Salt-tolerant drag reducer, preparation method thereof and fracturing fluid

Abstract

The invention provides a salt-tolerant drag reducer, a preparation method thereof and a fracturing fluid, and belongs to the technical field of acrylamide and acrylic acid copolymer derivative preparation, the preparation method comprises the following steps: using alkyl acyl chloride to carry out hydrophobic modification on a cross-linking agent to obtain a hydrophobic modified cross-linking agent; mixing acrylamide, acrylic acid, a hydrophobic modification cross-linking agent, an auxiliary agent, an azo initiator and water to obtain a water phase; mixing an emulsifier and white oil to obtain an oil phase; adding the water phase into the oil phase, and emulsifying to obtain an inverse emulsion; and adding a redox system initiator into the inverse emulsion to carry out inverse emulsion polymerization, and adding a phase inversion agent after the reaction is finished to obtain the polyacrylamide emulsion. According to the invention, two effects of cross-linking and hydrophobic association are simultaneously introduced to a polymer molecular chain by adding the hydrophobic modified cross-linking agent, so that the polymer has a better drag reduction effect in a hypersalinity environment.

Description

Technical Field

[0001] The present invention relates to the technical field of preparation of oilfield chemicals, and in particular to a salt - resistant drag reducer with integrated cross - linking and hydrophobic association for fracturing, its preparation method, and a fracturing fluid containing the same. Background Art

[0002] Shale gas is a typical unconventional oil reservoir, characterized by low porosity and low permeability. Usually, it has no natural productivity and needs to rely on hydraulic fracturing to achieve its industrial - scale development. Since the initial stage of unconventional resource development, slick - water fracturing fluids have developed rapidly and have now become the most commonly used fluid system in the industry. Conventional slick - water is mainly composed of polyacrylamide polymer drag reducers, which are usually transported to the operation site in liquid forms such as suspensions or emulsions.

[0003] Previous hydraulic fracturing operations generally used fresh water, which would cause environmental problems due to the excessive occupation of fresh water resources and increase the costs of produced - water treatment and fresh - water transportation. Considering environmental protection, cost pressure, and operation aspects, the goal of hydraulic fracturing operations is to establish a fracturing fluid system that can be directly formulated with produced water. Currently, the salinity components of produced water from unconventional oil wells are very high. In a high - salinity environment, polyacrylamide is prone to hydrolysis, degradation, molecular - chain curling, and precipitation, resulting in poor polymer drag - reduction effect. Therefore, it is necessary to develop a new type of salt - resistant drag reducer to adapt to the brine system and overcome this influence. Summary of the Invention

[0004] The present invention solves the problem of poor drag - reduction effect of polyacrylamide drag reducers in a high - salt environment. By hydrophobically modifying the cross - linker and adding the hydrophobically modified cross - linker, two effects of cross - linking and hydrophobic association are introduced into the polymer molecular chain simultaneously. The reversible (physical cross - linking of hydrophobic association) and irreversible (chemical cross - linking) molecular - chain binding enables the polymer to form a stable three - dimensional network structure, which brings hydrophobic association while increasing the polymer molecular weight, making the polymer have a better drag - reduction effect in a high - salinity environment.

[0005] One of the purposes of the present invention is to provide a preparation method of a salt - resistant drag reducer.

[0006] Another purpose of the present invention is to provide a salt - resistant drag reducer prepared by this preparation method.

[0007] Another purpose of the present invention is to provide a fracturing fluid containing this salt - resistant drag reducer.

[0008] In order to achieve the above - mentioned purposes of the present invention, the following technical solutions are specifically adopted:

[0009] In the first aspect, the present invention provides a preparation method of a salt - resistant drag reducer, including the following steps:

[0010] S1. Hydrophobically modify the crosslinking agent with alkyl acyl chloride to obtain a hydrophobically modified crosslinking agent, where the crosslinking agent is diallylamine;

[0011] S2. Mix acrylamide, acrylic acid, the hydrophobically modified crosslinking agent, additives, azo initiator and water to obtain an aqueous phase; mix an emulsifier and white oil to obtain an oil phase; emulsify the aqueous phase into the oil phase to obtain a reverse emulsion; add a redox initiator system to the reverse emulsion for inverse emulsion polymerization, and add a phase transfer agent after the reaction to obtain a polyacrylamide emulsion.

