Identification geothermal system based on 1D, 2D, 3D inversion and TDEM static shift correction study case Mt. Arjuno-Welirang, East Java

Abstract

Arjuno-Welirang Mountain is located in East Java province, which is a type of stratovolcano with an altitude of 3,339 m for Arjuno and 3,156 m for Welirang. The Arjuno-Welirang geothermal system is a volcanic geothermal system. Magnetotelluric is the most commonly used geothermal exploration method because of its deep penetration and sensitivity to conductive zones. The Magnetotelluric method measures 103 MT points in the field of geothermal systems in the South of Mount Arjuno-Welirang. In this study, the 3D inversion model of Magnetotelluric data was used to reduce the ambiguity of 2D Magnetotelluric inversion data. 3D Model Inversion uses WinGlink and 3DModEM. The steps of Magnetotelluric processing consist of time-domain conversion to the frequency domain, cross power selection, data smoothing, static effect correction, 2D and static strips, interpolation, masking, 3D inversion, and interpretation of inversion models. The 3D model inversion consists of 3D mesh grid parameters used by the NonLinear Conjugate Gradient Algorithm. 2D Inversion Modelling was done by the NLCG method, which produces a 2D model with an RMS error of 1.7%. 3D Inversion modeling was done by the NLCG method producing a 2D model with a value of RMS error of 2.83%. The geothermal system of the Arjuno-Welirang geothermal region consists of a layer of veil rock with a type of resistivity value of 5-11 Ωm, a middle resistivity zone with a value range of 11-76 m acting as a reservoir, and a high resistivity zone with a range of 76-500 Ωm or commonly called heat source. The results of the 3D inversion model indicated a range of low resistance types (hood rock layers) that have a thickness of 1200 - 1700 m, the value of this type of resistance is below the surface with a thickness of ±500-600 m. Thus, the Mt. Arjuno-Welirang is a geothermal prospect area.