CN118757133A - A method for producing hydrogen by coordinated injection of supercritical water and oxygen in situ from coal - Google Patents

Abstract

The invention discloses a method for producing hydrogen by coordinated injection of in-situ supercritical water and oxygen into coal, belonging to the technical field of underground energy mining. A plurality of first connected main fracturing surfaces are formed along the direction of a deep coal seam by arranging wells and fracturing. Supercritical water and oxygen are injected into the deep coal seam, and a redox reaction occurs in the deep coal seam to generate synthetic gas containing _H2 and _CO2 . During the reaction, the temperature of each area of the deep coal seam is monitored, and the temperature presents a gradient partition change along the advancing direction of the working face and is cyclically advanced to form an oxidation excitation heat generating area, a supercritical water gasification area, a pyrolysis reaction area, and a preheating area. Oxygen is stopped and preheated according to the temperature change. Cyclic preheating and oxygen supply are performed until the mining of the working face is completed. During the preheating process, the goaf is filled to ensure that the heat continues to move forward along the advancing direction of the working face. The invention ensures the continuous advancement of fracturing-gasification-filling by monitoring and regulating the temperature of the coal seam partitions, and accurately improves the hydrogen production effect.

Description

A method for producing hydrogen by coordinated injection of supercritical water and oxygen in situ from coal

Technical Field

The invention belongs to the technical field of underground energy mining and relates to a method for producing hydrogen by coordinated injection of in-situ supercritical water and oxygen into coal.

Background Art

The "in-situ modified fluidized mining method" is a new mining method that uses chemical leaching, dissolution, pyrolysis, gasification, liquefaction, and biological technologies in situ underground to transform the physical and chemical properties of the ore body and mine the useful minerals in it in a fluidized manner. When the water temperature reaches 374.3℃ and the pressure reaches 22.05MPa, the state changes to a supercritical state. Supercritical water has extremely strong mass transfer, heat transfer and solubility properties. It is often used as an excellent reaction medium and can achieve efficient and clean gasification of various biomass, coal, petroleum coke and organic waste solids and liquids. Under high temperature and high pressure environment, supercritical water interacts with coal to produce endothermic reduction reactions to generate _H2 and _CO2 , of which _H2 is regarded as a clean energy, promoting the development of energy structure in a more diversified and sustainable direction. The coal seam is buried at a depth of 1000m, and the ground stress it is subjected to has reached or exceeded 25MPa, which is very easy to form a high-pressure pyrolysis environment for supercritical water reaction.

Patent CN117211741A relates to a method for in-situ hydrogen production in medium-deep and deep water-invaded gas reservoirs. Natural gas is produced by injecting chemical ignition agents and oxygen-containing gases into the well network, and the competitive adsorption mechanism of carbon dioxide is used to displace the adsorbed natural gas, thereby improving the recovery rate of medium-deep water-invaded gas reservoirs and sealing carbon dioxide in situ.

Patent CN112878978A discloses a supercritical water fracturing method for underground coal gasification to produce hydrogen, which is to simultaneously perform backward staged fracturing on the production well and the combustion well, so that cracks appear between the extraction well and the combustion well. After the fracturing is completed, oxygen is injected into the combustion well for gasification, and the production well is sealed by adjusting the injection pressure and the temperature generated by the coal seam combustion to make the clean water reach a supercritical state, thereby generating secondary fracturing. At this stage, the traditional gasification mode reaction is promoted, and at the same time, a part of the supercritical water oxygen injection gasification reaction occurs, thereby increasing the hydrogen production.

Patent CN114876437A discloses a method for in-situ hydrogen production in coal seams using supercritical water. A homogeneous chamber is arranged at the bottom of a vertical well, and an annular electric heater is set outside the homogeneous chamber. A mixed slurry is first injected into the homogeneous chamber, and oxygen is injected to react when the water in the homogeneous chamber reaches a supercritical state. After the chemical reaction, carbon dioxide and hydrogen are dissolved in the supercritical water, and the hydrogen is collected by releasing pressure through a ground pipe.

Patent CN114876437A discloses an underground coal in-situ pyrolysis hydrogen production device and method, which is to set injection wells, production wells, and gas conversion production wells in the coal seam, implement fracturing and connection, and pyrolyze the coal seam by injecting a mixture of supercritical water vapor and supercritical carbon dioxide, or perform preliminary pyrolysis of the coal seam by inert gas and combustion-supporting agent pyrolysis gas, and then use a catalyst filling layer and a steam reforming catalyst filling layer to achieve distributed recovery of oil and gas.

The existing technology (patents CN117211741A and CN112878978A) is mainly based on traditional gasification technology, while patent CN112878978A adds supercritical water secondary fracturing to increase hydrogen production. Patent CN117780326A injects supercritical water and supercritical carbon dioxide mixed phase to enhance pyrolysis reaction and combines it with steam reforming reaction to produce hydrogen. Patent CN114876437A adopts a green and efficient supercritical water single-well gasification process and collects the gas products.

