Comparative study of the sources of exergy destruction on four North Sea oil and gas platforms

In this paper, the oil and gas processing systems on four North Sea offshore platforms are reported and discussed. Sources of exergy destruction are identified and the findings for the different platforms are compared. Different platforms have different working conditions, such as reservoir temperatures and pressures, gas- and water-to-oil ratios in the feed, crude oil properties, product specifications and recovery strategies. These differences imply that some platforms naturally need less power for oil and gas processing than others. Reservoir properties and composition also vary over the lifetime of an oil field, and to maintain the efficiency of an offshore platform is therefore challenging. In practice, variations in the process feed result in the use of control strategies such as anti-surge recycling, which cause additional power consumption and exergy destruction. For all four platforms, more than 27% of the total exergy destruction takes place in the gas treatment section while at least 16% occurs in the production manifold systems. The exact potential for energy savings and for enhancing system performances differ across offshore platforms. However, the results indicate that the largest potential for improvement lie (i) in gas compression systems where large amounts of gas are often compressed and might be recycled to prevent surge, and (ii) in production manifolds where well-streams are depressurised and mixed before being sent to the separation system.