Assessing geotechnical risk in geothermal areas using ESys computation
A snapshot of the equivalent stress rate distribution simulated by using PANDAS/ESyS_Crustal. Black lines indicate a position inside faults (Xing and Mora, 2006).
A recent research project by Curtin University and the University of Western Australia shows that safety is a key consideration in mining development. Geotechnical risk assessments in mining and other contexts often use numerical models as predicative tools.
However calculating the risk of steam outbursts, release of harmful gases, boiling or geysering water in production blast holes resulting from heat and mass low in geothermal systems is beyond most software systems.
Hydrogeologists from Coffey Geotechnics Pty Ltd partnered with academics from the Earth System Science Computational Centre, University of Queensland, to deploy the finite element methods of ESyS_Crustal to solve the large system of coupled, nonlinear differential equations describing heat and mass low in a geothermal system taking into account phase transition of condensable fluids as well as for transient boundary conditions of an open-cut mine pit.
The resulting code was demonstrated for risk analysis of geothermal hazards during mining in hot ground at the Kapit Pit extension of the Lihir Gold Limited open-cut gold mine. The mine is located in a geothermal active caldera on Lihir Island, in the New Ireland province of Papua New Guinea. The region is geothermally active with surface manifestations including acid sulfate hot springs, neutral chlorite springs, mud pools and low temperature fumaroles.
The model found that steam did not develop after deepening the pit by 90m despite computed temperatures exceeding 100 degrees Celsius due to high hydrostatic pressures, and demonstrated the practical utility of the method for assessing geotechnical risks such as pit wall stability, the likelihood of geysering water from blasts and the eiciency of steam release wells.
The partnership between Cofey Geotechnics and University of Queensland developed into an ARC Linkage project to employ ESyS_Crustal to model geomechanical-luid low-thermal systems in fractured geomaterials to support facility design, construction, risk assessment and production of Hot Fractured Rock (HFR) geothermal energy technology.
This case study exempliies how geoscience software developed with academic applications in mind can be adapted and developed to unforeseen but (by definition for industry) valuable applications that lead to ongoing collaborations.
This article was written by Lateral Economics and published in the AuScope Infrastructure Program – evaluation of impacts report of 2016.
Sources (Text & Image): Bringemeier D., Wang, X, Xing, H. L. and Zhang, J (2010). Modelling of Multiphase Fluid Flow for an Open Pit Development within a Geothermal Active Caldera, Proceedings of the 11th International Association for Engineering Geology and the Environment (IAEG) Congress, Auckland; http://www.auscope.org.au/geothermaldemonstrators/