Low molecular weight hydrophobically associating polymers, processes for their preparation and use

Abstract

The application discloses a low-molecular-weight hydrophobic associating polymer, and a molecular formula of the low-molecular-weight hydrophobic associating polymer is: wherein R is erucylamide propyl dimethyl quaternary amine, hexadecyl dimethyl quaternary amine, octadecyl dimethyl quaternary amine or behenyl dimethyl quaternary amine, x, y, z and m are monomer molar ratios, x is 69% to 80%, y is 16% to 23%, z is 3.5% to 7%, and m is 0.5% to 1%. The application further discloses a preparation method and application of the low-molecular-weight hydrophobic associating polymer. The fracturing fluid prepared from the low-molecular-weight hydrophobic associating polymer has excellent hydrophobic associating performance, shows the characteristics of low viscosity and high elasticity, can simultaneously meet the construction requirements of strong sand carrying capacity and easy pumping, and has a good application prospect in oilfield fracturing.

Description

Technical Field

[0001] This invention relates to a low molecular weight hydrophobic associative polymer, its preparation method, and its application. Background Technology

[0002] With the large-scale exploitation and consumption of conventional oil and gas reservoirs, unconventional oil and gas resources such as tight sandstone gas, coalbed methane, and shale gas, characterized by low permeability, ultra-low permeability, and deep, high-temperature formations, urgently need to be developed and utilized. Fracturing is a crucial method for enhancing oil and gas well production and water injection well injection. In particular, many tight oil and gas reservoirs have been discovered in recent years, but in the initial stages of production, yields are very low or even nonexistent, requiring fracturing to achieve a certain level of production value. Fracturing fluid is the working fluid used in the hydraulic fracturing process to enhance oil and gas formations. During fracturing, it plays a role in forming formation fractures, transmitting pressure, and carrying proppant into the fractures. The performance of the fracturing fluid directly affects the success of fracturing operations and the post-fracturing production enhancement effect. Currently, slickwater, used for drag reduction, is widely used in fracturing operations. However, due to its poor proppant-carrying capacity, the flow rate must be further increased to carry proppant. But since slickwater has virtually no ability to carry or suspend proppant, this leads to continuously increasing flow rates, resulting in excessively high pump pressures, excessive fluid volumes, and ever-increasing power requirements for fracturing trucks. Therefore, there is an urgent need for fracturing fluids with excellent performance.

[0003] Hydrophobic associating polymers are water-soluble polymers whose macromolecular chains contain a small number of hydrophobic groups. In aqueous solutions, due to the hydrophobic interactions of these groups, the molecular chains aggregate, forming intramolecular or intermolecular associations. When the solution concentration is below the critical association concentration, the polymer primarily forms intramolecular associations, the macromolecular chains coil, the polymer's hydrodynamic volume decreases, and the aqueous solution viscosity is low. When the concentration is above the critical association concentration, the polymer primarily exhibits intermolecular associations, the molecular chains form a network, the hydrodynamic volume increases sharply, and the viscosity increases.

[0004] To address the contradiction between the proppant-carrying capacity and pumpability of existing fracturing fluids, this invention utilizes a strongly associated hydrophobic functional monomer to synthesize a low-molecular-weight hydrophobic associative polymer, thereby preparing a low-viscosity, highly elastic water-based fracturing fluid. This provides a high-performance fracturing fluid for reservoir enhancement and stimulation technologies. Summary of the Invention

[0005] To address the shortcomings of the existing technology, this invention provides a low molecular weight hydrophobic associating polymer and its preparation method. This invention addresses the contradiction between the proppant-carrying capacity and pumpability of current fracturing fluids by providing a strongly associating hydrophobic functional monomer and a low molecular weight hydrophobic associating polymer for fracturing fluids, along with their preparation method. The low molecular weight hydrophobic associating polymer provided by this invention, as a fracturing fluid, exhibits low viscosity and high elasticity, simultaneously meeting the operational requirements of easy pumpability and strong proppant-carrying capacity. This fracturing fluid boasts high yield, low cost, and a simple synthesis process.

[0006] As one aspect of the present invention, a strongly associating hydrophobic monomer is provided, the structure of which is shown in formula (1):

[0007]

[0008] Wherein, R is erucamide propyl dimethyl quaternary ammonium, hexadecyl dimethyl quaternary ammonium, octadecyl dimethyl quaternary ammonium, or docosyl dimethyl quaternary ammonium.

[0009] As another aspect of the present invention, a method for preparing strongly associating hydrophobic monomers is provided, comprising:

[0010] (1) Using ethanol as a solvent, dimethyl tertiary amine: epichlorohydrin: hydrochloric acid were added to ethanol in a molar ratio of 1:1.5~1.8:2.5~3 to obtain intermediate PCL.