[0012] The following is a detailed description of each step:

[0013] S1:

[0014] In this step, add the solvent, crosslinking agent and catalyst into a three-necked flask, place it in a constant temperature water bath, start the stirrer, slowly dropwise add the modifier alkyl acyl chloride under an ice-water bath, react slowly, after the reaction is completed, filter, wash with alkali, extract with ethyl acetate, and purify by vacuum distillation to obtain the hydrophobically modified crosslinking agent.

[0015] The crosslinking agent is diallylamine;

[0016] The alkyl acyl chloride is one or more selected from lauroyl chloride, cetyl chloride (palmitoyl chloride), stearoyl chloride.

[0017] In some embodiments, the molar ratio of the crosslinking agent to the alkyl acyl chloride is 1:1.2 - 2.

[0018] The catalyst is one or more selected from anhydrous K2CO3, pyridine, triethylamine.

[0019] In some embodiments, the molar ratio of the catalyst to the crosslinking agent is 1.1 - 1.3:1.

[0020] In some embodiments, the reaction temperature of step S1 is 0 - 5°C, and the reaction time is 2 - 10 h.

[0021] The structure of the hydrophobically modified crosslinking agent after the reaction is as follows:

[0022] Hydrophobically modified crosslinking agent

[0023] R can be an alkyl group with C12 - C18.

[0024] S2:

[0025] In this step, S2 includes the following steps:

[0026] S21. Dissolve acrylamide and acrylic acid monomers in water and mix, add the hydrophobically modified crosslinking agent, additives, azo initiator, obtain an aqueous phase, and adjust the pH of the aqueous phase with an alkali solution;

[0027] In some embodiments, the total mass concentration of the acrylamide and acrylic acid monomers in the aqueous phase is 30-40%; preferably, the mass ratio of acrylamide to acrylic acid is 65-80:20-30.

[0028] In some embodiments, the addition amount of the hydrophobic modified crosslinking agent is 0.05-0.5% of the total mass of the monomers.

[0029] In some embodiments, the auxiliary agents include a metal ion chelating agent, a molecular weight regulator, and a dissolution promoter;

[0030] Preferably, the metal ion chelating agent is disodium ethylenediaminetetraacetate, and the addition amount is 0.05-0.15% of the total mass of the monomers;

[0031] Preferably, the molecular weight regulator is one selected from sodium formate and sodium acetate, and the addition amount is 0.05-0.15% of the total mass of the monomers;

[0032] Preferably, the dissolution promoter is urea, and the addition amount is 1-4% of the total mass of the monomers.

[0033] In some embodiments, the azo initiator is 2,2'-azobis(2-methylpropionamidine) dihydrochloride, and the addition amount of 2,2'-azobis(2-methylpropionamidine) dihydrochloride is 0.005-0.015% of the total mass of the monomers.

[0034] In some embodiments, the lye is an aqueous sodium hydroxide solution with a mass fraction of 25-30%, and the pH of the aqueous phase is adjusted to 6.5-7.5.

[0035] S22. Add the emulsifier to the white oil and mix to obtain an oil phase; after purging the aqueous phase with nitrogen to remove oxygen, slowly add it to the oil phase for emulsification to obtain a reverse emulsion;

[0036] In some embodiments, the emulsifier is a composite emulsifier, which is a combination of the lipophilic emulsifier sorbitan oleate (span-80) and the hydrophilic emulsifier octylphenol polyoxyethylene ether (op-10), and the addition amount of the composite emulsifier is 4-7% of the mass of the reverse emulsion.

[0037] In some embodiments, by weight, the oil phase is 9-16 parts and the aqueous phase is 15-35 parts.

[0038] S23. Cool the reverse emulsion, purge it with nitrogen to remove oxygen, start dropping the redox system initiator, slowly raise the temperature to carry out the reverse emulsion polymerization reaction, and after the reaction is completed and the emulsion is cooled, add a phase inversion agent to obtain a polyacrylamide emulsion.