However, the supercritical water gasification process of the above-mentioned prior art has the following significant disadvantages: 1) Compared with supercritical water, chemical ignition agents are easily affected by underground water inrush, which in turn affects the gasification efficiency. Although supercritical water has stronger heat and mass transfer properties, it can make up for this defect to a certain extent, but it cannot completely solve the problem. 2) If the energy required to directly inject supercritical water vapor in a high-temperature, high-pressure state is high, the corresponding ground costs will also increase relatively; or supercritical water vapor and supercritical carbon dioxide are mixed and injected at the same time for pyrolysis, the system links are relatively complex and difficult to control, which has a great impact on the recovery rate. 3) During the supercritical water gasification process, the reaction range and range are constantly changing. How to accurately detect the changes in its range (temperature, gas) is a technical problem for regulating the reaction. When the reaction continues to advance, if the parameter thresholds of each link cannot be quantified and monitored, and the gasification chamber is not filled in time, it is easy to leak, and even cause the roof to break, which will eventually continue to affect the surface; 4) The reaction range of a single well is limited, resulting in low gasification efficiency. At the same time, the downhole environment is complex, and the temperature and gas distribution are uneven, making it difficult to accurately monitor and control, affecting hydrogen production. If there is a problem at the wellhead, it is difficult to ensure the overall stability of the system; 5) After the synthesis gas (carbon dioxide, hydrogen, etc.) leaves the well, it is separated on the ground. Whether it is hydrogen storage off-site or carbon dioxide storage on-site, the process is relatively cumbersome and costly.

Summary of the invention

The present invention overcomes the shortcomings of the prior art and proposes a method for producing hydrogen by coordinated injection of in-situ supercritical water and oxygen into coal; under the premise of visual monitoring, the continuous advancement of fracturing-gasification-filling is guaranteed, while reducing the cost expenditure of storage, transportation, etc.

In order to achieve the above object, the present invention is achieved through the following technical solutions:

A method for producing hydrogen by coordinated injection of in-situ supercritical water and oxygen into coal, comprising the following steps:

S1. Well layout: from the ground to the deep coal seam, the first fracturing well, injection well, oxygen injection well, monitoring well, production well, and second fracturing well are arranged in sequence; among which, multiple monitoring wells are arranged along the direction of the deep coal seam;

S2, fracturing: hydraulically fracturing the interface between the deep coal seam and the bottom plate through the first fracturing well and the second fracturing well to generate cracks; and finally forming a plurality of first connected main fracturing surfaces along the direction of the deep coal seam;

S3, reaction: inject supercritical water into the deep coal seam through the injection well, and inject oxygen into the deep coal seam through the oxygen injection well, so that the supercritical water and oxygen undergo redox reaction in the deep coal seam to generate synthetic gas containing _H2 and _CO2 , and extract _H2 on the ground;

The redox reaction gradually advances and develops in the deep coal seam along the direction of the working face. During the reaction, the temperature of each area of the deep coal seam is monitored. When the redox reaction starts to operate normally, the temperature shows a gradient zone change and cyclic advancement along the direction of the working face: the oxidation excitation heat generation zone, with a temperature of 900℃~1200℃; the supercritical water gasification zone, with a temperature of 600℃~900℃; the pyrolysis reaction zone, with a temperature of 400℃~600℃; the preheating zone, with a temperature ≤400℃; when the preheating zone appears, when the percentage of gas production reduction in the production well and the monitoring well exceeds 20%, stop oxygen injection and only inject supercritical water to preheat the deep coal seam; after the preheating is completed, continue to introduce oxygen for redox reaction, and circulate the preheating and oxygenation operations until the working face mining is completed;

During the preheating process of deep coal seams, goafs are gradually formed in the oxidation-induced heat generation zone and the supercritical water gasification zone; the heat dissipation in the goaf causes the temperature to drop, and the goaf is filled at this time to ensure that the heat continues to advance along the direction of the working face.

Furthermore, the fracturing fluid used in hydraulic fracturing is added with metal proppants that respond to magnetic fields; magnetic particles are added to the slurry used for filling; a bottom hole electromagnetic flow emission detection device is set at the bottom of the monitoring well; the bottom hole electromagnetic flow emission detection device is used to monitor the flow of fracturing fluid and slurry.

Furthermore, a horizontal well fracturing pipeline is arranged at the interface fracture position, and both ends of the horizontal well fracturing pipeline are connected to the first fracturing well and the second fracturing well respectively; multi-stage directional fracturing is performed on the deep coal seam through the first fracturing well, the second fracturing well and the horizontal well fracturing pipeline to form multiple first connected main fracturing surfaces.

