“Geothermal energy in Australia”

Australian Institute of Energy
Australian Nuclear Association
Engineers Australia (NUC Engineering Panel)
The Royal Society of New South Wales

The meeting was hosted by Engineers Australia and the speaker was Dr Doone Wyborn.

Wednesday 23 February 2005, 6 pm
Harricks Auditorium, Eagle House, 118 Alfred Street, Milsons Point

ABSTRACT

Geodynamics Limited is nearing the completion of its “Proof of Concept” hot fractured rock (HFR) program to extract superheated hot water for electricity generation from granite buried beneath the Cooper Basin. In 2003 the Habanero-1 well penetrated permeable sub-horizontal fractures at more than 4,000 m depth. The well was completed at 4,421 m with overpressures in the fractures around this depth exceeding pressures projected from a hydrostatic gradient by more than 5,000 psi. The static rock temperature at the bottom of the well is approximately 250°C.

The overpressures assisted in the development of the world’s largest artificial underground heat exchanger, a volume of rock more than 0.7 km³ defined by more than 11,700 microseismic events located on-site during the injection of 23 million litres of fresh water into the granite fracture network.

The second well (Habanero-2) was located 500 m SW of the first. It intersecting a major fracture, interpreted to be an extension of a dominant fracture in Habanero-1, at a depth of 4,325 m. During the operation the lower 245 m of the drill stem was irretrievably lost, and the well was subsequently sidetracked to a total depth of 4,358 m, just below the major fracture.

Flow and circulation testing between the two wells in early 2005 is designed to demonstrate the economic potential of the discovered far-field geothermal system and the heat exchange volume between the two wells.

BIOGRAPHICAL NOTES

Dr Doone Wyborn is Executive Director (Science and Exploration) of Geodynamics Limited, and one of the founding Directors of Geodynamics. He is an internationally known geoscientist specialising in granitic rocks. He obtained his PhD on granite research in 1983, and served more than 25 years with the Bureau of Mineral Resources and the Australian Geological Survey Organisation, including research in Antarctica and other overseas locations.

Dr Wyborn has been working on the potential of HFR geothermal energy for the last 12 years and is recognised as a leading Australian expert authority on this subject. He is a member of the Executive Committee of the International Energy Agency Geothermal Implementing Agreement and has studied HFR geothermal projects in Japan, Europe and the USA. The topic of his talk will be Australian Geothermal Project nearing completion of “Proof of Concept”.

Report on the General Monthly Meeting by Jill Rowling

Dr Doone Wyborn introduced his talk by explaining that Geodynamics Limited is nearing the completion of its “Proof of Concept” hot fractured rock (HFR) program to extract superheated hot water for electricity generation from granite buried beneath the Cooper Basin. In 2003 the Habanero-1 well penetrated permeable sub-horizontal fractures at more than 4,000m depth. The well was completed at 4,421m with overpressures in the fractures around this depth exceeding pressures projected from a hydrostatic gradient by more than 5,000psi. The static rock temperature at the bottom of the well is approximately 250°C.

Dr Doone Wyborn went on to explain that so far, Geodynamics had confined their drilling to the far north of South Australia’s Cooper Basin. The geological structure they are working on to extract heat is unique in that it is possibly the closest and hottest granite body to the earth’s surface. The heat is maintained partly by a relatively insulating sedimentary layer over the granite, keeping in some of the heat that was present during the emplacement of the granite, and a little heat retention by the radioactive decay of elements naturally present in the granite. Fractures have developed in the rock as a natural part of cooling, and these are naturally filled with hot water under pressure. The fractures in the granite are uniquely horizontal in nature.

Dr Wyborn explained some of the problems and surprises they have encountered due to the heat and pressure, and how Geodynamics have two wells, both in hydraulic communication with each other based on pressure tests in one measured in the other. These two wells, Habanero-1 and Habanero-2, are being used to test the production of geothermal heat and then hopefully electricity generation.

Some of the tests involve pumping water down into one of the wells, under pressure, and carefully recording the microseismic activity in order to estimate the productive fractured area. The audience was treated to a visual presentation of these tests measured over time as well as fracture and heat models at various depths over time.

After the presentation, the audience asked numerous questions from a variety of areas to which Dr Wyborn was able to respond superbly. The questions and discussions continued out the door, up the street and over dinner which was held nearby.