Modelling subsurface geologic structures at the Ikogosi geothermal field, southwestern Nigeria, using gravity, magnetics and seismic interferometry techniques

Abstract

We present results and a technique for imaging the subsurface structures of a geothermal field with particular focus on the Ikogosi geothermal field in Nigeria. The intent was to provide an understanding of the subsurface structural setup in the region and assess its viability for further geothermal resources exploitation. High-resolution aeromagnetic and gravity data were used for the study. A constrained 2D forward modelling technique was applied to these datasets to map the shape and corresponding depths of geologic structures in the region. This study has gone deeper to ascertain the basement structure and configurations and how it influences the heat source of the Ikogosi Warm Spring (IWS) region. The dominant host quartzite rock unit at the IWS location reaches average depths of 2.5-3.0 km and is located directly on an intruded high-density geologic formation in the subsurface. Fault structures traversing the IWS source have also been uncovered. We infer that these structural setups are central to the geothermal system of the IWS. Valid reflection responses from the profile model have been retrieved from randomly induced noise sources, using a passive seismic interferometry technique. Pre-stack depth migration of the reflected responses suitably imaged the reflectors within the subsurface of the IWS region, tracing fault boundaries and delineating intruded geological structures. This has provided pre-survey insights into the subsurface seismic imagery of the region. Results derived from this study could assist informed decision making regarding geothermal exploration and exploitation in the region.