Air-bleeding coalbed methane desorption agent, preparation method and application thereof

Abstract

The application discloses a kind of air-repellent coalbed gas desorption agent and its preparation method and application, belong to coalbed gas desorption technical field.The structural formula of air-repellent coalbed gas desorption agent is as shown in formula I, wherein, R1 is C 3~8 Perfluoroalkyl, R2 is C 2~3 Alkyl.Its preparation method includes the following steps: under nitrogen atmosphere, perfluoroolefin is added to dichloromethane and stirred uniformly, and triethoxysilane or tripropoxysilane and chloroplatinic acid isopropanol solution are added dropwise under the condition of 80~85 ℃, and the reaction is carried out for 8~10 h, and after the reaction is completed, rotary evaporation is carried out, and it is obtained.The air-repellent coalbed gas desorption agent is applied to the development process of coalbed gas, which can effectively reduce the water lock effect of coalbed gas and the problem of difficult desorption of adsorbed gas, thereby significantly improving the coalbed gas recovery efficiency.

Description

Technical Field

[0001] This invention belongs to the field of coalbed methane desorption technology, specifically relating to a gas-repellent coalbed methane desorbent, its preparation method, and its application. Background Technology

[0002] Coalbed methane (CBM) development is extremely challenging, facing key constraints such as the "water-locking" effect and the difficulty in desorbing adsorbed gas, resulting in generally low recovery rates. Coal seams, as typical heterogeneous porous media, have a significant capillary structure formed by internal fractures and numerous developed nanoscale pores. In mainstream hydraulic fracturing processes, foreign fluids such as fracturing fluid or formation water can intrude into the reservoir capillary channels and be trapped by strong capillary forces, creating a "water-locking effect." Although CBM exists in both free and adsorbed states, adsorbed CBM accounts for as much as 80%–90%, making effective desorption and production a bottleneck in the extraction process. Summary of the Invention

[0003] In view of the above-mentioned prior art, the present invention provides a gas-repellent coalbed methane desorbent, its preparation method and application, which solves the problems of water-locking effect and difficulty in desorbing adsorbed gas in the coalbed methane development process of the prior art.

[0004] To achieve the above objectives, the technical solution adopted by the present invention is: to provide a gas-repellent coalbed methane desorbent, the structural formula of which is shown in Formula I; ; Where R1 is C 3~8 Perfluoroalkyl, R2 is C 2~3 Alkyl groups.

[0005] Based on the above technical solution, the present invention can be further improved as follows.

[0006] Furthermore, R1 is perfluoropropyl or perfluorooctyl, and R2 is ethyl or propyl.

[0007] Furthermore, the structural formula of the gas-repellent coalbed methane desorbent is shown in Formula II; .

[0008] Further, under nitrogen protection, perfluoroolefins are added to dichloromethane and stirred until homogeneous. Triethoxysilane or tripropoxysilane, along with an isopropanol solution containing chloroplatinic acid, are then added dropwise at 80-85°C. The reaction is carried out for 8-10 hours. After the reaction is complete, rotary evaporation is performed to obtain the final product.

[0009] Furthermore, the perfluoroolefin is perfluoropropylene or perfluorooctene.

[0010] Furthermore, the molar ratio of perfluoropropylene to triethoxysilane is 1~1.1:1.

[0011] Furthermore, the ratio of perfluoropropylene to dichloromethane is 1 mol: 20 mL.

[0012] Furthermore, the concentration of chloroplatinic acid in the isopropanol solution containing chloroplatinic acid is 0.1 mol / L.

[0013] Furthermore, the above-mentioned gas-repellent coalbed methane desorbents are applied in coalbed methane extraction.

[0014] Furthermore, gas-repellent coalbed methane desorbents promote the desorption of coalbed methane.

