Acoustic characterization of an artificial CO2 seep using split-beam echo sounders

Abstract

Geological carbon storage (GCS) has emerged as a promising method for reducing greenhouse gas emissions and achieving international climate goals. Currently, sub-seafloor GCS sites sequester about 1.8 MtCO2/yr. Additional sites are under development and by 2050, there is potential for storage of ≈ 100 Mt CO2/yr. For the expansion of sub-seafloor GCS to be successful, cost-efficient and effective leak monitoring systems must be available. The ACT4storage project is tasked with development of leak monitoring through the selection and use of available technologies. A part of the monitoring suite is the use of active acoustics to detect and quantify free CO2 bubbles and droplets. An artificial seep device was created to simulate leaks of CO2 bubbles. Leak simulations were quantified by two broadband split-beam echosounders (50-90 kHz and 250-450 kHz). The split-beam echosounders offer high sensitivity, broadband transmission and were calibrated to quantify flux from a leakage site. The split-beam echosounders show promise as cost-efficient and effective methods for the detection and quantification of free CO2.