Delineation of brine contamination in and near the East Poplar oil field, Fort Peck Indian Reservation, northeastern Montana

Problem:

Brine is a byproduct of crude oil production. Handling and disposal of brine during the last 50 years in the East Poplar oil field has resulted in contamination of not only the shallow Quaternary aquifers, but also the Poplar River. Previous investigations have documented and delineated a portion of the extent of brine contamination in the East Poplar oil field during the early 1990s. In the 10 years since the last study, the entire extent of contamination has likely grown larger. Brine-plume migration is toward the nearby City of Poplar, which relies on the shallow Quaternary aquifers as its sole source of water.

Objective:

The objective of the proposed project is to delineate brine contamination in shallow aquifers in and near the East Poplar oil field. The project area includes the entire East Poplar oil field, much of the Northwest Poplar oil field and the City of Poplar. The objective of this project will be accomplished in two phases. Phase 1 of this project is to delineate the lateral extent of high electromagnetic conductivity in and around the East Poplar oil field. Phase 1 includes a helicopter-borne electromagnetic survey and water-quality sampling at selected wells. Areas of high electromagnetic conductivity will be delineated as using the HEM survey data. During Phase 2 additional data will be combined with the HEM survey data to determine whether areas of high electromagnetic conductivity delineated as part of Phase 1 are brine plumes. Phase 2 of this project is to characterize and delineate brine plumes, determine plume migration since 1993, and identify active brine-contamination sources (such as leaking oil wells, injection wells, or evaporation pits). Phase 2 includes ground electromagnetic data collection at site-specific locations, water-quality sampling at newly installed wells, and aquifer tests at selected sites.

Approach:

Phase 1. Helicopter-borne electromagnetic (HEM) and magnetic equipment will be used to collect geophysical data over the entire study area. The HEM equipment collects data at five frequencies and represents apparent conductivity at five effective depths of penetration throughout the various geologic formations. Historical and recent analytical results of water samples from more than 150 wells in the study area will be compiled. A comprehensive map of historical and existing oil-production facilities will be compiled. Using the HEM data and water-quality information, areas of high conductivity will be delineated.

Phase 2. Ground electromagnetic (GEM) data will be collected at 2-3 small areas (<1 square mile) that are identified as having high electromagnetic conductivity with the HEM data. The detailed GEM and HEM data will be examined 3-dimensionally to determine possible source areas of brine. About 10 monitoring wells will be installed to provide lithologic, hydrologic, and water-quality information in areas of high electromagnetic conductivity. Two aquifer tests will be conducted in parts of the study area lacking hydrologic data to refine the range of hydraulic characteristics specific to the study area. The lithologic and water-quality information will be interpreted with the HEM and GEM data to delineate the lateral extent of brine contamination in and near the East Poplar oil field. Brine plumes mapped in the early 1990s will be compared with brine plumes mapped nearly a decade later for this study to determine brine-plume migration directions and rates.

Status:

Phase 1.The HEM survey was flown over nearly the entire study area in August 2004. Borehole geophysical data were collected at 32 monitoring wells during August 2004 and August 2005. Analytical results of water samples collected between 1952 and 2005 have been compiled. A comprehensive map of historical and existing oil-production facilities was compiled with historical and recent aerial photographs and field maps. Areas of high conductivity have been delineated.

Phase 2. GEM data was collected during August 2005 at 3 small areas. Possible drilling locations have been identified for installation of monitoring wells in August 2006.

Publications:

Smith, B.D., Thamke, J.N., and Paine, J.G., 2004, Electrical conductivity geophysical methods applied to subsurface mapping of produced water: American Association of Petroleum Geophysicists, Annual Meeting, Dallas, Texas, April 19-21, 2004.

Smith, B.D., Thamke, J.N., and Tyrrell, C., 2006, Geophysical and hydrologic studies of shallow aquifer contamination, East Poplar oil field area, northeastern Montana: Symposium on the Application of Geophysics to Engineering and Environmental Problems, Annual Meeting, Seattle, Washington, April 2-6, 2006.

Smith, B.D., Thamke, J.N., Cain, M.J., Tyrrell, C., and Hill, P.L., in review, Helicopter electromagnetic and magnetic survey maps and data, East Poplar oil field area, Fort Peck Indian Reservation, northeastern Montana, August 2004: U.S. Geological Survey Open-File Report xx-xxxx, xx p.

Thamke, J.N., Smith, B.D., and Tyrrell, C., 2005a, Electromagnetic methods to delineate areas of high conductivity in shallow aquifers, East Poplar oil field, northeastern Montana, 2004: Geological Society of America, Annual Meeting, Salt Lake City, Utah, October 16-19, 2005.

Thamke, J.N., Smith, B.D., and Tyrrell, C., 2005b, Electromagnetic methods to delineate areas of high conductivity in shallow aquifers, East Poplar oil field, northeastern Montana, 2004: American Water Resources Association, Montana Section Meeting, Bozeman, Montana, October 27-28, 2005.

Cooperator: Fort Peck Tribes, Office of Environmental Protection

Project Chief: Joanna Thamke, Hydrologist, Montana Water Science Center