CN117866607A - Preparation method of emulsion type thickening agent for fracturing - Google Patents

Abstract

The invention relates to the technical field of oil and gas exploitation, and discloses an emulsion type thickening agent for fracturing and a preparation method thereof, wherein the emulsion type thickening agent comprises the following components in percentage by weight: 70-85% of high molecular polymer framework, 5-10% of temperature-sensitive polymer, 1-4% of pH-sensitive polymer, 0.5-2% of cross-linking agent, 0.5-2% of anti-swelling agent, 2-5% of nonionic surfactant, 1-3% of emulsion stabilizer, and mineral oil or synthetic oil as a continuous phase, wherein the balance is filled to 100%. The invention can enable cracks to be formed and expanded more effectively through the optimized viscosity and sand carrying capacity, and improves the yield of petroleum or natural gas. By dual control of temperature and pH, the viscosity of the emulsion can be reduced when needed, facilitating rapid flowback of the fracturing fluid and reducing damage to the formation. The complexity of oilfield fracturing operation and the influence on the environment are fully considered, and an efficient and environment-friendly solution is provided.

Description

Preparation method of emulsion type thickening agent for fracturing

Technical Field

The invention relates to the technical field of oil and gas exploitation, in particular to a preparation method of an emulsion type thickening agent for fracturing.

Background

With the continuous increase of global energy demand, development and utilization of unconventional oil and gas resources are an important direction of petroleum industry. The hydraulic fracturing technology is used as an effective unconventional oil and gas yield increasing technology and has been widely applied to the fields of shale gas, compact oil and the like. In the hydraulic fracturing process, the use of a thickening agent is of great importance, and the thickening agent can increase the viscosity of the fracturing fluid, is beneficial to carrying propping agents such as sand grains and the like and keeping the cracks effectively opened, so that the yield of oil gas is improved.

However, existing thickeners for fracturing have several problems. First, conventional polymer-based thickeners are susceptible to degradation at high temperatures and high shear conditions, resulting in a decrease in viscosity and thus affecting the fracturing effect. Secondly, these thickeners are not easily degraded in the underground environment and may cause pollution to the groundwater resources. In addition, cross-linking agents and other additives used in the preparation of conventional thickeners can also pose a potential threat to the environment and human health.

Disclosure of Invention

Aiming at the defects of the prior art, the invention provides a preparation method of an emulsion type thickener for fracturing, which can adjust the viscosity and rheological property of the thickener under different temperature and pH environments, is simple and convenient and is easy to control, and the stable emulsion type thickener is formed by slowly adding a polymer solution in an aqueous phase into an oil phase and stirring under proper conditions.

In order to achieve the above purpose, the invention is realized by the following technical scheme: the emulsion type thickener for fracturing comprises the following components in percentage by weight:

70-85% of a high molecular polymer skeleton;

the high molecular polymer provides the base viscosity and structure of the overall emulsion thickener. In the oilfield fracturing process, these high molecular weight polymers can expand rapidly to form a three-dimensional network structure, significantly increasing the viscosity of the fluid and thus effectively carrying sand.

5-10% of a temperature-sensitive polymer;

temperature sensitive polymers are specialty polymers whose structure and swelling properties change with temperature. At low temperatures, these polymers remain in an expanded state, increasing the fluid viscosity; and under the high-temperature condition, the polymer can shrink, so that the viscosity is reduced sharply, and the backflow of the fracturing fluid and the damage to the stratum are facilitated.

1-4% of a pH sensitive polymer;

the pH-sensitive polymer can change its charge state and swelling at different pH values, thereby adjusting the viscosity and stability of the emulsion. In the fracturing process, the accurate control of the performance of the thickener can be realized by controlling the change of the pH value of the fluid.

0.5-2% of cross-linking agent;

the cross-linking agent is used for forming cross-linking points between high molecular polymer skeletons and enhancing the viscosity and stability of the emulsion. The cross-linking action enables the emulsion to maintain a relatively high viscosity in a high temperature and high pressure fracturing environment to carry sufficient proppants into the fracture.

