Stratigraphic Architecture and Connectivity of Lower Williams Fork Formation Meandering-Fluvial Deposits, Coal Canyon and Grand Valley Field, Colorado
University of Colorado at Boulder, Department of Geological Sciences Boulder, Colorado; [email protected]
This study addresses the reservoir-scale stratigraphic architecture and connectivity of sandstone-bodies within the lower Williams Fork Formation through analysis and comparison of outcrop analogs within Coal Canyon, Colorado and borehole-image data from Grand Valley field in the Piceance Basin. To document the stratigraphic architecture of the lower Williams Fork Formation in outcrop, sandstone-bodies present were analyzed for thickness, sedimentary structures, and grain size. In the subsurface, borehole-image analysis of two wells that contain twenty four gas-producing sandstone-bodies within the Piceance Basin suggests that the sandstone-bodies, as exposed in outcrop and present within the subsurface, represent similar deposits. Lithologic and gamma-ray analysis of one multi-story point-bar complex at Hoodoo Hill reveals very complex stacking patterns of individual sandstone-bodies, as well as scour surfaces and lag gravels that may be barriers to fluid flow. Also, vertical and lateral relationships are highly variable (lithofacies can change within a matter of feet).
Three-dimensional lithologic models and sandstone-body connectivity analysis of Hoodoo Hill reveal that at dense well spacings (40-, 20-, 10-, and 5-acre), sandstone-body connectivity is very high (64.4 % by volume for 40-acre spacings up to 74.7 % by volume for 5-acre spacings). Through applying outcrop statistics to build highly constrained reservoir models of subsurface analogs, better understanding of hydrocarbon-producing deposits is gained.
AAPG Search and Discovery Article #90083 © 2008 AAPG Foundation Grants in Aid