Feasibility Study of Marine CSEM in Monitoring CO₂ Deposits

The global search for renewable energy sources is intensifying, intending to replace fossil fuels and thereby reduce the emission of carbon dioxide gas (CO2). A further method of reducing atmospheric gas levels involves capturing and trapping such gases in subsurface reservoirs. It is becoming increasingly evident that this second strategy is gaining momentum, and geophysics plays a pivotal role in the success of this advance. After the capture and storage of CO2, monitoring its behavior in the subsurface is imperative to facilitate the control of these underground reservoirs. In this context, searching for geophysical methodologies optimally suited to this monitoring process is paramount. The present study investigates the application of the marine controlled source electromagnetic method (MCSEM) to the monitoring of carbon dioxide (CO2). This method has been extensively used within the oil and gas industry for detecting hydrocarbons. Given the physical property of CO2 (i.e., resistivity) that is analogous to those of hydrocarbons, identifying suitable matches for adequate gas monitoring is a conceivable proposition. The model selected for the assessment of the method’s viability is based on the Sleipner field situated in the northern part of the North Sea Basin, where gas injection has been ongoing since 1996. This field has achieved notable success in injecting substantial quantities of CO2 from the Utsira formation. It is evident that, from this model, a realistic approximation of all the horizons of this plume was created. This approximation was derived from seismic and well data obtained from the site. In the context of direct modeling of the MCSEM, the implementation of the vector finite element technique, utilizing tetrahedral elements, proved to be a successful approach. The efficacy of the method was evaluated concerning both frequency and the growth of the CO2 plume. It was determined that the method possesses the capacity to facilitate the requisite monitoring. However, it is imperative to possess prior knowledge of the injection site to select the most optimal survey arrangement and determine the optimal investigation frequencies.