MAPPING SURFACE DEFORMATION ASSOCIATED WITH NATURAL GAS EXTRACTION IN THE POWDER RIVER BASIN, WYOMING DETERMINED USING INTERFEROMETRIC SYNTHETIC APERTURE RADAR

Natural gas production in the United States has experienced significant growth over the past decade and is projected to continue, if not accelerate, into the future coincident with rises in population, demand, and consumption. The state of Wyoming, with a long tradition of coal industry, has recently experienced growth in natural gas exploration and production and ranks 2^nd in the nation for proved reserves of natural gas. Coalbed methane production is presently concentrated in the Powder River Basin, accounting for 98% of the coalbed methane natural gas produced in the state. Coalbed methane is naturally occurring in coal beds and is released by dewatering or fracturing, requiring the drilling of wells, hydraulic fracturing, gas and other fluid extraction, and disposal of waste water. The study’s objectives are to provide a better understanding of the spatial and temporal effects of these natural gas production activities, with a focus on detected surface deformation associated with natural gas wells in key areas of the Powder River Basin.

Interferometric Synthetic Aperture Radar (InSAR) techniques are utilized to reconstruct a detailed time series that allows the determination of surface deformation. The analysis is performed on 23 interferometric pairs of descending SAR scenes from ERS-1, ERS-2, and ENVISAT (obtained through WInSAR, the Western North America Interferometric Synthetic Aperture Radar Consortium) for various time intervals spanning a period of 15 years (from 1992 to 2007). Well locations and extraction histories from a state geodatabase (USGS Data Series 625) allow for spatial comparisons of well density and surface deformation. Results suggest that subsidence (on the order of several centimeters) is focused around several areas of high concentrations of natural gas extraction wells and that there is a positive linear relationship between volume extracted and amount of deformation. The study further confirms the effectiveness of InSAR as a powerful tool for monitoring effects related to natural gas extraction and provides a basis for expanding studies in other areas of rapid natural gas development.