Electrical Survey Results in a Sub-Seabed Co2 Release Experiment (QICS)

Abstract

A controlled sub-seabed CO2 release experiment was carried out during May–October 2012 in Ardmucknish Bay in Scotland, UK. A total of 4.2 tons of CO2 gas was released for 37 days from May to June at a maximum flow rate of 80 L/min (210 kg/d) at a depth of 11 m beneath 12 m deep sea floor. During and after the CO2 release experiment, electrical resistivity and self-potential (SP) surveys were conducted to monitor CO2 migration under the seabed. Three electrical survey lines with a length of 45 m were completed on the seabed. The electrical resistivity surveys were conducted September 23, 2012 and May 27, 2016. The resistivity survey data were acquired with a pole-pole electrode configuration. Two-imensional analysis was performed in the three lines. The determined resistivity structures showed that positive anomalies of the resistivity structure of 2012 compared with the structure of 2016 distributed 10-20 m south-west of the CO2 released point. In this area CO2 bubbles was seen escaping from the seabed by divers and video cameras. CO2 migration under the seabed was estimated in this area by the seismic survey. The SP survey results measured during the CO2 release experiment showed that positive SP anomaly of a maximum of 0.05 V was observed when CO2 flow rate increased from 60L/min to 80 L/min. The positive anomalies distributed south-west of CO2 released point. This area is almost same as the positive electrical resistivity anomaly area in 2012. These results show that the CO2 migration under the seabed caused positive electrical resistivity anomalies and also positive SP anomalies.