Diagnostics of Reservoir Fluid-Fill Cycle and Relevance for Tailoring Field Developments in Oman

Abstract

The development of reservoirs that are not in hydrostatic equilibrium or that have suffered deviations from primary drainage over geological time requires appropriate challenges to standard assumptions in order to optimize the field's full potential. Such circumstances are more frequent than usually acknowledged since the Earth is not static, structures get buried or change with tectonic activity and fluids re-arrange themselves to achieve a state of minimum potential energy. The focus of this paper is three fold: a) highlight geological processes that may affect fluid distribution and pressure regime in a reservoir; b) provide a template workflow and diagnostic tools for identification of alternative fluid-fill cycle and equilibrium state scenarios; c) illustrate through actual field examples the relevance of recognising tectonic imprint on fluid distribution, in particular for reservoirs with low permeability, oil wettability or low porosity. A companion paper1 published at the same time discusses methods to model saturation changes in some of such complex fields. In summary, the interpretation of variable contacts within a field can result in changes to development decisions (see fig 1): consequences are not limited to volumetric assessment but they can actually change the development, well count and well placement as well as impacting the design of the facilities. Based on risk and opportunity management optimization we advise against indiscriminate standard assumptions of primary drainage or hydrostatic equilibrium for all reservoirs in all basins.