[0015] The beneficial effects of this invention are as follows: This invention provides a coalbed methane desorbent based on coal seam surface wettability modification to relieve water lock and desorb adsorbed gas. A perfluoroalkylsiloxane compound (R1-Si-(OR2)3) is used to modify the surface of the coal seam throat (the formation rock surface has a large number of hydroxyl groups, and -OR2 in Formula I forms a covalent bond with the coal seam surface). In Formula I, -R1 enhances the hydrophobic and gas-repellent properties of the surface, relieving the water lock effect in the coalbed methane, while simultaneously promoting the replacement effect of CO2 on CH4, thus desorbing adsorbed gas. The gas-repellent coalbed methane desorbent chemically grafts onto the coal sample contact surface and significantly alters the contact surface properties, especially the wettability reversal, which transforms capillary resistance into a driving force, reducing fracturing fluid retention and improving coalbed methane recovery. Under real core conditions, the gas-repellent coalbed methane desorbent (CF3CF2CF2-Si-(OCH2CH3)3) can increase the cumulative CH4 production by 21.7% (mass ratio), achieving effective enhanced coalbed methane recovery. Attached Figure Description

[0016] Figure 1 The results show the wetting angle measurements before and after modification; Figure 2 The images are SEM images of the coal core surfaces; (a) is an unmodified coal core, (b) is an FSA-modified coal core, (c) is an FSB-modified coal core, and (d) is an FSC-modified coal core. Figure 3 The images are SEM-EDS images of the coal core surfaces; (a) is an unmodified coal core, (b) is an FSA-modified coal core, (c) is an FSB-modified coal core, and (d) is an FSC-modified coal core; yellow represents F element, pink represents S element, blue represents O element, green represents N element, and red represents C element. Figure 4 The adsorption-desorption curves are for coal; where (a) is for FSA-modified coal core, (b) is for FSB-modified coal core, (c) is for FSC-modified coal core, and (d) is the pore volume ratio. Figure 5 This is a graph showing the relationship between gas production and CH4 production. Detailed Implementation

[0017] The specific embodiments of the present invention will be described in detail below with reference to examples.

[0018] Example 1 A gas-repellent coalbed methane desorbent (CF3CF2CF2-Si-(OCH2CH3)3, FSA) is prepared as follows: Under nitrogen protection, perfluoropropylene (1.1 mol) was added to CH2Cl2 (20 mL) and stirred until homogeneous. Triethoxysilane (1 mol) and isopropanol solution containing 0.1 mol / L chloroplatinic acid (0.02 mL) were added dropwise at 80 °C. The reaction was allowed to proceed for 10 h. After the reaction was completed, rotary evaporation (65 °C) was performed to obtain the final product.

[0019] Example 2 A gas-repellent coalbed methane desorbent (FSA) is prepared as follows: Under nitrogen protection, perfluoropropylene (1 mol) was added to CH2Cl2 (20 mL) and stirred until homogeneous. Triethoxysilane (1 mol) and isopropanol solution containing 0.1 mol / L chloroplatinic acid (0.02 mL) were added dropwise at 85 °C. The reaction was allowed to proceed for 10 h. After the reaction was completed, rotary evaporation (65 °C) was performed to obtain the final product.

[0020] Example 3 A gas-repellent coalbed methane desorbent (CF3CF2CF2-Si-(OCH2CH2CH3)3, FSB) is prepared as follows: Under nitrogen protection, perfluoropropylene (1.1 mol) was added to CH2Cl2 (20 mL) and stirred until homogeneous. Tripropoxysilane (1 mol) and isopropanol solution containing 0.1 mol / L chloroplatinic acid (0.02 mL) were added dropwise at 80 °C. The reaction was allowed to proceed for 10 h. After the reaction was completed, rotary evaporation (65 °C) was performed to obtain the final product.

[0021] Example 4 A gas-repellent coalbed methane desorbent (CF3(CF2)7-Si-(OCH2CH3)3, FSC) is prepared as follows: Under nitrogen protection, perfluorooctene (1.1 mol) was added to CH2Cl2 (20 mL) and stirred until homogeneous. Triethoxysilane (1 mol) and isopropanol solution containing 0.1 mol / L chloroplatinic acid (0.02 mL) were added dropwise at 80 °C. The reaction was allowed to proceed for 10 h. After the reaction was completed, rotary evaporation (65 °C) was performed to obtain the final product.

[0022] Application example: Using CO2 gas as the desorbent carrier, a certain amount of gas-repellent coalbed methane desorbent is injected, followed by continuous CO2 introduction. The gas carries the desorbent and disperses it. The mass-to-volume ratio of desorbent to CO2 is 40-50 g / m³. 3 This desorbent can modify the wettability of coal seam surfaces; it can effectively reduce the water-locking effect of coalbed methane and the problem of difficult desorption of adsorbed gas, thereby improving the coalbed methane recovery rate.

