Field Evaluation of Toxic Effects and Dispersion of Produced Water Discharges From North Sea Oil Platforms

Abstract

Produced water is co-produced with oil or gas and is usually separated on the platform and discharged as a waste stream into the sea. It originates from water trapped in the geological structure from which the oil/gas is being recovered and also from water injected into the formation to maintain reservoir pressure. In 1993 148 million tonnes of produced water were discharged from oil production platforms in the U.K. sector of the North Sea (HMSO, 1994). The amount of produced water being discharged on the UK continental shelf rose steadily up until 1991/2 (Figure 1). Although the amount of oil and water discharged has reached a plateau since 1990 both are projected to rise as a function of the increased number of production units and because during the life of a producing oil field, the volume of produced water will increase. This occurs mainly as a consequence of the injection of increasing volumes of seawater to maintain reservoir pressure in older fields and the subsequent break-through of this water to the production wells. The volume of produced water may exceed that of the oil by as much as ten times and during the later stages of production, the produced water may account for as much as 98% of the total extracted fluids.