CN103670338B - A kind of coal bed gas and coal mining method altogether - Google Patents

Abstract

The invention relates to a method for co-mining coal bed methane and coal. The method comprises: a drilling step; a fracturing and penetration step; a step of extracting the coal bed methane; The method of the invention combines the underground coal gasification technology with the coalbed methane extraction technology, which can not only use the underground gasification to heat the coalbed at high temperature, increase the gas permeability of the coalbed, improve the recovery rate of the coalbed methane, but also use the coalbed methane for drilling and fracturing penetration process to improve the efficiency of underground gasification coal mining.

Description

A method for co-mining coalbed methane and coal

technical field

The invention relates to a mining technology of a novel underground carbon-containing organic mineral reservoir, in particular to a method for co-mining underground coal bed gas and coal.

Background technique

Coal is the main energy source in my country, accounting for about 70% of the primary energy composition, and the total amount of resources is relatively abundant. The total amount of resources is predicted to be about 4.5 trillion tons (shallow than 2000 meters), of which the resources with a depth of 600 meters or less The coal reserves only account for about 25%. Based on the current coal mining depth (400 meters), at least 80% of the total underground coal resources in my country have not been developed and utilized. The development of deep coal resources will be A long-term job. With the increase of mining depth, the content of coal-associated resources - gas (also known as coalbed methane) also increases rapidly. According to the evaluation of coalbed methane resources, the geological resources of shallow coalbed methane buried below 2000 meters in my country are about 36 trillion cubic meters. Ranking third in the world, it is equivalent to the amount of onshore conventional natural gas resources.

Although my country is rich in coalbed methane resources, the occurrence conditions of coalbed methane in my country vary widely among regions, and most areas are characterized by low pressure, low permeability, and low saturation. Except for the Qinshui Basin and the eastern edge of the Ordos Basin, other areas have achieved large-scale, Industrialization development is difficult. Moreover, there are many mines with high gas and coal and gas outbursts. With the increase of mining depth, the ground stress and gas pressure will further increase, and the difficulty of underground drainage will increase. Not only that, with the continuous increase of mining depth, the geological environment is more complex, the ground stress increases, the water inflow increases, and the ground temperature rises, leading to an increase in sudden engineering disasters and major vicious accidents, such as mine rock burst, gas Explosions, intensification of mine pressure, large deformation of roadway surrounding rock, rheology, and rising ground temperature have posed a huge threat to the safe and efficient mining of deep resources. Therefore, whether it is considered from the perspective of safety requirements in the coal mining process, or from the perspective of improving the utilization rate of coal resources and promoting the sustainable development of the coal industry, it is necessary to study and solve the mining and utilization of difficult coal and coalbed methane.

Publicly available information shows that the underground coal gasification technology can controllably burn the underground coal seam, and produce gas energy that can be effectively used through pyrolysis and chemical action, so as to realize the in-situ gasification of coal. The technology has achieved considerable success for the gasification of shallow coal seams and has achieved commercial operation in the former Soviet Union. After the oil crisis in the last century, some European countries used underground coal gasification technology to obtain energy from deep coal seams that cannot be exploited by conventional methods. Among them, from 1978 to 1986, Belgium and Germany jointly carried out the first deep coal seam gasification in Turin, Belgium. Underground gasification test (the depth of the coal seam is 860m); in 1988, six member states of the European Union established the European Underground Coal Gasification Working Group, and in 1998 conducted a medium-deep coal seam underground gasification (coal seam The depth is 550-650m) test, which verified the feasibility of deep underground coal seam gasification technology in Europe.

Underground coal gasification technology is currently the most effective technology for mining deep coal resources, but the existing underground coal gasification technology usually only considers the gasification of coal seams, and with the increase of coal mining depth, the content of coal seam gas will increase rapidly, so It is inevitable to encounter problems with the extraction of coalbed methane, and the specific problems include: (1) For coalbeds rich in coalbed methane, if the gasification of coalbeds is directly implemented, there will be problems such as threats to safety and waste of resources ; (2) If the conventional coalbed methane mining method is adopted without considering the combination with underground gasification technology, then the subsequent implementation of underground coal gasification will have overlapping functions such as drilling and increase investment costs; ( 3) Injecting CO ₂ into the coal seam can improve the recovery of CH ₄ in the coal seam, but it can only increase the production of coalbed methane in the early stage of coalbed methane extraction, but in the later stage, the cracks are easy to close, and the production of coalbed methane drops rapidly; (4) as One of the intermediates and products in the gasification process, CO ₂ participates in a series of redox reactions, and is an important component in the export gas, accounting for about 15-60%, which is related to the calorific value of the gas and the effective component content One of the important factors, but the existing technology usually does not consider the recovery and utilization of CO ₂ .

Contents of the invention

The inventors found that there are some similarities and synergistic effects between coalbed methane extraction and underground coal gasification in drilling, fracturing, porosity enhancement and other technological links, and the underground coal technology and coalbed methane extraction technology can be combined for comprehensive consideration Collaborative development and utilization of underground coal resources and coalbed methane resources. On the one hand, the high-temperature medium produced by underground coal gasification can be used to heat the coal seam. The adsorption capacity of CH ₄ in the coal seam gas is greatly reduced at high temperature. At the same time, the gas expands when the heat energy is transferred to the coal seam. CBM seepage velocity; on the other hand, the process of coalbed gas fracturing in the early stage to increase production, drainage and pressure reduction will improve the gas permeability of the coal seam, which will be conducive to the establishment of the fire zone of the underground coal gasification process and the subsequent gasification process. The permeability of the coal seam can be increased by 2 to 10 times after heating, which is more conducive to promoting the desorption of CH ₄ . In addition, from the perspective of products, the cost of separating carbon dioxide and methane is lower than that of nitrogen and methane. Carbon monoxide and hydrogen in coal gas can be directly synthesized into methane, and the final product is methane like coalbed methane. It can be seen that coalbed methane extraction can be combined with underground gasification, and the two promote and cooperate with each other, which can not only increase the recovery rate of coalbed methane, but also increase the reaction surface area by improving the gas permeability of the coal seam, which is also beneficial to coal. Underground gasification reaction.

In view of the difficulties of coalbed methane mining in my country, the advantages of underground coal gasification technology in coal mining, and the above-mentioned synergistic effect in the process technology of the two, the purpose of this invention is to provide a new method for co-mining coalbed methane and coal , this method couples coalbed methane mining and underground coal gasification technology, and a medium containing carbon dioxide is used in the co-mining process.

