Development and testing of a rapid, sensitive, high-resolution tool to improve mapping of CO2 leakage at the ground surface. (October 2022)

• Record Type: Journal Article
• Authors: Graziani, Stefano; Beaubien, Stan E.; Ciotoli, Giancarlo; Bigi, Sabina
• Is Part Of: Applied geochemistry. Volume 145(2022)
• Publication Date: 2022-10
• Subjects: Diffuse degassing -- CCS -- CO2 flux -- Soil gas -- Leakage mapping -- Uncertainty; Environmental geochemistry -- Periodicals; Water chemistry -- Periodicals; Geochemistry -- Social aspects -- Periodicals; Geochemistry -- Periodicals; 551.9
• DOI: 10.1016/j.apgeochem.2022.105424
• Languages: English
• ISSNs: 0883-2927

Abstract

Abstract: Locating and quantifying anomalous, deep-origin CO2 leakage from the soil to the atmosphere is typically accomplished by interpolating a dataset of point flux measurements, with overall accuracy and uncertainty strongly influenced by sample spacing relative to anomaly size and variability. To reduce this uncertainty we have developed the Ground CO2 Mapper, a low-cost complementary tool that rapidly measures, at high spatial resolution, the distribution of CO2 concentration at the ground-air contact as a proxy of CO2 flux. Laboratory tests show that the Mapper has a low noise level (2σ = 16 ppm) and fast response time (T90 = 1.55 s), while field tests at a small controlled-release site define a high level of reproducibility and sensitivity and illustrate the impact of wind and survey speed on instrument response. Modelling based on these results indicates that the Mapper has a greater than 60% probability of detecting an intersected 2 m wide anomaly having a maximum CO2 flux rate of 75 and 100 g m −2 d −1 at survey speeds of 2.5 and 4.8 km h −1, respectively, under the test conditions. Measurements in a large (4600 m 2 ) grassland field where natural geogenic CO2 is leaking show how the Mapper can produce, in <10% of the time, a more detailed map of CO2 flux distribution than a point flux survey conducted on a ca. 10 m grid spacing. Based on these results we believe the Ground CO2 Mapper can give a useful contribution to diffuse degassing studies in volcanic/geothermal areas and to monitoring of Carbon Capture and Storage (CCS) sites by reducing overall survey time, costs and uncertainty. Future work will test the Mapper's response and capabilities under more diverse site and meteorological conditions than those examined in this study. Graphical abstract: Image 1 Highlights: Mapping CO2 leakage with point flux measurements has a high level of uncertainty. New tool maps CO2 concentration at ground surface at high resolution as flux proxy. Lab/controlled release tests and natural geogenic leak surveys show capabilities. Rapid, sensitive, robust and low-cost tool supports soil gas and gas flux surveys. Useful for carbon capture and storage (CCS) monitoring/diffuse degassing studies.