Improving reservoir models of Cretaceous carbonates with digital outcrop modelling (Jabal Madmar, Oman): static modelling and simulating clinoforms

In Jabal Madmar in the Sultanate of Oman, Cretaceous epeiric carbonate platform architectures were characterized by employing a digital outcrop modelling workflow. A framework model for Natih Sequence I (Natih E member) was established, which embeds a meticulously studied platform-top incision and shoal complex. Outcrop-scale clinoforms are recognized in these shoals by hectometre-scale (100 m long) medium to high-angle (1-5 degrees) inclined stratal surfaces comprising texture-based facies transitions. These clinoforms are usually beneath the resolution of seismic data and as such are not easily recognized and correlated between wells. Geologically realistic clinoform models were built using a well-defined stratigraphic model that incorporated inclined surfaces in the model grid and if available, data on lateral facies transitions. Waterflood simulations demonstrated improved sweep efficiency in these models. In contrast, simple models without clinoform heterogeneities resulted in less efficient piston-like patterns of sweep. The study presented in this paper demonstrates an outcome contrary to previous studies, as in this study, barriers to flow are absent. Complex clinoform models must be considered in reservoir modelling workflows to correctly derive static and dynamic rock properties. This is because outcrop-scale clinoforms have a potential impact on reservoir behaviour under secondary and tertiary recovery mechanisms.