0.5-2% of anti-swelling agent;

the anti-swelling agent can inhibit excessive swelling of the polymer in water, prevent premature fracture of the polymer chain, and maintain viscosity and stability during fracturing.

2-5% of nonionic surfactant;

the nonionic surfactant is beneficial to reducing the surface tension of the emulsion, promoting the formation and stability of the emulsion, enhancing the compatibility of mineral oil or synthetic oil and water phase, and improving the sand carrying capacity of the whole fluid.

Emulsion stabilizer 1-3%;

the emulsion stabilizer is favorable for maintaining the stability of emulsion, preventing oil-water phase separation and ensuring the uniformity and effectiveness of the emulsion thickener in the fracturing process.

Mineral oil or synthetic oil as continuous phase, the balance being filled to 100%;

mineral oil or synthetic oil is used as a continuous phase of the emulsion, can provide good lubricity and sand carrying capacity, and meanwhile, due to the existence of an oil phase, the direct contact between a polymer and water can be reduced, the effective time of a polymer chain is prolonged, and the fracturing efficiency is improved.

By the technical scheme, the optimized viscosity and sand carrying capacity can enable cracks to be formed and expanded more effectively, and the yield of petroleum or natural gas is improved. By dual control of temperature and pH, the viscosity of the emulsion can be reduced when needed, facilitating rapid flowback of the fracturing fluid and reducing damage to the formation. The design of the emulsion thickener fully considers the complexity of oil field fracturing operation and the influence on the environment, and provides a high-efficiency and environment-friendly solution.

Preferably, the method further comprises: 0.1-0.5% of auxiliary agent, wherein the auxiliary agent is selected from one or a combination of antioxidants, preservatives and regulators;

antioxidant: antioxidants can prevent oxidation of the polymers and other components in the emulsion during long term storage or use. Common antioxidants include Butylhydroxybenzene (BHA), di-t-butyl-p-cresol (BHT), and the like.

Preservative: the addition of the preservative can prevent the growth and pollution of microorganisms in the emulsion and prolong the service life of the thickener. Common preservatives include benzoic acid, sodium benzoate, isothiocyanates and the like.

And (3) a regulator: the function of the regulator is to regulate the properties and performance of the emulsion to suit specific process requirements. For example, pH adjusters may be used to adjust the pH of the emulsion to achieve precise control of the viscosity and stability of the emulsion.

Through the technical scheme, the stability, oxidation resistance and corrosion resistance of the thickening agent can be improved by reasonably selecting the auxiliary agent, and the reliability and effect of the thickening agent in fracturing operation are further enhanced.

Preferably, the high molecular polymer skeleton is selected from one of polyacrylamide, polyvinyl alcohol, xanthan gum and carboxymethyl cellulose, and derivatives, copolymers and mixtures thereof;

polyacrylamide: polyacrylamide (PAM) is a commonly used high molecular polymer with good water solubility and high molecular weight. It can form a solution with higher viscosity in water for increasing the viscosity and sand carrying capacity of emulsion.

Polyvinyl alcohol: polyvinyl alcohol (Polyvinyl Alcohol, PVA) is a water-soluble high molecular polymer with good viscosity control properties and gelling ability. The three-dimensional network structure can be formed in the fracturing fluid, so that the viscosity and stability of the fluid are improved.

Xanthan gum: xanthan Gum (Xanthan Gum) is a natural product with excellent gelling and stabilizing properties. It forms a viscous solution in water, which can increase the viscosity of emulsion and increase sand carrying capacity.

Carboxymethyl cellulose: carboxymethyl cellulose (Carboxymethyl Cellulose, CMC) is a water-soluble high molecular polymer with good gelling and stabilizing properties. It can form a colloidal solution in water for increasing the viscosity and rheological properties of the emulsion.

