An Assessment of the Probability of Subsurface Contamination of Aquifers From Oil and Gas Wells in the Wattenberg Field, Modified for Water-Well Location

Abstract

Summary The United States National Science Foundation has funded a sustainability-research network focused on natural-gas development in the Rocky Mountain region of the United States. The objective of this specific study is the assessment of the use of existing water wells to monitor the risk of contamination by the migration of fracturing fluids or hydrocarbons to freshwater aquifers. An additional objective of the study is to modify existing risk estimates using the spatial relationships between the existing water wells and producing oil wells. This will allow estimates of single-barrier failure and multiple-barrier failure, resulting in contamination projections for oil and gas wells in areas without surrounding water wells to detect migration, dependent on well-construction type. Since 1970, the Wattenberg Field in Colorado has had a large number of oil and gas wells drilled. These wells are interspaced tightly with agricultural and urban development from the nearby Denver metropolitan area. This provides a setting with numerous water wells that have been drilled within this area of active petroleum development. Data from 17,948 wells drilled were collected and analyzed in Wattenberg Field, allowing wells to be classified by construction type and analyzed for barrier failure and source of aquifer contamination. The assessment confirms that although natural-gas migration occurring in poorly constructed wellbores is infrequent, it can happen, and the migration risk is determined by the well-construction standards. The assessment also confirms that there has been no occurrence of hydraulic-fracturing-fluid contamination of freshwater aquifers through wellbores. The assessment determines both the spatial proximity of oil and gas wells and surface-casing depth to water wells to then determine the utility of water wells to monitor migration in oil wells.