A Multidisciplinary Approach to Site Characterization and Remediation of Contamination From Oilfield-Produced Waters, East Poplar Oil Field, Fort Peck Indian Reservation, Roosevelt County, Montana

Abstract

Abstract Previous studies conducted by the United States Geological Survey (USGS), (Thamke and Craig 1997) and the Fort Peck Indian Tribes, Office of Environmental Protection (OEP) indicated that the shallow Quaternary aquifer in this region has been heavily impacted by historical oil and gas operations. In 1999 Pioneer Natural Resources (PNR) was notified that a plugged and abandoned well, the Mesa Biere #1–22 (now Pioneer), operated by Mesa Petroleum and plugged in 1986, appeared to have been improperly plugged and had released chloride-rich oilfield brine into the shallow aquifer. An investigation conducted by PNR in late 1999 and early 2000, revealed that the Biere #1–22 wellbore was still leaking outside of the casing in the Cretaceous, Judith River Formation at approximately 1,000 ft below ground and that brine was channeling upwards into the shallow aquifer approximately 40 ft. below the ground surface. The well was successfully plugged in 2000. From 2001–2005 PNR conducted further delineation drilling and aqueous geochemical analyses of the area around the Mesa Biere #1–22 well. Beginning in mid-2006, PNR initiated an integrated approach to characterize both the regional setting of the oilfield contamination including a detailed study of the geological, hydrological, aqueous-geochemical and geophysical setting the Biere #1–22 contaminant plume area. The results of the detailed study of the Biere #1–22 plume area revealed that the contaminant plume was located within an isolated, well-defined channel of fine to coarse-grained gravels of fluvioglacial origin. A detailed study of the aquifer and surrounding geological units was conducted with numerous pump and slug tests. The data was input into a 3-D groundwater model and plume capture scenarios utilizing different recovery well placements and pumping rates were run to evaluate the feasibility of undertaking remedial actions of the Biere #1–22 plume. Airborne electromagnetic (EM) conductivity data from previous USGS studies (Smith et al. 2004) were reworked and used to delineate subsurface areas of high conductivity. In addition, PNR conducted ground electromagnetic methods in 2008 to further delineate the extent and movement of the Biere #1–22 contamination plume near the City of Poplar. Subsequent ground electromagnetic surveys are planned to document the progress of ongoing plume remediation. Use of these methods to document remediation progress is unprecedented, and these techniques will likely be used to supplement future industry standards for monitoring remediation. Pioneer Natural Resources proactively and voluntarily committed more than $6 million USD to design and build a plume capture and aquifer restoration system. The system consists of ten "brine", groundwater extraction wells, five crude oil extraction wells and a newly drilled, deep, 7,500 ft, USEPA Class V, injection well completed in the Mississippian, Mission Canyon and Devonian, Nisku Formations. The brine remediation system became operational in August 2008. The designed system will remove the most contaminated portion of the plume at a rate of approximately 250,000 gallons per day (gal/D) and will significantly reduce any potential threat to the City of Poplar.