ABSTRACT

The upper Jurassic Frisco City Sandstone is a prolific oil reservoir in southwestern Alabama. To date, there is no consensus as to the reservoir depositional model for this sandstone. Interpretations include marine, braid delta-front deposits, braided stream deposits associated with alluvial fans, strandplain and beach deposits associated with shoal-water braid deltas, and tidal channel and ebb and braid delta deposits. In utilizing a fullbore Formation MicroImager (FMI) well logs in conjunction with a core study, the interpretation of the depositional environments of the Frisco City Sand were determined to be braid-delta, ebb-delta, tidal channel and strandplain. The FMI log provided paleocurrent direction and sandstone orientation data that are not attainable from core studies.

The FMI log is also useful in deciphering reservoir quality and reservoir grade sandstone. Not only is the FMI log beneficial in defining the porous and permeable sandstone intervals, it can also be utilized in identifying anisotropic features that could be barriers to flow. Reservoir characterization and evaluation are enhanced through the use of the FMI well log.