Trapping effects of small scale sedimentary heterogeneities

The presented modeling study illustrates how even small-scale heterogeneity has implications for how the CO₂ is distributed and trapped in sedimentary sequences, and outlines a workflow for the study of these effects. The starting point for the study is a 2D model for crossbedded shallow-marine/tidal sands with 8 sediment classes, ranging from high-permeable sand to low permeable clay included as thin layers. The very small grid cell size of 3.5 mm ensures that the sedimentary details and contrasts are reflected in the petrophysical model. The initial flow simulation results show that in addition to the capillary trapped CO ₂ which remains after an imbibition process and which is caused by well explained hysteresis, some is also arrested by the architecture of the low-permeability layers due to permeability and capillary heterogeneity and this fraction becomes partly or fully immobilized. This contribution from heterogeneity trapping could add an element of increased containment safety and may in some cases add hyper-trapping capacity exceeding the prior established endpoint values from the saturation functions normally used to reflect the process in the simulations as well as in other more simple capacity estimates.