[0039] In some embodiments, the redox initiator system is ammonium persulfate / sodium bisulfite system; preferably, the addition amount of ammonium persulfate is 0.01-0.02% of the total mass of the monomers, and the addition amount of sodium bisulfite is 0.003-0.015% of the total mass of the monomers.

[0040] In some embodiments, the phase inversion agent is one or more selected from octylphenol polyoxyethylene ether and polyoxyethylene sorbitan monooleate (Tween-80), and the addition amount is 3.0-5.5% of the mass of the inverse emulsion.

[0041] In a specific embodiment, S2 includes:

[0042] Dissolve acrylamide and acrylic acid monomers in water and mix them, add a hydrophobic modified crosslinking agent and additives, and adjust the pH of the aqueous phase with an alkali solution; add a composite emulsifier to white oil, and after deoxygenating the aqueous phase by passing nitrogen, slowly add it to the oil phase for emulsification. After adding the emulsion to a four-necked flask, cool it to 20°C, deoxygenate it by passing nitrogen for 60 min, heat it up to 30°C, start dropping and initiating with an oxidizing / reducing agent, slowly heat it up to 41°C, and maintain the reaction temperature at 45-50°C. During this period, the initiator is changed from a redox system to an azo initiator added to the aqueous phase in advance to continue initiating the polymerization. After the reaction ends and the emulsion cools down, add a phase inversion agent to obtain a polyacrylamide emulsion. The structure of the polyacrylamide is as follows:

[0043]

[0044] The present invention is a method for preparing an inverse emulsion polymer. First, a crosslinking agent diallylamine is hydrophobically modified with an acyl chloride, and then acrylamide and acrylic acid are used as polymerization monomers, a hydrophobic modified crosslinking agent and additives are added, a composite emulsifier is selected, and white oil is used as the continuous-phase oil phase to prepare an inverse emulsion; through redox and azo composite initiation copolymerization, a phase inversion agent is added after the reaction to obtain a polyacrylamide emulsion. This polyacrylamide inverse emulsion can dissolve quickly in a high-salt environment and has a high viscosity retention rate, which can effectively solve the problem of poor salt tolerance of existing polyacrylamide drag reducers.

[0045] In a second aspect, the present invention provides a salt-tolerant drag reducer prepared by the above preparation method.

[0046] In a third aspect, the present invention provides a fracturing fluid comprising the above salt-tolerant drag reducer.

[0047] Beneficial effects

[0048] The present invention hydrophobically modifies the cross-linking agent, and introduces both cross-linking and hydrophobic association effects to the polymer molecular chain by adding the hydrophobically modified cross-linking agent. The cross-linking can enable the polymer to form a three-dimensional network structure, increase the molecular weight of the polymer and bring about the hydrophobic association effect, so that the polymer has a better drag reduction effect in a high mineralization environment.

[0049] The present invention has been described in detail above, but the above embodiments are only illustrative in nature and are not intended to limit the present invention. In addition, this article is not limited by any theory described in the above prior art or invention content or the following examples. DETAILED DESCRIPTION

[0050] The present invention is further described below in conjunction with examples. It should be noted that the following examples are provided for illustrative purposes only and do not constitute a limitation on the scope of protection claimed for the present invention.

[0051] Unless otherwise specified, the raw materials, reagents, methods, etc. used in the examples are conventional raw materials, reagents, methods in the art.

[0052] The raw materials involved in the embodiments and comparative examples are as follows:

[0053] Acrylic acid (AA) was purchased from BASF-YPC Co., Ltd.; acrylamide (AM) was purchased from Jiangsu Changjiu Agricultural Science and Chemical Co., Ltd.; white oil was purchased from Kunshan Marine Lubricant Co., Ltd.; sorbitan oleate (span-80), octylphenol polyoxyethylene ether (OP-10), and polyoxyethylene sorbitan monooleate (Tween-80) were all purchased from Jiangsu Hai'an Petrochemical Plant; the remaining reagents were purchased from Aladdin Company.

