Effects of Heterogeneous Seal Layer Property on The Long-Term Behaviour of CO₂ Injected into Deep Multilayer Systems

Abstract

Heterogeneity in mudstone/shale layers has significant effects on seal layer integrity. The presence of intralayer sandstone channels in a seal layer may allow the buoyant CO₂ to escape from the reservoir, even if the globally averaged permeability of the seal layer seems low enough. On the other hand, multi-layered structures are known to work often as baffles for the upward migration of CO₂ in formations. In this paper, we investigate the storage capacity of multilayer formations with discontinuous seals. Numerical simulations are carried out to study the effects of seal layer discontinuity on the long-term behaviour of CO₂ injected into deep saline aquifers. To represent a seal layer composed of low permeability rocks intersected by sandstone channels, ‘MINC' doubleporosity model is adopted. Also conducted is sensitivity analysis to investigate the effects of key parameters such as capillary pressure, relative permeability, temperature, and the thickness of the formations. The results show that CO₂ injection into a sufficiently deep multi-layered reservoir enables CO₂ to be stored and trapped in and around the reservoir without reaching to a shallow aquifer, even though seal layers have discontinuities. The upward movement of CO₂ is greatly affected by capillary pressure of sandstone channels in seal layers. The relative permeability and the temperature-dependent CO₂ properties have a significant effect on the final plume spread and the amount of CO₂ dissolved or fixed by residual gas trapping.