--> Unconformity-Controlled Porosity Development in the Quintuco Formation (Lower Cretaceous), Neuquen Basin, Argentina, by N. F. Hurley, H. C. Tanner, and C. Barcat; #90986 (1994).

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Abstract: Unconformity-Controlled Porosity Development in the Quintuco Formation (Lower Cretaceous), Neuquen Basin, Argentina

Neil F. Hurley, Haydn C. Tanner, Carlos Barcat

Moldic, sucrosic dolomites are present at a distinctive stratigraphic horizon within the lower Quintuco Formation (Lower Cretaceous, Berriasian-lower Valanginian) in the eastern Neuquen basin, Argentina. The net thickness of these deposits ranges up to 30 m (100 ft). Moldic, sucrosic porosity, which is probably unconformity controlled, provides the main reservoir facies in Rio Neuquen oil field (4.5 × 106 m3; 28 MMBO recoverable) and perhaps other fields.

Lower Quintuco carbonates are composed of: (1) oolitic grainstones, (2) burrowed, dolomitized oolite-skeletal-peloid packstones/wackestones, (3) dolomudstones and bedded anyhdrites, and (4) very fine-grained, superficially coated oolite grainstones. These sediments are commonly packaged into shoaling-upward, coarsening-upward hemicycles.

Reservoir-quality porosity and permeability exist almost exclusively in burrowed, dolomitized packstones and wackestones. These deposits are interpreted

as off-bar facies that occurred mainly on the landward side of bar complexes. Modern analogs are known in the Joulters Cay area of the Bahamas. In the lower Quintuco Formation, dolomite preferentially attacked and replaced carbonate mud. Below a widespread karst exposure surface, ooid-skeletal-peloid grains were then leached to leave an open pore network with abundant moldic and intercrystalline porosity.

Published sequence-stratigraphic and microfacies studies have failed to recognize unconformity-related porosity in the Quintuco Formation. Sequence-stratigraphic studies suffered from poorly processed seismic lines and minimal sample examination. Microfacies studies had extensive sample examination, but little or no correlation to depositional models, well logs, and/or seismic lines.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994