Petrophysical Methods for Characterization of Geothermal Reservoirs

Abstract

Australia has a unique wealth of non-volcanic geothermal resources. To tap these for local and distributed energy needs, optimal targeting and development strategies for the reservoirs are needed. In the case of Hot Sedimentary Aquifers (HSA), many tools for formation evaluation developed in the oil and gas industry for High Pressure/ High Temperature environments could be applied directly; this applies both to downhole tools and laboratory characterization methods. The standard suite of petrophysical methods is adequate for determining basic matrix and fluid characteristics, but for full characterization of flow and geomechanical parameters advanced acoustic and nuclear magnetic resonance tools could find a place, at least for high value resources. In both crystalline rock and HSA plays, image logs are a vital tool, not least for enabling improved core-to-log workflows. Understanding of the thermal properties of rock and how that relates to field scale thermal structure is another challenge unfamiliar to most petrophysicists. Modelling from pore/grain through to formations scale is vital for assessing both thermal and flow performance. CSIRO and the Western Australian Geothermal Centre of Excellence have brought together experience and capabilities in rock physical and thermal properties and in this paper review what petrophysical tools and methods are available to the geothermal industry and illustrate some of the research currently underway.