Furthermore, multiple environmental parameter monitors are installed on the horizontal well fracturing pipeline, and the environmental parameter monitors include temperature sensors and high-temperature ultrasonic sensors. The temperature sensor monitors the temperature while emitting low-frequency ultrasonic waves for detection through the high-temperature ultrasonic sensor. When the high-temperature ultrasonic conversion image shows that the three-dimensional space inside the coal seam gradually appears an area with a temperature greater than 800°C, and the temperature sensor monitors the temperature to reach 800°C, the monitoring well and the production well are opened. At this stage, the coal undergoes an oxidation-reduction reaction with supercritical water and oxygen in situ to produce _H2 and _CO2 .

Furthermore, the first fracturing well and the second fracturing well extend through the deep coal seam into the deep formation; the deep formation is fractured by the same fracturing process as in step S2, and enters the deep formation close to the working surface in the form of a horizontal well, and is connected by multi-stage directional fracturing until multiple second connected main fracturing surfaces appear, and the second connected main fracturing surfaces are used to seal the subsequently separated _CO2 .

Furthermore, the synthesis gas containing _H2 and _CO2 produced by the reaction is discharged to the ground along the production well by an extraction pump, and _CO2 and _H2 are obtained after separation and purification, or the synthesis gas containing _H2 and _CO2 produced by the reaction is injected into the second fracturing well at high pressure by an injection pump until it enters the deep formation to convert _CO2 into liquid and separate from _H2 , and _CO2 is sealed in situ; _H2 is discharged from the first fracturing well.

Furthermore, in step S1, the wells are arranged in the form of a group of wells: the group of wells includes a first fracturing well located in the center, and six injection wells, six oxygen injection wells, multiple circles of monitoring wells, six production wells, and six second fracturing wells that are uniformly arranged in a circle outward around the first fracturing well; wherein each circle of monitoring wells has six wells; the distribution of the group of wells on the ground is in the shape of a hexagonal snowflake; the injection wells, production wells, oxygen injection wells, and monitoring wells all enter the deep coal seam in the form of vertical wells; the first fracturing well and the second fracturing well are vertical wells that pass through the deep coal seam and extend into the deep stratum.

Furthermore, an electric heater is installed at the bottom of the injection well, which heats the injected water to 600°C to make the water reach a supercritical state; the electric heater is connected to a temperature monitoring device; or a steam boiler is arranged above the injection well, which heats the water to generate high-temperature and high-pressure steam, and the high-temperature and high-pressure steam is injected into the deep coal seam through the injection well.

Furthermore, when the thickness of the deep coal seam is ≥10m, hydraulic fracturing is performed at the interface between the deep coal seam and the bottom plate, and at the interface between the deep coal seam and the top plate through the first fracturing well and the second fracturing well to produce cracks, forming double-interface fracturing; redox reactions are carried out simultaneously on the first connected main fracturing surface formed by the double interface.

The beneficial effects of the present invention compared with the prior art are as follows:

1. The process of supercritical water oxygen in-situ mining of coal resources to produce hydrogen rationally utilizes the dynamic evolution characteristics of the disappearance of the porous medium skeleton structure, optimizes the gasification process steps, and overcomes the technical bottlenecks of poor formation sealing, easy gas leakage, and difficult control of the gasification process in traditional underground coal combustion gasification. At the same time, the principle of high-pressure liquefaction and competitive adsorption of carbon dioxide is used to separate it from hydrogen underground, ultimately realizing fluidized mining of deep coal seams, hydrogen production and zero carbon emissions, with low hydrogen production costs and considerable resource conversion rates.

2. It integrates multifunctional real-time monitoring technology (electromagnetic induction detection and real-time temperature monitoring) to achieve visual detection of the three stages of "fracturing-gasification-filling", and real-time monitoring of fracturing crack expansion, gasification cavity evolution, gasification zoning, filling material flow, etc. Based on monitoring images and monitoring data, it can flexibly change the fracturing, filling, and gasification conditions to control the final gasification effect.

3. Use 600℃ supercritical water to preheat, pyrolyze and displace the multi-stage fracturing coal reservoir, avoiding the occurrence of initial fissure water or steam condensation in the coal seam, reducing heat dissipation in the gasification stage, and improving gasification efficiency; at the same time, combined with the oxygen injection link, the temperature is greatly increased, and while supplementing the heat source, the physical and chemical reactions in the preheating and pyrolysis intervals are intensified, which promotes the connectivity between the main fracturing surface and the fracture network and reduces the heat generation cost.

4. The multi-well linkage layout of the working face layer has significantly improved the reliability and efficiency of operations. It can be realized under the conditions of complex environment, uneven temperature and gas distribution, combined with precise real-time monitoring and control technology, to clarify the succession time of each link, and make flexible replacement and adjustment to maintain the continuous operation and stable output of the gas production system. Based on the zoning characteristics of the working face, the supercritical water gasification range is precisely controlled to the maximum, so as to positively guide the continuous progress of the hydrogen production reaction, thereby maximizing the hydrogen extraction efficiency.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of the connection of a device for producing hydrogen by coordinated injection of in-situ supercritical water and oxygen into coal in Example 1.

