Composition for forming viscous slick water, slick water and use thereof

Abstract

The invention provides a composition for forming variable-viscosity slick water, the slick water and application of the slick water. The composition for forming the variable-viscosity slick water is prepared from the following components in percentage by weight: 0.3 to 1.0 percent of acrylamide copolymer, 0.5 to 2.0 percent of organic boron cross-linking agent and the balance of water, the acrylamide copolymer is prepared by carrying out inverse emulsion random copolymerization reaction on acrylamide and a cross-linkable comonomer, and the organic boron cross-linking agent is prepared by carrying out an inverse emulsion random copolymerization reaction on the acrylamide copolymer and the organic boron cross-linking agent. Wherein the cross-linkable comonomer contains double bonds capable of being copolymerized with acrylamide and cis-dihydroxyl, and the molar ratio of acrylamide to the cross-linkable comonomer is in the range of (5000-60000): 1. The slickwater is prepared by cross-linking the composition for forming the variable-viscosity slickwater.

Description

Technical Field

[0001] The invention belongs to the technical field of slick water fracturing fluid synthesis, and in particular relates to a composition for forming viscous slick water, slick water and applications thereof. Background Art

[0002] With the rapid consumption of conventional oil and gas reserves at home and abroad, many low-permeability and difficult-to-mobilize reserves such as shale oil and gas have begun to be developed in large quantities, and there is an urgent need to increase the production of single wells. Hydraulic fracturing is an important means to improve the effect of oil and gas wells. The main goal is to create, expand and support the fracture network. The principle is to use hydraulic fracturing or natural fracture systems to inject fracturing fluid into the formation, expand the fractures and add proppants to prevent them from closing, thereby improving the conductivity of the fractures and achieving the purpose of increasing production; in order to achieve this goal, it is necessary to ensure that proppants such as quartz sand can be reasonably transported by the fracturing fluid in the fractures.

[0003] Due to the limitations of fracturing fluid viscosity and formation conditions, the ability of fracturing fluid to carry proppants has become the focus of attention. Unconventional oil and gas fracturing construction is large-scale, and the most commonly used fracturing fluid is slick water, which has low friction and is easy to communicate with natural fractures. This fracturing fluid is mainly composed of water and drag reducers. Due to the low viscosity of slick water, it is easier to produce a complex fracture network and rarely needs to be cleaned. It is a clean fracturing technology. The fractures produced by fracturing are longer and the fracturing proppants are transported to the fracture network. At the same time, there are certain disadvantages, mainly poor sand carrying capacity and difficulty in transporting proppants. If the sand ratio is too low, the sand concentration in the fracture will be low and the fracture conductivity will be small, which will affect the fracturing effect. Therefore, the transportation of proppants in the fracture is particularly important.

[0004] In response to the above-mentioned problems of conventional slippery water, people began to study high-viscosity slippery water, mainly using the hydrophobic association method to achieve high viscosity through physical cross-linking. However, hydrophobic associating polymers often have poor water solubility, poor liquid preparation and injectability, and the formed capsule, residue and residual liquid retention affect the permeability and conductivity of the proppant filling layer. In addition, the stability is not high. The high viscosity of the associating polymer solution decreases with time, and even drops sharply.

[0005] In view of the existence of the above problems, it is necessary to develop a slippery water with good water solubility, good viscoelasticity, high viscoelastic modulus and strong elastic sand carrying capacity. Summary of the invention

[0006] The main purpose of the present invention is to provide a composition for forming viscous slippery water, slippery water and its application, so as to solve the problems of poor water solubility, poor liquid preparation and injectability of existing highly viscous slippery water, the formation of a coating, residue and residual liquid retention affecting the permeability and conductivity of the proppant filling layer, and low stability.

[0007] In order to achieve the above-mentioned object, the present invention provides a composition for forming sticky and slippery water on one hand, which comprises, by weight percentage: 0.3-1.0% of an acrylamide copolymer, 0.5-2.0% of an organic boron crosslinking agent, and the balance of water, wherein the acrylamide copolymer is prepared by a reverse emulsion random copolymerization of acrylamide and a crosslinkable comonomer, wherein the crosslinkable comonomer contains a double bond and a cis-bishydroxyl group copolymerizable with acrylamide, and the molar ratio of acrylamide to the crosslinkable comonomer is in the range of 5000-60000:1.

