A coal seam wetting reversal agent and its preparation method

Abstract

This invention belongs to the field of coal seam development technology and discloses a coal seam wetting reversal agent and its preparation method. The coal seam wetting reversal agent provided by this invention exhibits excellent pH-affected behavior, and the wettability of the coal sample surface by the surfactant EBMAA-DMA12 can be altered by adjusting the pH value of the solution. When the solution pH is less than 6.87, it helps reduce capillary forces and can be used as a water-locking agent. When the pH of the surfactant solution is adjusted to greater than 6.87, it helps reduce the surface free energy of the coal seam and can be used as a coalbed methane desorbent. Furthermore, the method for preparing this coal seam wetting reversal agent involves first synthesizing the dicarboxylic acid intermediate N,N′-ethylenebismaleamic acid (EBMAA) using MAH and EDA, and then obtaining it through a neutralization reaction between N,N′-ethylenebismaleamic acid (EBMAA) and N,N-dimethyldodecylamine. This preparation method uses readily available raw materials, has a simple process, high repeatability and stability, and has significant potential for widespread application.

Description

Technical Field

[0001] This invention belongs to the field of coal seam development technology, specifically relating to a coal seam wetting reversal agent and its preparation method. Background Technology

[0002] Coalbed methane (CBM) extraction not only helps reduce the occurrence of coal mine gas emergencies but also serves as a clean fuel to meet global energy demands. However, the generally low permeability of coal seams limits CBM extraction. Hydraulic measures such as hydraulic fracturing can effectively improve coal seam permeability; however, when large amounts of external water invade the coal seam, the increased moisture content due to capillary forces creates a water-locking effect, blocking CBM diffusion channels and hindering CBM production.

[0003] Changing the wettability of coal seams is key to promoting coalbed methane desorption and eliminating water lock. However, current wetting reversal agents have relatively simple functions and most are composite surfactant systems, which are difficult to simultaneously meet the purpose of promoting desorption and eliminating water lock in coal seams during large-scale volumetric fracturing. Summary of the Invention

[0004] This invention aims to at least partially solve one of the technical problems in the related art. Therefore, the main objective of this invention is to provide a coal seam wetting reversal agent, which is a novel pseudo-gemini surfactant.

[0005] The main objective of this invention is to also provide a method for preparing and applying the coal seam wetting reversal agent.

[0006] The objective of this invention is achieved through the following technical solution:

[0007] A coal seam wetting reversal agent, characterized in that the molecular structural formula of the coal seam wetting reversal agent is:

[0008]

[0009] A method for preparing the aforementioned coal seam wetting reversal agent includes the following steps:

[0010] 1) After stirring and mixing MAH and anhydrous ethanol evenly, EDA was added dropwise to carry out the synthesis reaction. The reaction product was then washed and dried to obtain white solid powder EBMAA.

[0011] 2) After mixing the EBMAA obtained in step 1) with anhydrous ethanol, DMA12 was added dropwise to carry out the synthesis reaction. Then the solvent was evaporated and dried to obtain the pale yellow viscous target product EBMAA-DMA12.

[0012] In some specific embodiments, the molar ratio of MAH to EDA in step 1) is 2:1.

[0013] In some specific embodiments, the conditions for the synthesis reaction in step 1) are: reacting in a water bath at 0-5°C for 12-15 hours.

[0014] In some specific embodiments, the drying conditions in step 1) are: drying at a temperature of 60-80°C for 2-3 hours.

[0015] In some specific implementations, the molar ratio of EBMAA to DMA12 in step 2) is 1:2.

[0016] In some specific embodiments, the conditions for the synthesis reaction in step 2) are: reacting at 15-25°C for 18-24 hours.

[0017] The application of the aforementioned coal seam wetting reversal agent in the field of coal seam development technology.

[0018] Compared with the prior art, the present invention has at least the following advantages:

[0019] 1) The coal seam wetting reversal agent of the present invention exhibits excellent pH-affecting behavior, and the wettability of the coal sample surface by the surfactant EBMAA-DMA12 can be altered by adjusting the pH value of the solution. Specifically, when the solution pH value is less than 6.87, it helps to reduce capillary forces and can be used as a water-locking agent; when the pH value of the surfactant solution is adjusted to be greater than 6.87, it helps to reduce the free energy of the coal seam surface and can be used as a coalbed methane desorbent.