In addition, the use of derivatives, copolymers and mixtures of these high molecular weight polymers is also contemplated to further tailor the properties of the emulsion and to suit specific process requirements.

Through the technical scheme, the high molecular polymer skeleton can interact with other components to form a stable emulsion system, so that the phenomenon of phase separation or sedimentation of the emulsion is prevented, and the long-time stability of the emulsion is maintained. The proper high molecular polymer skeleton is selected to form colloid solution or network structure in water, so as to raise the viscosity and viscosity of emulsion and raise sand carrying capacity.

Preferably, the temperature-sensitive polymer is selected from one of poly (N-isopropyl acrylamide), polyethylene glycol and polyethylene acid;

poly (N-isopropylacrylamide): poly (N-isopropylacrylamide) (PNIPAM) is a commonly used temperature sensitive polymer with unique swelling behavior. At low temperatures, PNIPAM aqueous solutions exhibit a high swelling state, while at high temperatures they exhibit a low swelling state.

Polyethylene glycol: polyethylene glycol (PEG) is a water-soluble polymer with good biocompatibility and mild temperature sensitivity. PEG exhibits high solubility at low temperatures and low solubility at high temperatures.

Polyethylene acid: polyvinyl acid (PVA) is a water-soluble polymer and may also be temperature sensitive. By introducing specific functional groups or cross-linking structures, the PVA can be made to swell or swell-gel transition in a specific temperature range.

Through the technical scheme, the selected temperature-sensitive polymer can change the physical and chemical properties such as solubility, viscosity, hydrophilicity and hydrophobicity and the like of the temperature-sensitive polymer near a specific temperature threshold value, so that the rapid response of temperature control is realized.

Preferably, the pH sensitive polymer is selected from one of polymethacrylic acid, polyacrylic acid and poly (4-vinyl pyridine);

polymethacrylic acid: polymethacrylic acid (PMAA) is a commonly used pH-sensitive polymer with acidic functional groups. At low pH (acidic) the PMAA assumes a swollen state, whereas at high pH (basic) it assumes a swollen-gel transition.

Polyacrylic acid: polyacrylic acid (PAA) is also a common pH sensitive polymer, also with acidic functional groups. PAA exhibits a swollen state at low pH and a swollen-gel transition at high pH.

Poly (4-vinylpyridine): poly (4-vinylpyridine) (P4 VP) is a basic pH sensitive polymer with basic functional groups. At low pH, P4VP assumes a swollen state and at high pH, a swollen-gel transition.

Through the technical scheme, the pH-sensitive polymer can change the charge state and the swelling degree under different pH values, so that the viscosity and the stability of the emulsion are regulated, and the accurate control of the performance of the thickener can be realized by controlling the change of the pH value of the fluid.

Preferably, the cross-linking agent is selected from one of N, N' -methylene bisacrylamide, trimethylacryloyl chloride and divinylbenzene;

n, N' -methylenebisacrylamide: n, N' -Methylenebisacrylamide (MBAA) is a commonly used cross-linking agent with two acrylamide groups. It can form cross-linked structure in polymer system to raise the mechanical strength and stability of polymer.

Trimethylacryloyl chloride: trimethylacryloyl chloride (TMPTA) is a multifunctional crosslinker having three acryl groups. It can cross-link with other acrylic monomers through free radical polymerization reaction to form a three-dimensional network structure.

Divinylbenzene: divinylbenzene (DVB) is a commonly used cross-linking agent consisting of two vinyl phenyl groups. It can undergo cross-linking reaction with other acrylic monomers by free radical polymerization to form a highly cross-linked polymer network structure.

Through the technical scheme, the cross-linking agent forms cross-linking points among the high-molecular polymer frameworks, so that the viscosity and stability of the emulsion are enhanced, and the emulsion can still keep high viscosity under a high-temperature and high-pressure fracturing environment through the cross-linking effect, so that enough propping agent is carried into a crack.

