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ENTRY OF PETROBAS INTO RAUKUMARA BASIN CAPS OFF LONG CAMPAIGN

The recent announcement that Brazil’s state oil company, Petrobras, has been awarded a five-year permit to explore the Raukumara Basin caps off a successful campaign by GNS Science and Crown Minerals to put this sedimentary basin on the oil industry’s radar.

The recent announcement that Brazil’s state oil company, Petrobras, has been awarded a five-year permit to explore the Raukumara Basin caps off a successful campaign by GNS Science and Crown Minerals to put this sedimentary basin on the oil industry’s radar.

It had its origins in the 1980s when the then DSIR studied seismic data shot over this area, which extends north from East Cape (Gillies & Davey 1986). The data, rudimentary by today’s standards, showed the existence of a sedimentary basin that was unknown until then.

In the 1990s, GNS Science conducted extensive on-shore geological studies of the East Cape region and they proved very useful in piecing together the geology further north in the offshore Raukumara Basin.

Crown Minerals and GNS Science collaborated in 2005 and 2007 to collect 1200km of 2D seismic over Raukumara Basin. This was the first substantial seismic survey of the basin.

Crown Minerals contracted GNS Science to prepare a detailed prospectivity report of this data, which has been the main source of information for companies wanting to evaluate the geology and the likely petroleum potential of this basin (Stagpoole et al. 2008). Conference papers have also been prepared from this work (Uruski 2008; Uruski et al. 2008).

In addition to such prospectivity reports, GNS Science hosts technical field trips, including field trips to East Coast, but also many other parts of New Zealand. Petrobras has participated in GNS Science-led field trips to Taranaki, and in this way, oil industry specialists can increase their knowledge of New Zealand’s petroleum geology.

The Petroleum Exploration and Production Association (PEPANZ) has noted that Petrobras is the second significant new entrant to the New Zealand petroleum exploration scene in recent months following the decision of US major explorer Anadarko to take stakes in permits off the Canterbury coast and in the Deepwater Taranaki Basin.

PEPANZ Executive Officer John Pfahlert said Petrobras controlled significant oil and gas energy assets in 18 countries in Africa, North America, South America, Europe and Asia.

"These holdings, as well as properties in Brazil, give it total assets of US$133.5 billion (2008). It is Latin America’s largest company with 2008 sales of US$118.3 billion," Mr Pfahlert said.

Petrobras was formed in 1953 by then Brazilian President Getulio Vargas. It is a significant oil producer with output of more than two billion barrels of oil equivalent a year. The company also owns oil refineries and oil tankers.

"Petrobras is a world leader in development of advanced technology from deep water and ultra-deep water production."

The permit awarded to Petrobras came after a competitive tender allocation process under which Crown Minerals advertises a Petroleum Exploration Permit Block Offer. Crown Minerals evaluates the bids and awards permits accordingly. A successful bidder commits to a staged work programme in its permit area.

Rbasin_Figure 1 with caption

The 25,000sqkm Raukumara Basin extends about 300km north of East Cape and tapers from a width of about 100km in the south to about 50km in the north (Figure 1). Water depths range from shallow coastal to about 3000m at the outer-most point of the basin.

Data from seismic surveys undertaken in 2005 and 2007 reveal a sediment thickness of about 8 km in the north increasing to about 12km in the south (Figure 2). The basin is undrilled and in the absence of direct evidence from wells, scientists have drawn analogies with on-shore geology and with the adjacent East Coast Basin.

Regional work by GNS Science in geological mapping (Mazengarb & Speden 2000), and basin analysis of the onshore region (Field et al.1997), has been extremely important in helping understand the offshore geology.

Satellite, seismic and magnetic data suggest there is an active petroleum system in the basin. The size of the areas showing indications of hydrocarbons suggest they potentially contain large volumes of oil and gas. These positive indications are consistent with the adjacent East Coast Basin where petroleum is known to be present.

Frontier Basins Manager at GNS Science, Chris Uruski, said considering its close proximity to the active boundary between the Pacific and Australian tectonic plates, there was a surprising lack of faulting and deformation in the basin. This was a positive for oil exploration as accumulations of petroleum were more likely to have remained undisturbed.

Mr Uruski said Petrobras would be planning to collect more seismic data so they could better define prospective areas in the basin.

Rbasin_Figure 2 with caption_540pi

The exploration permit covers 12,333sqkm where seismic data and modelling work show the basin has geology capable of trapping hydrocarbons in commercial quantities.

In scale of companies exploring around New Zealand, Petrobras ranks behind only ExxonMobil, which soon must make a call on whether to drill in the Great South Basin.

References cited:

Uruski C. et al. 2008. The discovery of a new sedimentary basin: offshore Raukumara, East

Field, B.D., Uruski, C.I. 1997. Cretaceous-Cenozoic geology and petroleum systems of the East Coast region, New Zealand. GNS Monograph 19. GNS Science Ltd, Lower Hutt, New Zealand.

Gillies, P.N., Davey, F.J. 1986. Seismic reflection and refraction studies of the Raukumara forearc basin, New Zealand. NZ Journal of Geology & Geophysics 29, 391-403.

Mazengarb, C., Speden, I.G. 2000. Geology of the Raukumara area. GNS Science 1:250 000 Geological Map 6. GNS Science Ltd, Lower Hutt, New Zealand.

Stagpoole, V., Field, B., Sutherland, R., Uruski, C., Zink, K. 2008. Petroleum prospectivity of the Raukumara Basin, New Zealand. GNS Consultancy Report 2008/111.

Uruski, C. 2008. Petroleum potential of an enigma: the Raukumara sub-basin, east Coast, North Island. NZ Petroleum Conference Proceedings.