Manager of Geology, Greg Ambrose, spoke about unconventional hydrocarbons in the Amadeus and Georgina Basins in Central Australia
In the first of three brief presentations of a technical showcase, Ambrose said they had turned out to be very promising unconventional hydrocarbon provinces. “Here is the Georgina Basin acreage, which we are particularly interested in,” he said, while looking at a map on the screen behind him.
But first he dealt with the Amadeus Basin unconventional hydrocarbons – Ordovician Larapinta Group. “Many of you have probably heard of the Horn Valley Siltstone,” he said. “It’s a rather remarkable source rock.”
“It doesn’t look that spectacular often in core. It’s not overly thick. It doesn’t have a lot of shale, but we can prove its source of 200 million plus barrels of oil equivalent – that’s recoverable – in the Amadeus Basin and we believe it has vast potential for unconventional.”
A slide was presented to show the three transgressive cycles in the lower Larapinta Group. According to the slide, the three transgressive cycles are capped by marine shales, which become increasingly oxic up through the zone, and the most important source rock is the Horn Valley Siltstone – containing up to 9 per cent organic carbon. “Basically the environment was initially a deep epeiric marine basin which was anoxic at the base of the water column, but included a mid-water oxygen minimum zone above an oxygenated zone.”
Ambrose also showed a slide of shale gas/oil summary parameters, Horn Valley Siltstone. “Now the Horn Valley – it’s a bit deceptive – it’s a deceptive source rock,” he said. “Often the TOCs are only hovering around 1-2 percent, but they do actually rise up to 9 per cent.”
Ambrose showed a slide of the Horn Valley Siltstone Continuous Gas/Oil. “We have mean reserves of 11.3 Tcf,” he said.
Another slide showed a table of the Amadeus Basin Unconventional Probalistic Prospective Recoverable Resources (DSWPET, 2010). Under the assessment unit of ‘Total Gas all gas Aus’ there was mean 26.2 TCFG, and under ‘Horn Valley Continuous Oil AU’ was mean 1.061 Billions of BBLS.
Regarding the Lower Larapinta mean prospective recoverable resource 26 TCFG and 1 B BBLS, Ambrose said the next steps were to examine cores from Surprise-1 side track, “ he said. “We will undertake absorption studies.
“We will be drilling holes outside of closure and in the gas window and hopefully we will get enough encouragement to define a contingent resource. Then we will proceed to drill sweet spots and undertake exploration drilling.”
Ambrose said in the Southern Georgina Basin, the main target was the Middle Cambrian Arthur Creek Formation.
A slide appeared that showed the Cambrian carbonate ramp plays - the inner ramp facies (reservoir), middle ramp facies (source/seal reservoir) and the outer ramp facies (source).
Ambrose also talked about free gas porosity. While referring to a slide, he said the majority of gas resides in the nano-porosity in organic matter. “Sometimes the gas in the intra crystalline porosity and sometimes a percentage of gas is in the inter-particle porosity,” he said.
He showed a photo of what the rocks looked like from the outer ramp. “Good gas shows, good oil shows throughout the whole basin. It’s a delightful source rock”
Ambrose finished his presentation with the words, “We have only scratched the surface in Central Australia.”
Need more to read as to what potential
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