Abstract:
A gas injection apparatus with a controllable gas injection point, a gas injection process, and a gasification method. The gas injection apparatus comprises a directional well channel, where a continuous oil pipe is provided in the directional well channel. The continuous oil pipe is connected to an oxygen/oxygen-rich gas pipeline. An annular gap between the continuous oil pipe and the directional well channel is connected to an auxiliary gasification agent pipeline and a vapor pipeline. A gas injection wellhead is provided at the start end of the continuous oil pipe, and a nozzle is provided at the tail end. In the present invention, based on directional drilling and continuous oil pipe technologies, the movement of a gas injection point is implemented by using a manner of combining directional drilling and a continuous oil pipe; meanwhile, by using a principle of controlling reverse combustion by adjusting a gasification agent injection parameter, the movement of a working surface position and a combustion speed of a flame are regulated, so as to achieve the objective of ignition and gasification for reverse combustion of an underground coal layer.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to the technical field of coal resource development, particularly relates to a gas injection apparatus with controllable gas injection point, gas injection process and gasification method. 
       BACKGROUND ART 
       [0002]    Shaftless underground gasification technologies mainly employ the directional drilling and reverse burning to construct gasification channel, and inject gasification agents such as air and oxygen/steam to conduct underground gasification to produce coal gas. Its advantage lies in that gas production of single gasifier is large. Its disadvantage lies in that position of burning zone is not stable, loss rate of the gas is high, and it is necessary to add auxiliary boreholes if the gasification channel is very long. 
         [0003]    To solve the problems above, Lawrence Livermore national laboratory in USA has developed controlled retraction injection point (CRIP), which makes the injection point retract to form new burning zone by burning a section of the casing-tube so that the injection point can move towards the gas injection well, as shown in  FIG. 1 . The igniter has many pipes, which can carry fluid from ground to the underground. Start the igniter, the silane from one pipe encountered in the air will cause spontaneous combustion, the spark will ignite propane from another pipe, and the flame will burn off a section of the casing-tube and further ignite the coal seam. In Thulin, Belgium, the underground gasification test designs that the injection tube employs concentric annular tubes, wherein the center tube can move within the annular tube. There are three thermocouple electric wires and two combustible hollow pipes in the center tube. One hollow pipe is used for delivering triethylborine, which will burn once meets air, and CH 4 . The other hollow pipe is filled with oxygen. An igniter is fixed at the end of the center tube. 
         [0004]    The advantage of CRIP technology is that the gasification process can be effectively controlled, while its disadvantage is that this technology requires multiple ignitions to ignite the coal seam at different distance location within a directional well before gasification. Because the gas injection point movement is discontinuous, the gasification is unstable, and the apparatus for ignition and gas injection has complicated structure and is expensive, the ignition process is complicated, difficult to control and not safe enough. 
       SUMMARY OF THE INVENTION 
       [0005]    Aiming to solve a series of problem of existing CRIP process in the shaftless underground coal gasification including multiple ignition, complicated device, discontinuous gas injection point movement and unstable gasification process, the present invention provides a reverse burning ignition and gasification method of controllable gas injection point movement of shaftless underground gasification, thereby achieving the goal of improving gasification stable control and safety performance and reducing the production cost. The present invention also provides a gas injection apparatus and a gas injection process with controllable gas injection point. 
         [0006]    The present invention is based on the techniques of directional drilling and coiled tubing, utilizes the principle of directional drilling cooperating with coiled tubing to realize the movement of gas injection point and adjusting gasification agent injection parameter to control the reverse combustion, finally achieves the goal of modulating movement and burning rate of flame working face position to conduct reverse burning ignition and gasification of the underground coal seam. 
