Underground coal gasification furnace and underground coal gasification method

Abstract

An underground coal gasification furnace comprises an ignition system and a gas injection system. The ignition system is provided with a first vertical drilling well and a first horizontal directional drilling well in communication with the first vertical drilling well. The gas injection system is provided with a second drilling well introduced into a coal seam. At least one second horizontal directional drilling wells of a horizontal section in the coal seam serves as the second drilling well. Also provided is an underground coal gasification method. The method comprises: enabling a flaming fire region of a first horizontal directional drilling well to withdraw in a second horizontal directional drilling well until withdraw to near a coal feeding point. The underground coal gasification furnace eliminates the defects of low cut-through speed and unstable structure in a gasification production stage in the prior art.

1 . An underground coal gasification furnace, comprising:
 an ignition system having a first vertical drilling well entering into coal seam, and a first horizontal directional drilling well with a horizontal section in the coal seam and in communication with the first vertical drilling well;   a gas injection system having a second drilling well entering into the coal seam and in communication with the first horizontal directional drilling well,   wherein, the second drilling well is at least one second horizontal directional drilling wells with a horizontal section in the coal seam.   
     
     
         2 . The underground coal gasification furnace according to  claim 1 , wherein, the first horizontal directional drilling well is communicated with the second horizontal directional drilling wells by means of reverse combustion. 
     
     
         3 . The underground coal gasification furnace according to  claim 1 , wherein, the second drilling wells are at least two second horizontal directional drilling wells parallel to each other, which are arranged on one side or on both sides of the first horizontal directional drilling well in the direction of intersecting the first horizontal directional drilling well. 
     
     
         4 . The underground coal gasification furnace according to  claim 3 , wherein, the second horizontal directional drilling wells forms an angle of 30°-90° with the first horizontal directional drilling well. 
     
     
         5 . The underground coal gasification furnace according to  claim 1 , wherein, at least one second vertical drilling wells is disposed along the first horizontal directional drilling well,
 wherein all of the second vertical drilling wells are in communication with each other by means of reverse combustion of the first horizontal directional drilling well to form a gas production well.   
     
     
         6 . The underground coal gasification furnace according to  claim 5 , wherein, the end of the horizontal section of the first horizontal directional drilling well is communicated with the first vertical drilling well by means of combustion penetration or directional blasting or cold-state fracturing. 
     
     
         7 . The underground coal gasification furnace according to  claim 5 , wherein, the end of the horizontal section of the first horizontal directional drilling well is communicated with the first vertical drilling well directly. 
     
     
         8 . The underground coal gasification furnace according to  claim 1 , wherein, the second drilling wells are at least two second horizontal directional drilling wells, which are arranged on the same side of the first horizontal directional drilling well,
 wherein one second horizontal directional drilling wells is directed to and is communicated with the first vertical drilling well by means of fracturing penetration; and at least one third vertical drilling wells is arranged along said one second horizontal directional drilling well, wherein said one second horizontal directional drilling well is communicated with the third vertical drilling wells by means of reverse combustion and form together the gas production wells.   
     
     
         9 . The underground coal gasification furnace according to  claim 1 , wherein, the nude section of each of all drilling wells located in the coal seam is supported and protected by a supporting and protection arrangement. 
     
     
         10 . The underground coal gasification furnace according to  claim 9 , wherein, the supporting and protection arrangement is a sieve pipe or seamless pipe. 
     
     
         11 . The underground coal gasification furnace according to  claim 1 , wherein, a towable gasifying agent-introduction pipe is at least arranged in one of said second horizontal directional drilling wells, the gas injection end of which moves when the gasifying agent-introduction pipe is towed. 
     
     
         12 . An underground coal gasification process, comprises:
 the step of constructing an underground coal gasification furnace according to  claim 1 ; and   the step of performing gasification in the constructed gasification furnace, comprising: guiding the combustion zone of the first horizontal directional drilling well to retreat in the second horizontal directional drilling wells until back to the vicinity of the coal feeding point of the second horizontal directional drilling wells.   
     
     
         13 . The underground coal gasification process according to  claim 12 , wherein, the step of constructing an underground coal gasification furnace includes the following sub-steps 1-2, which are performed sequentially:
 the sub-step 1: the following drilling wells are drilled one after another: a first vertical drilling well entering into the coal seam, a first horizontal directional drilling well with a horizontal section in the coal seam, at least two second vertical drilling wells arranged along the first horizontal directional drilling well, and at least two second horizontal directional drilling wells arranged on one side or on both sides of the first horizontal directional drilling well and having a horizontal section in the coal seam, wherein all these drilled drilling wells are separated from each other; and   the sub-step 2: firstly communicating the first horizontal directional drilling well with the first vertical drilling well, and then igniting the coal seam at the bottom of the first vertical drilling well, injecting gasifying agent from the first horizontal directional drilling well, guiding the movement of the combustion zone to perform reverse combustion to the first horizontal directional drilling well, until realizing the communication with the rest of drilling wells in the sub-step 1.   
     