[0011] (2) Using dichloromethane as a solvent, 3,3'-iminobis(N,N-dimethylpropylamine):methacryloyl chloride:triethylamine = 1:1.1~1.2:1.2~1.3 was added to dichloromethane to react and obtain intermediate TYJ;

[0012] (3) Using ethanol as a solvent, the above intermediate PCL and the above intermediate TYJ with a molar ratio of 2 to 2.1:1 are added to ethanol to react and obtain a strongly associated hydrophobic monomer.

[0013] In a feasible specific implementation, in the above method, in step (1), the dimethyl tertiary amine is one of erucamide propyl dimethyl tertiary amine, hexadecyl dimethyl tertiary amine, octadecyl dimethyl tertiary amine and docosyl dimethyl tertiary amine or any combination thereof;

[0014] Step (1) is carried out at 60-80℃; Step (2) is carried out at room temperature; Step (3) is carried out at 50-70℃.

[0015] As another aspect of the present invention, a low molecular weight hydrophobic associative polymer is provided, the structural formula of which is shown in formula (2):

[0016]

[0017] Wherein, R is erucamide propyl dimethyl quaternary ammonium, hexadecyl dimethyl quaternary ammonium, octadecyl dimethyl quaternary ammonium, or docosyl dimethyl quaternary ammonium, and x, y, z, and m are the monomer molar ratios, where x is 69%–80%, y is 16%–23%, z is 3.5%–7%, and m is 0.5%–1%.

[0018] As another aspect of the present invention, a method for preparing the above-mentioned low molecular weight hydrophobic associative polymer is provided, comprising:

[0019] (1) Add acrylamide, acrylic acid, 2-acrylamido-2-methylpropanesulfonic acid and the above-mentioned strongly associating hydrophobic monomers to water in a molar ratio of 69-80:16-23:3.5-7:0.5-1, stir to dissolve, and prepare an aqueous solution;

[0020] (2) Nitrogen gas is introduced into the above aqueous solution to remove dissolved oxygen;

[0021] (3) Add a mixed initiator to carry out a free radical polymerization reaction to obtain a low molecular weight hydrophobic associative polymer.

[0022] In a feasible specific implementation, in step (3), the mixed initiator is a mixture of 2,2-azobisisobutylammonium dihydrochloride (V50), ammonium persulfate (APS), and sodium sulfite.

[0023] As another aspect of the present invention, a fracturing fluid is provided, comprising the aforementioned low molecular weight hydrophobic associative polymer.

[0024] As another aspect of the present invention, a method for preparing the above-mentioned fracturing fluid is provided, the method comprising: dissolving the above-mentioned low molecular weight hydrophobic associative polymer in water to obtain the fracturing fluid.

[0025] As another aspect of the present invention, it relates to the application of the above-mentioned fracturing fluid in oil and gas field development.

[0026] The beneficial effects of this invention include:

[0027] (1) The method for preparing low molecular weight hydrophobic associative polymers provided by the present invention has high yield, low cost and simple production process.

[0028] (2) The low molecular weight hydrophobic associating polymer provided by the present invention has excellent hydrophobic associating properties;

[0029] (3) The low molecular weight hydrophobic associative polymer provided by the present invention has the characteristics of low viscosity and high elasticity as a fracturing fluid, which can simultaneously meet the construction requirements of strong sand carrying capacity and easy pumping. Detailed Implementation

[0030] To better understand the technical content of this invention, specific embodiments are described below. The embodiments disclosed herein are not necessarily defined to include all aspects of this invention. It should be understood that the various concepts and embodiments described above, as well as those described in more detail below, can be implemented in any of many ways, because the concepts and embodiments disclosed in this invention are not limited to any particular implementation. Furthermore, some aspects of this invention can be used alone or in any suitable combination with other aspects of this invention.

[0031] Example 1:

[0032] Synthesis of the strongly associating hydrophobic monomer TTH:

[0033] (1) Using ethanol as a solvent, erucic acid-amyl dimethyl tertiary amine: epichlorohydrin: hydrochloric acid were added to ethanol at a molar ratio of 1:1.5:2.5. The mixture was kept at 60°C for 24 hours to obtain intermediate PCL. After removing the ethanol by rotary evaporation, a pale yellow viscous liquid was obtained. The liquid was washed with acetone and dried under vacuum to constant weight for later use. The reaction equation is as follows:

[0034]

[0035] (2) Intermediate TYJ was obtained by reacting 3,3'-iminobis(N,N-dimethylpropylamine) and methacrylamide chloride in a molar ratio of 1:1.1: Using dichloromethane as a solvent, at 5°C, 3,3'-iminobis(N,N-dimethylpropylamine):triethylamine:methacryloylamide chloride = 1:1.2:1.1 molar ratio was added to dichloromethane, the temperature was raised to room temperature, and maintained for 9 hours to obtain intermediate TYJ. It was washed with saturated brine until neutral, dried, and then rotary evaporated for later use. The reaction equation is as follows:

[0036]

[0037] (3) React the intermediate PCL obtained in step (1) and the intermediate TYJ obtained in step (2) to obtain a strongly associated hydrophobic monomer: Using ethanol as a solvent, add intermediate PCL to intermediate TYJ in a molar ratio of 2:1, and maintain at 50℃ for 68 h to obtain the strongly associated hydrophobic monomer TTH. Remove the ethanol by rotary evaporation, resulting in a pale yellow paste. Wash with acetone and vacuum dry to constant weight for later use. The reaction equation is as follows:

[0038]

[0039] In this embodiment, the yield of the strongly associating hydrophobic monomer TTH was 72%.

