Abstract: A Methodology for Obtaining Detailed Geologic Descriptions to Constrain 3-D Reservoir Fluid-Flow Simulation Models in Delta-Front Lithofacies

R. D. Adams, S. H. Snelgrove, C. Forster

The Cretaceous Ferron Sandstone Member of the Mancos Shale in east-central Utah is the focus of a multidisciplinary study designed to integrate geological and petrophysical data into 3-D fluid-flow simulations of fluvial-deltaic reservoirs. Geologists and reservoir engineers refined a methodology for collecting and integrating outcrop information to define input parameters for simulations. Geologists first develop a sequence stratigraphic framework, delineate parasequence sets and parasequences, and define facies architecture within parasequences. Next, a detailed geologic data set Is gathered in the delta-front lithofacies and stored in digital form. Sequence stratigraphy, parasequence geometries, and facies architecture of the study site must be understood first in orde to place detailed geological and petrophysical data sets within their geologic context.

The detailed geologic data set was collected within an outcrop "window" defined with a height:width ratio of ^approx 1:5 and located on a 50-70 ft (15-20 m) high cliff exposing the entire delta front. A photomosaic of the cliff provided a base for mapping large-scale geometry and distribution of architectural elements within the reservoir analog. Detailed variations in lithology, sedimentary structures, and bed thickness (>=0.02 ft; >=5 mm) were recorded along three equidistant, vertical transects within the window. Small-scale photographs yielded 4×6 ft (1.2×1.8 m) "mini-windows" located at ^approx50 ft (15 m) intervals within the window. Transparent overlays on the mini-windows recorded geometry and internal architecture of several adjacent, representative, delta-fro t clinoforms. Clinoform characterization was extended proximally outside of the window to capture the full range of delta-front variation. Petrophysical data were collected from 1-inch (2.5 cm) diameter core holes spaced at 0.3 ft (9 cm) intervals along the central vertical transect and at 0.3-0.5 ft (9-15 cm) intervals along both vertical and horizontal transects within several of the mini-windows. Permeabilities were measured on core and in core holes using a field mini-permeameter. Characterization of detailed reservoir architecture and permeabilities across scales ranging from several feet to 100s of feet (1-10s m) provides the quantitative data needed to define scaled-up and averaged reservoir properties for simulator grid blocks ranging in size from 10s to 100s of feet (1-10s m).

AAPG Search and Discovery Article #90959©1995 AAPG Rocky Mountain Section Meeting, Reno, Nevada