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This paper reports logging results for well integrity conducted at the CO2 injection site in Japan. Well integrity is one of the essential issues for safety in geological CO2 storage. Wells in the Nagaoka site have been used for monitoring logging of CO2 behavior for more than ten years, and have experience of large earthquakes near the site. Time-lapse ultrasonic and cement bond logging have been employed to investigate the well integrity of the observation wells. Results of the ultrasonic logging showed that there was no sever damage or deformation in the casing at the reservoir depth. No clear change in cement can be seen in either logging results, even at the depth where the cement was exposed to the CO2. These results showed that there was no clear evidence of CO2 leakage at Nagaoka.

An electromagnetic (EM) field can be treated as a static field in free space when the induction number is considerably low. In such a case, measured EM field should include information on magnetic susceptibility. As transmitting frequency is increased, the measured EM field are increasingly affected by induction phenomena that include information on resistivity. This paper proposes a tomographic method for imaging two EM properties of the ground, magnetic susceptibility and resistivity, using a multifrequency and multicomponent EM data acquisition system. Scale modeling, numerical experiments and field tests were conducted to evaluate this method. The authors developed a multifrequency and multicomponent EM data acquisition system. Actual field experiments were conducted to examine if their data acquisition system could measure EM field with accuracy. Measured amplitudes at low frequencies agreed with the amplitude of the calculated magnetic field in free space because magnetic susceptibility in the test field is small. Measurements at high frequencies agreed with the results of the forward modeling conducted to calculate EM induction phenomena. This demonstrates that their data acquisition system can acquire data required for resistivity imaging. These experimental studies indicate that multifrequency and multicomponent EM tomography has the potential to become a practical method formore » imaging both magnetic susceptibility and resistivity of the ground.« less

We propose a new technique called controlled source magnetic susceptibility tomography (CSMST). An electromagnetic field generated by a solenoid coil source with alternating current can be treated as a static field in free space when the induction number is considerably low. Under this assumption, we examined if magnetic susceptibility tomography using controlled source is feasible. We have studied several survey parameters for crosshole CSMST measurement under realistic survey conditions. The results indicate that the transmission frequency and borehole separation of the CSMST measurement should be less than 10 Hz and less than 100 m, respectively, when the ground resistivity is 100 ohm-m. Sensitivity analysis is also performed to study the effective transmitter-receiver configuration. We conducted numerical model studies using two models, a cylinder model and a steel pipe model. These results show that a significant secondary magnetic field caused by underground magnetic anomalies can be induced by using borehole controlled source and that the CSMST has potential to become a useful exploration tool.