CN108250355B - Preparation method of thickening agent and fracturing fluid for oil field acid produced water dispensing - Google Patents

Abstract

A method for preparing a thickening agent and a fracturing fluid used for liquid preparation of acid produced water in an oil field, in terms of mass percentage, the fracturing fluid consists of 1.00%-3.00% thickening agent, 0.80%-2.40% cross-linking agent, 0.10%～0.60 drainage aid, 0.01%～0.08 gel breaker and oil field acid produced water (salinity is 1000～10000mg/L, total suspended matter content is 5～500mg/L, total bacterial content is 10～ ¹⁰⁵ A/L, pH value is 4～6) composition. The fracturing fluid of the invention has rapid viscosity and good stability, good sand-carrying properties of the cross-linked jelly, and complete gel breaking, which solves the problems that flocculation, sedimentation and corruption often occur when guar gum and conventional polymers are directly mixed in the produced water of acid oil fields. The problem of deterioration and inability to cross-link provides a new way for the green development of oilfields.

Description

A kind of preparation method of thickening agent and pressure for oil field acid produced water dispensing fissure

technical field

The invention belongs to the field of oil field stimulation, and in particular relates to a preparation method of a thickening agent and a fracturing fluid used for liquid preparation of acid produced water in oil fields.

Background technique

Fracturing has been rapidly developed and widely used as the main measure to increase production and injection of oil and gas reservoirs. Fracturing is the use of pressure to open the formation to form fractures, and support it with proppant to reduce the fluid flow resistance and increase the production and injection measures. The purpose of fracturing is to form fractures with conductivity in the formation. The fracturing fluid used determines the fracturing effect to a large extent. Fluids known as low viscosity flow back easily to avoid damage to hydrocarbon formations in the formation.

Hydraulic fracturing technology is a key technology for the reconstruction of low-permeability reservoirs. Hydraulic fracturing needs to consume a lot of fresh water, which has an impact on local water resources, especially in areas where water resources are scarce. At present, the domestic environmental protection requirements have been significantly improved. With the deepening of oilfield development, the comprehensive water content has gradually increased, and the cost of harmless treatment of a large amount of produced water is high and low. This efficiency increase is significant.

In some acid oilfield produced water, guar gum fracturing fluid often has problems such as flocculation, sedimentation, spoilage, and inability to cross-link; conventional polymers are directly formulated, and the polymer is often hydrophilic at one end and hydrophobic at the other end. Not to mention hydrophilic ones, the key is hydrophobic ones, which are generally hydrocarbon organics with strong oil absorption, but they have poor resistance to acids. Mainly, the hydrophobic group is decomposed under the action of acid, and then the whole molecule loses its surface activity. Therefore, it is necessary to develop a new type of fracturing fluid that can be directly mixed with the produced water of an acid oil field to solve the environmental protection pressure of the current oil field and the cost pressure of development.

SUMMARY OF THE INVENTION

In order to overcome the problems in the prior art, the purpose of the present invention is to provide a preparation method of a thickening agent and a fracturing fluid used for the preparation of acid produced water in oil fields.

For achieving the above object, the present invention adopts the following technical scheme:

A method for preparing a thickening agent. The hydrophilic propylene-based monomer is dissolved in water, and the pH value is adjusted to 7.0 to 7.5 to obtain a mixed liquid; Enter nitrogen, then heat to 40°C to 60°C, add an initiator to initiate the reaction, cool to room temperature, rinse with absolute ethanol, vacuum dry, and granulate to obtain a thickening agent.

The further improvement of the present invention is that the hydrophilic propylene monomer accounts for 25% to 35% of the mass of the thickener, the mass of the hydrophobic monomer accounts for 6% to 9% of the mass of the thickener, and the mass of the emulsifier accounts for the mass of the thickener The mass of the initiator accounts for 2% to 7% of the mass of the thickener, and the mass of the initiator accounts for 0.1% to 0.7% of the mass of the thickener.

A further improvement of the present invention is that the specific process of carrying out the initiation reaction is: the initiator is divided into two parts, the first part is 1/3 of the total mass of the initiator, and the second part is 2/3 of the total mass of the initiator; Add 1/3 of the initiator to initiate the polymerization reaction for 8-10 hours, and continue to add the second part of the initiator to carry out the reaction until the viscosity of the system is greater than 9 mPa·s and continue the reaction for 4-8 hours.

