Optimization of Riser Design and Drill Centers With a Coupled Reservoir and Facility-Network Model for Deepwater Agbami

Abstract

The use of multiple wells connected at a subsea manifold provides the opportunity to reduce the number of risers and capital expense. The problem is the proper modeling of the reservoir well flow coupled with the combined flow into the facility network (i.e., manifolds, flowlines, and risers), which is necessary to prevent underdesign, resulting in flow-rate bottlenecks, or overdesign, resulting in extra expenditures. This paper presents a tool and methodology for better modeling of the well-to-riser flow and the optimization of riser count and configuration.Although reservoir models coupled with facility networks is not new, software enhancements provided the capability of including operation logic that could duplicate operations in the field. The reservoir model coupled with the facility network provided more reasonable and accurate modeling of multiphase rates and pressures as wells were combined into a single riser.To optimize the riser count, operation logic was applied to maximize rate in the riser at all times against the erosional-velocity limit. This in turn prevented overdesigning by placing more risers than needed to obtain the field-facility capacities.The use of the coupled model and operation logic allowed the optimization of the riser count for any particular reservoir model. The optimum riser count was then determined for 3 earth (geologic) models. Reservoir SimulationDescription of Reservoir-Simulation Model. The Earth models were upscaled to be read by the reservoir-simulation model. The reservoir model had the xyz-grid dimensions of 72×91×260 and consisted of approximately 120,000 active cells (depending on the Earth model). The cells with a predominant shale facies were inactivated. The full-field reservoir model contained the three stacked reservoirs, as described in the Geological-Modeling Framework section.Because the fluid-property analyses indicated that the injected gas would be first-contact miscible with the reservoir oil, the reservoir was modeled as black oil with the miscible option. Fluidproperty data were obtained from three wells. An equation-of-state model was used to match the laboratory data and then to generate