Coalbed gas production systems

Abstract

A method of stimulating coalbed methane production by injecting gas into a producer and subsequently placing the producer back on production is described. A decrease in water production may also result. The increase in gas production and decrease in water production may result from: (1) the displacement of water from the producer by gas; (2) the establishment of a mobile gas saturation at an extended distance into the coalbed, extending outward from the producer; and (3) the reduction in coalbed methane partial pressure between the coal matrix and the coal's cleat system.

1 . An apparatus for coalbed gas production comprising: 
 a coalbed structure having a permeability characteristic;    at least one production well which communicates with said coalbed structure;    a stimulation gas having a pressure in a range which alters said permeability characteristic of said coalbed structure and which avoids disruption of said coalbed structure;    a stimulation gas transfer element;    a production well coupling element responsive to said stimulation gas transfer element and said production well; and    a reduced water permeability coalbed.    
   
   
       2 . An apparatus for coalbed gas production as described in  claim 1  wherein said stimulation gas having said pressure in a range which alters said permeability characteristic of said coalbed structure and which avoids disruption of said coalbed structure is not greater than a pressure necessary to reduce said water permeability coalbed.  
   
   
       3 . An apparatus for coalbed gas production as described in  claim 2  further comprising: 
 coalbed gas sorbed on said coalbed structure;    desorbed coalbed gas from said reduced water permeability coalbed;    a desorbed coalbed gas removal system; and    desorbed coalbed gas removed from said reduced water permeability coalbed through said production well.    
   
   
       4 . An apparatus for coalbed gas production as described in  claim 1  or  3  further comprising: 
 water in at least a portion of a coalbed gas reservoir;    a calculated water displacement pressure not substantially larger than a hydrostatic pressure to displace at least a portion of said water from said coalbed gas reservoir;    a water displacement perimeter; and    at least one water confinement well to communicate with said water located at about said water displacement perimeter.    
   
   
       5 . An apparatus for coalbed gas production as described in  claim 4  wherein said at least one water confinement well has a location at about said water displacement perimeter and assists said production well to remove coalbed gas at a rate which is never less than a desorption rate of said coalbed structure.  
   
   
       6 . An apparatus for coalbed gas production as described in  claim 5  further comprising: 
 an appropriate volume of said stimulation gas based upon said permeability characteristic.    
   
   
       7 . An apparatus for coalbed gas production as described in  claim 6  wherein said appropriate volume of said stimulation gas based upon said permeability characteristic results in coalbed gas removed from said stimulated coalbed gas reservoir which contains less than four percent stimulation gas per unit volume.  
   
   
       8 . An apparatus for coalbed gas production as described in  claim 3  further comprising: 
 a calculated coalbed gas desorption rate at which said coalbed gas desorbs from said coalbed structure; and    a coalbed gas removal element having a calculated coalbed gas removal rate which is never less than said calculated coalbed gas desorption rate.    
   
   
       9 . An apparatus for coalbed gas production as described in  claim 4  wherein said at least one production well has a location approximately at a centroid of an approximately 40 acre to 320 acre tract of land.  
   
   
       10 . An apparatus for coalbed gas production as described in  claim 9  wherein said approximately 40 acre to 320 acre tract of land has a substantially square perimeter.  
   
   
       11 . An apparatus for coalbed gas production as described in  claim 10  wherein said at least one water confinement well comprises locating four water confinement wells located at corners of said substantially square perimeter around said tract of land.  
   
   
       12 . An apparatus for coalbed gas production as described in  claim 10  wherein said approximately 40 acre to 320 acre tract of land having said substantially square perimeter has a location adjacent to another approximately 40 acre to 320 acre tract of land having a production well.  
   
   
       13 . An apparatus for coalbed gas production as described in  claim 1 ,  3  or  8  wherein said stimulation gas is selected from a group consisting of nitrogen, carbon dioxide, air, and gas less sorptive to coal than methane.  
   
