Geophysical technologies for geothermal well field development in sedimentary basins

Summary

Deep sedimentary basins across the globe hold massive untapped reserves of geothermal energy. The economics of developing these resources is yet to be fully understood however it is likely that project scale will be a key factor for success. I investigate the geophysical methods that may be of value in the design and monitoring of geothermal well fields. Such well fields may utilize networks of pumping and injection wells installed in aquifers at multiple depth for heat exchange and or power generation. The Perth basin in Western Australia has at least four distinct expansive aquifers levels below the city. I compute simplified multi-layer hydrothermal numerical models for parameter distributions broadly based on the Perth basin to depths of over 5000m. The possible radial extent of changes in pressure, solute concentration and temperature are considered. The modelling demonstrates that pressure changes spanning hundreds of square kilometres could occur for large projects with a 50 to 100 year life span. Given the above it is clear that surface seismic reflection methods should be routinely used for multilevel geothermal developments in sedimentary basins. The benefit of 2D and 3D seismic is that a robust base-line hydrothermal framework can be developed. This means the entire well field and its impacts can be mapped out over hundreds of years. Australia is highly urbanized and there are good arguments for locating large geo-thermal projects in or proximal to cities where suitable deep basins exist. However cities like Perth tend to be dead zones for deep wells and seismic coverage. So it will be necessary to design and execute seismic surveys within cities. If the geothermal industry is to be a serious provider of energy it will need to build on lessons already learned in the petroleum industry.

Key words::

• Geothermal
• Well-field
• Geophysics
• 3D seismic reflection