Crosshole EM Utilizing HTS-SQUID Magnetometer

We have developed the component technology necessary to realize high-performance EM system with HTS-SQUID sensors. Concerning the SQUID magnetometer system, a pressure- and heat-resistant outer vessel made of CFRP and an inner container including a liquid nitrogen Dewar were designed and trial fabricated. Test results indicated that they are almost tolerant in a 30 MPa and 200 °C environment. A SQUID magnetometer probe system for field test consisting of the outer vessel, inner container, sensor probe for three-axis SQUID sensors, and a FLL circuit was developed and actually inserted in wells. Correct operation of the SQUID sensor and its low field noise properties were confirmed in a 50 m deep borehole with steel casing. Crosshole TEM responses through steel-casing were also measured and compared with numerical simulation. The results show reasonably good match between them, showing promising result of crosshole EM through steel-casing. In the future work, in order to develop the monitoring system for EOR, we will continue to examine more details of crosshole EM by simulation and to acquire many different types of field data to estimate influence of steel casing more accurately.