   
       14 . A method of producing coalbed gas, which comprises the steps of: 
 locating a coalbed structure having a water permeability characteristic;    establishing at least one production well to communicate with said coalbed structure;    providing a stimulation gas;    injecting said stimulation gas in a manner which avoids disturbing said coalbed structure; and    altering said water permeability characteristic of said coalbed structure through injection of said stimulation gas in a vicinity of said at least one production well.    
   
   
       15 . A method of producing coalbed gas as described in  claim 14  wherein said step of providing said stimulation gas comprises providing stimulation gas having a pressure which is not greater than a pressure necessary to reduce said water permeability of said coalbed structure.  
   
   
       16 . A method of producing coalbed gas as described in  claim 15  and further comprising the steps of: 
 locating coalbed gas sorbed on said coalbed structure;    desorbing coalbed gas from said coalbed having said water permeability characteristic altered by said stimulation gas; and    removing desorbed coalbed gas from said coalbed structure.    
   
   
       17 . A method of producing coalbed gas as described in  claim 15  wherein said step of providing said stimulation gas having a pressure which is not greater than a pressure necessary to reduce said water permeability of said coalbed structure comprises using a stimulation gas pressure calculation element.  
   
   
       18 . A method of producing coalbed gas as described in  claim 1  or  16  and further comprising the step of calculating an appropriate volume of said stimulation gas to inject into said coalbed structure based upon a characteristic of said coalbed structure which results in produced coalbed gas from said production well having less than four percent stimulation gas per unit volume of produced coalbed gas.  
   
   
       19 . A method of producing coalbed gas as described in  claim 1  or  16  and further comprising the step of calculating an appropriate volume of said coalbed stimulation gas to inject into said coalbed based upon a characteristic of said coalbed which results in produced coalbed gas from said production well having less than ten percent stimulation gas per unit volume of produced coalbed gas.  
   
   
       20 . A method of producing coalbed gas as described in  claim 14  which further comprises the steps of: 
 locating water in at least a portion of a coalbed gas reservoir;    calculating a water displacement pressure not substantially larger than said hydrostatic pressure to displace at least a portion of said water from said coalbed gas reservoir;    displacing said water in said at least a portion of said coalbed gas reservoir;    establishing a water displacement perimeter;    establishing at least one water confinement well to communicate with said water located at about said water displacement perimeter; and    maintaining said water displacement perimeter by removing said water encroaching upon said water displacement perimeter.    
   
   
       21 . A method of producing coalbed gas as described in  claim 20  which further comprises the steps of calculating a coalbed gas desorption rate at which said coalbed gas desorbs from said coal and wherein said step of removing coalbed gas from said coalbed gas reservoir has a rate which is never less than said calculated coalbed gas desorption rate.  
   
   
       22 . A method of producing coalbed gas as described in  claim 21  wherein said step of removing coalbed gas from said coalbed gas reservoir at said rate comprises removing coalbed gas from said water confinement wells.  
   
   
       23 . A coalbed gas produced in accordance with the method of  claim 14 ,  16  or  20 .  
   
   
       24 . A method of producing coalbed gas as described in  claim 14  wherein said step of establishing said at least one production well comprises locating said production well approximately at a centroid of an approximately 40 acre to 320 acre tract of land.  
   
   
       25 . A method of producing coalbed gas as described in  claim 24  wherein said locating said production well approximately at said centroid of said approximately 40 acre to 320 acre tract of land comprises establishing a substantially square perimeter having four confinement wells located at about the corners of said substantially square perimeter.  
   
   
       26 . A method of producing coalbed gas as described in  claim 25  further comprising the step of locating said at least one production well at a centroid of an approximately 40 acre to 320 acre tract adjacent to an approximately 40 acre to 320 acre tract having a production well.  
   
   
       27 . A method of producing coalbed gas as described in  claim 14 ,  16 ,  20  or  21 , wherein said step of injecting a stimulation gas into said coalbed structure comprises injecting a gas selected from a group consisting of nitrogen, carbon dioxide, air, and gas less sorptive to coal than methane.