[0020] 2) The preparation method of this invention first synthesizes the dicarboxylic acid intermediate N,N'-ethylenebismaleamic acid (EBMAA) using MAH and EDA, and then obtains a novel pseudogemini surfactant by neutralizing N,N'-ethylenebismaleamic acid (EBMAA) with N,N-dimethyldodecylamine. This preparation method uses readily available raw materials, has a simple process, high repeatability and stability, and has great potential for widespread application. Attached Figure Description

[0021] To more clearly illustrate the specific embodiments of the present invention, the accompanying drawings used in the description of the specific embodiments or the prior art will be briefly introduced below.

[0022] Figure 1 The infrared spectra of MAH, EDA, and EBMAA in step 1) of the preparation method of Example 1 of the present invention are shown in (a); the infrared spectra of DMA12, EBMAA, and EBMAA-DMA12 in step 2) are shown in (b).

[0023] Figure 2 This is a graph showing the relationship between surface tension and mass fraction of EBMAA-DMA12 in Example 1 of the present invention;

[0024] Figure 3 The surface tension of the surfactant EBMAA-DMA12 solution under different pH conditions was observed.

[0025] Figure 4 The contact angle of coal before and after treatment with surfactant EBMAA-DMA12 solution at different pH values;

[0026] Figure 5 Coal before and after treatment with surfactant EBMAA-DMA12 solution at different pH values ;

[0027] Figure 6 The adhesion work value of coal before and after treatment with surfactant EBMAA-DMA12 solution at different pH values. Detailed Implementation

[0028] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. The following embodiments are merely descriptive and not limiting, and should not be construed as limiting the scope of protection of the present invention.

[0029] When a quantity, concentration, or other value or parameter is described as a range, preferred range, or preferred upper and lower limits, it should be understood that it is equivalent to specifically disclosing any range by combining any pair of upper or preferred values ​​with any lower or preferred values, regardless of whether the range is specifically disclosed. Unless otherwise stated, the numerical range values ​​listed herein include the endpoints of the range and all integers and fractions within that range.

[0030] Unless otherwise stated, all percentages, parts, ratios, etc. in this document are by weight.

[0031] The materials, methods, and embodiments described herein are exemplary and should not be construed as limiting unless otherwise stated.

[0032] In the following examples, the experimental materials used were: ethylenediamine (EDA), maleic anhydride (MAH), N,N-dimethyldodecylamine (DMA12), and anhydrous ethanol, all of analytical grade; deionized water, prepared in the laboratory; and coal samples taken from the Dingxin block in Guizhou Province, whose industrial analysis is shown in Table 1. According to the coal classification standard GB / T 5751-2009, the coal sample belongs to anthracite.

[0033] Table 1 Industrial Analysis of Coal Samples

[0034]

[0035] Experimental instruments: Sigma 700 tensiometer; SDC-200S contact angle meter; NICOLET iS10 Fourier transform infrared spectrometer; JNM-ECZ400S / L1 nuclear magnetic resonance spectrometer; PHS-3E pH meter.

[0036] Example 1: Preparation of Coal Seam Wetting Reversal Agent

[0037] This embodiment provides a method for preparing a coal seam wetting reversal agent, comprising the following steps:

[0038] 1) Add 0.1 mol MAH and 50 mL anhydrous ethanol to a 100 mL round-bottom flask, stir at room temperature until completely dissolved, then transfer the flask to a 3 °C water bath and add 0.05 mol EDA dropwise. Under these conditions, react for 15 h, then wash the reaction product with a large amount of distilled water and dry in an 80 °C oven for 2 h to obtain a white solid powder N,N'-ethylidene bismaleamic acid (EBMAA).

[0039] The synthetic route for N,N'-ethylenebismaleamic acid (EBMAA) is as follows:

[0040]

[0041] 2) Add 0.01 mol EBMAA and 50 mL anhydrous ethanol to a 100 mL round-bottom flask, stir until completely dissolved, then add 0.02 mol DMA12 dropwise. React at room temperature (25℃) for 18 h. Evaporate and dry the solvent to obtain the pale yellow viscous target product EBMAA-DMA12. The synthetic route of EBMAA-DMA12 is as follows:

[0042]

[0043] Performance test example:

[0044] Test Example 1: Substance Identification

[0045] Test method: In the preparation method of Example 1, MAH, EDA, EBMAA in step 1) and DMA12, EBMAA, EBMAA-DMA12 and KBr in step 2) were mixed at a ratio of 1:100 and ground thoroughly with an agate mortar until there were no obvious particles. The mixture was then pressed into transparent sheets using an infrared tablet press and tested with a Fourier transform infrared spectrometer.