         [0007]    To achieve this goal, the present invention employs the following technical solutions: One goal of the present invention is to provide a gas injection apparatus with controllable gas injection point. The gas injection apparatus comprises a directional well channel. The directional well channel is disposed with coiled tubing. The coiled tubing is connected with oxygen/oxygen-enriched gas line. The annular space between the coiled tubing and the directional well has connection to an auxiliary gasfication agent line and a steam line. The start end of the coiled tubing is disposed with gas injector head and the terminal end is disposed with a nozzle. 
         [0008]    The coiled tubing is sealed by a blowout preventer (box) and placed in the well. 
         [0009]    The second goal of the present invention is to provide a gas injection process with controllable gas injection point. In the gas injection process, the oxygen/oxygen-enriched gas is delivered by the coiled tubing deposited within the directional well channel. The oxygen/oxygen-enriched gas, and the auxiliary gasification agent delivered through the annular space between the coiled tubing and the directional well will be uniformly mixed at the nozzle location at the terminal end of coiled tubing. The mixed gasification agent enters the predetermined gasification location of the coal seam through the directional well channel or the pore channels within the coal seam. 
         [0010]    The oxygen/oxygen-enriched gas and auxiliary gasification agent are mixed at the position of nozzle at the terminal end of the coiled tubing, that is, within the drill-hole or the channel. 
         [0011]    The gas injection point movement control of the present invention during the gas injection, can realize gas injection position change by lifting and lowering action to control movement of the coiler tubing and nozzle. 
         [0012]    The directional well channel of the present invention is formed with directional drilling method. Directional drilling technology is one of the most advanced well drilling technologies in the field of petroleum exploration and development in the current time. It is a well-drilling process technology that utilizes special under-well tools, measurement devices and process technology to effectively control the well trajectory, making drilling bit drill to the predetermined underground position along a specific direction. It is widely used in oilfield development in current. Directional drilling technology can economically and effectively develop petroleum resources with limited ground and underground conditions and greatly improve petroleum production and reduce well-drilling cost, thus it is good to natural circumstance protection and has significant economical and social benefit. 
         [0013]    The directional drilling method of the present invention preferably employ any one of directional well drilling technology, horizontal well drilling technology, lateral drilling technology, radial horizontal well technology, multilateral well technology, cluster wells technology and extended reach well technology in petroleum or coal seam gas drilling technologies. The directional well channel is longer than 10 meters. 
         [0014]    The directional well channel of the present invention is unsupported channel or supported channel. In practical implementation process, whether supporting the channel or not is determined according to the factors such as coal rock and geological condition. 
         [0015]    The supported channel utilizes sieve-tube support and/or casing-tube support, preferably sieve-tube support or the combination of sieve-tube support and casing-tube support. In the practical implementation process, different support pattern can be selected according to the factors that influence reverses burning ignition speed, such as support tube intensity, coal gangue and coal water. Preferably, sieve-tube support or combination of sieve-tube support and casing-tube support is employed to improve the contact area of gasification agent and coal seam to be ignited. 
         [0016]    The support tube materials are combustible materials, more preferably organic materials, most preferably glass fiber reinforced plastics or PE pipe materials. During the implementation process, organic materials such as glass fiber reinforced plastics or PE pipe materials are preferred due to factors such as intensity or burning features. 
         [0017]    The oxygen/oxygen-enriched gas is provided by the gasification agent preparation system. The oxygen-enriched gas is a mixed gas composed of oxygen and one or both of nitrogen and carbon dioxide, wherein the concentration by volume of oxygen is larger than 21%. 
         [0018]    The auxiliary gasification agent is one of nitrogen, carbon dioxide and water, or mixture thereof. A person skilled in the art can select one or two of the gases according to the gas injection requirement. The nitrogen is provided by a nitrogen production device. The carbon dioxide is provided by a decarbonization device. The auxiliary gasification agent has the following functions: firstly, it will take part in the underground gasification reduction reaction, such as CO 2  or H 2 O; secondly, its remixing with oxygen/oxygen-enriched gas can reduce the oxygen concentration of the mixed gasification agent, thereby protecting gasification process and equipment. 
