Synthesis method and application of active fracturing proppant

Abstract

The application discloses a synthesis method of active fracturing proppant, which comprises the following steps: first, preparing a core solid mixture with catalytic activity and a colloidal SiO2 precursor; then, mixing the core solid mixture with the colloidal SiO2 precursor to prepare an emulsion after the core solid mixture is made into a suspension; finally, adding a shell curing agent to the prepared emulsion, so that the active fracturing proppant with a core-shell structure is obtained after the shell is cured. Through the above method, the fracturing proppant with catalytic activity is prepared by adopting the colloidal-emulsion method for core-shell coupling coating, the fracturing proppant has an inert support shell and an inner core structure with catalytic activity, can play a role in expanding the gasification contact surface during the pumping delivery period and the initial underground ignition period, and can release the active agent with the function of generating more CO during the underground high-temperature gasification stage, so that the selectivity of CO in the product is improved, the emission of CO2 is reduced, and the utilization rate of coal resources is improved.

Description

Technical Field

[0001] This invention relates to the field of underground coal gasification development and production enhancement technology, and in particular to a method for synthesizing and applying an active fracturing proppant. Background Technology

[0002] Coal is one of the world's largest and most widely distributed energy mineral resources. China, as a major coal-producing country, possesses abundant coal resources. However, the amount of coal suitable for open-pit mining is relatively small, accounting for only about 7% of the total reserves. Deep and ultra-deep coal seam mining operations are extremely difficult, posing a challenge to the utilization of my country's coal resources. In 1888, the Russian chemist Mendeleev proposed the development method of underground coal gasification. Underground coal gasification (UCG) is the controlled combustion of underground coal, producing combustible gas through thermal and chemical reactions. Since the 1930s, major coal-producing countries such as the United States, Germany, and the Soviet Union have invested heavily in technological research in this field, achieving numerous scientific results. my country began experimental work on underground coal gasification under natural conditions in 1958. After more than 20 years of exploration, pilot tests were conducted in more than ten mining areas, including Xuzhou, Shandong, Tangshan, Hebi, Feicheng, and Xinwen, laying a rich foundation of experience for the development of underground coal gasification in my country.

[0003] In the underground gasification process, coal seams that have not undergone reservoir modification can only achieve heat transfer and gas-phase mass transfer through the combustion surface, afterburning cavity, and existing fractures. Introducing coal seam fracturing technology into underground coal gasification engineering operations can create coal seam fracturing fractures inside the coal reservoir, forming efficient flow-guiding fracture channels, expanding the extension space and gas supply area, increasing coal seam permeability, and thus improving the coal seam gas migration and production rate.

[0004] On the other hand, in-situ coal gasification is a key characteristic of underground coal gasification technology. Coal releases effective gaseous components such as H2, CH4, and CO through reactions like aerobic combustion and water-gas shift reaction. However, incomplete gasification also results in the release of a large amount of ineffective gaseous component CO2. Commonly used coal reservoir fracturing proppants, primarily composed of materials like quartz sand and ceramsite, lack chemical reactivity and do not participate in the gasification reaction. Therefore, while existing reservoir stimulation proppants can increase the utilization rate of underground coal resources and improve crude gas production to some extent, they also correspondingly increase CO2 emissions and the carbon neutralization costs in the post-processing stage.

[0005] In view of this, it is necessary to propose an improved coal seam fracturing proppant to solve the above problems. Summary of the Invention

[0006] The purpose of this invention is to address the problems of low effective component yield and high CO2 yield caused by incomplete underground coal gasification during underground coal gasification. A novel proppant material with an inert outer shell and an active core is designed. This proppant can perform its original proppant function during the pumping and initial underground ignition phase, while simultaneously releasing a catalytically active core activator through shell melting during the high-temperature underground gasification stage. This activator, upon contact with the coal seam, improves coal conversion efficiency, increases CO selectivity in the products, and reduces CO2 selectivity, thereby achieving effective crude gas production increase and CO2 emission reduction on the basis of its original proppant function.

[0007] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0008] A method for synthesizing an active fracturing proppant, the method comprising:

[0009] Preparation of a catalytically active core solid mixture;

[0010] Preparation of colloidal SiO2 precursor;

[0011] The suspension of the core solid mixture is uniformly mixed with the colloidal SiO2 precursor to obtain a mixed emulsion;

[0012] A shell curing agent is added to the mixed emulsion, and after curing, an active fracturing proppant with a core-shell structure is obtained.

[0013] As a further improvement of the present invention, the preparation of the core solid mixture with catalytic activity includes:

[0014] A silane coupling agent was uniformly sprayed onto the surface of an alkali metal compound, and after standing, a solid mixture A was obtained.

