Simple analytic tools are presented to predict a horizontal or slanted well's inflow performance relationship (IPR) producing from a solution-gas drive reservoir. Although a great body of work has been reported for a vertical well's performance during two-phase flow in the reservoir, only a few papers describe the same for a slanted/horizontal well.
Two recent studies developed empirical correlations for horizontal wells along the lines of Vogel, who had correlated flowing bottomhole pressure with flow rate for vertical wellbores by using numerical simulations. This work shows the difficulty of using these new correlations for evaluating the absolute open flow potential (AOFP), thereby limiting their applications in a predictive mode when field data are unavailable.
We also show that once the AOFP or the maximum oil flow rate is properly evaluated, both Vogel and Fetkovich correlations, originally intended for vertical wells, can be used to describe a well's IPR regardless of its orientation. Likewise, methods available for future prediction of a vertical well's IPR are equally applicable for wells having a different orientation. The AOFP can be computed by using any of the productivity index expressions developed for horizontal wells for various outer-boundary conditions. For slanted wells, the Cinco et al. correlation is used to calculate an effective wellbore radius and hence the well's productivity index.
Synthetic examples are used to show the application of the proposed methodology for computing a slanted well's IPR. On the other hand, a field example illustrates the method's applicability in a horizontal well.
The productivity of horizontal wells has been the subject of much study in recent years. Although the potential for improved productivity through horizontal wells were recognized in the mid 1950s, the advent of new drilling technology led to the resurgence of interest in this area. Scores of papers have been written to predict the performance of horizontal wells for single-phase and two-phase flow situations. Use of different boundary conditions have led to various analytic formulas for single-phase reservoir flow. In all these formulations, wellbore pressure-drop was neglected.
While the analytic methods are invaluable for initial prospect evaluation, numerical modeling is required to account for complex wellbore/reservoir interaction and for two-phase wellbore pressure drop calculations, as shown by Nghiem et al. and Wasserman.