New Estimate for the Radius of a Condensate Bank from Well Test Data Using Dry Gas Pseudo-Pressure

Abstract

Abstract Published well test analyses in gas-condensate reservoirs where the pressure drops below the dew point are usually based on a two-or three-zone radial composite well test interpretation model to represent condensate dropout around the wellbore and initial gas in place away from the well. Gas condensate specific results from well test analysis are the mobility ratios between the various regions and the condensate bank radius. Unfortunately, for a given region, well test analysis cannot un-couple the storativity ratio from the region radius. The storativity ratio must therefore be estimated separately to obtain the bank radius. In this study, a new method is introduced to estimate the storativity ratios between the different zones as a function of the saturation profile during the test. The paper describes an application of the method to the analysis of a transient pressure test in a gas condensate field in the North Sea. The analysis uses single-phase pseudo-pressures and two- and three-zone radial composite well test interpretation models and yields the condensate bank radius. The calculated condensate bank radius is verified by comparing analytical well test analysis results with results from compositional simulations that include capillary number and inertia effects. It is shown that the proposed relationship between the condensate saturation profile at the time of shut-in and that at the end of shut-in yield a consistent interpretation of build-up data.