[0015] The solid mixture A is thoroughly mixed with the aluminate coupling agent, and after standing, solid mixture B is obtained.

[0016] The solid mixture B is thoroughly mixed with an alkaline earth metal compound and allowed to stand to obtain a core solid mixture with catalytic activity.

[0017] As a further improvement of the present invention, the alkali metal compound includes one or more of sodium carbonate, sodium bicarbonate, sodium hydroxide, sodium chloride, potassium hydroxide, potassium carbonate, potassium bicarbonate, and potassium chloride.

[0018] The silane coupling agent includes one or more of 3-glycidyl etheroxypropyltrimethoxysilane, (3-(2,3-epoxypropoxy)propyltriethoxysilane), 3-(2,3-epoxypropoxy)propylmethyldimethoxysilane, and isobutyltriethoxysilane.

[0019] As a further improvement of the present invention, the ratio of the silane coupling agent to the alkali metal compound is 0.1 to 2.7 by mass.

[0020] As a further improvement of the present invention, the aluminate coupling agent includes one or more of distearyloxyisopropyl aluminate, aluminum isopropoxide, and anti-settling aluminate.

[0021] As a further improvement of the present invention, the alkaline earth metal compound includes one or more of calcium oxide, calcium carbonate, and magnesium hydroxide.

[0022] As a further improvement of the present invention, the preparation of the colloidal SiO2 precursor includes:

[0023] An organic solvent is mixed with an acidity regulator, and the pH value of the mixture is adjusted to obtain a composite acidity regulator.

[0024] Two silica precursor solutions were uniformly mixed at a certain temperature to obtain a mixed solution;

[0025] After adjusting the pH value of the mixed solution with the composite acidity regulator, a composite silica precursor solution is obtained.

[0026] The composite silica precursor solution was allowed to stand and then distilled under reduced pressure to obtain a colloidal SiO2 precursor.

[0027] As a further improvement of the present invention, the silicon oxide precursor liquid includes any two of hexamethylcyclotrisiloxane, octamethylcyclotetrasiloxane, tetraethyl orthosilicate, methyltrioxysilane, and vinyltriethoxysilane.

[0028] As a further improvement of the present invention, the molar ratio of the two silica precursor solutions is 1 to 15, and the mixing temperature is 25 to 50°C.

[0029] As a further improvement of the present invention, the organic solvent includes one or more of methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, and pentanol;

[0030] The acidity regulator includes one or more of citric acid, acetic acid, lactic acid, and hydrochloric acid.

[0031] As a further improvement of the present invention, the pH value of the composite acidity regulator is 5.5 to 6.5.

[0032] As a further improvement of the present invention, the pH value of the composite silica precursor solution is 5.5 to 6.5.

[0033] As a further improvement of the present invention, the step of uniformly mixing the suspension of the core solid mixture with the colloidal SiO2 precursor to obtain a mixed emulsion includes:

[0034] The core solid mixture is uniformly mixed with the core solvent at a certain temperature to obtain a core suspension;

[0035] The core suspension and the colloidal SiO2 precursor were uniformly mixed in an ultrasonic emulsifier to obtain a mixed emulsion.

[0036] As a further improvement of the present invention, the core solvent includes one or more of dimethyl sulfoxide, diethyl ether, and acetone;

[0037] The ratio of the core solid mixture to the core solvent is 0.05 to 2 by mass.

[0038] As a further improvement of the present invention, the mixing temperature of the core solid mixture and the core solvent is 30 to 60°C.

[0039] As a further improvement of the present invention, the ratio of the core suspension to the colloidal SiO2 precursor is 0.1 to 1.9 by mass.

[0040] As a further improvement of the present invention, the ultrasonic emulsification frequency is set to 20-25 kHz; the shear stress stirring speed is set to 10000-30000 rad / min; and the emulsification time is set to 2-8 h.

[0041] As a further improvement of the present invention, the shell curing agent includes one or more of ammonia, a blend of propionate and ethanol, trimethylolpropane, ethylenediamine, and hexamethylenediamine modified products.

[0042] As a further improvement of the present invention, when the shell curing agent is added to the mixed emulsion, the ratio of the shell curing agent to the mixed emulsion is 0.01 to 0.1 by mass.

[0043] As a further improvement of the present invention, a shell curing agent is added to the mixed emulsion, the pH is adjusted to neutral after standing, and the active fracturing proppant is obtained after supercritical CO2 freeze-drying.

[0044] The present invention also provides an active fracturing proppant, wherein the active fracturing proppant is prepared by any of the preparation methods described above.