For this reason, the present invention provides a kind of coalbed methane and coal mining method, comprising:

1) Drilling step: Drilling from the ground to the underground carbon-containing organic mineral reservoir, such as a coal seam, to provide at least one air inlet borehole and at least one gas outlet borehole to communicate the coal seam with the ground;

2) Fracturing penetration step: injecting a fracturing medium containing carbon dioxide into the coal seam through the air inlet borehole, forcing the fracturing medium to flow in the coal seam, and discharging it from the gas outlet borehole, so that The air inlet borehole and the air outlet borehole are connected through connecting cracks in the coal seam;

3) The step of extracting coalbed methane: injecting a displacement medium into the coal seam through the inlet borehole, displacing the coalbed methane in the coal seam, and collecting it through the gas outlet borehole;

4) Ignition step: establishing a fire zone in the coal seam at the bottom of the gas outlet borehole to ignite the coal seam; and

5) Underground gasification step: injecting a carbon dioxide-containing gasification agent into the coal seam through the air inlet borehole, the gasification agent and the coal seam undergo gasification and pyrolysis reactions to generate heat energy and gasification gas, The thermal energy is transferred to the interior of the coal seam to generate pyrolysis gas, and the coal seam gas is displaced synchronously to generate free methane. Drain and collect.

However, it needs to be emphasized that the method of the present invention is not a simple combination of underground gasification and coalbed methane extraction technology, and the respective original processes must be improved to adapt to the coupling of the two process technologies. Specifically, the following at least An improvement:

a. When drilling for coalbed methane, it is preferable to drill horizontal wells in the vertical direction of the main fractures in the coal seam. The direction of the main fracture is located in the horizontal plane of the coal seam, which can be determined by means of in-situ stress measurement and directional coring analysis. The current extraction of coalbed methane does not consider the direction of the horizontal well

b. The distance of the horizontal section of the coalbed methane horizontal well is determined according to the vertical extension range of the underground gasification fire zone (that is, the direction of the horizontal well), and the main parameters that determine this extension range include the distribution and size of the in-situ stress of the coal seam, and the original permeability of the coal seam And the permeability at different temperatures, the reactivity of coal, the structure and faults of coal seams, the rock mechanical properties of coal rocks at different temperatures, etc. If necessary, it is also necessary to combine field tests to sum up the appropriate length. The current coalbed methane extraction does not consider the length of the horizontal section of the horizontal well according to this standard;

c. The specifications of coalbed gas inlet and outlet pores (ie material, inner and outer diameters, well structure, and construction technology) are determined according to the underground gasification process, specifically the gas inlet and outlet volume, temperature, operating pressure, service life, etc. However, in coalbed methane extraction, the specifications of the inlet and outlet pores are only determined according to the pressure and the gas output;

d. When drilling vertical wells for coalbed methane extraction, consider the lowering depth of the casing and the trajectory of the horizontal section of the horizontal well in the lower part of the coal seam, close to the floor, so as to ensure the recovery rate of the coal seam. This is not considered in coalbed methane drainage;

e. When designing the gasifier for underground gasification, consider the range of coal bed gas fracturing (determined by the distribution of the pressure value of each hole on site), and determine the layout range of the furnace area; when designing the gasifier for underground gasification, it is only based on the influence range of the thermal state of the coal seam (Determined by on-site temperature measuring holes) Determine the layout range of the furnace area, and the range of coalbed gas fracturing is obviously larger than this thermal state influence range;

f. Before the underground gasification is ignited, monitor the methane content of the inlet and outlet pores, control the oxygen content in the intake air, and ensure that no explosion accidents occur; since the coalbed methane extraction is carried out in a cold state without oxygen intervention, there is no need to consider the explosion of methane question.

In a preferred embodiment, the drilling is based on drilling horizontal wells at the coal seam level and along the vertical direction of the main fractures of the coal seam.

In a preferred embodiment, coalbed methane drainage considers the lowering depth of the casing and the trajectory of the horizontal section of the horizontal well in the lower part of the coal seam, 1 to 3 meters away from the coal seam floor, when drilling the vertical well.

In a preferred embodiment, the fracturing medium is a mixture of carbon dioxide and oxygen, and the volume concentration of oxygen is below 20%.

In a preferred embodiment, the displacement of the coalbed methane in the coal seam in the step 3) of extracting the coalbed methane is to inject CO ₂ or nitrogen for displacement.

In a preferred embodiment, the method further includes: 6) recovering CO ₂ step: recovering the CO ₂ produced in the underground gasification step, and using a part of the recovered CO ₂ as the gasification agent.

In a preferred embodiment, the CO _{2 recovered in the CO 2 recovering} step is used as a fracturing medium in the fracturing through-through step or as a displacement medium in the coalbed methane extraction step.

In a preferred embodiment, the method further includes: 7) CO ₂ sequestration step: after the coal seam between the inlet borehole and the gas outlet borehole completes the underground gasification, part of the recovered CO _2. Store in the burn-out area (the burn-out area is the cavity left after the coal seam gasification), for burial and storage.

In a preferred embodiment, it also includes performing a safety detection step before the ignition step 4) to ensure ignition safety.

In a preferred embodiment, the fracturing medium in the fracturing penetration step is gaseous, liquid or supercritical carbon dioxide, or a mixture of carbon dioxide and oxygen in which the volume concentration of oxygen is below 20%, or is made of liquid CO _2. Hydrogel (such as guar gum, whose function is to increase the consistency of the fracturing medium, reduce the fluid loss of the fracturing medium, and increase the width of the fracture) and chemical additives (such as potassium chloride, whose function is to make the fracturing medium form stable system).

In a preferred embodiment, the volume concentration of oxygen in the carbon dioxide-containing gasification agent in the underground gasification step is 20-70%, so as to ensure that the ash does not melt.

In a preferred embodiment, the volume concentration of oxygen in the carbon dioxide-containing gasification agent in the underground gasification step is 20-50%, so as to construct a gasification channel.

In a preferred embodiment, the volume concentration of oxygen in the carbon dioxide-containing gasification agent in the underground gasification step is 40-70%, which is used for coalbed gasification after the gasification channel is constructed.

In a preferred embodiment, if the water content of the coal seam is less than the water required for coal seam gasification after the coal bed methane is extracted, the gasification agent is a mixture of oxygen, carbon dioxide and water vapor. The amount of water vapor added should be the amount of water required for coal seam gasification minus the water content of the coal seam and divided by the decomposition rate of water vapor.

In a preferred embodiment, the fire zone is set up by electric ignition (for example, an electric heater is placed in the coal seam of the fire zone to be established, the pressure of the ignition hole is controlled to be greater than the hydrostatic head, and the ignition hole is guaranteed to be anhydrous, and then energized to heat , ignite the coal seam to establish a fire zone) or solid fuel ignition (for example, place hot coke in the coal seam to be established in the fire zone, feed oxygen to burn the coke and then ignite the coal seam to establish a fire zone) to complete.

