About This Item
- Full TextFull Text(subscription required)
- Pay-Per-View PurchasePay-Per-View
Purchase Options Explain
Share This Item
The AAPG/Datapages Combined Publications Database
AAPG Bulletin
Abstract
AAPG Bulletin, V.
1Manuscript received December 19, 1997;
revised manuscript received January 28, 1999; final acceptance May 25,1999.
2Elf Exploration and Production, CSTJF,
64018 Pau Cedex, France; e-mail: [email protected]
ABSTRACT
Reservoir prediction is substantially improved
by an integrated approach combining high-resolution sequence stratigraphy
with carbonate geochemistry. As high-resolution stratigraphy documents,
most of the important sandstone reservoirs formed at the base of stratigraphic
sequences during shoreface transgression. Pisolitic dolostones with moldic
porosity are the best carbonate reservoirs. They developed as transgressive
shoreface sand sheets above the basal sandstone reservoirs. Regressive
facies tracts contain oolitic and pisolitic dolomites with intercrystalline
and moldic porosity that originated in progradational barrier and sand-belt
settings.
The combined stratigraphic and geochemical approach
allowed us to determine the Pinda Group dolomites as early diagenetic in
origin, whereas fluid inclusion and oxygen isotope analysis alone suggested
a late burial dolomite formation. Dolomite neomorphism at higher burial
temperatures modified most of the original geochemical signatures of early,
near-surface dolomitization. Cathodoluminescence data and trace element
analysis suggest that dolomitization was associated with gradually decreasing
pore water salinity. Accordingly, barrier oolites were completely dolomitized
and developed intercrystalline porosity during the earliest stages of diagenesis.
At a later phase of early diagenesis, as waters became less saline and
undersaturated with respect to calcium carbonate, fabric-selective dissolution
of the remaining calcareous components occurred. The decrease in pore water
salinity and associated porosity generation are genetically linked with
high-frequency events of relative sea level lowering. This possible relationship
implies that high-resolution sequence stratigraphy can be a valid reservoir
prediction tool even in pervasively dolomitized series.
Pervasively dolomitized, oolitic to siliciclastic
ramp sequences are prolific oil reservoirs in the Albian Pinda Group of
northern Angola. During the Late Cretaceous, this reservoir series was
segmented by salt tectonic gravitational gliding into halokinetic "turtle-back"
and raft structures that provide hydrocarbon traps today. The Albian ramp
sequences contain a large variety of reservoir facies, reaching from littoral
sandstones with interparticle porosity to various types of dolomitized
marine shelf to shoreline carbonates with moldic, vuggy, and intercrystalline
porosity.
Pay-Per-View Purchase Options
The article is available through a document delivery service. Explain these Purchase Options.
Watermarked PDF Document: $14 | |
Open PDF Document: $24 |
AAPG Member?
Please login with your Member username and password.
Members of AAPG receive access to the full AAPG Bulletin Archives as part of their membership. For more information, contact the AAPG Membership Department at [email protected].