4D reservoir geomechanics: a case study from the HP/HT reservoirs of the Elgin and Franklin fields

The quest for better predictability of reservoir behaviour has led to the need to construct more realistic and complex models, where the geoscience and reservoir engineering disciplines interact more effectively. In this paper we present an integrated workflow that combines results from 4D seismic inversion, geomechanics modelling, and reservoir simulations in a shared earth model. It has been applied to the Elgin and Franklin high-pressure/high-temperature fields located in the UK Central Graben of the North Sea. These structurally complex fields are a challenge for a shared earth model approach. The 4D seismic datasets have been inverted into interval time-shifts using an in-house warping method. In parallel, a coupled faulted reservoir and geomechanical model has been used to determine both the stress redistribution within and around the reservoir including associated reactivated fault slips, and to derive synthetic 4D time-shifts with the help of a rock physics model. Good matches have been achieved between observed and synthetic 4D time-shifts. This integrated study proved to be a useful tool for understanding the reservoir and production behaviour of the Elgin and Franklin fields, with the ultimate goal being identification of new drilling targets and mitigation of casing integrity risks.