LAB SCALE MODELING OF POROSITY IN THE MIAMI LIMESTONE USING HIGH FREQUENCY GROUND PENETRATING RADAR

The Miami Limestone in the Biscayne aquifer is difficult to characterize due to the heterogeneous and anisotropic distribution of porosity and permeability beyond the pore scale. The heterogeneous distribution of porosity is linked to the depositional environment of the eogenetic karst and the subsequent bioturbation and dissolution processes which created macroporous zones. In these zones porosity values reach near 100 % and in some cases, permeability exceeds the classical "Super-K" zones of the Jurassic age Ghawar oil fields by 2-5 orders of magnitude. These zones allow for the pumping of nearly a billion gallons of water per day, used by population of south Florida. In this work, we present results from a geophysical study at the laboratory scale to infer porosity variability in a large (1.17 m by 0.19 m by 0.19 m) block of Miami Limestone using ground penetrating radar (GPR). Geophysical results were coupled with the complex refractive index model (CRIM), a three phase petrophysical model, in order to infer porosity variability as related to changes in the electromagnetic wave velocity and associated dielectric permittivity. Surveys were conducted both under dry and water saturated conditions to test the certain parameters used in our model to infer porosity. GPR porosity estimates were further constrained with digital imaging in order to determine the potential amount of error in the measures and asses the parameters used in the petrophysical model.

The results presented depict a two dimensional spatial variability of porosity of the Miami limestone at the centimeter scale. This work has implications for surface and ground water modeling including the impact of high permeability areas on Everglades restoration projects.