Intergrasi Studi Geofisika-Geologi Untuk Memetakan Struktur Bawah Permukaan Lapangan Panas Bumi Dieng
The geological structures is the main drilling target for exploitation because it can act as permeable media for the geothermal fluid movement from reservoir to the surface. Drilling failures can occur because of errors in the determination of the structure of drilling targets. To minimize the risk of drilling failure,it necessary to conduct the integrated study of geological and geophysical studies to map the geological structures.
Geophysical data which is used to map the geological structures are gaya berat and magnetotelluric. Gaya berat data which is used is the Complete Bougeur Anomaly (CBA). This data was aquired in 1995 from 371 stations that concern an area of 6 km2. Magnetotelluric data which is used is the result of digitation of apparent resistivity and phase curves of the period that was acquired from 159 stations in 1984 and 126 stations in 1997. Geological data which is used is a regional geological map of Banjarnegara and geological map of Dieng geothermal field. The well data which are used is well generating capacity.
The Geophysical approach is using the CBA derivative data and resisitivity of magnetotelluric which can be used to map the existence of the structure in detail. Derivative analysis of the CBA is to combine the maximum or minimum value of the FHD data and thevalue around zero of FVD data to map the presence of structural zones. The 500 meters data spacing can detect the structure with derivative method at a minimum depth of 2 kilometers. Validate of presence the structure from CBA derivative data is using the resistivity map of magnetotelluric from 2-D modelling results, also indicated the presence of the structure at elevation of -500 m asl and 500mdpl. Identification of geology structure from regional geology map and volcanic stratigraphy suggest the association of this structure with the geology structural mapped from geophysical data because most of structure which is mapped on the surface is continuity to the subsurface . From the integration of geophysical and geological studies, the mapped structure in Dieng geothermal field is patterned Meratus, northeast - southwest, which estimate active again, and Sunda pattern with orientation east-west
The existence manifestations around the structure which is mapped be the indication of presence the permeable structure. Productivity data from existing wells is also an important parameter for determining the drilling. The sorting of structure is expected to minimize the drilling failure which using three criteria: the presence of stucture integration from geophysical and geological mapping studies, permeability from manifestation existantions and productivity of the wells.
Dr. Ir. Prihadi Sumintadiredja
Dr. Eng Suryantini ST. Dipl. Geothermal Tech., M.Sc