Analysis of Internal Wellbore Flow

Abstract

Most two-phase geothermal wells are located in fractured rocks and intersect a few major feedzones. It is well known that internal wellbore flow between feedzones often occurs during warmup or pressure recovery periods. The internal flow can occur even when the reservoir is initially in pressure equilibrium, because of the different phase composition that develops within the wellbore. Internal flow can cause large apparent pressure drawdowns and significantly affect pressure and temperature surveys as well as pressure buildup tests. This paper presents an analytic method for using static pressure surveys to calculate internal flowrates between two zones when the reservoir characteristics are known. Conversely, the transmissivity of the feedzone with the lowest transmissivity can be calculated from measurements of internal flowrates and wellbore pressures.