Paper No. 10
Presentation Time: 3:50 PM
DISSOLVED GAS GEOCHEMISTRY OF SHALLOW GROUNDWATER IN AREAS OF OIL AND GAS EXTRACTION, DENVER-JULESBURG BASIN, COLORADO
Higher energy demands have amplified oil and natural gas extraction efforts in Colorado and throughout the U.S. Advancements in oil and natural gas extraction technologies, such as, direction drilling and hydraulic fracturing, have increased production efficiencies from organic-rich-shales, while also raising concerns over the potential for environmental impacts. Yet, there is still a general lack of publically available data focused on thoroughly understanding risks. Research on stray dissolved gases in shallow groundwater aquifers overlying the Marcellus organic-rich shale in Pennsylvania has, arguably, supported some of these concerns (Osborn et al., 2011; Jackson et al., 2013), demonstrating further need for more publically available data in areas with intensive natural gas extraction. The Wattenberg natural gas play is one of the largest gas reservoirs in the US, situated in the Denver-Julesburg basin. Yet, there is little publically available data addressing environmental concerns to shallow groundwater resources. The focus of this study was to investigate the source of dissolved gases and mixing relationships in shallow groundwater systems near intensive oil/gas extraction in the Denver-Julesburg basin.
In July (2013), forty shallow groundwater samples were collected from private and municipal drinking-water wells throughout Weld, Boulder, and Adams counties north of the Denver metropolitan area. Samples were analyzed for dissolved gas composition and methane concentration (mg of dissolved methane per liter of water), carbon isotopes of methane (d13C-CH4), carbon isotopes of dissolved inorganic carbon (d13C-DIC) and total alkalinity of groundwaters (titrated within 24-hours of sampling). The combined geochemical data will be used to understand the source of dissolved gases (shallow microbial methane or deeper thermogenic methane) in shallow groundwater aquifers as well as possible mixing relationships between different sources. In addition, geospatial relationships between shallow groundwater sample locations and oil/gas well extraction will be investigated and presented.