At Petratherm’s annual general meeting, held in Adelaide this morning, chief executive Peter Reid said the company had found it could achieve the required temperatures for geothermal energy production by circulating water through porous strata above the target hot rocks.

Currently, Australian hot rocks projects are based on forcing waters through the dense hot rocks, deeper below the surface, adding to the cost and risks of geothermal drilling.

Petratherm aims to implement the strata-level geothermal process at its Paralana-1B well, 130 kilometres east of Leigh Creek in South Australia.

Drilling at the Paralana-1B site has already reached 491 metres, where the company recorded a bottom-hole temperature of 58oC at 485 metres.

The reading indicated a temperature gradient of 81.5oC per kilometre, one of the hottest gradients recorded in Australian geothermal exploration, according to Petratherm.

Subsurface engineering studies at the site indicate the required temperature of 200 degrees Celcius can be achieved at a depth of 3.5km, one kilometre above the granite that forms the hot rock deposit.

Reid said the rock strata 3.5km below the Paralana-1B site comprised an “overlying insulating cover” above the hot granite.

“This insulation is primarily sedimentary rocks which exhibit the hot temperatures needed, but are likely to be more porous and permeable than the hot granites beneath them, allowing the flow of water without excessive stimulation requirements,” Reid told shareholders.

“This situation provides a more natural flow path as a heat exchange area compared to having to ‘build’ such a flow path in the denser basement granites beneath.”

Reid said regional stratigraphic and seismic studies indicated the likely presence of several sandstone or limestone layers within which the reservoir at Paralana-1B could be formed at about 3.5 kilometres depth.

By avoiding the denser granite below, new methods of creating waterflow channels became available, including “chemical stimulation” options similar to those used in the oil and gas industry, according to Petratherm.

These new options are expected to enhance the economics and throughput profile of the Paralana-1B geothermal well.

Reid said if the strata-level geothermal project can be realised, it could eliminate the expensive and uncertain fracture stimulation within dense hot rocks, significantly reducing the risk and costs of major geothermal power stations.

“Moreover, this approach is more closely aligned with proven conventional geothermal operations; an already established commercial producer of cheap electricity,” Reid said.

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