The Starzach site in Southern Germany: a site with naturally occurring CO2 emissions recovering from century-long gas mining as a natural analog for a leaking CCS reservoir

Abstract

In this paper, we present the Starzach site, a region featuring numerous natural CO2 emission spots, such as mofettes, that reappeared after a longer period of extensive industrial CO2 mining. We discuss the results of a detailed literature study on the geological setting and the activities related to the gas mining in combination with own measurements to introduce the site as an example on how gas leakage from an insecure CCS reservoir could manifest at the surface. The site is in particular interesting for such investigations as the CO2 emissions started to replenish after the end of the CO2 mining and offers the unique possibility to investigate an increase in degassing activity as it might be expected for an active CCS site where leakage is suspected. Based on the geological setting and soil, gas emission, and isotope investigations, we further discuss the source of the CO2 emission and the gas ascent to the ground surface via deep-reaching faults, latter being so far excluded by previous work. The combination of our extensive literature review and recent field investigations allowed us to draw new geological conclusions for the site that were under discussion for a long time and to give insight into the site’s potential for CCS-related analog studies in the future.