Method of Monitoring Underground Diffusion of Carbon Dioxide

Abstract

An object is to provide a monitoring method for monitoring underground diffusion of carbon dioxide, which is used when injecting carbon dioxide into an underground coal seam to cause it to be adsorbed to the coal seam, and collecting hydrocarbon gases that have been displaced by the carbon dioxide and released from the coal seam, and with which the behavior of carbon dioxide injected into the ground can be continuously measured over a long period of time at a low cost, using a relatively simple device. A plurality of wells including an injection well 3 and a production well 4 extending to underground coal seams (main layer 1 and lower layer 2 ) are formed. When injecting carbon dioxide into the injection well under pressure, and collecting hydrocarbon gases displaced by the carbon dioxide stored in the coal of the coal seams from the production well 4, high-precision tiltmeters are placed on the bottoms of observation holes drilled in the ground at a plurality of points (A, B, C, D, E and F) between the injection well 3 and the production well 4, and by checking chronological changes in the inclination angles at these points with the tiltmeters, diffusion of underground carbon dioxide gas is monitored.

1 . A method of monitoring diffusion of carbon dioxide into the ground, comprising providing at least one injection well and at least one production well which both lead to an underground coal seam, providing a plurality of tiltmeters at intervals in the ground above the coal seam and between the injection well and the production well, injecting under pressure carbon dioxide gas into the injection well to allow the carbon dioxide gas to diffuse into the coal seam, producing hydrocarbon gases in the coal seam which have been displaced by the carbon dioxide gas that has diffused into the coal seam from the production well, and simultaneously monitoring how the carbon dioxide has diffused into the ground corresponding to the amount of production of the hydrocarbon gases by checking chronological changes in inclinations angles as indicated on the tiltmeters. 
   
   
       2 . The method of monitoring diffusion of carbon dioxide into the ground as recited in  claim 1  wherein said tiltmeters can measure inclination angles in increments of 10 −6  to 10 −9  radians. 
   
   
       3 . The method of monitoring diffusion of carbon dioxide into the ground as recited in  claim 1  wherein said tiltmeters are provided in the ground above a cap rock layer which lies above the coal seam. 
   
   
       4 . The method of monitoring diffusion of carbon dioxide into the ground as recited in  claim 1  wherein said tiltmeters are provided in the ground at a depth of 10 to 60 m. 
   
   
       5 . The method of monitoring diffusion of carbon dioxide into the ground as recited in  claim 2  wherein said tiltmeters are provided in the ground above a cap rock layer which lies above the coal seam. 
   
   
       6 . The method of monitoring diffusion of carbon dioxide into the ground as recited in  claim 2  wherein said tiltmeters are provided in the ground at a depth of 10 to 60 m.