Sequence-stratigraphic principles and three-dimensional (3-D) geostatistical modeling were integrated to create a geologic model of the Second Eocene reservoir. This reservoir has produced more than 330 million bbl and is one of several prolific carbonate reservoirs located in the giant Wafra oil field of the Partitioned Neutral Zone. The Second Eocene is of Paleocene age and consists of a stacked series of complex ramp, dolomite reservoir units. The reservoir interval represents an overall regressive sequence composed of four high-frequency sequences reflecting a change from a transgressive to a highstand systems tract.

Modeling the Second Eocene involved three key steps: (1) establishing a relationship between core-derived lithofacies and log response, thereby enabling the prediction of lithofacies in noncored wells; (2) constructing the sequence-stratigraphic framework using the predicted lithofacies curves; and (3) applying geostatistics to integrate the lithofacies, sequence-stratigraphic framework, and spatial correlation.

Multiple versions or realizations of the geologic model were created. Facies, porosity, and water saturation varied in each of 30 equally probable models. The models were evaluated visually, statistically, and volumetrically to select a single realization for use in reservoir simulation. The single realization yielded an excellent agreement between areas of high cumulative oil production and areas predicted to have grainstone facies and large hydrocarbon accumulations. The 3-D geostatistical model also explained pressure depletion and water encroachment problems in the field.