MARTINIUS, ALLARD W., and MARGARITA C. CUEVAS GOZALO, Delft University of Technology, Delft, Netherlands

ABSTRACT: Characterization and Architecture of Fluvial Sand Bodies in an Intracratonic Alluvial Fan

The fluvial deposits of the Tortola alluvial fan of late Oligocene to early Miocene were deposited in the intracratonic Loranca Basin (Spain). The fluvial facies comprise individual and amalgamated sand bodies embedded in flood-plain fines. The succession is a labyrinth-type reservoir analog. A distal and proximal fan locality have been compared.

The sand bodies were characterized and quantified by means of three-dimensional (3-D) morphology and facies analysis, sand-body size statistics, permeability and gamma-ray log profiles, and geometry of permeability baffles.

A classification of the sand bodies in six genetic types was established: meander-loop, low-sinuosity channel-fill, braided channel-fill, deltaic, interchannel bar, and crevasse-splay deposits. This classification is conditioned by a set of geological rules. The external geometry, internal organization, and spatial arrangement of the genetic types is determined by variation in hydrodynamic conditions, sediment supply, fan morphology, and basin subsidence.

Significant differences in reservoir quality exist between the genetic types, and between the two fan localities. Analysis of the sequential development of the two localities shows that the 3-D architecture is the result of coalescing fan depositional systems: a major fluvial fan system from the eastern basin margin, and local minor fluvial systems. Shifting of the channels on the fan surface due to avulsion processes, differential basin subsidence, and tectonic movements influenced fan formation and hence reservoir quality.

AAPG Search and Discovery Article #90990©1993 AAPG International Conference and Exhibition, The Hague, Netherlands, October 17-20, 1993.