[0008] Further, the crosslinkable comonomer is represented by formula (I)

[0009]

[0010] Wherein, Z is an ester group or an amide group, X is an alkyl group, and Y and R are each independently an alkyl group or a hydrogen atom.

[0011] Further, the crosslinkable comonomer is represented by formula (II) to formula (IV), preferably formula (II):

[0012]

[0013] Further, the organoboron compound is a product of the reaction of boric acid or borax with an organic ligand, and the organic ligand includes triethanolamine, ethylene glycol or glycerol.

[0014] Furthermore, the molar ratio of acrylamide to the cross-linkable comonomer is in the range of 5000 to 60000:1.

[0015] Furthermore, the molar ratio of acrylamide to the cross-linkable comonomer is 5000-10000:1.

[0016] Furthermore, the relative molecular weight of the acrylamide copolymer is 8 million to 16 million.

[0017] Furthermore, the composition for forming sticky and slippery water includes, by weight percentage: 0.3-0.6% of acrylamide copolymer, 0.5-1.0% of organic boron crosslinking agent, and the balance of water.

[0018] In order to achieve the above object, another aspect of the present invention provides slippery water, which is prepared by cross-linking the above composition for forming sticky slippery water.

[0019] Another aspect of the present invention provides the above composition for forming viscous slick water or the use of the above slick water in the field of shale gas production.

[0020] The technical scheme of the present invention is applied, and a reverse emulsion copolymerization method is adopted to randomly copolymerize acrylamide and a cross-linkable comonomer to introduce chemical cross-linking points with large spacing, and then an organic boron cross-linking agent is added for large-spacing cross-linking to prepare a novel polyacrylamide viscous slippery water system with elastic sand-carrying capacity. The slippery water has good water solubility and is a liquid emulsion, which can be mixed online. At the same time, the viscous slippery water system has good viscoelasticity, high viscoelastic modulus, and strong elastic sand-carrying capacity. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The drawings constituting a part of the present application are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0022] Figure 1 It is a curve diagram of the viscosity modulus of the four slippery water samples in the examples (samples 1-4 are examples 1, 5, comparative examples 8, and 7, respectively) at different frequencies.

[0023] Figure 2 It is a curve diagram of the elastic modulus of the four slippery water samples in the examples (samples 1-4 are examples 1, 5, comparative examples 8, and 7, respectively) at different frequencies.

[0024] Figure 3 This is a curve diagram of the sand carrying situation of the slippery water sample prepared in Example 1 during on-site construction. DETAILED DESCRIPTION

[0025] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present invention will be described in detail below in conjunction with the embodiments.

[0026] As described in the background art, the existing highly viscous slippery water has the problems of poor water solubility, poor liquid preparation and injectability, the formed capsule, residue and residual liquid retention affecting the permeability and flow conductivity of the proppant filling layer, and low stability. In order to solve the above technical problems, the present application provides a composition for forming viscous slippery water, which comprises, by weight percentage: 0.3-1.0% acrylamide copolymer, 0.5-2.0% organic boron crosslinking agent, and the balance water, wherein the acrylamide copolymer is prepared by random copolymerization of acrylamide and a crosslinkable comonomer in an inverse emulsion, wherein the comonomer contains a double bond and a cis-dihydroxyl group that can copolymerize with acrylamide, and the molar ratio of acrylamide to the crosslinkable comonomer is in the range of 5000-60000:1.

