Underground coal gasification and associated systems and methods

Abstract

Methods and systems for gasifying coal are disclosed herein. In some embodiments, a representative coal gasification system can comprise (i) an injection well extending from a ground surface to an underground coal gasification (UCG) reaction region of a coal seam; (ii) a production well spaced apart from the injection well and extending from the ground surface to the UCG reaction region, and (iii) conduits each extending from the ground surface to areas of the coal seam. End portions of the conduits within the coal can be laterally peripheral to the UCG reaction region. The conduits are configured to deliver a primary fluid from the ground surface to the primary region, the injection well is configured to deliver an oxidant gas to the UCG reaction region, and the production well is configured to deliver the product gas from the UCG reaction region to the ground surface.

1 - 20 . (canceled) 
     
     
         21 . An underground injection system, comprising:
 conduits extending to an underground area comprising a coal seam, wherein the underground area is laterally outward of a reaction region that supports a reaction in which product gas comprising hydrogen is produced, wherein (i) the underground area has a depth corresponding to a lithostatic pressure of at least 300 bar and (ii) the coal seam has a hydrostatic reservoir pressure less than the lithostatic pressure; and   a compressor fluidly coupled to a primary fluid and configured to pressurize the primary fluid to or above the lithostatic pressure, wherein the compressor is fluidly coupled to the conduits such that, in operation, the pressurized primary fluid (i) is injected to the underground area via the conduits and (ii) causes a secondary fluid comprising water and/or methane to be released from the underground area.   
     
     
         22 . The system of  claim 21 , wherein the pressurized primary fluid has a pressure approximately equal to the lithostatic pressure. 
     
     
         23 . The system of  claim 21 , wherein the hydrostatic reservoir pressure is at least 150 bar. 
     
     
         24 . The system of  claim 21 , further comprising a production well fluidically coupled to the conduits, such that, in operation, the product gas is removed from the reaction region. 
     
     
         25 . The system of  claim 24 , wherein the product gas has product pressure, and wherein the hydrostatic reservoir pressure is between the product pressure and a pressure of the pressurized primary fluid. 
     
     
         26 . The system of  claim 21 , further comprising an injection well fluidically coupled to the conduits, such that, in operation, an oxidant is injected into the reaction region. 
     
     
         27 . The system of  claim 21 , further comprising a production well spaced apart from an injection well and extending from the underground area. 
     
     
         28 . The system of  claim 21 , further comprising:
 an injection well extending to the reaction region and configured to deliver an oxidant to the reaction region; and   a production well extending from the reaction region and configured to receive the product gas from the reaction region.   
     
     
         29 . The system of  claim 28 , wherein end portions of the conduits are disposed within the coal seam and are each laterally peripheral to end portions of each of the injection well and the production well. 
     
     
         30 . The system of  claim 28 , wherein end portions of the conduits define a perimeter at least partially surrounding the injection well and the production well. 
     
     
         31 . The system of  claim 21 , wherein injection of the pressurized primary fluid causes the coal seam to form a barrier around or above the reaction region. 
     
     
         32 . The system of  claim 21 , wherein injection of the pressurized primary fluid causes the coal seam to form a barrier or a sequestration cap around the reaction region and/or above the coal seam. 
     
     
         33 . An underground injection system, comprising:
 conduits extending to an underground area comprising coal, wherein the underground area is laterally outward of a reaction region that supports a reaction in which product gas comprising hydrogen is produced, wherein the underground area has a depth corresponding to a lithostatic pressure of at least 300 bar;   a compressor fluidly coupled to a primary fluid and to the conduits, the compressor configured to pressurize the primary fluid to or above the lithostatic pressure; and   a controller configured to monitor injection of the primary fluid, such that the primary fluid is injected from the compressor to the underground area via the conduits at a pressure at or above the lithostatic pressure.   
     
     
         34 . The system of  claim 33 , wherein the controller is configured to regulate a flow rate of the primary fluid injected from the compressor into the underground area. 
     
     
         35 . The system of  claim 33 , wherein the controller is configured to adjust operation of the compressor to vary the injection pressure of the primary fluid based on the lithostatic pressure. 
     
     
         36 . The system of  claim 33 , wherein the controller is configured to adjust operation of the compressor to vary the injection pressure of the primary fluid based on a flow rate and/or composition of the product gas. 
     
     
         37 . The system of  claim 33 , wherein the primary fluid is injected at a pressure approximately equal to the lithostatic pressure. 
     
     
         38 . The system of  claim 33 , wherein the primary fluid causes a secondary fluid comprising water and/or methane to be released from the underground area. 
     
     
         39 . The system of  claim 33 , wherein the underground area comprises a coal seam, and wherein the injected primary fluid causes the coal seam to form a barrier around or above the reaction region. 
     
     
         40 . The system of  claim 33 , further comprising:
 an injection well extending to the reaction region and configured to deliver an oxidant to the reaction region; and   a production well extending from the reaction region and configured to receive the product gas from the reaction region.