[0045] The present invention also provides an application of the aforementioned active fracturing proppant in the underground coal gasification process.

[0046] The beneficial effects of this invention are:

[0047] The present invention provides a method for synthesizing an active fracturing proppant. First, a catalytically active core solid mixture and a colloidal SiO2 precursor are prepared. Then, the core solid mixture is made into a suspension and uniformly mixed with the colloidal SiO2 precursor to form an emulsion. Finally, a shell curing agent is added to the resulting emulsion to cure the shell, yielding an active fracturing proppant with a core-shell structure. Through this method, the present invention proposes a method for preparing a catalytically active fracturing proppant using a colloidal-emulsion method with core-shell coupling coating. This fracturing proppant has an inert supporting shell and a catalytically active core structure. It not only expands the gasification contact surface during the pumping and delivery period and the initial underground ignition stage, but also releases an active agent with catalytic CO generation function during the high-temperature underground gasification stage, thereby improving the CO selectivity in the products, achieving CO2 emission reduction, and ultimately improving the utilization rate of coal resources.

[0048] Other features and advantages of the invention will be set forth in the following description, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention may be realized and obtained by means of the structures pointed out in the description and the drawings. Attached Figure Description

[0049] Figure 1 This is a schematic flowchart of the synthesis method of the active fracturing proppant of the present invention;

[0050] Figures 2-5 The particle size distribution of the active fracturing proppant prepared in Examples 1 to 4 of this invention is shown. Detailed Implementation

[0051] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0052] To address the problems of incomplete underground coal gasification, low yield of effective components, and high CO2 production in existing underground coal gasification technologies, this invention provides a synthesis process for a core-shell type active fracturing proppant, mainly consisting of three steps: ① preparation of catalytic active centers; ② preparation of colloidal SiO2 precursors; ③ preparation of core-shell particles. For details, please refer to... Figure 1As shown, a catalytically active core solid mixture and a colloidal SiO2 precursor were prepared. The core solid mixture was then made into a suspension and uniformly mixed with the colloidal SiO2 precursor to form an emulsion. Finally, a shell curing agent was added to the resulting emulsion, and after curing, an active fracturing proppant with a core-shell structure was obtained. The main preparation methods in each step are detailed below:

[0053] 1. Preparation of active sites;

[0054] The silane coupling agent is uniformly sprayed onto the surface of the alkali metal compound at a mass ratio of 0.1 to 2.7. The solid alkali metal compound can be continuously stirred during spraying. After spraying, the mixture is allowed to stand for 5 to 12 hours to obtain solid mixture A.

[0055] Solid mixture A is mechanically mixed thoroughly with aluminate coupling agent, and then allowed to stand for 2–12 hours to obtain solid mixture B.

[0056] Solid mixture B and alkaline earth metal compound were thoroughly ball-milled and mixed. After mixing, the mixture was allowed to stand for 2–12 hours to obtain a core solid mixture with catalytic activity.

[0057] Alkali metal compounds include one or more combinations of sodium carbonate, sodium bicarbonate, sodium hydroxide, sodium chloride, potassium hydroxide, potassium carbonate, potassium bicarbonate, and potassium chloride.

[0058] The silane coupling agent includes one or more combinations of 3-glycidyl etheroxypropyltrimethoxysilane, (3-(2,3-epoxypropoxy)propyltriethoxysilane), 3-(2,3-epoxypropoxy)propylmethyldimethoxysilane, and isobutyltriethoxysilane.

[0059] Among them, the aluminate coupling agent includes one or more combinations of distearyloxyisopropyl aluminate, aluminum isopropoxide, and anti-settling aluminate.

[0060] Alkaline earth metal compounds include one or more combinations of calcium oxide, calcium carbonate, and magnesium hydroxide.

[0061] 2. Preparation of colloidal SiO2 precursor;

[0062] A composite acidity regulator was prepared by mixing an organic solvent with an acidity regulator at room temperature, with the pH value controlled between 5.5 and 6.5.

[0063] Two silica precursor solutions were uniformly mixed, with the molar ratio controlled at 1–15. The mixture was thoroughly mixed at 25–50°C and stirred for 1–3 hours to obtain a mixed solution.

[0064] The acidity adjuster was added dropwise to the above mixed solution using an acid dropper, while the reaction temperature of the mixed solution was controlled at 25–50°C and continuously stirred. The pH was monitored online using an online pH meter. The titration was completed when the pH value of the solution reached between 5.5 and 6.5, yielding the composite silica precursor solution.