[0027] In view of the above problems, the present invention adopts a reverse emulsion copolymerization method, by randomly copolymerizing acrylamide and a crosslinkable comonomer, introducing large-spacing chemical crosslinking points, and then adding an organic boron crosslinking agent for large-spacing crosslinking, to prepare a new polyacrylamide viscous slippery water system with elastic sand carrying capacity, the slippery water has good water solubility, is a liquid emulsion, can be mixed online, and the viscous slippery water system has good viscoelasticity, high viscoelastic modulus, and strong elastic sand carrying capacity. Among them, the reverse emulsion random copolymerization of acrylamide and a crosslinkable comonomer according to a molar ratio of 5000 to 60000: 1 can introduce long-distance crosslinking points, and the copolymer thus formed is then crosslinked with organic boron to form a complex elastic network structure with high elasticity and high viscosity stability, which provides a new solution to the current conventional slippery water sand carrying difficulty problem.

[0028] As described above, the crosslinkable comonomer used in the above composition has a double bond that can copolymerize with acrylamide and a cis-dihydroxyl group that can crosslink with an organic boron crosslinking agent, thereby being able to undergo an inverse emulsion random copolymerization reaction with acrylamide to obtain an acrylamide-based copolymer, and then crosslinking with an organic boron to form a complex elastic network structure. Those skilled in the art know the preparation method or the way to obtain the crosslinkable comonomer that meets this requirement. In a preferred embodiment, the crosslinkable comonomer is represented by formula (I):

[0029]

[0030] Wherein, Z is an ester group or an amide group, X is an alkyl group, and Y and R are each independently an alkyl group or a hydrogen atom.

[0031] In a preferred embodiment, the crosslinkable comonomer is represented by formula (II) to formula (IV), preferably formula (II):

[0032]

[0033] It can be seen from the results of the following examples that the viscous slippery water prepared by using the cross-linkable copolymerizable monomer has excellent viscoelastic properties.

[0034] In the above composition, the organic boron compound is a product of the reaction of boric acid or borax with an organic ligand, and the organic ligand includes triethanolamine, ethylene glycol or glycerol.

[0035] As described above, the inverse emulsion random copolymerization of acrylamide and a crosslinkable comonomer in a molar ratio of 5000 to 60000:1 can introduce long-distance crosslinking points. As explained in detail below, the distance between crosslinking points in the copolymer synthesized from acrylamide and a crosslinkable comonomer is determined by the molar ratio of acrylamide to the crosslinkable comonomer. In a preferred embodiment, the molar ratio of acrylamide to the crosslinkable comonomer is in the range of 5000 to 60000:1. As shown by the experimental results of the examples below, when the molar ratio of acrylamide to the crosslinkable comonomer is within this range, slippery water with excellent viscoelastic properties can be obtained.

[0036] In a preferred embodiment, the molar ratio of acrylamide to the crosslinkable comonomer is in the range of 5000 to 10000: 1. As shown by the experimental results of the following examples, when the molar ratio of acrylamide to the crosslinkable comonomer is within this range, slippery water with excellent viscoelastic properties can be obtained.

[0037] In a preferred embodiment, the relative molecular weight of the acrylamide copolymer is 8 million to 16 million.

[0038] In a preferred embodiment, the composition for forming sticky slippery water comprises, by weight percentage: 0.3-0.6% acrylamide copolymer, 0.5-1.0% organic boron crosslinking agent, and the balance water. As shown by the experimental results of the following examples, when the weight percentages of the acrylamide copolymer and the organic boron crosslinking agent in the composition for forming sticky slippery water are within the above ranges, slippery water with more excellent viscoelastic properties can be obtained.

[0039] In the above composition for forming sticky and slippery water, the organoboron crosslinking agent may be an organoboron crosslinking agent commonly used in the art. The organoboron crosslinking agent used in the present application is described in detail in the following examples.

[0040] Another aspect of the present application provides slippery water, which is prepared by cross-linking the above composition for forming sticky slippery water.

[0041] The method of reverse emulsion copolymerization is adopted, by randomly copolymerizing acrylamide and a cross-linkable comonomer, introducing large-spacing chemical cross-linking points, and then adding an organic boron cross-linking agent for large-spacing cross-linking, a new polyacrylamide variable sticky slippery water system with elastic sand carrying capacity is prepared. The slippery water has good water solubility and is a liquid emulsion, which can be mixed online. At the same time, the variable sticky slippery water system has good viscoelasticity, high viscoelastic modulus, and strong elastic sand carrying capacity. Among them, the reverse emulsion random copolymerization of acrylamide and a cross-linkable comonomer according to a molar ratio of 5000 to 60000:1 can introduce long-distance cross-linking points, and the copolymer formed is then cross-linked with organic boron to form a complex elastic network structure with high elasticity, which provides a new solution to the current problem of conventional slippery water carrying sand difficulties.