     
         14 . The underground coal gasification process according to  claim 13 , wherein, the pressure air is introduced into the second horizontal directional drilling wells while the first horizontal directional drilling well is subjected to reverse combustion, wherein the pressure of the pressure air is greater than that in the first horizontal directional drilling well. 
     
     
         15 . The underground coal gasification process according to  claim 13 , wherein, the guiding the movement of the combustion zone in the sub-step 2 is realized by towing the coiled tubing in the first horizontal directional drilling well to make its gas injection end move. 
     
     
         16 . The underground coal gasification process according to  claim 13 , wherein, the first horizontal directional drilling well is drilled towards the first vertical drilling well against the developing direction of cracks in coal seam. 
     
     
         17 . The underground coal gasification process according to  claim 12 , wherein, the step of constructing an underground coal gasification furnace includes the following sub-steps 1-3, which are performed sequentially:
 the sub-step 1: the first vertical drilling well and at least two second vertical drilling wells are drilled successively in the developing direction of cracks in coal seam, which enter into the coal seam and are separated from each other, and then the first horizontal directional drilling well is drilled against the developing direction of cracks in coal seam towards the direction of the first vertical drilling well, the first horizontal directional drilling well communicates the first vertical drilling well and some of the second vertical drilling wells in the coal seam;   the sub-step 2: at least two second horizontal directional drilling wells are drilled on one side of the first horizontal directional drilling well, wherein the ends of said at least two second horizontal directional drilling wells are directed to the first horizontal directional drilling well, wherein the end of some second horizontal directional drilling wells is communicated with the first horizontal directional drilling well, and the end of the other second horizontal directional drilling wells keeps a certain distance from the first horizontal directional drilling well;   the sub-step 3: the coiled tubing is inserted into the first horizontal directional drilling well, and the gasifying agent is injected into the first horizontal directional drilling well through the coiled tubing, igniting the coal seam at the bottom of the first vertical drilling well, the coiled tubing is towed to guide the movement of the combustion zone to perform reverse combustion in the first horizontal directional drilling well, until the other second horizontal directional drilling wells and the other second vertical drilling wells are communicated with the first horizontal directional drilling well.   
     
     
         18 . The underground coal gasification process according to  claim 17 , wherein, the sub-step 2 further comprises: a fourth vertical drilling wells are drilled into the coal seam on one side of the first horizontal directional drilling well, and are respectively communicated with the second horizontal directional drilling wells in one-to-one manner,
 when the combustion zone in the second horizontal directional drilling well moves to the bottom of the fourth vertical drilling wells, the fourth vertical drilling wells are used as gas production wells instead of the first vertical drilling well, the second vertical drilling wells and the first horizontal directional drilling well during the gasification in the constructed gasification furnace.   
     
     
         19 . The underground coal gasification process according to  claim 13 , wherein, the other second horizontal directional drilling wells are used as gas production wells, when the gasifying agent introduction pipe in some second horizontal directional drilling wells is towed to move the combustion zone,
 wherein the gasifying agent introduction pipe in the other second horizontal directional drilling wells is drawn out when these second horizontal directional drilling wells are used as gas production wells, the first horizontal directional drilling well, the first vertical drilling well and the arranged second vertical drilling well are closed.   
     
     
         20 . The underground coal gasification process according to  claim 12 , wherein, the step of constructing an underground coal gasification furnace includes:
 (I) to construct an ignition system and production wells system for gasification furnace by means of the following way: the following drilling wells entering into the coal seam are drilled one after another: the first vertical drilling well; the first horizontal directional drilling well and one second horizontal directional drilling well which are perpendicular to each other and have the horizontal section in the coal seam; a second vertical drilling wells and a third vertical drilling wells, which are respectively arranged crosswise along these two horizontal directional drilling wells; then these two horizontal directional drilling wells are communicated with the first vertical drilling well through fracturing, and then the first horizontal directional drilling well is subjected to reverse combustion until the second vertical drilling wells along the line are penetrated to form the ignition system, as well as the second horizontal directional drilling well is subjected reverse combustion until the third vertical drilling wells along the line are penetrated to form the production wells system; and   (II) the rest of second horizontal directional drilling parallel to said one second horizontal directional drilling well are drilled while the ignition system and the production wells system for gasification furnace are constructed, wherein the horizontal sections of said rest of second horizontal directional drilling wells are located in the coal seam, and the ends of the horizontal sections are directed to the first horizontal directional drilling well and are communicated with the same by means of pressure air fracturing.   
     
     
         21 . The underground coal gasification process according to  claim 20 , wherein, the reverse combustion is realized in the following manner: igniting the coal seam in the first vertical drilling well, towing the gas injection end of the coiled tubing in the first horizontal directional drilling well and said one second horizontal directional drilling well to guide the combustion zone to move along these two horizontal directional drilling wells to realize reverse combustion.