Results of Subsurface Shut-In Analyses

Vent wells have enabled controlled release of subsurface pressure over most of the affected area. In general, higher surface shut-in pressures have been noted closer to Yaggy and along the crest of the Yaggy-Hutchinson anticline. Current flow rates and shut-in pressures indicate that limited volumes of gas are venting from the remaining wells. Areas of the subsurface continue to be pressurized, though sub-hydrostatically, along the crest of the anticline; thus, select wells have been kept open for continued monitoring. The present slow decline in subsurface pressures associated with negligible gas flow at vent wells suggests reduced permeabilities and loss of apparent connectivity. This is consistent with a fracture model where, with reduced gas pressure, fracture apertures are reduced and closed due to decreased pore pressure.

Calculated shut-in pressures (psi) at 3-finger dolomite
(Bhattacharya and Watney, 2001, 2002, 2003)

March 2001 Survey

Shut-in times varied between 14 to 50 hrs to operate within safety limits of surface equipment

August 2001 Survey

Shut-in times varied between 70 to 96 hrs

January 2002 Survey

Shut-in times varied between 70 to 96 hrs

July 2002 Survey

Shut-in times varied between 75 to 95 hrs

Jan-Feb 2003 Survey

Shut-in times varied between 75 to 95 hrs. Group 2 wells (that never flowed gas) were plugged.

July-Aug 2003 Survey

Shut-in times varied between 70 to 96 hrs

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Last updated June 2004
http://www.kgs.ku.edu/PRS/publication/2004/AAPG/NG_Migration/P3-03.html