Numerical investigation of the influence of vertical permeability heterogeneity in stratified formation and of injection/production well perforation placement on CO2 geological storage with enhanced CH4 recovery

Depleted natural gas fields provide promising CO2 storage sites with the additional benefit of enhancing natural gas recovery. This paper performs numerical investigations of CO2 storage with enhanced CH4 recovery (CSEGR) in large stratified reservoirs with neglecting the absence of aqueous phase in the reservoir, focusing on the influence of the reservoir vertical permeability heterogeneity and injection/production well perforation placement. The reservoir vertical permeability heterogeneity accelerates the CO2 transport in the reservoir resulting in less CO2 storage than in a homogeneous reservoir during the EGR process, with this unwelcome effect increasing as the reservoir vertical heterogeneity increases. The effects of the injection and production well perforation placement on the CSEGR performance are investigated for two reservoirs with different ratios of horizontal to vertical permeabilities. Placing both the injection and production well perforation in the lowest permeability layer gives the best CO2 storage for both modeled layered reservoirs. However, the well perforation placements for the best CH4 recovery differ for the two reservoirs. In addition, the CO2 storage, CH4 recovery, injection power and cost of modifying the well perforations also affect the determination of the optimal well perforation placements with the best well perforation placements for the overall performance also differ for the two layered reservoirs.