Abstract

During the operation of offshore production platforms, sea contamination occurs from leakage, spillage and from the overboard discharge of produced water. Produced water is the terminology applied to water which is obtained during oil production from two main sources. These are naturally from within the oil reservoirs and from sea water used in the oil recovery process. Legislative limits are set in the most of the major oil production regions world wide. These limits vary from region to region but are generally set between 15ppm and 40ppm for dispersed hydrocarbon concentration in water. The volumes of produced water are exceeding that of crude oil production in many offshore oil fields, such as in the North Sea fields to the north-east of the U.K. where in 1994 for a total crude oil production of 114.4 million tonnes, 147 million tonnes of water was produced, the majority of which was discharged back into the sea. The volumes of oil discharged within produced water are the single greatest source of oil contamination from oil production facilities in the North Sea and with similar situations replicated world wide represents a global concern to sensitive marine environments. The present methods for the detection of oil in produced water are based either on chemical analysis of intermittent samples or bypass pipelines with instrumentation to detect either dissolved or dispersed hydrocarbons by a variety of optical techniques including absorption, scattering and fluorescence. Tests in the U.K. on a range of commercially available instruments have shown that no single one entirely meets either the present needs or satisfies the requirements of the more stringent future legislation which is likely to be introduced in the atmosphere of growing concern for our environment. New instrumentation is required to meet these needs and will require a specification to include both in-line and on-line operation and sensitive measurements on dissolved and dispersed hydrocarbons. The requirement for in-line operation introduces further complexities to the specification due to the optical scattering which can be introduced by sand and other sediments which could not be filtered, and from the high sample flow rates and turbulence which is introduced by the flow rate of 1ms 1 typically encountered in the discharge pipes. To meet these needs a new generation of in-line systems for environmental monitoring are being developed based upon the Photoacoustic Spectroscopy technique. The instrumentation is being developed initially for the on­line monitoring of hydrocarbons in produced water but may also find application in the detection of oil and other pollutants in the open sea, rivers, lakes and sewage.

© 1996 Optical Society of America