         [0019]    During gasification process, the oxygen content of the auxiliary gasification agent delivered between the coiled tubing and directional well wall should be controlled to prevent self-burning of coal seam or gas injection string tempering in the delivery process. The oxygen concentration is determined by the lower limit of oxygen concentration which can cause the coal self-burning. For the thickness of loose coal seam is less than 0.5 meter, the oxygen concentration by volume of the auxiliary gasification agent is generally required to be less than 5%. 
         [0020]    For the coiled tubing and nozzle of the present invention can select the formed materials and equipment of the current petroleum and natural gas industry. In coiled tubing selection, the processing parameters such as oxygen concentration, pressure and flow rate of delivered gasification agent are key factors to be considered; the coiled tube with different pressure, material and diameter can be selected to reduce the composite cost. 
         [0021]    The pore channels within the coal seam is formed by artificial drilling or fracturing process, or formed by coal seam under thermal effect of burning. 
         [0022]    The third goal of the present invention is to provide two controlled gas injection point gasification method utilizing the above-mentioned gas injection process. 
         [0023]    The first controlled gas injection point gasification method conducts reverse burning, gasification channel processing and gasification production by segmentally moving the coiled tubing to make the gas injection point segmentally move to the predetermined gasification position, and then adjusting the gas injection technology parameters. 
         [0024]    The gasification method comprises the following steps: 
         [0025]    1) according to the parameters such as thickness and reserves of gasifiable coal seam in gasification area, segmentally moving coiled tubing according to the gas injection process to make the gas injection point position segmentally move to the predetermined gasification position; 
         [0026]    2) adjusting the pressure and flow rate of a single gas and controlling the parameters such as flow rate, pressure and oxygen concentration of the injected gasification agent; segmentally moving the flame working face to the predetermined gasification position in the manner of reverse burning and making gasification channel process at the same time; 
         [0027]    3) after completing the ignition and process of the gasification channel, improving intensity of the gasification agent injection, enhancing the gasification of underground coal and conducting gas production of underground gasification on a large scale; 
         [0028]    4) when the coal seam gasification of the predetermined gasification position is done, determining stopping or reducing gasification agent injection according to the consumed amount of the gasification coal, and heat value and composition of coal gas, and starting the injector head to move the oxygen/oxygen-enriched gas injection point to the next predetermined gasification position; 
         [0029]    5) conducting the next segment gasification channel process according to step 2), and completing the underground gasification of the predetermined coal seam area according to step 3) and 4); repeating those steps until the coal resource around the directional well channel is gasified completely. 
         [0030]    The gas injection point segmental movement distance in the step 1) is 10˜150 m. 
         [0031]    Preferably, the gasification flow rate during the gasification channel ignition and processing is limited within 300˜3000 m 3 /h. 
         [0032]    Preferably, the oxygen concentration by volume in the gasification agent is 21˜55%. 
         [0033]    In the present invention, the gas injection movement is estimated according to the parameters such as the amount of coal has gasified, the heat value and composition of coal gas. The movement standard determined by general process operation is as follows: the amount of coal has gasified is more than 50% of the total gasifiable coal in the section of directional well channel; and the heat value and composition of the production gas reduce by more than 20% compared with normal value. 
         [0034]    Another controllable gas injection point gasification method provided by the present invention conducted reverse burning, gasification channel processing and gasification production by continuously or intermittently lifting the coiled tubing to make the gas injection point continuously move to the predetermined gasification position, and then adjusting the gas injection technology parameters. 
