On the sensitivity of CO2 injectivity to reservoir facies architecture

This study seeks to investigate the effect of geological heterogeneity in channelized sandstone formations on pressure buildup during CO2 injection by using dynamic simulation. Four geological models of fluvial and turbidite depositional systems were constructed, typical of those which occur in the Southern North Sea (Triassic, Bunter fluvial) and Central North Sea regions. These are largely comprised of stochastic sand channel networks contained within a low permeability shale matrix. Incorporating the fine-scale heterogeneity associated with channel structures led to a basin-scale reservoir model containing 4,443,960 model cells. The results of the simulations show that the impact of fine-scale stratigraphic heterogeneity on CO2 injectivity is significant, although the importance was found to vary depending on the contrast of permeability between shale and sand assumed. It is concluded that the incorporation of fine scale heterogeneity (<10s m) is necessary for CO2 storage simulation when basin scale modelling is required to capture pressure response and impact of interference with other activity in the connected pore volume. Such work again highlights the importance of developing reliable upscaling methodologies so as to reduce computational time of simulations and better allow for the practical possibility of probabilistic assessments, using multi-realisation methods such as Monte Carlo simulation.