[0040] The strongly associative hydrophobic monomer TTH in this embodiment is the compound shown in formula (1), wherein R is erucamide propyl dimethyl quaternary ammonium.

[0041] Example 2:

[0042] Synthesis of strongly associating hydrophobic monomer TTH

[0043] (1) Using ethanol as a solvent, erucic acid ammonium dimethyl tertiary amine: epichlorohydrin: hydrochloric acid = 1:1.8:3 molar ratio was added to ethanol, and the mixture was kept at 80°C for 36 hours to obtain intermediate PCL. After cooling, the ethanol was removed by rotary evaporation, resulting in a pale yellow viscous liquid. The liquid was washed with acetone and dried under vacuum to constant weight for later use. The reaction equation is the same as step (1) in Example 1.

[0044] (2) Intermediate TYJ was obtained by reacting 3,3'-iminobis(N,N-dimethylpropylamine) and methacryloyl chloride at a molar ratio of 1:1.2: 3,3'-iminobis(N,N-dimethylpropylamine) was dissolved in dichloromethane and added to a three-necked round-bottom flask. The reaction system was placed in an ice-water bath to lower the temperature to below 5°C. Triethylamine was added at a molar ratio of 3,3'-iminobis(N,N-dimethylpropylamine):triethylamine = 1:1.3. A mixed solution of methacryloyl chloride and dichloromethane was slowly added dropwise using a constant-pressure funnel at a molar ratio of 3,3'-iminobis(N,N-dimethylpropylamine):methacryloyl chloride = 1:1.2. The temperature was then raised to room temperature and maintained at room temperature for 11 hours to obtain intermediate TYJ. It was washed with saturated brine until neutral, dried, and then rotary evaporated for later use. The reaction equation is the same as step (2) in Example 1;

[0045] (3) React the intermediate PCL obtained in step (1) and the intermediate TYJ obtained in step (2) to obtain a strongly associated hydrophobic monomer: Dissolve intermediate PCL in ethanol as a solvent, heat to 70°C, and add a mixed solution of intermediate TYJ and ethanol dropwise using a constant pressure funnel. The molar ratio of intermediate PCL to intermediate TYJ is 2.1:1. Maintain at 70°C for 72 hours to obtain the strongly associated hydrophobic monomer TTH. Remove the ethanol by rotary evaporation, resulting in a pale yellow paste. Wash with acetone, and vacuum dry to constant weight for later use. The reaction equation is the same as step (3) in Example 1.

[0046] In this embodiment, the yield of the strongly associating hydrophobic monomer TTH was 93%.

[0047] The structural formula of the strongly associating hydrophobic monomer TTH in this embodiment is shown in formula (1), where R is erucamide propyl dimethyl quaternary ammonium.

[0048] Example 3:

[0049] Synthesis of the strongly associating hydrophobic monomer TTH-16

[0050] (1) Dissolve hexadecyl dimethyl tertiary amine in ethanol, add epichlorohydrin in a molar ratio of hexadecyl dimethyl tertiary amine: epichlorohydrin = 1:1.8, add dilute hydrochloric acid in a molar ratio of hexadecyl dimethyl tertiary amine: hydrochloric acid = 1:3, keep at 80°C for 36 hours, cool, remove ethanol by rotary evaporation, and obtain a pale yellow viscous liquid. Then add acetone to soak and wash, and vacuum dry to constant weight to finally obtain intermediate PCL-16;

[0051] (2) Another intermediate was obtained by reacting 3,3'-iminobis(N,N-dimethylpropylamine) and methacryloyl chloride in a molar ratio of 1:1.2: 3,3'-iminobis(N,N-dimethylpropylamine) was dissolved in dichloromethane and added to a three-necked round-bottom flask. The reaction system was placed in an ice-water bath to lower the temperature of the reaction system to below 5°C. Triethylamine was added in a molar ratio of 3,3'-iminobis(N,N-dimethylpropylamine):triethylamine = 1:1.3. A mixed solution of methacryloyl chloride and dichloromethane was slowly added dropwise in a constant pressure funnel in a molar ratio of 3,3'-iminobis(N,N-dimethylpropylamine):methacryloyl chloride = 1:1.2. The temperature was raised to room temperature and maintained at room temperature for 11 h. The solution was washed with saturated brine until neutral. After drying and rotary evaporation, intermediate TYJ was obtained.

