Application of Superconducting Quantum Magnetic Sensors Based Transient Electromagnetic Method (SQUID-TEM) for Geothermal Resource Exploration

We have introduced a novel method of geothermal exploration based on highly sensitive SQUID (Superconducting Quantum Interference Device) magnetic sensors and an electric bipole transmitter located over the study area. The advantage of the SQUID receivers over the conventional induction coils is that SQUID measures with high precision the components of the transient magnetic field, B(t), generated by the transmitter, while the induction coils measure the time derivatives dB(t)/dt. This results in a significant increase in the signal-to-noise ratio and, therefore, the sensitivity of the method.

We have also developed the 3D modeling and inversion methods and software for transforming the SQUID-TEM data into the 3D subsurface resistivity model. Our method is based on the contraction integral equation (CIE) forward modeling and re-weighted regularized conjugate gradient (RRCG) inversion algorithm.

We conducted a SQUID TEM survey at the geothermal field test site of the NEDO program in Japan to determine the potential geothermal reservoir associated with the area of lower resistivity caused by hydrothermal fluids. The field SQUID-TEM survey conducted at the Takigami geothermal field onshore Kyushu Island, Japan, helped to reveal the electrical conductivity anomaly associated with the deep geothermal reservoir.