[0065] The above-mentioned composite silica precursor solution was allowed to stand for 6–24 hours at a constant temperature and humidity of 25–50°C to obtain a composite solution. The composite solution was then subjected to vacuum distillation to obtain a colloidal SiO2 precursor.

[0066] The organic solvents include one or more combinations of methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, and pentanol.

[0067] Acidity regulators include one or more combinations of citric acid, acetic acid, lactic acid, and hydrochloric acid.

[0068] The preferred silica precursor is two of the following: hexamethylcyclotrisiloxane (D3), octamethylcyclotetrasiloxane (D4), tetraethyl orthosilicate (TEOS), methyltrioxysilane (MTMS), and vinyltriethoxysilane (A151).

[0069] 3. Preparation of core-shell particles

[0070] The core solid mixture and the core solvent are uniformly mixed at 30-60°C, with a mixing ratio of core solid mixture / core solvent of 0.05-2 by mass. The mixture is stirred continuously for 1-2 hours to obtain a core suspension.

[0071] The core suspension and SiO2 precursor were placed in an ultrasonic emulsifier, with a mixing ratio of core suspension / SiO2 precursor of 0.1–1.9 by mass. The ultrasonic emulsification frequency was controlled at 20–25 kHz, the shear stress stirring speed was set in the range of 10,000–30,000 rad / min, and the emulsification time was controlled in the range of 2–8 h to form an emulsion.

[0072] Add an appropriate amount of shell curing agent to the above emulsion. The addition ratio is based on the mass ratio: shell curing agent / emulsion A = 0.01~0.1.

[0073] The mixture was allowed to stand for 1–5 hours, and then centrifuged and washed with water 3–10 times until the pH was neutral. Finally, it was freeze-dried with supercritical CO2 for 5–24 hours to obtain the target product.

[0074] The core solvent includes one or a combination of dimethyl sulfoxide, diethyl ether, and acetone.

[0075] The curing agent includes one or more of the following: ammonia, a blend of propionate (TMPTA-MAZ) and ethanol, trimethylolpropane tris(TMP), ethylenediamine (EDA), and hexamethylenediamine-modified AMINE248.

[0076] In addition, the present invention also provides an active fracturing proppant prepared by the aforementioned method and its application in the underground coal gasification process.

[0077] The synthesis method of the active fracturing proppant of the present invention will be illustrated below with specific embodiments and test examples.

[0078] Example 1

[0079] (1) Preparation of catalytic active centers:

[0080] 3-Glycidyl etheroxypropyltrimethoxysilane was uniformly sprayed onto the surface of sodium carbonate at a mass ratio of 0.7 (3-glycidyl etheroxypropyltrimethoxysilane / sodium carbonate). The sodium carbonate particles were continuously stirred during spraying. After spraying, the mixture was allowed to stand for 5 hours, then thoroughly mechanically mixed with the aluminate coupling agent aluminum isopropoxide. After standing for 5 hours, it was thoroughly ball-milled with calcium carbonate. The mixture was then allowed to stand for 2 hours to obtain a catalytically active core solid mixture ①.

[0081] (2) Preparation of colloidal SiO2 precursor:

[0082] A composite acidity regulator was prepared by mixing 2-propanol and citric acid at room temperature and controlling the pH value to 5.5. A mixed solution was prepared by uniformly mixing hexamethylcyclotrisiloxane (D3) and vinyltriethoxysilane (A151) at a molar ratio of 2:1, thoroughly mixing at 35°C, and stirring for 1 hour.

[0083] The acidity regulator was added dropwise to the above mixed solution using an acid dropper, while the reaction temperature of the mixed solution was controlled at 25℃ and the mixture was continuously stirred. The pH was monitored online using an online pH meter. The titration was stopped when the pH of the solution reached 5.5, yielding the composite silica precursor solution. This solution was then allowed to stand at a constant temperature and humidity of 25℃ for 6 hours to obtain the composite solution. The solution was then subjected to vacuum distillation to obtain the colloidal SiO2 precursor ①.

[0084] (3) Preparation of core-shell particles:

[0085] The core solid mixture ① was uniformly mixed with diethyl ether at 30°C, with a mixing ratio of solid mixture ① / diethyl ether = 0.05 by mass. The mixture was stirred continuously for 1 hour to obtain a core suspension ①. This core suspension ① was then placed in an ultrasonic emulsifier with a mixing ratio of core suspension ① / SiO2 precursor ① = 1.9 by mass. The ultrasonic emulsification frequency was controlled at 20 kHz, the shear stress stirring speed was set at 10000 rad / min, and the emulsification time was controlled at 2 hours to form a mixed emulsion ①. An appropriate amount of a propionate and ethanol blend was then added dropwise to the emulsion, with a dropwise ratio of propionate and ethanol blend / mixed emulsion ① = 0.01 by mass.

