Time-lapse seismic analysis and Synthetic Modeling of CO2 injection at the Snøhvit storage site in the SW Barents Sea

Abstract

Given substantial emissions of greenhouse gases, carbon capture and storage (CCS) plays an increasingly important role in efforts to reduce emissions. The Snøhvit CO2 injection project began in 2008 with injection into the Tubåen Formation through well F-2 H, which due to rapid pressure build-up was terminated in 2011 and moved to the shallower Stø Formation. A second injection well G-4H was drilled in 2016, also injecting into the Stø Formation and is the active injector today, while the F-2H serves as a back-up. This study applies 4D seismic difference interpretation to better understand the CO2 plume development from the different injection sites. The 4D seismic difference dataset is computed from a baseline survey acquired in 2003 and a monitor survey acquired in 2022. Using this difference dataset, amplitude anomalies from injected CO2 are observed as high-amplitude softening responses. The amplitude anomalies are found in the Tubåen and Stø Formations with particularly strong amplitude responses near the injection points. Lateral fluid migration towards structural high is observed, especially in the Stø Formation. However, amplitude responses from gas out of solution in the reservoir show similar softening responses, and therefore complicate interpretation of CO2 plume development. Synthetic 4D seismic modeling has been conducted for several injection scenarios with varying saturation levels alongside the interpretation of 4D seismic difference. The model was built using Petrel subsurface software and then used as input in the NORSAR synthetic 3D seismic Petrel plug-in which generates a synthetic seismic cube based in the inputs. The model underscores that higher saturation levels produce stronger amplitude anomalies, although not necessarily as a linear relationship. A multi-phase fluid flow simulation is recommended for higher accuracy in plume distribution, which would take structural features and lateral property variations into account. This simplified modeling is used for exploring the synthetic seismic responses from varying saturations, and to enhance how modeling can be a valuable tool for further understanding and predicting CO2 plume development.