Otway Basin

Otway Basin (Hot Sedimentary Aquifer Geothermal Project)

Surveys undertaken in the Otway Sedimentary Basin suggest that the the abundance of hot basalt that exists as a result of recent volcanic activity renders this area as being very suitable for commercial geothermal electricity generation.  It is estimated that the area could produce 1,750 MWe of electricity, which is equal to about 35% of the current base load electricity demand in Victoria.

The HotRock Limited (HRL) group was granted Geothermal Exploration Permits (or GEPs) number 6, 7, 8, 9 and 23 located in the Otway Sedimentary Basin of Victoria over a total area of 27,521 km2. Rocks beneath the sedimentary basin in this area have been perturbed by the elevated heat flow which is related to crustal thinning caused by rifting, recent volcanism and underlying hot granites. This constitutes what is known as a “sedimentary geothermal system (SGS)”. These differ from the HFR (or hot fractured rocks) hot granite geothermal prospects being vigorously explored elsewhere in Australia in that they require shallow drilling depths and hence lower drilling costs and risks. Further expense is saved because of the fact that the geological composition is naturally relatively permeable and hence does not require artificial stimulation to create or enhance permeability in order to bring fluids to the surface.

Large reservoirs of geothermal water have been determined throughout HRL’s five geothermal permits, contained within what is known as the ‘Crayfish Subgroup’ – a thick and widespread rock sequence dominated by high porosity sandstones deposited along the northern margin of the Otway Basin as a number of individual deposits. Measurements have confirmed subsurface water temperatures of at least 158 C at a depth of around 3,700m in these areas. HRL regards these reservoirs as being suitable for commercial electricity generation using modern power plants, with conservative estimates indicating a potential for eventually generating up to 1,750 MWe of electricity within four GEP’s. This represents approximately 35% of the base load electricity demand of Victoria.

The interpretation of previous data and appreciation of the geothermal significance of it has enabled HRL to accelerate its geothermal program in one exploration area, located northwest of Koroit, directly into a proof of concept testing stage called the ‘Koroit Project’. With geothermal temperatures of 130 C at depths of 2,800m, this region alone has power generation potential of some 200 MWe.

Having carried out the largest ever magneto-telluric geophysical survey for geothermal energy in Australia from May to July of 2008 at Koroit in GEP8, HRL’s proof of concept program for the Otway Basin geothermal development comprises;
•    completing interpretation of geophysical data to identify the best drilling location,
•    subsequent power developments in the Koroit Project Area, with plant sizes of up to 50 MWe each, with a total development capacity currently estimated at about 200 MWe (assuming  the temperature and flow rates prove to be as is presently expected). This development program will be carried out over a time frame of three years, commencing in mid 2010; and
•    appraisal drilling, pilot and large power plant developments at other target areas within all their permitted GEP’s following results from the Koroit project.

The primary aim of the Koroit Hot Sedimentary Aquifer (HSA) Geothermal Project is to test the potential of the geothermal reservoir to supply hot water to a geothermal power plant. This involves drilling two holes roughly 3,700m deep to test water temperature and fluid flow rate from the geothermal reservoir.

Two potential drill sites have been finalised, with the drilling pad and ponds close to completion. Commercial discussions to source a suitable rig to drill the wells in 2011 are currently being finalised.

Further information from the proponent can be found here.