Coal seam wetting reversal agent and preparation method thereof

Abstract

The invention belongs to the technical field of coal seam development, and discloses a reverse wetting agent for a coal seam and a preparation method thereof. The coal seam wetting reversal agent provided by the invention has an excellent pH influence behavior, and the change of the surface wettability of a coal sample by the surfactant EBMAA-DMA12 can be realized by adjusting the pH value of a solution. When the pH value of the solution is smaller than 6.87, capillary force can be reduced, and the surfactant can be used as a water blocking preventing agent, and when the pH value of the surfactant solution is adjusted to be larger than 6.87, free energy on the surface of a coal seam can be reduced, and the surfactant can be used as a coal seam gas desorption agent. Besides, according to a method for preparing the reverse wetting agent for the coal seam, MAH and EDA are adopted to synthesize a binary acid intermediate N, N '-ethylidene bismaleamic acid (EBMAA), and then the N, N'-ethylidene bismaleamic acid (EBMAA) and N, N-dimethyl dodecylamine are subjected to a neutralization reaction to obtain the reverse wetting agent for the coal seam. The preparation method has the advantages of easily available raw materials, simple process, high repeatability and stability, and good popularization value.

Description

Technical Field

[0001] The invention belongs to the technical field of coal seam development, and in particular relates to a coal seam wettability reversal agent and a preparation method thereof. Background Art

[0002] The exploitation of coalbed methane is not only conducive to reducing the occurrence of coal mine gas accidents, but also can be used as a clean fuel to meet the world's energy needs. However, the permeability of coal seams is generally low, so coalbed methane exploitation is limited. Hydraulic measures such as hydraulic fracturing can effectively improve the permeability of coal seams. However, when a large amount of external water invades the coal seam, due to the existence of capillary force, the moisture content in the coal seam increases to form a water lock effect, blocking the diffusion channel of coalbed methane and hindering the production of coalbed methane.

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

[0004] The present invention aims to solve one of the technical problems in the related art at least to a certain extent. To this end, the main purpose of the present invention is to provide a coal seam wettability reversal agent, which is a new type of pseudo-gemini surfactant.

[0005] The main purpose of the present invention is to provide a preparation method and application of the coal seam wettability reversal agent.

[0006] The objective of the present invention is achieved through the following technical solutions:

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

[0008]

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

[0010] 1) After MAH and anhydrous ethanol are stirred and mixed evenly, EDA is added dropwise to carry out a synthesis reaction, and then the reaction product is washed and dried to obtain a white solid powder EBMAA;

[0011] 2) After the EBMAA prepared in step 1) is evenly mixed with anhydrous ethanol, DMA12 is added dropwise to carry out a synthesis reaction, and then the solvent is evaporated and dried to obtain a light yellow viscous target product EBMAA-DMA12.

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

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

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

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

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

[0017] An application of the aforementioned coal seam wettability 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 wettability reversal agent of the present invention has excellent pH-affecting behavior, and can change the wettability of the coal sample surface by the surfactant EBMAA-DMA12 by adjusting the pH value of the solution. Specifically, when the pH value of the solution is less than 6.87, it helps to reduce the capillary force and can be used as a waterproof lock agent. When the pH value of the surfactant solution is adjusted to be greater than 6.87, it is beneficial to reduce the surface free energy of the coal seam and can be used as a coalbed methane desorbent.

[0020] 2) The preparation method of the present invention first synthesizes the dibasic acid intermediate N,N′-ethylenebismaleamic acid (EBMAA) by using MAH and EDA, and then neutralizes N,N′-ethylenebismaleamic acid (EBMAA) with N,N-dimethyldodecylamine to obtain a new type of pseudo-gemini surfactant. The preparation method has easy-to-obtain raw materials, simple process, high repetitive stability, and good promotion value. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the specific embodiments of the present invention, the drawings required for use in the specific embodiments or the description of the prior art will be briefly introduced below.

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

[0023] Figure 2 The surface tension and mass fraction relationship diagram of EBMAA-DMA12 in Example 1 of the present invention;

[0024] Figure 3 The surface tension changes of surfactant EBMAA-DMA12 solution at different pH;

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

[0026] Figure 5 is the σcosθ of coal before and after treatment with surfactant EBMAA-DMA12 solution at different pH;

[0027] Figure 6 is the adhesion work value of coal before and after treatment with surfactant EBMAA-DMA12 solution at different pH values. DETAILED DESCRIPTION

[0028] The present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. The following embodiments are only illustrative and not restrictive, and the protection scope of the present invention cannot be limited thereto.