[0052] (3) React the intermediate PCL-16 obtained in step (1) and the intermediate TYJ obtained in step (2) to obtain a strongly associated hydrophobic monomer: Dissolve the intermediate PCL-16 in ethanol, heat to 70°C, and add a mixed solution of intermediate TYJ and ethanol dropwise using a constant pressure funnel. The molar ratio of intermediate PCL to intermediate TYJ is 2:1. Keep at 70°C for 72 hours, cool, and evaporate using a rotary evaporator to remove ethanol, obtaining a pale yellow paste. Then, add acetone to soak and wash, and vacuum dry to constant weight to finally obtain a strongly associated hydrophobic monomer, denoted as the strongly associated hydrophobic monomer TTH-16.

[0053] In this embodiment, the yield of the strongly associating hydrophobic monomer TTH-16 was 91%.

[0054] The structural formula of the strongly associating hydrophobic monomer TTH-16 in this embodiment is shown in formula (1), wherein R is hexadecyl dimethyl quaternary ammonium.

[0055] Example 4:

[0056] Synthesis of the strongly associating hydrophobic monomer TTH-18

[0057] (1) Dissolve octadecyl dimethyl tertiary amine in ethanol, add epichlorohydrin in a molar ratio of octadecyl dimethyl tertiary amine: epichlorohydrin = 1:1.8, add dilute hydrochloric acid in a molar ratio of octadecyl dimethyl tertiary amine: hydrochloric acid = 1:3, keep at 80°C for 36 hours, cool, remove ethanol by rotary evaporation, and obtain a pale yellow viscous liquid. Then add acetone to soak and wash, and vacuum dry to constant weight to finally obtain the intermediate, which is denoted as intermediate PCL-18;

[0058] (2) Another intermediate was obtained by reacting 3,3'-iminobis(N,N-dimethylpropylamine) and methacryloyl chloride in a molar ratio of 1:1.2: 3,3'-iminobis(N,N-dimethylpropylamine) was dissolved in dichloromethane and added to a three-necked round-bottom flask. The reaction system was placed in an ice-water bath to lower the temperature of the reaction system to below 5°C. Triethylamine was added in a molar ratio of 3,3'-iminobis(N,N-dimethylpropylamine):triethylamine = 1:1.3. A mixed solution of methacryloyl chloride and dichloromethane was slowly added dropwise in a constant pressure funnel in a molar ratio of 3,3'-iminobis(N,N-dimethylpropylamine):methacryloyl chloride = 1:1.2. The temperature was raised to room temperature and maintained at room temperature for 11 h. The solution was washed with saturated brine until neutral. After drying and rotary evaporation, intermediate TYJ was obtained.

[0059] (3) The intermediate PCL-18 obtained in step (1) and the intermediate TYJ obtained in step (2) are reacted to obtain a strongly associated hydrophobic monomer: the intermediate PCL is dissolved in ethanol, heated to 70°C, and a mixed solution of intermediate TYJ and ethanol is added dropwise using a constant pressure funnel. The molar ratio of intermediate PCL to intermediate TYJ is 2:1. The reaction is maintained at 70°C for 72 hours. After cooling, the ethanol is removed by rotary evaporation to obtain a pale yellow paste. Then, acetone is added for soaking and washing, and the paste is dried under vacuum to constant weight to finally obtain a strongly associated hydrophobic monomer, which is denoted as the strongly associated hydrophobic monomer TTH-18.

[0060] In this embodiment, the yield of the strongly associating hydrophobic monomer TTH-18 was 94%.

[0061] The structural formula of the strongly associating hydrophobic monomer TTH-18 in this embodiment is shown in formula (1), wherein R is octadecyl dimethyl quaternary ammonium.

[0062] Example 5:

[0063] Synthesis of the strongly associating hydrophobic monomer TTH-22

[0064] (1) Dissolve docosyldimethyl tertiary amine in ethanol, add epichlorohydrin in a molar ratio of docosyldimethyl tertiary amine: epichlorohydrin = 1:1.8, add dilute hydrochloric acid in a molar ratio of docosyldimethyl tertiary amine: hydrochloric acid = 1:3, keep at 80°C for 36 hours, cool, remove ethanol by rotary evaporation, and obtain a pale yellow viscous liquid. Then add acetone to soak and wash, and vacuum dry to constant weight to finally obtain intermediate PCL-22;

[0065] (2) Another intermediate was obtained by reacting 3,3'-iminobis(N,N-dimethylpropylamine) and methacryloyl chloride in a molar ratio of 1:1.2: 3,3'-iminobis(N,N-dimethylpropylamine) was dissolved in dichloromethane and added to a three-necked round-bottom flask. The reaction system was placed in an ice-water bath to lower the temperature of the reaction system to below 5°C. Triethylamine was added in a molar ratio of 3,3'-iminobis(N,N-dimethylpropylamine):triethylamine = 1:1.3. A mixed solution of methacryloyl chloride and dichloromethane was slowly added dropwise in a constant pressure funnel in a molar ratio of 3,3'-iminobis(N,N-dimethylpropylamine):methacryloyl chloride = 1:1.2. The mixture was kept at room temperature for 11 h. After washing with saturated brine until neutral, the intermediate TYJ was obtained after drying and rotary evaporation.