[0046] Results and Discussion:

[0047] The infrared spectra of MAH, EDA, and EBMAA in step 1) are as follows: Figure 1 As shown in (a), from Figure 1(a) It can be seen that, due to the reaction between the primary amine in the EDA molecule and MAH, the reaction occurs at a temperature of 3500~3000 cm⁻¹. -1 The absorption peak of the NH stretching vibration of primary amines is 3354 cm⁻¹. -1 and 3281 cm -1 The absorption peak for the NH stretching vibration of the secondary amine is 3293 cm⁻¹. -1 (Single peak), 1697 cm -1 The absorption peak is the C=O stretching vibration peak in the carboxylic acid group, at 1436 cm⁻¹. -1 An absorption peak appears at 900 cm⁻¹ due to the in-plane bending vibration of the OH group in the carboxylic acid group. -1 An out-of-plane bending vibration absorption peak appears at 1618 cm⁻¹ in the OH group of the carboxylic acid group. -1 An absorption peak for amide I with C=O and C=C stretching vibrations appears at 1577 cm⁻¹. -1 The appearance of an in-plane bending vibration absorption peak of NH in amide II indicates that the above functional group changes demonstrate the successful preparation of EBMAA.

[0048] The infrared spectra of DMA12, EBMAA, and EBMAA-DMA12 in step 2) are as follows: Figure 1 As shown in (b), from Figure 1 (b) It can be seen that 3271 cm -1 The absorption peak for the NH stretching vibration of secondary amines is 1713 cm⁻¹. -1 The absorption peak is the C=O stretching vibration peak in the carboxylic acid group, at 1659 cm⁻¹. -1 The absorption peaks for amide I are C=O and C=C stretching vibrations, at 1563 cm⁻¹. -1 The absorption peak for the in-plane bending vibration of NH in amide II is 1436 cm⁻¹. -1 900 cm -1 The absorption peak of the in-plane / out-plane bending vibration of the OH group in the carboxylic acid group disappears, 3000~2500 cm⁻¹ -1 The presence of numerous CH stretching vibration absorption peaks of alkanes within the range indicates the successful preparation of EBMAA-DMA12, reflecting the changes in these functional groups.

[0049] Test Example 2: Surface Tension and Contact Angle Test

[0050] Test method: Prepare a 0.1 wt% solution of surfactant EBMAA-DMA12, adjust its pH to acidic and alkaline, and determine the surface tension of the surfactant solution at different pH values ​​using the platinum ring method. Each group of experiments was measured three times and the average value was taken. The coal sample was soaked in a pH-adjusted solution for 3 hours, then dried in a forced-air drying oven at 105 ℃ for 30 minutes. After cooling to room temperature, the contact angle was measured using distilled water as the titration solution and a contact angle measuring instrument. Each group of experiments was measured three times and the average value was taken.

[0051] Results and Discussion:

[0052] The surface tension of EBMAA-DMA12 in this application ( ) - solution mass fraction ( The curve is as follows Figure 2 As shown in the figure, the surface tension gradually decreases and tends to level off as the mass fraction of EBMAA-DMA12 increases. After reaching the critical micelle concentration (CMC) value, the surface tension does not change significantly. The mass fraction corresponding to this point is 0.05 wt%. Therefore, the CMC of the pseudogemini surfactant EBMAA-DMA12 is 0.05 wt%, and it has a low surface tension of 25.89 mN / m at this concentration, which indicates that this pseudogemini surfactant has excellent surface activity.

