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Ethridge, Frank G.1, Sally J Sutton1, William C. Dawson2, William R. Almon2, Jarrad G. Berg1
(1) Colorado State University, Fort Collins, CO
(2) ChevronTexaco, Bellaire, TX

ABSTRACT: Sealing Capacity and Petrographic Characteristics of Eocene Marine Mudrocks, South-Central Pyrenean Foreland Basin, Spain

The goal of this research is to develop a predictive model for estimating the sealing capacity of marine mudrocks for use in hydrocarbon exploration and risk analysis/mitigation. Research to date has concentrated on Cretaceous shales of the Western Interior foreland basin in Colorado and Wyoming and Eocene shales in the Ventura basin, California. This research focuses on Eocene rocks of the central Pyrenean foreland basin, Spain. Outcrop mudrock samples were collected from the Ainsa slope-turbidite channel and the Jaca outer fan and basin plain sub-basins. Sealing capacity of these rocks, as determined by mercury injection capillary pressure analysis, varies with texture and composition, and with location in the foreland basin.
Samples analyzed range from laminated and bioturbated, calcareous mudstones, to silty biomicrites and calcareous siltstones. Some samples contain thin, normally graded, laminations of silt-size quartz grains. Mercury injection capillary pressure values range from 500 PSIA to in excess of 60,000 PSIA. More proximal slope deposits have the lowest average sealing capacity, the highest mean silt grain size, highest porosity, greatest permeability, little preferred grain orientation, and the highest degree of bioturbation Basin floor deposits have the highest average sealing capacity, the lowest mean silt grain size, lowest porosity, high preferred grain orientation, and the lowest degree of bioturbation. Factors that influence the relative sealing capacity of these carbonate-rich mudstones are similar to those for non-calcareous shales from other foreland basins and include the size and percent of silt-size grains, degree of disruption of depositional fabric by bioturbation, and location within the basin.


AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.