HYDROLOGY AND SUBSURFACE TRANSPORT OF OIL-FIELD
BRINE AT THE OSAGE-SKIATOOK PETROLEUM
ENVIRONMENTAL RESEARCH (OSPER B) SITE, OKLAHOMA
William N. Herkelrath*
Yousif K. Kharaka
U.S. Geological Survey
345 Middlefield Road, MS 496
Menlo Park, CA 94025
Voice: 650-329-4625
Fax: 650-329-5590
E-mail: wnherkel@usgs.gov
As a part of a multidisciplinary study of the impact of oil wells and oil production on the environment, we are investigating the hydrology of the OSPER B site, which is located at Skiatook Lake in Osage County, Oklahoma. Salt and crude oil from oil well brine pits and accidental releases from oil-tank batteries have contaminated soil, ground water, and surface water at this site. Coring near a brine pit at the site showed that low permeability shale underlies 0.5-2 meters of surficial deposits (fill, soil, colluvium, and alluvium). The land slopes down from the pit at about a 1:10 slope to the lake, which is located about 20 meters from the pit. More than 40 shallow wells were installed at site B in order to enable periodic ground-water sampling for chemical analysis, to monitor water table elevations, and to delineate the subsurface contamination plume at the site. Five wells were instrumented with pressure transducers in order to continuously monitor water table elevation. Dielectric probes were installed to monitor soil water content. Probes were installed in the brine pit in order to continuously monitor pit water depth and electrical conductivity. A tracer test was carried out in order to estimate travel time from the pit to nearby observation wells. Results of computer simulations and field measurements indicate that subsurface brine flows slowly from the pit to the lake in a shallow saturated zone above the shale layer. Little brine has penetrated into the shale. In response to rainfall, the water table rises rapidly to the soil surface and runoff begins. Soil moisture content is very high at all times; there is little capacity to absorb rainfall, and recharge and mixing of rainwater with subsurface brine is limited. Breakthrough of tracer to observation wells was not observed, apparently because of very slow recharge through the pit bottom and high adsorption of rhodamine and fluorescein tracer in the surficial deposits.