         [0035]    The gasification method comprises the following steps: 
         [0036]    1) according to the parameters such as thickness and reserves of gasifiable coal seam in gasification area, and continuously or intermittently lifting coiled tubing to make the gas injection point continuously move to the predetermined gasification position; 
         [0037]    2) adjusting the pressure and flow rate of a single gas and controlling the parameters such as flow rate, pressure and oxygen concentration of the injected gasification agent; achieving continuously processing gasification channel and underground gasification production on a large scale in a manner of reverse burning; 
         [0038]    3) adjusting the gasification agent injection parameters whenever necessary, to guarantee relative stable status of coal gas composition and heat value; 
         [0039]    4) when coal seam gasification of the predetermined gasification position is done, controlling reverse movement speed of coiled tubing according to burning speed of the coal gasification, heat value and composition of coal gas, and the gasifiable coal reserves, until the coal resource around the directional well channel is gasified completely. 
         [0040]    The flow rate of the gasification agent in the step 2) is larger than 2000 m 3 /h; preferably, the oxygen concentration by volume of gasification agent is 21˜95%. 
         [0041]    Preferably, when the oxygen concentration by volume is larger than 60%, water steam or water can be injected to adjust the temperature and gas quality in the cavity. 
         [0042]    The movement speed of the gas injection point is determined according to the amount of coal burned per unit of time (m), heat value and composition fluctuation of coal gas. In the practical operation of underground gasification, the movement standard determined by process operation is as follows: the gas injection point can begin to continuously move till the gasification rate (η) is larger than 50%, which is the ratio of coal burned to the gasifiable coal (T) per unit length of the directional well channel. and the reduction of heat value and composition is more than 20% of normal value, wherein the gas injection point movement rate (V) control satisfies the following equation: V=T*η/m. 
         [0043]    The controllable gas injection point gasification method of the present invention includes the following steps: 
         [0044]    1) employing directional drilling technology to build up a directional well channel connecting to the existing burn zone in the predetermined gasification coal seam; 
         [0045]    2) delivering the coiled tubing and the nozzle to the predetermined gasification position along the directional well through the gas injection well using the injector head; 
         [0046]    3) injecting the auxiliary gasification agent into the annular space between the coiled tubing and the directional well wall to conduct replacement protection of the channel, and then injecting oxygen/oxygen-enriched gas into the coiled tubing; 
         [0047]    4) delivering the oxygen/oxygen-enriched gas through the coiled tubing to output at the nozzle, allowing its uniform mixture with the auxiliary gasification agent delivered through the annular space at the predetermined gasification position; mixed gasification agent enters the predetermined ignition position through the directional well channel or the pore channel within the coal seam; 
         [0048]    5) adjusting pressure and flow rate of a single gas and controlling the parameters such as pressure, flow rate and oxygen concentration of the mixed gasification agent injected into the gasifier by the ground control system; segmentally guiding the flame working face move to the predetermined gasification position in the manner of reverse burning; at the same time, processing the gasification channel and making underground gasifier to produce syngas; 
         [0049]    6) determining the condition of coal seam burning and gasification at the predetermined gasification position according to the coal burned, the heat value and composition of coal gas; when the stability of the heat value and composition decrease, starting the injector head to make the oxygen injection point move to the next predetermined gasification position; 
         [0050]    7) accomplishing the coal underground gasification in the predetermined area according to the steps 5) and 6); repeating those steps until the coal resource around the directional well channel is gasified completely; and 
         [0051]    8) stopping oxygen/oxygen-enriched gas input of the coiled tubing, then stopping auxiliary gasification agent input of the annular space of sieve-tube; taking out the gasification agent injection apparatus from the directional well channel and moving it to the next gasification area. 
         [0052]    Compared with the existing technical solutions, the gas injection apparatus of the present invention employs directional drilling and coil tubing technologies so that it can control the movement of the gas injection position and can stably adjust the gasification agent injection parameters. 
         [0053]    In the gas injection process of the present invention, the gas injection point being able to move in any distance within the directional well channel according to requirement, and effectively improve gasification recycling rate of the coal along the directional well channel. Besides, employing annular space between the coiled tubing and the directional well wall to deliver auxiliary gasification agent can effectively prevent channel coal self-burning and gas injection tube backfire, can form mixed gasification agent at the gas injection point (nozzle position), and can continuously controlling various gas injection parameters. 
