Offshore versus onshore produced water characterization and models

Organic contamination of produced water is of direct environmental concern. Oak Ridge National Laboratory, with support of the DOE and the Petroleum Energy Research Forum, has embarked on a program to characterize produced water contaminants and to model the solubilities of these contaminants as a function of such variables as pH, temperature, and salinity. Although these efforts have primarily been directed toward offshore remediation, it is recognized that there may be parallels in the concerns of onshore producers. The produced water data sets showed a great degree of variation, but a few trends were apparent. Unless contamination of the reservoir occurs, the paraffinic oil and grease load in produced water is very low. Other heteronuclear organics were not particularly prevalent in the water soluble fraction, unless introduced to enhance production. Volatile aromatic compounds could represent a significant fraction of the water soluble organic material, depending on the source of the oil and the degree to which the oil and the water has been outgassed before sampling. There are few data on some organic compounds that might be relatively soluble in produced water, such as ketones, aldehydes, mixed heteronuclear organics, mercaptans, and thiols. A phenomenological approach to produced water modeling was performed, employing the assumption of chemical equilibrium.