Spatial Variation in Texture and Facies in Confined Sheet Sands

Vanessa R. Kertznus¹, Ben Kneller¹, and Mason Dykstra^2
1Department of Geology and Petroleum Geology, University of Aberdeen, Aberdeen, United Kingdom
²Department of Geology and Geological Engineering, Colorado School of Mines, Golden, CO

Continental slopes are often characterized by complex seafloor morphology comprising relatively small depositional intra-slope basins generated by growth faulting, shale- or salt-based detachment faults, and salt-withdrawal. Examples of such slopes include the Gulf of Mexico, Trinidad and Tobago, Nigeria, Angola and Brunei. Turbidite systems within these mini-basins can be of economic importance as petroleum exploration targets. Turbidity currents that flow into these areas are in some cases sufficiently large to spread across the entire basin floor, and can thus be considered confined flows. To date, the dynamics of confined turbidity currents and their impact on depositional characteristics are poorly understood.

It is generally not possible to determine fine-scale facies variability within petroleum reservoirs, at least not with sufficient resolution. Seismic data provides information over a large area, but with limited resolution. Studies of modern confined systems provide information about depositional processes and body geometries, but offer little information on lateral facies distribution. Log data and core data provide detailed measurements, but the data are restricted to essentially one dimension and are often not correlatable in detail. Given these limitations, we have studied outcrops of a confined turbidite system of Carboniferous age in north-western Argentina, in which the degree of three-dimensionality allows the fine-scale spatial characterization of part of a basin fill characterized by layered and amalgamated sheet-like turbidite deposits confined laterally within a paleofjord. This study illustrates how the surrounding topography controlled spatial variation of bed thicknesses and textural properties of individual beds; the resulting spatial variations of reservoir properties may significantly increase reservoir heterogeneity.

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