Applying Innovations in MT Technology for Reducing Geothermal Exploration Risks

In the exploration stage (even in the development stage), geophysics is the most important surface method used to image the subsurface physical parameters associated with a geothermal system. Magnetotelluric (MT) imaging is the most powerful method to reconstruct a geothermal system model based on resistivity distribution. MT can be used to define top of reservoir, delineate geometry of reservoir and determine well target zones. The subsurface information derived from the MT data is then confirmed through drilling. Many geothermal fields in Indonesia have had wells drilled. The wellbore data (from both 'successful' and 'unsuccessful' drilling) contain valuable subsurface information that can be utilized for confirming the MT resistivity imaging data. Comparison between surface (MT resistivity) and subsurface (wellbore) data should be done iteratively in order to obtain more accurate MT imaging with higher resolution. This iterative process should be done continuously as new drilling data becomes available. Accordingly, such iteration contributes to innovation in MT technology that leads to better imaging and subsequently more accurate well targeting. Recent innovations of the MT technology such as applying advanced data processing, selection of a more appropriate modeling/inversion scheme, and joint interpretation with other geophysical methods, have been done and these should also be applied to the iterative process. The iterative process can be employed in many geothermal systems with different geological settings to improve the reservoir characterization and to increase drilling success ratio. Such innovations could provide a practical solution to mitigate the exploration risks.