3D joint Gramian inversion of airborne gravity gradiometry and magnetotelluric data for geothermal resource exploration

Abstract

Extensive geophysical surveys were conducted over the geothermal field by Japan Oil, Gas and Metals National Corporation (JOGMEC) and Idemitsu Kosan Co. Ltd. (Idemitsu), which included airborne gravity gradiometry (AGG) and magnetotelluric (MT) surveys. The goal of this project was to study the location and structure of geothermal energy sources in the surveys area. The observed AGG and MT data were analyzed separately and jointly using 3D inversion methods. For joint inversion, we used the approach based on Gramian constraints (Zhdanov et al., 2012; Zhdanov, 2015). The Gramian method enforces the correlation between the different physical parameters of the inverse models, or their transforms, thus ensuring that the inversion produces a consistent image of the subsurface geological formation. This paper summarizes the principles of the joint inversion algorithm used in the project. We also present the results of the standalone and joint inversions to demonstrate the effectiveness of the developed method for geothermal resource exploration.