[0086] The mixture was left to stand for 2 hours, and then centrifuged and washed with water 5 times until the pH was neutral. After being freeze-dried with supercritical CO2 for 6 hours, the target product, active fracturing proppant, was finally obtained, referred to here as WHK-①.

[0087] Example 2

[0088] (1) Preparation of catalytic active centers:

[0089] Isobutyltriethoxysilane was uniformly sprayed onto the surface of potassium carbonate at a mass ratio of 2.6 (isobutyltriethoxysilane / potassium carbonate). The potassium carbonate particles were continuously stirred during spraying. After spraying, the mixture was allowed to stand for 12 hours, then thoroughly mechanically mixed with the aluminate coupling agent distearate. After standing for 10 hours, it was then thoroughly ball-milled with calcium carbonate. The mixture was then allowed to stand for 8 hours to obtain a catalytically active core solid mixture ②.

[0090] (2) Preparation of colloidal SiO2 precursor:

[0091] A composite acidity regulator was prepared by mixing pentanol and lactic acid at room temperature and controlling the pH value to 6.5. A mixed solution was obtained by uniformly mixing methyltrioxysilane (MTMS) and vinyltriethoxysilane (A151) at a molar ratio of 12:1 and stirring thoroughly at 35°C for 3 hours.

[0092] The acidity regulator was added dropwise to the above mixed solution using an acid dropper, while the reaction temperature of the mixed solution was controlled at 45℃ and the mixture was continuously stirred. The pH was monitored online using an online pH meter. The titration was stopped when the pH of the solution reached 6.5, yielding the composite silica precursor solution. This solution was then allowed to stand at a constant temperature and humidity of 45℃ for 12 hours to obtain the composite solution. The solution was then subjected to vacuum distillation to obtain the colloidal SiO2 precursor ②.

[0093] (3) Preparation of core-shell particles:

[0094] The core solid mixture ② was uniformly mixed with acetone at 60°C, with a mixing ratio of solid mixture ② / acetone = 0.05 by mass. The mixture was stirred continuously for 1 hour to obtain a core suspension ②. This suspension was then placed in an ultrasonic emulsifier with a mixing ratio of core suspension ② / SiO2 precursor ② = 0.1 by mass. The ultrasonic emulsification frequency was controlled at 25 kHz, the shear stress stirring speed was set at 30000 rad / min, and the emulsification time was controlled at 5 hours to form a mixed emulsion ②. A suitable amount of trimethylolpropane tris(TMP) was added dropwise to the mixed emulsion, with a dropwise ratio of TMP / mixed emulsion ② = 0.1 by mass.

[0095] The mixture was allowed to stand for 5 hours, and then centrifuged and washed with water 8 times until the pH was neutral. Finally, it was freeze-dried with supercritical CO2 for 24 hours to obtain the target product, abbreviated as WHK-②.

[0096] Example 3

[0097] (1) Preparation of catalytic active centers:

[0098] 3-(2,3-epoxypropoxy)propylmethyldimethoxysilane was uniformly sprayed onto the surface of potassium carbonate at a mass ratio of 3-(2,3-epoxypropoxy)propylmethyldimethoxysilane / potassium carbonate = 2. The potassium carbonate particles were continuously stirred during the spraying process. After spraying, the mixture was allowed to stand for 12 hours, then thoroughly mechanically mixed with the aluminate coupling agent distearate. After standing for 8 hours, it was then thoroughly ball-milled with calcium carbonate. The mixture was then allowed to stand for 8 hours to obtain a catalytically active core solid mixture ③.

[0099] (2) Preparation of colloidal SiO2 precursor:

[0100] A composite acidity regulator was prepared by mixing methanol and acetic acid at room temperature and controlling the pH value to 6.0. A mixed solution was obtained by uniformly mixing methyltrioxysilane (MTMS) and hexamethylcyclotrisiloxane (D3) at a molar ratio of 7:1 and stirring thoroughly at 45°C for 2.5 h.

[0101] The acidity regulator was added dropwise to the above mixed solution using an acid dropper, while the reaction temperature of the mixed solution was controlled at 45℃ and the mixture was continuously stirred. The pH was monitored online using an online pH meter. The titration was stopped when the pH of the solution reached 6.0, yielding the composite silica precursor solution. This solution was then allowed to stand at a constant temperature and humidity of 45℃ for 12 hours to obtain the composite solution. The solution was then subjected to vacuum distillation to obtain the colloidal SiO2 precursor ③.

