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Stratigraphic Architecture of Slope Deposits Associated with Prograding Margins, Sobrarbe Formation: Ainsa Basin, Spain

Henri Sahat MP Silalahi1, David Pyles, Ph.D1, Dr. Renaud Bouroullec, Ph.D1, Donna Anderson, Ph.D2, Julian Clark, Ph.D3, and Stephen A. Sonnenberg, Ph.D4
1Chevron Center of Research Excellence, Colorado School of Mines, Golden, CO, USA; Email : [email protected]; [email protected]; [email protected]
2Research Assistant Professor Colorado School of Mines, Golden, CO, USA
3ETC Chevron, USA
4Professor and Charles Boettcher Distinguished Chair in Petroleum Geology, Colorado School of Mines, Golden, CO, USA

The link between delta systems and deposition in the slope and basin environment has important applications to petroleum exploration and the development of reservoirs within deepwater systems. Few studies have addressed the reservoir-scale stratigraphic architecture along the depositional profile in prograding systems. The Eocene Sobrarbe Formation contains 12 km of continuous outcrop exposure from the shelf-edge delta through the slope depositional environments. The Sobrarbe Formation records a prograding system deposited during the final phases of the Ainsa Basin fill succession. This study, conducted on one fourth-order parasequence of the Sobrarbe Formation (maximum thickness 120 m), utilizes stratigraphic columns, photo panels, paleocurrent measurements, and boundary data to document how stratigraphic architecture changes along the physiographic profile.

The stratigraphic architecture of the Sobrarbe Formation shows a succession of deepwater channel and delta mouth bar elements at the shelf-edge/proximal slope and is followed by vertical stacking channels, overbank deposits, and mudstone-sheets at the medial slope. The distal slope is dominated by mudstone sheet and channel-lobe transition elements. The channel geometries increase in aspect ratio and width from proximal to distal slope and decrease in thickness from the medial to distal slope. Grain size distribution decreases from coarse- to medium-grained sand at the proximal slope to medium- to very fine-grained sand at the lower medial to distal slope. Paleocurrent data increase in range and diversity going down the slope. This increase is interpreted to reflect that channel sinuosity increases down slope. These results provide an analog for reservoir prediction and modeling within deepwater prograding systems such as West Siberia Basin, Northwest Slope Australia and Sahakalin Island.

AAPG Search and Discovery Article #90083 © 2008 AAPG Foundation Grants in Aid