min to enable the hydrophobic association polymer to be completely dissolved. Then sequentially adding the viscoelastic surfactant under stirring: oleic acid amidopropyl betaine 7.5g, ph regulator: 0.40g of sodium carbonate, 3.0g of cleanup additive and 5.50g of clay stabilizer, and obtaining the viscosity-reducing fracturing fluid-1 system after uniform stirring.
The clay stabilizer consists of the following components: in mass percent, 10% of choline chloride, 10% of tetramethyl ammonium chloride, 20% of trimethylamine hydrochloride and 60% of water.
The hydrophobically associating polymer was prepared by the method described in example 2:
self-viscosity reduction fracturing fluid-1 performance test
(1) Viscosity: the viscosity of the system is 126 mPas;
(2) Shear resistance: 170S (170S) -1 Shearing for 10min, wherein the viscosity is 71.6mPa.s, and the shearing resistance is higher than 50mPa.s required by technical indexes;
(3) Sand carrying performance: settling time of quartz sand with 40 meshes is 75s;
(4) Gel breaking performance: adding ammonium persulfate, breaking gel at 80 ℃ for 90min, wherein the viscosity of the broken gel is 2.37mPa.s, and the surface/interface tension is 26.34/1.36mN/m;
(5) Viscosity reduction performance: the viscosity reduction rate of the aged 3XX thick oil of the victory oil field is 98.93 percent, and the initial viscosity is reduced from 23690Pa.s to 244mPa.s.
Example 6
The preparation method of the self-viscosity-reducing fracturing fluid for the low-permeability heavy oil reservoir comprises the following steps: 1000ml of distilled water is added into a Wu Yin stirrer, stirring is started, the rotating speed is regulated to 1500 r/min-3000 r/min, 10.0g of hydrophobic association polymer is added under stirring, and stirring is carried out for 30min to enable the hydrophobic association polymer to be completely dissolved. Then sequentially adding the viscoelastic surfactant under stirring: 10g of erucic acid amide propyl betaine and 10g of oleic acid amide propyl betaine; pH regulator: 0.8g of sodium hydroxide, 4.0g of cleanup additive and clay stabilizer: 5.0g of potassium chloride, and uniformly stirring to obtain the viscosity-reducing fracturing fluid-2 system.
The hydrophobically associating polymer was prepared by the method described in example 3:
self-viscosity reduction fracturing fluid-2 performance test
(1) Viscosity: the system viscosity is 231 mPa.s;
(2) Shear resistance: 170S (170S) -1 Shearing for 10min, wherein the viscosity is 78.4 mPas, and the shearing resistance is 50 mPas higher than the technical index requirement;
(3) Sand carrying performance: settling time of 40-mesh quartz sand is 129s;
(4) Gel breaking performance: the gel breaking method is the same as in example 5, the viscosity of the gel breaking solution is 2.87mPa.s, and the surface/interface tension is 26.14/1.38mN/m;
(5) Viscosity reduction performance: the viscosity reduction rate of the aged 3XX thick oil of the victory oil field is 99.23 percent, and the initial viscosity is reduced from 23690mPa.s to 214mPa.s; the viscosity reduction rate of the thick oil of pile 1XX was 99.03% and was reduced from the initial viscosity of 33561mPa.s to 325mPa.s.
Example 7
The preparation method of the self-viscosity-reducing fracturing fluid for the low-permeability heavy oil reservoir comprises the following steps: 1000ml of distilled water is added into a Wu Yin stirrer, stirring is started, the rotating speed is regulated to 1500 r/min-3000 r/min, 8.0g of hydrophobic association polymer is added under stirring, and stirring is carried out for 30min to enable the hydrophobic association polymer to be completely dissolved. Then sequentially adding the elastic surfactant under stirring: 10g of oleamide propyl betaine and 10g of erucic acid amide propyl hydroxysulfobetaine; pH regulator: triethanolamine 1g, sodium hydroxide 0.5g; cleanup additive 6.0g, clay stabilizer: 8.0g of potassium chloride, and uniformly stirring to obtain the viscosity-reducing fracturing fluid-3 system.