[0023] Performance testing: (1) Wetting angle test The wetting angle of the modified coal sample surface was measured using a KRÜSS DSA25 wetting angle measuring instrument. Five measurements were taken at different positions on the core slice for each set of wetting angle data to obtain representative wettability results with a relative uncertainty of less than 2%.

[0024] Unmodified surface ( Figure 1 The medium BG has a low wetting angle (74.30°). After the desorber FSA (Formula II) is used to modify the surface of the coal sample hydrophobically and reduce the surface energy, the wetting angle reaches 128.68°. Comparing FSA and FSB (CF3CF2CF2-Si-(OCH2CH2CH3)3), it can be seen that the wettability of FSX (R1-Si-(OR2)3) decreases with the increase of the chain length of R2. The main influencing factor may be that R2 is close to the Si tetrahedron, and its increase leads to an increase in steric hindrance when grafting with the hydroxyl groups on the coal sample surface. Comparing FSA and FSC (CF3(CF2)7-Si-(OCH2CH3)3), it can be seen that the wettability of FSX also decreases with the increase of the chain length of R1. The main influencing factor may be that the increase of R1 leads to a sharp increase in molecular weight. In the experiment, the amount of FSX dispersed with carbon dioxide to modify the coal sample surface was reduced.

[0025] (2) Surface testing (SEM-EDS) The surface modification morphology and F element grafting of the coal samples were characterized using an HHT Regulus 8100 field emission scanning electron microscope (SEM) and its accompanying energy-dispersive spectrometer (EDS). The coal sample surface was first dried at low temperature to avoid morphological shrinkage and deformation. Then, a 5-10 nm thick platinum layer was sputtered to eliminate surface charge accumulation. The microstructure of the coal sample surface was observed using secondary electron imaging mode at 100-500x magnification. Combined with point scanning and area scanning EDS modes, common coal elements such as C, O, N, S, and F were detected.

[0026] The surface morphology of the coal before and after modification was characterized by scanning electron microscopy (SEM, Regulus 810, HHT, Japan). SEM images showed that the unmodified surface had a strip / layered structure and relatively large particles. Figure 2 a), this is mainly attributed to the microscopic evolution of the aromatic layer of organic macromolecules in coal samples (especially vitrinite, accounting for 60%-85%), which involves aromatization, preferred orientation, and ordered stacking. After FSX modification ( Figure 2 b、 Figure 2 c and Figure 2 After d), the coal sample surface changed, exhibiting small surface particles and micro / nano-scale protrusions. This structure may be due to the directional alignment or aggregation of FSX molecules on the reservoir surface, thus altering the microstructure. Furthermore, after FSA modification ( Figure 2 b) The surface showed relatively more fine particles in the SEM results, after modification with FSB and FSC ( Figure 2 c and Figure 2 d) The surface appears relatively smoother in the SEM results, which may be due to the difference in the network structure after modification caused by the influence of the length of the main chain or the side chain.

[0027] In addition, energy-dispersive X-ray spectroscopy (EDS) analysis was performed on the sample surface simultaneously. EDS images formed by backscattered electrons were collected, and the results showed that the unmodified surface morphology was relatively smooth and did not contain F element (…). Figure 3 a), modified by FSX ( Figure 3 b、 Figure 3 c and Figure 3 After d), the presence and uniform distribution of F element on the surface indicate that F-branched FSX has effectively chemically reacted with the coal sample surface; further confirmation Figure 3 b、 Figure 3 c and Figure 3 The F content (elemental percentage) in d was 3.45%, 2.02%, and 0.64%, respectively, showing a decreasing trend. This indicates that, compared with FSA and FSB, shorter branches are more favorable for this chemical reaction, while compared with FSA and FSC, longer main chains are less favorable for this reaction. This is consistent with the results of the wetting angle determination.

[0028] It is worth noting that the formation of this rough surface is itself a spatial network structure formed by the aggregation of FSX molecules. This structure does not completely block the reservoir pores, indicating that FSX maintains the permeability of the reservoir while modifying the performance of the coal sample, thus avoiding formation damage.