[0053] Meanwhile, the surface tension of the surfactant EBMAA-DMA12 solution changes at different pH values, as follows: Figure 3 As shown. The original solution had a pH of 6.87 and a surface tension of 25.07 mN / m. When the pH was adjusted to be less than 6.87, the surface tension increased slightly, reaching 27.12 mN / m at pH 1.81. This is because, under acidic conditions, the pseudogemini surfactant EBMAA-DMA12 protonated to form N,N'-ethylenebismaleamic acid (EBMAA) and N,N-dimethyldodecylamine, resulting in a slight increase in surface tension. As the pH increased, when it was greater than 6.87, the solution changed from clear and transparent to milky white, and the surface tension increased, reaching 39.99 mN / m at pH 13.5. This is because, under alkaline conditions, the pseudogemini surfactant EBMAA-DMA12 deprotonated to form N,N'-ethylenebismaleamic acid salt and N,N-dimethyldodecylamine, leading to a decrease in surface activity. In summary, this pseudogemini surfactant exhibits pH-dependent behavior, and its surface activity can be regulated by adjusting the pH of the solution.

[0054] Test Example 3: Calculation of Capillary Force and Adhesive Work

[0055] Test method: Based on the experimental data of surface tension and contact angle (Test Example 2), the capillary force and adhesion work were calculated.

[0056] The formula for calculating capillary force is shown in equation (1):

[0057] (1)

[0058] In the formula: For capillary force, Pa / cm; Surface tension, mN / m; The contact angle is (°). denoted as capillary radius, in cm.

[0059] The formula for calculating adhesion work is shown in equation (2):

[0060] (2)

[0061] In the formula: For adhesion work, mJ / m 2 ; Surface tension, mN / m; The contact angle is (°).

[0062] Results and Discussion:

[0063] a) The wettability of coal samples is determined by the size of the contact angle. This application measured the contact angle of coal before and after treatment with surfactant EBMAA-DMA12 solution at different pH values, such as... Figure 4 As shown in the figure, comparing the contact angle of the coal sample with that of the original sample, it was found that when treated with a surfactant EBMAA-DMA12 solution with a pH less than 6.87, the contact angle of the coal sample increased, ranging from 9.71 to 14.4°, indicating increased hydrophobicity. Conversely, when treated with a surfactant EBMAA-DMA12 solution with a pH greater than 6.87, the contact angle of the coal sample decreased, ranging from 21.46 to 32.96°, indicating increased hydrophilicity. Therefore, it can be concluded that adjusting the pH of the solution alters the surface wettability of the coal sample caused by the surfactant EBMAA-DMA12.

[0064] b) Since the change in wettability is closely related to the magnitude of capillary force, it plays a key role in the effectiveness of the waterproof lock. As can be seen from equation (1), the magnitude of capillary force is related to... The value is directly proportional, that is The smaller the value, the weaker the capillary force. This application calculated the capillary force at different pH values. Value, such as Figure 5 As shown. Compared to the original coal sample. Value comparison: When the pH of the surfactant EBMAA-DMA12 solution is adjusted to less than 6.87, the coal sample... The value decreased; when the pH of the surfactant EBMAA-DMA12 solution was adjusted to be greater than 6.87, the coal sample... An increase in the pH value indicates that the capillary force of the coal sample can be regulated by adjusting the pH value of the surfactant EBMAA-DMA12 solution. Therefore, the pH value of the surfactant solution can be adjusted to less than 6.87 to reduce the capillary force, thus acting as a waterproofing lock-in agent.

[0065] c) Adhesion work It represents the minimum work required for an aqueous solution of a surfactant to detach from a solid surface; in other words, it indicates the minimum work required to overcome resistance when the aqueous solution comes into contact with the coal surface. A higher adhesion work indicates that the solution spreads more easily on the coal sample surface.

[0066] This application calculated the adhesion work of water on the coal sample surface before and after treatment with surfactant EBMAA-DMA12 solution at different pH values, such as... Figure 6 As shown. Compared to the original coal sample. Value comparison: When the pH of the surfactant EBMAA-DMA12 solution is adjusted to less than 6.87, The value decreases; when the pH of the surfactant EBMAA-DMA12 solution is adjusted to be greater than 6.87, The increase in pH value indicates that the surface wettability of coal samples treated with surfactant EBMAA-DMA12 solution at pH greater than 6.87 increases. This is because the free energy of the coal surface decreases after treatment with surfactant EBMAA-DMA12, making the coal surface easier to wet. This helps to reduce the adsorption of gas on the coal surface and promotes the desorption of coalbed methane. Therefore, surfactant EBMAA-DMA12 solution at pH greater than 6.87 can be used as an ideal coalbed methane desorbent.