FIG. 2 is a schematic diagram showing the connection of a device for producing hydrogen by coordinated injection of in-situ supercritical water and oxygen into coal in Example 2.

FIG3 is a schematic diagram of the in-situ supercritical water and oxygen coordinated injection production process.

FIG. 4 is a schematic diagram of the local structure after deep coal seam mining and filling.

Figure 5 is a schematic diagram of the partition and advancement direction.

Figure 6 is a schematic diagram of the surface well pattern layout.

Numbers in the figure:

1-computer; 2-first pressure regulating fracturing pump; 3-injection pump; 4-temperature monitoring device; 5-supercritical water injection system regulating valve; 6-oxygen injection pump; 7-oxygen injection valve; 8-temperature monitoring meter; 10-filling pump; 13-ground filling system; 1901-first gas separation device; 1902-second gas separation device; 20-extraction pump; 2201-first purification device; 2202-second purification device; 23-second pressure regulating fracturing pump; 24-second fracturing fluid storage tank; 29-top plate; 30-electric heater; 31-deep coal seam; 32-bottom plate; 33-rock layer; 34-deep formation; 35-first fracturing well; 36-injection well; 3 7-oxygen injection well; 38-monitoring well; 41-gas storage workshop; 43-production well; 44-second fracturing well; 45-hydrogen storage tank; 46-first connected main fracturing surface; 47-directional fracturing surface; 48-first fracturing fluid storage tank; 49-second connected main fracturing surface; 50-grouting range; 51-goaf; 52-horizontal well fracturing pipeline; 53-environmental parameter monitor; 5301-high-temperature ultrasonic sensor; 5302-low-frequency ultrasonic wave; 54-bottom hole electromagnetic flow emission and detection device; 5501-oxidation excitation heat generation zone; 5502-supercritical water gasification zone; 5503-pyrolysis reaction zone; 5504-preheating zone; 56-working face advancement direction.

DETAILED DESCRIPTION

In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention clearer, the present invention is further described in detail in conjunction with the embodiments and the accompanying drawings. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. The technical solutions of the present invention are described in detail below in conjunction with the embodiments and the accompanying drawings, but the scope of protection is not limited thereto.

Example 1

This embodiment proposes a method for producing hydrogen by coordinated injection of in-situ supercritical water and oxygen into coal, which is mainly used for converting deep coal seams into hydrogen under the action of supercritical water and directly sealing the produced _CO2 gas deep underground.

The object of pyrolysis mining in this embodiment is a deep coal seam 31 with a depth of 1000m and a thickness of 4m. The top of the deep coal seam 31 is the roof 29; the bottom of the deep coal seam 31 is the floor 32, the rock layer 33, and the deep stratum 34 from top to bottom.

The specific implementation steps are:

S1. Referring to FIG6, a group of wells are arranged on the ground with a spacing of 300 to 500 meters, and the group of wells includes a first fracturing well 35 located in the center, and six injection wells 36, six oxygen injection wells 37, four circles of monitoring wells 38 (each circle has six monitoring wells 38), six production wells 43, and six second fracturing wells 44 arranged uniformly in a circle around the first fracturing well 35; the group of wells are distributed on the ground in a hexagonal snowflake shape. The injection well 36, the production well 43, the oxygen injection well 37, and the monitoring well 38 all use vertical wells to enter the deep coal seam 31; the first fracturing well 35 and the second fracturing well 44 use vertical wells to pass through the deep coal seam 31 and extend all the way to the deep formation 34.

A temperature monitoring meter 8 is connected to the top of the monitoring well 38; a bottom hole electromagnetic flow transmitting and detecting device 54 is arranged at the bottom of the monitoring well 38; the bottom hole electromagnetic flow transmitting and detecting device 54 comprises an electromagnetic flow coil and an electromagnetic induction receiver, the electromagnetic flow frequency is 10~500kHz, and the current intensity is 100~300A. It can detect the migration of the proppant based on electromagnetic induction, thereby realizing the perspective detection of the fracturing surface and the connection of the fracture, and can be used for the flow monitoring of the modified proppant and the modified filling material.

Referring to Fig. 1, hydraulic fracturing is performed to generate cracks at the interface between the deep coal seam 31 and the bottom plate 32 through the first fracturing well 35 and the second fracturing well 44. During fracturing, the water injection peak fracturing is 40-100 MPa, the water temperature is controlled at 15-30°C, the fracturing fluid is mainly water, and metal proppants are added. The metal proppants used are responsive to the magnetic field, and the materials can be selected from Fe, Al, etc., and the selected materials are subjected to anti-corrosion modification.

