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The AAPG/Datapages Combined Publications Database
Houston Geological Society Bulletin
Abstract
Abstract: The Tano Basin of Western Ghana – a Complex,
Intriguing and Prolific Deepwater Play
Vanco Exploration Company
Houston, Texas
The offshore Tano-Ivorian basin straddling the Ghana-Côte d’Ivoire border along the West African transform margin has become one of the most active deepwater exploration plays in the world, resulting in multiple significant discoveries. Vanco is playing a significant part in this exciting play.
Vanco’s recent Dzata-1 well targeted a
structural
trap
formed by compression of
a unique succession of outboard foredeep
basin sediments adjacent to the Ghana Marginal Ridge. It is an
internally-faulted, elongate, three-way dip closure at multiple levels
within the Cenomanian and Albian section with the seal provided
by the overlying Late Cretaceous and
Tertiary claystones. The well was located
based on a strong Class IIP AVO anomaly
and encountered a gross hydrocarbon
column of 94 meters with 25 meters of net
stacked oil and gas pay in Albian
sandstones opening a new prospective
trend in the previously undrilled
Romanche sub-basin in the eastern part of
the Tano basin. The primary reservoir
sandstone between the depths of 3,663 and 3,690 meters contains
gas and light oil. Volatile black oil was recovered from a zone
between 3,701 and 3,709
meters. Geochemical analysis
of these hydrocarbons and
penetrated source rocks
suggest a two-phase petroleum
system
consisting of early oil
and gas charge from a
lacustrine source facies and a
subsequent oil charge from a
marine source facies. Increased
gas influx from continued
burial of the source facies
appears to have depressed the
original oil water contact
further down structure and
increased reservoir pressure
until the seal for gas was
breached charging the gas
chimney evident on the
structure.
The Dzata-1 provided positive
seismic anomaly calibration
which has allowed regional
application of AVO and seismic inversion technology exploring the
large 3,200 sq km 3D survey within Vanco’s Cape Three Points
Deep Water license. These technologies combined with seismic
facies analysis and 3D visualization has revealed multiple
opportunities in both the Lower and Upper Cretaceous deepwater
plays that will be the focus of an upcoming drilling campaign in
addition to appraising the Dzata discovery. Opportunities include
structural
/stratigraphic plays on the flanks of Dzata and nearby
structures, stratigraphic plays in amalgamated channelized slope
fans similar to Jubilee Field and an interesting unconventional sand
injectite play.