Identifying Fault Compartmentalization in the
Middle Frio Sandstones, Redfish Bay, South Texas 

Randy Remington
BEG Research Scientist Associate

Project STARR is working in conjunction with IBC Petroleum to delineate fault compartmentalization in the Middle Frio sandstones in Redfish Bay. The Redfish Bay field is located on the downthrown side of the major Ingleside growth-fault zone. Approximately 32 wells have penetrated the Middle Frio section (~10,000 to 11,000 ft) and 14 wells have produced or are producing from this interval. Total production is 35 Bcf gas and 0.8 MMbbls condensate.

The Middle Frio section is composed of 12 fourth-order, lowstand prograding wedges deposited within three third-order lowstand system tracts. The sands appear to have good reservoir quality (tens to hundreds of millidarcys.) However, these sands are extensively faulted resulting in complex compartmentalization. At least two periods of mobile shale related deformation (shale tectonics) occurred. The older growth-fault system (Ingleside/Frio) parallels the paleoshoreline, whereas the younger fault system is roughly perpendicular to the paleoshoreline. Where the two fault systems intersect, the structural complexity is extremely high.

Detailed integration of wireline-line logs, 3-D seismic, and engineering analyses are necessary to delineate these fault compartments. The basic approach taken to delineate the fault compartments is as follows: (1) detailed correlation of flooding shales (MFS) and fault picking on wireline logs, (2) horizon and fault picking on 3-D seismic incorporating coherency analysis, (3) integration of previous results with seismic amplitude anomaly analyses and engineering pressure analysis, and (4) delineation of new compartmentalized fault prospects. Several prospective undrained compartments are being evaluated.