System, method, and apparatus for degassing tool for coal bed methane gas wells

Abstract

A coal bed methane degassing tool is installed at the bottom of a first joint of production casing. As the casing is lowered into the well hole, the tool is fished to the top of the casing as more joints are added. The pressure at the tool may be recorded and logged. Any excessive pressure observed at the tool may be bled off by the tool automatically or manually. As more casing is tripped in, the tool is brought to the top. At the end of the run a log of formation pressure is established. Reservoir engineers can determine reserves in coal bed methane wells drilled and completed before the well is bled off and the tool is removed.

1 . A downhole tool for installing a well, comprising: 
 a body having a plug shaft including a distal end, a fishing shaft located opposite the distal end, and a bore extending from the distal end;    a plug mounted to the plug shaft and having an outer diameter adapted to engage and seal the inner wall of production casing; and    a pressure gage in fluid communication with the bore and extending from the fishing shaft, the pressure gage being adapted to measure pressure in the well downwell from the downhole tool.    
   
   
       2 . A downhole tool according to  claim 1 , wherein the plug shaft has a diameter that is less than a diameter of the fishing shaft, a shoulder is formed at an interface between the plug and fishing shafts, and the plug abuts the shoulder.  
   
   
       3 . A downhole tool according to  claim 1 , wherein the body has an axis and the bore in the body extends along the axis from the threaded end to the fishing shaft.  
   
   
       4 . A downhole tool according to  claim 1 , wherein the plug is a cementing plug.  
   
   
       5 . A downhole tool according to  claim 1 , wherein the distal end of the plug shaft is threaded, and a nut is fastened to the threaded end of the plug shaft for securing the plug to the body such that the plug is axially restrained by the nut.  
   
   
       6 . A downhole tool according to  claim 1 , further comprising a safety relief valve in fluid communication with the bore and extending from the fishing shaft, the safety relief valve being adapted to relieve excessive pressure in the well downwell from the downhole tool.  
   
   
       7 . A method of installing a well, comprising: 
 (a) positioning a downhole tool in a joint of production casing such that the downhole tool seals against an inner surface of the joint of production casing;    (b) installing the joint of production casing in the well;    (c) fishing the downhole tool upward in a string of the production casing;    (d) reading the downhole tool for a gas formation pressure of the well beneath the downhole tool;    (e) installing additional joints of production casing in the surface casing to a desired depth of the well; and    (f) reading the downhole tool for the gas formation pressure of the well during step (e).    
   
   
       8 . A method according to  claim 7 , further comprising bleeding off any excessive formation pressure through the downhole tool.  
   
   
       9 . A method according to  claim 8 , wherein the excessive formation pressure is a low pressure formation in excess of 50 psi.  
   
   
       10 . A method according to  claim 7 , wherein the downhole tool is positioned at lower ends of the joints of production casing.  
   
   
       11 . A method of installing a well, comprising: 
 (a) drilling a well bore;    (b) installing surface casing in the well bore to a nominal depth;    (c) positioning a downhole tool in an initial joint of production casing such that the downhole tool seals against an inner surface of the initial joint of production casing;    (d) installing the initial joint of production casing in the surface casing;    (e) fishing the downhole tool to an upper end of the initial joint of production casing adjacent a surface of the well;    (f) reading the downhole tool at the surface of the well for a gas formation pressure of the well beneath the downhole tool;    (g) installing additional joints of production casing in the surface casing to a desired depth of the well;    (h) reading the downhole tool for the gas formation pressure of the well during step (g); and    (i) bleeding off any excessive formation pressure through the downhole tool during steps (d) through (h).    
   
   
       12 . A method according to  claim 11 , wherein step (c) comprises positioning the downhole tool at a lower end of the initial joint of production casing.  
   
   
       13 . A method according to  claim 11 , wherein step (i) comprises low pressure gas formation pressures on the order of 50 psi.