Coupled multiphase flow, geochemical, and geomechanical modelling of the impact of shale interlayers on CO2 migration

The need to find sufficient capacity for geological carbon dioxide (CO2) storage to meet demand means less-than ideal, heterogeneous reservoirs need to be considered. Many such reservoirs are apparently compartmentalised by inter-layers, which may help, or hinder, CO2 migration and storage capacity, depending upon their nature. The impact of shale inter-layers of thicknesses below seismic resolution are generally neglected in plume migration simulations, but have been shown here to be important. Only simulations of plume migration that include coupling of all three of mass transport, geo-chemical and geo-mechanical processes together provide proper prediction of the barrier efficiency of relatively thin shale inter-layers. A series of feedback inter-actions between these three process types has been studied in detail, and, for example, leads to the unexpectedly higher barrier efficiency of thin inter-layers compared to slightly thicker inter-layers. The results show that capillary breakthrough pressure, diffusion processes and re-activation of natural fractures played a vital role in enhancing the migration of the CO2 plume via the thicker shale inter-layers towards the overburden. This paper identifies significant research gaps regarding the effects of complicated, intricate processes affecting shale inter-layer (or seal) integrity under realistic reservoir conditions