The invention also provides a preparation method of the emulsion type thickener for fracturing, which comprises the following steps:

s1, adding a nonionic surfactant and an emulsion stabilizer into mineral oil or synthetic oil, and stirring for 10-15 minutes at a speed of 500-800 revolutions per minute;

in this step, a nonionic surfactant and an emulsion stabilizer are added to the mineral oil or the synthetic oil, and stirring is performed at a certain speed. The purpose of this step is to uniformly disperse these chemicals in the oil phase for the subsequent emulsification process.

S2, dissolving the high molecular polymer framework, the temperature-sensitive polymer and the pH-sensitive polymer in deionized water in another container, and stirring at a speed of 300-500 rpm until the high molecular polymer framework, the temperature-sensitive polymer and the pH-sensitive polymer are completely dissolved;

in this step, the high molecular polymer backbone, the temperature sensitive polymer and the pH sensitive polymer are dissolved in deionized water. These materials may form a polymer solution in the aqueous phase that requires complete dissolution by stirring.

S3, slowly adding the water phase in the step S2 into the oil phase in the step S1, and continuously stirring at a high speed to form stable emulsion, wherein the stirring speed is 1000-2000 rpm, and the duration is about 30 minutes;

this step is a critical step in emulsification. In this step, an aqueous phase (a solution containing a high molecular polymer backbone, a temperature-sensitive polymer, and a pH-sensitive polymer) is slowly added to the oil phase, and a stable emulsion is formed while stirring at a high speed. This step needs to last for a certain time to ensure adequate emulsification.

S4, adding a cross-linking agent into the emulsion, and stirring for 20-30 minutes at a speed of 500-800 rpm;

in this step, the crosslinking agent is added to the emulsion and stirred at a certain speed. The purpose of this step is to allow the crosslinker to react sufficiently with the other components in the emulsion to form a crosslinked structure.

S5, continuously adding an anti-swelling agent, and stirring for 10-15 minutes at the speed of 500-800 rpm to obtain the emulsion type thickening agent for fracturing;

in this last step, an anti-swelling agent is added to the emulsion and stirring is carried out at a certain speed. The purpose of this step is to uniformly disperse the expansion inhibitor in the emulsion, ultimately forming the desired emulsion thickener for fracturing.

Preferably, before the step S5, the method further includes: adding an auxiliary agent into the emulsion, and continuously stirring for 10-20 minutes;

through the technical scheme, the stability, oxidation resistance and corrosion resistance of the thickening agent can be improved by reasonably selecting the auxiliary agent, and the reliability and effect of the thickening agent in fracturing operation are further enhanced.

Preferably, in the stirring process of the step S2, the temperature is controlled to be 20-40 ℃;

through the technical scheme, the thickener with optimal performance can be obtained by controlling the stirring temperature of the polymer within the range.

Preferably, in the stirring process of the step S2, the pH value is controlled to be 5.0-7.0;

by the technical scheme, the thickening agent with optimal performance can be obtained by controlling the pH value of the polymer during stirring in the range.

The invention provides a preparation method of an emulsion type thickener for fracturing. The beneficial effects are as follows:

the invention can enable cracks to be formed and expanded more effectively through the optimized viscosity and sand carrying capacity, and improves the yield of petroleum or natural gas. By dual control of temperature and pH, the viscosity of the emulsion can be reduced when needed, facilitating rapid flowback of the fracturing fluid and reducing damage to the formation. The complexity of oilfield fracturing operation and the influence on the environment are fully considered, and an efficient and environment-friendly solution is provided.

The pH value of the polymer in the stirring process is controlled within a certain range, so that the prepared thickener has the best comprehensive performance, higher viscosity, excellent stability and controllable decomposition time. Therefore, controlling the pH of the polymer during agitation within this range can result in a thickener with optimal properties.

