Development of Cost-Efficient CO₂ Monitoring for Medium-Scale Injection Projects

Monitoring of a CO₂ underground storage site is one of the key operating costs for a storage site after theinvestments in injection well(s) and facilities. To achieve cost-efficient storage, the operator therefore has an interestin developing a monitoring strategy that is as low cost as possible while still providing the necessary informationabout the storage site behaviour.In this work we have combined geology, reservoir simulations, rock physics modelling, and seismic inversion, toallow for conformance verification and to better understand how to set the best strategies/acquisitions for cost-effective geophysical monitoring. We have been able to test a workflow for cost-effective monitoring on a syntheticdataset based on data from Smeaheia. Two different scenarios for the geological input have been tested; with andwithout including the effect on vertical communication from reservoir heterogeneities such as thin shale layers, so-called maximum flooding surfaces in the Sognefjord and Fensfjord Formations:• Case I: With thin shale layers in the reservoir units• Case II: Without thin shale layers in the reservoir unitsUsing the two cases, we simulated 3 Mt/year CO₂ injected in one well north of Alpha structure for 20 years. Adetailed rock physics model was set up, and P-wave, S-wave, and density changes were calculated. Thereafter changesin amplitude impedance were calculated based on the inversion results of different acquisition seismic systems,including traditional marine and VSP-DAS setups. The results indicate that the thin shale layers, will have influenceon the migration paths, and thereby can be observed using P-waves. Denser acquisitions will provide the best possibledelineation of the plume and allow for differentiating cases with and without the intra sand shales. On the other hand,we found that limited data acquisitions are also able to provide sufficient information on the CO₂ distribution andpresence of shales as long as we are not too fare from the injection well. This combined with the associated costs ofthe different acquisitions results in a complex problem that can only be properly addressed by following acomprehensive analysis like the one we present here.We see this work as a first step towards a workflow for effective assessment of monitoring strategies, andwe have identified several steps in future workflows depending on the site and the risk scenarios.

(PDF) Development of Cost-Effective CO₂ Monitoring for Medium-Scale Injection Projects. Available from: https://www.researchgate.net/publication/387774498_Development_of_Cost-Effective_CO2_Monitoring_for_Medium-Scale_Injection_Projects [accessed Jan 28 2025].