[0066] (3) React the intermediate PCL-22 obtained in step (1) and the intermediate TYJ obtained in step (2) to obtain a strongly associated hydrophobic monomer: Dissolve the intermediate PCL-22 in ethanol, heat to 70°C, and add a mixed solution of intermediate TYJ and ethanol dropwise using a constant pressure funnel. The molar ratio of intermediate PCL to intermediate TYJ is 2:1. Keep at 70°C for 72 hours, cool, and evaporate using a rotary evaporator to remove ethanol, obtaining a pale yellow paste. Then, add acetone to soak and wash, and vacuum dry to constant weight to finally obtain a strongly associated hydrophobic monomer, denoted as the strongly associated hydrophobic monomer TTH-22.

[0067] In this embodiment, the yield of the strongly associating hydrophobic monomer TTH-22 was 93%.

[0068] The structural formula of the strongly associating hydrophobic monomer TTH-22 in this embodiment is shown in formula (1), wherein R is docosyldimethyl quaternary ammonium.

[0069] Example 6:

[0070] Synthesis of low molecular weight hydrophobic associative polymer HELVP

[0071] (1) Add 20.7g of acrylamide, 4.17g of acrylic acid, 1.25g of 2-acrylamido-2-methylpropanesulfonic acid and 1.75g ​​of the strongly associating hydrophobic monomer TTH from Example 2 to 70g of deionized water (the molar ratio of each monomer is acrylamide: acrylic acid: 2-acrylamido-2-methylpropanesulfonic acid: strongly associating hydrophobic monomer TTH = 80:16:3.5:0.5), stir to dissolve, and prepare an aqueous solution;

[0072] (2) Nitrogen gas was passed through the above aqueous solution for 45 minutes to remove dissolved oxygen from the aqueous solution;

[0073] (3) An initiator is added, namely 2,2-azobisisobutylamidine dihydrochloride (V50), ammonium persulfate (APS), and sodium sulfite. The amount of 2,2-azobisisobutylamidine dihydrochloride (V50) is 0.12 g, the amount of ammonium persulfate (APS) is 0.03 g, and the amount of sodium sulfite is 0.015 g. Under the condition of being wrapped with thermal insulation cotton, a free radical polymerization reaction is carried out. The desired low molecular weight hydrophobic associative polymer can be obtained after 4 hours of reaction. The polymer, denoted as low molecular weight hydrophobic associating polymer HELVP, was finally cut into pieces, soaked in anhydrous ethanol and dried, and ground into powder to obtain the low molecular weight hydrophobic associating polymer HELVP used in fracturing fluid. Its structural formula is shown in formula (2), where R is erucamide propyl dimethyl quaternary ammonium, and x, y, z, and m are the monomer molar ratios, where x is 80%, y is 16%, z is 3.5%, and m is 0.5%.

[0074] The reaction equation for this embodiment is:

[0075]

[0076] Wherein, R is erucamide propyl dimethyl quaternary ammonium, and x, y, z, and m are the monomer molar ratios, where x is 80%, y is 16%, z is 3.5%, and m is 0.5%.

[0077] Example 7:

[0078] Synthesis of low molecular weight hydrophobic associative polymer HELVP-16

[0079] (1) Add 18g of acrylamide, 6g of acrylic acid, 2.5g of 2-acrylamido-2-methylpropanesulfonic acid and 3.5g of the strongly associating hydrophobic monomer TTH-16 from Example 3 to 70g of deionized water (the molar ratio of each monomer is acrylamide: acrylic acid: 2-acrylamido-2-methylpropanesulfonic acid: strongly associating hydrophobic monomer TTH = 69:23:7:1), stir to dissolve, and prepare an aqueous solution;

[0080] (2) Nitrogen gas was passed through the above aqueous solution for 45 minutes to remove dissolved oxygen from the aqueous solution;

[0081] (3) An initiator is added, namely 2,2-azobisisobutylamidine dihydrochloride (V50), ammonium persulfate (APS), and sodium sulfite. The amount of 2,2-azobisisobutylamidine dihydrochloride (V50) is 0.12 g, the amount of ammonium persulfate (APS) is 0.03 g, and the amount of sodium sulfite is 0.015 g. Under the condition of being wrapped with thermal insulation cotton, a free radical polymerization reaction is carried out. The desired low molecular weight hydrophobic associative polymer can be obtained after 4 hours of reaction. The compound, denoted as low molecular weight hydrophobic associative polymer HELVP-16, was finally cut into pieces, soaked in anhydrous ethanol and dried, and ground into powder to obtain the low molecular weight hydrophobic associative polymer HELVP-16 used in fracturing fluid. Its structural formula is shown in formula (2), where R is hexadecyl dimethyl tertiary amine, and x, y, z, and m are the monomer molar ratios, where x is 69%, y is 23%, z is 7%, and m is 1%.