A further improvement of the present invention is that the hydrophilic propylene monomer is a mixture of ethylene glycol, hydroxyethyl acrylate, methacrylic acid and acrylamide with a mass ratio of 1:3:5:6; the emulsifier is nonyl A mixture of one or more of phenol polyoxyethylene ether, phenethylphenol polyoxypropylene polyoxyethylene ether, and phenethylnaphthol polyoxyethylene ether.

A further improvement of the present invention is that the hydrophobic monomer is a mixture of dimethylallyl-N-alkylammonium chloride and vinyl methacrylate with a mass ratio of 1:(1.5-2.5); the initiator is azo Diisobutyronitrile, potassium persulfate, a mixture of ammonium persulfate and sodium sulfite, a mixture of ammonium persulfate and sodium bisulfite, benzoyl peroxide or a mixture of potassium persulfate and sodium thiosulfate.

A further improvement of the present invention is that the mass ratio of ammonium persulfate and sodium sulfite in the mixture of ammonium persulfate and sodium sulfite is 1:(1～1.5), and in the mixture of ammonium persulfate and sodium bisulfite, ammonium persulfate and bisulfite are The mass ratio of sodium is 1:(0.8-1.2), and the mass ratio of potassium persulfate and sodium thiosulfate in the mixture of potassium persulfate and sodium thiosulfate is 1:(1.2-1.8).

A fracturing fluid used for the preparation of sour produced water in oil fields, by mass percentage, comprising:

A further improvement of the present invention is that the crosslinking agent is an amphoteric surfactant, the gel breaker is ammonium persulfate or potassium persulfate, and the drainage aid is a fluorocarbon surfactant.

The further improvement of the present invention is that the crosslinking agent is one of dodecyldimethylhydroxypropyl sulfobetaine and dodecylethoxysulfobetaine; the drainage aid is sulfonate Anionic fluorocarbon surfactant.

The further improvement of the present invention is that the salinity of the acid produced water in the oil field is 1000-10000 mg/L, the total suspended matter content is ^5-500 mg/L, the total bacterial content is 10-105/L, and the pH value is 4- 6.

Compared with the prior art, the present invention has the beneficial effects: the present invention adopts the mode of emulsion polymerization, through the preferred hydrophilic propylene monomer, hydrophobic monomer and initiator, especially the selection and proportion of hydrophobic monomer, The acid-resistant thickener is synthesized. Since both the hydrophilic and hydrophobic monomers have cationic groups, the main chain and hydrophobic side chains of the thickener have sufficient cationic groups, which can coexist stably with H ⁺ in the solution without shielding effect. The degradation of the thickener in an acidic environment is reduced, and the surface activity is retained to the greatest extent.

By selecting the acid produced water from the oil field and combining thickeners, cross-linking agents, drainage aids and gel breakers, the invention makes the fracturing fluid sticky quickly and has good stability, the cross-linked gel has good sand-carrying properties, and the gel is broken completely. It solves the problems of flocculation, sedimentation, spoilage and inability to cross-link when guar gum and conventional polymers are directly mixed in acid oilfield produced water, and provides a new way for the green development of oilfields.

Further, the sulfonate fluorocarbon surfactant is used as the drainage aid, which has relatively better oxidation resistance, less sensitivity to strong acids and electrolytes, and the drainage aid effect is not affected by the acidic environment.

Detailed ways

The present invention will be described in detail below through specific embodiments.

The fracturing fluid provided by the present invention for the preparation of sour oil field produced water is formed by mixing the following components according to the following mass percentages:

In the present invention, the thickener is an acid-resistant polymer. The specific preparation method is as follows: a certain quality of hydrophilic propylene monomer is fully dissolved in water, and a certain amount of ammonium bicarbonate solution is slowly added to adjust the pH value of the system to neutral (7.0-7.5). Then add a certain amount of hydrophobic monomer and emulsifier, stir and heat, and then introduce nitrogen for 50min~130min, and heat to 40℃~60℃; then add a certain amount of initiator to initiate polymerization, react for 8~10h, and continue to add the rest amount of initiator. After a certain period of time, the viscosity of the system becomes larger. When the viscosity is greater than 9mPa·s, the reaction is continued for 4 to 8 hours, and then cooled to room temperature. granules to obtain a pure polymer product, which is a thickener. Among them, the mass of hydrophilic propylene-based monomer accounts for 25% to 35% of the mass of the thickener, the mass of hydrophobic monomer accounts for 6% to 9% of the mass of the thickener, and the mass of emulsifier accounts for 2% of the mass of the thickener ~7%, and the mass of the initiator accounts for 0.1% ~ 0.7% of the mass of the thickener.

