Sub-Hydrostatic Pore Pressure in the Powder River Basin, Wyoming and Montana, and Implications for Re-injection of Coalbed Methane Produced Waters

Ross, Hannah E. ¹, Mark D. Zoback¹ (1) Stanford University, Stanford, CA

Coalbed methane (CBM) production in the Powder River Basin (PRB) is often accompanied by production of large volumes of CBM water. The discharge of CBM water can have significant environmental impacts if the water contains high concentrations of salts or other contaminants. One option for the disposal of contaminated water is re-injection into aquifers. For re-injection to be feasible, the pore pressure of the aquifer needs to be low, and porosity and permeability of the sand needs to be relatively high. In addition, re-injection can only happen in aquifers where the quality of water being disposed of is comparable to the water quality of the aquifer. At present we have analyzed pore pressures from ~200 wells that monitor water levels in coalbeds and adjacent sands within the PRB. These waterlevel monitoring wells are located in the central part of the PRB in Wyoming and the south central part of the basin in Montana. Over 95% of these wells have pore pressures below hydrostatic pressure, which has important implications for re-injection of CBM waters. Currently we are extending our analysis of pore pressures in the PRB to look at the aerial extent and controls on sub-hydrostatic pore pressures and the possible hydraulic communication between coalbeds and adjacent sands.

AAPG Search and Discovery Article #90055©2006 AAPG Rocky Mountain Section Meeting, Billings, Montana