Design Perspectives for Selection of Subsea Gas Lift Technology for Deep Water Fields

Riser base gas lift is conventionally used in deep water fields to minimize backpressure on wells, smooth start-up transients, and mitigate slugging in the flowline-riser system which can cause disruption in the topside facilities. The effectiveness of riser base gas lift depends on several factors, such as the reservoir performance, the fluid properties, the field architecture, and the topography. There are several technical solutions available to deliver the lift gas to the riser base. Such technical solutions differ in terms of lift-gas supply method (distributed vs point-to-point), riser specifications, and overall system complexity. The selection of technical solution has the potential for minimizing infrastructure. Available solutions include bundled risers and concentric riser configurations that allow gas lift functions to be integrated with the main production conduit. The evaluation of riser base gas lift effectiveness and the selection of the most appropriate technical solution is typically performed early in the field development cycle. This paper presents a review of the available subsea gas lift technical solutions and discusses an evaluation process, including criteria for the selection of the most appropriate solution. The presented case study assumes a deep water Gulf of Mexico field, in which the main subsea system consists of two wet insulated piggable flowline loops. Key decision drivers were flow assurance requirements, complexity, operability, impact on field layout, interfaces, installation, and schedule are discussed. This holistic approach aids the selection of the most appropriate riser base gas lift system in the early field development cycle.