Determining the sparsest acquisition geometry required to meet a known 4D monitoring objective

Abstract

Carbon storage (CS) sites require a measurement, monitoring, and verification (MMV) plan, which provides assurance regarding the conformance and containment of the stored carbon dioxide (CO₂). Costs associated with the acquisition, processing, and interpretation of conventional time-lapse seismic are high. A step change in the cost and environmental impact of MMV for CS is a common goal across the industry. To meet this challenge, we demonstrate how dynamic subsurface modelling can be used to design time-lapse surveys that target specific changes in a known subsurface model and introduce a workflow to determine the sparsest acquisition geometry required to meet a known 4D monitoring objective (e.g. to verify conformance). Using the presented workflow, we can confirm anticipated CO₂ plume migration but also resolve and delineate unexpected migration within the storage unit. We designed a perturbation analysis based on full-waveform inversion that enables the model and perturbation to be probed with different acquisition geometries. The analysis determines which geometry provides the most cost-effective solution to detect and localise the targeted change. The workflow can additionally test the robustness of the geometry to unknown changes outside the storage unit (e.g. identifying potential breach of containment), thereby meeting the two primary monitoring objectives of CS. The workflow is tied to the monitoring plan, associated dynamic modelling, and the evergreening of the subsurface model. It is adaptive and varies proportionally as the understanding of the injection site evolves.