Introduction

When hydrocarbons (crude oil, condensate, and natural gas) are produced, the well stream typically contains water produced in association with these hydrocarbons. The produced water is usually brine, brackish, or salty in quality but in rare situations may be nearly "fresh" in quality. The water must be separated from the hydrocarbons and disposed of in a manner that does not violate established environmental regulations. Typically, the produced water is separated from the hydrocarbons by passing the well stream through process equipment such as three-phase separators, heater-treaters, and/or a free-water knockout vessel. These gravity separation devices do not achieve a full 100% separation of the hydrocarbons from the produced water. The produced water separated from the hydrocarbons in these gravity separation devices will contain 0.1 to 10 volume percent of dispersed and dissolved hydrocarbons. Produced water treating facilities are used to further reduce the hydrocarbon content in the produced water prior to final disposal.

Regulatory standards for overboard disposal of produced water into offshore surface waters vary from country to country. Failure to comply with such regulations can often result in civil penalties, large fines, and lost or deferred production. Intentional violation of these regulations can result in criminal prosecution of officers and other individuals acting on behalf of the company who intentionally neglected compliance. Currently, regulations require the "total oil and grease" content of the effluent water to be reduced to levels ranging between 15mg/l to 50mg/l depending upon the host country. For U.S. offshore operations, the current standard...