Erwin W. Adams

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

ABSTRACT 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°) 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.

Rule-Based Modelling of Modern-Day and Past Carbonate Shoals Environments

Carbonate reservoirs tend to be particularly heterogeneous because, besides physical sedimentary processes, biological and chemical inputs play an important role in shaping the initial depositional architecture. In addition to these processes, diagenetic overprints, which can either follow or cross cut the primary depositional architecture, introduce another level of complexity by altering the primary depositional porosity and permeability. This combination of multiple processes interacting in both a temporal and spatial sense creates carbonate reservoir characteristics with complex architectures and heterogeneities on various scales, i.e. geobodies. As a result, pattern-based modelling is not always applicable, especially because of the difficulties arising in the identification and definition of discrete geobodies. In order to better predict and model geobodies, research developments are steered toward process-oriented methods for interwell modelling. This extended abstract presents a process-oriented approach using cellular automata applied to interwell-modelling.