Frictional and sealing behavior of simulated anhydrite fault gouge: Effects of CO2 and implications for fault stability and caprock integrity
Anne Pluymakers, researcher at PGP, will present her PhD work on "Frictional and sealing behavior of simulated anhydrite fault gouge: Effects of CO2 and implications for fault stability and caprock integrity"
Sketch of CO2 storage reservoir (in the Dutch subsurface). Main questions with respect to CO2 storage in depleted gas reservoirs concern risks of leakage and/or seismicity.
Faults crosscutting the CO2 reservoir and topseal systems of subsurface storage sites are considered one of the most likely leakage pathways for CO2 storage in depleted oil and gas reservoirs, especially if reactivation leads to fault dilation. Anhydrite is a common caprock mineral in many hydrocarbon fields worldwide, and particularly in the Netherlands. In cases where faults crosscut the caprock, it is likely that these contain fine-grained, anhydrite-rich, damage material, or “fault gouge”. I will present results from the different sets of experiments I performed during my PhD. These aimed at 1) understanding compaction creep and investigating the potential for self-sealing, and 2) at understanding the frictional behavior of anhydrite gouges, so to investigate the potential for earthquake nucleation. All experiments were performed under pressure and temperature conditions representative for CO2 storage conditions (80-150°C; with effective stresses up to 25 MPa), under dry and wet conditions, but also using dry CO2 and CO2 saturated solution. Our results yield insight into the processes active within anhydrite-rich faults, which is relevant to our understanding of leakage and induced seismicity along faults cross-cutting anhydrite caprocks topping geological storage systems, as well as understanding natural seismic events in anhydrite-bearing sequences, such as found in the seismically active Italian Apennines.