Tectono-Stratigraphic Analysis of a Deep-Water Growth Basin, Ainsa Basin, Northern Spain

Hoffman, Matthew ¹; Bouroullec, Renaud ¹; Guzofski, Chris ²; Pyles, David R.¹; Clark, Julian ³; Setiawan, Prianto ¹; Moody, Jeremiah D.¹; Silalahi, Henri S.¹; Moss-Russell, Amy C.^1
1 Chevron Center of Research Excellence (CoRE) Department of Geology and Geological Engineering, Colorado School of Mines, Golden, CO.
² Chevron Energy Technology Company, Houston, TX.
³ Chevron Energy Technology Company, San Ramon, CA.

Growth structures influence coeval deep-water deposition in many of the world's largest hydrocarbon producing regions (i.e. Gulf of Mexico, Indonesia, Nigeria, and Angola). Outcrop studies of analog basins provide important insight into both the reservoir- and basin-scale stratigraphic architecture. The Ainsa Basin in the Spanish Pyrenees is unique in that it is one of the few locations in the world where the interaction of deep-water deposits and compressional growth structures can be studied in detail and in three-dimensions. The Middle to Upper Eocene Ainsa Basin fill consist of multiple turbidite systems, including the well-known Ainsa system, that exhibit geometries indicative of syn-growth deposition related to large basin-bounding structures (Mediano, Boltaña, and Añislco anticlines).

This study focuses on the reconstruction of four syn-growth horizons and one pre-growth horizon using Gocad modeling software in a three-dimensional structural model of the basin. The base of each syn-growth turbidite system (condensed section) is mapped across the basin and used in the reconstruction to define successive basin paleo-bathymetry during stages of basin-fill. Syn- and pre-growth horizon reconstruction is constrained by (1) new surface orientation measurements, (2) balanced cross-sections, and (3) published sub-surface data. Deep pre-growth and detachment geometries are interpreted from surface data and two depth-converted seismic lines that trend roughly perpendicular and parallel to the basin axis.

Combined with a detailed stratigraphic analysis of the Morillo depositional system, the structural model provides 3-D geometric constraints on a feeder canyon identified on the western limb of the Mediano anticline. The structural model also enhances the understanding of the relationship between the basin-fill and growth of the Boltaña Anticline, which initiated during Morillo deposition, with increased shortening to the north leading to sediment shedding off a paleo-high. This structural growth constrained and focused the Morillo deep-water channels from a lateral offset-stacked geometry at the basin axis to vertical-stacking at the basin exit point. This study can be used as an analog for complex tectono-stratigraphic settings where syn-depositional structures play a major role in the distribution and evolution of deep-water reservoirs.

AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009