Delineation Hydrothermal Demagnetization and Subsurface Modelling with 3D Magnetic Inversion

The delineation problem of the geothermal system is important to examine, because it could determine how big the geothermal prospects in the subsurface. Magnetic method could make zonation on the subsurface region undergoing thermal demagnetization processes. The rocks that make up the reservoir have changed the susceptibility from high to low due to the influence of fluid and heat from the heat source in the system. This research has proved the existence of Geothermal Field's delineation of Field "E" with Magnetic and Magnetotelluric method, 674 points magnetic data corrected by diurnal variation and undistributed earth magnetic field or better known as IGRF. After that continuity has been carried out to a height of 700 m asl, and visible dipole oriented body with NE-SW direction in intermediate inclination. Reduction to Pole was performed on uplift and obtained a low negative anomaly indicating the presence of hydrothermally demagnetization rock. The RTP results are also correlated with the apparent resistivity MT curve, and the low negative anomaly values tend to be associated with the Type H MT curve. The RTP contour is modeled by a 3D magnetic. And the reservoir zonation is in the mean sea level to 1900 m bsl. Cross correlation was performed between magnetic 3D Inversion and MT inversion, that reservoir rock zone has a susceptibility of 0.04-0.06 Cgs and with resistivity of 20-80 ohm.m The existence of geothermal reservoir is suspected to be in the upflow zone up to SW direction is in the vicinity of the main fault in the "E" field area associated with a negative low anomaly -300 s / d -550 nT.