Integrating Sequence Stratigraphy and Multiple Three-dimensional Geostatistical Realizations in Constructing a Model of the Second Eocene Reservoir, Wafra Field, Partitioned Neutral Zone, Kuwait and Saudi Arabia
Dennis W. Dull, 2004. "Integrating Sequence Stratigraphy and Multiple Three-dimensional Geostatistical Realizations in Constructing a Model of the Second Eocene Reservoir, Wafra Field, Partitioned Neutral Zone, Kuwait and Saudi Arabia", Integration of Outcrop and Modern Analogs in Reservoir Modeling, G. Michael Grammer, Paul M. “Mitch” Harris, Gregor P. Eberli
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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 trans-gressive 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.
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Building robust 3-D reservoir models is a major challenge that requires incorporation of geologically defined input parameters. This publication provides an overview of current approaches used in the development of geologically constrained and integrated reservoir models. Each of the 18 papers addresses various stages in the process of creating a reservoir model through the development and incorporation of an analog, extracting the quantitative input parameters on lateral and vertical variability, and the development and modification of a 3-D reservoir model based upon geologically constrained data. This applied volume is divided into two sections. The first is a set of papers illustrating the value and methodology of acquiring geometrical data on the lateral and vertical distribution of reservoir facies, within a sequence stratigraphic framework, using both outcrop analogs and detailed study of modern depositional systems. The second section includes both case studies where outcrop and modern analog data have been incorporated into subsurface reservoir models, as well as papers that illustrate recent advances in simulation and geostatistical methodologies. Together, the two sections provide a comprehensive look at integrated reservoir modeling.