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The AAPG/Datapages Combined Publications Database
Houston Geological Society Bulletin
Abstract
Abstract:
Balanced
-Filled Lakes Worldwide:
Insights for Optimum Source Character and Distribution
in Brazilian Continental Margin Basins
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By
Exxon Production Research Company,
Houston, Texas
Exxon has developed the concept of lake-basin type, which is
useful for sorting out the complexities of lacustrine deposition
to derive a predictive framework. Balanced
-filled lakes are
one of three lake-basin types recognized from recurring lithofacies
associations and stratal stacking patterns.
Balanced
-filled
lake systems contain the most prolific lacustrine source rocks
and beneficent facies juxtapositions for hydrocarbon accumulation,
based on observations of lacustrine strata of many different
ages and basins (e.g., East Africa Quaternary, USA Tertiary,
China and Africa Cretaceous).
Balanced
-filled lakes can be shallow or deep with thick or
thin sequences, but they share similar geochemical and
sequence-stratigraphic attributes. Parasequences and sequences
are meters to tens of meters thick, distinctly expressed in seismic,
logs, and geochemistry, and formed by a combination of progradation
and desiccation. Lake-water chemistry varies systematically
from fresh to saline/alkaline. Most organic-rich rocks are
deposited in the profundal zone, with subordinate amounts in
the lake plain behind mixed biogenic-clastic shorelines. Organic
matter is dominantly algal Type I, typically with TOC < 30% and
HI < 650 mgHC/g C. Organic facies are relatively constant laterally,
changing only relatively close to shore. Sequence boundaries
are formed by a mix of erosion and desiccation--erosion may be
best developed during transgression.
Comparison of geochemical, geological, and geophysical
data from balanced
-filled lakes worldwide with Brazilian basins
provides a greater understanding of source rocks in the lacustrine
systems responsible for most of the giant oil accumulations
in offshore Brazil and suggests strategies for successful exploration
and exploitation.
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