Drilling overpressured and deep reservoirs is a challenge in itself, but can be complicated by the need to drill through depleted (depressurized) shallower reservoirs. The field under study consists of multiple stacked clastic reservoirs bounded by steeply dipping sealing faults. The deeper reservoirs fall in the high pressure high temperature (HPHT) category and account for one third of the in-place volumes. Ideally, field development for such stacked reservoirs is recommended through the "bottom-up" strategy to prevent late-in-life drilling through depleted zones with reduced drilling window and increased risk of fluid losses and well failure. Here, this would imply drilling and developing the deeper HPHT reservoirs before the shallow, normally pressured reservoirs. From a technical and financial perspective, it is tempting to develop and produce the shallow, normally pressured reservoirs (that contain 70% of the volumes and also have better flow properties) first, and bring the deeper HPHT reservoirs on-stream later. But, is such phased development of the reservoirs possible? Or would producing from the shallower reservoirs first permanently damage our ability to drill and produce the deeper HPHT reservoirs at a later stage in field life? These were the questions we tried to answer in this work.
We built a full-field finite element model to simulate the geomechanical response of the reservoirs to pressure depletion i.e. quantify the displacement, strains and total stress changes in and around the reservoirs as a function of production. Such geomechanical models can serve as a predictive tool to help answer the questions above. In this paper, we show the construction and application of such a geomechanical model in field development planning. Our paper highlights how our geomechanical model results were applied, together with other work, to develop this field safely and efficiently, emphasizing field life cycle value.