The hydrophilic propylene-based monomer used in the synthesis of the acid-resistant polymer is a mixture of ethylene glycol, hydroxyethyl acrylate, methacrylic acid and acrylamide in a mass ratio of 1:3:5:6.

The emulsifier is one or more mixtures of nonylphenol polyoxyethylene ether, phenethylphenol polyoxypropylene polyoxyethylene ether, and phenethylnaphthol polyoxyethylene ether.

The hydrophobic monomer used in the synthesis of the acid-resistant polymer is a mixture of dimethylallyl-N-alkylammonium chloride and vinyl methacrylate with a mass ratio of 1:(1.5-2.5).

The initiators used in the synthesis of acid-resistant polymers are azobisisobutyronitrile, potassium persulfate, mixture of ammonium persulfate and sodium sulfite, mixture of ammonium persulfate and sodium bisulfite, benzoyl peroxide or potassium persulfate and A mixture of sodium thiosulfate. Wherein, in the mixture of ammonium persulfate and sodium sulfite, the mass ratio of ammonium persulfate and sodium sulfite is 1:(1～1.5), and in the mixture of ammonium persulfate and sodium bisulfite, the mass ratio of ammonium persulfate and sodium bisulfite is 1:(0.8～1.2), the mass ratio of potassium persulfate and sodium thiosulfate in the mixture of potassium persulfate and sodium thiosulfate is 1:(1.2～1.8). The initiator in the present invention is not limited to the above-mentioned initiators.

In the present invention, the crosslinking agent is an amphoteric surfactant, and specifically, one of dodecyl dimethyl hydroxypropyl sulfobetaine and dodecyl ethoxy sulfobetaine is selected.

The gel breaker in the present invention is a commonly used product in the oil field, and ammonium persulfate or potassium persulfate is selected. The type and addition amount are selected according to the reservoir temperature and construction conditions.

In the present invention, the drainage aid is a commonly used product in the oil field, and a fluorocarbon surfactant (R _f SO ₃ -M) is selected, which is specifically a sulfonate-type anionic fluorocarbon surfactant. The type and dosage are selected according to the specific water quality and reservoir requirements.

In the present invention, the salinity of oil field produced water is 1000-10000 mg/L, the total suspended matter content is 5-500 mg/L, the total bacterial content is 10-10 ⁵ cells/L, and the pH value is 4-6.

Example 1

A new Jurassic well (1#) has a burial depth of 1270m and a formation temperature of 45℃. On June 15, 2015, 50m ³ of fracturing fluid was prepared on site according to the following formula.

The formulation of fracturing fluid, in mass percentage, includes:

Wherein, the specific preparation method of the thickener is as follows: divide the initiator into two parts, the first part is 1/3 of the total mass of the initiator, and the second part is 2/3 of the total mass of the initiator; the hydrophilic propylene The base monomer is fully dissolved in water, and ammonium bicarbonate solution is added to adjust the pH value to 7.0-7.5 to obtain a mixed solution; add the hydrophobic monomer and emulsifier to the mixed solution, and then introduce nitrogen for 50min under stirring, and then heat to At 40°C, firstly add 1/3 of the total initiator mass to initiate the polymerization reaction for 8h, continue to add the second part of the initiator for the reaction for 2h, continue the reaction for 8h when the viscosity of the system is greater than 9mPa s, and then add the remaining initiator to initiate the reaction After the reaction, it was cooled to room temperature, then washed repeatedly with absolute ethanol, dried under vacuum for 3 days, and granulated to obtain a thickening agent.

Among them, the hydrophilic propylene monomer accounts for 25% of the mass of the thickener, the mass of the hydrophobic monomer accounts for 6% of the mass of the thickener, the mass of the emulsifier accounts for 7% of the mass of the thickener, and the total mass of the initiator It accounts for 0.4% of the mass of the thickener.

The hydrophilic propylene monomer is a mixture of ethylene glycol, hydroxyethyl acrylate, methacrylic acid and acrylamide with a mass ratio of 1:3:5:6;

The emulsifier is nonylphenol polyoxyethylene ether.