The temperature of the polymer stirring process is controlled within a certain range, so that the prepared thickener has the best comprehensive performance, higher viscosity, excellent stability and controllable decomposition time. Therefore, a thickener with optimal performance can be obtained by controlling the stirring temperature of the polymer within the range.

Detailed Description

The technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention, and it is apparent that the described embodiments are only some embodiments of the present invention, not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.

Example 1

1. 2% of nonionic surfactant and 1% of emulsion stabilizer were added to the mineral oil and stirred at 600 rpm for 12 minutes.

2. In another vessel, 75% of polyacrylamide (high molecular polymer skeleton), 7% of poly (N-isopropyl acrylamide) (temperature-sensitive polymer) and 2% of polymethacrylic acid (pH-sensitive polymer) were dissolved in deionized water, and stirred at a speed of 400 rpm until complete dissolution was achieved, the temperature was controlled at 30℃and the pH was controlled at 5.6 during stirring.

3. The aqueous phase from step 2 was slowly added to the oil phase from step 1 while continuing to stir at a high speed of 1500 rpm to form a stable emulsion for 30 minutes.

4. 1% of N, N' -methylenebisacrylamide (crosslinker) was added to the emulsion and stirred at 600 revolutions per minute for 25 minutes.

5. And continuously adding 1% of the anti-swelling agent, stirring for 12 minutes at the speed of 600 revolutions per minute, then adding 0.2% of an antioxidant (auxiliary agent), and continuously stirring for 15 minutes to obtain the emulsion type thickening agent for fracturing.

Example 2

1. 3% of nonionic surfactant and 2% of emulsion stabilizer were added to the synthetic oil and stirred at 700 rpm for 10 minutes.

2. In another vessel, 80% of polyvinyl alcohol (high molecular polymer skeleton), 8% of polyethylene glycol (temperature sensitive polymer) and 3% of polyacrylic acid (pH sensitive polymer) are dissolved in deionized water, and stirred at a speed of 350 revolutions per minute until the polyvinyl alcohol is completely dissolved, wherein the temperature is controlled at 25 ℃ and the pH value is controlled at 6.0 during stirring.

3. The aqueous phase from step 2 was slowly added to the oil phase from step 1 while continuing to stir at a high speed of 1800 rpm to form a stable emulsion for 30 minutes.

4. To the emulsion was added 0.8% trimethylacryloyl chloride (crosslinker) and stirred at 700 rpm for 20 minutes.

5. And continuously adding 1.5% of an anti-swelling agent, stirring at the speed of 700 revolutions per minute for 10 minutes, then adding 0.3% of a preservative (auxiliary agent), and continuously stirring for 20 minutes to obtain the emulsion type thickening agent for fracturing.

Example 3

1. 4% of nonionic surfactant and 3% of emulsion stabilizer were added to the mineral oil and stirred at 500 rpm for 15 minutes.

2. In another vessel 85% xanthan gum (high molecular polymer backbone), 5% polyvinyl acid (temperature sensitive polymer), 1% poly (4-vinylpyridine) (pH sensitive polymer) were dissolved in deionized water and stirred at 300 rpm to complete dissolution with temperature controlled at 20 ℃ and pH controlled at 5.5.

3. The aqueous phase from step 2 was slowly added to the oil phase from step 1 while continuing to stir at 2000 rpm for 30 minutes at high speed to form a stable emulsion.

4. 1.5% of N, N' -methylenebisacrylamide (crosslinker) was added to the emulsion and stirred at 800 revolutions per minute for 30 minutes.

5. Continuously adding 0.5% of an anti-swelling agent, stirring at the speed of 800 revolutions per minute for 15 minutes, then adding 0.1% of a regulator (auxiliary agent), and continuously stirring for 10 minutes to obtain the emulsion type thickening agent for fracturing.

Example 4

1.5% of nonionic surfactant and 1% of emulsion stabilizer were added to the synthetic oil and stirred at 800 rpm for 10 minutes.

