Mass Balance of Production Chemicals

Abstract

Abstract Estimates of the amount of discharged production chemicals are most often calculated using octanol/water partition coefficients. This is due to the lack of any better methods to predict how much of the chemicals is water soluble and would thus follow with the produced water to sea. Here a laboratory method for determining the partitioning of some typical production chemicals between oil and water is reported. The experimental parameters that influence the partitioning have been examined and partition coefficients for a range of chemicals have thus been established. The validity of this laboratory method has been verified in a field trial in the North Sea. By combining the partition coefficients with production data and putting these into a spreadsheet the so-called ‘Mass Balance Simulator’ is obtained. With this it is possible to predict how much of a chemical is discharged to sea and how much is retained in the crude oil leaving the platform. Introduction Chemicals are added to the oil/gas value chain at different positions during the physical flow from well stream to the traded product. All the different stages in oil and gas production generally require chemicals to assist in specific operations, for the drilling of wells, for the production of the oil or for the transport of oil through pipelines. The chemicals are used for different purposes (like defoaming, demuls-ification and hydrate and scale inhibition/ dissolution) and are added in varying amounts, continuously or in batch. It is generally accepted that efficient and cost-effective oil and gas production is not possible without the use of chemicals. Over the last 10 years, the chemical usage has increased, as is apparent from Fig. 1. Here the amount of production chemicals used at Statoil-operated fields is shown on an annual basis1. A similar trend can be found for drilling chemicals. The increase is not only due to the fact that new fields are brought to production (Sleipner 1993, Heidrun 1995, Troll 1996, Norne 1997, Åsgard 1999). In addition, new solutions have been applied, for instance the use of methanol for multiphase well stream transport from subsea wells. And mature fields like Gullfaks and Statfjord have increased needs for chemical-based treatments like well treatment or water treatment. Consequently, a lot of attention has been paid to this use of chemicals from the oil industry itself as well as from the public authorities due to the environmental strain this may represent.