Application of a Turbidite Bed Amalgamation Metric to Slope Deposits of the Tres Pasos Formation of Southern Chile: Implications for Evaluating Reservoir Connectivity and Sedimentary Body Architecture from One-Dimensional Data

Brian Romans¹, Stephen M. Hubbard², and Jacob A. Covault^1
1Dept. of Geological and Environmental Sciences, Stanford University, Stanford, CA
²Dept. of Geology and Geophysics, University of Calgary, Calgary, AB, Canada

A method for quantifying the degree of amalgamation in sandstone-rich turbidite successions is applied to the deep-marine slope deposits of the Upper Cretaceous Tres Pasos Formation of southern Chile. Amalgamation index is defined as the number of sand-on-sand bedding contacts (i.e., amalgamation surfaces) divided by the total number of sedimentation units. Amalgamation index is complementary to net-to-gross (sand thickness divided by gross thickness) with respect to tracking sand richness; however, amalgamation index is a better measure of vertical connectivity than sand percentage because it incorporates sand-on-sand contacts. Additionally, because only numbers of attributes are used (not thicknesses), amalgamation index is independent of compaction effects and, therefore, can be useful for comparison between analogous systems from outcrop, deep subsurface, or near-surface datasets.

Amalgamation index and net-to-gross measurements were compiled from more than 2,000 m of detailed outcrop-measured sections and compared for different scales of thickness as well as sedimentary body types (e.g., channel-fill, sheet, etc.). Results show a distinct nonlinear relationship between amalgamation index and net-to-gross. Additionally, a robust grouping of turbidite sedimentary body types is recognized when amalgamation index and net-to-gross values are compared. The results from the Tres Pasos Formation outcrops encourage further application of this metric within the context of evaluating connectivity in turbidite reservoirs.

AAPG Search and Discover Article #90078©2008 AAPG Annual Convention, San Antonio, Texas