The hydrophobically associating polymer was prepared by the method described in example 3:
performance test of self-viscosity-reducing fracturing fluid-3 system
(1) Viscosity: the viscosity of the system is 180 mPa.s;
(2) Shear resistance: 170S (170S) -1 Shearing for 10min, and viscosity of 70.4mPa.s, and resistanceThe shearing property is higher than 50mPa.s required by technical indexes;
(3) Sand carrying performance: settling time of quartz sand with 40 meshes is 96s;
(4) Gel breaking performance: the gel breaking mode is the same as that of the gel breaking solution in the example 5, the viscosity of the gel breaking solution is 2.87mPa.s, and the surface/interface tension is 26.25/1.28mN/m;
(5) Viscosity reduction performance: the viscosity reduction rate of the aged 3XX thick oil of the victory oil field is 98.93 percent, and the initial viscosity is reduced from 23690Pa.s to 244mPa.s; the viscosity reduction rate of the single 1XX thick oil is 99.13%, and the initial viscosity is reduced from 55681mPa.s to 458 mPa.s;
example 8
The preparation method of the self-viscosity-reducing fracturing fluid for the low-permeability heavy oil reservoir comprises the following steps: 1000ml of distilled water is added into a Wu Yin stirrer, stirring is started, the rotating speed is regulated to 1500 r/min-3000 r/min, 8.0g of hydrophobic association polymer is added under stirring, and stirring is carried out for 30min to enable the hydrophobic association polymer to be completely dissolved. Then 18g of viscoelastic surfactant were added sequentially with stirring: erucamide propyl hydroxysulfobetaine, pH adjuster: triethanolamine 1g, sodium hydroxide 0.5g; cleanup additive 6.0g, clay stabilizer: 8.0g of potassium chloride, and uniformly stirring to obtain the viscosity-reducing fracturing fluid-4 system.
The hydrophobically associating polymer was prepared by the method described in example 4:
self-viscosity reduction fracturing fluid-4 performance test
(1) Viscosity: the system viscosity is 117 mPa.s;
(2) Shear resistance: 170S (170S) -1 Shearing for 10min, wherein the viscosity is 65.8mPa.s, and the shearing resistance is 50mPa.s higher than the technical index requirement;
(3) Sand carrying performance: settling time of quartz sand with 40 meshes is 82s;
(4) Gel breaking performance: the gel breaking method is the same as in example 5, the viscosity of the gel breaking solution is 2.57mPa.s, and the surface/interface tension is 25.35/1.36mN/m;
(5) Viscosity reduction performance: the viscosity reduction rate of the 13X thick oil of the victory oilfield pile is 98.25 percent, and the initial viscosity is reduced to 150mPa.s from 8569 mPa.s; the viscosity reduction rate of the crude XXX thick oil is 98.64%, and the viscosity is reduced from the initial viscosity 17580mPa.s to the viscosity of 239mPa.s.
Experimental example
(1) Hydrophobically associating polymers
The effect of reaction temperature and reaction time on the molecular weight of hydrophobically associative polymer was studied as described in example 1, and is shown in Table 1 below.
TABLE 1 influence of reaction temperature and reaction time on molecular weight of hydrophobically associative polymers
Figure GDA0004122360840000131
(2) Viscoelastic surfactants
The main function of the viscoelasticity surfactant in the self-viscosity-reduction fracturing fluid is to be thickened in a synergistic way with the hydrophobic association polymer, and meanwhile, the viscoelasticity of the self-viscosity-reduction fracturing fluid is enhanced, and the sand carrying capacity of the fracturing fluid is improved. The concentration of the fixed hydrophobically associating polymer was 0.6%, and the synergistic thickening effect of the different viscoelastic surfactants was examined, and the results are shown in table 2.
TABLE 2 viscoelastic surfactant Performance experiments
Figure GDA0004122360840000141
The experiments continue to examine the synergistic effect of different viscoelastic surfactant concentrations with hydrophobically associative polymers, as shown in table 3.
