Is 4D seismic monitoring of CCS in abandoned North Sea reservoirs effective?

In this paper, we will address one of the many challenges of injecting CO₂ into abandoned hydrocarbon reservoirs. With the complexity of the fluid-fluid interactions, is 4D seismic monitoring effective in such situations, and if so, when, and where? As a step towards answering these questions, we have evaluated the magnitude and nature of 4D signals in a geological and complex fluid setting by running simulations, examining fluid interactions, and generating synthetic seismic using well log data (Log2Seis). A fluid analysis and rock physics modelling was conducted prior to our Log2Seis analysis. From the preliminary results, we concluded that injecting CO₂ into an oil reservoir appears much more visible on a good, towed streamer as compared to CO₂ injection into a gas reservoir. To determine if seismic monitoring of CCS is effective for a field, one should compare the magnitude of 4D signals against the non-repeatability of the existing 4D seismic acquisition. We also conclude that planning for such 4D seismic surveys is dependent on the time scales required, whether short term during the major injection period or longer term to monitor conformance and integrity.