2. In another vessel, 70% of carboxymethyl cellulose (high molecular polymer backbone), 10% of poly (N-isopropyl acrylamide) (temperature sensitive polymer), 4% of polymethacrylic acid (pH sensitive polymer) were dissolved in deionized water, and stirred at a speed of 500 rpm until the solution was completely dissolved, the temperature was controlled at 35℃and the pH was controlled at 6.5 during stirring.

3. The aqueous phase from step 2 was slowly added to the oil phase from step 1 while continuing to stir at a high speed of 1500 rpm to form a stable emulsion for 30 minutes.

4. To the emulsion was added 0.5% divinylbenzene (crosslinker) and stirred at 600 rpm for 20 minutes.

5. Adding 2% of the anti-swelling agent continuously, stirring for 10 minutes at the speed of 600 revolutions per minute, adding 0.4% of an antioxidant (auxiliary agent), and stirring for 18 minutes continuously to obtain the emulsion type thickening agent for fracturing.

Example 5

1. 2% of nonionic surfactant and 3% of emulsion stabilizer were added to the mineral oil and stirred at 750 rpm for 13 minutes.

2. In another vessel 82% polyacrylamide (high molecular polymer backbone), 9% polyethylene glycol (temperature sensitive polymer), 2% poly (4-vinylpyridine) (pH sensitive polymer) were dissolved in deionized water and stirred at a speed of 450 rpm until completely dissolved, the temperature was controlled at 38 ℃ and the pH was controlled at 5.8 during stirring.

3. The aqueous phase from step 2 was slowly added to the oil phase from step 1 while continuing to stir at 1750 rpm for 30 minutes at high speed to form a stable emulsion.

4. To the emulsion was added 1% trimethylacryloyl chloride (crosslinker) and stirred at 700 rpm for 25 minutes.

5. And continuously adding 1% of the anti-swelling agent, stirring for 12 minutes at the speed of 700 revolutions per minute, then adding 0.5% of preservative (auxiliary agent), and continuously stirring for 20 minutes to obtain the emulsion type thickening agent for fracturing.

Test experiment:

the performance of the emulsion type thickening agents for fracturing prepared in examples 1 to 5 under different temperature and pH conditions was evaluated and verified.

Experiments set up a control group and 5 experimental groups:

control group: conventional thickeners that do not contain temperature-sensitive and pH-sensitive polymers.

The formulation and preparation method of the control group were substantially the same as in example 1, except that the temperature-sensitive polymer and ph-sensitive polymer were removed from the formulation.

Experimental groups 1 to 5: thickeners containing different proportions of temperature-sensitive and pH-sensitive polymers were formulated as in examples 1-5.

Environmental condition setting:

a constant temperature water bath or temperature controller was set to achieve the desired experimental temperature (25 ℃, 50 ℃, 75 ℃).

The pH of the solution was adjusted to the desired conditions (pH 4, 7, 10) using a pH meter, using dilute hydrochloric acid or dilute sodium hydroxide.

Test items:

viscosity test: the viscosity of each experimental group solution was measured using a viscometer under the set temperature and pH conditions.

Stability assessment: the prepared thickener solution was placed in a constant temperature environment for 24 hours, and the separation of the emulsion was observed and recorded.

Determination of the decomposition time: after the thickener reaches the maximum viscosity, the heating is stopped or the pH is adjusted, and the time for the thickener to recover from the thickened state to near the original viscosity is recorded.

Test experimental data for control group and experimental groups 1-5 are shown in tables 1-6:

TABLE 1

TABLE 2

TABLE 3 Table 3

TABLE 4 Table 4

TABLE 5

TABLE 6

Description: viscosity is a key indicator of thickener performance, high viscosity means better sand carrying capacity; the stability score is a qualitative assessment of emulsion stability, 1 indicating severe separation, 5 indicating excellent stability; the breakdown time reflects the time required for the thickener to recover from a high viscosity state to a low viscosity state, and a longer breakdown time means that the thickener takes longer to sand in the fracture, but should not be too long to affect subsequent fluid flowback.