Afterwards, a horizontal well fracturing pipeline 52 is arranged at the interface fracture position, and both ends of the horizontal well fracturing pipeline 52 are connected to the first fracturing well 35 and the second fracturing well 44 respectively; multi-stage directional fracturing is performed on the deep coal seam 31 through the first fracturing well 35, the second fracturing well 44 and the horizontal well fracturing pipeline 52.

During the fracturing process, the bottom hole electromagnetic flow emission and detection device 54 at the bottom of the monitoring well 38 is synchronously opened to emit electromagnetic flow to monitor the migration of metal proppants until multiple directional fracturing surfaces 47 appear in the horizontal direction of the deep coal seam 31, and multiple first connected main fracturing surfaces 46 appear in the vertical direction. At this time, the first stage of fracturing is completed. A multi-section environmental parameter monitor 53 is set on the horizontal well fracturing pipeline 52. The environmental parameter monitor 53 is a collection of a series of monitoring equipment, including temperature sensors, pressure sensors, component detection and analysis devices, and high-temperature ultrasonic sensors 5301, which are used to monitor the temperature, pressure, gas composition and sound wave propagation speed in the medium of each section, and are used to determine the subsequent reaction range. The spacing between environmental parameter monitors 53 is 10m.

The first fracturing well 35 is connected to a first pressure-regulating fracturing pump 2, which is connected to a first fracturing fluid storage tank 48; the second fracturing well 44 is connected to a second pressure-regulating fracturing pump 23, which is connected to a second fracturing fluid storage tank 24; the first pressure-regulating fracturing pump 2 and the second pressure-regulating fracturing pump 23 can control the pressure and flow rate of the injected fracturing fluid, and combine with the bottom hole electromagnetic flow emission and detection device 54 to sense the proppant with magnetic particles, coordinate and control the fracturing to achieve uniform distribution of the proppant, present a three-dimensional sensing image, and ensure visual monitoring and regulation of fracturing.

S2. On the basis of the first fracturing well 35 and the second fracturing well 44, the deep formation 34 is fractured by the same fracturing process as in step S1, and the deep formation 34 close to the working surface is entered in the form of a horizontal well, and is connected by means of multi-stage directional fracturing until multiple second connected main fracturing surfaces 49 appear. The second connected main fracturing surfaces 49 are used to seal the subsequently separated carbon dioxide, and the preliminary preparations are completed.

S3. Connect the supercritical water injection system to the injection well 36 through the injection pump 3. An electric heater 30 is installed at the bottom of the injection well 36. The electric heater 30 uses 4 20×100 single-strand electric heating rods to heat the high-pressure injected water. First, the injected water is heated to 600°C to ensure that it reaches the supercritical state, and the deep coal seam 31 is preheated to make the deep coal seam 31 reach a temperature at which an oxidation reaction can occur. The electric heater 30 is connected to a temperature monitoring device 4. Of course, a steam boiler can also be arranged above the injection well 36 to heat the water to generate high-temperature and high-pressure steam, and the supercritical water vapor is injected into the deep coal seam 31 through the injection well 36.

By adjusting the injection pump 3, the injected steam reaches a supercritical state with a temperature as high as 600°C, and then is injected into the deep coal seam 31; after preheating part of the coal body to reach the oxidation reaction temperature, oxygen is injected through the oxygen injection pump 6 connected to the upper part of the oxygen injection well 37, and the temperature is monitored by the temperature sensor in the environmental parameter monitor 53. The high-temperature ultrasonic sensor 5301 emits a 600KHz low-frequency ultrasonic wave 5302 for detection. When the high-temperature ultrasonic conversion image shows that a large area with a temperature higher than 800°C gradually appears in the three-dimensional space inside the coal seam, and the temperature monitoring of multiple temperature sensors reaches 800°C, the monitoring well 38 and the production well 43 are opened at this time, and the gas pressure is monitored. The gas production of the monitoring well 38 and the production well 43 gradually increases. At this stage, the coal undergoes an oxidation-reduction reaction with supercritical water and oxygen in situ to produce _H2 and _CO2 . The redox temperature refers to the temperature at which oxygen reacts with pyrolysis gas at a certain temperature to release heat and increase the internal temperature of the reservoir. When the temperature at which coal and oxygen react is reached, the temperature at which oxygen and pyrolysis gas react is regarded as the critical temperature of the reaction between coal and oxygen, that is, the redox temperature.

