3-D Reservoir-Analog Characterization of Focused-Flow, Deepwater Carbonate Deposits, Upper Miocene Agua Amarga Basin, SE Spain

Rachel A. Dvoretsky¹, Evan K. Franseen², Robert H. Goldstein¹, and Alan P. Byrnes^2
1Geology, University of Kansas, Lawrence, KS
²Kansas Geological Survey, Lawrence, KS

Deepwater carbonates of the Agua Amarga basin (~8x4 km; ~200 m relief) in SE Spain reveal a point-sourced, basin-floor succession of laterally restricted sediment gravity-flow deposits intercalated with hemi-pelagic sediments. The lateral and vertical facies relationships observed challenge traditional deepwater carbonate models; sediments were focused onto an underlying ramp and point-sourced through a paleovalley, displaying complex geometries that formed in response to relative fluctuations in sea level, climate, and paleotopography.

A large paleovalley in the southwest corner of the basin served as the predominant focus of sediment gravity flows into the basin. Proximally, coarse debrites, high-density turbidites, and low-density turbidites within the valley axis display facies truncation, backstepping, local mounding and filling, onlap, and drape. Retrogradational and progradational geometries suggest both autogenic and allogenic controls. Distally, coarseness decreases as low-density sediment gravity flows and hemi-pelagic deposition become dominant. North of the paleovalley, a gentle ramp produced by earlier deposition of heterozoan grainstone served as an additional focus for sediment gravity flows into the basin.

Outcrop data, core petrophysical data and spectral gamma ray data are combined to build a 3-D model to assess reservoir-analog potential of these deposits for subsurface hydrocarbon exploration. Known reservoir facies include heterozoan grainstones, high-density turbidites, and debrite matrices (20-40% porosity; 10-1000 md permeability). Hemi-pelagic deposits and low-density turbidites exhibit poorer reservoir properties and may constrain flow within the model (25-55% porosity; 1-100 md permeability). Overall relations indicate excellent potential, but great internal complexity for point-sourced, deepwater carbonate reservoirs.

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