GreenRock Energy with large inferred resource at North Perth Basin

Green Rock Energy, Perth Basin exploration permits (source: Green Rock Energy)
Alexander Richter 29 Oct 2010

Australian Green Rock Energy releases independent estimates on geothermal resources in its North Perth Basin permits, with a potential target of up to 100MW in power generation capacity.

In a release by the compay, Australian “Green Rock Energy says it had engaged Hot Dry Rocks Pty Ltd (HDR), a leading Australian geothermal consulting company, to provide an estimate of in place Geothermal Resources for its seven North Perth Basin Permits GEP23, 24, 25, 26, 27, 28 and GEP41 (Permits) covering 2,100 square kilometers.”

Key highlights include: very large geothermal resources at the North Perth Basin Permits as identified by Hot Dry Rocks, indicated geothermal resources sufficient for a target of up to 100MW in power generation capacity in a region with rapid power demand growth.

The Permits are near the Dongara, Hovea, and Mt Horner oil and gas fields, 275 to 330 km north of Perth and close to power infrastructure. HDR has estimated stored heat Resources in the Permits to total just over 1,000,000 petajoules thermal (PJt) contained in Hot Sedimentary Aquifer (HSA) and Engineered Geothermal System (EGS; also known as ‘hot rock’) reservoirs. HDR’s estimate was determined specifically for the purpose of electricity generation by industry-standard binary cycle technology or similar, but could also be used for other uses if suitable markets become available.

For the purposes of identifying the most prospective targets so that Green Rock can be ready to drill in its North Perth Basin Permits in 2011, it is the Indicated Geothermal Resource in the selected Hot Sedimentary Aquifer reservoir units (described below) of 26,000 PJt that is the most relevant. Data from five wells provided direct and reliable indications of temperatures greater than
125oC in the selected reservoir units.

The Geothermal Reporting Code 2008 Edition defines an Indicated Geothermal Resource as “that part of a Geothermal Resource which has been demonstrated to exist through direct measurements that indicate temperature and dimensions so that the thermal energy in place can be estimated with a reasonable level of confidence…..It is based on direct measurements and assessments of volumes of hot rock and possibly fluid, with sufficient indicators to characterize the temperature and chemistry. Direct measurements are sufficiently spaced so as to indicate the extent of the Geothermal Resource.”

The Indicated Geothermal Resource of 26,000 PJt is equivalent to over 820,000 MWt.yrs. To put this into context, if only 5% of the Indicated Geothermal Resource in these seven Green Rock Permits was produced, for an assumed project life of 25 years, a power conversion efficiency of 10% and a parasitic load of 25%, this would approximate 123 MWe of power generation capacity.

HDR estimated that the seven Permits contain stored heat with temperatures over 125ºC in HSA reservoirs amounting to 336,859 PJt (equivalent to 10.68 million MWt.yrs). HDR has also estimated Inferred Geothermal Resources of stored heat with temperatures over 150ºC within the basement down to a depth 5,000m in the Permits to total 663,923 PJt (equivalent to 20.93 million MWt.yrs). This stored heat in the basement represents an EGS Inferred Geothermal Resource.

Of the estimate of 336,859 PJt of stored heat in HSA reservoirs only the portion amounting to 77,182 PJt (equivalent to 2.45 million MWt.yrs) contained within four reservoir units nominated by Green Rock has been classified by HDR as a HSA Geothermal Resource. These sandstone units containing natural geothermal water are the Upper Permian Sandstone equivalents, Carynginia
Formation, Irwin River Coal Measures and High Cliff Sandstone. HDR has further classified this HSA Geothermal Resource into both Inferred Geothermal Resources amounting to 51,000 PJt.(equivalent to 1.62 million MWt.yrs) and Indicated Geothermal Resources amounting to 26,000PJt. Green Rock intends to investigate if any portion of the substantial quantity of stored heat in the HSA formations within the Permits, which has not yet been classified as a HSA Geothermal Resource, may in future be classified as a Geothermal Resource recoverable from natural fractures in the sedimentary formations.

Green Rock’s Director of Operations Adrian Larking said “The HDR estimate supports our view of the huge potential of our Permits in the North Perth Basin within a region of rapid power demand growth. Our work now is to collect additional data and interpretations so that we can define drilling targets in the HSA formations where there is a high water temperature as well as natural permeability and therefore the best chance of high water flow rates. We expect to be making significant progress in the first half of 2011 towards the definition of drilling targets.”

Source: Company release via e-mail