Abstract

The evaluation of complex carbonate reservoirs is a challenging task for petrophysicists and reservoir engineers, and a detailed understanding of reservoir heterogeneity and its relation to wettability, fluid distribution and flow properties is still lacking.

In previous publications we investigated the effect of sample sizes on poroperm variations and cementation factors derived from resistivity measurements. Whole cores were essential in capturing representative data in heterogeneous carbonates. In this study the effect of static rock type and sample size (i.e. plugs versus whole cores) was investigated on SCAL data derived from capillary pressure and resistivity index experiments at reservoir temperature and net confining stress. The plugs and whole cores were initially selected according to static rock types comprising lithofacies classification and petrophysical grouping.

The obtained SCAL data from plugs and whole cores in each rock type grouping were studied in light of the initial static rock type. Data variations within the same rock type were detected among the plugs and between the plugs and the whole cores. Those variations were investigated in details to understand the degree of local heterogeneity and its effect on static and dynamic SCAL data. Data variations between the different static rock types were also investigated and assessed on the basis of dynamic imbibition data. Whole cores were generally found to yield different capillary pressure and saturation exponents that may not be possible to derive from average plug data. Those petrophysical variations will have large impact on reservoir rock types and saturation functions for optimum reservoir performance predictions.

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