Reservoir hydrocarbon fluids complicated properties and phase behavior with associated physics often reflect the complexities of reservoir architecture. Hence, it is of great importance to determine fluid heterogeneities at the early exploration and appraisal stage. Conventionally, however, gathering information on fluid heterogeneities and phase behaviors is a challenging process that requires numerous fluid samples and associated laboratory analysis. Although pressure gradients are often used to evaluate in-situ fluid densities, contacts, or connectivity, this method may be misleading as fluid compositional changes and compartmentalization give distortions to the pressure gradient fitting. Nowadays, Downhole Fluid Analysis (DFA) measurements are being effectively used to reveal fluid heterogeneities by providing various reservoir fluid properties in real-time. In order to allow an objective assessment of reservoir architecture, it is needed to incorporate a rigorous mathematical approach in respect of all data available.

This work demonstrates with field data an effective and reliable methodology for evaluating fluid variations with depth through an equation-of-state (EOS) approach by interpreting DFA measurements integrated with other conventional data. Using an established method, the topmost DFA data in a column was delumped and characterized, and then an EOS model is established for the reservoir fluids. The EOS parameters can be tuned to match DFA measurements at different depths. The tuned EOS is applied to predict compositional and property gradients with depth. If the difference between the predictions and DFA data is significant, then potential vertical discontinuity between the top pay zone and current depth must be investigated. Case studies are presented to illustrate how this methodology is applied. This work demonstrates that the EOS based methodology of integrating DFA data with other openhole logs provides a powerful tool of characterizing reservoir architecture, which is invaluable for optimal reservoir management and development.

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