To understand basic sediment properties that control fluid flow in sandy sediments. To be able to calculate a quantitative relationship between sediment microfabric and flow properties, we must model the relationship between grain properties (shape, surface morphology, orientation, and contacts), pore properties (network, pore size distribution, dimensions, chord lengths, specific surface area, coordination number, and tortuosity) and microfabric.
We are using a combination of field, lab, and modeling techniques to quantify the primary variables affecting permeability. In the field we are making direct in-situ bulk measurements of permeability in order to ground truth our modeling predictions. We are collecting diver cores for (a) constant head laboratory measurements of permeability, and (b) basic physical properties, including grain size, bulk density, grain density, void ratio, and porosity. We are impregnating diver cores to provide material for thin sections, which will allow us to investigate grain and pore properties using thin sections, SEM, or CT scanning techniques. We are currently developing an in-situ impregnation system, which will minimize microfabric disturbance.
We are investing a significant effort in modeling permeability. We have implemented Effective Medium Theory, which involves image analysis techniques to quantify pore factors and tortuosity, and the Kozeny-Carmen equation, which involves grain factors and tortuosity. We’re investigating the usefulness of Percolation Theory to quantify permeability and tortuosity.
We have completed direct in-situ and laboratory measurements of permeabilty off Panama City. We have successfully impregnated wet cores on board ship and will be attempting an in-situ impregnation of bottom sands before the main DRI experiment.
Initial permeability modeling of Panama City sands using Effective Medium Theory and Kozeny Carmen equation differ, perhaps because the angular Panama City sands diverge from the ideal spheres required by the Kozeny-Carmen equation. In-situ and laboratory values corroborate the EMT results. For more rounded grains, such as the ooids recovered from Bimini, the EMT and Kozeny-Carmen predictions of permeability agree quite well with each other and the laboratory measurements of permeability. In-situ measurements of permeability are low, owing to probable instrument problems at this site.
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