Bureau of Economic Geology, The University of Texas at Austin (www.beg.utexas.edu).
HGS NorthSiders Dinner, The Woodlands, Texas, February 17, 2004
Prediction of Reservoir Architecture in Carbonate Systems
Carbonate reservoirs hold more than half of the world's remaining hydrocarbon resource base. Much of this resource is well delineated in terms of in-place volumetrics, but major hurdles still exist in terms of maximizing the recovery efficiency of this resource. With more than 70 years of carbonate reservoir development in basins like the Permian Basin of West Texas, both major and independent oil producers have arrived at an important conclusion .carbonate reservoirs are complex! Recovery efficiencies rarely exceed 30 percent through secondary recovery. Tertiary recovery can be effective in many fields, but an equal number are probably unsuited. The additive effect of depositional, diagenetic, and structural heterogeneities contribute to the mystique that is carbonate reservoir development, and the through going message is that these systems must be unraveled one reservoir at a time. Notwithstanding this complexity, observations from a wide range of reservoirs have led to important generalizations regarding our ability to predict reservoir style and substantially improve static reservoir model construction.
Prediction of stratigraphic architecture and heterogeneity style in carbonate reservoirs has advanced greatly over the past decade. Integration of core, log, and seismic data, aided by outcrop analogs, has proved to be the most successful approach to unraveling the stratigraphic or "matrix" plumbing systems of carbonate fields. Sequence concepts such as accommodation history and Milankovitch setting are important, but geologically oriented petrophysical analysis and seismic processing are both critical for proper delineation of the 3D reservoir model. Examples of heterogeneity styles and reservoir architectures found in greenhouse, transitional, and icehouse settings, with examples from the Middle East, U.S., and other areas will provide examples of how reservoir architectures can be predicted, analyzed, and converted into 3D models.