[0102] (3) Preparation of core-shell particles:

[0103] The core solid mixture ③ was uniformly mixed with acetone at 45°C, with a mass ratio of solid mixture ③ / acetone = 1.5. The mixture was stirred continuously for 1.5 hours to obtain a core suspension ③. This suspension was then placed in an ultrasonic emulsifier with a mass ratio of core suspension ③ / SiO2 precursor ③ = 1.2. The ultrasonic emulsification frequency was controlled at 22 kHz, the shear stress stirring speed was set at 20000 rad / min, and the emulsification time was controlled at 6 hours to form a mixed emulsion ③. An appropriate amount of ammonia was then added dropwise to the emulsion, with a mass ratio of ammonia / mixed emulsion ③ = 0.16.

[0104] The mixture was allowed to stand for 3 hours, and then centrifuged and washed with water 6 times until the pH was neutral. Finally, it was freeze-dried with supercritical CO2 for 12 hours to obtain the target product WHK-③.

[0105] Example 4

[0106] (1) Preparation of catalytic active centers:

[0107] (3-(2,3-epoxypropoxy)propyltriethoxysilane) was uniformly sprayed onto the surface of sodium chloride at a mass ratio of (3-(2,3-epoxypropoxy)propyltriethoxysilane) / sodium chloride = 1.7. The sodium chloride particles were continuously stirred during the spraying process. After spraying, the mixture was allowed to stand for 10 hours, then thoroughly mechanically mixed with an aluminate coupling agent (anti-settling aluminate). After standing for 10 hours, it was thoroughly ball-milled with calcium carbonate. The mixture was then allowed to stand for 10 hours to obtain a catalytically active core solid mixture ④.

[0108] (2) Preparation of colloidal SiO2 precursor:

[0109] A composite acidity regulator was prepared by mixing ethanol and hydrochloric acid at room temperature and controlling the pH value to 6.2. A mixed solution was prepared by uniformly mixing hexamethylcyclotrisiloxane (D3) and methyltrioxysilane (MTMS) at a molar ratio of 8:1 and stirring thoroughly at 35°C for 1 hour.

[0110] The acidity regulator was added dropwise to the above mixed solution using an acid dropper, while the reaction temperature of the mixed solution was controlled at 30℃ and continuous stirring was maintained. The pH was monitored online using an online pH meter. The titration was stopped when the pH of the solution reached 5.5, yielding the composite silica precursor solution. This solution was then allowed to stand at a constant temperature and humidity of 20℃ for 10 hours to obtain the composite solution. The solution was then subjected to vacuum distillation to obtain the colloidal SiO2 precursor ④.

[0111] (3) Preparation of core-shell particles:

[0112] The core solid mixture ④ was uniformly mixed with dimethyl sulfoxide at 40°C, with a mixing ratio of solid mixture ④ / dimethyl sulfoxide = 0.05 by mass. The mixture was stirred continuously for 1.5 h to obtain a core suspension ④. This core suspension ④ was then placed in an ultrasonic emulsifier with a mixing ratio of core suspension ④ / SiO2 precursor ④ = 0.5 by mass. The ultrasonic emulsification frequency was controlled at 22 kHz, the shear stress stirring speed was set at 12000 rad / min, and the emulsification time was controlled at 5 h to form an emulsion ④. An appropriate amount of hexamethylenediamine modifier was then added dropwise to the emulsion, with a dropwise addition ratio of hexamethylenediamine modifier / emulsion ④ = 0.8 by mass.

[0113] The mixture was allowed to stand for 3 hours, and then centrifuged and washed with water four times until the pH was neutral. Finally, it was freeze-dried with supercritical CO2 for 10 hours to obtain the target product WHK-④.

[0114] Test Example 1

[0115] Particle size and distribution testing

[0116] Information about particle diffusion velocity can be obtained from dynamic light scattering (DLS), and then the hydrodynamic radius can be obtained from the Stokes-Einstein equation (Equation 1).

[0117]

[0118] In the formula, d(h) is the hydrodynamic diameter—equivalent diameter; kB is the Boltzmann constant; T is the absolute temperature; h is the viscosity; and D is the diffusion coefficient—the particle diffusion rate—the rate of fluctuation.

