An Integrated Approach to Optimise an Offshore Field Development Plan

Abstract

The ADNOC Offshore oilfield located in the Arabian Gulf is being developed utilising various wellhead towers, infield pipelines and a standalone super complex. The field development team devised an updated subsurface plan to achieve production targets beyond the original plan. The incremental oil necessitated assessment of original surface facilities design to identify any bottlenecks and unlock constraints. A set of production forecasts were initially provided as basis for assessment covering various scenarios and range of reservoir uncertainties. To manage these uncertainties, the facilities and subsurface development teams worked in an integrated and iterative way. The production profiles were used to assess and develop understanding of surface facilities such as oil flowline network, water injection supply and network, gas lift networks and the major equipment. The assessment results provided guidelines on the process facilities constraints which were feedback to subsurface team. An optimised subsurface development plan was then generated respecting the facility constraint and leveraging the existing facilities design to utilise ullages. An initial view of investment to produce incremental oil considered installing three new wellhead towers, a new manifold platform and a new water injection platform both linked to the super complex and a new main oil line installation to transfer partially stabilised oil from super complex to oil processing plant. The technical evaluations and the decision analysis resulted in a low-cost solution that was needed to ensure that the field's incremental oil production is economically viable. The integrated approach not only allowed selection of techno-commercial robust solution but also allowed optimisation of investment providing flexibility to accommodate the key project uncertainties. This was achieved by deferring the investment to future by descoping the overall development plan in two separate projects - achieve production plateau and sustain plateau. The interim period between the two projects would provide time to resolve the subsurface uncertainties and an opportunity to revisit future development strategy without committing any investment. In addition, the original UTC was significantly improved. This approach emphasised the importance of having a flexible surface facilities solution in accommodating the developments in the subsurface field development strategy especially in an offshore environment and during the early field production period. This paper presents an approach followed for optimisation of an offshore oilfield development plan under various surface facilities constraints.