Sub-hydrostatic pore pressure in coalbed and sand aquifers of the Powder River Basin, Wyoming and Montana, and implications for disposal of coalbed-methane-produced water through injection

摘要

Coalbed methane (CBM) production in the Powder River Basin (PRB), Wyoming, is associated with the production of large volumes of water. Locally, water in coalbeds from the PRB has high saline and sodium contents, making it unsuitable for agricultural use and potentially environmentally damaging if discharged at the surface. One option for the disposal of CBM-produced water is injection into aquifers. For injection to be feasible, however, the porosity and permeability of the sands need to be high, the pore pressure ideally needs to be sub-hydrostatic, and the aquifer cannot be in hydraulic communication with coalbeds or aquifers used for irrigation use. In order to determine if pore pressures in the aquifers are low enough to allow for significant water injection (and to determine whether the coals and nearby sands are in hydraulic communication), we have compiled pore pressures in 250 wells that monitor water levels in coalbeds and adjacent sands within the PRB.