A free-air Bouguer Gravity Map of the oceanic region in the Atlantic Basins (from Smith and Sandwell, 2003).

Hyperdynamics is in search of hydrocarbons offshore the Republic of Guinea. Its concession consists of more than 30,888 sq miles (80,000 sq km) and it is working under a production sharing contract (PSC) agreement that was consummated in September 2006 with the government.

Combined with its operational status under the terms of the 1986 Petroleum Code, Hyperdynamics is working with a portfolio of both stratigraphic and structural prospects.

Its principal prospects are turbidites found in the Upper Cretaceous section of the geologic section of a sub-basin known as the Bove Basin. This mini-basin is part of a greater basin known as the Greater Senegal Basin that hugs the West African coast. Hyperdynamics sees its exploration in this part of West Africa as part of the extension of the Transform Marginal Play that has received notoriety along the transpressional/extensional tectonic regimes offshore the coasts of countries like Ghana and Cote d’Ivoire.

The geologic province of the Transform Marginal Play captured the attention of oil and gas companies (both major and independents alike) with the discovery of the Jubilee field offshore of Ghana. This field discovery is projected to have reserves between 1.5 Bboe and 2 Bboe as estimated by Kosmos Energy and Tullow Oil, the principal operators of the field. The Transform Marginal Play (Figure 1) consists of a series of offsetting orthogonal and oblique faults acting upon the continental shelf areas of West Africa.

The Transform Margin is defined by differential movement acting from a rifting oceanic crust as part of the plate tectonic movement from the Central Atlantic Rift running down the central part of the North Atlantic and South Atlantic Basins (Figure 2). The spatial accommodation of this plate motion occurs as a result of the slippage along these transform faults. The transform margins are frequently known to be associated with restricted oceanic circulation patterns from the earliest inception of the basin.

This early history sets up anoxic conditions that help preserve the organic materials for the generation of hydrocarbons in a “kitchen soup” fashion. If these organic materials are buried to great enough depths, conditions are conducive to the generation of hydrocarbons.

During early Aptian time (122 million years ago) there occurred the opening and division of the Demarara Plateau offshore Guinea and Suriname between the African and
South American plates as they parted. The larger part of the Demarara Plateau makes up the continental shelf-slope offshore of present-day Republic of Guinea. This area received sediments from onshore and provided an environment of deposition rich in organic matter, which became the source rock for the present-day clastic reservoirs.

The source rocks in this region are principally Turonian-age rocks and the older syn-transform, Barremian-Albian rocks. The formation of a deep basin with a multifluvial system existing onshore acted to feed the deposition of large turbidite fan/channel complexes in this deeperwater environment. Continued extension and subsidence resulted in the deposition of a thick shale section that acted to seal and encase the turbidites for future hydrocarbon entrapment. These turbidite fans are the principal target of Hyperdynamics’ prospectivity in the region offshore the Republic of Guinea.

The turbidite fans form the stratigraphic traps for oil in the lower section of the Upper Cretaceous section. The analog to this similar setting along the West African Transform Margin is the Jubilee discovery. The Jubilee field is representative of several of the oldest fans along this margin. With the drilling of the Mahogany wells by Kosmos Energy and Tullow Oil, more delineation has enlarged the potential reserves for Upper Cretaceous clastics in this region. The completion of the Mahogany #3 well, a deeper sand section downdip of the earlier first two wells, has extended this play into a deeper water environment.

Hyperdynamics’ completed a 2,435-mile (4,000-km) regional 2-D seismic survey in 2008 to ascertain the prospectivity of several turbidites and future structural plays offshore Guinea. This 2-D regional seismic further delineated turbidite targets in anticipation of a 2009 3-D seismic acquisition program by Bergen Oilfield Services (BOS).

The turbidite target shows an interesting example of discontinuous seismic events in the upper two sands with a “dim-out” of the lower package of sands in this seismic target. The company’s model indicates the possibility of wet charged sands in the upper two events within the turbidite target. The “dim-out” events (Figure 3) apparent in the lower sand interfaces within the turbidite believed to be oil-charged.

Direct hydrocarbon indicators are diagnostic when extending the low-frequency domain. At the same time, if one expands the high-frequency domain, one can better delineate the geometry of the edges on the turbidite. To date, with independent confirmation, amplitude vs. offset (AVO) responses are evident, but more work needs to be done to better understood the play. The company has used several geophysical methods both in processing and in rock physics properties to mitigate these questions. Most of the turbidites are found at depths of 5,900 to 8,200 ft (1,800 to 2,500 m) within the fairway where the relationship to the shelf-slope defines its position relative to the deeper Valanginian carbonate bank edge. The occurrence of these turbidites occurs between 2,625- and 3,935-ft (800- and 1,200-m) water depths.

Hyperdynamics is also investigating extended elastic impedance (EEI) studies to further understand the AVO effects beyond the traditional gradient-intercept methods.

Hyperdynamics has also followed the more traditional gradient-slope approach. The extrapolated gathers from the processing of this 2008 seismic program reveals an AVO effect for the turbidite.

In reviewing the bathymetry plot conducted by GSI for Hyperdynamics in 2008, many features show incised canyons and channels cutting across the bathymetry of this surface. This downward cutting action can be observed in the geologic record, and many pulses in the geologic past can be attributed to similar conditions such as what occurs in the Upper Cretaceous section for the presence of turbidite channels and fans in this part of the shelf-slope. This environment was conducive to the deposition of turbidite fans across past continental shelf-slope breaks and upwards through time. It was in one of these pulses in the lower section of the Upper Cretaceous time that our target turbidite was formed.

At this time of writing, Hyperdynamics believes the merit of its investigation of seismic exploration of this turbidite warrants further work in acquiring 3-D seismic to be acquired over the first of several turbidite targets in the area. The company plans to conduct this 3-D, the first 3-D seismic coverage offshore the Republic of Guinea ever, in spring 2009. Currently, Hyperdynamics is seeking joint venture (JV) partners to share in this endeavor. Company officials believe that the opportunity offshore Guinea holds promise for large reserves of hydrocarbons.