PERMEABILITY MEASUREMENT OF BISCAYNE AQUIFER TOUCHING-VUG MACROPOROUS CARBONATE ROCK WITH LATTICE BOLTZMANN AND SPECIALIZED LABORATORY METHODS

The Biscayne aquifer of southeastern Florida contains laterally-extensive bioturbated zones characterized by centimeter-scale touching-vug macropores that make the Pleistocene carbonate rock extremely permeable. Standard petrophysical core laboratory techniques may not be capable of accurately measuring such high permeabilities. Therefore innovative procedures have been developed that can measure the permeability of such samples from the Biscayne aquifer.

Because these rocks are fragile, they cannot easily be cored or cut to shapes convenient for conducting permeability measurements. Hence, the sample that will be used for measurements in the laboratory is a 3-D epoxy print of a cylindrical core of the macro-porous rock. This core was printed from computed tomography data obtained from an outcrop sample of a vuggy portion of the aquifer rock.

For the laboratory measurements, a viscous ISO 680 grade gear oil (680 cST at 40 degrees Celsius) is utilized in order to permit easily measurable head gradients (~2 cm over 1 m) to be maintained simultaneously with low Reynolds number flow. This should ensure that Darcian flow conditions exist inside the core and permit accurate estimation of the intrinsic permeability. Preliminary work is focused on validation of the method with pipe flows where permeabilites are known from Poiseuille’s equation. Laboratory measurements of oil viscosity have also been conducted to establish its value at laboratory temperatures.

For the second form of permeability measurement, Lattice Boltzmann methodology is employed on the 3D renderings of the core. Reynolds numbers will be matched with those in the laboratory measurements. Preliminary modeling indicates that pipe flow can be accurately simulated when the resolution is high enough. Preliminary modeling was also used to assess flow through the laboratory apparatus.

The permeability of the rocks that make up these macro-porous zones, which are said to be responsible for most of the aquifer flow, has never been adequately determined. Corroboration between the two permeability estimation methods should indicate that accurate results have been obtained and that the results can be confidently applied to future studies of the Biscayne Aquifer.