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.

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.

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The Lower Jurassic Tilje Formation on the Halten Terrace, offshore mid-Norway, forms an important reservoir in a number of hydrocarbon fields. A high volume fraction (80 percent) of the formation is heterolithic in nature, showing various styles of sandstone-mudstone intercalated bedding at several scales. The depositional model is based on a general facies classification scheme applicable to all fields. The stratigraphic interval discussed was deposited in a narrow basin during overall rising relative sea level as a tide/wave-dominated, mud-rich delta with well-developed prodelta, delta-front, and estuarine-type distributary-channel facies. The main heterolithic deposits are found in the prodelta, delta-front, and distal parts of the estuarine-type distributary-channel-mouth areas, whereas relatively “clean” facies occur in medial areas of these distributaries. Lithofacies associations are modeled in 3D using stochastic, object-based methods, and the heterolithic architecture at the lithofacies scale is modeled using a process-based sedimentary architecture tool. Multiple data sources (core, log, and outcrop-analogs) are used to establish a data-rich procedure for estimating the effective reservoir properties within a step-wise upscaling procedure. Our results show the importance of integrating multiscale data with good sedimentary models to accurately estimate reservoir properties in these heterolithic formations. We derive effective property functions (for example kv/kh) for different facies and identify important reservoir flow units using flow simulations of stochastic realizations.

The diffusion of 99 Tc in granite was investigated with small-sized diffusion cells, composed of a radioactive source solution cell and a sampling cell. Water in the two cells was kept at the same level. 1 ml aliquots were taken from the sampling cells daily during the first 50 days, then at intervals of several days, and measured via liquid scintillation counting. The experimental results indicate that the diffusion of 99 Tc and 3 H in granite follows the one-dimensional diffusion equation when diffusion time is long enough (> 100 days). The calculated average diffusion coefficient of 99 Tc (1.4 × 10 −12 m 2 /s) is about one half of that of 3 H (3.2 × 10 −12 m 2 /s).