Quantification of Stratigraphic Heterogeneity within a Fluvial Point-Bar Sequence, Williams Fork Formation, Piceance Basin, Colorado: Application to Reservoir Modeling

Ellison, Amanda¹, Matthew J. Pranter¹, Rex D. Cole², Penny E. Patterson^3
1 University of Colorado, Boulder, CO
² Mesa State College, Grand Junction, CO
³ ExxonMobil Upstream Research Company, Houston, TX

The internal stratigraphic architecture and heterogeneity of fluvial deposits affect the distribution, connectivity, and quality within a reservoir sand body. Detailed sedimentologic and stratigraphic analyses of outcrops of the Lower Williams Fork Formation in Coal Canyon, near Grand Junction, Colorado, are conducted to characterize the internal complexity of a fluvial point-bar sequence at a sub-seismic scale. These data provide important analog information to condition 3-D geologic models of similar subsurface petroleum reservoirs.

Measured sections, photomosaics, and outcrop correlation panels capture the variation of internal sand body geometry (e.g. lateral accretion deposits, sheet flow deposits), stacking, and sedimentology. Lidar data (LIght Detection And Ranging) have also been acquired to provide a digital image of the outcrop for use in interpreting stratigraphic architecture. Lidar is a high-resolution (cm-scale) digital elevation model, with light intensity data. Digital lidar images have been interpreted in a 3-D environment and are used to define fluvial elements and bounding surfaces, and to extract dimensional data for sandstone bodies. Using a combination of outcrop photomosaics and interpreted lidar images, key surfaces, internal geometries, and dimensional data are extracted and combined with lateral and vertical facies variations and trends (e.g. fining-upward sequences). These data are used to build and condition 3-D outcrop models of analogous gas reservoirs to gain a better understanding of sub-seismic sand body internal heterogeneity and the effect on fluid flow within a reservoir.