An Innovative Reservoir Engineering Program for Assessing EGSs in Australian Conditions

Abstract

The Geothermal Research Initiative (GRI) a group of university, CSIRO and Geoscience Australia researchers have agreed to collaborate on the research and development of geothermal energy resources across a broad range of technologies and geographical locations in Australia. This paper describes the work of a subgroup dedicated to developing a Reservoir Engineering Program specifically designed for extracting heat from the high stress and high temperature structures encountered in Australian conditions. The program was specifically designed to incorporate the insights gained from the failure of the commercial exploitation and the conventional stimulation techniques employed in EGS targets in Australia. The outcomes emphasize the necessity to understand the geological structure providing the pathways for deep fluids. Progress on the understanding of these geological structures led to the identification of high temperature creep fractures in the middle to lower crust that presumably formed during the past 5-10 Myrs compressional deformation as identified in a companion paper (Regenauer-Lieb et al. 2013) The current paper explores the use of an innovative 3D numerical technique to characterize these pre-existing geological structures in the context of high temperature deformation and fracture mechanical behaviour at geological scales. Next a stimulation technique for effective stimulation of these pre-existing fractures in the light of the material laws derived in the previous step is presented. This numerically assisted reservoir engineering program has been tested and compared with field observations and laboratory analyses of source rocks under similar tectonic, fluid pressure, chemistry and thermal conditions reproduced in the laboratory. The consideration of previously ignored high temperature deformation mechanisms is expected to provide new unexplored opportunities for the stimulation strategy of EGS plays. The validated numerical reservoir program is then used to evaluate geothermal energy potential of a typical Australian deep hot crystalline basement in Central Australia. Results of this study include subsurface fracture maps, injection pressure for different flow rates, produced fluid temperature for different circulation periods and flow rates, matrix temperature drawdown and finally the thermal energy recovery factor for different flow rates and production periods. References: Regenauer-Lieb et al. Stimulating Granites: From Synchrotron Microtomography to Enhancing Reservoirs, WGC2015 abstract Gholizadeh Doonechaly, N. and S.S. Rahman, 3D hybrid tectono-stochastic modeling of naturally fractured reservoir: Application of finite element method and stochastic simulation technique. Tectonophysics, 2012. 541–543(0): p. 43-56. Gholizadeh Doonechaly N., Rahman S.S., Evaluation of Recoverable Energy Potential from Enhanced Geothermal Systems: A 2 Sensitivity Analysis in a Poro-Thermo-Elastic Framework, Geofluids, 2014, In Press.