Geometric and Infill Effects on Flow Patterns and Production Rates in Paleokarst Reservoir Models

Summary Paleokarsts are products of carbonate cave deactivation, collapse and burial. The cave geometry and most of the petrophysical properties are preserved and could act as petroleum reservoirs. In this study, test flow simulations were done on a porous media with dimensions of 614x100x30 m3 and cells of 2x2x2 m3. The cave diameter is varied from 2 to 18 m while the geometry configuration consists of varying sizes, branching and complexities to capture flow patterns and sensitivities. High and low petrophysical properties were assigned to the karst and background matrix, respectively, to create contrasts. At background permeability less than 5 mD, the flow patterns follow the cave resulting into a relatively early water cut. However, when the background permeability is at least 40 mD, the cave geometry is no longer preferred but and rather the entire reservoir pay-zone is uniformly swept instead. In instances where the cave sections consisted of sand and collapse breccia, excellent oil- sweep efficiency was observed in more homogeneous and permeable compositions. The results from this study are valid for generic reservoir models and are yet to be tested on real reservoir models.