Investigation of Fluid Segregation and Phase Redistribution in Wellbore Pressure Buildup

Summary During wellbore pressure buildup tests, fluid segregation and phase redistribution commonly introduce oscillations and anomalies into pressure measurements that complicate Pressure Transient Analysis (PTA) interpretation. Fluid segregation and redistribution lead to three distinct pressure response types, with pronounced effects observed at high water cuts, where redistribution is most significant. Corrective techniques, such as rate normalization and type-curve matching, proved effective in mitigating the impact of redistribution on pressure analysis. However, these solutions fail to capture complex physics in the wellbore and cannot accurately represent phase redistribution effects at early times. This paper presents an integrated framework combining analytical solutions to overcome these challenges and improve reservoir characterization. We first review conventional type-curve techniques and identify their inability to capture early-time distortions. Building on the models of Fair (1981), Hegeman et al. (1993), and Li et al. (2014), we show that existing formulations cannot reproduce the varying timing of the pressure hump. To address these limitations, we derive a new analytical solution that incorporates a flexible time-delay term which allows the hump to be displaced in time and match field observations. We also introduce a cleanup strategy that removes phase redistribution effects directly from the measured pressure data rather than relying on pressure-adjustment fitting or matching in data affected by phase redistribution. A synthetic dimensionless example demonstrates that our approach accurately reproduces hump characteristics, recovers the ideal pressure response, and eliminates redistribution artifacts. The resulting framework equips engineers with practical tools for reliable data interpretation, improved reservoir parameter estimation, optimized well-testing procedures, and enhanced operational efficiency under multiphase flow conditions.