         [0054]    In the implementation process of the present invention, there is no need igniter at gas injection point to ignite, whereas it controls gasification agent injection parameters including oxygen concentration, flow rate, pressure, to make gasification channel reverse burning, quick ignition and processing, thus the gas injection point movement is continuous and the gasification process is highly stable. 
     
    
     
       DESCRIPTION OF FIGURES 
         [0055]      FIG. 1  shows the schematic diagram of the present shaftless CRIP technology. 
           [0056]      FIG. 2  shows the schematic diagram of gasification furnace employing controllable gas injection gasification. 
           [0057]      FIG. 3  shows the underground gasification furnace with supported structure at horizontal segment of directional well channel as described in Embodiment 1. 
           [0058]      FIG. 4  shows the schematic diagram of controllable gas injection point movement gasification process of Embodiment 1 (plane sectional view). 
           [0059]      FIG. 5  shows the underground gasification furnace with bare hole structure (no support structure) at horizontal segment of the directional well channel as described in Embodiment 2. 
       
    
    
       [0060]    In the figures:  1 -coiled tubing reel ;  2 -gas injection well head;  3 -coiled tubing;  4 -nozzle;  5 - glass fiber reinforced plastics sieve-tube;  6 -directional well channel;  7 -cavity;  8 -the roof of coal seam;  9 -the floor of coal seam;  10 - production well;  11 -bare hole segment of horizontal well. 
         [0061]    Hereinafter, the present invention is described in further details. However, the following embodiments are merely simple examples of the present invention and do not represent or limit the protection scope of the present invention. The scope of protection of the invention is prescribed by the attached claims. 
       DETAILED DESCRIPTION 
       [0062]    For better illustrating the present invention and helping to understand the technical solution of the present invention, the typical but non-limiting embodiments of the present invention are described in the following: 
       Embodiment 1 
       [0063]    Gas injection apparatus with controllable gas injection point comprises directional well channel  6 , the directional well channel  6  is disposed with coiled tubing  3 . The coiled tubing  3  is connected with oxygen/oxygen-enriched gas line. The annular space between the coiled tubing  3  and the directional well  6  has connection to the auxiliary gasification agent line and steam line. The start end of the coiled tubing  3  is disposed with gas injection well head  2  and the terminal end is disposed with nozzle  4 . 
         [0064]    Coiled tubing reel  1  is used for carrying the coiled tubing  3 . 
       Embodiment 2 
       [0065]    A gas injection technology with controllable gas injection point, wherein oxygen/oxygen-enriched gas is delivered by the coiled tubing deposited within the directional well channel; the oxgen/oxygen-enriched gas and the auxiliary gasification agent delivered through the annular space between the coiled tubing and the directional well wall are uniformly mixed at the nozzle at the terminal end of coiled tubing; the mixed gasification agent enters the predetermined gasification position of the coal seam through the directional well channel or the pore channel within the coal seam. 
         [0066]    The directional well channel is formed by the directional drilling method. The directional drilling method preferably employ any of directional well drilling technology, horizontal well drilling technology, lateral drilling technology, radial horizontal well technology, multilateral well technology, cluster wells technology and extended reach well technology in petroleum or coal seam gas drilling technologies. The directional well channel is longer than 10 meters. 
         [0067]    The pore channel within the coal seam is formed by artificial drilling or fracturing process, or formed by coal seam under thermal effect of burning. 
         [0068]    The directional well channels are unsupported channel or supported channel. The supported channels employ sieve-tube and/or casing-tube, preferably sieve-tube or the combination of sieve-tube and casing-tube for support. The support tube materials are combustible materials, more preferably organic materials, most preferably glass fiber reinforced plastics or PE pipe materials. 
