Enhancing early-stage geothermal resource assessment through uncertainty modelling of the clay cap

Abstract

The development of new geothermal fields faces high subsurface uncertainty and economic risks. This study builds on a new numerical method developed at the University of Auckland for early-stage resource assessment. We introduce an automated tool designed to enhance this method by generating variable geometries of the clay cap. The tool interpolates between two given clay cap geometries, typically an optimistic and a conservative estimate, based on magnetotelluric (MT) data and expert knowledge, extending the range of possible resource potential estimates.
The methodology was validated using a synthetic teaching model and a small-scale model of the undeveloped Maritaing geothermal field in Indonesia. Additionally, the tool was applied to the Kotamobagu geothermal field model, which is larger in scale and currently being explored for development. The tool successfully generated interpolated clay cap geometries for each model. Early results indicate a significant influence of the size of the clay cap on the magnitude of the total upflow and its location at the bottom of the model. This highlights the importance of early-stage resource assessment, as the estimated clay cap geometry depends on limited and uncertain data combined with expert interpretations.
By automating the generation of the clay cap geometry, this tool enhances the new resource assessment method by incorporating additional geological uncertainty. Future research will focus on including this tool in a full resource assessment of an undeveloped geothermal field.