3D modelling of flow units and petrophysical properties in brazilian presalt carbonate

Abstract

Rock typing into flow units (FU) is a well-known technique for characterizing flow heterogeneities in reservoirs and producing reliable estimations of petrophysical properties, as porosity and permeability. Several methods that correlate pore-throat size with permeability and porosity in the core and well-log domains are available in the literature, being the flow zone indicator (FZI) method the most common used in both clastic and carbonate reservoirs. Extrapolating the flow units rock typing from the core and well-log scales into the whole reservoir is a major challenge due to the lack of correlation with sedimentological facies and available data scale differences. Most 3D generations of flow units and petrophysical properties are merely a geostatistical procedure, without any spatial data constraints (like seismic attribute). We propose a new approach to create flow units occurrence probability volumes as well as seismic derived porosities and permeabilities that are more robust than the usual estimate of petrophysical properties considering sedimentological facies. Considering the seismic scale characteristics and using the concept of decametre flow units and quantitative seismic interpretation in a Brazilian presalt dataset, we indirectly quantified superimposed small-scale effects that obliterate/generate porosity on a larger scale and established a minimum number of correlatable FUs with elastic seismic attributes. We produced 3D volumes of permeability and porosity that are still capable of obtaining complex reservoir flow characteristics and could be directly considered as variables in lateral interpolation of reservoir parameters, seismic 4D interpretations and seismic-assisted history matching.