[0042] Another aspect of the present application provides the use of the composition for forming viscous slick water or slick water in the field of shale gas production.

[0043] The slippery water provided by the present application has good water solubility, good viscoelasticity, high viscoelastic modulus, strong elastic sand carrying capacity, can be directly mixed and configured online, and the proppant carrying ratio is 0% to 40%.

[0044] The preparation process of the slippery water is as follows: (1) synthesizing or obtaining a cross-linkable comonomer; (2) adding acrylamide and the cross-linkable comonomer to water in a specific molar ratio to perform reverse emulsion random copolymerization to form an emulsion of acrylamide copolymer; (3) continuously mixing the emulsion of acrylamide copolymer with an organic boron cross-linking agent online to form elastic sand-carrying polyacrylamide sticky slippery water.

[0045] Taking the crosslinkable comonomer of formula (II) as an example, the acrylamide copolymer formed by copolymerization of acrylamide and the crosslinkable comonomer can be represented by formula (V):

[0046]

[0047] In short:

[0048]

[0049] The slippery water is prepared by crosslinking the composition for forming sticky slippery water with an organic boron crosslinking agent. The crosslinked acrylamide copolymer in the slippery water can be represented by formula (VI):

[0050]

[0051] Abbreviated as

[0052]

[0053] Those skilled in the art will appreciate that since acrylamide copolymers are products of random copolymerization, the above chemical formula is only a statistical average chemical formula. Wherein, y represents the number of repeating units in the acrylamide copolymer, and x represents the number of acrylamide monomers in each repeating unit. It can be seen that each repeating unit contains a crosslinkable comonomer. It can be seen that x is equivalent to the molar ratio of acrylamide to the crosslinkable comonomer in the composition for forming sticky slippery water. It can also be seen that in the acrylamide copolymer, the crosslinkable sites provided by the crosslinkable comonomer are separated by the polymerized acrylamide monomer, and the number of acrylamide monomers in each repeating unit determines the spacing of the crosslinkable sites. Therefore, by adjusting the molar ratio of acrylamide to the crosslinkable comonomer, the spacing of the crosslinkable sites in the acrylamide copolymer can be adjusted, thereby achieving large spacing crosslinking through a molar ratio of acrylamide to the crosslinkable comonomer of 5000 to 60000:1.

[0054] The present application is further described in detail below in conjunction with specific embodiments. These embodiments should not be construed as limiting the scope of protection claimed in the present application.

[0055] Example

[0056] Using acrylamide, a crosslinkable comonomer of formula (II), and an organic boron crosslinking agent, a composition for forming sticky slippery water and slippery water are prepared successively through the above process. The molar ratio, proportion, and molecular weight of the slippery water synthesis reagents used in Examples 1-8 are shown in Table 1.

[0057] The specific synthesis steps of the slippery water of Examples 1-6 are as follows: (a) Add kerosene and emulsifier to a three-necked flask, install the reaction device, adjust the water bath to the reaction temperature and maintain constant temperature, stir the kerosene and emulsifier until fully dissolved as the oil phase; (b) Add acrylamide and the crosslinkable comonomer of formula (II) to a beaker according to the molar ratio shown in Table 1. Add distilled water and stir to fully dissolve it, and the oil-water ratio is 1.2. Then use sodium hydroxide to neutralize the monomer solution to pH 7-9. Drop the water phase into the three-necked flask containing the oil phase and emulsify it under high-speed stirring, stir and pass nitrogen for 30 minutes; (c) Dilute ammonium persulfate and sodium bisulfite 50 times and drip them. At a constant temperature water bath of 40°C, stir at high speed for 6 hours to obtain a viscous milky white latex, i.e., an inverse emulsion copolymer; (d) Blend the acrylamide copolymer emulsion with the organic boron crosslinker according to the amount shown in Table 1 to form elastic sand-carrying polyacrylamide viscous slippery water.