TABLE 3 Effect of viscoelastic surfactant concentration on synergistic thickening effects
Figure GDA0004122360840000142
(3) PH regulator
The pH value of the base fracturing fluid is one of the key factors affecting the swelling performance of the thickener and the thickening performance of the fracturing fluid. The fracturing fluid uses a pH adjuster, typically a pH required to control the particular cross-linking agent and cross-linking time. The self-viscosity-reducing fracturing fluid is thickened by the synergistic effect between the hydrophobic association polymer and the viscoelastic surfactant, a cross-linking agent is not required to be added, and the pH regulator mainly has the effect of regulating the pH value of the fluid to a proper pH value, so that the polymer and the viscoelastic surfactant achieve the optimal synergistic effect.
The effect of the pH adjuster at 0.6% and 1.5% of the viscoelastic surfactant on the viscosity of the polymer was examined, and the results are shown in Table 4.
TABLE 4pH regulator screening
Figure GDA0004122360840000151
(4) Gel breaker
The influence of different gel breakers on the gel breaking performance of a self-viscosity-reducing fracturing fluid system at 90 ℃ is examined, and the experimental results are shown in table 5.
TABLE 5 influence of different breakers on breaking time and breaking viscosity
Figure GDA0004122360840000152
Figure GDA0004122360840000161
(5) Clay stabilizer
The clay stabilizer mainly plays a role in preventing clay from expanding and migrating in the fracturing fluid so as not to cause secondary damage to a reservoir. The results of the clay stabilizer experiments are shown in Table 6.
TABLE 6 results of clay stabilizer experiments with different formulations
Figure GDA0004122360840000162
Figure GDA0004122360840000171
The formula of the self-viscosity-reducing fracturing liquid system is as follows: 0.6% of a hydrophobically associating polymer which is the polymer corresponding to number 2 of table 1, 1.5% of a viscoelastic surfactant erucamide propyl betaine, 0.08% of a ph adjuster sodium carbonate, 0.03% of a breaker sodium persulfate, 0.5% of a clay stabilizer which is the clay stabilizer formulation of number 6 of table 6. After the fracturing fluid system is prepared according to the formula, rheological property (no gel breaker is added during testing), gel breaking property, viscosity reduction property and the like of the fracturing fluid system are tested, and the results are shown in table 7. As shown in Table 7, the viscosity of the self-viscosity-reducing fracturing fluid is 70mPa.s or more after being sheared for 2 hours at 90 ℃, and the viscosity of the gel breaking fluid is lower than 3mPa.s, so that the on-site fracturing construction requirement is met. After the fracturing fluid breaks the gel, the viscosity reduction performance of the gel breaking fluid is evaluated, the viscosity reduction rate of the gel breaking fluid on various thickened oils in a victory oil field is over 98 percent, and the viscosity reduction effect is excellent.
TABLE 7 evaluation results of self-viscosity-reducing fracturing fluid fluids
Figure GDA0004122360840000172
Figure GDA0004122360840000181
Table 8 viscosity breaking performance test of self-viscosity breaking fracturing fluid
Figure GDA0004122360840000182
The above examples are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above examples, and any other changes, modifications, substitutions, combinations, and simplifications that do not depart from the spirit and principle of the present invention should be made in the equivalent manner, and the embodiments are included in the protection scope of the present invention.

Claims (14)

1. The self-viscosity-reduction fracturing fluid for the low-permeability heavy oil reservoir is characterized by comprising the following components in percentage by weight: 0.3 to 1.5 percent of hydrophobic association polymer, 0.5 to 2.5 percent of viscoelasticity surfactant and 0.01 to 0.15 percent of pH regulator; 0.01 to 0.1 percent of gel breaker, 0.2 to 0.8 percent of cleanup additive, 0.2 to 1.0 percent of clay stabilizer and the balance of water;
the structural formula of the hydrophobically associating polymer is shown as follows:
Figure QLYQS_1
wherein R is alkyl with 8-18 carbon atoms; r is R 1 Is an alkyl group having 6 to 16 carbon atoms.