[0029] (3) Pore / pore volume test The modification of the internal pores of the coal samples was characterized using a BSD-PM2 high-performance specific surface area and micropore analyzer. Based on the static volumetric isotherm test principle, nitrogen (N2) was used as the adsorbate. After sufficient desorption (T=105℃, t=8 h), the sample mass loss rate was 4.73%, which is within the reasonable range of pretreatment. Subsequent continuous adsorption (T=77.3K, t=3 h) was then performed, with the equilibrium time at each pressure point set at 120 s to ensure that nitrogen reached adsorption-desorption equilibrium in the coal sample pores. This ensured the accuracy and repeatability of the isotherm data, providing a reliable basis for calculating parameters such as the pore structure of the modified coal samples.

[0030] The changes in internal porosity of coal samples before and after modification were characterized using a low-temperature nitrogen adsorption analyzer (SSA-PSA analyzer, BSD-PM2, Best Instrument, China). Adsorption-desorption hysteresis loops were constructed based on the experimental data. Figure 4 )show: Adsorption-desorption cyclone of desorbent FSA ( Figure 4 The blue line in section a represents the overall difference compared to the blank control group ( Figure 4 The pink wavy line in section a moves towards the high-pressure region (lower right), indicating that the characteristic pore size of the material has increased, and the pore size distribution ( Figure 4 d) also directly proves this point. Compared to similar features, FSB ( Figure 4 (b) brown wavy line and FSC ( Figure 4 c. The cyan lapis lazuli line compared to the blank control group ( Figure 4 b or Figure 4 The pink loop in c is less pronounced. This may be because the FSA can more easily enter some micropores and small mesopores (pore size D≤10 nm) during the modification process. After modification, the hysteresis loop shape formed by the adsorption-desorption loop remains good, and the possibility of disordered blockage causing increased fluid resistance is reduced. Although the total pore volume decreases after the FSA enters, the connectivity of the channels is better, and the average pore size is larger, thereby reducing capillary resistance during fluid transport.

[0031] (4) Displacement of natural core To verify the effectiveness of the displacement experiment on coal samples, it is necessary to determine the concentration of CH4 in the collected gas after displacement. An Agilent 7890B gas chromatograph (GC) was used, utilizing its flame ionization detector (FID) for high sensitivity to hydrocarbon compounds to achieve quantitative analysis of CH4. The experimental procedure involved first separating CH4 using a chromatographic column, followed by quantification using the external standard method (preparing five gradient concentrations of CH4 standard gas) with the FID detector. Each sample was tested in triplicate, and the average value was taken as the final result. The relative standard deviation (RSD) was controlled within 2%.

[0032] Based on the core properties (D=2.53 cm, L=5.04 cm, and porosity 2.96%), the saturation amount of CH4 gas in the pores at a saturation pressure of 4 MPa was calculated to be 19.4 mg (i.e., 1 PV). Because the gas is compressible and there is a continuous gas production capacity during displacement in the large fractures of the core, the horizontal axis cannot be represented by PV in this study. Therefore, the cumulative gas production was used as the expression, and the relationship between the displaced gas and CH4 was finally obtained (Table 1). Due to the high cost of GC-FID testing and the excessively large sample size required for this experiment, only FSA, which has the best wetting effect, was used for the displacement experiment in the actual experiment.

[0033] Table 1. Relationship between gas output and CH4 content

[0034] Based on the data in Table 1, the relevant data for CH4 were collected in the experiment. Figure 5 )show: During the initial displacement process, the CH4 content in the gas expelled from the unmodified coal sample continuously decreased. When it reached a certain level (0.3 mg), it reached equilibrium. This may be due to some coalbed methane entering the ink bottle-shaped micropores (consistent with low-temperature nitrogen adsorption results) or forming adsorbed gases on the coal sample surface that are difficult to desorb. It should be noted that in this displacement process, the CH4 expelled in the early stage was mainly free gas in the pores, while in the later stage it was mainly partially adsorbed gas desorbed through competitive desorption by carbon dioxide. Therefore, this displacement process exhibited a phenomenon of a sharp decrease in CH4 content in the early stage, followed by a slow decrease in the middle stage until finally reaching equilibrium.

