Sedimentology, Statistics, and Flow Behavior for a Tide-influenced Deltaic Sandstone, Frontier Formation, Wyoming, United States
Christopher D. White, Brian J. Willis, Shirley P. Dutton, Janok P. Bhattacharya, Keshav Narayanan, 2004. "Sedimentology, Statistics, and Flow Behavior for a Tide-influenced Deltaic Sandstone, Frontier Formation, Wyoming, United States", Integration of Outcrop and Modern Analogs in Reservoir Modeling, G. Michael Grammer, Paul M. “Mitch” Harris, Gregor P. Eberli
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Astudy of a tide-influenced deltaic sandstone investigated geologic variations that affect hydrocarbon production in analogous reservoirs. The Cretaceous-aged Frewens Allomember was deposited by a delta prograding into a narrow shoreline embayment between an older, wave-dominated delta lobe to the south and a basin-floor ridge created by subtle structural uplift to the north. The Frewens Allomember is exposed in outcrops of the Frontier Formation in central Wyoming (United States). It comprises two 5-km-wide by 20-km-long upward-coarsening sandstone bodies. Each body contains basinward-dipping internal beds. Heterolithic beds capped by extensive shale drapes record episodic tidal deposition in the lower portions of the sandstone bodies, whereas sandier cross-stratified beds in the upper parts of bodies record stronger and more uniformly ebb-directed currents. During diagenesis, calcite concretions formed preferentially at the top of the upper sandstone body as water circulated down from overlying shales.
Diagrams of bedding, facies, calcite concretions, and bed-draping shales were compiled from high-resolution photomosaics and field observations. Sedimentologic logs, field permeameter measurements, and thin-section observations describe petrophysical properties of facies in the delta lobes. Variograms quantify the spatial correlation of permeability in lithofacies. The lengths of bed-draping shales were estimated from outcrop data using a termination frequency model. The spatial distribution of concretions was modeled with indicator geostatistics.
Flow models integrated bedding geometry, lithofacies, and petrophysical properties in an appropriate structure for reservoir simulation. These models were used to analyze sensitivity of reservoir behavior to different geologic features and to investigate methods for modeling and upscaling interwell-scale heterogeneity. Intrafacies variability of permeability has negligible effects at the sandstone-body scale but significant effects at the bed scale. Shale lengths increase toward the lateral margins and toward the base of the sandstone bodies. Inclined shales reduce upscaled permeability, recovery efficiency, and breakthrough time. Calcite concretions decrease upscaled permeability. An upscaling method based on flow simulation and response-surface models accurately and efficiently represents the effects of geologic heterogeneity and flow rate on a coarse simulation grid.
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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.