4D seismic feasibility study for enhanced oil recovery (EOR) with CO2 injection in a mature North Sea field

A mature North Sea field with a long history of water flooding has been modelled to predict the potential for enhanced oil recovery (EOR) with CO2 injection. This technique has the potential to further extend the life of the field by extracting more oil and to store the injected CO2 in the reservoir. A feasibility study
was conducted to assess whether 4D (time-lapse) seismic could be used as a monitoring tool during CO2 injection. Different approaches were employed in this project; the initial examination using a 4D risk assessment table (Lumley et al., 1997) suggests that 4D seismic can be applied. For a more quantitative
analysis, a petro-elastic model was designed to capture both the saturation and pressure signatures from the injected CO2. 1D modelling using fluid substitution at well locations, and simulator to seismic modelling in conjunction with the compositional simulation model was performed to predict the three dimensional 4D signatures within the simulation model grid. Based on this analysis a seismic impedance change of up to 9% is predicted which is above the limit that is typically considered for 4D applications. The discrimination between pressure and saturation signals is also discussed and the possibility to use 4D
seismic to detect pressure changes was evaluated. This study makes suggestions regarding the seismic survey characteristics and appropriate timing to acquire the monitor surveys.