Integration of Remote Sensing Outcrop Data and Subsurface Information to Define High-Resolution Depositional Facies Variability within Interbedded Sandstones of the Upper Cretaceous Mancos Shale of Western Colorado
Dallas B. Dunlap¹, Peter P. Flaig¹, Darrin Burton², Timothy Prather¹, and Lesli J. Wood¹
¹Bureau of Economic Geology, University of Texas at Austin, Austin, TX, USA
²Newfield Exploration Company- Denver, CO, USA
The Loyd Sandstone member of the Buck Tongue of the Upper Cretaceous Mancos Shale is found stratigraphically below the more extensively studied Upper Cretaceous Sego Formation in Eastern Utah and Western Colorado. Due to the more regionally restricted extent of the Loyd Sandstone and its depositional similarities to the Sego Formation, it is critical to build a high-resolution geologic model to differentiate it from the overlying Sego Formation while accurately predicting its lateral facies variability. Laterally extensive outcrop exposures near Rangley, Colorado present an excellent, new analogue for subsurface reservoirs in both the Sego and what we believe to be the Loyd Sandstone.
Previous work with LIDAR remote sensing technology was successful in identifying the thickness variations, directionality of incised valleys, and surface truncation styles of four sand-rich sequences identified in the Sego Formation of Eastern Utah. The extracted geomorphologic measurements conditioned the shape and orientation of architectural features distributed in a Sego reservoir model. The imaging of small-scale intra-sequence depositional features from LIDAR data proved to be less effective due to the high percentage of sand (lack of sand/mud luminosity contrast along bedding planes) and the inability to image features below the LIDAR's far offset minimum resolution (~6 cm). Furthermore, LIDAR datasets are costly to acquire, difficult to fully evaluate in the field, and painstaking to process. In the Rangley, Colorado area, GigaPan automated photogrammetry technology was deployed to record high-resolution imagery of facies, sand/shale geometries and vertical/lateral architectural changes not previously observed with LIDAR. GigaPan technology allowed this to be done rapidly and more cost effectively.
Five kilometers of relatively continuous GigaPan data were obtained and integrated with ten measured sections to build the initial Loyd Sandstone stratigraphic framework. The GigaPan provided sub-centimeter resolution geo-rectified mosaics that highlighted the depositional environment of the Loyd Sandstone comprising tidal inlets, rare incision (valleys), embayments, and a potential river dominated delta. The mosaics were geo-referenced and converted to XYZ point clouds to assist in visualization and conditioning of the Loyd reservoir model.
While LIDAR data has consistently better geo-spatial accuracy, GigaPan photomosaics exhibit unique advantages including: (1) speed and relatively low cost of acquisition, (2) high pixel resolution (< 1 cm), (3) lack of signal noise and/or false echoes, and (4) durability of the system during field work.
AAPG Search and Discovery Article #90206 © AAPG Hedberg Conference, Interpretation Visualization in the Petroleum Industry, Houston, Texas, June 1-4, 2014