Origin plans deepwater well on potential giant prospect off Dunedin

Rob Willink, executive general manager exploration for Origin, said the Carrack -Caravel structural complex is two to three times the areal extent of the Maui field in Taranaki.

He said Origin’s technical studies had high graded the Carrack and Caravel prospects which have the potential to host either several trillions of cubic feet of gas or many hundreds of millions of barrels of oil and condensate. Mr Willink said the Carrack and Caravel structures were the largest Origin has come across in its exploration endeavours in Australia and New Zealand over the last decade.

The prospects lie in about 800 metres of water 50 km off the South Island coast east of Dunedin. Together they extend approximately 80 km from north to south.

Mr Willink was interviewed at the New Zealand Petroleum Conference in Auckland after a presentation by Origin’s geophysicist Wayne Mogg on the company’s results of recent exploration work on its two large offshore Canterbury Basin permits PEP 38262 and PEP 38264 [5.3 MB PDF].

Origin Energy, a large Australian-based integrated energy company, is the operator and 100% interest holder of both permits which together cover some 36,000 sq km. Origin also owns a significant stake in New Zealand‘s Contact Energy and operates the Kupe offshore gas-condensate development project.

Mr Willink said Origin was confident enough in these prospects to begin the search for a large semi-submersible drilling rig or drillship capable of drilling in the deep sea over the prospects.

“We are also looking for international partners with expertise operating in deep waters. There are only about 15-20 oil exploration companies in the world with such experience,” he said.

Origin Energy hopes to make the commitment to drill by the third quarter of this year, though drilling was not likely until late 2009 or 2010 due to the acute shortage of available deep water rigs around the world.

“And because of the very high cost of mobilizing a suitable rig to New Zealand, Origin intends to liaise closely with other operators actively exploring in adjacent areas including AWE, and OMV and ExxonMobil in the Great South Basin to share a common rig”, Mr Willink said.

Carrack is a very large structure covering an area in excess of 200 sq km. Late Cretaceous marine sandstones are inferred to provide a viable reservoir target. The Caravel structure to the immediate north east has an areal extent of some 80 sq km.

Both prospects are formed by sediments draping over a large basement fault block that formed in the mid-Cretaceous. The prospects, now buried just beyond the edge of the continental shelf, are located some 30-50 km southeast of the Galleon-1 gas/condensate discovery well drilled by BP in 1985 but at the time was considered uncommercial. Galleon 1 well encountered good reservoirs in the Late Cretaceous but was only partly filled with hydrocarbons.

Mr Willink said the character of seismic data over Carrack-Caravel is almost identical to that over Galleon, suggesting comparable reservoir development can be expected.

Regional work completed by Origin Energy, including the acquisition, processing and interpretation of extensive new seismic data, has significantly altered the picture of the distribution of hydrocarbon source rocks in the Canterbury Basin.

Origin concludes that the source potential of Late Cretaceous source rocks is limited because of their restricted distribution and low maturity. However the company believes that geologically older mid-Cretaceous syn-rift source rocks had considerably greater generative potential regionally.

Mr Willink said Origin had identified the presence of mid-Cretaceous coal measures up to 800 m thick immediately to the east and north of the new prospects. Basin modelling predicts that some 15 trillion cubic feet of gas and over 6000 million barrels of oil may have been generated and expelled from these source rocks over many millions of years in the Carrack and Caravel drainage areas, more than enough to completely fill both structures.

Furthermore, Mr Willink said Origin was encouraged by the observation of seismic amplitude anomalies which may reflect from hydrocarbon-charged rocks. These anomalies substantially coincide with the shape of both the Carrack and Caravel structures.