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Australian Mining magazine looks into geothermal drilling

Australian Mining magazine looks into geothermal drilling Geothermal drilling rig at Jolokia, Australia (source: Geodynamics)
Alexander Richter 18 Apr 2010

The Australian Journal of Mining, looks at the geothermal resource styles targeted in Australia and some of the major technical challenges.

A recent article by Dr. Cameron Huddlestone-Holmes and Prof. Klaus Regenauer-Lieb in the Australian Journal of Mining, describes “the geothermal resource styles targeted in Australia and looks at some of the major technical challenges that need to be overcome to take geothermal from its current position and deliver on the potential it promises.

The challenge in the development of geothermal energy resources is getting the heat energy from the reservoir to the surface. To do this we need to be able to efficiently drill wells into the reservoir and produce a sufficient flow rate of working fluid to bring the heat energy to the surface.

Technological advancement in drilling and reservoir enhancement and management will have a significant impact on the success of the geothermal energy industry in Australia.
Geothermal resources, by their nature, will generally be deep; current targets in Australia are typically at depths between 3 km and 5 km. The geothermal industry is currently relying on technologies developed in the petroleum industry, where wells are routinely drilled to depths of 4 km to 5 km. However, there are several key differences between geothermal drilling and petroleum drilling.

Geothermal reservoirs are usually hotter than the petroleum reservoirs (although the petroleum industry is working in deeper and hotter reservoirs as shallow reservoirs are depleted). The adverse effects of the higher temperatures on the durability of downhole equipment such as drill bits and on geophysical logging tools need to be overcome. Casing has to be able to tolerate thermal expansion caused by the high temperatures.

Wells drilled in HR reservoirs will encounter crystalline (granitic/metamorphic) formations that are harder and more fractured than the sedimentary formations typically encountered in petroleum reservoirs.

Novel drilling techniques such as thermal spallation, which removes rock by thermal expansion (Augustine et al. 2007), are being developed to improve penetration rates in these harder formations. To achieve the required flow rates, geothermal wells are usually completed at larger diameters than typical petroleum wells. Drilling techniques that maintain the natural permeability in the near-well environment will be critical for HSA and HR resources.

Hot Rock resources do not normally have high enough natural permeability to allow the production of sufficient flow rate of hot fluid from the reservoir to be viable. The permeability of the reservoir must be enhanced so that high enough flow rates can be achieved. Hydraulic fracturing is a proven technology applied in the petroleum and minerals industries and has been demonstrated at some of the experimental HR geothermal sites around the world. The application of these technologies to HR is complicated by the strength of the rock, high confining stresses, the need to avoid thermal breakthrough, risks of induced seismicity and the effect of temperature on stimulation hardware.

Drilling and reservoir enhancement are two areas where technological advancement will be crucial to the success of geothermal energy in Australia. There are many other avenues of research that will improve the viability of the industry including the development of better exploration technologies, improving the efficiency of power generating equipment, development geophysical methods for reservoir characterisation and monitoring and development of direct use applications.

The challenges are not insurmountable and the Australian geothermal industry has grown to 47 companies holding over 384 geothermal exploration licence areas covering ~360,000 km2 (Goldstein et al. 2009). Significant research effort is underway with three Centres of Excellence in geothermal energy established in the last 18 months. The industry and research community are working toward demonstrating the viability of geothermal energy and have been supported by the award of over $250 million in government grants in 2009. The heat rush is well and truly on.”

For the full article see link below.

Source: Australian Journal of Mining