The synthesis gas such as H ₂ , CO ₂ , and CH ₄ produced by the reaction is discharged to the ground along the production well 43 through the extraction pump 20, and is initially recovered through the first gas separation device 1901 and the first purification device 2201, mainly separating the gas mainly composed of a small amount of oil and gas such as CH ₄ , and recovering it to the gas storage workshop 41. The separated synthesis gas of CO ₂ and H ₂ is then injected into the second fracturing well 44 at high pressure through the injection pump 23 until it enters the deep formation 34. The high pressure in the deep formation 34 converts CO ₂ into a liquid state and separates it from H _2. At the same time, as the deep ground temperature increases in a gradient, CO ₂ is converted into a supercritical state, and a series of chemical reactions occur with the minerals in the rock formation, and physical adsorption promotes the on-site storage of CO _{2. H 2} is discharged from the first fracturing well 35, and then is recovered through the second gas separation device 1902 and the second purification device 2202 in turn, and is recovered to the hydrogen storage tank 45.

The reaction equation involved in the in-situ storage of _CO2 is:

S4. The redox reaction gradually advances and develops in the deep coal seam 31 along the working face advancement direction 56. Simultaneously, the high-temperature ultrasonic sensor 5301 is used to monitor the shape of the gasification cavity. When a large area of temperature reduction appears in the gasification cavity and the temperature measured by multiple temperature sensors at the front end decreases, that is, the temperature gradient along the working face advancement direction 56 changes to a temperature trend of "600°C→800°C→1200°C→450°C". At the same time, when the gas production in the production well 43 and the monitoring well 38 decreases by more than 20%, the oxygen injection valve 7 on the oxygen injection well 37 is closed, and the supercritical water injection system regulating valve 5 on the injection well 36 is kept open to preheat the deep coal seam 31.

It should be noted that the temperature trend of "600°C → 800°C → 1200°C → 450°C" along the working face advancement direction 56 corresponds to the four stages of preheating, pyrolysis, gasification heating, and cooling after gasification. This temperature change characteristic is used as a periodic temperature cycle to advance forward.

Referring to FIG5 , when the gasification system starts to operate normally, that is, oxygen injection starts to stimulate a series of chemical reactions, the temperature values of the distributed multiple environmental parameter monitors 53 show a gradient partition change from left to right, namely, the oxidation excitation heat generation zone 5501, whose temperature is 900°C~1200°C; the supercritical water gasification zone 5502, whose temperature is 600°C~900°C; the pyrolysis reaction zone 5503, whose temperature is 400°C~600°C; and the preheating zone 5504, whose temperature is ≤400°C. In the supercritical water gasification zone 5502, supercritical water and coal body react violently to produce a large amount of high-temperature H ₂ , CO ₂ , and H ₂ O. This area is the main gas production area. At the same time, supercritical water and oxygen are alternately injected into the injection well 36 and the oxygen injection well 37 to enable the reaction to continue.

When the pyrolysis reaction zone 5503 is at 400℃～600℃, the supercritical water and a large amount of generated gas carry heat, so that the volatile organic matter in the coal reacts with the supercritical water to generate pyrolysis gas such as _CH4 . Oxygen reacts with pyrolysis gas at a certain temperature to release heat and increase the temperature inside the reservoir. When the temperature at which the coal and oxygen react is reached, the temperature at which the oxygen and pyrolysis gas react is regarded as the critical temperature of the reaction between the coal and oxygen, that is, the redox temperature.

The temperature of the preheating zone 5504 is ≤400°C. The reaction enters the preheating zone, which is mainly reflected in the change of the physical structure of the coal. At this time, hydrocarbon gases such as H ₂ and CO ₂ are extracted to the ground through the extraction system.

S5. At this time, referring to Figures 3 and 4, a goaf 51 is formed in the area of the deep coal seam 31 that has fully reacted. After the gasification proceeds to a certain distance, the area of the goaf 51 increases, and it is difficult for the supercritical water to maintain high temperature and high pressure. The front temperature gradually decreases to 400-500°C, and there is a risk of the roof breaking. At this time, oxygen injection is stopped and the filling and temperature recovery phase is started. When the goaf 51 is gradually filled, the front temperature gradually rises.

The specific method of filling the goaf 51 is as follows: connect the ground filling system 13 to the monitoring well 38 via the filling pump 10, and the monitoring well 38 is used as a filling well. Fill the filling slurry with magnetic particles into the goaf 51, and simultaneously open the bottom hole electromagnetic flow emission detection device 54. When the front temperature rises from 450°C to 600°C again, and the detection image shows that the grouting range 50 in the goaf 51 has a filling height of 4m, the filling slurry injection rate is reduced by 18%, the filling work is gradually stopped, and the bottom hole electromagnetic flow emission detection device 54 is turned off. The purpose of the filling work is to support the overlying rock formation in time through the filling material, prevent heat from escaping from the top and bottom plates of the goaf 51, and prevent problems such as leakage of the gasification cavity and surface collapse. After filling, the goaf 51 can ensure that heat is continuously pushed forward to promote the normal reaction of the subsequent working face.