[0119] In this invention, the shell thickness is adjusted by varying the ratio of the core suspension to the colloidal SiO2 precursor. With a consistent amount of core suspension, the core suspension / SiO2 precursor ratios in examples WHK-① to WHK-④ are 1.9, 0.1, 1.2, and 0.5, respectively, arranged from smallest to largest as follows: WHK-② < WHK-④ < WHK-③ < WHK-①. Dynamic light scattering test results show the mechanical radii and their distribution range (e.g., ...) of examples WHK-① to WHK-④. Figures 2-5The particle sizes shown are 1000–1400 μm, 1300–1800 μm, 1000–1600 μm, and 1200–1800 μm, respectively (see Table 1). The test results indicate that the particles in the embodiments of this invention are all millimeter-scale, with a particle size range between 1000 and 1800 μm, and the particle size distribution of samples under the same formulation is uniform. Proppants within this particle size range can well meet the fracturing requirements for coalbed methane reservoir stimulation. Furthermore, given a consistent amount of core suspension, the more colloidal SiO2 precursor used (i.e., the smaller the ratio of core suspension to SiO2 precursor), the larger the particle size, indicating a thicker shell layer. This obvious inverse relationship between the two is consistent with the design concept of this invention; the thickness of the proppant shell layer can be adjusted by regulating the ratio of their amounts.

[0120] Table 1. Particle size distribution of each embodiment

[0121] WHK-① 1000～1400 WHK-② 1300～1800 WHK-③ 1000～1600 WHK-4 1200～1800

[0122] Test Example 2

[0123] To ensure that the pumping pipeline is not corroded by the core active catalyst material, underground coal gasification projects require that the active proppant material involved in this invention maintain a shell fracture rate of less than 10% during the pumping process underground. Therefore, compressive strength tests were conducted on Examples ① to ④. The breakage rates of Examples WHK-① to WHK-④ at 15 MPa are shown in Table 2. The results show that their breakage rates are all less than 10%, thus meeting the above requirements.

[0124] Table 2 Breakage rate of each embodiment

[0125] WHK-① 3 WHK-② 10 WHK-③ 8 WHK-4 9

[0126] Test Example 3

[0127] Core catalytic activity test

[0128] Examples WHK-① to WHK-④ underwent artificial shell-breaking treatment. Using existing inert proppant particles as a reference, the carbon conversion rate of the five types of samples was tested using a thermogravimetric analyzer. The experimental conditions were: heating to 120℃ at a rate of 15℃ / min under N2 atmosphere, holding for 15min, then heating to 900℃, stabilizing for 10min, and switching to CO2. Coal gasification experiments showed (see Table 3) that, compared with the inert reference sample, the introduction of catalyst in the active fracturing proppant prepared in Examples 1 to 4 of this invention improved CO selectivity (i.e., the yield of CO production) while significantly reducing the CO2 component concentration. CO selectivity = (CO production / total crude gas production) × 100%.

[0129] Table 3 CO selectivity and CO2 yield for each example

[0130] inert particles 17 43 WHK-① 21 32 WHK-② 23 31 WHK-③ 32 26 WHK-4 49 16

[0131] In summary, this invention is the first to propose improving the carbon conversion rate during underground coal gasification by altering the structure and composition of the fracturing proppant, thus addressing issues such as low coal resource utilization and high CO2 production. The final experimental results show that the prepared active fracturing proppant material has a core-shell structure with a particle size between 1000 and 1800 μm, and the particle size distribution is uniform under the same formulation. The outer shell has a maximum temperature resistance of 300℃, and the core-shell proppant breakage rate is less than 10% at 15 MPa. Furthermore, the thickness of the outer shell can be controlled by adjusting the ratio of the core suspension to the SiO2 precursor. Simultaneously, while expanding the gasification contact surface, this proppant can release a catalytically active gasifying agent at the coal seam support point, thus significantly improving CO selectivity during carbon conversion rate testing. In addition, the solid active center involved in the invention has low cost and is environmentally friendly. After release, it can directly contact coal, significantly reducing the activation energy of the reaction when the coal surface reacts with water and oxygen to generate the effective component CO, thus improving the carbon conversion rate. Experiments show that the CO selectivity is increased by 4-32% compared with the condition without a catalyst, and the CO2 component concentration in the crude coal gas is reduced by 11-27%.