[0082] Example 8:

[0083] Synthesis of low molecular weight hydrophobic associative polymer HELVP-18

[0084] (1) Add 18g of acrylamide, 6g of acrylic acid, 2.5g of 2-acrylamido-2-methylpropanesulfonic acid and 3.5g of the strongly associating hydrophobic monomer TTH-18 from Example 4 to 70g of deionized water (the molar ratio of each monomer is acrylamide: acrylic acid: 2-acrylamido-2-methylpropanesulfonic acid: strongly associating hydrophobic monomer TTH = 69:23:7:1), stir to dissolve, and prepare an aqueous solution;

[0085] (2) Nitrogen gas was passed through the above aqueous solution for 45 minutes to remove dissolved oxygen from the aqueous solution;

[0086] (3) An initiator is added, namely 2,2-azobisisobutylamidine dihydrochloride (V50), ammonium persulfate (APS), and sodium sulfite. The amount of 2,2-azobisisobutylamidine dihydrochloride (V50) is 0.12 g, the amount of ammonium persulfate (APS) is 0.03 g, and the amount of sodium sulfite is 0.015 g. Under the condition of being wrapped with thermal insulation cotton, a free radical polymerization reaction is carried out. The desired low molecular weight hydrophobic associative polymer can be obtained after 4 hours of reaction. The compound, denoted as low molecular weight hydrophobic associating polymer HELVP-18, was finally cut into pieces, soaked in anhydrous ethanol and dried, and ground into powder to obtain the low molecular weight hydrophobic associating polymer HELVP-18 used in fracturing fluid. Its structural formula is shown in formula (2), where R is octadecyl dimethyl tertiary amine, and x, y, z, and m are the monomer molar ratios, where x is 69%, y is 23%, z is 7%, and m is 1%.

[0087] Example 9:

[0088] Synthesis of low molecular weight hydrophobic associative polymer HELVP-22

[0089] (1) Add 18g of acrylamide, 6g of acrylic acid, 2.5g of 2-acrylamido-2-methylpropanesulfonic acid and 3.5g of the strongly associating hydrophobic monomer TTH-22 from Example 5 to 70g of deionized water (the molar ratio of each monomer is acrylamide: acrylic acid: 2-acrylamido-2-methylpropanesulfonic acid: strongly associating hydrophobic monomer TTH = 69:23:7:1), stir to dissolve, and prepare an aqueous solution;

[0090] (2) Nitrogen gas was passed through the above aqueous solution for 45 minutes to remove dissolved oxygen from the aqueous solution;

[0091] (3) An initiator is added, namely 2,2-azobisisobutylamidine dihydrochloride (V50), ammonium persulfate (APS), and sodium sulfite. The amount of 2,2-azobisisobutylamidine dihydrochloride (V50) is 0.12 g, the amount of ammonium persulfate (APS) is 0.03 g, and the amount of sodium sulfite is 0.015 g. Under the condition of being wrapped with thermal insulation cotton, a free radical polymerization reaction is carried out. The desired low molecular weight hydrophobic associative polymer can be obtained after 4 hours of reaction. The compound, denoted as low molecular weight hydrophobic associating polymer HELVP-22, was finally cut into pieces, soaked in anhydrous ethanol and dried, and ground into powder to obtain the low molecular weight hydrophobic associating polymer HELVP-22 used in fracturing fluid. Its structural formula is shown in formula (2), where R is docosyl dimethyl tertiary amine, and x, y, z, and m are the monomer molar ratios, where x is 69%, y is 23%, z is 7%, and m is 1%.

[0092] Example 10:

[0093] Low molecular weight hydrophobic associating polymers HELVP, HELVP-16, HELVP-18, and HELVP-22 from Examples 6-9 were prepared into polymer solutions using deionized water. The molecular weights of the polymers were determined according to standard GB / T 12005.1-1989, "Determination of Intrinsic Viscosity of Polyacrylamide." The molecular weights of the four polymers were determined by the dilution method, and the results are shown in Table 1. Table 1 shows that the molecular weights of the low molecular weight hydrophobic associating polymers range from 8.57 to 9.86 × 10⁻⁶. 5 g / mol, while the molecular weight of traditionally synthesized polymers is generally 1 to 2 × 10⁻⁶ g / mol. 7 The low molecular weight hydrophobic associative polymer prepared in the embodiments of the present invention has a relatively smaller molecular weight than that of traditional synthetic polymers, and thus possesses the characteristic of low molecular weight.

[0094] Table 1 Polymer molecular weight

[0095] Polymer Molecular weight HELVP 9.03 x 10 5 g / mol HELVP-16 9.86 x 10 5 g / mol HELVP-18 8.57 x 10 5 g / mol HELVP-22 9.62 x 10 5 g / mol

[0096] Example 11:

[0097] The low molecular weight hydrophobic associating polymers HELVP, HELVP-16, HELVP-18, and HELVP-22 from Examples 6-9 were used to prepare fracturing fluids of different concentrations with deionized water. Using a HAAKE MARS III (006-1322) rheometer, the viscosity of the fracturing fluids at different polymer concentrations was tested at 25°C. The test results are shown in Table 2. The fracturing fluids exhibit variable viscosity. When the mass concentration of the low molecular weight hydrophobic associating polymers in the fracturing fluid is ≤0.3wt%, the viscosity of the fracturing fluid is less than 100 mPa·s, which is a characteristic of low viscosity.

