The seismic interpretability of a 4D data, a case study: the FRS project

Davood Nowroozi, Donald C. Lawton, Hassan Khaniani

The Field Research Station (FRS) is a project developed by CMC Research Institutes, Inc. (CMC) and the University of Calgary. During the injection CO₂ in the shallow target layer (300 m depth), dynamic parameters of the reservoir as pressure and brine/CO₂ saturation will change, and they can be derived from the fluid simulation result. The injection is in the shallow target to monitor possible gas leakage and detection by geophysical methods. For the project, the injection strategy is five years’ CO₂ gas phase injection with a constant bottom hole pressure equal to 49.4 bar.

In the first part of the seismic modeling, we used synthetic velocity models to compare seismic responses of a reservoir with different saturation, pressure, and plume size. Based on the synthetic models, there is an amplitude change in the reservoir and a time delay in the deeper levels because of velocity change. The effect of time delay is removed after migration with the realistic velocity model. The seismic models include VSP and cross well surveys and show high amplitudes due to gas injection, and because of lower noise content in these methods, we expect to map the reservoir properties in the early injection step by well seismic acquisition.

The surface seismic models show lower amplitudes than the well seismic methods after injection. Considering the surface related noises, the monitoring by surface seismic may not be possible in the first years when saturation and plume size are small, but the surface seismic should generate better images after several years of injection.