         [0069]    The oxygen/oxygen-enriched gas is provided by the gasification agent production system. The oxygen-enriched gas is a mixed gas composed of oxygen and one or both of nitrogen and carbon dioxide, wherein the concentration by volume of oxygen is larger than 21%. 
         [0070]    The auxiliary gasification agent is one of nitrogen, carbon dioxide and water, or mixture thereof. The nitrogen is provided by a nitrogen production device. The carbon dioxide is provided by a decarbonization device. 
       Embodiment 3 
       [0071]    A controllable gas injection point gasification method, wherein reverse burning, gasification channel process and gasification production is conducted by segmentally moving the coiled tubing to make the gas injection point segmentally move to the predetermined gasification position, and then adjusting the gas injection technology parameters. 
         [0072]    The gasification method comprises the following steps: 
         [0073]    1) according to the parameters such as thickness and reserves of gasifiable coal seam in gasification area, segmentally moving coiled tubing according to the gas injection process to make the gas injection point position segmentally move to the predetermined gasification position; 
         [0074]    2) adjusting the pressure and flow rate of a single gas and controlling the parameters such as flow rate, pressure and oxygen concentration of the injected gasification agent; segmentally moving the flame working face to the predetermined gasification position in the manner of reverse burning and making gasification channel process at the same time; 
         [0075]    3) after completing the ignition and process of the gasification channel, improving intensity of the gasification agent injection, enhancing the gasification of underground coal and conducting gas production of underground gasification on a large scale; 
         [0076]    4) when the coal seam gasification of the predetermined gasification position is done, determining stopping or reducing gasification agent injection according to the amount of the coal gasified, and heat value and composition of coal gas, and starting the injector head to move the oxygen/oxygen-enriched gas injection point to the next predetermined gasification position; 
         [0077]    5) conducting the next segment gasification channel process according to step 2), and completing the underground gasification of the predetermined coal seam area according to step 3) and 4); repeating those steps until the coal resource around the directional well channel is gasified completely; 
         [0078]    wherein, the gas injection point segmental movement distance in the step 1) is 10˜150 m, the gasification flow rate during the gasification channel ignition and processing is limited within 300˜3000 m 3 /h, and the oxygen concentration by volume in the gasification agent is 21˜55%. 
       Embodiment 4 
       [0079]    A controllable gas injection point gasification method, wherein reverse burning, gasification channel processing and gasification production is conducted by continuously or intermittently lifting the coiled tubing to make the gas injection point continuously move to the predetermined gasification position, and then adjusting the gas injection technology parameters. 
         [0080]    The gasification method comprises of the following steps: 
         [0081]    1) according to the parameters such as thickness and reserve of gasifiable coal seam in gasification area, and continuously or intermittently lifting coiled tubing according to the gas injection process to make the gas injection point continuously move to the predetermined gasification position; 
         [0082]    2) adjusting the pressure and flow rate of a single gas and controlling the parameters such as flow rate, pressure and oxygen concentration of the injected gasification agent; achieving continuously processing gasification channel and underground gasification production on a large scale in a manner of reverse burning; 
         [0083]    3) adjusting the gasification agent injection parameters whenever necessary, to guarantee relative stable status of coal gas composition and heat value; 
         [0084]    4) when coal seam gasification of the predetermined gasification position is done, controlling reverse movement speed of coiled tubing according to burning speed of the coal gasification, heat value and composition of coal gas, and gasifiable coal seam storage situation, until the coal resource around the directional well channel is gasified completely; 
         [0085]    wherein, the flow rate of the gasification agent in the step 2) is set to larger than 2000 m 3 /h, and the oxygen concentration by volume of gasification agent is 21˜95%; and wherein when the oxygen volume concentration is larger than 60%, water steam or water can be injected to adjust the temperature and gas quality in the cavity. 