The hydrophobic monomer is a mixture of dimethylallyl-N-alkylammonium chloride and vinyl methacrylate with a mass ratio of 1:2.5;

The initiator is azobisisobutyronitrile.

The cross-linking agent is dodecyl dimethyl hydroxypropyl sulfobetaine, the designed cross-linking volume ratio is 100:6, and 3.6 m ³ is prepared on site.

The drainage aid is a sulfonate type anionic fluorocarbon surfactant.

The gel breaker is ammonium persulfate, and the prepared amount is 50kg.

The acid produced water of the oilfield used is the No. 1 joint station in the operation area where the well is located. The salinity measured by analysis is 6879mg/L, the total suspended matter content is 78mg/L, the bacterial content is 10 ² /mL, and the pH value is 4.5 , The water is pulled to the well site by the tanker and stored in the liquid preparation tank. The liquid preparation on site is all smooth. After adding the thickener, the viscosity of the base fluid (ie fracturing fluid) reaches 18mPa.s at 15min, and basically tends to be stable. Good dissolution and swelling properties.

The designed construction displacement of the well is 1.0m ³ /min. The cross-linking agent is injected into the sand mixing tank through the sand mixing truck liquid pump on site. The cross-linking gel is well picked up, the construction is smooth, and the pressure is stable. The designed sand addition volume is 5 m ³ . . After the well was shut in for 30 minutes, it started to blow out. The viscosity of the gel breaking liquid was 1.3 mPa.s measured by sampling, and the gel was broken completely. The well swabbed 8 shifts in total, with a flowback rate of 62.1%, and the daily production of pure oil was 28.9m ³ , which was comparable to the average level of the block, achieving the dual purpose of saving clean water and effectively utilizing excess produced water.

Example 2

A new Triassic well (2#) has a burial depth of 2150m and a formation temperature of 61℃. On August 11, 2016, 150m ³ of fracturing fluid was prepared on site according to the following formula.

Fracturing fluid formulation, in mass percent, including:

Wherein, the specific preparation method of the thickener is as follows: divide the initiator into two parts, the first part is 1/3 of the total mass of the initiator, and the second part is 2/3 of the total mass of the initiator; the hydrophilic propylene The base monomer is fully dissolved in water, and ammonium bicarbonate solution is added to adjust the pH value to 7.5 to obtain a mixed solution; the hydrophobic monomer and emulsifier are added to the mixed solution, and nitrogen gas is introduced for 130 min under stirring, and then heated to 60 ° C , firstly add 1/3 of the total mass of the initiator to initiate the polymerization reaction for 9h, continue to add the second part of the initiator for the reaction for 2h and continue the reaction for 6h when the system viscosity is greater than 9mPa s, and then add the remaining initiator to initiate the reaction , cooled to room temperature, rinsed repeatedly with absolute ethanol, dried in vacuum for 5 days, and granulated to obtain a thickening agent.

Among them, the hydrophilic propylene monomer accounts for 35% of the mass of the thickener, the mass of the hydrophobic monomer accounts for 7% of the mass of the thickener, the mass of the emulsifier accounts for 5% of the mass of the thickener, and the total mass of the initiator It accounts for 0.1% of the mass of the thickener.

The hydrophilic propylene monomer is a mixture of ethylene glycol, hydroxyethyl acrylate, methacrylic acid and acrylamide with a mass ratio of 1:3:5:6;

The emulsifier is phenethylphenol polyoxypropylene polyoxyethylene ether.

The hydrophobic monomer is a mixture of dimethylallyl-N-alkylammonium chloride and vinyl methacrylate with a mass ratio of 1:2;

The initiator is potassium persulfate.

The cross-linking agent is dodecyl ethoxy sulfobetaine, the designed cross-linking volume ratio is 100:2, and 5.5 m ³ is prepared on site.

The drainage aid is a sulfonate type anionic fluorocarbon surfactant.

The gel breaker is ammonium persulfate, and the prepared amount is 80kg.

The acid produced water of the oilfield used is the No. 2 joint station in the operation area where the well is located. The salinity measured by analysis is 3996 mg/L, the total suspended matter content is 55 mg/L, the bacterial content is 10 ³ /mL, and the pH value is 4.0 , The water is pulled to the well site by the tanker and stored in the liquid preparation tank. The liquid preparation on site is all smooth. After adding the thickener, the viscosity of the base liquid reaches 21mPa.s at 18 minutes, and basically tends to be stable, with good dissolution and swelling performance. Due to weather factors, the well was constructed on the 3rd day after liquid preparation. The viscosity of the base fluid was measured at 19.5 mPa.s on the day of construction. The viscosity of the liquid tank was relatively uniform, and no delamination and obvious viscosity reduction were found, and the stability was good.

