IS BARITE THE MINERALOGICAL SITE OF RADIUM IN SEDIMENTS EXPOSED TO OILFIELD BRINES WITH ELEVATED NORM?

Formation waters with elevated concentrations of NORM are a byproduct of petroleum production in selected oilfields in southern Louisiana. We report the results of an investigation of the effects of releasing these waters into a wetlands environment. We also report the preliminary results of a reinvestigation of the same site 20 years after the release of NORM was discontinued.

The area surrounding an oil-skimming pond where NORM enriched waters were released was sampled in 1980. Radium concentrations were found to be slightly and significantly elevated over background levels. A correlation of Ra with clay percentage was found, a result common to similar studies of NORM in fine-grained sediments. Such correlations are invoked to validate clay minerals as the principle radium exchange sites. An alternative explanation of this correlation is the occurrence of variable amounts of quartz, which would co-dilute both the amount of clay and the concentration of Radium.

The same area in 1999 contains only background levels of Ra to depths of at least 20cm. The only sample site with elevated Ra was adjacent to the tank facility, and was also found to contain barite in the heavy mineral fraction. Barite scales from production facilities have been reported with elevated NORM. It is a strong possibility that the 1981 samples had barite as the host for the Ra, a site less likely to allow exchange of Ra to the environment. As the sediment with elevated NORM was buried, the Ra was effectively removed from environmental concerns.