MONITORING OIL FIELD BRINE PLUME CAPTURE AND REMEDIATION USING ELECTROMAGNETIC SURVEYS, EAST POPLAR OIL FIELD, EASTERN MONTANA

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.

Pioneer Natural Resources voluntarily designed and built a plume capture and remediation system consisting of thirteen “brine”, groundwater removal wells, five crude oil recovery wells and a deep, 7,800 foot, USEPA Class V, injection well. The brine remediation system became fully operational in August 2008 and is operating at an average daily rate of approximately 5,046 barrels per day (212,646 gallons/day). As of July 2013 the system has removed 6,454,965 barrels (271,108,530 gallons) of brine contaminated water with an average concentration >20,000 mg/L Chlorides.

An airborne frequency domain helicopter EM survey flown by the USGS in 2004 mapped the subsurface conductivity of the SE part of the Poplar Oil Field. This survey provided a hydrogeologic framework and plume mapping over a large area. In the Biere #1-22 area Pioneer Natural Resource personnel have conducted more detailed ground EM surveys with a loop-loop EM 34XL system with separations of 10, 20, and 40 meters. These surveys were used in conjunction with water well sampling to develop an estimate of the extent of the brine and crude oil plumes in the Mesa Biere #1-22 area.

Traditional monitoring of plume removal efficiencies has been based on groundwater sampling of wells within the plume area and related interpretations of the spatial and temporal changes of the plume are restricted to interpolated data between monitor well locations. The usefulness of the EM surveys are that they are inexpensive and easy to conduct and can give useful information over a much more detailed area within the plume. The Biere #1-22 survey consists of 237 stations over a 1.03 mi² grid on 300 ft and 400 ft spacing. The survey is approximately 16 linear miles. A unique aspect of the ground geophysics has been that the repeated EM34XL surveys conducted since system startup shows decreases in the area of high subsurface conductivity that correlate with a decrease in the area of the plume geometry.