Salt-resistant emulsion fracturing fluid system and preparation method thereof

Abstract

The invention relates to the technical field of oil and gas well reservoir transformation, in particular to a salt-resistant emulsion fracturing fluid system and a preparation method of the salt-resistant emulsion fracturing fluid system. The salt-tolerant emulsion is prepared from the following raw materials in parts by weight: 60 to 80 parts of white oil, 5 to 10 parts of an emulsifier, 70 to 90 parts of acrylamide, 10 to 20 parts of hydroxyethyl methylacrylate, 10 to 30 parts of 2-acrylamide-2-methylpropanesulfonic acid, 10 parts of dimethyl carbonate and 3 to 7 parts of an initiator. The salt-tolerant emulsion prepared by the invention can be directly mixed with highly mineralized water on line; according to the present invention, the highly mineralized water does not need to be treated to remove calcium and magnesium ions, and the liquid preparation vehicle does not need to be configured and stored in the liquid storage tank in advance, such that the water treatment cost, the on-site liquid preparation cost, the liquid storage tank carrying cost and the like can be saved, and the recycling of the flowback liquid has good applicability.

Description

Technical Field

[0001] The invention relates to the technical field of oil and gas well reservoir transformation, and in particular to a salt-resistant emulsion fracturing fluid system and a preparation method thereof. Background Art

[0002] At present, the fracturing fluids used in domestic oil and gas well reservoir fracturing are mostly online mixed types, mainly conventional salt-intolerant emulsion types. In order to reduce the time of liquid preparation and improve construction efficiency, when linear glue and high viscosity liquid need to be pumped, the emulsion concentration is increased to achieve switching between different liquids.

[0003] At present, the effective content in conventional salt-intolerant emulsions is low, and the linear gel and high mucus viscosity formed after encountering highly mineralized water cannot meet the requirements of on-site construction. Therefore, salt-resistant emulsion fracturing fluids with relatively high solid content are increasingly receiving attention. In addition, environmental protection requirements and the high cost of backflow fluid treatment have prompted the current preparation water to be mostly pure backflow fluid with a high degree of mineralization, which puts higher requirements on the salt resistance of the emulsion. The existing high-mineralized water fracturing fluid mostly uses a hydroxypropyl guar gum system. When using it, it is necessary to first treat the calcium and magnesium ions in the highly mineralized water, and then prepare the fracturing fluid base fluid, and then add a cross-linking agent for use. However, this system has the following disadvantages:

[0004] (1) Treatment equipment is needed to treat highly mineralized water to remove calcium and magnesium ions, generating new waste liquid and waste solid;

[0005] (2) It requires a liquid dispensing vehicle and a large number of liquid storage tanks;

[0006] (3) Cross-linking agents need to be added during the fracturing process, making the construction steps more complicated;

[0007] (4) The liquid distribution vehicle and liquid storage tank occupy a large area and are not suitable for smaller well sites. Summary of the invention

[0008] The present invention aims at the problem that the existing conventional salt-intolerant emulsion cannot be prepared with high-mineralized water such as flowback fluid, and the use of hydroxypropyl guar gum system has shortcomings; the present invention provides a salt-resistant emulsion fracturing fluid system suitable for high-mineralized water fracturing and a preparation method thereof, thereby increasing the viscosity of the system under high mineralization conditions to meet on-site construction requirements.

[0009] In order to solve the above technical problems, the technical solution provided by the present invention is:

[0010] In the first aspect, the salt-resistant emulsion fracturing fluid system provided by the present invention is prepared by the following raw materials in parts by weight:

[0011] 60-80 parts of white oil, 5-10 parts of emulsifier, 70-90 parts of acrylamide, 10-20 parts of hydroxyethyl methacrylate, 10-30 parts of 2-acrylamide-2-methylpropanesulfonic acid, 10 parts of dimethyl carbonate, and 3-7 parts of initiator.

[0012] Furthermore,

[0013] The emulsifier is a nonionic emulsifier, and the hydrophilic-lipophilic balance value of the nonionic emulsifier is 4-7.

[0014] Furthermore,

[0015] The emulsifier is at least one of Tween-20, OP-10, OP-15 and polyether silicone oil.

[0016] Furthermore,

[0017] The initiator is an oxidizing agent.

[0018] Furthermore,

[0019] The oxidant is a mixture of one or more of sodium persulfate, potassium persulfate and hydrogen peroxide.

[0020] Furthermore,

[0021] The white oil is 65-75 parts.