[0029] When a certain amount, concentration or other value or parameter is expressed in the form of a range, a preferred range, or a preferred upper and lower numerical limit, it should be understood that it is equivalent to specifically revealing any range by combining any pair of upper range limits or preferred numerical values ​​with any lower range limit or preferred numerical value, regardless of whether the range is specifically disclosed. Unless otherwise indicated, the numerical range values ​​listed herein include the endpoints of the range, and all integers and fractions within the range.

[0030] Unless otherwise indicated, all percentages, parts, ratios, etc. herein are by weight.

[0031] The materials, methods, and examples herein are illustrative and are not to be construed as limiting unless specifically stated.

[0032] In the following examples, the experimental materials: ethylenediamine (EDA), maleic anhydride (MAH), N,N-dimethyldodecylamine (DMA12), and anhydrous ethanol used were all analytical grade; deionized water was homemade in the laboratory; the experimental coal sample was taken from the Dingxin block in Guizhou, and its industrial analysis is shown in Table 1. According to the coal classification standard GB / T5751-2009, the coal sample belongs to anthracite.

[0033] Table 1 Industrial analysis of coal samples

[0034]

[0035] Experimental instruments: Sigma 700 mechanical 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 wettability reversal agent

[0037] This embodiment provides a method for preparing a coal seam wettability 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, transfer the flask to a 3°C water bath and add 0.05 mol EDA dropwise, react under this condition for 15 h, wash the reaction product with a large amount of distilled water, and dry it in a forced air drying oven at 80°C for 2 h to obtain a white solid powder N,N′-ethylenebismaleamic acid (EBMAA);

[0039] The synthetic route of N,N′-ethylenebismaleamic acid (EBMAA) is:

[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°C) for 18 h, evaporate and dry the solvent to obtain the light yellow viscous target product EBMAA-DMA12; the synthetic route of EBMAA-DMA12 is:

[0042]

[0043] Performance test example:

[0044] Test Example 1: Substance Identification

[0045] Test method: MAH, EDA, EBMAA in step 1) and DMA12, EBMAA, EBMAA-DMA12 and KBr in step 2) in the preparation method of Example 1 were mixed in a ratio of 1:100 and ground thoroughly with an agate mortar until no obvious particles were present. They were then pressed into transparent thin sheets with an infrared tablet press and tested using 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), Figure 1(a) It can be seen that the primary amine in the EDA molecule reacts with MAH to form a -1 The NH stretching vibration absorption peak of primary amine is 3354 cm -1 and 3281cm -1 Transformed into secondary amine NH stretching vibration absorption peak 3293cm -1 (single peak), 1697cm -1 is the C=O stretching vibration absorption peak in the carboxylic acid group, 1436 cm -1 The OH in-plane bending vibration absorption peak of the carboxylic acid group appears at 900 cm -1 The out-of-plane bending vibration absorption peak of OH in the carboxylic acid group appears at 1618 cm -1 The C=O and C=C stretching vibration absorption peaks of amide I appeared at 1577 cm -1 The absorption peak of NH in-plane bending vibration of amide II band appeared. The changes of the above functional groups indicated that EBMAA was successfully prepared.

[0048] The infrared spectra of DMA12, EBMAA, and EBMAA-DMA12 in step 2) are as follows Figure 1 As shown in (b), Figure 1 (b) It can be seen that 3271cm -1 The secondary amine NH stretching vibration absorption peak is 1713 cm -1 is the C=O stretching vibration absorption peak in the carboxylic acid group, 1659 cm -1 It is the stretching vibration absorption peak of amide I with C=O and C=C, 1563cm -1 The absorption peak of the NH in-plane bending vibration of the amide II band is 1436 cm -1 、900cm -1 The absorption peak of the inward / outward bending vibration of the OH plane in the carboxylic acid group disappears, 3000~2500cm -1 There are many CH stretching vibration absorption peaks of alkanes in the range. The changes of the above functional groups indicate the successful preparation of EBMAA-DMA12.