In a preferred embodiment, in the step of breaking through the fracturing, when the pressure in the air inlet hole drops sharply (meaning that the pressure drop reaches about 5% of the original pressure per day or greater) and the air outlet hole When the gas outlet flow rate is above 100Nm ³ /h, the gas inlet borehole and the gas outlet borehole have formed connected fractures in the coal seam.

In a preferred embodiment, the underground gasification includes forward combustion (that is, the gasification working face flame moves in the same direction as the gas flow direction), reverse combustion (that is, the gasification working face flame moves in the opposite direction to the gas flow direction) or backward injection Gas-point combustion (that is, insert a set of coiled tubing into a horizontal well, pull the coiled tubing on the ground, realize the coiled tubing moving backward in the horizontal well, and perform ignition and gasification at different positions).

In a preferred embodiment, the gasification gas, pyrolysis gas and coal bed gas are discharged through the gas outlet borehole and collected for methane synthesis, methane-power generation or methane-methanol production.

In a preferred embodiment, the gasification agent in the underground gasification step is transported from the ground to the fire area through an annular (that is, double-layer casing) pipeline or directly from the ground through boreholes. Transport to said fire zone.

In a preferred embodiment, the CO _{2 recovered in the CO 2 recovering} step is used as a fracturing medium in the fracturing through-through step or as a displacement medium in the coalbed methane extraction step.

The method of the invention combines the underground coal gasification technology with the coal bed gas extraction technology, which can not only use the underground gasification to heat the coal bed at high temperature, increase the gas permeability of the coal bed, and improve the recovery rate of the coal bed gas; but also can realize the coupling of the drilling process and the fracturing technology At the same time, CO ₂ can be directly captured as a medium for coalbed methane displacement and a gasification agent in the underground gasification process, and the content of effective components in coal gas can be adjusted. Through the coupling of technologies, the recovery rate of coalbed methane can be improved, the effective gas composition of coal gas can be adjusted, the production cost of coal gas can be reduced, and _CO2 capture and resource utilization can be realized at the same time.

Description of drawings

Fig. 1 is a schematic flow sheet of the coalbed methane and coal mining method according to the present invention;

Fig. 2 is a schematic diagram of a coalbed methane and coal co-mining method according to an embodiment of the present invention, wherein the coal seam between the boreholes is subjected to cold fracturing, and _CO is injected to extract the coalbed methane;

Fig. 3 is a schematic diagram of a coalbed methane and coal co-mining method according to an embodiment of the present invention, wherein a fire zone is established to thermally process the fissures, expand them into gasification channels, and simultaneously displace the coalbed methane;

Fig. 4 is a schematic diagram of a method for co-mining coalbed methane and coal according to another embodiment of the present invention, wherein the coalbed methane is extracted using the pinnate branch horizontal drilling technology;

Fig. 5 is a schematic diagram of a coalbed methane and coal co-mining method according to another embodiment of the present invention, in which ignition and channel thermal processing are carried out to expand into a gasification channel and simultaneously displace the coalbed methane;

Fig. 6 is a schematic diagram of a coalbed methane and coal co-mining method according to yet another embodiment of the present invention, wherein the directional horizontal drilling technology is used to extract the coalbed methane; and

Fig. 7 is a schematic diagram of a method for co-mining coalbed methane and coal according to another embodiment of the present invention, in which ignition and channel thermal processing are performed to expand gasification channels and simultaneously displace coalbed methane.

Explanation of reference signs

1- Seam

2- Ground

3- Overburden

4-connected fissure

5- Air intake drilling

6-Outlet drilling

7-O ₂ line

8-CO ₂ pipeline

9- Drain line

10-Coalbed methane pipeline

11 - Initial Fire Zone

12-gasification channel

13-Gas pipeline

14-pinnate branch horizontal well

15-horizontal well

detailed description

In view of the difficulties in mining coalbed methane in my country and the advantages of underground coal gasification technology in coal mining, the present invention provides a new method for co-mining coalbed methane and coal.

In view of these aspects, the method of the present invention couples coalbed methane mining and underground coal gasification technology. Since both underground gasification and ground coalbed methane extraction processes need to be realized by means of drilling, an underground gasification unit usually requires at least one A gasification borehole, a gas outlet borehole, and a gasification channel connecting the two boreholes. The gasification channel is usually realized by means of fracturing and fire penetration; while a coalbed methane extraction unit usually requires at least one blind hole, For example, a vertical hole or a multi-branched horizontal well, which needs to be fractured to increase porosity, can also include a gas injection well and multiple production wells. Therefore, underground gasification and surface coalbed methane extraction are technically similar to a certain extent. Combining underground coal gasification technology with coalbed methane extraction technology can not only use underground gasification to heat coal seams at high temperatures, increase coal seam permeability, and improve Coalbed methane recovery rate; it can also realize the coupling of drilling technology and fracturing technology, and at the same time, CO ₂ can be directly captured as the medium of coalbed methane displacement and the gasification agent of underground gasification process, and the content of effective components of coal gas can be adjusted. Through the coupling of technologies, the recovery rate of coalbed methane can be improved, the effective gas composition of coal gas can be adjusted, the production cost of coal gas can be reduced, and _CO2 capture and resource utilization can be realized at the same time.

As shown in Fig. 1, the method of the present invention may include the steps of drilling, fracture penetration, coalbed methane extraction, coal seam ignition, underground gasification, CO ₂ recovery, and CO ₂ sequestration.

More specifically, the method for co-mining coalbed methane and coal of the present invention includes the following steps:

Step a1: Drill at least 2 boreholes from the ground into the coal seam. The connecting line at the bottom of the two boreholes is in the same direction as the main fracture of the coal seam. One of them is used as the air inlet hole and the other is used as the air outlet hole. Hole injection as a fracturing medium of high pressure (i.e. higher than the fracture pressure of the coal seam) containing carbon dioxide fracturing medium, forcing _CO2 to move along the pores and fractures in the coal seam and be discharged from the gas outlet borehole, thereby creating a fracturing medium in the coal seam between the boreholes create connectivity gaps;

Step a2: Close the gas outlet borehole, continue to inject CO ₂ into the coal seam continuously from the inlet borehole, then stop injecting CO ₂ , close the inlet borehole and close the gas outlet borehole for brine, so that CO ₂ can displace CH ₄ in the coal seam, Afterwards, the gas outlet borehole is reopened to extract coalbed methane;

