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Abstract

Porous dolomites are present below a distinctive stratigraphic marker within the lower Quintuco Formation (Lower Cretaceous, Berriasian-lower Valanginian) in the eastern Neuquén basin, Argentina. Dolomitized pack-stones and wackestones with moldic and sucrosic porosity provide the main reservoir facies in Rio Neuquén field and perhaps other oil fields in the area.

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

Reservoir-quality porosity and permeability exist almost exclusively in burrowed, dolomitized packs tones and wackestones. These strata are interpreted as off-bar facies deposited on the landward side of bar complexes, similar to modern facies analogs known in the Joulters Cay area of the Bahamas. In the lower Quintuco Formation, dolomite preferentially replaced carbonate mud. Below an inferred widespread paleo-exposure surface, ooid-skeletal-peloid grains were then dissolved to leave an open pore network with abundant moldic and intercrystalline porosity.

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