Optimal design and scheduling for offshore oil-field development

Oil-and-gas field development projects are capital-intensive, and optimizing profitability has always been a critical subject for the industry. This paper presents a mixed-integer linear programming (MILP) model to facilitate scenario comparison and selection at the design stage for green offshore oil-field development. The model solves an allocation-scheduling problem with the objective of maximizing the project's net present value (NPV). Decision variables include the drilling schedule for both production and injection wells, well assignment to FPSO (floating, production, storage and offloading unit), FPSO oil and water production capacity, and water injection capacity. The model represents the waterflood scheme through an injection-production relationship matrix, leading to consistent scheduling of producer-injector pairs. Also, the model allows the assignment of development priorities to blocks or well groups, which corresponds to the phased-development concept in real-world application. Methods to estimate production rates are proposed, and a production prediction model is established. Production rates considering scheduling effect are generated by a linear superposition of base production curves from reservoir simulations. Two synthetic reservoirs with properties resembling deepwater offshore Brazil illustrated the performance of the modeling approach. It is observed that in early development years, drilling capacity and oil production capacity are active constraints to the system, while in late development years, active constraints change to water capacity, which propels the capacity expansion concept in the late production years, such as subsea water separation. Higher recovery is obtained with expedited production, but NPV does not necessarily increase with increased oil recovery when there is considerable investment on extra FPSOs. (C) 2019 Elsevier Ltd. All rights reserved.