[0022] Furthermore,

[0023] Acrylamide is 75-85 parts.

[0024] Furthermore,

[0025] Hydroxyethyl methacrylate is 15-20 parts.

[0026] Furthermore,

[0027] 2-Acrylamide-2-methylpropanesulfonic acid is 16-26 parts.

[0028] In a second aspect, the method for preparing the salt-resistant emulsion fracturing fluid system provided by the present invention comprises the following steps:

[0029] Step 1: Add 60-80 parts of white oil and 5-10 parts of emulsifier into the reaction kettle according to the weight ratio, introduce nitrogen, and stir until all are dissolved to obtain a uniform oil phase for use;

[0030] Step 2: In a reactor under an oxygen-free environment, 70-90 parts of acrylamide, 10-20 parts of hydroxyethyl methacrylate, 10-30 parts of 2-acrylamide-2-methylpropanesulfonic acid, and 10 parts of dimethyl carbonate are dissolved in deionized water, stirred until completely dissolved to form an aqueous phase solution, and nitrogen is continuously introduced during the stirring process, an oil phase medium is added, and stirring is continued until a uniform and stable emulsion is formed, and finally, an initiator is added to react;

[0031] Step 3: After the reaction is completed, the product is dispersed under an ultrasonic environment to obtain a salt-resistant emulsion.

[0032] Based on the above technical solutions, the technical effects that can be achieved by the present invention are:

[0033] The salt-resistant emulsion prepared by the present invention can be directly mixed with high-mineralized water online, and the high-mineralized water does not need to be treated to remove calcium and magnesium ions, and does not need to be configured in advance by a liquid preparation vehicle to be stored in a liquid storage tank, which can save water treatment fees, on-site liquid preparation fees, and liquid storage tank transportation fees, etc. At the same time, the needle return liquid has good applicability for repeated reuse. DETAILED DESCRIPTION

[0034] In order to make the purpose, technical scheme and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention, that is, the embodiments described are only part of the embodiments of the present invention, rather than all of the embodiments.

[0035] Therefore, the following detailed description of the embodiments of the present invention is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without making creative work are within the scope of protection of the present invention.

[0036] Unless otherwise specified, the experimental methods used in the following examples are all conventional methods; the reagents, materials, etc. used in the following examples, unless otherwise specified, can be obtained from commercial channels.

[0037] First, a hydrophobic associating polymer with good salt resistance is selected as a thickener. In order to meet the requirements of the on-site high-mineralized water return liquid preparation, a method for preparing a salt-resistant emulsion is proposed. The salt-resistant emulsion is prepared by inverse emulsion polymerization, and 2-acrylamide-2-methylpropanesulfonic acid is introduced into the macromolecular chain to greatly improve the temperature and salt resistance of the molecule; the steric hindrance group dimethyl carbonate is introduced to reduce the curling effect of the macromolecular chain under high mineralization conditions.

[0038] The invention provides a salt-resistant emulsion fracturing fluid system, which is prepared from the following raw materials in parts by weight: 60-80 parts of white oil, 5-10 parts of emulsifier, 70-90 parts of acrylamide, 10-20 parts of hydroxyethyl methacrylate, 10-30 parts of 2-acrylamide-2-methylpropanesulfonic acid, 10 parts of dimethyl carbonate, and 3-7 parts of initiator. The white oil is preferably 65-75 parts, and the best is 65 parts; the emulsifier is preferably 6 parts; the acrylamide is preferably 75-85 parts, and the best is 85 parts; the hydroxyethyl methacrylate is preferably 15-20 parts, and the best is 17 parts; the 2-acrylamide-2-methylpropanesulfonic acid is preferably 16-26 parts, and the best is 21 parts; the best is 10 parts of dimethyl carbonate; and the best initiator is 5 parts.

[0039] The initiator is an oxidant, or a redox system composed of an oxidant and a reductant, preferably sodium persulfate.

[0040] The emulsifier is a nonionic emulsifier, and its hydrophilic-lipophilic balance value is 4 to 7. The preferred emulsifier is OP-15.

[0041] Example 1

[0042] (1) Add 65 g of white oil and 6 g of emulsifier to a 1000 mL reactor in proportion, introduce nitrogen, and stir at a speed of 500 r / min until all the oil is dissolved to obtain a uniform oil phase for use.

