Non-Darcy flow reduces the productivity of fractured and frac and pack wells and causes erroneous results if ignored when analyzing well test data.1  Current practices to quantify the non-Darcy flow effect in a vertically fractured well are mostly based on the work of Guppy et al.,2-6  where simple empirical correlations were developed in the form of apparent dimensionless fracture conductivity as a function of the true dimensionless conductivity and the inertia resistance factor. However, based on the parameter matrices of their numerical analysis, restrictions were also imposed on the variables for the correlations to be valid. In this paper, the same problem of non-Darcy flow in a vertically fractured well is revisited for the cases of rate-controlled drawdown tests. We argue that the relationships between the apparent fracture conductivity and the true conductivity is a function of time and that the restrictions on variables can be relaxed. In addition, the issue of flow convergence near the perforation tunnels is also discussed. A comparative study of the relative effect of flow convergence vs. flow in the perforation tunnels is also presented to allow a quick assessment of the most dominant factor.

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