Temperature Regime in the Perth Metropolitan Area: Results of temperature and gamma logging and analysis, June/July 2010.

[摘要] Exploration of Perth’s geothermal potential has been performed by the Western Australian Geothermal Centre of Excellence (WAGCOE) and two honours students from the University of Western Australia and Curtin University.Detailed vertical temperature and gamma ray logging of seventeen WA Department of Water’s (DoW) Artesian Monitoring (AM) wells was performed throughout the Perth Metropolitan Area (PMA).In addition, temperature logs from fifty-three DoW AM wells measured in the 1980s were digitised into LAS format.The logged data are available in the WAGCOE Data Catalogue.The temperature logs provide a picture of true formation temperatures within shallow sediments in the Perth Basin.A three-dimensional model of the temperature distribution was used to produce temperature maps at depth, and on the top of the Yarragadee Aquifer.The temperature data were interpreted with a one-dimensional conductive heat assumption.Significant difference between the model and the observations was indicative of heat moving via non-conductive mechanisms, such as advection or convection.Evidence of advective heat flow is demonstrated in most formations in the PMA, with significant effects in the aquifer zones.The temperature data were analysed to produce average geothermal gradients, which range from a low of 13 °C km-1 in the surficial formations to 39 °C km-1 in the South Perth Shale.In general, the gradients follow lithological characterisation, with sandstone formations exhibiting gradients of approximately 25 °C km-1, while insulating silt/shale formations show higher gradients of over 30 °C km-1.To produce preliminary heat flow estimates, temperature gradients were combined with thermal conductivities estimated by HDRPL [2008] for formations considered applicable to the PMA. The geometric mean heat flow estimates range between 64 mW m-2 to 91 mW m-2, with the standard deviation of the arithmetic mean heat flow ranging between 15 and 23 mW m-2.Analysis of the gamma-ray logs yielded the first estimates of radiogenic heat production in Perth Basin formations. Values by formation ranged between 0.19 and 0.85 μW m-3. The gamma-ray logs also helped produce a consistent set of stratigraphic formation elevations in the PMA.Although extensive, the present study points to several areas where future investigations will provide a more comprehensive overview of the thermal regime in the Perth area.In particular, additional temperature and calibrated three-component gamma-ray logging will enhance the modern dataset.Older datasets should be digitised to provide inexpensive, albeit less accurate, spatial coverage.Quantification of the movement of heat by advective groundwater flow would indicate the significance of this mode of heat transport.Thermal properties such as thermal conductivity, specific heat, and thermal expansion should be measured in the PMA.In particular, thermal conductivity measurements are required to produce more accurate estimates of heat flow, although inversion techniques may provide site-specific, initial spatial estimates of heat flow and thermal conductivity in shallow formations.Prediction of temperature at depth should include uncertainty estimates.

[发布日期] 2011-06-06 [发布机构] CSIRO

[学科分类] 地球科学(综合)