Influence of Shale and Mudstone Heterogeneity on Permeability-driven Fluid Flow - Sample to Geophysical Well Log Scale

The flow properties of shales and mudstones are important for petroleum systems, hydrogeology and CO2 storage sites. However, these flow properties have been mainly studied on laboratory sample scale in the past, assuming homogeneity on larger scales, although shale and mudstones can be highly heterogeneous, depending on their depositional environment. In this study, we investigate the influence of heterogeneities of shales and mudstones on fluid flow on the next larger scale compared to the laboratory sample scale: the geophysical well log scale. To do so, we have quantitatively investigated more than 500 m of mud-rich core and borehole images from six wells of an offshore gas field in the Nile Delta, Egypt. The quantitative approach allowed for subsequent modeling of the observed heterogeneities, which serve as geometry input for 2D numerical fluid flow simulation to calculate effective permeabilities. The fluid flow models were integrated with grain size measurements and published stress-porosity-permeability relationships. As a final result, stress-dependent effective porosity-permeability relationships for a range of shale and mudstone heterogeneities and associated lithological variability can be provided along with probability distributions of heterogeneity occurrence for most of the depositional environments encountered in the investigated Nile Delta wells.