       Working Example 1 
       [0086]    The present example is to apply the controllable gas injection point gasification method of the present invention in the brown coal seam with low metamorphic degree. As lithology intensity of coal seam is low so that the borehole is easy to collapse and shrink, the present example select the directional horizontal well structure supported with glass fiber reinforced plastics sieve-tube, which has the common advantage of the present invention and is also beneficial to improve drilling stability and reduce drilling accident rate. 
         [0087]      FIG. 3  shows an underground gasification furnace, wherein coal seam floor  9  is at a depth of 255 meters, coal seam roof  8  is at a depth of 238 meters, and the coal is lignite. The gasification furnace comprises directional well channel  6 , production well  10 , gasification burning channels, etc. The diameter of the directional well channel  6  is 177.8 mm. The supported glass fiber reinforced plastics sieve-tube at horizontal segment of the coal seam has diameter of 139.7 mm, length of 300 meters and opening rate of 15%. The gas injection apparatus with controllable gas injection point comprises coiled tubing  3  (diameter: 66.7 mm, pressure grade: 6.0 MPa, material:316 stainless steel), gas injection well head  2 , which comprises coiled tubing operating Bop (single side door style) and coiled tubing injector head (ZRT series coiled tubing injector head); and nozzle  4  (65 mm diameter, high temperature resistance up to 1200° C.). 
         [0088]    In the example, the gas injection apparatus is employed to make gasification for the coal seam of the directional well channel  6  of the underground gasification furnace, as shown in  FIG. 4 . The gasification operating pressure of the gasification furnace is 1.5 MPa and O 2 /CO 2  is used as gasification agent for gasification production of syngas. After the gasification furnace is successfully ignited and stable gasification burning area  7  is established i at the bottom of the production well  10 , directional drilling technology is employed to build up a directional well channel  6  in predetermined gasification coal seam, then the controllable gas injection point gasification production is carried out. The detailed process and implementing steps are as follows: (1) delivering coiled tubing along directional well channel  6  to the predetermined gasification position A through gas injection well head  2  by using the injector head; avoiding to send the oxygen nozzle into the burning zone directly; (2) injecting CO 2  into the annular space between the coiled tubing and directional well wall to conduct replacement protection for the channel with initial flow rate of 300˜400 Nm 3 /h; (3) slowly injecting oxygen into the degreased coiled tubing and through oxygen nozzle to mix with CO 2  injected through the annular space; (4) controlling the total amount of injected gasification agent and oxygen concentration, segmentally moving flame working face to the predetermined gasification position in the manner of reverse burning, and making gasification channel processing at the same time; the amount of the gasification agent for reverse ignition and processing channel is 500˜3000 Nm 3 /h and the oxygen concentration is 25˜35%; (5) after the channel ignition and processing is completed, gradually improving the injection amount of the gasification agent to 4000˜6000 Nm 3 /h, and the oxygen concentration to 60˜70% and then conducting coal gas production on a large scale; (6) when the gasification at the predetermined gasification position is completed, determining stopping or reducing gasification agent injection according to the condition of gasification coal burning amount, gas production heat value and composition, and starting the injector head and continuously moving coiled tubing  3  to make the oxygen injection point move to the next predetermined gasification position B; the distance between the predetermined gasification position A and B is 0˜100 m; (7) conducting gasification channel processing according to steps (2)-(4) and accomplishing the underground gasification of the predetermined area according to steps (4) and (5); repeating those steps until the coal resource around the directional well channel  6  is gasified completely. 
       Working Example 2 
       [0089]    The present example is to apply controllable gas injection point gasification method of the present invention on the lean coal seam with high metamorphic degree. As coal seam lithology is good and intensity is high, the present example selects unsupported directional horizontal well structure, which has the common advantage of the present invention and is also beneficial to reduce furnace building cost and improve coal seam ignition efficiency. 
