Method for enhancing methane production from coal seams

Abstract

Discloses a three step process to stimulate well production of methane from coal seams, wherein step one provides for injection of a treating gas into a well bore intersecting a coal seam, step two includes a shut-in period and step three comprises the placement of a propped fracture treatment. In step one, the injection of the treating gas physically opens pre-existing paths of weakness in the coal. As the treating gas travels along these planes of weakness, it preferentially adsorbs onto the coal and displaces the methane. This displacement process induces shrinkage of the coal matrix, which further increases the size of the intervening existing fractures. The second step, or shut-in period, allows time for this gas exchange process to substantially complete, thereby maximizing the effect of matrix shrinkage and enhancement of the intervening fractures. The third step provides for placement of a propped fracture treatment into this enhanced fracture system. Propping of the enhanced fractures ensures that they remain open, even as removal of water and methane work to close the fractures by increasing effective stress within the coals. The result is a stimulated coal seam that maintains enhanced permeability during production operations.

1 . A method for in situ stimulation of a methane production from a coal seam comprising the steps of: 
 i) supplying a treating gas containing nitrogen into a subterranean methane bearing coal seam via a wellbore intersecting said subterranean coal seam; and    ii) closing the well bore for a shut-in period.    
   
   
       2 . The method of  claim 1  further including the step of pressing of a fracture treatment containing proppant into said methane bearing subterranean coal seam.  
   
   
       3 . The method of  claim 1  step of closing includes further supply of treating gas to maintain a predetermined pressure at the point of supply over at least a portion of the shut-in period.  
   
   
       4 . The method of  claim 1  step of closing includes further supply of treating gas to maintain a predetermined pressure above atmospheric pressure at the point of supply over at least a portion of the shut-in period.  
   
   
       5 . The method of  claim 1  step of closing includes further supply of treating gas at a predetermined supply rate or over at least a portion of the shut-in period.  
   
   
       6 . The method of  claim 3  further including the step of pressing of a fracture treatment containing proppant into said methane bearing subterranean coal seam.  
   
   
       7 . The method of  claim 4  further including the step of pressing of a fracture treatment containing proppant into said methane bearing subterranean coal seam.  
   
   
       8 . The method of  claim 5  further including the step of pressing of a fracture treatment containing proppant into said methane bearing subterranean coal seam.  
   
   
       9 . The method of  claim 1  wherein the treating gas is ambient or atmospheric air.