Acoustic determination of CO2 bubble rise heights during a controlled release experiment

Abstract

Carbon capture and storage (CCS), where CO2 is captured from industrial sources and stored in geological formations, has emerged as a promising method for reducing the amount of CO2 released into the atmosphere. Current regulations require monitoring the water column above a storage site to verify that there are no indications of leakage. Determining the rise height of CO2 bubbles is important in order to understand the environmental consequences of a potential CO2 leak, as well as to establish an efficient monitoring strategy. The rapid dissolution of CO2 in seawater is likely to limit the rise height of CO2 bubbles. However, few quantitative studies have been published. During a controlled release experiment in the Oslo Fjord, we simulated a CO2 leak at a water depth of 60 m. CO2 bubbles were released at rates of 0.575 l/min and 1.15 l/min, from a 3 mm orifice. Rise heights were determined using multiple echo sounders and sonars mounted on the Simrad Echo R/V. We observed consistent scattering from bubbles as high as 50 m above the leak point. We also experienced that it is challenging to locate the top of the plume using most echo sounders, due to the imaging geometry of the system.