Numerical modeling of the fluid flow impact of thin baffle laminae in cross bedding

Thin layers of less permeable materials can occur in cross-bedded rocks and may function as flow baffles, thus influencing the bulk fluid flow. However, it can be challenging to model their flow impact using standard grid-based techniques that can only capture the topology and geometry of the layers accurately using a large number of small cells. In this paper, a numerical method, recently developed by the authors for modeling fluid flow in fault damage zones that contain thin low-permeability fault strands, is demonstrated as being applicable to modeling the flow impact of thin baffle laminae in cross beds. This method does not require thin baffles to be discretized explicitly. For a range of permeability contrasts between the thin baffle layers and the rest of the matrix, upscaled permeability values are derived for models that have the same volumetric fraction of baffle material. The results show that when the baffles are completely connected, the upscaled permeability is less than for cases where the baffles do not form a continuous impediment for all levels of permeability contrast and declines more steeply with the increase of the permeability contrast. The flow effect of the layer configuration becomes more apparent for the disconnected situation when the permeability contrast is high. The method is shown to be accurate and efficient for this type of work. These results highlight the importance of capturing the topology and volume of the thin baffle layers in flow modeling of cross beds and the necessity of using appropriate numerical techniques. Copyright 2008 by the American Geophysical Union.