The designed construction displacement of the well is 2.6m ³ /min. The cross-linking agent is injected into the sand mixing tank through the sand mixing truck liquid pump on site. The cross-linked jelly is well picked up, the construction is smooth, and the pressure is stable. The designed sand addition volume is 35 m ³ . . After the well was shut in for 30 minutes and started to blow out, the viscosity of the gel breaking liquid was measured to be 3.9 mPa.s by sampling, and it continued to decrease to 1.6 mPa.s, indicating that the gel was broken completely. The well swabbed 15 shifts in total, with a flowback rate of 74.6%, and the daily production of pure oil was 19.3m ³ , which was comparable to the average level of the block.

Example 3

A new Triassic well (3#) has a burial depth of 2475m and a formation temperature of 75℃. On August 19, 2016, 180m ³ of fracturing fluid was prepared on site according to the following formula.

Fracturing fluid formulation, in mass percent, including:

Wherein, the specific preparation method of the thickener is as follows: divide the initiator into two parts, the first part is 1/3 of the total mass of the initiator, and the second part is 2/3 of the total mass of the initiator; the hydrophilic propylene The base monomer was fully dissolved in water, and ammonium bicarbonate solution was added to adjust the pH value to 7.2 to obtain a mixed solution; the hydrophobic monomer and emulsifier were added to the mixed solution, and then nitrogen was introduced for 80 min under stirring, and then heated to 50 °C , firstly add 1/3 of the total mass of the initiator to initiate the polymerization reaction for 10h, continue to add the second part of the initiator for the reaction for 2h, and continue the reaction for 4h when the viscosity of the system is greater than 9mPa s, and then add the remaining initiator to initiate the reaction , cooled to room temperature, rinsed repeatedly with absolute ethanol, dried in vacuum for 5 days, and granulated to obtain a thickening agent.

Among them, the hydrophilic propylene monomer accounts for 30% of the mass of the thickener, the mass of the hydrophobic monomer accounts for 9% of the mass of the thickener, the mass of the emulsifier accounts for 2% of the mass of the thickener, and the total mass of the initiator It accounts for 0.7% of the mass of the thickener.

The hydrophilic propylene monomer is a mixture of ethylene glycol, hydroxyethyl acrylate, methacrylic acid and acrylamide with a mass ratio of 1:3:5:6;

The emulsifier is phenethyl naphthol polyoxyethylene ether.

The hydrophobic monomer is a mixture of dimethylallyl-N-alkylammonium chloride and vinyl methacrylate with a mass ratio of 1:1.5;

The initiator is a mixture of ammonium persulfate and sodium sulfite with a mass ratio of 1:1.

The cross-linking agent is dodecyl dimethyl hydroxypropyl sulfobetaine, the designed cross-linking volume ratio is 1004, and the on-site preparation is 6.8 m ³ .

The drainage aid is a sulfonate type anionic fluorocarbon surfactant.

The gel breaker is ammonium persulfate, and the prepared amount is 75kg.

The acid produced water of the oilfield used is the 3# joint station in the operation area where the well is located. The salinity measured by analysis is 2562mg/L, the total suspended matter content is 23mg/L, the bacteria content is 10 ³ /mL, and the pH value is 5.5 , The water is pulled to the well site by the tanker and stored in the liquid preparation tank. The liquid preparation on site is all smooth. After adding the thickener, the viscosity of the base liquid reaches 24mPa.s at 35min, and basically tends to be stable, with good dissolution and swelling performance.

The designed construction displacement of the well is 3.0m ³ /min. The cross-linking agent is injected into the sand mixing tank through the sand mixing truck liquid pump on site. The cross-linking gel is well picked up, the construction is smooth, and the pressure is stable. The designed sand addition volume is 40 m ³ . . After the well was shut in for 30 minutes, it started to blow out. The viscosity of the glue breaking liquid was 1.2 mPa.s measured by sampling, and the glue breaking was complete. The well swabbed 22 shifts in total, with a flowback rate of 88.2%, and the daily production of pure oil was 35.0m ³ , which was comparable to the average level of the block.

