HR: 0800h
AN: U31A-0002    [Abstracts]
TI: Using 3D Geospatial Models to Improve Outcrop Analog Studies: an Example Using Crevasse Splay and Point Bar Outcrops, Upper Cretaceous, NW Colorado
AU: * Carr, M M
EM: mcarr@mines.edu
AF: Department of Geology and Geological Engineering, Colorado School of Mines, Golden, CO 80123,
AU: Anderson, D S
EM: dsanders@mines.edu
AF: Department of Geology and Geological Engineering, Colorado School of Mines, Golden, CO 80123,
AB: The use of outcrop data as analogs for subsurface reservoirs presents challenges to the user in comparing scales as well as sedimentary body volumetrics. It is difficult to accurately estimate volumes of sedimentary bodies in outcrop if one is dealing with 2D maps and measured sections. The application of 3D geospatial models to outcrop settings helps address inherent unknowns associated with discontinuous 3D outcrops. Crevasse splay bodies are likely effective reservoirs in many thick tight-gas fluvial successions, yet they are incompletely recognized and lack the same level of dimensional data as point bars and channelbelts. A 200-ft thick vertical succession of strata within a 160-acre outcrop area within the nonmarine part of the Upper Cretaceous, lower Iles Formation, north of Rangely, Colorado, shows the dramatic differences between crevasse-splay and point-bar bodies. The outcrop contains an upward stratigraphic change from isolated, stacked crevasse channel/splay sandstone bodies to those of isolated, paired point bars within a laterally migrating 1500-ft wide, sinuous meanderbelt. A largely deterministic 3-D model of the outcrop shows critical differences in shape, facies architecture, areal distribution, and rock volume between crevasse splays and point bars. It also shows a lack of vertical and lateral connectivity among four crevasse-splay and four point-bar bodies. All sandstone bodies show similar "average" statistics: they contain the same types and gross proportions of grain sizes and facies classified by sedimentary structures, with high net-to-gross sandstone (over 90%), similar gross rock volumes (1000 to 1500 acre-ft), and average thicknesses (about 18 ft). However, the map-view dimensions, geometries, internal facies architecture and proportions are completely different due to dissimilar, yet linked, depositional processes. In addition, individual point bars are in poor lateral communication within the meanderbelt, whereas individual crevasse- splay bodies are laterally widespread and internally more contiguous. The overall geometry and connectivity of these bodies has critical implications when considering whether well downspacing is taping into new reserves or simply draining existing reserves faster.
DE: 8094 Instruments and techniques
DE: 9350 North America
DE: 9610 Cretaceous
DE: 9820 Techniques applicable in three or more fields
SC: Union [U]
MN: 2007 Fall Meeting