[0132] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for synthesizing an active fracturing proppant, characterized in that, The method includes: Preparation of a catalytically active core solid mixture; The preparation of the catalytically active core solid mixture includes: A silane coupling agent was uniformly sprayed onto the surface of an alkali metal compound, and after standing, a solid mixture A was obtained. The solid mixture A is thoroughly mixed with the aluminate coupling agent, and after standing, solid mixture B is obtained. The solid mixture B is thoroughly mixed with an alkaline earth metal compound and allowed to stand to obtain a core solid mixture with catalytic activity. The alkali metal compounds include one or more of sodium carbonate, sodium bicarbonate, sodium hydroxide, sodium chloride, potassium hydroxide, potassium carbonate, potassium bicarbonate, and potassium chloride. The silane coupling agent includes one or more of 3-glycidyl etheroxypropyltrimethoxysilane, (3-(2,3-epoxypropoxy)propyltriethoxysilane), 3-(2,3-epoxypropoxy)propylmethyldimethoxysilane, and isobutyltriethoxysilane. The ratio of the silane coupling agent to the alkali metal compound is 0.1 to 2.7 by mass. Preparation of colloidal SiO2 precursor; The suspension of the core solid mixture is uniformly mixed with the colloidal SiO2 precursor to obtain a mixed emulsion; The step of uniformly mixing the suspension of the core solid mixture with the colloidal SiO2 precursor to obtain a mixed emulsion includes: The core solid mixture is uniformly mixed with the core solvent at a certain temperature to obtain a core suspension; The core suspension and the colloidal SiO2 precursor were uniformly mixed in an ultrasonic emulsifier to obtain a mixed emulsion. By mass ratio, the ratio of the core suspension to the colloidal SiO2 precursor is 0.1 to 1.

9. The ultrasonic emulsification frequency was set to 20–25 kHz; the shear stress stirring speed was set to 10,000–30,000 rad / min; and the emulsification time was set to 2–8 h. A shell curing agent is added to the mixed emulsion, and after curing, an active fracturing proppant with a core-shell structure is obtained.

2. The method for synthesizing the active fracturing proppant according to claim 1, characterized in that, The aluminate coupling agent includes one or more of distearyloxyisopropyl aluminate, aluminum isopropoxide, and anti-settling aluminate.

3. The method for synthesizing the active fracturing proppant according to claim 1, characterized in that, The alkaline earth metal compounds include one or more of calcium oxide, calcium carbonate, and magnesium hydroxide.

4. The method for synthesizing the active fracturing proppant according to claim 1, characterized in that, The preparation of the colloidal SiO2 precursor includes: An organic solvent is mixed with an acidity regulator, and the pH value of the mixture is adjusted to obtain a composite acidity regulator. Two silica precursor solutions were uniformly mixed at a certain temperature to obtain a mixed solution; After adjusting the pH value of the mixed solution with the composite acidity regulator, a composite silica precursor solution is obtained. The composite silica precursor solution was allowed to stand and then distilled under reduced pressure to obtain a colloidal SiO2 precursor.

5. The method for synthesizing the active fracturing proppant according to claim 4, characterized in that, The silica precursor solution includes any two of hexamethylcyclotrisiloxane, octamethylcyclotetrasiloxane, tetraethyl orthosilicate, methyltrioxysilane, and vinyltriethoxysilane.

6. The method for synthesizing the active fracturing proppant according to claim 5, characterized in that, The molar ratio of the two silica precursor solutions is 1 to 15, and the mixing temperature is 25 to 50°C.

7. The method for synthesizing the active fracturing proppant according to claim 4, characterized in that, The organic solvent includes one or more of methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, and pentanol; The acidity regulator includes one or more of citric acid, acetic acid, lactic acid, and hydrochloric acid.

8. The method for synthesizing the active fracturing proppant according to claim 4, characterized in that, The pH value of the composite acidity regulator is 5.5~6.

5.

9. The method for synthesizing the active fracturing proppant according to claim 4, characterized in that, The pH value of the composite silica precursor solution is 5.5~6.

5.

10. The method for synthesizing the active fracturing proppant according to claim 1, characterized in that, The core solvent includes one or more of dimethyl sulfoxide, diethyl ether, and acetone; The ratio of the core solid mixture to the core solvent is 0.05 to 2 by mass.

11. The method for synthesizing the active fracturing proppant according to claim 1, characterized in that, The mixing temperature of the core solid mixture and the core solvent is 30~60℃.

12. The method for synthesizing the active fracturing proppant according to claim 1, characterized in that, The shell curing agent includes one or more of the following: ammonia, a blend of propionate and ethanol, trimethylolpropane, ethylenediamine, and hexamethylenediamine modified products.

13. The method for synthesizing the active fracturing proppant according to claim 12, characterized in that, When the shell curing agent is added to the mixed emulsion, the ratio of shell curing agent to mixed emulsion is 0.01 to 0.1 by mass.

14. The method for synthesizing the active fracturing proppant according to claim 1, characterized in that, A shell curing agent was added to the mixed emulsion, and after standing, the pH was adjusted to neutral. The active fracturing proppant was then obtained by supercritical CO2 freeze-drying.

15. An active fracturing proppant, characterized in that, The active fracturing proppant is prepared by the preparation method according to any one of claims 1-14.

16. The application of the active fracturing proppant as described in claim 15 in the underground coal gasification process.

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