Example 4

A kind of fracturing fluid for oil field acid produced water dispensing, characterized in that, by mass percentage, comprising:

Wherein, the specific preparation method of the thickener is as follows: divide the initiator into two parts, the first part is 1/3 of the total mass of the initiator, and the second part is 2/3 of the total mass of the initiator; the hydrophilic propylene The base monomer was dissolved in water, and ammonium bicarbonate solution was added to adjust the pH value to 7.0 to obtain a mixed solution; the hydrophobic monomer and emulsifier were added to the mixed solution, and then nitrogen was introduced for 70 min under stirring, and then heated to 55 °C, First add 1/3 of the initiator to initiate the polymerization reaction for 8h, continue to add the second part of the initiator to react until the viscosity of the system is greater than 9mPa·s and continue to react for 5h, cool to room temperature, then repeatedly rinse with absolute ethanol, vacuum dry, and granulate 3 days, thickening agent is obtained.

The hydrophilic propylene-based monomer accounts for 32% of the mass of the thickener, the mass of the hydrophobic monomer accounts for 8% of the mass of the thickener, the mass of the emulsifier accounts for 4% of the mass of the thickener, and the mass of the initiator accounts for the mass of the thickener 0.3% of the mass of the agent.

The hydrophilic propylene monomer is a mixture of ethylene glycol, hydroxyethyl acrylate, methacrylic acid and acrylamide with a mass ratio of 1:3:5:6;

The emulsifier is a mixture of nonylphenol polyoxyethylene ether and phenethylphenol polyoxypropylene polyoxyethylene ether.

The hydrophobic monomer is a mixture of dimethylallyl-N-alkylammonium chloride and vinyl methacrylate with a mass ratio of 1:1.8;

The initiator is a mixture of ammonium persulfate and sodium bisulfite with a mass ratio of 1:1.2.

The crosslinking agent was dodecyldimethylhydroxypropylsulfobetaine.

The breaker is ammonium persulfate.

The drainage aid is a sulfonate type anionic fluorocarbon surfactant.

The oil field acid produced water has a salinity of 1000 mg/L, a total suspended solids content of 500 mg/L, a total bacterial content of 10 cells/L, and a pH value of 5.

Example 5

A kind of fracturing fluid for oil field acid produced water dispensing, characterized in that, by mass percentage, comprising:

Wherein, the specific preparation method of the thickener is as follows: divide the initiator into two parts, the first part is 1/3 of the total mass of the initiator, and the second part is 2/3 of the total mass of the initiator; the hydrophilic propylene The base monomer was dissolved in water, and ammonium bicarbonate solution was added to adjust the pH value to 7.4 to obtain a mixed solution; the hydrophobic monomer and emulsifier were added to the mixed solution, and nitrogen was introduced for 110 min under stirring, and then heated to 45°C, First add 1/3 of the initiator to initiate the polymerization reaction for 9h, continue to add the second part of the initiator to react until the viscosity of the system is greater than 9mPa·s and continue to react for 7h, cool to room temperature, then repeatedly rinse with absolute ethanol, vacuum dry, and granulate In 4 days, a thickener was obtained.

The hydrophilic propylene-based monomer accounts for 27% of the mass of the thickener, the mass of the hydrophobic monomer accounts for 6.5% of the mass of the thickener, the mass of the emulsifier accounts for 3.5% of the mass of the thickener, and the mass of the initiator accounts for the mass of the thickener 0.5% of the mass of the agent.

The hydrophilic propylene monomer is a mixture of ethylene glycol, hydroxyethyl acrylate, methacrylic acid and acrylamide with a mass ratio of 1:3:5:6;

The emulsifier is a mixture of nonylphenol polyoxyethylene ether, phenethylphenol polyoxypropylene polyoxyethylene ether and phenethylnaphthol polyoxyethylene ether.

The hydrophobic monomer is a mixture of dimethylallyl-N-alkylammonium chloride and vinyl methacrylate with a mass ratio of 1:2.3;

The initiator is benzoyl peroxide.

The crosslinking agent was dodecylethoxysulfobetaine.

The breaker is potassium persulfate.

The drainage aid is a sulfonate type anionic fluorocarbon surfactant.

The oil field acid produced water has a salinity of 10,000 mg/L, a total suspended solids content of 5 mg/L, a total bacterial content of 10 ⁵ cells/L, and a pH of 6.

