We are investigating the technical feasibility of injecting CO2 for carbon sequestration with enhanced gas recovery (CSEGR) in the depleted Altmark natural gas reservoir, Germany. Our approach is numerical simulation using TOUGH2/EOS7C. Our earlier simulation studies have shown early CO2 breakthrough due to fast-flow through the high-permeability sand layers. In order to extend the period of enhanced CH4 recovery, we propose the preinjection of gelling fluids for the purpose of limiting the mobility of injected CO2 and thereby improving CO2 sweep and delaying CO2 breakthrough. We have implemented a simple gel model into EOS7C and simulated gel injection followed by CSEGR. Preliminary simulations to date show minimal improvements in CSEGR with breakthrough times delayed by only a few months to a year. While mobility control using pre-injected gelling fluids appears to be a promising strategy in controlling early breakthrough, more work is needed to design and simulate an effective procedure.