A method for estimation of vertical permeability in heterolithic tidal deltaic sandstones is proposed. Three-dimensional, stochastic, process-based models of sedimentary bedding are used to give estimates for the effective permeability of heterolithic tidal sandstone units where heterogeneities in the sandstone and mudstone components are evaluated explicitly.
Subsurface core (probe permeameter) data from two contrasting reservoir intervals in the Tilje Formation, offshore mid-Norway, have been used to derive representative petrophysical properties for the models. These data illustrate the nature of petrophysical variability in heterolithic sandstones and provide estimates of the mean and standard deviation of sandstone permeability at the lamina scale. The coefficient of variation, Cv, for permeability within sandstone beds is found to be around 0.5 while the Cv for heterolithic units is in the range of 1.0 to 4.0 (i.e. very heterogeneous). Measurement of mudstone permeability is a challenge; however, a limited set of mudstone (pulse-decay) measurements gives values in the range of 10−6 mD to 10−2 mD.
Effective vertical permeability is mainly a function of mudstone fraction with different characteristics above and below the percolation threshold. Vertical permeability functions have been integrated with conventional well logs and compared with available subsurface estimates for vertical permeability.