In the present invention, the initiator can also be: the mixture of ammonium persulfate and sodium sulfite, the mixture of ammonium persulfate and sodium bisulfite, the mixture of benzoyl peroxide or potassium persulfate and sodium thiosulfate, and the mixture of ammonium persulfate and sodium bisulfite The mass ratio of ammonium persulfate and sodium sulfite in the mixture of sodium sulfite is 1:(1～1.5), and the mass ratio of ammonium persulfate and sodium bisulfite in the mixture of ammonium persulfate and sodium bisulfite is 1:(0.8～1.2 ), the mass ratio of potassium persulfate and sodium thiosulfate in the mixture of potassium persulfate and sodium thiosulfate is 1:(1.2～1.8).

Claims (8)

1. The preparation method of the thickening agent is characterized in that a hydrophilic propenyl monomer mixture is dissolved in water, and the pH value is adjusted to 7.0-7.5 to obtain a mixed solution; adding a hydrophobic monomer and an emulsifier into the mixed solution, introducing nitrogen while stirring, heating to 40-60 ℃, adding an initiator to perform an initiation reaction, cooling to room temperature, washing with absolute ethyl alcohol, drying in vacuum, and granulating to obtain a thickening agent;

wherein the hydrophilic propenyl monomer mixture is a mixture of ethylene glycol, hydroxyethyl acrylate, methacrylic acid and acrylamide in a mass ratio of 1:3:5: 6; the emulsifier is one or a mixture of nonylphenol polyoxyethylene ether, phenethyl phenol polyoxypropylene polyoxyethylene ether and phenethyl naphthol polyoxyethylene ether;

the hydrophobic monomer is a mixture of dimethylallyl-N-alkyl ammonium chloride and vinyl methacrylate with the mass ratio of 1 (1.5-2.5); the initiator is azodiisobutyronitrile, potassium persulfate, a mixture of ammonium persulfate and sodium sulfite, a mixture of ammonium persulfate and sodium bisulfite, and benzoyl peroxide or a mixture of potassium persulfate and sodium thiosulfate.

2. The preparation method of the thickening agent according to claim 1, wherein the hydrophilic acryl-based monomer mixture accounts for 25-35% of the mass of the thickening agent, the hydrophobic monomer accounts for 6-9% of the mass of the thickening agent, the emulsifier accounts for 2-7% of the mass of the thickening agent, and the initiator accounts for 0.1-0.7% of the mass of the thickening agent.

3. The method for preparing the thickening agent according to claim 1, wherein the specific process for carrying out the initiation reaction is as follows: dividing the initiator into two parts, wherein the first part is 1/3 of the total mass of the initiator, and the second part is 2/3 of the total mass of the initiator; firstly adding 1/3 initiator to initiate polymerization for 8-10 h, and continuously adding a second part of initiator to react until the viscosity of the system is more than 9mPa · s, and continuously reacting for 4-8 h.

4. The method for preparing the thickening agent according to claim 1, wherein the mass ratio of the ammonium persulfate to the sodium sulfite in the mixture of the ammonium persulfate and the sodium sulfite is 1 (1-1.5), the mass ratio of the ammonium persulfate to the sodium bisulfite in the mixture of the ammonium persulfate and the sodium bisulfite is 1 (0.8-1.2), and the mass ratio of the potassium persulfate to the sodium thiosulfate in the mixture of the potassium persulfate and the sodium thiosulfate is 1 (1.2-1.8).

5. A fracturing fluid for an acidic produced water fluid of an oil field based on the thickening agent prepared by the preparation method of any one of claims 1 to 4, which is characterized by comprising the following components in percentage by mass:

6. the fracturing fluid for the acidic produced water fluid of the oilfield according to claim 5, wherein the cross-linking agent is an amphoteric surfactant, and the gel breaker is ammonium persulfate or potassium persulfate; the cleanup additive is a fluorocarbon surfactant.

7. The fracturing fluid for the acidic produced water fluid of the oil field according to claim 6, wherein the cross-linking agent is one of dodecyl dimethyl hydroxypropyl sulfobetaine and dodecyl ethoxy sulfobetaine; the cleanup additive is sulfonate anionic fluorocarbon surfactant.

8. The fracturing fluid for the acidic produced water fluid of the oil field according to claim 5, wherein the mineralization degree of the acidic produced water of the oil field is 1000-10000 mg/L, the content of total suspended matters is 5-500 mg/L, and the content of total bacteria is 10-10⁵The pH value is 4-6.