[0054] Preparation Example 1 Preparation of hydrophobically modified cross-linking agent:

[0055] 4.85g (50mmol) of diallylamine, 15g of anhydrous THF, and 8.28g (60mmol) of anhydrous potassium carbonate were added to a three-necked flask in sequence, and stirred for 30min. 16.5g of palmitoyl chloride (60mmol) was weighed and diluted with 15g of anhydrous THF, and slowly added to the three-necked flask in an ice-water bath using a constant pressure funnel, and the ice-water bath was kept for 10h. After the reaction was completed, the mixture was filtered, washed with 10g of 0.5mol / LNaOH solution, extracted with 40g of ethyl acetate, and the ethyl acetate phase was subjected to reduced pressure distillation after separation to obtain a hydrophobically modified crosslinking agent.

[0056] Example 1

[0057] Add 130 g of AM, 42 g of AA, 3.5 g of urea, 0.172 g of sodium formate, 0.09 g of EDTA-2Na, 0.8 g of the hydrophobic modified crosslinking agent prepared in Preparation Example 1, 0.02 g of 2,2'-azobis(2-methylpropionamidine) dihydrochloride, and 100 g of water to a beaker in sequence. Stir and slowly add 30% by mass of sodium hydroxide to adjust the pH of the solution to 7.2. Add water to make the mass of the aqueous phase up to 450 g to obtain the aqueous phase.

[0058] Take another beaker and add 180 g of white oil, 32 g of span-80, and 8 g of op-10 in sequence. Stir until clear to obtain the oil phase. After degassing the aqueous phase with nitrogen, slowly add it to the oil phase and emulsify it with an emulsifier at 3000 rpm / min for 20 min.

[0059] Transfer the emulsion to a four-necked flask, place it in a 20°C water bath and degas it with nitrogen for 1 h. Slowly raise the temperature to 30°C and start dropping 0.5% by mass concentration of ammonium persulfate and 0.2% by mass concentration of sodium bisulfite at a dropping rate of 2 ml / h to initiate the polymerization reaction. After 2 h, stop dropping the above initiators and continue the reaction for 1 h. Then raise the water bath temperature to 45°C and keep it warm for 1 h. Then lower the temperature to 30°C, start dropping 30 g of tween-80, and take it out of the pot.

[0060] Comparative Example 1

[0061] Add 130 g of AM, 42 g of AA, 3.5 g of urea, 0.172 g of sodium formate, 0.09 g of EDTA-2Na, 0.02 g of 2,2'-azobis(2-methylpropionamidine) dihydrochloride, and 100 g of water to a beaker in sequence. Stir and slowly add 30% by mass of sodium hydroxide to adjust the pH of the solution to 7.2. Add water to make the mass of the aqueous phase up to 450 g to obtain the aqueous phase.

[0062] Take another beaker and add 180 g of white oil, 32 g of span-80, and 8 g of op-10 in sequence. Stir until clear to obtain the oil phase. After degassing the aqueous phase with nitrogen, slowly add it to the oil phase and emulsify it with an emulsifier at 3000 rpm / min for 20 min.

[0063] Transfer the emulsion to a four-necked flask, place it in a 20°C water bath and degas it with nitrogen for 1 h. Slowly raise the temperature to 30°C and start dropping 0.5% by mass concentration of ammonium persulfate and 0.2% by mass concentration of sodium bisulfite at a dropping rate of 2 ml / h to initiate the polymerization reaction. After 2 h, stop dropping the above initiators and continue the reaction for 1 h. Then raise the water bath temperature to 45°C and keep it warm for 1 h. Then lower the temperature to 30°C, start dropping 30 g of tween-80, and take it out of the pot.

[0064] Comparative Example 2

[0065] Add 130 g of AM, 42 g of AA, 3.5 g of urea, 0.172 g of sodium formate, 0.09 g of EDTA-2Na, 0.8 g of diallylamine, 0.02 g of 2,2'-azobis(2-methylpropionamidine) dihydrochloride, and 100 g of water to a beaker in sequence. Stir and slowly add 30% sodium hydroxide by mass fraction to adjust the pH of the solution to 7.2. Add water to make the mass of the aqueous phase up to 450 g to obtain the aqueous phase.

[0066] Take another beaker and add 180 g of white oil, 32 g of span-80, and 8 g of op-10 in sequence. Stir until clear to obtain the oil phase. After deoxygenating the aqueous phase by passing nitrogen, slowly add it to the oil phase and emulsify it with an emulsifier at 3000 rpm / min for 20 min.