[0043] (2) Add deionized water to a 500mL beaker, dissolve 75g of acrylamide, 15g of hydroxyethyl methacrylate, 16g of 2-acrylamide-2-methylpropanesulfonic acid, and 10g of dimethyl carbonate in deionized water in turn, and stir until completely dissolved to form an aqueous phase solution. Under high-speed stirring conditions of 1500r / min, use a constant pressure dropping funnel to slowly add the aqueous phase solution to the oil phase medium. After the addition is completed, continue stirring for 40 minutes to form a uniform and stable emulsion, and continue to introduce nitrogen during the stirring process. Finally, set the reactor temperature to 30°C, maintain a certain stirring rate at this temperature, and slowly add 5g of initiator to react.

[0044] (3) After the initiator is added dropwise, the stirring of the mixed system is stopped and the mixture is placed in a constant temperature water bath. After a constant temperature reaction at 30° C. for 3 h, the emulsion is cooled to room temperature and dispersed under an ultrasonic environment to obtain a salt-resistant emulsion.

[0045] Example 2

[0046] (1) Add 70 g of white oil and 6 g of emulsifier to a 1000 mL reactor in proportion, introduce nitrogen, and stir at a speed of 500 r / min until all the oil is dissolved to obtain a uniform oil phase for use.

[0047] (2) Add deionized water to a 500mL beaker, dissolve 80g of acrylamide, 17g of hydroxyethyl methacrylate, 20g of 2-acrylamide-2-methylpropanesulfonic acid, and 10g of dimethyl carbonate in deionized water in turn, and stir until completely dissolved to form an aqueous phase solution. Under high-speed stirring conditions of 1500r / min, use a constant pressure dropping funnel to slowly add the aqueous phase solution to the oil phase medium. After the addition is completed, continue stirring for 40 minutes to form a uniform and stable emulsion, and continue to introduce nitrogen during the stirring process. Finally, set the reactor temperature to 30°C, maintain a certain stirring rate at this temperature, and slowly add 5g of initiator to react.

[0048] (3) After the initiator is added dropwise, the stirring of the mixed system is stopped and the mixture is placed in a constant temperature water bath. After a constant temperature reaction at 30° C. for 3 h, the emulsion is cooled to room temperature and dispersed under an ultrasonic environment to obtain a salt-resistant emulsion.

[0049] Example 3

[0050] (1) Add 75 g of white oil and 6 g of emulsifier to a 1000 mL reactor in proportion, introduce nitrogen, and stir at a speed of 500 r / min until all the oil is dissolved to obtain a uniform oil phase for use.

[0051] (2) Add deionized water to a 500mL beaker, dissolve 85g of acrylamide, 15g of hydroxyethyl methacrylate, 16g of 2-acrylamide-2-methylpropanesulfonic acid, and 10g of dimethyl carbonate in deionized water in turn, and stir until completely dissolved to form an aqueous phase solution. Under high-speed stirring conditions of 1500r / min, use a constant pressure dropping funnel to slowly add the aqueous phase solution to the oil phase medium. After the addition is completed, continue stirring for 40 minutes to form a uniform and stable emulsion, and continue to introduce nitrogen during the stirring process. Finally, set the reactor temperature to 30°C, maintain a certain stirring rate at this temperature, and slowly add 5g of initiator to react.

[0052] (3) After the initiator is added dropwise, the stirring of the mixed system is stopped and the mixture is placed in a constant temperature water bath. After a constant temperature reaction at 30° C. for 3 h, the emulsion is cooled to room temperature and dispersed under an ultrasonic environment to obtain a salt-resistant emulsion.

[0053] Example 4

[0054] (1) Add 65 g of white oil and 6 g of emulsifier to a 1000 mL reactor in proportion, introduce nitrogen, and stir at a speed of 500 r / min until all the oil is dissolved to obtain a uniform oil phase for use.

[0055] (2) Add deionized water to a 500mL beaker, dissolve 85g of acrylamide, 17g of hydroxyethyl methacrylate, 21g of 2-acrylamide-2-methylpropanesulfonic acid, and 10g of dimethyl carbonate in deionized water in turn, and stir until completely dissolved to form an aqueous phase solution. Under high-speed stirring conditions of 1500r / min, use a constant pressure dropping funnel to slowly add the aqueous phase solution to the oil phase medium. After the addition is completed, continue stirring for 40 minutes to form a uniform and stable emulsion, and continue to introduce nitrogen during the stirring process. Finally, set the reactor temperature to 30°C, maintain a certain stirring rate at this temperature, and slowly add 5g of initiator to react.