Step a3: Repeat step a2 according to the analysis of coalbed methane. When the content of CH ₄ in the gas from the gas outlet borehole decreases significantly (for example, the volume concentration of methane is less than 5%), the coal seam at the bottom of the gas outlet borehole is ignited, and then the CO ₂ and pure Oxygen is made into a certain concentration of CO ₂ oxygen-enriched gas (called CO ₂ oxygen-enriched gas), which is continuously transported to the fire area through the air inlet drilling along the connected cracks formed in the coal seam between the holes, so that the fire source faces the CO ₂ oxygen-enriched flow The direction moves toward the direction of the air inlet drilling, and the CO ₂ enriched oxygen reacts with the coal seam for gasification and pyrolysis reactions, and the connected cracks are processed into gasification channels and continue to be gasified to generate gasification gas and pyrolysis gas at the same time:

C+O ₂ →CO ₂ -394kJ/mol

C+CO ₂ →2CO+173kJ/mol

C+H ₂ O→H ₂ +CO+131kJ/mol

Coal→H ₂ +CH ₄ +CO ₂ +Tar+Semi-coke+…

At the same time, the released heat is transferred to the coal seam, which promotes the desorption of CH ₄ , and dries the coal seam to increase the air permeability of the coal seam. The desorbed methane is discharged from the gas outlet borehole together with gasification gas and pyrolysis gas;

Step a4: When the difference between the CO ₂ oxygen-enriched inlet pressure and the gas outlet pressure significantly decreases (generally about 0.3 MPa), increase the CO ₂ oxygen-enriched flow rate or increase the CO ₂ oxygen-enriched oxygen concentration to further improve the reaction Intensify the desorption of _CH4 , and make the fire source move against the direction of _CO2 -enriched oxygen flow to the direction of the gas outlet borehole, so as to ensure that _CO2 fully contacts and reacts with the hot coal seam, and at the same time completes the in-situ gasification of the coal seam between the boreholes. ;

Further, CO ₂ in the step can be gaseous, liquid, or supercritical CO ₂ , or can be made of liquid CO ₂ , hydrogel (such as guar gum, whose function is to increase the consistency of the fracturing medium and reduce the amount of fracturing medium. fluid loss, increasing the fracture width) and chemical additives (such as potassium chloride, whose function is to make the fracturing medium form a stable system).

Further, during the fracturing operation, monitor the pressure change of the CO ₂ injection borehole, when the borehole pressure drops rapidly (that is, the pressure drop reaches about 5% of the original pressure value per day or more), and the gas outlet flow rate is not less than 100Nm ³ / h, it indicates that connected fractures have been formed in the coal seam between the boreholes.

Further, the CO ₂ enriched with oxygen requires that the oxygen volume concentration in step a3 is 20-50%, and that in step a4 is 40-70%, so as to ensure that the ash does not melt. If the amount of water in the coal seam is not enough to gasify the required coal, water vapor should be added to the gasification agent, and the amount of water vapor should be determined as described above.

Further, the CO ₂ oxygen-enriched transport can be transported from the ground to the fire area through an annular transport pipeline; it can also be directly transported from the ground to the fire area through boreholes.

The method may also include step a5, recovering CO ₂ : recovering the CO ₂ produced in the underground coal seam gasification process, and using part of the CO ₂ as a gasification agent for the underground coal seam gasification to regulate the gas components and heat value.

The method may also include step a6, CO ₂ sequestration: after the gasification of the coal seam between the two boreholes is completed, part of the recovered CO ₂ is filled into the burn-out area formed after the coal seam gasification, for burial and sequestration.

Among the boreholes, the gasification process can be guaranteed in two boreholes, one is used for air intake and the other is used for gas outlet; at the same time, during the coalbed methane extraction process, one borehole can be used for gas injection to displace coalbed methane , a borehole used to produce and collect coalbed methane displaced from the coal seam;

The coal seam fracturing method in the method at least includes: gas fracturing, hydraulic fracturing or foam fracturing, and mechanical drilling technology.

In the method, step a1 may also use O ₂ and CO ₂ for fracturing, and the concentration of O ₂ is within 20%, which is specifically determined according to the methane content in the coal seam and the explosion limit of methane.

The method of establishing the fire zone in the method can be that the mixed gas of high temperature and high pressure carbon dioxide and oxygen is passed into the bottom of the borehole, wherein the temperature is determined according to the oxygen concentration, the ignition point of the coal seam, the exposed area of the coal seam, the heat loss of the pipeline, etc., and the pressure is determined according to the static state of the coal seam. The water head is determined.

The way of establishing the fire area in the method also includes: electric ignition, solid fuel ignition, or using the original fire area or high-temperature coal seam in the burnout area in the operation area.

The underground gasification method in the method at least includes: forward combustion, reverse combustion or backward gas injection point combustion. Forward combustion means that the moving direction of the flame working surface is consistent with the airflow direction, reverse combustion means that the moving direction of the flame working surface is opposite to the direction of airflow, and the retreating gas injection point combustion means that a set of continuous pipes are inserted in a horizontal well and pumped on the ground. Pulling this set of coiled tubing enables the coiled tubing to move backward in the horizontal well and perform ignition and gasification at different positions.

In the method, CO ₂ can be recovered in various ways, mainly depending on the use and quality of the gas. If it is used for power generation, the CO ₂ in the flue gas generated after the gas power generation can be recovered. If it is used for chemical synthesis, it can be used in In the decarbonization section of gas purification, the CO ₂ in the gas is separated and recovered, and the flue gas generated by the direct combustion of coal gas or coal bed methane can also be used.

In the method, the gasification gas, pyrolysis gas, and coalbed methane can be used for methane synthesis after being discharged through gas outlet drilling holes, or for polygeneration production, such as methane-power generation, methane-methanol, etc., to produce various energy chemical products.

The present invention also provides a co-extraction method of optimized coalbed methane and coal. The whole process takes the resource utilization of _CO as the core. The specific advantages of the method are as follows:

The present invention combines coalbed methane mining with underground gasification. Compared with other coalbed methane extraction technologies, it greatly improves the recovery rate of coalbed methane and reduces costs. At the same time, it also considers the recovery and utilization of _CO2 , and is especially suitable for low permeability Coal seams, coalbed methane mining and underground gasification have a strong mutual synergy, which is specifically manifested in:

The boreholes drilled in the first step can be used not only for coalbed gas fracturing and second-step coalbed methane extraction wells, but also for inlet and outlet holes for third-step ignition and fourth-step pyrolysis and gasification, so that coalbed methane Drilling and underground gasification drilling are coupled with each other, which is beneficial to reduce drilling investment and save costs, especially for the exploitation of deep coal seam resources;

