Geosciences

Diagenesis-upscaling-techniques for reservoir simulation by means of geostatistic al methods - Study of the applicability of the semivariogram method -

A large data set on the diagenesis of Rotliegend (Lower Permian)-Sandstone from a graben system of the North German Basin was created by petrographic thin section analysis, examination of petrographic drill core logs of three wells, and evaluation of petrophysical data. Because of low data density compared to a high spatial variability and a non-warrantable presumption of given normal distribution multivariate statistics are of limited use for petrographic data (as logratios). To avoid mingling of segments with obviously different properties, these subpopulations must be separated first.

In semivariograms of porosity there is a strong spatial correlation. Possibly the thickness of Micro-, Meso- and Macro-Cycles results in multiple ranges. Thus, the porosity within Rotliegendprofiles can be analysed by variography and exerted for upscaling-techniques by utilisation of depositional cycles. The permeability only shows a weak spatial correlation, because of decreasing dependence of diagenesis on facial patterns at greater burial depths. Therefore upscaling of permeability related to facies or depositional cycles is uncertain. Authigenic minerals indicate a weak spatial correlation, with a great nugget-effect, which is probably caused by a too big sampling distance. Within single subpopulations the number of thin sections is mostly too sparse to recognise any possible spatial correlation in semivariograms.