2. The self-viscosity-reducing fracturing fluid according to claim 1, wherein said hydrophobically associating polymer is polymerized from acrylamide, acrylic acid, gemini type cationic Gemini surfactant functional monomer and 2-acrylamidoalkylsulfonic acid functional monomer;
the specific reaction comprises the following steps:
(1) Adding acrylic acid and distilled water into a reactor, neutralizing with a pH value regulator under stirring until the pH value is 5-6,
(2) Adding acrylamide under stirring, introducing nitrogen into a reactor, and after the air in the reactor is exhausted, adding Gemini cationic Gemini surfactant functional monomer and 2-acrylamidoalkylsulfonic acid functional monomer;
(3) Stirring until all the system solids are dissolved, and adding ammonium persulfate and sodium bisulphite initiator aqueous solution under the condition of introducing nitrogen; the ratio of ammonium persulfate to sodium bisulphite is 0.01-0.05% of the total material;
(4) After the materials are added, the reaction is continued for 5 to 12 hours at the temperature of 50 to 80 ℃ under the condition of keeping the nitrogen gas.
(5) And taking out the gel block after the reaction is finished, crushing and granulating, placing the gel particles in a vacuum oven at 50 ℃ for drying for 6-8 hours, taking out and crushing by a crusher, and thus obtaining the hydrophobic association polymer product.
3. The self-viscosity reducing fracturing fluid according to claim 1 or 2, characterized in that said hydrophobically associating polymer has a molecular weight comprised between 100 and 200 thousand g/mol.
4. The self-viscosity reducing fracturing fluid of claim 1, wherein said viscoelastic surfactant is selected from one or more of oleamide propyl betaine, erucamide propyl hydroxysulfobetaine.
5. The self-viscosity reducing fracturing fluid of claim 1, wherein said pH modifier is selected from one or more of sodium carbonate, sodium bicarbonate, sodium hydroxide, potassium hydroxide, triethanolamine.
6. The self-viscosity reducing fracturing fluid of claim 1, wherein said breaker is selected from one or more of ammonium persulfate, sodium persulfate, potassium persulfate, sodium hypochlorite, sodium bromate.
7. The self-viscosity-reducing fracturing fluid according to claim 1, wherein said clay stabilizer is selected from the group consisting of aqueous solutions of one or more of choline chloride, tetramethyl ammonium chloride, trimethylamine hydrochloride, potassium chloride, sodium chloride, ammonium chloride.
8. The self-viscosity-reducing fracturing fluid according to claim 7, wherein said clay stabilizer consists of the following components in percentage by mass: 10% of choline chloride, 10% of tetramethyl ammonium chloride, 20% of trimethylamine hydrochloride and the balance of water.
9. The self-viscosity reducing fracturing fluid of claim 7, wherein said clay stabilizer is an aqueous solution of chlorinated choline having a mass concentration of 40%.
10. The self-viscosity reducing fracturing fluid of claim 7, wherein said clay stabilizer is a trimethylamine hydrochloride aqueous solution with a mass concentration of 40%.
11. The self-viscosity reducing fracturing fluid of claim 7, wherein said clay stabilizer is comprised of: the weight percentage is 5% of choline chloride, 15% of tetramethyl ammonium chloride, 20% of trimethylamine hydrochloride and the balance of water.
12. The self-viscosity reducing fracturing fluid of claim 7, wherein said clay stabilizer is comprised of: the weight percentage is 15 percent of choline chloride, 5 percent of tetramethyl ammonium chloride, 20 percent of trimethylamine hydrochloride and the balance of water.
13. The self-viscosity-reducing fracturing fluid according to claim 1, wherein the drainage aid consists of the following components in parts by mass: 5% of cocamidopropyl betaine, 3% of sodium perfluorononenoxybenzenesulfonate, 10% of ethanol, 2% of isopropanol and the balance of water.
14. The method for preparing the self-viscosity-reducing fracturing fluid according to any one of claims 1 to 13, comprising the following steps: mixing the hydrophobic association polymer with water, stirring until the hydrophobic association polymer is completely dissolved, adding the viscoelastic surfactant, the pH regulator, the cleanup additive and the clay stabilizer, and stirring uniformly to obtain the modified hydrophobic association polymer.
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