[0058] Wherein, the cross-linkable comonomer of formula (II) was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd., CAS No.: 201594-54-9. The organic boron cross-linking agent was synthesized according to the following scheme:

[0059]

[0060] The specific synthesis conditions are: the ratio of boric acid or borax to ligand is 1:1 to 1:2, the ligand can be propylene glycol, triethanolamine, glycerol, etc., the reaction temperature is 30 to 80°C, 30% to 70% water is added, and the reaction is carried out for 3 to 5 hours.

[0061] Table 1 Molar ratio, proportion and molecular weight of the slick water synthesis reagents used in Examples 1-6 and the slick water properties obtained

[0062]

[0063] In Examples 1-4, the molar ratio of acrylamide to the crosslinkable comonomer is 5000:1. The acrylamide copolymers prepared in Examples 1-4 can be represented by the abbreviated formula (VII):

[0064]

[0065] In Example 5, the molar ratio of acrylamide to the crosslinkable comonomer is 10000:1. The acrylamide copolymer prepared in Example 5 can be represented by the abbreviated formula (VIII):

[0066]

[0067] In Example 6, the molar ratio of acrylamide to the crosslinkable comonomer is 60000:1. The acrylamide copolymer prepared in Example 6 can be represented by the abbreviated formula (IX):

[0068]

[0069] Comparative Example

[0070] The same steps as in Examples 1-6 were used to synthesize the slippery water of Comparative Examples 1-9. The molar ratio, proportion and molecular weight of the slippery water synthesis reagents used and the viscosity of the obtained slippery water are shown in Table 2.

[0071] Table 2 Molar ratio, proportion and molecular weight of the slick water synthesis reagents used in Comparative Examples 1-9 and the slick water properties obtained

[0072]

[0073] The viscoelastic properties of the slick water of the embodiment and comparative example are measured by using a Haake RS6000 rheometer to perform a stress scan on the prepared solution, and then perform a frequency scan using the stress value in the linear region near the inflection point of the stress scan to obtain a viscous modulus and elastic modulus curve, and determine the viscoelasticity of the solution based on the intersection value of the two.

[0074] From the above description, it can be seen that the above embodiments of the present invention achieve the following technical effects:

[0075] From Tables 1 and 3 and Figure 1-2 It can be seen from the results that the slippery water of the present application has excellent viscoelastic properties, wherein the slippery water of the present application has a lower viscoelastic modulus intersection, indicating that the slippery water of the present application has excellent sand carrying performance. Comparing the viscoelastic properties of the slippery water of Examples 1-6 with those of Comparative Examples 4 and 6, it can be seen that slippery water with excellent viscoelastic properties can be obtained when the molar ratio of acrylamide to the crosslinkable comonomer is in the range of 5000 to 60000:1. Comparing the viscoelastic properties of the slippery water of Examples 1-6 with those of Comparative Examples 1, 2, 5, and 8, it can be seen that when the weight percentage of the organic boron crosslinking agent in the composition for forming the viscous slippery water is in the range of 0.5 to 2.0%, slippery water with excellent viscoelastic properties can be obtained. Comparing the viscoelastic properties of the slippery water of Examples 1-6 with Comparative Examples 3 and 7, it can be seen that when the weight percentage of the acrylamide copolymer in the composition for forming the sticky slippery water is in the range of 0.3 to 1.0%, slippery water with excellent viscoelastic properties can be obtained. Comparing the viscoelastic properties of the slippery water of Examples 1-6 with Comparative Examples 1, 4, 6, and 9, it can be seen that when the relative molecular weight of the acrylamide copolymer in the composition for forming the sticky slippery water is 8 million to 16 million, slippery water with excellent viscoelastic properties can be obtained. Comparing the viscoelastic properties of the slippery water of Examples 1-6 with Comparative Example 9, it can be seen that when the acrylamide copolymer in the composition for forming the sticky slippery water contains the specific crosslinkable comonomer of the present invention, slippery water with excellent viscoelastic properties can be obtained. Comparison of the viscoelastic properties of the slippery water of Examples 1-6 shows that when the weight percentage of the acrylamide copolymer in the composition for forming the viscous slippery water is in the range of 0.3-0.6%, the weight percentage of the organic boron crosslinking agent is in the range of 0.5-1.0%, and the molar ratio of acrylamide to the crosslinkable comonomer is 5000-10000:1, slippery water with particularly excellent viscoelastic properties can be obtained. In addition, comparison of the viscosity of the slippery water of Examples 1-3 shows that as the content of the acrylamide copolymer increases, the growth rate of the viscosity of the slippery water of the present invention gradually slows down, thereby making it easier to control the appropriate viscosity of the slippery water of the present invention.

