seismic reveals much larger mcarthur basin

Seismic reveals much larger McArthur Basin
Thursday, 20 March 2014
David Upton
THE Northern Territory’s highly prospective McArthur Basin is much larger than previously believed and could cover up to one quarter of the territory, according to seismic surveys by the private sector.
The news was one of the highlights of this week’s Annual Geoscience Exploration Seminar held in Alice Springs by the NT Geological Survey.
AGES has had a mineral exploration focus in the past, but this year the program was evenly split between petroleum and minerals.
NTGS executive director Ian Scrimgeour told Energy News that energy and minerals explorers did not easily mix, but the geology of the NT had led the way.
“In the Northern Territory, the minerals and petroleum guys are often looking at the same stratigraphic unit, which I think is quite unique,” he said.
“A great example is the Barney Creek formation, which is the host of the McArthur River zinc deposit.
“We had a presentation this week from Teck on a new discovery, Teena, in what is the same unit that is also potentially a very significant source rock and unconventional reservoir.
“There is a really interesting cross-fertilisation of skills. The mineral explorers are very excited about what’s coming out of the petroleum sector, and equally the petroleum guys are finding they can learn a lot from the minerals side.”
NTGS released at the conference its first comprehensive volume on petroleum geology, which is a stocktake of public knowledge about the petroleum potential of the many basins in the NT.
The big news about the larger expanse of the McArthur Basin is based on new seismic surveys by Santos and unlisted Pangaea Resources.
Santos is earning interests from unlisted Tamboran Resources in three exploration permits in the centre of the basin covering an area of more than 25,000 square kilometres.
The Adelaide-based company’s 2013 seismic survey proved the Beetaloo sub-basin extends eastwards.
Meanwhile, Pangaea’s seismic appears to extend the McArthur Basin over large distances to the west.
Pangaea has three permits in the western McArthur Basin and the Beetaloo sub-basin, and another permit (EP 198) further west in the Victoria River and Birrindudu Basins.
A stratigraphic hole by the NTGS in 1999 produced live oil shows and encouraged Pangaea to take up acreage in what is an otherwise unexplored area.
Scrimgeour said he was appreciative that both companies had shared highlights of the new seismic data in the interests of building knowledge about the territory’s geology.
“We now have a whole body of new seismic data from the petroleum sector that is demonstrating continuity under cover between the McArthur Basin and other basins such as the Birrindudu Basin in the Victoria River district and the Thomson province,” he said.
“There has always been speculation that the basins might be linked. Now there is really significant evidence of those links and we will look at it as one large basin.”
The seismic shows continuity of what appears to be source rock horizons in both the McArthur Group (which includes the Barney Creek formation) and the Roper Group.
“Clearly, it’s very early days and there needs to be caution,” Scrimgeour said.
“We need to see drilling to demonstrate the extent of those source rocks.
“But it is generating a lot of interest because of the scale of the potential. These highly prospective units appear to extend into large areas where they were never previously considered.
“We are talking about an area that represents about 25% of the Northern Territory.”
Scrimgeour said the McArthur Basin would be a focus of pre-competitive data gathering and study by the NTGS over the next four years.
“At the conference we presented extensive new gravity data from the McArthur Basin, and the first stage of a 3D geological model,” he said.
“This recent work is shedding more light on the structures in the basin and the controls on its sub-basins.
“We are combining that with the new seismic to look at the depth of basement. There are a lot of new insights.”
Another highlight of the conference was a presentation by Santos of seismic sections from 1800km of 2D surveys conducted last year in the Amadeus Basin.
Santos has the option under the farm-in of acquiring in-fill seismic surveys over another 1000km in the second half of this year.
Scrimgeour said the Santos data was of outstanding quality.
“It shows so much detail on the structures, particularly for conventional reservoirs,” he said.
“The demonstration of the salt tectonics and the structure in that seismic is very exciting.”
Santos has operated the Merrenie oil and gas fields in the Amadeus Basin for decades. Three years ago, it quietly began sinking significant sums into the basin on the basis of its conventional and unconventional potential.
First was the buyout of partner Magellan Petroleum in 2011, then a joint venture with Central Petroleum that could have Santos spending as much as $150 million to earn a 70% stake in an area covering of almost 65,000sq.km.
The Santos seismic was regional in nature and designed to provide a better understanding of basin architecture, salt tectonics and large structural leads.
It reveals, in surprising detail, the complexity of deeper structures under shallow folds in post-salt layers.
The survey is also showing some immediate exploration targets. For example, Magee-1, the last exploration well drilled in the southeastern Amadeus Basin, has significant closure up dip. The 1992 well intersected a thin pay zone in Neoproterozoic rocks.
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