From the experimental data of tables 1-6, the following conclusions can be drawn:

viscosity performance: under all test conditions, the thickeners of experimental groups 1-5 exhibited higher viscosities than the control group. This indicates that the thickener added with the temperature and pH sensitive polymer can provide better sand carrying capacity under different environmental conditions. The viscosity increase of the experimental group is most pronounced especially at low temperature and neutral pH conditions, since the composite sensitive polymer reaches an optimal swelling state under these conditions.

Stability: the thickener stability of experimental groups 1-5 is generally higher than that of control group at different temperature and pH. In particular, at 25 ℃ and neutral pH, the stability scores of all experimental groups reached the highest level (level 5), indicating that these composite sensitive polymers are effective in maintaining emulsion stability at normal temperature and neutral environment. The stability of the experimental group is generally better than the control group even at a high temperature of 75 c, since the thermal stability design of the polymer is effective.

The decomposition time is as follows: the thickener of experimental groups 1-5 generally decomposed longer under all test conditions than the control group, meaning that they carried sand longer in the fracture, helping to improve the fracturing effect. However, the decomposition times of these thickeners also show good controllability, which is very important for fluid flowback after fracturing operations to avoid reduced flowback efficiency due to excessive decomposition times.

The thickeners of experimental groups 1-5 exhibited superior performance over the control group at a variety of temperature and pH conditions. The improvement of viscosity and stability of the thickeners, as well as the controllable decomposition time, indicate the effectiveness of the composite sensitive polymer system in the present solution. In this way, the properties of the thickener are successfully tuned to accommodate different environmental conditions, which is of great importance to improve the efficiency and effectiveness of the fracturing operation of the oil and gas well.

Comparative examples 1 to 5:

the same formulation and preparation method as in example 1 were different in that in step 2, the temperature during stirring was controlled, and in step 2, the stirring temperatures in comparative examples 1 to 5 were controlled to 10 ℃, 20 ℃, 30 ℃, 40 ℃ and 50 ℃ respectively.

Comparative experiment 1:

the effect of the polymer agitation temperature on the final product properties in the preparation of the thickener was evaluated.

The test groups are comparative examples 1 to 5, and the test indexes are the same as the test experiments.

The test experimental data are shown in table 7:

TABLE 7

From the experimental data in table 7, the following can be concluded:

viscosity: the highest viscosity of the thickener obtained in comparative examples 2 and 3 at stirring temperatures of 20℃and 30℃indicates that the polymer chains are more easily developed in this temperature range to form a more effective network structure, thereby increasing the viscosity of the thickener.

Stability: the highest thickener stability ratings (grade 5) for comparative examples 2, 3 and 4 were in the range of 20 ℃ to 40 ℃, indicating that the thickener structure was more stable and less susceptible to temperature fluctuations in this temperature range.

The decomposition time is as follows: comparative example 2, which had a stirring temperature of 20 c, showed the shortest decomposition time because the polymer structure formed at this temperature was both stable and easily decomposed within a predetermined time.

The thickener exhibits the best overall properties in the stirring temperature range of 20 ℃ to 40 ℃ with higher viscosity, excellent stability and controlled decomposition time. Therefore, a thickener with optimal performance can be obtained by controlling the stirring temperature of the polymer within the range.

Comparative examples 6 to 12:

the same formulation and preparation method as in example 1 were carried out, except that in step 2, the ph value at the time of stirring was controlled, and the ph values in step 2 of comparative examples 6 to 12 were controlled to be 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0, respectively.

Comparative experiment 2:

the effect of different pH values on the properties of the polymer when stirred in the preparation of the thickener was evaluated.

The test groups are comparative examples 6 to 12, and the test indexes are the same as the test experiments.

