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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, C v , for permeability within sandstone beds is found to be around 0.5 while the C v 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.

Models of hydrocarbon reservoirs are often used to support management decisions about field development and redevelopment. Typical modelling workflows result in a reservoir and simulation model with a property distribution generally comparable to the well data, and this is often considered sufficient. The current study tests this assumption on the fluvial reservoir in the Upper Lunde Member of the Snorre Field where sedimentary heterogeneities at multiple scales influence reservoir properties such as porosity and permeability. This work shows that, by describing and modelling the sedimentary heterogeneities at several length scales in the reservoir, and by using a flow-based local upscaling method, the resulting porosity and permeability distribution at the scale of the reservoir and simulation model are significantly different from porosity and permeability distribution at the well data scale; the variance tends to reduce and, for permeability, the distribution type is changed from log-normal to normal. Reservoir property distributions based on multiscale modelling, sensitive to the representative elementary volumes for permeability, and upscaled in a realistic sedimentological framework, give a better representation of the effective permeability architecture.

Heterolithic lithofacies in the Jurassic Tilje Formation, offshore mid-Norway, consist of three components -sand, silt and mud intercalated at the centimetre scale -and are generally difficult to characterize petrophysically with core and wireline data. A near-wellbore model of the lower part of the Tilje Formation in the Heidrun Field is constructed to illustrate the application of these results to formation evaluation studies. The sedimentological model is developed by detailed parameterization of a cored well interval and the petrophysical properties are based on core plug data, taking into account sampling bias and length scale. The variation in petrophysical properties as a function of sample volume is examined by calculating the representative elementary volume. The sensitivity of the representative permeability values to the contrast between the three components is studied and gives a better understanding of the flow behaviour of this system. These results are used to rescale the core plug data to a representative value and thereby quantify the uncertainty associated with the wireline-based estimates of porosity and horizontal permeability and to give an improved estimate of the k v /k h ratio.