Integrated geophysical and geological methods to identify structure existence as a permeable zone in a geothermal field

Abstract

At the development stage of a geothermal field, a comprehensive survey is needed to obtain an accurate picture of the geothermal system to identify the subsurface condition on the prospect field. The geological structure is one of the important aspects of geothermal exploration. It creates permeability, which allows geothermal fluids to flow to the surface. Locating geological structures in the prospect area will be a powerful tool to determine the drilling target for exploration or production wells. One of the methods to identify geological structure on the surface is using satellite imagery. It is based on visual interpretation of the morpho-structural aspect combined with the lithological aspect and then confirmed with field data. The remote sensing data is built from DEMNAS data and a regional geological map. DEMNAS has spatial resolution 0,27-arcsecond, vertical datum EGM2008. While the subsurface geological structure can be identified by using the Gravity Second Vertical Derivative (SVD) and First Horizontal Derivative (FHD) method. Gravity method identifies structure by slicing the SVD grid, which has suspected structure and then confirmed with FHD slicing in the same suspected area. The geological structure will be confirmed if the value of FHD maximum and SVD value 0. The results of the data processing above are then integrated to obtain the distribution of geological structures as a permeable zone in the geothermal field which then can be used as a guide in determining the location of exploration and production wells.