[0049] Test Example 2: Surface tension and contact angle test

[0050] Test method: prepare a surfactant EBMAA-DMA12 solution with a mass concentration of 0.1wt%, adjust its pH to acidic and alkaline, and use the platinum ring method to determine the surface tension value σ of the surfactant solution with different pH values. Take the average value of three measurements for each test. Soak the coal sample in the solution with adjusted pH for 3 hours, then put it into a forced air drying oven at 105℃ for 30 minutes and take it out. After the coal sample is cooled to room temperature, use distilled water as the titration solution, and use a contact angle meter to determine the contact angle θ. Take the average value of three measurements for each test.

[0051] Results and Discussion:

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

[0053] At the same time, the surface tension of the surfactant EBMAA-DMA12 solution at different pH changes as shown in Figure 3 As shown. The pH value of the original solution is 6.87, and the surface tension value is 25.07mN / m. When the pH of the solution is adjusted to less than 6.87, the surface tension value of the solution increases slightly. When the pH is 1.81, the surface tension is 27.12mN / m. This is because the pseudo-gemini surfactant EBMAA-DMA12 is protonated in an acidic environment to form N,N′-ethylenebismaleamic acid (EBMAA) and N,N-dimethyl dodecylamine salt with surfactant, and the surface tension increases slightly; with the increase of the pH value of the solution, when the pH is greater than 6.87, the solution changes from clear and transparent to milky white, and the surface tension of the solution increases. At pH 13.5, the surface tension is 39.99mN / m. This is because the pseudo-gemini surfactant EBMAA-DMA12 is deprotonated in an alkaline environment to form N,N′-ethylenebismaleamic acid and N,N-dimethyl dodecylamine, resulting in reduced surface activity. In summary, this pseudo-gemini surfactant has pH-influencing behavior, and the surface activity can be adjusted by adjusting the pH of the solution.

[0054] Test case 3: Capillary force and adhesion work calculation

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

[0056] The capillary force calculation formula is shown in formula (1):

[0057]

[0058] Where: P c is the capillary force, P a / cm; σ is the surface tension, mN / m; θ is the contact angle, (°); r is the capillary radius, cm.

[0059] The calculation formula of adhesion work is shown in formula (2):

[0060] W A =σ(cosθ+1) (2)

[0061] Where: W A is the adhesion work, mJ / m 2 ; σ is the surface tension, mN / m; θ is the contact angle, (°).

[0062] Results and Discussion:

[0063] a) The wettability of coal samples is determined by the size of the contact angle. This application measures the contact angle of coal before and after treatment with surfactant EBMAA-DMA12 solution at different pH values, such as Figure 4 As shown. Compared with the original contact angle of the coal sample, it is found that when the coal sample is treated with the surfactant EBMAA-DMA12 solution with a pH less than 6.87, the contact angle of the coal sample becomes larger, and the increase range is 9.71~14.4°, that is, the hydrophobicity increases. When the coal sample is treated with the surfactant EBMAA-DMA12 solution with a pH greater than 6.87, the contact angle of the coal sample becomes smaller, and the decrease range is 21.46~32.96°, that is, the hydrophilicity increases. It can be seen that the surfactant EBMAA-DMA12 can change the wettability of the coal sample surface by adjusting the pH value of the solution.

[0064] b) Since the change in wettability is closely related to the magnitude of the capillary force, it plays a key role in the effect of waterproof lock. From equation (1), it can be seen that the magnitude of the capillary force is proportional to the σcosθ value, that is, the smaller the σcosθ value, the smaller the capillary force. This application calculates the σcosθ value at different pH values, such as Figure 5 As shown. Compared with the σcosθ value of the original coal sample, when the pH of the surfactant EBMAA-DMA12 solution is adjusted to less than 6.87, the σcosθ value of the coal sample decreases; when the pH of the surfactant EBMAA-DMA12 solution is adjusted to greater than 6.87, the σcosθ value of the coal sample increases, which means that the capillary force of the coal sample can be regulated by regulating 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, so as to use it as a waterproof lock agent.

[0065] c) Adhesion work W A It is the minimum work required for the surfactant aqueous solution to separate from the solid surface, that is, the minimum work required to overcome the resistance when the aqueous solution contacts the coal surface. The greater the adhesion work, the easier it is for the solution to spread on the coal sample surface.

