Interpretation of the Data Collected as Part of U.S. EPA's Investigation at Pavillion, WY
The US EPA released a draft report in 2011 that asserted there were potential groundwater quality impacts from hydraulic fracturing of gas wells near Pavillion, Wyoming. This conclusion was based on water sampled from two deep monitoring wells (much deeper than typical domestic wells and in proximity to natural gas-bearing strata) installed by US EPA and was hotly debated and refuted by many, ultimately leading to additional sampling of the two deep monitoring wells by both the US EPA and USGS in April, 2012. Subsequent interpretation of the entire dataset collected from the Pavillion monitoring program was never attempted by either the US EPA or USGS, and the investigation has now been transferred to the state of Wyoming. In this presentation, we evaluate all data collected at Pavillion and interpret it within the context of the regional hydrogeological setting and information on the construction and installation of the two deep monitoring wells. The chemistry of the groundwater samples obtained from these wells represents water in equilibrium with cement, which was pumped into the well annuli, but not hydraulically isolated from the screened interval of the wells. Thus the chemistry of water samples is in sharp contrast to what would be expected if fracturing fluid (predominantly CO2 foam) had leaked upward into the strata in which the US EPA monitoring wells were screened. It is also clear that the vertical direction of groundwater flow in the area is downward, meaning that there is no mechanism to drive hydraulic fracturing fluid upward after a well stimulation. Overall, there is no evidence that the US EPA deep monitoring wells or shallower groundwater resources in the Pavillion area have been affected by hydraulic fracturing fluids. Furthermore, it is unlikely that groundwater samples from the deep monitoring wells will be able to provide useful information about potential groundwater impacts due to the severe effects of cement on water chemistry in the vicinity of these wells.
AAPG Datapages/Search and Discovery Article #90189 © 2014 AAPG Annual Convention and Exhibition, Houston, Texas, USA, April 6–9, 2014