ERHC Energy Inc (ERHE)

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The character of the basement, together with some seismic evidence for the presence of thin salt in places is an indication that stretched continental crust may extend into a significant proportion of the EEZ east of Principe. There is some seismic evidence for an early syn-rift and possible pre-rift sequence. These lines of evidence increase the relative prospectivity of the EEZ, making the geology more similar to offshore Gabon, a known petroleum-rich province.

The recognition of a Lower Cretaceous succession increases the likelihood that viable source rocks equivalent to those in Gabon extend into the EEZ. The thickness of the Cretaceous source rocks is controlled by a regional series of ENE trending fracture zones, so that much of the deepest Cretaceous section was deposited in half-graben features. Anoxia developed in deeper water areas, resulting in the accumulation of good quality source rocks. Tilted block highs associated with the half-graben development provide a prospective target within the EEZ. Pre-break-up sediments form the oldest potential reservoir in the area. Changes to the rate and nature of opening of the developing ocean in the earliest part of the late Cretaceous led to the deposition of successions dominated by turbidite fans in Gabon and Equatorial Guinea. The distal equivalent of these fans extends into the EEZ, where draping of sandstone reservoirs over the underlying tilted block highs provides the next major prospective target in the area. The proportion of sandstone within this interval may be less than in Gabon, with intra-formational mudstones providing effective top seals and possibly also intra-reservoir baffles. Continued minor diapirism of the mud-rich intervals and possibly of undetected underlying salt provides some additional small-scale prospective structures in the form of four-way dip closures above developing uplifts. In addition, a component of compressional folding, related to changes in oceanic opening patterns, may have developed some additional highs, in particular along the strike of the fracture zones.
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Prospectivity Summary

The coverage of seismic data provides a regional geological model but in many areas the spacing of lines is not enough for adequate prospect recognition. However in the area to the north and east of Principe seismic coverage is greater, and although more seismic data are required prior to exploration drilling, several potentially very large prospects are recognised. Because of the frontier status of this region, the risks associated with exploration – in particular the presence of mature source rocks, good reservoirs and seals, and clearly mapped structures are significant. The next phase of exploration would focus on further analysis of existing data and the collection and interpretation of additional 2D or 3D seismic data.

http://www.anp-stp.gov.st/pt/wp-content/uploads/2009/12/BGS-Summary-public-report.pdf