[0066] This application calculates 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 with the original coal sample W A When the pH of the surfactant EBMAA-DMA12 solution is adjusted to less than 6.87, W A When the pH of the surfactant EBMAA-DMA12 solution is adjusted to be greater than 6.87, W A The value increases, which indicates that the water wettability of the coal sample surface treated with the surfactant EBMAA-DMA12 solution with a pH greater than 6.87 increases. This is because the surface free energy of the coal treated with the surfactant EBMAA-DMA12 decreases and the coal surface is easy to wet, which helps to reduce the adsorption of gas on the coal surface and promote the desorption of coalbed methane. Therefore, the surfactant EBMAA-DMA12 solution with a pH greater than 6.87 can be used as an ideal coalbed methane desorbent.

[0067] In summary, adjusting the pH value of the solution can change the wettability of the coal sample surface by the surfactant EBMAA-DMA12. When the pH value of the surfactant EBMAA-DMA12 solution is adjusted to less than 6.87, it helps to reduce the capillary force and can be used as a waterproof lock agent. When the pH value of the surfactant solution is adjusted to greater than 6.87, it is beneficial to reduce the surface free energy of the coal seam and can be used as a coalbed methane desorbent. Therefore, this surfactant EBMAA-DMA12 can be used as a multi-effect coal seam wettability reversal agent, and one dose can be used for multiple purposes by adjusting the pH value of the solution.

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

[0069] Test method: The experiment was conducted in accordance with the industry standard NB / T 10034-2016 "Method for evaluating the performance of water-based fracturing fluids for coalbed methane reservoirs". The specific experimental steps are as follows: First, the coal sample was saturated with standard brine and displaced with standard brine to test the permeability K1 of the coal sample; a surfactant solution was injected using a multifunctional core displacement device, and the pressure was maintained at room temperature, and the coal sample was soaked for another 2 hours to simulate the effect of the surfactant on the coal sample; the coal sample was reversely displaced with standard brine, and the permeability K2 of the coal sample was tested; the permeability changes before and after the surfactant action were compared, and the influence on the permeability of the coal sample was calculated and analyzed.

[0070] Results and Discussion:

[0071] This application tests 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 at different pH on coal sample permeability

[0073]

[0074] As can be seen from Table 2, under alkaline conditions (pH = 10.26), the permeability damage of the coal sample after the treatment with surfactant EBMAA-DMA12 was 6.77%, which is because the hydrophilicity of the treated coal sample increased, water was easy to wet the surface of the coal sample, and the water lock damage increased. Under acidic conditions (pH = 3.93, 6.57), the permeability recovery rate of the coal sample after the treatment with surfactant EBMAA-DMA12 was 19.31% and 32.71%, which is because the hydrophobicity of the treated coal sample increased, and the surface tension of the surfactant solution was low (~25mN / m), so it had a lower capillary force, which was conducive to unlocking water lock and promoting coalbed methane desorption.

[0075] 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 by equivalents. These modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be included in the scope of the claims and specification of the present invention.

Claims

1. A coal seam wettability reversal agent, characterized in that: The molecular structural formula of the coal seam wetness reversal agent is:

2. The method for preparing the coal seam wettability reversal agent according to claim 1, characterized in that: The steps include: 1) After MAH and anhydrous ethanol are stirred and mixed evenly, EDA is added dropwise to carry out a synthesis reaction, and then the reaction product is washed and dried to obtain a white solid powder EBMAA; 2) After the EBMAA prepared in step 1) is evenly mixed with anhydrous ethanol, DMA12 is added dropwise to carry out a synthesis reaction, and then the solvent is evaporated and dried to obtain a light yellow viscous target product EBMAA-DMA12.

3. The method for preparing the coal seam wettability reversal agent according to claim 2, characterized in that: The molar ratio of MAH to EDA in step 1) is 2:

1.

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

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

6. The method for preparing the coal seam wettability reversal agent according to claim 2, characterized in that: The molar ratio of EBMAA to DMA12 in step 2) is 1:

2.

7. The method for preparing the coal seam wettability reversal agent according to claim 6, characterized in that: Step 2) The conditions of the synthesis reaction are: reacting at 15-25°C for 18 to 24 hours.

8. Use of the coal seam wettability reversal agent according to claim 1 in the field of coal seam development technology.

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