CN110257043B

CN110257043B - Stimulus-response type clean fracturing fluid and preparation method thereof

Info

Publication number: CN110257043B
Application number: CN201910606721.XA
Authority: CN
Inventors: 郑存川; 黄志宇; 张太亮
Original assignee: Southwest Petroleum University
Current assignee: Southwest Petroleum University
Priority date: 2019-07-06
Filing date: 2019-07-06
Publication date: 2021-06-04
Anticipated expiration: 2039-07-06
Also published as: CN110257043A

Abstract

The invention discloses a stimulus response type clean fracturing fluid and a preparation method thereof, and the technical scheme is as follows: (1) reacting long-chain methyl acrylate with a dimethylamine aqueous solution for 24 hours at 20-60 ℃ according to a molar ratio of 1: 1-3, and removing excessive dimethylamine by rotary evaporation to obtain long-chain tertiary amine; (2) taking 1-5% of long-carbon-chain tertiary amine as a thickening agent, adding HCl to protonate the long-carbon-chain tertiary amine to obtain a clear and transparent thickening agent solution, and then adding 1-5% of a counter-ion salt, wherein the molar ratio of the thickening agent to the counter-ion salt is 1: 2-3: 1, so as to obtain the viscoelastic surfactant clean fracturing fluid. The thickening agent has pH responsiveness, NaOH is added into fracturing flowback fluid after construction, the quaternary ammonium salt thickening agent is deprotonated and converted into tertiary amine, the tertiary amine is separated out from the solution, clean fracturing fluid can be repeatedly prepared after recovery, and the cost of the clean fracturing fluid is greatly reduced. The clean fracturing fluid is simple to prepare, has adjustable performance, and has wide application prospect in fracturing of dense gas, coal bed gas and shale gas.

Description

Stimulus-response type clean fracturing fluid and preparation method thereof

Technical Field

The invention relates to a stimulus-responsive clean fracturing fluid for fracturing fluids of natural gas wells, coal-bed gas wells and shale gas wells and a preparation method thereof.

Background

In 1997, schrenberger company reported that a clean fracturing fluid, namely viscoelastic surfactant fracturing fluid (VES), is a fracturing fluid system which can form wormlike micelles under certain conditions and intertwine with each other to form a reversible three-dimensional network structure and show special rheological properties, and is also commonly called polymer-free fracturing fluid and clean fracturing fluid due to the small molecular weight of the surfactant or auxiliary agent in the system.

The fracturing fluid consists of a surfactant, isopropanol, potassium chloride and the like, and has the characteristics of few additive types (no need of adding a cross-linking agent or a gel breaker), simplicity in field mixing, convenience in construction, thorough gel breaking, high flowback rate, low damage to stratum and the like, so that the fracturing fluid is widely researched and applied in the world. According to data reports, foreign oil companies have successfully performed more than 2400 times of fracturing operations by about 2000 years, and good fracturing effects are achieved. From 2000 years, the 'ClearFRAC' VES fracturing fluid of Schlumberger corporation is respectively introduced into the Changqing oil field, the Daqing oil field, the Sichuan gas field and the like in China, field tests of dozens of wells are carried out, and the yield increasing effect of partial oil and gas wells is obvious.

Although research applications of VES fracturing fluids have been successful, problems remain. Firstly, the electronegativity of the rock surface of the stratum enables a high-concentration cationic surfactant to easily generate a serious adsorption retention phenomenon in the stratum, so that the wetting reversal is caused, and the stratum is damaged; secondly, the temperature resistance is poor, most of the currently used VES fracturing fluids can resist the temperature of about 70 ℃, and in addition, thin filter cakes cannot be formed on the surface of the rock, and the filtration loss is serious at high temperature; thirdly, a large amount of difficultly-degradable cationic surfactant contained in the flowback VES gel breaking solution pollutes the environment; and fourthly, the dosage is larger, the filtration property is strong, and the cost is still higher compared with the conventional guanidine gum fracturing fluid. The above problems limit the large scale application of VES fracturing fluids in various fields of oil fields.

Thus, the invention provides a long-carbon-chain tertiary amine as thickener, which has CO₂Responsive in CO₂Under the action of the surfactant, the surfactant can be protonated to form a quaternary ammonium salt type surfactant, so that the surfactant can be used as a thickening agent to form wormlike micelles after a counter ion salt is added. In the continuous introduction of CH₄Under the condition, the quaternary ammonium salt surfactant is unstable, can be deprotonated and converted into tertiary amine, and the clean fracturing fluid automatically breaks gel. The long carbon chain tertiary amine is insoluble and can be separated out from the fracturing fluid and recovered for recycling. Is particularly suitable for fracturing and yield increasing of natural gas wells, coal bed gas wells and shale gas wells.

Disclosure of Invention

The invention aims to provide a clean fracturing fluid which has good sand carrying performance and low reservoir damage and can be recycled.

In order to achieve the above object, the present invention adopts the following technical solutions.

The preparation method comprises the following steps: (1) reacting long-chain methyl acrylate with a dimethylamine aqueous solution at room temperature for 24 hours according to a molar ratio of 1: 1-3, and removing excessive dimethylamine by rotary evaporation to obtain long-chain tertiary amine; (2) taking 1-5% of long-carbon-chain tertiary amine as a thickening agent, adding HCl to completely protonate the long-carbon-chain tertiary amine to obtain a clear and transparent thickening agent solution, and then adding 1-5% of a counter-ion salt, wherein the molar ratio of the long-carbon-chain tertiary amine to the counter-ion salt is 1: 2-3: 1, so as to obtain the viscoelastic surfactant clean fracturing fluid. The long carbon chain tertiary amine has pH responsiveness, and is protonated to generate a quaternary ammonium salt type cationic surfactant under an acidic condition to serve as a thickening agent of the clean fracturing fluid; after NaOH is added, the quaternary ammonium salt surfactant is deprotonated and converted into tertiary amine, and the surface activity is lost, and the structural formula of the quaternary ammonium salt surfactant is shown in the figure:

wherein R is a long carbon chain normal alkyl group having 12 to 18 carbon atoms.

