Modeling CO2 saturation distribution in eolian systems

Eolian sandstone hydrocarbon-bearing reservoirs have been target of CO2 enhanced oil recovery as well as potential CO2 sequestration sites. These sandy reservoirs are compartmentalized by the presence of bounding surfaces, which can function as flow barriers. In this study, eolian packages of a specific outcrop are modeled and their bounding surfaces effects on multiphase flow in CO2 upward migration are simulated through adequate enforcement of capillary barriers in a compositional simulator. We investigate how two-scale dune foresets strike directions of the outcrop could hint on the choice of well direction to increase storage in this particular model. The genetic unit of eolian strata is small and therefore their corresponding heterogeneity features, such as bounding surfaces, require higher resolution than that available through well logs. We build a synthetic eolian simulation model with associated bounding surfaces, geometrically inspired by the Permian Cedar Mesa Sandstone in southern Utah, USA. Permeability values of sand bodies and bounding surfaces are taken from actual outcrop reported data and surface examples to produce a lower bound of absolute permeability contrast. Capillary pressure is parameterized by the gridblock permeability, which implies that the capillary pressure contrast also represents a lower bound on the basis of published information. Our results show that bounding surfaces markedly reduce accessibility ratio (sweep efficiency), up to 55%, compared with cases where bounding surfaces are ignored, resulting in a larger plume size beneath the caprock and also higher leakage risk. Interestingly, well direction with respect to foreset strike direction has negligible effects on trapping and accessibility ratio for the low inclination angle. The methodology developed in this study could be applied to study CO2 storage in other eolian formations. (c) 2012 Elsevier Ltd. All rights reserved.