At the Annual Geoscience Exploration Seminar (AGES) in Alice Springs last week, the executive director of the NT's Geological Survey, Ian Scrimgeour, said petroleum exploration hit record levels in calendar 2014.

Total exploration spending (onshore and offshore) almost doubled from $283 million in 2013 to $554 million.

The numbers were helped by some offshore wells in the Arafura Basin, but there is a genuine boom onshore.

Onshore petroleum explorers spent almost $135 million in 2013-14, almost three times the guaranteed work value of $52 million.

The force behind this surge of activity is the mighty and mysterious McArthur Basin, which covers 550,000sq.km, or almost 40% of the entire Northern Territory.

The huge size of the basin is quite recent news. It was only 18 months ago that seismic surveys by unlisted explorer Pangaea Resources in the central western part of the Basin showed it actually extended all the way to the NT-WA border.

The McArthur is also a surprise because its Mesoproterozoic age. It is a very old rock basin that is way outside the comfort zone of Australian petroleum explorers.

It even stretches the limits of petroleum exploration thinking anywhere in the world. The gas from Glydne-1 is thought to be oldest in the world at about 1500 million years of age.

Petroleum explorers would not normally go hunting there, but mineral explorers have been all over it because of it hosts big strata-bound deposits of lead and zinc.

Many of these mineral exploration holes have encountered oil and gas shows, and some have even flowed gas to the surface. The petroleum potential was found by serendipity and has been impossible to ignore.

The focus of exploration has been on the unconventional potential of very organic rich shales.

There are two large exploration programs now in full swing in the Beetaloo sub-basin, led by Origin and Santos. Pangaea's program is smaller in size, but no less ambitious.

The Origin-led joint venture with Sasol and Falcon last year began a $165 million program of nine wells - four vertical exploration wells and five stimulated horizontal exploration-appraisal wells.

The partners are not messing around. They expect to production test and go along way to commercialise the project by 2019.

The program for the Santos joint venture with Tamboran Resources in the eastern Beetaloo Sub-basin does not have a big forward program, but the results from the first well, Tanumbirini-1, has generated a lot of excitement.

The 3945m deep well intersected multiple thick intervals of organic-rich rock and significant mud gas shows. Elevated gas readings were encountered over a total gross interval in excess of 500m.

The focus on unconventionals presents a couple of significant hurdles - the most recent being the slump in oil prices and the additional challenges that could create for economic development, depending on the timing and extent of price recovery.

The major hurdle is the lack of infrastructure, although there are wildly different views on that issue.

Some proponents, including Origin, have their eye on Darwin as a hub for LNG export of gas.

But there are many others, including the NT government, that want a pipeline built to connect the McArthur Basin to the east coast gas market. This would also bring on line the Amadeus Basin east of Alice Springs.

A lot will depend on just how much petroleum there is in the McArthur Basin, and that's a very big question that explorers and researchers are racing to answer.

The McArthur is so large and lightly explored that we can't even say with confidence how much sediment thickness we have to work with, or whether there are depocentres or even sub-basins yet to be discovered.

This is of major relevance to unconventional explorers because recent work by NT Geological Survey suggests the thickest sequences have the highest organic content.

The AGES conference featured a number of presentations with important new results, including the first regional structural framework for the greater McArthur Basin. This showed the importance of large-scale WNW-ESE structures.

There is pioneering exploration work taking place in other NT basins, including the onshore Bonaparte, where Beach last year drilled Cullen-1.

Further south in the Amadeus Basin, Santos last year drilled the Mt Kitty well and managed to flow gas from fractured basement.

Santos presented to AGES some the results of the first regional study of the Heavitree quartzite, which is a key reservoir rock and a major unit of the Amadeus Basin.

The unit, ranging in thickness between 200m and 1000m, was deposited when the Amadeus was part of the Central Australian Superbasin. It extends into neighbouring basins, including the Officer Basin on the other side of the Musgrave Ranges.

The Heavitree quartzite was previously thought to be a simple, thick sheet sandstone, but the new research show it is highly variable, reflecting different sources of sediment that are thousands of kilometres apart.

This has huge implications for petroleum exploration, and highlights how far we have to go before we truly understand the petroleum potential of the Northern Territory and most of our onshore basins.