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The AAPG/Datapages Combined Publications Database
AAPG Bulletin
Abstract
AAPG Bulletin, V.
1Manuscript received January 13, 1997;
revised manuscript received March 30, 1998; final acceptance April 20,
1998.
2Centre de Géochimie de la
Surface (CNRS-ULP), 1 rue Blessig, 67084 Strasbourg, France; e-mail: [email protected]
3Total-SA, CST de Beauplan, route
de Versailles, 78470 St Remy-les-Chevreuse, France.
4Department of Geology, Kansas State
University, Manhattan, Kansas 66506.
5Department of Geological Sciences,
University of Michigan, Ann Arbor, Michigan 48109-1063.
ABSTRACT
In the Handil field on the nearshore anticline,
evolution of the mixed-layer illite/smectite is characterized by a decrease
in expandability with depth. In the Tunu field, located on the next offshore
anticline, variable amounts of expandable layers suggest a different evolution.
The conversion process of smectite to illite layers in the mixed layers
depends on the lithology of the host rocks, transformation in the shales,
and dissolution-precipitation in the sandstones. Sample location also played
a role in the conversion process because the types of illite clays in the
two locations differ when they are compared at similar degrees of evolution.
Present-day temperatures and paleotemperatures, vitrinite reflectance,
and illitization of the mixed-layer illite/smectite all suggest that organic
matter and clay particles evolved differently in the Handil field, but
similarly in the Tunu field.
Integration of the analytical results obtained
here and comparison with a two-dimensional numerical model suggest that
hydrocarbon generation took place in the deeper synclinal zones of the
sequence, and that oil migrated upward with brines, probably inducing most
of the illitization in the upper sequence. Both models emphasize the role
of faults in channelizing fluid flow during the final stages of evolution
of the basin.
The clay fraction of the Mahakam Delta Basin
(eastern Kalimantan, Indonesia) consists of mixed-layer illite/smectite,
kaolinite/dickite, detrital illite, and chlorite. Kaolinite formed early
as vermicular particle aggregates, and thick dickite booklets formed late
in pore spaces. The dickite particles probably grew in deeper intervals
of the sequence, in contact with brines acidified by decarboxylation of
organic matter, during dissolution of K-feldspar and upward migration of
potassium.
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