| Popis: |
Summary Based on standard core measurements and image analyses, we determined that the carbonate rock from the Ocala Group, South Florida is formed by moldic, vuggy, intergranular, intraparticle and intercrystalline pores. The thin section analysis provided information on the matrix porosity and the x-ray computed tomography (CT) image provided information on the vuggy porosity. We constructed vuggy porosity models to calculate synthetic ultrasonic responses based on the finite difference method, and we compared the synthetic with ultrasonic data. The results explain the velocity changes associated with vugs in the carbonate rock at the core scale. We used the modeling results to explain the scattering of velocity versus permeability relations based on core measurements for different flow units of the carbonate aquifer. Velocity correlates well with permeability for each carbonate flow unit. To determine whether we can assess the degree of connectivity between vugs or between the matrix and the vugs based on acoustic data, we calculated the squirtflow lengths using a poroelastic model by fitting the calculated and observed velocities at the ultrasonic dominant frequency of 250 kHz. The results show a good correlation between the squirt-flow lengths and the increase in permeability for each flow unit. In addition, we calculated dispersion and attenuation curves based on core data in the frequency range of sonic logs. We found that the attenuation can be related to the fluid flow between the matrix and the vugs. We therefore conclude that the sonic log data has the potential to estimate whether vugs contribute to permeability in the region surrounding the borehole by examining P-wave attenuation and dispersion. |