         [0090]      FIG. 5  shows an underground gasification furnace, wherein coal seam floor  9  is at a depth of 957 meters, coal seam roof  8  is at a depth of 950 meters, and the coal is lean coal. The gasification furnace comprises directional well channel  6 , production well  10 , gasification burning channels, etc. The diameter of the directional well channel  6  is 177.8 mm. Bare hole segment  11  in horizontal well (the horizontal well of the coal seam has unsupported bare hole) is 200 meters long. The gas injection apparatus with controllable gas injection point comprises coiled tubing  3  (diameter: 50.8 mm, pressure grade: 6.0 MPa, material: 316 stainless steel, Jiang Su Dong Tai Hua Xuan Company), gas injection well head  2 , which comprises coiled tubing operating Bop (single side door style, Ao Lan Petroleum Company) and coiled tubing injector head (ZRT series coiled tubing injector head, Yan Tai Jie Rui Company) and nozzle  4  (50 mm diameter, high temperature resistance up to 1200° C., ENN Coal Gasification mining Co., Ltd.). 
         [0091]    In the example, gas injection apparatus is employed to conduct gasification for the coal seam of the directional well channel  6  of the underground gasification furnace, as shown in  FIG. 5 . The gasification operating pressure of the gasification furnace is 2.5 MPa and O 2 /CO 2  is used as gasification agent for gasification production of syngas. After the gasification furnace is successfully ignited and stable gasification burning area  7  is established at the bottom of the production well  10 , directional drilling technology is employed to build up directional well channel  6  in predetermined gasification coal seam and then controllable gas injection point gasification production is carried out. The detailed process and implementing steps are as follows: (1) delivering coiled tubing along directional well channel  6  to the predetermined gasification position A through gas injection well head  2  by using the injector head; avoiding to send the oxygen nozzle into the burning zone directly; (2) injecting CO 2  into the annular space between the coiled tubing and directional well wall to conduct replacement protection for the channel with initial flow rate of 400˜600 Nm 3 /h; (3) slowly injecting oxygen into the degreased coiled tubing and through oxygen nozzle to mix with CO 2  injected through the annular space; (4) controlling the total amount of the injected gasification agent and oxygen concentration, segmentally moving the flame working face to the predetermined gasification position in the manner of reverse burning, and conducting gasification channel processing at the same time; the gasification agent amount for reverse ignition and processing channel is 600˜3500 Nm 3 /h and the oxygen concentration is 25˜55%; (5) after channel ignition and processing is completed, gradually improving the injection amount of the gasification agent to 4000-7500 Nm 3 /h and oxygen concentration to 60˜70% and then conducting coal gas production on a large scale; (6) when the gasification at the predetermined gasification position is completed, determining stopping or reducing gasification agent injection according to the condition of the amount of coal gasified, gas production heat value and composition, and starting the injector head and continuously moving coiled tubing  3  to make the oxygen injection point move to the next predetermined gasification position B; the distance between the predetermined gasification position A and B is 0˜40 m; (7) conducting gasification channel processing according to steps (2)-(4) and accomplishing the underground gasification of the predetermined area according to steps (4) and (5); repeating those steps until the coal resource around the directional well channel  6  is gasified completely. 
         [0092]    When the syngas (including H 2 , CO, CH 4 , CO 2 , H 2 O, etc.) produced by the gasification method of the present invention is delivered to the ground through the production well  10  and purified, the product mainly comprising H 2 , CO, CH 4  is obtained. 
         [0093]    The applicant stated that the present invention employ the embodiments and examples above to describe the detailed structure feature and the gas injection and gasification methods of the present invention, but the present invention is not limited to the detailed structure feature and the injection and gasification methods above, i.e. it does not mean that the present invention must rely on the detailed structure feature and the gas injection and gasification methods above to implement. Persons skilled in the art should understand, any improvement of the present invention, the equivalent replacement to the raw materials of the present invention product, adding auxiliary ingredients, specific mode selection, etc. fall within the protection scope and disclosure scope of the present invention.