[0098] Table 2

[0099]

[0100] Example 12:

[0101] The low molecular weight hydrophobic associative polymers HELVP, HELVP-16, HELVP-18 and HELVP-22 from Examples 6-9 were used to prepare fracturing fluids with a mass concentration of 0.2 wt% using deionized water. The viscoelasticity of the fracturing fluids was tested using a HAAKE MARS III (006-1322) rheometer at 25°C. The test results are shown in Table 3. The storage modulus was always greater than the loss modulus, indicating excellent viscoelasticity.

[0102] Table 3 Viscoelasticity of Fracturing Fluid

[0103] Polymer Average storage modulus (Pa) Average loss modulus (Pa) HELVP 6.31 3.23 HELVP-16 5.87 2.92 HELVP-18 6.02 3.11 HELVP-22 6.18 3.34

[0104] Example 13:

[0105] Low molecular weight hydrophobic associating polymers HELVP, HELVP-16, HELVP-18, and HELVP-22 from Examples 6-9 were used to prepare fracturing fluids with a mass concentration of 0.2 wt% using deionized water. A common HPAM polymer purchased from Sichuan Guangya Polymer Chemical Co., Ltd. was also used to prepare a fracturing fluid with a mass concentration of 0.2 wt% using deionized water. Quartz sand proppant was mixed with the above fracturing fluids at a mass ratio of 1:10, and then added to a 50 mL graduated cylinder for comparison. The time required for the quartz sand to settle to the bottom was observed, and the settling velocity was calculated to evaluate the proppant carrying capacity of the fracturing fluids. The experimental results are shown in Table 4. The fracturing fluids prepared with low molecular weight hydrophobic associating polymers HELVP, HELVP-16, HELVP-18, and HELVP-22 showed lower settling velocities and better suspension effects. The comparison demonstrates that the fracturing fluids prepared using the low molecular weight hydrophobic associating polymer HELVP series prepared in Examples 6-9 have excellent proppant carrying capacity.

[0106] Table 4. Sand-carrying capacity of fracturing fluid

[0107] Polymer Settling velocity (mm / s) HELVP 0.21 HELVP-16 0.29 HELVP-18 0.25 HELVP-22 0.24 HPAM 0.47

[0108] Comparing the above examples and comparative examples, it can be seen that the yield of the strongly associating hydrophobic monomer TTH prepared in Examples 1-5 is high; the preparation method of the low molecular weight hydrophobic associating polymer HELVP in Examples 6-9 is simple and efficient; Examples 10-13 show that the fracturing fluid prepared using the low molecular weight hydrophobic associating polymer HELVP has the characteristics of low viscosity and high elasticity, and excellent sand-carrying capacity. Examples 1-5 can be summarized as follows:

[0109] Preparation method of strongly associating hydrophobic monomers:

[0110] (1) Using ethanol as a solvent, dimethyl tertiary amine: epichlorohydrin: hydrochloric acid were added to ethanol in a molar ratio of 1:1.5~1.8:2.5~3 to obtain intermediate PCL.

[0111] (2) Using dichloromethane as a solvent, 3,3'-iminobis(N,N-dimethylpropylamine):methacryloyl chloride:triethylamine = 1:1.1~1.2:1.2~1.3 was added to dichloromethane to react and obtain intermediate TYJ;

[0112] (3) Using ethanol as a solvent, the above intermediate PCL and the above intermediate TYJ with a molar ratio of 2 to 2.1:1 are added to ethanol and reacted to obtain a strongly associated hydrophobic monomer, denoted as the strongly associated hydrophobic monomer TTH.

[0113] In step (1), the dimethyl tertiary amine is one of erucamide propyl dimethyl tertiary amine, hexadecyl dimethyl tertiary amine, octadecyl dimethyl tertiary amine and docosyl dimethyl tertiary amine or any combination thereof;

[0114] Step (1) is carried out at 60–80 °C;

[0115] Step (2) is carried out at room temperature;

[0116] Step (3) is carried out at 50–70°C.

[0117] Examples 6-9 can be summarized as follows:

[0118] Preparation method of low molecular weight hydrophobic associative polymer HELVP:

[0119] (1) Add acrylamide, acrylic acid, 2-acrylamido-2-methylpropanesulfonic acid and the strongly associating hydrophobic monomer TTH to water, wherein the molar ratio of acrylamide, acrylic acid, 2-acrylamido-2-methylpropanesulfonic acid and the strongly associating hydrophobic monomer TTH is 69-80:16-23:3.5-7:0.5-1, to prepare an aqueous solution;

[0120] (2) Nitrogen gas is passed through the above aqueous solution to remove dissolved oxygen from the aqueous solution;

[0121] (3) Add a mixed initiator and carry out free radical polymerization to obtain a low molecular weight hydrophobic associative polymer, denoted as low molecular weight hydrophobic associative polymer HELVP.

