Development of a passive sampling technique for offshore CO2 monitoring: Preliminary results from laboratory experiments

Monitoring of sequestered CO2 at storage sites is essential to provide assurance of long-term storage integrity. Thus, the objective of this study was to develop a sorbent-based offshore monitoring concept to monitor CO2 leakage during CO2-EOR operations. The study site, where the CO2-EOR operation is planned to be undertaken, is located in the pre-salt layer offshore Brazil. Perfluorocarbons (PFCs) were selected as tracers for monitoring possible CO2 leakage. A passive sampling technique was proposed to adsorb the injected tracer. Several commercially available sampler materials were initially chosen, among which Carboxen 569 placed inside a polyethersulphone (PES) membrane was tested and selected to be the preferred passive sampler combination. In order to perform tracer uptake rate experiments, a flow through experimental setup was built, optimized and tested under in-situ conditions of 300 bar and 15°C. In addition, a desorption unit was designed to quantify the tracer amount sorbed to the sampler during the experiments. The developed passive sampler combination proved to be successful in sorbing the tracers. The phase distribution of the tracer candidates in a CO2-water-oil system were investigated in a slimtube setup. It is shown that the PFCs have a shorter travel time through the system than CO2 and will potentially provide a warning of CO2 leakage from the reservoir.