It should be noted that the ground filling system 13 adds magnetic particles such as iron powder and nickel powder to the filling slurry to ensure fluidity while providing electrical conductivity of the slurry. The bottom hole electromagnetic flow emission detection device 54 measures the distribution within the grouting range 50, that is, the flow of the filling slurry. The grouting pressure range is 15~50MPa, and the grouting rate range is 50~200L/min, which are adjusted appropriately according to the on-site conditions. The detection image shows that the filling height reaches 90%~100% of the coal seam thickness, and the filling slurry injection rate is reduced by 15%~30%. At the same time, with the continuous injection of the filling slurry in the goaf 51, when the filling space is basically full, the pumping pressure gradually increases, the pumping pressure increases by 10%~30%, and the temperature rises to above 600℃, and the filling work can be stopped. It should be noted that the number and spacing of the filling wells can be flexibly adjusted. The water in the filling slurry can react with coal and oxygen to produce hydrogen and carbon dioxide. The remaining solid filling plays a role in supporting the overburden and controlling the stability of the mining site, thus achieving mining, reaction and filling at the same time.

S6. Loop steps S3 to S5, and continue to advance along the working face advancement direction 56 until the mining of the working face is completed.

It should be noted that the computer 1 is connected to the above-mentioned electronic control equipment to realize automatic control and monitoring of the operation of the entire system.

Example 2

Different from Example 1, the object of pyrolysis mining in this embodiment is a deep coal seam 31 with a depth of 1500m and a thickness of 10m. For pyrolysis of a coal seam with a thickness of 10m or even thicker, as shown in Figure 2, hydraulic fracturing is performed at the interface between the deep coal seam 31 and the bottom plate 32 and the interface between the deep coal seam 31 and the top plate 29 through the first fracturing well 35 and the second fracturing well 44 to generate cracks, forming double-interface fracturing. Subsequent redox reactions are carried out simultaneously on the first connected main fracturing surface 46 formed by the double interface. The remaining steps are the same as in Example 1.

The above content is a further detailed description of the present invention in combination with a specific preferred embodiment. It cannot be determined that the specific embodiments of the present invention are limited to this. For ordinary technicians in the technical field to which the present invention belongs, several simple deductions or substitutions can be made without departing from the present invention, which should be regarded as belonging to the present invention and the scope of patent protection determined by the submitted claims.

Claims (9)

1. The hydrogen production method by the coordinated injection of the supercritical water and the oxygen in situ of the coal is characterized by comprising the following steps of:

S1, well arrangement: a first fracturing well (35), an injection well (36), an oxygen injection well (37), a monitoring well (38), a production well (43) and a second fracturing well (44) are sequentially arranged from the ground to the deep coal seam (31); wherein, a plurality of monitoring wells (38) are arranged along the trend of the deep coal seam (31);

S2, fracturing: performing hydraulic fracturing to generate cracks at the interface of the deep coal seam (31) and the bottom plate (32) through the first fracturing well (35) and the second fracturing well (44); and finally forming a plurality of first communicated main fracture surfaces (46) along the trend of the deep coal seam (31);

S3, reaction: injecting supercritical water into the deep coal seam (31) through an injection well (36), injecting oxygen into the deep coal seam (31) through an oxygen injection well (37), and enabling the supercritical water and the oxygen to undergo oxidation-reduction reaction in the deep coal seam (31) to generate synthesis gas containing H ₂ and CO ₂, and extracting H ₂ on the ground;

The oxidation-reduction reaction gradually advances and develops along the advancing direction (56) of the working surface in the deep coal seam (31), the temperature of each region of the deep coal seam (31) is monitored in the reaction process, and when the oxidation-reduction reaction starts to normally operate, the temperature shows gradient partition change along the advancing direction (56) of the working surface and is cyclically advanced: the temperature of the oxidation heat generating area (5501) is 900-1200 ℃ in sequence; a supercritical water gasification zone (5502) with a temperature of 600-900 ℃; the pyrolysis reaction zone (5503) has the temperature of 400-600 ℃; a preheating zone (5504) with a temperature of 400 ℃ or less; stopping oxygen injection when the percentage of gas yield reduction in the simultaneous production well (43) and the monitoring well (38) exceeds 20% when a preheating zone (5504) appears, and only injecting supercritical water to preheat the deep coal seam (31); after the preheating is finished, continuing to introduce oxygen to perform oxidation-reduction reaction, and circularly preheating and introducing oxygen until the working face mining is finished;

In the preheating process of the deep coal seam (31), a goaf (51) is gradually formed in the oxidation-induced thermal zone (5501) and the supercritical water gasification zone (5502); the heat dissipation in the goaf (51) reduces the temperature, and the goaf (51) is filled at the moment so as to ensure that the heat is continuously pushed forward along the pushing direction (56) of the working surface.

2. The method for producing hydrogen by the coordinated injection of supercritical water and oxygen in situ of coal according to claim 1, wherein a metal propping agent responsive to a magnetic field is added into a fracturing fluid adopted by hydraulic fracturing; magnetic induction particles are added into the slurry adopted in filling; a bottom hole electromagnetic current emission detection device (54) is arranged at the bottom of the monitoring well (38); the bottom hole electromagnetic current emission detection device (54) is used for carrying out flow monitoring on fracturing fluid and slurry.