The test experimental data are shown in table 8:

TABLE 8

From the experimental data of table 8, the following can be concluded:

viscosity: the thickeners of comparative examples 8 and 9 had the highest viscosity at a pH controlled in the range of 5.0 to 6.0. This is because in this pH range, the charge state of the polymer favors the formation of a tighter network structure, thereby increasing viscosity.

Stability: comparative examples 8 and 9 gave the highest thickener stability at pH 5.0 and 6.0 (grade 5). This suggests that within this pH range, the polymer chain interactions of the thickener are balanced and can maintain a stable three-dimensional network structure.

The decomposition time is as follows: comparative example 8 shows the shortest decomposition time at a pH of 5.0. This is because at pH 5.0, the polymer chains in the thickener are more prone to break down at a predetermined time after sand is carried in the fracture.

The thickener exhibits the best overall properties in the pH range of 5.0 to 7.0, with higher viscosity, excellent stability and controlled disintegration time. Therefore, controlling the pH of the polymer during agitation within this range can result in a thickener with optimal properties.

Although embodiments of the present invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made therein without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.

Claims (10)

1. The emulsion type thickener for fracturing is characterized by comprising the following components in percentage by weight: 70-85% of high molecular polymer framework, 5-10% of temperature-sensitive polymer, 1-4% of pH-sensitive polymer, 0.5-2% of cross-linking agent, 0.5-2% of anti-swelling agent, 2-5% of nonionic surfactant, 1-3% of emulsion stabilizer, and mineral oil or synthetic oil as a continuous phase, wherein the balance is filled to 100%.

2. The emulsion thickener for fracturing according to claim 1, further comprising: 0.1-0.5% of auxiliary agent, wherein the auxiliary agent is selected from one or a combination of antioxidant, preservative and regulator.

3. The emulsion thickener for fracturing according to claim 1, wherein the high molecular polymer skeleton is one selected from the group consisting of polyacrylamide, polyvinyl alcohol, xanthan gum, carboxymethyl cellulose, derivatives, copolymers and mixtures thereof.

4. The emulsion thickener for fracturing according to claim 1, wherein the temperature-sensitive polymer is one selected from poly (N-isopropylacrylamide), polyethylene glycol and polyethylene acid.

5. The emulsion thickener for fracturing according to claim 1, wherein the pH-sensitive polymer is one selected from the group consisting of polymethacrylic acid, polyacrylic acid and poly (4-vinylpyridine).

6. The emulsion thickener for fracturing according to claim 1, wherein the crosslinking agent is one selected from the group consisting of N, N' -methylenebisacrylamide, trimethylacryloyl chloride, and divinylbenzene.

7. A method for preparing the emulsion thickener for fracturing according to any of claims 1 to 6, comprising the steps of:

s1, adding a nonionic surfactant and an emulsion stabilizer into mineral oil or synthetic oil, and stirring for 10-15 minutes at a speed of 500-800 revolutions per minute;

s2, dissolving the high molecular polymer framework, the temperature-sensitive polymer and the pH-sensitive polymer in deionized water in another container, and stirring at a speed of 300-500 rpm until the high molecular polymer framework, the temperature-sensitive polymer and the pH-sensitive polymer are completely dissolved;

s3, slowly adding the water phase in the step S2 into the oil phase in the step S1, and continuously stirring at a high speed to form stable emulsion, wherein the stirring speed is 1000-2000 rpm, and the duration is about 30 minutes;

s4, adding a cross-linking agent into the emulsion, and stirring for 20-30 minutes at a speed of 500-800 rpm;

s5, continuously adding an anti-swelling agent, and stirring for 10-15 minutes at the speed of 500-800 rpm to obtain the emulsion type thickening agent for fracturing.

8. The method according to claim 7, further comprising, before the step S5: an auxiliary agent is added to the emulsion and stirring is continued for 10-20 minutes.

9. The method according to claim 7, wherein the temperature is controlled to 20-40 ℃ during the stirring process of step S2.

10. The method according to claim 7, wherein the pH is controlled to be 5.0-7.0 during the stirring in the step S2.