Bureau of Economic Geology, The University of Texas at Austin (www.beg.utexas.edu).
AAPG Annual Convention, Houston, Texas, April 9–12, 2006
Fundamentals of Rock-based Reservoir Modeling; A Case History from the Lower Permian Fullerton Field, Permian Basin
Recovery of the >1.7 Billion barrels of oil in Fullerton field, a shallow water platform carbonate reservoir of Early Permian age, has proven difficult despite more than 60 years of production history. A major contributing factor to low recovery efficiency (18 %) is an incomplete understanding of the geological controls on reservoir architecture. Our multidisciplinary study was based on the following crucial rock-based approaches: (1) geological models of analogous outcrops, (2) description of >14,000 feet of core, and (3) new core data for rock fabric analysis. These data were used to guide correlations (more than 850 wireline log suites) and development a 3-D seismic inversion porosity model, ultimately leading to the construction of rock-based, full field and flow simulation models.
Key rock-driven insights from the study include: (1) seismic reflectors define depositional and diagenetic facies not time lines or sequence boundaries. (2) permeability is a function of depositional facies, whereas porosity is a function of diagenetic facies, (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, and (5) porosity logs can be better tools for identifying and correlating depositional cycles than other wireline logs.
Full integration of outcrop and core data is a fundamental basis for more accurate interpretation and modeling of subsurface data sets and for better understanding of reservoir development in carbonate platform reservoirs.