In this talk, I will focus on what we can learn from large-scale sequestration in the USA.  Since 2020, 12 Class II and 5 Class VI wells have been permitted for CO2 sequestration in the USA.  Currently, 13 projects report against their M&V plans annually.  This body of experience gives a good idea of what practical M&V plans entail and shows that monitoring geological storage need not be elaborate or expensive.

Distributed fibre optic sensing is attracting more and more attention in CO₂ geological storage. Temperature sensing (DTS) and acoustic sensing (DAS) have been used for pipeline leak monitoring and CO₂ plume imaging in the subsurface. We propose the distributed optical fibre strain sensing technology for deformation monitoring, aiming to provide early warning of well/caprock integrity in fluid injections.

This talk will introduce the latest field results and the great potential for fault integrity/fault zone leak monitoring in geological CO₂ storage.

In the CO₂ release near a shallow fault zone, significant subsurface changes occur within several weeks, and thus require frequent monitor surveys. Thus, this experiment will be monitored with so-called reverse 4D vertical seismic profiling (VSP) with a sparker source in the well and over 1000 receivers on the surface. This method avoids the need for shooting many shot points in each survey as required in conventional 4D VSP, which would make each monitor survey duration too long.  The sparker source also provides ultra-high spatial resolution required for this small injection.

The reverse VSP will be complemented by a trial of time-lapse surface seismic monitoring using refracted waves, with a mobile source and the same array of surface receivers. The monitoring program for the deep injection includes continuous offset-VSP acquisition with permanently mounted surface orbital vibrators as seismic sources and downhole distributed acoustic sensors (DAS) complemented by vibroseis 4D VSP, a combination that proved its efficacy in the Otway Stage 3 Project. It would be useful to complement this proven technology with trials of new approaches, including real-time and in-depth analysis of induced seismicity, real-time continuous reflection data interpretation using machine learning, estimation of CO₂ saturation from direct 

Near-surface environmental monitoring, targeting groundwater and soil gas, plays an important role in the Monitoring, Measurement and Verification (MMV) program at on-shore deep-well carbon capture and storage (CCS) sites. The purpose of environmental monitoring is not only for regulatory compliance but also to assure the public that injection activities do not impact the near-surface environment. 

At the Otway International Test Centre (OITC), environmental monitoring has been conducted annually since before the first injection in 2008, establishing baseline conditions and obtaining 17-year data for soil gas and 18-year data for groundwater. Since mid-2020, the Deakin University team has collected groundwater samples from up to seven monitoring bores and eleven private bores of the local landholders. 

A variety of parameters were gathered to assess groundwater quality, including major ions, trace elements, and tracers (i.e., SF6 and noble gases). Meanwhile, over 100 soil gas sampling points were installed across an area of approximately 3.8 km2, including dairy paddocks and roadsides. Samples were analysed for concentrations of CO2, N2, O2, CH4, and carbon isotopes in CO2 (δ13CCO2), along with the measurement of tracers in selected samples. Significant natural variabilities have been observed temporally and spatially within both groundwater and soil gas systems. 

A multi-step verification process was employed to identify potential influence on the near-surface environment. The verification process incorporates tracer analysis, along with historical values, baseline values, and analysis methodologies established by researchers between 2008 and 2023. Research objectives were established to optimise monitoring strategies based on a substantial database, focusing on risk-based soil gas monitoring. To date, valuable insights have been gained throughout the work at OITC, providing lessons that are invaluable for developing cost-effective monitoring strategies in future largescale CCS projects.
 

We present recent advances in pressure-based monitoring techniques for tracking migrating CO₂ plumes, with field results from the Otway Stage 3 project. We focus on integrating our measurements with other complimentary methods, such as seismic imaging, to reduce uncertainty and provide risk-based monitoring solutions.

We present updated results for pressure tomography using an uncertainty approach with reduced wells and perform simultaneous multi-vintage inversions to help constrain the solution space. We also discuss a joint seismic inversion scheme, which can reconcile results across monitoring modalities.

Finally, we present our recent findings from earth-tide monitoring, which reveals complex amplitude, diurnal and semi-diurnal phase behaviour in the presence of a nearby CO₂ plume.