From Bureau of Economic Geology, The University of Texas at Austin (
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AAPG Annual Convention, Calgary, Alberta, Canada, June 19–22, 2005

Surprising Lessons from Multi-Disciplinary Characterization of a Permian Carbonate Platform Reservoir

Stephen C. Ruppel


Geological characterization of Fullerton field, a 30,000 acre (12,000 hectare), 1.5 Billion barrel, shallow water platform reservoir in West Texas, has revealed a broad spectrum of geological, petrophysical, and geophysical relationships that provide new insights into controls of reservoir development and the interpretation of subsurface datasets.

Among the surprising, non-intuitive lessons learned from this study are (1) major seismic reflectors define facies changes instead of time lines or sequence boundaries. (2) permeability is a function of depositional facies, whereas porosity is a function of diagenesis, (3) porosity development is a response to early diagenesis and stabilization: in peritidal rocks, by dolomitization and in subtidal rocks by calcite lithification, (4) limestones in this dominantly dolostone reservoir are low permeability flow baffles in peritidal rocks, but permeable, high-flow layers in subtidal rocks (5) borehole geophysical data can provide almost as much geological information as cores, (6) properly calibrated porosity logs are better tools for identifying and correlating depositional cycles than gamma ray logs, (7) 3D seismic data are a more robust measure of interwell and extrawell porosity distribution than well log data, and (8) diagenesis and porosity development are locally the result of reactivation of deep structures. An important key to these insights is the integration of both outcrop and subsurface data.

Although all of the observations cited above derive from specific circumstances associated with Fullerton field, each provides important insights into the interpretation of subsurface data sets in carbonate reservoirs worldwide.