Abstract
IPR is a fundamental equation in production optimization and reservoir simulation modeling. The existing practices mainly rely on bottom-hole pressure measurements. Nonetheless, obtaining such field data is usually costly. Consequently, Production Engineers would favor the implementation of readily available well data such as wellhead pressures (Pwh). This paper will discuss a developed mathematical approach using Vogel/Fetkovich equations to correlate between Pwh and flow rates in oil reservoirs with high bubble point pressure. To illustrate this method, a comparison between implementing Vogel's equation "Rate dependent" and Fetkovich's approximation "PI dependent" will be explicitly clarified. The employed parameters will be explained briefly below.
First, PI is obtained from both flow rates -measured by Multi-Phase Flow Meter (MPFM) – and their corresponding ΔP. Second, reservoir pressure (Pr) and its corresponding bubble point are derived from its unique characteristics. Third, shut-in wellhead pressures (SIWHP) are attained from field‘s safety requirements. Last, the modified Pb (CWHP) –at which the graph curves- is calculated based on a developed empirical correlation that accounts for fluid column pressure and marginalizes temperature role. In addition, an elucidation behind substituting Pr with SIWHP and Pwf with Pwh in Vogel/Fetkovich equations will be discussed. The limitations and assumptions will be meticulously explained.
The results –based on actual field data with two distinct reservoirs– reflect marginal error percentages (around 5%) compared to MPFM testing results at identical Pwh. Furthermore, an adequate prediction of Pwh at which Pr goes below its bubble point (common problem in oil reservoirs with high Pb) is achieved. In conclusion, the field's IPRs will be effectively updated and tracked which will mimic the actual reservoir performance and positively impact both field optimization processes and simulation runs.
