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Exploration procedures
Impact's strategy is to implement a five-stage exploration program in its frontier licenses, starting with airborne gravity and magnetic geophysical data acquisition, followed by surface heat-flow measurements, multi-beam bathymetry for ocean floor mapping, high-resolution seabed sampling, and finally 2D and 3D seismic data acquisition. For the initial three-year phase of the Tugela Exploration permit, where water depths range from 500-2,500 m (1,640-8,202 ft), the company committed to shoot 5,000 km (3,107 mi) of 2D seismic, which Seabird and PGS acquired during two campaigns in 2011 and 2012. In the second survey, PGS used its deep-towed, noise-suppressing Geostreamer technology, which had advantages, as the area is prone to large ocean swells.
Tugela, which covers 10,245 sq km (4,025 sq mi), is named after the river that flows from the Karoo region, entering the ocean at Durban. Sediments deposited by the river comprise a sandstone/shale series in a progradational shelf, on the slopes of which are turbidites and submarine fan systems that comprise the main reservoir targets for hydrocarbons. Previous exploration on the acreage was directed entirely in the shallower waters close to the coast, including a well drilled by Phillips Petroleum in 2000. "In their report, their geologists said drilling should have targeted deeper turbidites as the well did recover traces of oil," Doherty said.
One of Tugela's geological features is the Dolphin prospect, which exhibits similar characteristics to the deepwater Jubilee field offshore Ghana. Evidence for source material over the Tugela area includes direct hydrocarbon indicators on the seismic data such as gas chimneys, chemotropic mounding, and pockmarks on the seafloor. Surface seeps have also been reported. Another report commissioned by Impact suggests that during the early Cretaceous period the license area was at the edge of an enclosed sea, where the anoxic conditions would have produced the material required for source generation.
"The new players in South Africa in general are focused on deepwater turbidites and fans in early and mid-Cretaceous sandstones, the same plays that have brought substantial oil discoveries off the Falklands and the West African transform margin," Doherty explained. "One attraction for ExxonMobil is that our acreage too sits on a transform margin related to the break-up of the Gondwanaland super-continent. This is something they can bring experience of via their program in their deepwater concessions offshore West Africa."
Premier, operator of the Sea Lion oil and gas development in the North Falkland basin, has expressed interest in exploration offshore South Africa.
"They see the early Cretaceous as the main period when the oil was sourced, and we are looking at the same source rocks. The Falklands shelf is very broad and long – Sea Lion is more analogous to the Orange basin, where we also recently acquired an interest in an exploration block offshore Namibia. Shell and Anadarko are exploring in that area. The South Falkland basin, where there have been gas and gas/condensate discoveries, is thought to have originated from the south of South Africa."
As for Impact's three TCPs, where evaluation is still in the early phases, the 4,720-sq km (1,822-sq mi) Tugela TCP comprises four blocks inshore from the exploration permit, over which the company has interpreted 5,000 km (3,107 mi) of reprocessed seismic data. Western Bredasdorp, 14,378 sq km (5,551 sq mi) in area, comprises six blocks offshore Cape Agulhas in the western part of the Bredasdorp basin. It contains promising oil and wet gas-prone source rocks, and various channel sand systems similar to the systems that host the Mossel Bay oil and gas field. Impact has reprocessed and interpreted 2,000 km (1,243 mi) of existing 2D data in this area. Over the Transkei and Algoa TCP area, PGS is currently acquiring and extensive regional seismic survey under a Reconnaissance Permit and the processed data should be available later this year. In all three cases, Impact has applied for conversions to an Exploration Right in order to bring ExxonMobil onboard as operator.
To date, interpretation has revealed no evidence of problematic features such as carbonates or salt. "There are some volcanics, but these are quite deep, so we don't see them interfering with the seismic." A greater issue is the need to restrict all seismic activity to the summer months to avoid endangering whales, turtles and other mammals during seasonal migration. This also explains the planned mid-winter start for the Total/CNR well, which is due to take three months to drill.