Carbon dioxide fracturing in the first step can improve the analysis of methane gas in the second step of coalbed methane extraction, and the large amount of carbon dioxide adsorbed in the coal seam can be used to control the temperature of the coal bed in the subsequent third step ignition and fourth step pyrolysis and gasification. Prevent local overheating of the coal seam, spontaneous combustion or gasification channel melting and other problems that are not conducive to ignition and gasification, and can also increase the output of coal seam pyrolysis gas in the fourth step; in addition, the first step of fracturing greatly improves the permeability of the coal seam, Provide favorable heat and mass transfer conditions for the fourth step of pyrolysis and gasification, increase the expansion range of the gasification working face, and increase the recovery rate of coalbed gasification; if the mixture of carbon dioxide and oxygen is added as the fracturing medium in the first step , the oxygen staying in the coal seam is conducive to ignition and can react with combustible gas in the fourth step of gasification process to further increase the temperature of the coal seam, which can prevent the coal seam crack closure after carbon dioxide fracturing and accelerate The analysis of methane in coalbed methane and the pyrolysis of coal can increase the content of methane in the generated coal gas, and the quality of coal gas can also be significantly improved. However, the oxygen content in the mixed gas must be controlled beyond the explosion limit of methane, which can be achieved by controlling the oxygen concentration;

A large amount of methane is precipitated during the second step of coalbed methane extraction, and the coal seam undergoes repeated pressurization and decompression processes, and the permeability of the coal seam is greatly improved, which is conducive to the expansion of the gasification working face in the fourth step, and the enriched methane around the gas outlet well is also conducive to ignition;

In the fourth step, the high temperature generated by the underground gasification reaction promotes the formation of coal seam fissures (i.e., hot-state interstitial increase), so that the cold-state fracturing of the coal seam and the hot-state interstitial increase complement each other to produce a synergistic effect, which improves the seepage capacity of coalbed methane. After the coal bed is warmed up, it is also greatly beneficial to the analysis of methane, and prevents the coal seam crack closure problem after the first step of carbon dioxide fracturing; through the combination of physical desorption and chemical reaction, the production of coal bed methane can be greatly increased; _CO2 can accelerate the production rate of CO , inhibit the water-gas shift reaction, effectively adjust the content of effective components in the gas, the hydrogen-carbon ratio is suitable for the synthesis of methane, and at the same time CO ₂ is used to displace CH ₄ and also improve the recovery rate of coalbed methane, and realize CO ₂ capture and resource utilization , to achieve CO ₂ emission reduction.

The present invention will be described in further detail below through specific embodiments in conjunction with the accompanying drawings, but it should be understood that the present invention is not limited to these embodiments.

Example 1

This embodiment is described with reference to FIGS. 2 and 3 . Fig. 2 is a schematic diagram of a coalbed methane and coal co-mining method according to the present invention, wherein the coal seam between boreholes is through cold fracturing, and CO is injected to extract the coalbed methane; and Fig. ₃ is the coalbed methane and coal mine Schematic diagram of the co-mining method, in which a fire zone is established to thermally process the fissures, expand them into gasification channels, and simultaneously displace coalbed methane. As shown in Fig. 2 and Fig. 3, in the present embodiment, drill holes are set according to the scope of the proposed gasification coal seam, and the number of drill holes is determined by coal seam reserves and gas production scale, etc., but for realizing the present invention, at least one air inlet and An air outlet, the specific implementation is as follows:

Referring to Fig. 2 and Fig. 3, a vertical hole is constructed from the ground 2 to the coal seam 1 via the overlying rock formation 3 as the air intake borehole 5, within a certain distance from the air intake borehole 5 (generally between 200 meters and 600 meters) Specifically, it can be determined by those skilled in the art according to the type of coal. For example, the deeper the degree of metamorphism, the longer the borehole length. Generally, about 200 meters are selected for lignite, and about 500 meters for bituminous coal). The construction vertical hole is used as the gas outlet borehole 6. , the bottom of the gas outlet borehole is located in the coal seam 1, 2 meters away from the coal seam floor, the bottom connection line of the air inlet borehole 5 and the gas outlet borehole 6 is consistent with the direction of the main crack of the coal seam, and the distance between the gas inlet and outlet boreholes can be determined by those skilled in the art Determined according to coal seam, stratum, etc.

_O2 pipeline 7 and _CO2 pipeline 8 are installed at the inlet borehole 5, and drainage pipeline 9, coalbed methane pipeline 10, and gas pipeline 13 are installed at the outlet borehole 6, of which _O2 pipeline 7 is used to transport pure oxygen, CO _2. The pipeline 8 is used to transport CO ₂ and mix it in the air inlet borehole 5 to form a certain volume concentration of CO ₂ enriched in oxygen (in this embodiment, the oxygen concentration is about 10%); the drainage pipeline 9 is used for fracturing and coalbed methane extraction stage to drain coalbed water, the coalbed methane pipeline 10 is used to discharge coalbed methane during the coalbed methane extraction stage, and transport CO ₂ after gasification is completed, so as to store CO ₂ after coalbed gasification In the formed burn-out zone, the gas pipeline 13 is used to transport the raw gas generated in the gasification process after ignition. The specific operation process is:

The high-pressure carbon dioxide transported by the _CO2 pipeline 8 and the oxygen transported by the _O2 pipeline 7 are continuously injected into the coal seam 1 through the inlet borehole 5, and the injection pressure is 1.1 times the fracture pressure of the coal seam, forcing the gas medium to move along the natural pores and fractures of the coal seam, The coal body is fractured to generate connecting fractures 4, which communicate with the gas outlet borehole 6 in the coal seam 1, and the gas after fracturing is discharged from the coalbed gas pipeline 10 to the ground through the gas outlet borehole 6.

Close the gas outlet borehole 6, and continue to inject high-pressure CO ₂ into the coal seam 1 from the air inlet borehole 5. The injection pressure is not greater than the coal seam fracture pressure. The total amount of injection is determined according to the saturated gas content of the coal seam. Stop injecting after the total CO ₂ injection amount meets the requirements , close the air inlet borehole 5, and close the air outlet hole for 1 to 15 days to ensure that CO ₂ fully contacts with the coal seam and displaces the CH ₄ adsorbed in the coal seam; The coalbed water is pumped to dehydrate the coalbed 1, and the coalbed methane pipeline 10 is opened to reduce the pressure of the gas outlet borehole 6 to facilitate the desorption or desorption of the coalbed methane, and the coalbed methane pipeline 10 is collected to the ground pipe network. After a period of extraction, when the pressure at the bottom of outlet borehole 6 drops below 10kPa, the next cycle of injection and extraction will be performed.

When the CH content in the gas outlet borehole ₆ gas significantly decreased (that is, its volume concentration was less than 5%), the gas outlet borehole 6 was opened, the drainage pipeline 9 was proposed, and the gas pipeline 13 was installed. Then open the connecting valve between the gas outlet borehole 6 and the gas pipeline 13, and continue to inject high-pressure _CO2 into the coal seam 1 through the inlet borehole 5. The injection pressure is greater than the hydrostatic pressure of the coal seam. 13 is discharged to take out the moisture in the coal seam between the drilling holes, that is, to dry the coal seam moisture, and to keep the coal seam at the bottom of the gas outlet drilling hole 6 holes dry.

