Coupling Production and Injection Systems with Multiple Reservoir Models: A Novel Method of Optimizing Development Strategies in a Mature Giant Oilfield

Abstract

Abstract The building of an integrated asset model for a giant carbonate oil field located offshore Abu Dhabi, consisting of two separate subfields with common production and injection networks, is presented with selected use cases. Coupling is performed periodically at the wellhead, using a reservoir simulator in which the field manager controls the reservoir models by supplying well constraints and controls the network models by supplying well performance curves. Allocation strategies and pressure and flow constraints are imposed by the field manager, for which the different sub-models are black boxes; the models themselves are controlled hydraulically without embedded production or injection constraints. This explicit approach has been selected for its flexibility. In particular, by expressing rates at the surface-subsurface interface at standard conditions, it is possible for the two reservoir models to have different equations of state and different treatments of injected water salinity, while the surface models use a black-oil fluid description. This project required ensuring rate continuity at the transition from history to forecast for over 600 active production and injection strings, even when the reservoir and network models are not perfectly history-matched. This was achieved by introducing pressure shifts in each vertical flow performance curve to ensure continuity of the choking margins (i.e., differences between wellhead pressures and backpressures) and by overriding the default guide rate flow allocation method of the field manager to prevent abrupt changes in the production split of wells currently producing below potential. The use cases described here are based on an eight-year (2015–2023) drilling schedule followed by no further activity. We focus on assessing the impact on production and injection arising from: replacing pipelines or changing network topologies; relaxing the constraint of producing at initial solution gas-oil ratio with and without reduction of separator pressures; and redistributing or increasing the water injection capacity.