The counter ion salt is at least one of sodium salicylate, sodium benzoate, sodium chloride and potassium chloride.

And after the construction is finished, NaOH is added into the fracturing flowback fluid, the quaternary ammonium salt thickener is deprotonated to be converted into tertiary amine, the clean fracturing fluid automatically breaks gel, the tertiary amine is separated out from the solution, and the clean fracturing fluid can be repeatedly prepared after the tertiary amine is recovered.

Compared with the prior art, the invention has the beneficial effects that:

(1) the pH response type clean fracturing is simple to prepare, the performance can be flexibly regulated and controlled, and the damage to a reservoir stratum is small;

(2) the pH response type surfactant has good thickening performance under an acidic condition;

(3) the pH response type surfactant can be recycled, and the cost of cleaning the fracturing fluid is greatly reduced.

Detailed Description

The invention is further illustrated by the following examples.

Example 1

1) Reacting dodecyl methacrylate with a dimethylamine aqueous solution at room temperature for 24 hours according to a molar ratio of 1:1.5, and performing rotary evaporation to remove excessive dimethylamine to obtain long-chain tertiary amine; 2) 3% of long carbon chain tertiary amine is taken as a thickening agent, HCl is added to ensure that the long carbon chain tertiary amine is completely protonated to obtain a clear and transparent thickening agent solution, then 1% of sodium salicylate is added to obtain the viscoelastic surfactant clean fracturing fluid, and the temperature resistance of the clean fracturing fluid is over 60 ℃. And after NaOH is added into the clean fracturing fluid, the thickening agent is deprotonated, the clean fracturing fluid automatically breaks gel, and the viscosity is reduced to be below 5 mPa.s. The tertiary amine is separated out of the solution, and the clean fracturing fluid can be prepared after the tertiary amine is separated out.

Example 2

1) Reacting tetradecyl methacrylate with a dimethylamine aqueous solution at room temperature for 24 hours according to a molar ratio of 1:2, and removing excessive dimethylamine by rotary evaporation to obtain long-chain tertiary amine; 2) 4% of long-carbon-chain tertiary amine is taken as a thickening agent, HCl is added to ensure that the long-carbon-chain tertiary amine is completely protonated to obtain a clear and transparent thickening agent solution, then 1.5% of sodium p-toluenesulfonate is added to obtain the viscoelastic surfactant clean fracturing fluid, and the temperature resistance of the clean fracturing fluid is over 90 ℃. And after NaOH is added into the clean fracturing fluid, the thickening agent is deprotonated, the clean fracturing fluid automatically breaks gel, and the viscosity is reduced to be below 5 mPa.s. The tertiary amine is separated out of the solution, and the clean fracturing fluid can be prepared after the tertiary amine is separated out.

Example 3

1) Reacting octadecyl methacrylate with a dimethylamine aqueous solution for 24 hours at room temperature according to the molar ratio of 1:3, and removing excessive dimethylamine by rotary evaporation to obtain long-chain tertiary amine; 2) adding HCl into 5% long-carbon-chain tertiary amine serving as a thickening agent to ensure that the long-carbon-chain tertiary amine is completely protonated to obtain a clear and transparent thickening agent solution, and then adding 2% sodium salicylate to obtain the viscoelastic surfactant clean fracturing fluid, wherein the temperature resistance of the clean fracturing fluid is over 90 ℃. And after NaOH is added into the clean fracturing fluid, the thickening agent is deprotonated, the clean fracturing fluid automatically breaks gel, and the viscosity is reduced to be below 5 mPa.s. The tertiary amine is separated out of the solution, and the clean fracturing fluid can be prepared after the tertiary amine is separated out.

Claims

1. A stimulus-responsive clean fracturing fluid prepared by the steps of: (1) reacting long-carbon-chain methyl acrylate with a dimethylamine aqueous solution at room temperature for 24 hours according to a molar ratio of 1: 1-3, and removing excessive dimethylamine by rotary evaporation to obtain long-carbon-chain tertiary amine; (2) and (2) taking 1-5% of long-carbon-chain tertiary amine as a thickening agent, adding HCl to completely protonate the long-carbon-chain tertiary amine to obtain a clear and transparent thickening agent solution, and then adding 1-5% of a counter-ion salt, wherein the molar ratio of the long-carbon-chain tertiary amine to the counter-ion salt is 1: 2-3: 1, so as to obtain the viscoelastic surfactant clean fracturing fluid.

2. A stimulus responsive clean fracturing fluid as claimed in claim 1, wherein: the long carbon chain tertiary amine has pH responsiveness, and is added with hydrochloric acid for protonation to generate a quaternary ammonium salt cationic surfactant serving as a thickening agent of the clean fracturing fluid; after NaOH is added, the quaternary ammonium salt cationic surfactant is deprotonated and converted into long carbon chain tertiary amine, and the surface activity is lost, and the structural formula is shown as the following figure:

3. A stimulus responsive clean fracturing fluid as claimed in claim 1, wherein: the counter ion salt is at least one of sodium salicylate, sodium benzoate, sodium chloride and potassium chloride.