Lower the electric igniter to the coal seam section at the bottom of hole 6 of the gas outlet hole, open the communication valve between the gas outlet hole 6 and the gas pipeline 13, and transfer the pure oxygen from the _O2 pipeline 7 and the CO2 from the _CO2 pipeline ₈ , In the air inlet borehole 5, CO ₂ enriched with oxygen volume concentration of 20 to 30% is mixed as a gasification agent, and sent into the coal seam at the bottom of the air outlet borehole 6 along the connecting crack 4. Then monitor the methane content of the outlet hole, control the oxygen content in the intake air, and ensure that the _O2 concentration in the outlet hole is not within the limit range of methane explosion. After the _O2 concentration or methane content meets the requirements, start the igniter to ignite the coal seam at the bottom of hole 6 of the gas outlet borehole, and establish the initial fire zone 11. The crude gas produced by the reaction of gasification agent and coal seam 1 is discharged through the gas pipeline 13, and the CO ₂ oxygen-enriched flow rate (about 300-500m ³ /hour) is controlled so that the temperature of the fire zone is not lower than the spontaneous combustion ignition temperature of the coal seam.

After the temperature of the fire zone exceeds 1000°C, if the intake pressure drops by more than 10%, increase the CO ₂ oxygen-enriched flow rate by 500-1000Nm ³ /h each time until the flow rate reaches 5000-8000Nm ³ /h, so that The fire source moves toward the direction of the air intake drilling in the direction of the _CO2 -enriched oxygen flow, because _CO2 -enriched oxygen reacts with the coal seam for gasification and pyrolysis reactions:

C+O ₂ →CO ₂ -394kJ/mol

C+CO ₂ →2CO+173kJ/mol

C+H ₂ O→H ₂ +CO+131kJ/mol

Coal→H ₂ +CH ₄ +CO ₂ +Tar+Semi-coke+…

Gasify part of the coal seam along the connecting fissure 4, expand the connecting fissure, and gradually form a gasification channel 12 to facilitate the discharge of coal gas; at the same time, the released heat is transferred to the coal seam to promote the desorption of CH ₄ and dry the coal seam to increase the ventilation of the coal seam The desorbed methane is discharged from the gas outlet borehole 6 and the gas pipeline 13 together with gasification gas and pyrolysis gas.

Then maintain the flow rate and _O2 concentration, carry out reverse combustion (that is, the flame front expands in the opposite direction to the flow direction of the feed gas), and monitor the pressure of the inlet borehole 5 in real time. When the pressure difference between the air inlet borehole 5 and the air outlet borehole 6 is not large (the pressure difference is less than about 0.3MPa), it indicates that the gasification channel 12 between the lower end of the inlet borehole 5 and the lower end of the air outlet borehole 6 has been successfully constructed .

After the gasification channel 12 completes the construction, increase the _CO2 oxygen-enriched gas supplied from the upper end of the inlet borehole 5 to the downhole The increase oxygen concentration (increase 2～5% every day) to 40～60% to improve the reaction zone temperature, and Carry out forward gasification (that is, the expansion direction of the flame front is the same as the flow direction of the gas supplied), to ensure that CO ₂ fully contacts and reacts with the hot coal seam in the gasification channel, so as to complete the gasification of the coal seam between the boreholes; at the same time, due to The gasification space expands, the in-situ stress appears, and under the joint action of heat, the coal seam around the gasification channel produces a fractured zone, which accelerates the release of coalbed methane. In actual operation, the CO ₂ oxygen-enriched gas flow rate and/or oxygen concentration can be adjusted according to the coal seam inclusion thickness, water content, and drilling distance. If the coal seam water content is less than the water required for gasification reaction, it can be injected For carbon dioxide, oxygen-enriched and water vapor gas, the amount of water vapor injected is the difference between the amount of water required for the gasification reaction and the water content of the coal seam divided by the water vapor decomposition rate.

After the coalbed gasification process, a burn-out area is formed, and its space is filled with ash, coke residue, gangue, roof rock, and ungasified coal seam, which can be used as a space for CO ₂ sequestration. After the storage starts, close the gas outlet drilling 6, open the CO ₂ pipeline 7, and inject high-pressure CO ₂ . The CO ₂ pressure is generally controlled at 6-8 MPa, and the CO ₂ injection rate is generally controlled at 400-500 Nm ³ /m ³ (per unit volume 400-500 standard cubic meters of CO ₂ can be stored in the burn-up area, which is determined according to the volume of the burn-up area and the hydrogeological conditions of the coal seam.

The gasification coal gas, pyrolysis coal gas and coal bed gas produced in the present invention are used for methane synthesis after being discharged through gas outlet drilling holes.

Example 2

In Example 2, the pinnate branch horizontal drilling technology is used to speed up the extraction speed of coalbed methane, and at the same time, the branch well technology is used to communicate the natural cracks and cleats of the coal seam to increase the exposed area of the coal seam, which is beneficial to the subsequent gasification process. This embodiment refers to Figure 4 and Figure 5 for description. Fig. 4 is a schematic diagram of a method for co-mining coalbed methane and coal according to the present invention, wherein the coalbed methane is extracted using the pinnate branch horizontal drilling technology; Fig. 5 is a schematic diagram of the method for co-mining coalbed methane and coal according to the specific implementation as follows:

From the ground 2 through the overburden 3 to the coal seam 1 construction vertical borehole as the gas outlet borehole 6, in the construction of the air intake borehole 5 in a certain distance range (referring to embodiment 1) apart from the gas outlet borehole 6, so that the borehole 5 and The boreholes 6 are connected in the coal seam, and the air intake boreholes 5 are pinnate horizontal boreholes, including several groups of pinnate branch horizontal wells 14, and the bottom of the boreholes is located in the pre-gasified coal seam 1. The diameter, length and quantity of the main horizontal well and the branch wells of the pinnate branch horizontal wells are determined according to the coal seam and the coalbed methane production area. In order to prevent the borehole wall from collapsing, screen pipes can also be run in the main horizontal well for support.

After the plume horizontal drilling is completed, in the outlet borehole 6, lower the suction rod pump, install the drainage pipeline 9 and the coalbed methane pipeline 10; install the _O2 pipeline 7 and the _CO2 pipeline 8 at the wellhead of the inlet borehole 5, and close the outlet The connection valve between the hole 6 and the gas pipeline 10 is used to continuously inject high-pressure N ₂ into the coal seam ₁ from the inlet borehole 5. The injection pressure is not greater than the fracture pressure of the coal seam. After meeting the requirements, stop the injection, close the air inlet borehole 5, and close the air outlet hole for 10-20 days to ensure that the _N2 fully contacts the coal seam and displaces the _CH4 adsorbed in the coal seam; then reopen the air outlet borehole 6, The coal seam water is pumped through the drainage pipeline 9 to dehydrate the coal seam 1. At the same time, the coal seam gas pipeline 10 is opened to reduce the pressure of the gas outlet borehole 6 to facilitate desorption or desorption of the coal seam gas, and the coal seam gas pipeline 10 is collected to the surface pipe. network. After a period of extraction, when the pressure at the bottom of outlet borehole 6 drops below 10kPa, the next cycle of injection and extraction will be performed.