[0067] Transfer the emulsion to a four-necked flask, place it in a 20 °C water bath, and deoxygenate it by passing nitrogen for 1 h. Slowly raise the temperature to 30 °C and start dropping 0.5% ammonium persulfate and 0.2% sodium bisulfite by mass concentration at a dropping rate of 2 ml / h to initiate the polymerization reaction. After 2 h, stop dropping the above initiators and continue the reaction for 1 h. Then raise the temperature of the water bath to 45 °C and keep it warm for 1 h. Then lower the temperature to 30 °C, start dropping 30 g of tween-80, and take out of the pot.

[0068] Test experiment

[0069] Test the drag reduction rates of the products obtained in the examples and comparative examples in fresh water and high salinity water (brine with a salinity of 20000 g / L) respectively. The test method is as follows:

[0070] Use a pipeline friction meter that complies with NB / T 14003.1-2015 to measure the drag reduction rate of the polymer. Turn on the pipeline friction meter, add the required amount of fresh water or high salinity water to the circulating liquid storage tank, slowly adjust the rotation speed of the power pump, and read the pressure difference of fresh water or high salinity water at this linear velocity from the computer. When the pressure difference change within 1 min is less than 1%, take the average value of the pressure difference within this 1 min as the friction pressure difference of fresh water or high salinity water (ΔP1); Test the friction pressure difference (ΔP2) of the drag reducer prepared with fresh water or high salinity water flowing through this pipeline according to the drag reducer preparation procedure under the same program and conditions (the displacement change range is less than 1% and the temperature difference is less than 2 °C compared with the fresh water experiment).

[0071] Calculation of drag reduction rate:

[0072] In the formula:

[0073] DR - the drag reduction rate of the indoor drag reducer for fresh water or high salinity water, in percentage (%);

[0074] ΔP1 - the pressure difference when fresh water or high salinity water flows through the pipeline, in pascal (Pa);

[0075] ΔP2 is the pressure difference when the drag reducer is flowing through the pipeline in the clear water or the slippery water prepared under the condition of high salinity water, and the unit is Pascal (Pa).

[0076] The test results are shown in Table 1:

[0077] Table 1

[0078] Use concentration Drag reduction rate Comparative example 1 0.15％ 75.56％ Comparative example 1 + 20000 g / L salinity 0.15％ 57.06％ Comparative example 2 0.15％ 74.46％ Comparative example 2 + 20000 g / L salinity 0.15％ 61.00％ Example 1 0.15％ 77.06％ Example 1 + 20000 g / L salinity 0.15％ 70.20％

[0079] It can be seen from the table that the drag reduction performance of the conventional drag reducer can reach 75.5% in clear water, but in high salinity water, it drops to 57%, and the reduction rate of the drag reduction effect is 75%. The crosslinking and hydrophobic association integrated salt-tolerant drag reducer obtained in this application can reach a maximum drag reduction rate of 70.2% in high salinity salt water, and the drag reduction retention rate is 91%, which has better salt tolerance than the conventional drag reducer. Thus, it can be seen that the crosslinking and hydrophobic association integrated salt-tolerant drag reducer obtained in this application can have a better drag reduction effect in a high salinity environment.

[0080] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: within the scope of the spirit and essence defined by the claims of the present invention, the technical solutions recorded in the foregoing embodiments can be modified, or some or all of the technical features can be equivalently replaced; and these modifications or replacements are still within the scope defined by the claims of the present invention.

Claims

1. A preparation method of a salt-tolerant drag reducer, characterized in that, It includes the following steps: S1. Hydrophobically modify the crosslinker with alkyl acyl chloride to obtain a hydrophobically modified crosslinker, where the crosslinker is diallylamine; S2. Mix acrylamide, acrylic acid, the hydrophobically modified crosslinker, an auxiliary agent, an azo initiator and water to obtain an aqueous phase; mix an emulsifier and white oil to obtain an oil phase; add the aqueous phase to the oil phase for emulsification to obtain a reverse emulsion; add a redox initiator system to the reverse emulsion for inverse emulsion polymerization, and add a phase inversion agent after the reaction ends to obtain a polyacrylamide emulsion.

