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.

3D perspective showing far stack seismic amplitudes on a Middle Albian surface. The warm colors are areas of sandy slope fan turbidites fed by amalgamated slope channels updip spilling downdip into a basin floor setting which are then remobilized and injected into overlying younger sediments.