In-situ experiment reveals CO(2) enriched fluid migration in faulted caprock

The sealing characteristics of the geological formation located above a CO(2) storage reservoir, the so-called caprock, are essential to ensure efficient geological carbon storage. If CO(2) were to leak through the caprock, temporal changes in fluid geochemistry can reveal fundamental information on migration mechanisms and induced fluid–rock interactions. Here, we present the results from a unique in-situ injection experiment, where CO(2)-enriched fluid was continuously injected in a faulted caprock analogue. Our results show that the CO(2) migration follows complex pathways within the fault structure. The joint analysis of noble gases, ion concentrations and carbon isotopes allow us to quantify mixing between injected CO(2)-enriched fluid and resident formation water and to describe the temporal evolution of water–rock interaction processes. The results presented here are a crucial complement to the geophysical monitoring at the fracture scale highlighting a unique migration of CO(2) in fault zones.