Modelling, analysis and optimisation of energy systems on offshore platforms

Nowadays, the offshore production of oil and gas requires on-site processing, which includes operations such as separation, compression and purification. The offshore system undergoes variations of the petroleum production rates over the field life – it is therefore operated far from its nominal operating conditions, which results in poorer performance. The present thesis addresses the question of how offshore platforms should be modelled, analysed and optimised from an energy system perspective. The research challenges can be classified into three main areas: (i) the simulation and assessment of oil and gas facilities, (ii) the means to reduce their performance losses, and (iii) the systematic design of future plants. This work builds upon a combination of modelling tools, performance evaluation methods and multi-objective optimisation routines to reproduce the behaviour of five offshore platforms, quantify the potentials for energy savings, and design more efficient conversion units. The findings show that the differences in the field and operating conditions directly impact the energy demand and performance profiles of these facilities. Most inefficiencies are associated with the combustion, pressure-change and cooling operations, but these processes are ranked differently depending on the plant layout and on the field production stage. The most promising improvements consist of introducing a multi-level production manifold, avoiding anti-surge gas recirculation, installing a waste heat recovery cycle, and implementing a CO2-capture unit. The benefits of such measures vary widely across offshore platforms, pinpointing that no generic improvement can be proposed, and that caution should be exercised when giving recommendations to the stakeholders. Finally, the several studies stress the importance of developing site-scale solutions, which account for the synergies between the processing and utility plants, to enhance the overall platform performance and intensify the petroleum production.