HYDROLOGIC AND GEOCHEMICAL CONTROLS ON SOLUBLE BENZENE MIGRATION WITHIN THE UINTA BASIN

Field sampling and mathematical modeling are used to study the long-distance transport and attenuation of petroleum-derived benzene within the Uinta Basin, Utah. Benzene was measured from oil and oil field brines of the Altamont-Bluebell oil field and the Pariette Bench oil field in the north central Uinta Basin. It was also measured in springs located at regional groundwater discharge area of the basin, hydraulically down gradient from the oil fields. The average benzene concentration in oils and co-produced brines was 1946 and 4.9ppm at the Altamont-Bluebell field and 1533 and 0.6ppm at the Pariette Bench field, respectively. Benzene was below the detection limit in all springs sampled. To quantify the soluble benzene transport and degradation processes in the basin, mathematical models were constructed along a northwest-south transect across the basin through both fields, following the general direction of the regional groundwater flow. The model represents groundwater flow, heat transfer and advective-dispersive benzene transport in the basin as well as benzene diffusion within the oil reservoir. Benzene attenuation in groundwater is represented with a retardation factor and a first-order biodegradation rate constant. The model was able to reproduce the observed excess heads within the lower Green River Formation as well as the observed convective temperature anomalies within the Duchesne-Uinta aquifers. Without representing benzene attenuation, dissolved benzene is able to reach the regional groundwater discharge area (springs) in measurable concentration. When attenuation is represented, benzene concentrations diminish to below the detection limit within 1 to 4 km from the oil reservoirs.