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The AAPG/Datapages Combined Publications Database

AAPG Special Volumes

Abstract


AAPG Memoir 69: Previous HitReservoirNext Hit Quality Prediction in Sandstones and Carbonates, 1997
Edited by J. A. Kupecz, J. Gluyas, and S. Bloch
Pages 79-89

Burial History and Previous HitPorosityNext Hit Evolution of Brazilian Upper Jurassic to Tertiary Previous HitSandstoneNext Hit Reservoirs

Cristiano Leite Sombra, Chang, Hung Kiang

ABSTRACT

The parameter time-depth index (TDI) is applied in this study to quantify empirically the influence of burial history on Previous HitsandstoneNext Hit Previous HitporosityNext Hit evolution. The TDI, expressed in kilometers per million years of age, is defined as the area in the burial history diagram enclosed by the burial curve of the Previous HitreservoirNext Hit and the axes of the diagram. In practice, Previous HitreservoirNext Hit depths during burial history are integrated at regular time intervals of 1 m.y. The calculations exclude present-day bathymetry or paleobathymetry.

Previous HitSandstoneNext Hit reservoirs from several sedimentary basins along the Brazilian continental margin (Santos, Campos, Espirito Santo, Cumuruxatiba, Reconcavo, Sergipe, Alagoas, and Potiguar) were analyzed to investigate the evolution of Previous HitporosityNext Hit against TDI. These Upper Jurassic to Tertiary sandstones lie in depths of 700 to 4900 m, and are hydrocarbon charged (oil or gas). Average porosities of most of these reservoirs were obtained from core analysis, and a few Previous HitporosityNext Hit data were taken from well log interpretations. Detrital constituents of the sandstones are mainly quartz, feldspar, and grantic/gneissic rock fragments. Sandstones were grouped into three main Previous HitreservoirNext Hit types, based on composition (detrital quartz content) and grain sorting: Type I (average quartz content <50%) are very coarse grained to conglomeratic, poorly to very poorly sorted lithic arkoses. Rock fragments are mainly granitic/gneissic and coarse grained. Type II (average quartz content ranging from 50% to 70%) are fine- to coarse-grained (pebbles absent or occurring in small percentages), moderately sorted arkoses. Type III (average quartz content >80%) are fine to coarse, moderately to poorly sorted quartz arenites or subarkoses.

End_Page 79-------------------------

Plots of average Previous HitporosityNext Hit against depth show great dispersion in Previous HitporosityNext Hit values; such dispersion is mostly due to differences in the Previous HitreservoirNext Hit burial histories. However, plotting Previous HitporosityNext Hit values against the TDI for individual Previous HitreservoirNext Hit types produces well-defined trends. The decrease in Previous HitporosityNext Hit is less marked in Type III reservoirs, intermediate in Type II, and faster in Type I. Such plots suggest that it is possible to make relatively accurate Previous HitporosityNext Hit predictions based on Previous HitreservoirNext Hit TDI, texture, and composition, within the constraints of Previous HitreservoirTop depth/age and basin tectonics analyzed in this study.


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