A Comprehensive Determination of Produced Water Composition

Abstract

Concomitant with the production of oil from North Sea oilfields is the recovery of water associated with the oil in the reservoir. Produced oil and water are usually separated on the production platform before the oil is pumped ashore via a pipeline. The separated water is discharged overboard into the sea. In 1990 approximately 159 × 10⁶ tons of produced water were discharged in the UK sector of the North Sea (HMSO, 1991). The current study is concerned with the detailed characterization of produced waters on the Murchison (block 211/19) and Hutton TLP (block 211/28) platforms in the Northern North Sea, both of which are operated by Conoco (UK) Limited. The proportion of water to oil production during the lifetime of the reservoir is not constant. In the early stages of production from the reservoir, the water cut is low (zero to a few percent) with a constant increase until production is no longer economically feasible (80% or so). During the lifetime of a reservoir water-injection (water flooding) is usually practiced during part of the production with “breakthrough” water contributing to the produced water. Both Murchison and Hutton have been under water flood for several years; Murchison has been under pressure maintenance (water flood) since 1981 and Hutton since 1985. Currently Murchison produces 180,000 barrels per day (bpd) and Hutton 130,000 bpd of water. Produced waters discharged from these platforms comprise a variable mixture of formation water, injection water and deck drainage, which may include lubricating oil, grease and diesel from leaks and spillages.