API DR 351-1996

Produced water is the aqueous phase that comes to the surface along with oil and gas produced from underground formations. At offshore production platforms, produced water is typically treated to remove all but minute amounts of oil and grease and then discharged into the ocean. On December 3, 1993 the U.S. Environmental Protection Agency issued an NPDES General Permit for the western portion of the Outer Continental Shelf of the Gulf of Mexico which included a limit on produced water toxicity, The Permit requires operators to demonstrate that the concentration of discharged produced water at a distance of 100 m from the outfall does not exceed the threshold for chronic toxicity measured in a laboratory test. To assist operators inmeeting this limit, the American Petroleum Institute (API) formed a Toxicity Reduction Evaluation (TRE) Workgroup to guide research on produced water treatment for toxicity reduction. As an initial step in their strategy development process, the TRE Workgroup sponsored a workshop to identify promising technologies for the treatment of produced water toxicity.

This Workshop took place on October 11 and 12, 1994 at the South Shore Harbor Conference Center, League City, Texas and brought together a variety of experts in the field of produced water toxicity and its treatment. The Workshop agenda and list of participants are shown in Tables 1-1 and 1-2, respectively.

PURPOSE

The purpose of the workshop was to identify promising technologies that could beutilized on offshore platforms for the treatment of produced water toxicity. To this end,information was presented on produced water toxicity and characteristics, the resultsof TIEs carried out on produced waters, and the engineering restrictions imposed byoffshore platforms. In addition, presentations were given describing five treatmenttechnologies and their applicability to produced water treatment, including cost data.The treatment technologies evaluated were membrane filtration, carbon adsorption,chemical oxidation, stripping/extraction, and UV oxidation. Additional discussionyielded a sixth technology for evaluation, biological treatment.

Having defined the characteristics of produced water, the factors affecting toxicity, andthe challenges involved with the offshore treatment of the effluent, six workgroupswere assembled to discuss the suitability of the treatment technologies for thisapplication. The aim of these workgroups was to review and evaluate the practicabilityand the economics of the technologies, and to recommend areas for further researchand testing. In addition, the approaches of effluent dilution and reinfection werecompared to the treatment options in order to assess the relative applicability of thetechnologies for achieving compliance with the toxicity limit.

Finally a group discussion was held which summarized the previous discussions andreached conclusions with respect to the offshore treatment of produced water toreduce toxicity.