[0067] In summary, adjusting the pH of the solution can alter the wettability of the coal sample surface by the surfactant EBMAA-DMA12. When the pH of the EBMAA-DMA12 solution is adjusted to less than 6.87, it helps reduce capillary forces and can act as a water-locking agent. When the pH of the surfactant solution is adjusted to greater than 6.87, it helps reduce the surface free energy of the coal seam and can act as a coalbed methane desorbent. Therefore, this surfactant EBMAA-DMA12 can be used as a multi-functional coal seam wetting reversal agent, achieving multiple uses with a single agent through pH adjustment.

[0068] Test Example 4: Coal Seam Damage Performance Test

[0069] Test Method: The experiment was conducted in accordance with industry standard NB / T 10034-2016 "Performance Evaluation Method of Water-Based Fracturing Fluid for Coalbed Methane Reservoirs". The specific experimental steps are as follows: First, the coal sample was saturated with standard brine, and the permeability of the test coal sample was displaced by the standard brine. A multifunctional core displacement device was used to inject a surfactant solution, and the coal sample was soaked for another 2 hours at room temperature and pressure to simulate the effect of surfactant on the coal sample. The coal sample was then reverse-displaced with standard brine, and the permeability of the coal sample was tested. By comparing the changes in permeability before and after the action of surfactants, the effect on the permeability of coal samples was calculated and analyzed.

[0070] Results and Discussion:

[0071] This application tested the effect of surfactant EBMAA-DMA12 solution on the permeability of coal samples at different pH values, and the results are shown in Table 2.

[0072] Table 2. Effect of surfactant solution on coal sample permeability at different pH levels

[0073]

[0074] As shown in Table 2, under alkaline conditions (pH=10.26), the permeability damage of the coal samples after displacement treated with surfactant EBMAA-DMA12 was 6.77%. This is because the hydrophilicity of the treated coal samples increased, making it easier for water to wet the coal sample surface and increasing water-lock damage. Under acidic conditions (pH=3.93 and 6.57), the permeability recovery rates of the coal samples after displacement treated with surfactant EBMAA-DMA12 were 19.31% and 32.71%, respectively. This is because the hydrophobicity of the treated coal samples increased, and the surface tension of the surfactant solution was low (~25 mN / m), thus exhibiting lower capillary force, which is beneficial for dewatering and promoting coalbed methane desorption.

[0075] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions 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, and they should all be covered within the scope of the claims and specification of the present invention.

Claims

1. A coal seam wetting reversal agent, characterized in that, The molecular structural formula of the coal seam wetting reversal agent is: 。 2. The method for preparing the coal seam wetting reversal agent according to claim 1, characterized in that, Includes the following steps: 1) After mixing maleic anhydride and anhydrous ethanol evenly, ethylenediamine was added dropwise to carry out the synthesis reaction. The reaction product was then washed and dried to obtain a white solid powder N,N'-ethylenebismaleamic acid. 2) Take the N,N'-ethylenebismaleamic acid prepared in step 1) and mix it evenly with anhydrous ethanol, then add N,N-dimethyldodecylamine dropwise to carry out the synthesis reaction. Subsequently, evaporate and dry the solvent to obtain the light yellow viscous target product, which is the coal seam wetting reversal agent.

3. The method for preparing the coal seam wetting reversal agent according to claim 2, characterized in that, The molar ratio of maleic anhydride to ethylenediamine mentioned in step 1) is 2:

1.

4. The method for preparing the coal seam wetting reversal agent according to claim 3, characterized in that, The conditions for the synthesis reaction described in step 1) are: reacting in a water bath at 0-5℃ for 12-15 hours.

5. The method for preparing the coal seam wetting reversal agent according to claim 4, characterized in that, The drying conditions described in step 1) are: drying at a temperature of 60~80℃ for 2~3 hours.

6. The method for preparing the coal seam wetting reversal agent according to claim 2, characterized in that, The molar ratio of N,N'-ethylenebismaleamic acid to N,N-dimethyldodecylamine in step 2) is 1:

2.

7. The method for preparing the coal seam wetting reversal agent according to claim 6, characterized in that, The conditions for the synthesis reaction in step 2) are: react at 15-25℃ for 18-24 hours.

8. The application of the coal seam wetting reversal agent according to claim 1 in the field of coal seam development technology.

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