[0076] Depend on Figure 3 It can be seen from the results that the slippery water of the present application has a good sand carrying effect during on-site construction, the pressure remains stable, and the sand ratio can reach more than 30%. According to the pressure drop curve and the on-site Brassius water friction calculation formula ΔP = 7.779 × 10 - 6 D -4.75 Q 1.75L (see Su Quansheng, Calculation of Friction Resistance of Fracturing Pipe String [J], Inner Mongolia Petrochemical, 2015), it can be calculated that the drag reduction rate of the variable viscosity slick water of the present application is 70.40%, which is better than the currently commonly used slick water (drag reduction rate is 50-70%).

[0077] It should be noted that the terms "first", "second", etc. in the specification and claims of the present application are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the terms used in this way can be interchangeable where appropriate, so that the embodiments of the present application described herein can be implemented in an order other than those described herein, for example.

[0078] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A composition for forming sticky and slippery water, characterized in that: The composition for forming sticky and slippery water comprises, by weight percentage: 0.3-1.0% of an acrylamide copolymer, 0.5-2.0% of an organic boron crosslinking agent, and the balance of water, wherein the acrylamide copolymer is prepared by a reverse emulsion random copolymerization of acrylamide and a crosslinkable comonomer, wherein the crosslinkable comonomer contains a double bond and a cis-dihydroxyl group copolymerizable with the acrylamide, and the molar ratio of the acrylamide to the crosslinkable comonomer is in the range of 5000-60000:

1.

2. The composition for forming sticky and slippery water according to claim 1, characterized in that: The crosslinkable comonomer is represented by formula (I) Wherein, Z is an ester group or an amide group, X is an alkyl group, and Y and R are each independently an alkyl group or a hydrogen atom.

3. The composition for forming sticky and slippery water according to claim 1, characterized in that: The crosslinkable comonomer is represented by formula (II) to formula (IV), preferably formula (II):

4. The composition for forming sticky and slippery water according to claim 1, characterized in that: The organic boron compound is a product of the reaction of boric acid or borax with an organic ligand, and the organic ligand includes triethanolamine, ethylene glycol or glycerol.

5. The composition for forming sticky and slippery water according to any one of claims 1 to 4, characterized in that: The molar ratio of the acrylamide to the cross-linkable comonomer is in the range of 5000 to 60000:

1.

6. The composition for forming sticky and slippery water according to claim 5, characterized in that: The molar ratio of the acrylamide to the cross-linkable comonomer is 5000-10000:

1.

7. The composition for forming sticky and slippery water according to any one of claims 1 to 4, characterized in that: The relative molecular weight of the acrylamide copolymer is 8 million to 16 million.

8. The composition for forming sticky and slippery water according to claim 1, characterized in that: Calculated by weight percentage, the composition for forming sticky and slippery water comprises: 0.3-0.6% of the acrylamide copolymer, 0.5-1.0% of the organic boron crosslinking agent, and the balance of water.

9. A slippery water, characterized in that: The slippery water is prepared by cross-linking the composition for forming sticky slippery water according to any one of claims 1 to 8.

10. Use of the composition for forming viscous slick water according to claims 1 to 8 or the slick water according to claim 9 in the field of shale gas extraction.

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