The development of pressure transient analysis was based on the assumption of a single phase slightly compressible fluid. This assumption was later relaxed to handle dry gas reservoirs and multiphase situations. The literature reported several methods for multiphase well test analysis [e.g., Perrine-Martin method (1956), pressure squared method proposed by A1-Khalifah (1987), and the two-phase pseudopressure function by Raghavan (1976), and 3-zone Fevang and Whitson approach (1995)].
In this paper, we develop new formulation for generalized multiphase pseudo-pressure and pseudo-time functions that can handle any type of multiphase flow system. In particular, the new formulation uses the modified black-oil (MBO) approach and can handle volatile oils and gas condensate reservoirs in more accurate ways than presented previously in the literature. These generalized multiphase pseudo-functions were validated through the analysis of many simulated drawdown and pressure buildup tests covering comprehensive inner (radial wells, partial penetration, fractured, and horizontal wells). The simulated cases also covered all multiphase flow situations. In every simulated case, analysis using the new functions was compared with single phase, Perrine-Martin, and the multiphase approaches proposed by Raghavan and Fevang and Whitson analyses. The new technique proved to be the most accurate among the other techniques. The new technique also uses one generalized form to handle any multiphase situation including volatile oils and gas condensates. As an example, application of the new generalized multiphase pseudo-functions to analyze transient data generated in gas-water multiphase flow system, at different water cut values; it was found that the new multiphase pseudo-function technique was able to predict the flow capacity with error percentage less than 10% when the water cut value was less than 50%. This was at least 2 folds better than other existing techniques. It was also found that this error percentage increased when the water cut value exceeded 80%.
Applying the new pseudo-functions techniques also improves the quality of data for analysis in multiphase flow situations.