Transition Radial Flow in Slanted Well Test Analysis

Abstract

Abstract The applicability of permanent downhole gauges (PDG) has been proved to be of great contribution to reservoir monitoring and well performance analysis. By the interpretation of any each build-up and/or fall-off from PDG readings it is possible to improve the near wellbore characterization, mainly because PDG signatures usually are not significantly affected by wellbore storage. This last advantage has motivated this work to review and further evaluates flow regimes in the wellbore surroundings that wasn't possible to be characterized due to wellbore storage effects. From this assumption, this paper presents a new study of transient pressure behavior in deviated wells. The investigation was based on an analytical solution derived for an infinite radial extent reservoir limited with both bottom-up impermeable reservoir boundary layers and uniform flow condition at the wellbore. From that, type curves were generated for different slant angles of the well and dimensionless formation thickness. The analysis showed a new flow regime called Transition Radial Flow (TRF), in a zone where, before PDG, was mainly dominated by wellbore storage. The TRF develops between early time and late time infinite acting radial flow (IARF), where the reservoir permeability can be estimated before the IARF development. Together, an alternative procedure was developed for interpreting transient pressure data using this new flow regime. This procedure was based on the TDS (Tiab's Direct Synthesis) technique, which allows interpreting the pressure data through a direct analysis of the derivative curve. The solution presented here provides a feasible alternative to the analysis of short duration pressure derivative curve in slanted wells.