Integrated Modeling of the Mature Ashtart Field, Tunisia

Abstract Ashtart, a large fracture enhanced carbonate oil field offshore Tunisia, required a new reservoir model with high prediction confidence to optimize tail end production and to evaluate its remaining upside potential requiring drilling or tertiary recovery methods. Due to the complexity of the field, a synergistic approach was adopted by teaming up the different disciplines and partners. This approach entailed the creation of a fine scaled structural and petrophysical 3D matrix geomodel. The model was subsequently scaled up and supplemented with observed dynamically acting features such as fault or fracture flow paths and flow barriers. Modeled matrix permeabilities were systematically adjusted to match established well productivities, without arbitrarily changing flow conditions in the vicinity of wells. Crucial to this process were not only thorough studies of fracture distributions and attributes, but also the integration of all observed fluid dynamic aspects. Pressure transient analyses proved to be a valuable tool, leading to consistent effective permeabilities and the identification of previously unknown lateral and vertical boundaries. Superior history matches following iterative numerical modeling demonstrate the success of this single permeability modeling approach with improved prediction capabilities.