Implicit net-to-gross in the petrophysical characterization of thin-layered reservoirs

A new workflow has been devised to characterize the petrophysical properties of two, thin-layered, heterolithic log facies from a turbidite reservoir. The methodology is based on a published modelling technique that enables an extremely accurate reconstruction of the fine-scale lithological and sedimentological reservoir heterogeneities and a thorough integration of petrophysical data from core plugs. A large number of fine-scale rock models (geometrical grids) are: (1) stochastically generated to investigate the variability of the sedimentological features observed in cores; and (2) stochastically populated with porosity and permeability values of the pure lithological components (sandstone, siltstone and mudstone) to generate petrophysical grids. The petrophysical grids are subsequently upscaled using analytical and flow-based techniques, thus providing distributions of porosity, horizontal permeability and vertical permeability that are further analysed to characterize the aforementioned log facies. The results obtained using this workflow are exhaustive, in the sense that they implicitly take into account all of the possible ranges of variation of ‘net-reservoir’ (sandstone and siltstone) and ‘non-net-reservoir’ (mudstone) lithologies. The use of net-to-gross in petrophysical characterization is thus made redundant.

Paolo Scaglioni, Livio Ruvo and Mauro Cozzi, ENI

Published in Petroleum Geoscience, November 2006

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