[0056] (3) After the initiator is added dropwise, the stirring of the mixed system is stopped and the mixture is placed in a constant temperature water bath. After a constant temperature reaction at 30° C. for 3 h, the emulsion is cooled to room temperature and dispersed under an ultrasonic environment to obtain a salt-resistant emulsion.

[0057] Effect comparison

[0058] Performance comparison between this product and conventional products:

[0059] The products of Examples 1-4 were compared with conventional emulsions, and fracturing fluids were prepared with clean water and 50000ppm of highly mineralized water, respectively. By comparison, it can be seen that the effective content in conventional emulsion products is relatively low, and the viscosity effect of fracturing fluids prepared with clean water is average. After being prepared with high-mineralized flowback fluid, the viscosity of the fracturing fluid decreases significantly, making it difficult to meet the requirements of on-site construction. The products in the examples significantly increase the solid content while using the inverse emulsion polymerization method to prepare salt-resistant emulsions, introduce salt-resistant groups and steric hindrance groups on the macromolecular chain, and improve the salt resistance of the product, which can give full play to the advantages of high solid content, thereby showing excellent viscosity-increasing properties under the conditions of fracturing fluids prepared with highly mineralized water.

[0060] Table 1 Comparison of active ingredient content of products Lotion Type Conventional emulsion type Example 1 Example 2 Example 3 Example 4 Active ingredient content, % 25-30 46.0 46.7 48.2 49.1

[0061] Table 2 Performance comparison of fracturing fluid products prepared with clean water (fracturing fluid formula: clean water + 1.0% emulsion)

[0062] Table 3 Performance comparison of fracturing fluid products prepared with high mineralized water (50000ppm) (fracturing fluid formula: clean water + 1.0% emulsion)

[0063] Finally, it should be noted that 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 aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A salt-resistant emulsion fracturing fluid system, characterized in that: Prepared by the following raw materials in parts by weight: 60-80 parts of white oil, 5-10 parts of emulsifier, 70-90 parts of acrylamide, 10-20 parts of hydroxyethyl methacrylate, 10-30 parts of 2-acrylamide-2-methylpropanesulfonic acid, 10 parts of dimethyl carbonate, and 3-7 parts of initiator.

2. The salt-resistant emulsion fracturing fluid system according to claim 1, characterized in that: The emulsifier is a nonionic emulsifier, and the hydrophilic-lipophilic balance value of the nonionic emulsifier is 4-7.

3. The salt-resistant emulsion fracturing fluid system according to claim 1, characterized in that: The emulsifier is at least one of Tween-20, OP-10, OP-15 and polyether silicone oil.

4. The salt-resistant emulsion fracturing fluid system according to claim 1, characterized in that: The initiator is an oxidizing agent.

5. The salt-resistant emulsion fracturing fluid system according to claim 4, characterized in that: The oxidant is a mixture of one or more of sodium persulfate, potassium persulfate and hydrogen peroxide.

6. The salt-resistant emulsion fracturing fluid system according to claim 1, characterized in that: The white oil is 65-75 parts.

7. The salt-resistant emulsion fracturing fluid system according to claim 1, characterized in that: Acrylamide is 75-85 parts.

8. The salt-resistant emulsion fracturing fluid system according to claim 1, characterized in that: The amount of hydroxyethyl methacrylate is 15-20 parts.

9. The salt-resistant emulsion fracturing fluid system according to claim 1, characterized in that: 2-Acrylamide-2-methylpropanesulfonic acid is 16-26 parts.

10. A method for preparing the salt-resistant emulsion fracturing fluid system according to any one of claims 1 to 9, characterized in that: The following steps are involved: Step 1: Add 60-80 parts of white oil and 5-10 parts of emulsifier into the reaction kettle according to the weight ratio, introduce nitrogen, and stir until all are dissolved to obtain a uniform oil phase for use; Step 2: In a reactor under an oxygen-free environment, 70-90 parts of acrylamide, 10-20 parts of hydroxyethyl methacrylate, 10-30 parts of 2-acrylamide-2-methylpropanesulfonic acid, and 10 parts of dimethyl carbonate are dissolved in deionized water, stirred until completely dissolved to form an aqueous phase solution, and nitrogen is continuously introduced during the stirring process, an oil phase medium is added, and stirring is continued until a uniform and stable emulsion is formed, and finally, an initiator is added to react; Step 3: After the reaction is completed, the product is dispersed under an ultrasonic environment to obtain a salt-resistant emulsion.

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