The estimation of permeability in openhole horizontal drains in carbonate reservoirs poses petrophysical and reservoir engineering challenges. The usual approach relies on the pressure transient analysis (PTA) from well testing data to estimate the average reservoir permeability. The attempt to estimate the permeability from production logging (PLT) usually fails due to many unknown parameters and to complex flow regimes. However, we believe that the average permeability estimated from PTA combined with PLT results can be used to evaluate the distributed permeability across the drain.

In this paper, several approaches for deriving permeability from PLT were evaluated. Considering that PLT is usually performed during early linear flow regime, the Babu and Odeh (1990) equation is used for average permeability estimation. The zonal permeability is calculated proportionally to productivity index (PI) per zone per foot.

In the proposed method, the distributed permeability calculation along the horizontal drain is closer to the average permeability estimated from PTA than other methods, such as core and nuclear magnetic resonance (NMR) permeability index log. Downhole rates and flowing bottom hole pressure are used as reference for history matching. The results from different methods were inconsistent in some zones. A wide range of permeability values were obtained in few zones and could be explained by the presence of fractures.

The paper demonstrates a novel approach of permeability calculation based on PLT data, and could be applicable for previous and upcoming well logging. The method clearly helps to reduce the uncertainties in permeability estimations. The conclusive findings from this study are considered to be a good integration practice that will help to improve reservoir flow characterization and eventually reservoir modeling.

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