When the CH content in the gas outlet borehole ₆ gas obviously decreases (volume concentration is less than 5%), the gas outlet borehole 6 is opened, the drainage pipeline 9 is proposed, and the gas pipeline 13 is installed. Then open the connecting valve between the gas outlet borehole 6 and the gas pipeline 13, and continue to inject high-pressure _CO2 into the coal seam 1 through the inlet borehole 5. The injection pressure is greater than the hydrostatic pressure of the coal seam. 13 is discharged to take out the moisture in the coal seam between the drilling holes and promptly dry the coal seam moisture, so that the coal seam at the bottom of the gas outlet drilling hole 6 is kept dry.

The pure oxygen sent by the _O2 pipeline 7 and the _CO2 sent by the _CO2 pipeline 8 are mixed in the air inlet borehole 5 to form _CO2 oxygen-enriched with a volume concentration of 20-30% as a gasification agent, along the communication Fissure 4 is fed into the coal seam at the bottom of hole 6 in gas outlet borehole. Then monitor the methane content of the outlet hole, control the oxygen content in the intake air, and ensure that the _O2 concentration in the outlet hole is not within the limit range of methane explosion. After the _O2 concentration or methane content meets the requirements, open the connecting valve between the gas outlet borehole 6 and the gas pipeline 13, and put hot coke into the bottom of the gas outlet borehole 6. Wait for determination, make the bottom coal seam of outlet drilling 6 holes ignite, set up initial fire zone 11. The gasification agent reacts with the coal seam 1, and the raw gas generated by the reaction is discharged through the gas pipeline 13, and the CO ₂ oxygen-enriched flow rate is controlled so that the temperature of the fire zone is not lower than the spontaneous combustion ignition temperature of the coal seam

After the fire zone temperature exceeds 1000°C, if the inlet pressure drops by more than 10%, increase the CO ₂ oxygen-enriched flow by 300-500Nm ³ /h each time until the flow reaches 3000-5000Nm ³ /h. To make the fire source move toward the direction of the air intake drilling in the direction of the _CO2 -enriched oxygen flow, because the _CO2 -enriched oxygen reacts with the coal seam for gasification and pyrolysis reactions:

C+O ₂ →CO ₂ -394kJ/mol

C+CO ₂ →2CO+173kJ/mol

C+H ₂ O→H ₂ +CO+131kJ/mol

Coal→H ₂ +CH ₄ +CO ₂ +Tar+Semi-coke+…

Gasify part of the coal seam along the connecting fissure 4, expand the connecting fissure, and gradually form a gasification channel 12 to facilitate the discharge of coal gas; at the same time, the released heat is transferred to the coal seam to promote the desorption of CH ₄ and dry the coal seam to increase the ventilation of the coal seam The desorbed methane is discharged from the gas outlet borehole 6 and the gas pipeline 13 together with gasification gas and pyrolysis gas.

Then maintain the flow rate for reverse combustion (that is, the flame front expands in a direction opposite to the flow direction of the feed gas), and monitor the pressure of the inlet borehole 5 in real time. When the pressure shown by the pressure gauge connected to the upper end of the air inlet borehole 5 significantly decreases (the pressure drop is generally 10 to 60% of the initial pressure), it indicates that the initial fire zone 11 expands to near the bottom of the air inlet borehole 5 . When the pressure difference between the air inlet borehole 5 and the air outlet borehole 6 is not large (or the pressure difference is less than 0.3MPa), it indicates that the gasification channel 12 between the lower end of the inlet borehole 5 and the lower end of the air outlet borehole 6 is successfully constructed .

After the gasification channel 12 has been constructed, increase the _CO2 oxygen-enriched gas oxygen concentration (increase 2-5% per day) to 50-70% to increase the temperature of the reaction zone from the upper end of the inlet borehole 5 to the downhole supply, and carry out Forward gasification (that is, the expansion direction of the flame front is the same as the flow direction of the supplied gas) ensures that CO ₂ fully contacts and reacts with the hot coal seam in the gasification channel to complete the gasification of the coal seam between the boreholes. The gasification space expands, the in-situ stress effect appears, and under the joint action of heat, the coal seam around the gasification channel produces a fractured zone, which accelerates the release of coalbed methane. Specifically, the CO ₂ oxygen-enriched gas flow rate and/or oxygen concentration are adjusted according to the coal seam inclusion thickness, water content, and drill hole spacing.

The gasification coal gas, pyrolysis coal gas and coal bed gas produced in the present invention are used for methane-power generation after being discharged through the gas outlet drilling.

Example 3

Embodiment 3 is basically the same as Embodiment 2, except that directional horizontal drilling technology is used to establish the channel for initial drainage and gas recovery, and the arrangement of horizontal wells 15 with a U-shaped structure is formed. The horizontal wells are perpendicular to the direction of the main fractures of the coal seam, and Use the vertical well, that is, the gas outlet borehole 6 to drain water, and the inlet borehole 5 to produce gas. After the initial extraction of coalbed methane is completed, a fire zone is established in the gas outlet borehole 6, and a thermal processing channel is started to displace the coalbed methane synchronously. Coalbed gasification between boreholes is completed, and this embodiment will be described with reference to FIG. 6 and FIG. 7 . Fig. 6 is a schematic diagram of a method for co-mining coalbed methane and coal according to the present invention, wherein the directional horizontal drilling technology is used to extract the coalbed methane, and Fig. 7 is a schematic diagram of the method for co-mining coalbed methane and coal according to the present invention, wherein ignition is carried out And channel thermal processing, expanding into a gasification channel, and displacing coalbed methane synchronously. The gasification coal gas, pyrolysis coal gas and coal bed gas produced by the invention are used for methane-methanol production after being discharged through gas outlet drilling holes.