[0122] The mixed initiator is synthesized by mixing 2,2-azobisisobutylammonium dihydrochloride (V50), ammonium persulfate (APS), and sodium sulfite.

[0123] Preparation method of fracturing fluid: Dissolve the prepared low molecular weight hydrophobic associative polymer HELVP in water to obtain fracturing fluid.

[0124] The structural formula of the strongly associating hydrophobic monomer is:

[0125] Wherein, R is erucamide propyl dimethyl quaternary ammonium, hexadecyl dimethyl quaternary ammonium, octadecyl dimethyl quaternary ammonium, or docosyl dimethyl quaternary ammonium.

[0126] The structural formula of the hydrophobic associating polymer is:

[0127] Wherein, R is erucamide propyl dimethyl quaternary ammonium, hexadecyl dimethyl quaternary ammonium, octadecyl dimethyl quaternary ammonium, or docosyl dimethyl quaternary ammonium, and x, y, z, and m are the monomer molar ratios, where x is 69%–80%, y is 16%–23%, z is 3.5%–7%, and m is 0.5%–1%.

[0128] While the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the invention. Those skilled in the art can make various modifications and refinements without departing from the spirit and scope of the invention. Therefore, the scope of protection of the present invention shall be determined by the claims.

Claims

1. A strongly associating hydrophobic monomer, characterized in that, The structural formula of the strongly associating hydrophobic monomer is shown in formula (1). Wherein, R is erucamide propyl dimethyl quaternary ammonium, hexadecyl dimethyl quaternary ammonium, octadecyl dimethyl quaternary ammonium, or docosyl dimethyl quaternary ammonium.

2. A method for preparing strongly associating hydrophobic monomers, characterized in that, include: (1) Using ethanol as a solvent, dimethyl tertiary amine: epichlorohydrin: hydrochloric acid = 1:1.5~1.8:2.5~3 was added to ethanol to react and obtain intermediate PCL; (2) Using dichloromethane as a solvent, 3,3'-iminobis(N,N-dimethylpropylamine):methacryloyl chloride:triethylamine = 1:1.1~1.2:1.2~1.3 was added to dichloromethane to react and obtain intermediate TYJ; (3) Using ethanol as a solvent, the above intermediate PCL and the above intermediate TYJ with a molar ratio of 2 to 2.1:1 are added to ethanol and reacted to obtain a strongly associated hydrophobic monomer.

3. The method according to claim 2, characterized in that, In step (1), the dimethyl tertiary amine is one of erucamide propyl dimethyl tertiary amine, hexadecyl dimethyl tertiary amine, octadecyl dimethyl tertiary amine and docosyl dimethyl tertiary amine or any combination thereof.

4. The method according to claim 2, characterized in that, Step (1) is carried out at 60-80℃; Step (2) is carried out at room temperature; Step (3) is carried out at 50-70℃.

5. A low molecular weight hydrophobic associative polymer, characterized in that, The structural formula of the low molecular weight hydrophobic associative polymer is shown in formula (2). Wherein, R is erucamide propyl dimethyl quaternary ammonium, hexadecyl dimethyl quaternary ammonium, octadecyl dimethyl quaternary ammonium, or docosyl dimethyl quaternary ammonium, and x, y, z, and m are the monomer molar ratios, 69%–80%, y is 16%–23%, z is 3.5%–7%, and m is 0.5%–1%.

6. A method for preparing low molecular weight hydrophobic associative polymers, characterized in that, include: (1) Add acrylamide, acrylic acid, 2-acrylamido-2-methylpropanesulfonic acid and the strongly associating hydrophobic monomer of claim 1 or the strongly associating hydrophobic monomer prepared by any of the methods of claims 2-4 to water in a molar ratio of 69-80:16-23:3.5-7:0.5-1, stir to dissolve, and prepare an aqueous solution. (2) Nitrogen gas is introduced into the above aqueous solution to remove dissolved oxygen; (3) Add a mixed initiator to carry out a free radical polymerization reaction to obtain a low molecular weight hydrophobic associative polymer.

7. The method according to claim 6, characterized in that, In step (3), the mixed initiator is synthesized by mixing 2,2-azobisisobutylammonium dihydrochloride, ammonium persulfate and sodium sulfite.

8. A fracturing fluid, characterized in that, Contains the low molecular weight hydrophobic associating polymer of claim 5 or the low molecular weight hydrophobic associating polymer prepared by any of the methods of claims 6-7.

9. A method for preparing fracturing fluid, characterized in that, Dissolve the low molecular weight hydrophobic associating polymer of claim 5 or the low molecular weight hydrophobic associating polymer prepared by any of the methods of claims 6-7 in water to obtain fracturing fluid.

10. The application of fracturing fluid in oil and gas field development, characterized in that, The fracturing fluid is the fracturing fluid of claim 8 or the fracturing fluid prepared by the method of claim 9.

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