USING INSAR TECHNOLOGY AND GROUNDWATER PUMPING DATA TO MODEL LAND SUBSIDENCE FROM COAL BED METHANE PRODUCTION IN THE POWDER RIVER BASIN, WYOMING

In coal bed methane production (CBM), groundwater pumping releases methane gas by reducing pore-water pressure in the source rock. In Wyoming’s Powder River Basin (PRB), groundwater has been extracted for CBM at rates greater than 94 million gallons per day, or 65 thousand gallons per minute. Land subsidence can result from aquifer compaction as groundwater is removed, as is observed in the PRB. Synthetic Aperture Radar Interferometery (InSAR) can measure subsidence at a sub-centimeter scale. In the PRB, InSAR data collected from 1997 to 2000 and 2004 to 2007 indicate several centimeters of subsidence; in the east-central part of the study area, the largest subsidence values of 4 cm and 6 cm can be correlated to large clusters of CBM pumping wells. Other subsidence in the area might be related to oil production and other groundwater use.

The PRB is ideal for groundwater model development and calibration because the aquifer stress (pumping) and response (subsidence) data are both available. This research combines pumping well, monitoring well, subsidence data, and geologic information to develop a groundwater model that predicts the rock compaction observed in the PRB; progress on this model will be presented. Because CBM production requires a well field that is designed to pump groundwater for optimal methane release, understanding aquifer mechanics through groundwater and subsidence modeling could improve well field engineering in the future. Ultimately, an empirical equation could be developed to predict subsidence from groundwater pumping.