Hydraulic stimulation at Geodynamics’ Habanero-1 exploration well has enlarged the Bottom Zone reservoir by 52%, as well as significantly improving the zone’s already high permeability, the company claimed.

Injecting 20,000 cubic metres of water triggered 12,000 micro-seismic recorded events, of which 6,000 were located with the assistance from Q-con, Germany, Geodynamics said.

Hydraulic tests before and after stimulation showed the injection capacity of the well improved by at least 30%. The tests also confirmed that Habanero-1 was optimally connected to the bottom stimulated fracture zone, the company said.

“The above results confirm that hydraulic stimulation is highly effective in the granites beneath the Cooper Basin,” said managing director Bertus de Graaf.

“It also indicates the Bottom Zone has the qualities required for a decision to develop a small demonstration plant.”

But a firm decision on this would wait until the circulation test was completed, with results expected to support the establishment of a geothermal reserve between Habanero-1 and Habanero-2, de Graaf said.

Meanwhile, the company has decided to drill a 500-metre sidetrack from Habanero-2, after a blockage was reported in the connection between the well and the reservoir. The most likely cause for the blockage was the dropped, but apparently retrievable, bridge plug within the fracture zone near the bottom of the well, said Geodynamics.

Attempts to unblock the well in September using artesian pressure did not work.

Meanwhile, Petratherm recently announced that temperature logging taken two weeks after drilling Paralana-1B has recorded a bottom hole temperature of 58 degrees Celsius at 485 metres, equating to a gradient of 81.5 degrees per kilometre. This is one of the hottest temperature gradients recorded in geothermal exploration in Australia, the company claimed.

“This result is at the upper level of company expectations to meet the key objective of a hot rock resource in excess of 220 degrees Celsius at a depth of 3.5 kilometres,” CEO Peter Reid said.

Temperature logging of Paralana-1B, 130 kilometres east of Leigh Creek, was undertaken two weeks after the first stage drilling was completed last month, so the hole could reach thermal equilibrium with the surrounding rock.

“In time there may be a further, 1-2 degree increase in bottom hole temperature. If so, that would increase the readings to around 85 degrees per kilometre,” Reid said.

“As a result, we have elected to drill Paralana-1B to the next stage, an intermediate depth of over 1,500 metres, with this work scheduled to commence around the end of this year.”

The assessment of thermal and rock properties at this depth would determine whether to drill a third and final stage production well at Paralana to a depth of about 3.5 kilometres, using an oil exploration drilling rig.

“The exceptionally high temperature gradient encountered at Paralana, and earlier at the nearby Yerila-1 well in the Callabonna anomaly, is highly encouraging, leading to expectations of proving hot rock reserves at relatively shallow depths, close to infrastructure,” Reid said.

“The success to date also gives us confidence that the approach adopted to find and test geothermal hot rock targets is well founded.”

Reid said further exploration work could potentially encounter a natural hot water system in fractures at depth in Paralana. Such an occurrence could result in commercially viable temperatures at shallower depths than previously proposed, according to Petratherm.