2. The preparation method according to claim 1, wherein Step S1 includes: Add the solvent, crosslinker and catalyst to a three-necked flask, place it in a constant temperature water bath, start the stirrer, slowly dropwise add the modifier alkyl acyl chloride under an ice-water bath, react slowly, after the reaction ends, filter, wash with alkali, extract with ethyl acetate, and purify by vacuum distillation to obtain the hydrophobically modified crosslinker.

3. The preparation method according to claim 2, wherein The alkyl acyl chloride is one or more selected from dodecanoyl chloride, hexadecanoyl chloride, octadecanoyl chloride; Preferably, the molar ratio of the crosslinker to the alkyl acyl chloride is 1:1.2 - 2; Preferably, the catalyst is one or more selected from anhydrous K2CO3, pyridine, triethylamine; Preferably, the molar ratio of the catalyst to the crosslinker is 1.1 - 1.3:1; Preferably, the reaction temperature of step S1 is 0 - 5°C, and the reaction time is 2 - 10 h.

4. The preparation method according to claim 1, characterized in that, Step S2 includes: S21. Dissolve acrylamide and acrylic acid monomers in water and mix, add the hydrophobically modified crosslinker, an auxiliary agent, and an azo initiator to obtain an aqueous phase, and adjust the pH of the aqueous phase with an alkali solution; S22. Add the emulsifier to the white oil and mix to obtain an oil phase; deoxygenate the aqueous phase by passing nitrogen and slowly add it to the oil phase for emulsification to obtain a reverse emulsion; S23. Cool the reverse emulsion, deoxygenate it by passing nitrogen, start to dropwise add the redox initiator system, slowly raise the temperature for inverse emulsion polymerization reaction, and add a phase inversion agent after the emulsion temperature drops after the reaction ends to obtain a polyacrylamide emulsion.

5. The preparation method according to claim 4, wherein In step S21, The total mass concentration of acrylamide and acrylic acid monomers in the aqueous phase is 30 - 40%; preferably, the mass ratio of acrylamide to acrylic acid is 65 - 80:20 - 30; Preferably, the addition amount of the hydrophobically modified crosslinker is 0.05 - 0.5% of the total mass of the monomers.

6. The preparation method according to claim 4, characterized in that In step S21, The auxiliary agent includes a metal ion chelating agent, a molecular weight regulator and a dissolution promoter; Preferably, the metal ion chelating agent is disodium ethylenediaminetetraacetate, and the addition amount is 0.05 - 0.15% of the total mass of the monomers; Preferably, the molecular weight regulator is one selected from sodium formate and sodium acetate, and the addition amount is 0.05 - 0.15% of the total mass of the monomers; Preferably, the dissolution promoter is urea, and the addition amount is 1 - 4% of the total mass of the monomers; Preferably, the azo initiator is 2,2'-azobis(2-methylpropionamidine) dihydrochloride, and the addition amount of 2,2'-azobis(2-methylpropionamidine) dihydrochloride is 0.005 - 0.015% of the total mass of the monomers.

7. The preparation method according to claim 4, characterized in that, In step S22, The emulsifier is a composite emulsifier of a lipophilic emulsifier sorbitan oleate and a hydrophilic emulsifier octylphenol polyoxyethylene ether, and the addition amount of the composite emulsifier is 4 - 7% of the mass of the reverse emulsion; Preferably, by weight parts, the oil phase is 9 - 16 parts and the water phase is 15 - 35 parts.

8. The preparation method according to claim 4, characterized in that, In step S23, The redox initiator system is ammonium persulfate / sodium bisulfite system; preferably, the addition amount of ammonium persulfate is 0.01 - 0.02% of the total mass of monomers, and the addition amount of sodium bisulfite is 0.003 - 0.015% of the total mass of monomers; Preferably, the phase transfer agent is one or more selected from octylphenol polyoxyethylene ether and polyoxyethylene sorbitan monooleate, and the addition amount is 3.0 - 5.5% of the mass of the inverse emulsion.

9. A salt-tolerant drag reducer, characterized in that, Prepared by the preparation method according to any one of claims 1 - 8.

10. A fracturing fluid, characterized in that, Comprising the salt - resistant drag reducer according to claim 9.

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