[0035] When the CH4 content in the expelled gas remains unbalanced, the introduction of a carbon dioxide gas stream with FSA modifier modifies the pore surface of the coal sample. After modification, the mass and proportion of expelled CH4 gas instantly increase, reaching a level comparable to the adsorbed gas level from competitive desorption of carbon dioxide before FSA modification; then it gradually decreases until it eventually reaches equilibrium. This pattern is mainly due to the fact that when the carbon dioxide gas stream with FSA modifier is initially introduced, it simultaneously acts as a "water lock" and reduces surface energy desorption in the core pores, leading to a rapid increase in CH4 content in the 11th gas collection. The subsequent gradual decrease is also due to the reduction in pores after the "water lock" is released, resulting in gas production relying solely on desorption from reduced surface energy.

[0036] In the unmodified coal sample displacement stage, free gas was already displaced. The CH4 gas added after FSA modification consisted entirely of water-locked and adsorbed gas from the core. The cumulative CH4 mass collected in the first 10 tests (13.15 mg) was compared with the subsequent production increase (estimated at equilibrium state in the 10th test for the subsequent 6 unmodified tests, 2.85 mg), resulting in a cumulative production increase of 21.7% after FSA introduction. This cumulative CH4 increase accounts for 14.7% of the total saturated CH4 mass. It should be noted that the FSA consumption in this modification process was 0.077 g, with a low effective concentration (57.9 g / m³). 3 The reaction time of FSA with the pore surface of coal sample is short (the experiment of adding FSA modified gas to complete displacement equilibrium took 148 min).

[0037] Therefore, the chemical grafting of the desorbent (FSA) at the coal sample contact surface significantly alters the surface properties, particularly the wettability reversal, which transforms capillary resistance into a driving force, reduces fracturing fluid retention, and improves coalbed methane recovery. Under real core conditions, the FSA can increase the cumulative CH4 production by 21.7% (by mass), achieving effective enhanced coalbed methane recovery.

[0038] Although specific embodiments of the present invention have been described in detail with reference to examples, they should not be construed as limiting the scope of protection of this patent. Various modifications and variations that can be made by those skilled in the art without inventive effort within the scope described in the claims are still within the scope of protection of this patent.

Claims

1. A gas-repellent coalbed methane desorbent, characterized in that: The structural formula of the gas-repellent coalbed methane desorbent is shown in Formula I. ； Where R1 is C 3~8 Perfluoroalkyl, R2 is C 2~3 Alkyl groups.

2. The gas-repellent coalbed methane desorbent according to claim 1, characterized in that: R1 is perfluoropropyl or perfluorooctyl, and R2 is ethyl or propyl.

3. The gas-repellent coalbed methane desorbent according to claim 2, characterized in that: The structural formula of the gas-repellent coalbed methane desorbent is shown in Formula II. 。 4. The method for preparing the gas-repellent coalbed methane desorbent according to any one of claims 1 to 3, characterized in that, Includes the following steps: Under nitrogen protection, perfluoroolefins are added to dichloromethane and stirred until homogeneous. Triethoxysilane or tripropoxysilane, along with an isopropanol solution containing chloroplatinic acid, are then added dropwise at 80-85°C. The reaction is carried out for 8-10 hours. After the reaction is complete, rotary evaporation is performed to obtain the final product.

5. The method for preparing the gas-repellent coalbed methane desorbent according to claim 4, characterized in that: The perfluoroolefin is perfluoropropylene or perfluorooctene.

6. The method for preparing the gas-repellent coalbed methane desorbent according to claim 4, characterized in that: The molar ratio of perfluoropropylene to triethoxysilane is 1~1.1:

1.

7. The method for preparing the gas-repellent coalbed methane desorbent according to claim 4, characterized in that: The ratio of perfluoropropylene to dichloromethane is 1 mol: 20 mL.

8. The method for preparing the gas-repellent coalbed methane desorbent according to claim 4, characterized in that: The concentration of chloroplatinic acid in the isopropanol solution containing chloroplatinic acid is 0.1 mol / L.

9. The application of the gas-repellent coalbed methane desorbent according to any one of claims 1 to 3 in coalbed methane extraction.

10. The application according to claim 9, characterized in that: The gas-repellent coalbed methane desorbent promotes the desorption of coalbed methane.

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