Integrated Optimization of the Overall Gas Mass Balance in a Deep-Water Production System

The current oil and gas market context is characterised by low prices, high uncertainties and a subsequent reduction in new investments. This leads to an ever-increasing attention towards more efficient exploitation of resources. This scenario underlines the need for existing assets production optimization, especially for deep-water applications. This paper presents the methodology of an innovative integrated production optimization tool and presents the results obtained in a real application on a deep-water asset. The optimization tool aggregates in a single integrated platform all the different aspects of the asset, from well performances to topside process simulation through gathering system thermo-hydraulic calculations. It effortlessly orchestrates several pieces of software that model the different parts of the asset. Those are typically used by different disciplines, such as reservoir, well area, flow assurance, process and operations. Therefore, the tool promotes the essential collaborations between disciplines. The production optimization is based on genetic algorithms and is able to increase the production of an asset respecting all the operative and flow-assurance constraints. The optimization was applied on a deep-water field, posing particular attention on the delicate ecosystem that is the gas lifecycle of an FPSO. In this case, a global and holistic approach is of paramount importance: in fact, the gas associated to the oil production plays a role in the hydraulics of the pipelines and after being dehydrated and compressed, is used as fuel gas, as gas for wells artificial lifting and for re-injection into the reservoir. The application resulted in a global optimisation of the gas utilization and had manifold impacts. Firstly, it resulted in an increase in oil production. Secondly, a reduction in the overall gas lift led to a more energy efficient use of the compressors. Finally, a higher use of the gas for re-injection resulted more effective for pressure maintenance. As a consequence of the theoretical study, the optimization actions identified by the tool lead to a successful application in the field. This paper presents a novel approach to overall asset optimization that integrates different engineering disciplines. The approach accounts for the overall gas balance of an FPSO from bottom hole to separation, lifting and re-injection.