The invention utilizes underground gasification to generate a large amount of heat, while heating the coal seam and improving the analysis ability of coal bed methane, the channel for coal bed gas fracturing is greatly expanded, which can greatly increase the output of coal bed methane, and fundamentally solve the problem of coal bed methane storage in China. The problem of low permeability of the layer. At the same time, underground gasification chemically utilizes the coal seams that have been extracted from coalbed methane, and the produced coal gas contains a large amount of methane, carbon monoxide and hydrogen, and clean methane is obtained through the conversion of ground processes. In the present invention, the coordinated development and comprehensive utilization of coalbed methane and coalbed itself can not only greatly reduce production and development costs, but also increase the output of the final product methane, greatly improve the quality of coal gas, and realize the co-production of coal and coalbed methane. Pick. In addition, using fluids containing carbon dioxide as processing media such as fracturing and gasification can not only improve the methane analysis ability in coal seams, improve the recovery rate of coal bed methane, but also increase the content of effective gas components such as methane in underground gasification coal gas. , the carbon dioxide produced in the process can also be recycled, and the invention is a low-carbon, high-efficiency and clean new method.

The present invention has been described in detail above, but the present invention is not limited to the specific embodiments described herein. Those skilled in the art understand that other changes and modifications can be made without departing from the scope of the present invention. The scope of the invention is defined by the appended claims.

Claims (20)

1. a coal bed gas and coal mining method altogether, described method comprises:

1) drilling well step: carried out drilling well by ground to coal seam and to provide, at least one air inlet that described coal seam is communicated with ground is holedGo out gas drilling hole with at least one;

2) pressure break connects step: inject to described coal seam the pressure break medium that contains carbon dioxide by described air inlet boring, described in pressurePressure break medium flows in described coal seam, and by described go out gas drilling hole discharge, thereby make described air inlet boring and described in go out gas drilling holeIn described coal seam, be communicated with;

3) extraction coal bed gas step: inject displacing medium by described air inlet boring to described coal seam, to the coal bed gas in described coal seamCarry out displacement, and by described go out gas drilling hole collect;

4) lighting up procedure: set up flame range in the coal seam of the described foot of hole of giving vent to anger, with the described coal seam of igniting; And

5) underground gasification step: inject carbonated gasifying agent by described air inlet boring to described coal seam, described gasifying agent withGasification reaction and pyrolytic reaction are carried out in described coal seam, produce heat energy and gasification gas, described heat energy to described coal seam internal delivery withProduce pyrolysis coal gas, described in synchronous displacement coal bed gas to produce free methane, described free methane and described gasification gas, described inPyrolysis coal gas together from described go out gas drilling hole discharge and collect;

Wherein, described pressure break medium is the mixture of carbon dioxide and oxygen, and wherein the volumetric concentration of oxygen be 20% withUnder.

2. coal bed gas according to claim 1 and coal mining method altogether, is characterized in that, described method also comprises:

6) reclaim CO₂Step: by the CO producing in described underground gasification step₂Reclaim, and by reclaimed CO₂A part as described gasifying agent.

3. coal bed gas according to claim 2 and coal mining method altogether, is characterized in that, described method also comprises:

7)CO₂Seal step up for safekeeping: described air inlet boring and described in the coal seam that goes out between gas drilling hole complete after described underground gasification, willThe part CO reclaiming₂Be filled into combustion dead zone, bury and seal up for safekeeping.

4. coal bed gas according to claim 1 and coal mining method altogether, is characterized in that, is also included in described lighting up procedure4) carry out before safety detection step to guarantee a fire safety.

5. coal bed gas according to claim 1 and coal mining method altogether, is characterized in that, in described extraction coal bed gas step3), in, it is to inject CO that the coal bed gas in described coal seam is carried out to displacement₂Or nitrogen carries out displacement.

6. altogether mining method of coal bed gas according to claim 1 and coal, is characterized in that, described air inlet boring or described in go outGas drilling hole is made up of directional drilling and vertical drilling.

7. altogether mining method of coal bed gas according to claim 1 and coal, is characterized in that, described air inlet boring and described in go outGas drilling hole is made up of vertical drilling.

8. coal bed gas according to claim 1 and coal mining method altogether, is characterized in that, the described flame range of setting up is by electric pointFire or solid fuel igniting.

9. coal bed gas according to claim 1 and coal mining method altogether, is characterized in that, described underground gasification comprises forwardBurning, reverse combustion or retreat gas injection point burning.

10. coal bed gas according to claim 1 and coal mining method altogether, is characterized in that, described drilling well is split according to coal seam is mainGap vertical direction horizontal well drilling.

11. coal bed gas according to claim 1 and coal be mining method altogether, it is characterized in that, described pressure break connects in step and makesWith CO₂For gaseous state, liquid state or above-critical state CO₂, or by liquid CO₂, water frozen glue and chemical addition agent compositionMixed liquor.

12. coal bed gas according to claim 1 and coal be mining method altogether, it is characterized in that, connect in step in described pressure break,When the pressure in described air inlet boring decline rapidly and described in go out gas drilling hole the throughput that goes out be 100Nm³When/h is above, described inAir inlet boring and described in go out gas drilling hole and in described coal seam, formed connection.

13. coal bed gas according to claim 1 and coal be mining method altogether, it is characterized in that, and in described underground gasification step,Carrier of oxygen volume concentrations in described carbonated gasifying agent is 20～70%, to ensure that melting does not occur ash content.

14. a kind of coal bed gas according to claim 13 and coal be mining method altogether, it is characterized in that, described underground gasification stepIn rapid, the carrier of oxygen volume concentrations in described carbonated gasifying agent is 20～50%, for building gasification tunnel.

15. a kind of coal bed gas according to claim 14 and coal be mining method altogether, it is characterized in that, described underground gasification stepIn rapid, the carrier of oxygen volume concentrations in described carbonated gasifying agent is 40～70%, has built for described gasification tunnelCoal seam gasification after one-tenth.

16. a kind of coal bed gas according to claim 1 and coal be mining method altogether, it is characterized in that, if in coal bed gas extractionComplete, when the water content in coal seam is less than the required water yield of coal seam gasification, described in contain carbon dioxide gasifying agent be oxygen, titanium dioxideThe mixture of carbon and steam.

17. a kind of coal bed gas according to claim 1 and coal be mining method altogether, it is characterized in that described underground gasification stepIn described gasifying agent conveying by annulus type conveyance conduit or boring be delivered to described flame range by ground.

18. a kind of coal bed gas according to claim 2 and coal be mining method altogether, it is characterized in that described recovery CO₂StepThe CO of middle recovery₂Come from gas to generate electricity produce flue gas or gas purification in decarbonizing section.

Altogether mining method of 19. a kind of coal bed gas according to claim 1 and coal, is characterized in that, the gasification gas that produces,Pyrolysis coal gas and coal bed gas through described go out after gas drilling hole discharges,, methane-generating synthetic for methane or methane-methanol production.

20. a kind of coal bed gas according to claim 2 and coal be mining method altogether, it is characterized in that described recovery CO₂StepThe CO of middle recovery₂Connect the pressure break medium of step or the displacing medium as described extraction coal bed gas step as described pressure break.