Inversion of acoustic logs to predict secondary porosity and pore aspect ratios for characterizing flow zones at borehole and field scales in a south Florida Aquifer

Detecting and delineating thin channels and conduits within flow zones in a carbonate aquifer at field scale is a complex process. To achieve this task, an algorithm is applied that inverts sonic logs to determine the secondary porosity and pore aspect ratios of the carbonate structure. This information helps to characterize flow zones at the pore and borehole scales integrated with Formation microimager(FMI), permeability, and micro-resistivity logs. The inversion of the velocity logs for wells MF37 and EXPM1 from the South Florida Water Management District’s Port Mayaca Aquifer site shows similar results. Data from both wells are combined to characterize the structure in the inter-well region of 1200 ft. Because the structure information at the well EXPM1 defines detailed flow zone characteristics, the analysis is initiated at this well. In the inter-well region, the flow zones are defined by micro-resistivity anomalies and by relating the aspect ratio logs to the pore space observed in the FMI logs. The well logs are displayed and analyzed together to evaluate the connectivity of the flow zones in the inter-well region, where we identified and delineated three flow zones associated with water production zones. The FMI logs are used to describe the pore structure and the fractures intercepted by the wells. The ELemental Log Analysis porosity image delineates the flow zone structure, confirming the presence of the heterogeneous porous limestone formation at the field scale. This interpretation suggests a methodology for monitoring fluid transmission in flow zones by measuring changes in pore structure using seismic reflection.