3. The method for producing hydrogen by the coordinated injection of supercritical water and oxygen in situ of coal according to claim 1, wherein a horizontal well fracturing pipeline (52) is arranged at the position of an interface fracture, and two ends of the horizontal well fracturing pipeline (52) are respectively communicated with a first fracturing well (35) and a second fracturing well (44); the deep coal seam (31) is subjected to multistage directional fracturing through a first fracturing well (35), a second fracturing well (44) and a horizontal well fracturing pipeline (52) to form a plurality of first communicated main fracturing surfaces (46).

4. The method for producing hydrogen by the coordinated injection of supercritical water and oxygen in situ of coal according to claim 3, wherein a plurality of sections of environment parameter monitors (53) are arranged on a horizontal well fracturing pipeline (52), and the environment parameter monitors (53) comprise a temperature sensor and a high-temperature ultrasonic sensor (5301); the temperature sensor monitors the temperature and emits low-frequency ultrasonic waves (5302) through the high-temperature ultrasonic sensor (5301) to detect, the high-temperature ultrasonic conversion image shows that the three-dimensional space inside the coal bed gradually has a region with the temperature higher than 800 ℃, meanwhile, the temperature sensor monitors the temperature to 800 ℃, a monitoring well (38) and a production well (43) are opened at the moment, and oxidation-reduction reaction is carried out on the coal in situ, supercritical water and oxygen at the moment, so that H ₂ and CO ₂ are generated.

5. The method for producing hydrogen by in situ supercritical water and oxygen co-injection of coal according to claim 1, wherein the first fracturing well (35) and the second fracturing well (44) extend all the way through the deep coal seam (31) into the deep formation (34); and (2) fracturing the deep stratum (34) by the same fracturing process in the step (S2), entering the deep stratum (34) close to the working surface in a horizontal well mode, and communicating in a multi-stage directional fracturing mode until a plurality of second communicating main fracturing surfaces (49) appear, wherein the second communicating main fracturing surfaces (49) are used for sealing and storing the subsequently separated CO ₂.

6. The method for producing hydrogen by the coordinated injection of supercritical water and oxygen in situ of coal according to claim 5, wherein the synthesis gas containing H ₂ and CO ₂ generated by the reaction is discharged to the ground along a production well (43) through a discharge pump (20), and CO ₂ and H ₂ are obtained through separation and purification; or the synthesis gas containing H ₂ and CO ₂ generated by the reaction is injected into the second fracturing well (44) through an injection pump (23) under high pressure until the synthesis gas enters into a deep stratum (34) to convert CO ₂ into liquid state to be separated from H ₂, and CO ₂ is sealed in place; h ₂ is discharged from the first fracturing well (35).

7. The method for producing hydrogen by the coordinated injection of supercritical water and oxygen in situ of coal according to claim 5, wherein in step S1, well arrangement is performed in a group well mode: the group of wells comprise a first fracturing well (35) positioned at the center, six injection wells (36), six oxygen injection wells (37), a plurality of circles of monitoring wells (38), six production wells (43) and six second fracturing wells (44) which are sequentially and uniformly circumferentially arranged outwards around the first fracturing well (35); six monitoring wells (38) are arranged in each circle; the group wells are in a hexagonal snowflake shape at the distribution position of the ground; the injection well (36), the production well (43), the oxygen injection well (37) and the monitoring well (38) all adopt a vertical well mode to enter the deep coal seam (31); the first fracturing well (35) and the second fracturing well (44) extend into the deep stratum (34) through the deep coal seam (31) by adopting a vertical well.

8. The method for producing hydrogen by the coordinated injection of supercritical water and oxygen in situ of coal according to claim 1, wherein an electric heater (30) is arranged at the bottom of an injection well (36), and the electric heater (30) heats the injected water to 600 ℃ so as to enable the water to reach a supercritical state; the electric heater (30) is connected with a temperature monitoring device (4); or a steam boiler is arranged above the injection well (36), water is heated by the steam boiler to generate high-temperature and high-pressure steam, and the high-temperature and high-pressure steam is injected into the deep coal seam (31) through the injection well (36).

9. The method for producing hydrogen by the in-situ supercritical water and oxygen coordinated injection of coal according to claim 1, wherein when the thickness of the deep coal seam (31) is more than or equal to 10m, hydraulic fracturing is performed to the interface between the deep coal seam (31) and the bottom plate (32) and the interface between the deep coal seam (31) and the top plate (29) through the first fracturing well (35) and the second fracturing well (44) to generate cracks, so that double-interface fracturing is formed; the redox reactions proceed simultaneously on the first communicating major fracture face (46) formed by the dual interface.