Analyses of porosity and permeability variations captured by cross‐well seismic measurements and geophysical well logs at Port Mayaca aquifer, south Florida

Abstract

Summary High-resolution seismic reflection between wells provides images of the subsurface about one order of magnitude greater than surface seismic reflection. Cross-well seismic images outline the zones of high matrix porosity and permeability that are associated with high water production at the Port Mayaca test site. The top of the Floridan Aquifer System (FAS) and the lower boundary of the intermediate confining unit (the basal Hawthorn) are delineated with an impedance image. Impedance, porosity, and permeability images capture the variation of the aquifer matrix in the interwell region. In particular, the impedance image provides the stiff and soft zones of the aquifer. The stiff zones contain conduits, which may not be connected, that are associated with secondary porosity features such as pore/vugs/fractures near the wells. The soft zones of low impedance are associated with high water production. Furthermore, the impedance and porosity images, combined with the Fullbore Formation Micro Imager (FMI) resistivity image logs, provide information that can explain the development of conduits in the stiff intervals. The permeability image gives a good visualization of low and high matrix permeability distribution intervals, and the FMI image data provides information on the secondary porosity distribution at the borehole scale that cannot be detected with any other log. In particular, the FMI image logs show a sequence of dark (conductive) and white (resistive) bands. This suggests that the conductive bands are porous and saturated with brackish water (high permeability spikes). Some of the resistive bands may be connected between wells, but the dark zones embedded in the white bands likely are not. Zones characterized by these sequences are intervals with low water production.