Integrating 4D Seismic, Geomechanics and Reservoir Simulations in the Elgin and Franklin Fields

Summary In recent years, the quest for better predictability of reservoir behaviour has led to the need to construct more complex and realistic models, where geosciences and reservoir engineering disciplines interact. Time-lapse (4D) seismic has been applied in both quantitative and qualitative manner to better understand and predict the dynamic behaviour of reservoirs. For stress sensitive reservoirs, hydrocarbon production induces changes in the effective stress field within and outside the reservoir, which result in predictable effects, including changes in seismic velocities and layer thickness. In this study, 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 HPHT fields located in the North Sea Central Graben. These structurally complex fields are a challenge for a shared earth model approach. The 4D seismic have been inverted into interval time-shifts using an in-house warping method. In parallel, a coupled geomechanics and reservoir model has been used to determine the actual stresses within and around the reservoir, and to derive synthetic time-shifts with help of a rock physics model. Good match has been achieved between real and synthetic 4D time-shifts. This integrated study proved to be a useful tool for progressing understanding of Elgin and Franklin fields behaviour, with the ultimate goal being new drilling targets definition and casing integrity risk mitigation.