Theory and Analysis of Injectivity Tests on Horizontal Wells

Abstract

Summary This work presents information on the pressure behavior at a horizontal water-injection well completed in an oil reservoir. We show that, quite remarkably, the pressure and pressure derivative behavior is similar to that of the single-phase solution calculated with oil properties evaluated at initial water saturation. This behavior is quite different from the injectivity solution for a vertical well where, except at early times, the injectivity solution is similar to the single-phase solution based on water properties. It is shown that flow regimes can be identified with the standard log-log diagnostic plots. The Thompson-Reynolds steady-state theory for multiphase-flow well testing is applied to derive a simple accurate approximate analytical solution for the wellbore pressure during injection for both the horizontal and vertical well cases. The horizontal well solution is completely new. Unlike the previous solutions for the vertical well case, we have incorporated a skin zone based on Hawkins' formula. The analytical solution, verified by reservoir simulation results using hybrid grids and local grid refinement, shows that the movement of injected water in a damaged zone has a strong and distinctive effect on both the pressure and pressure-derivative behavior at early times. Based on the analytical solution, we propose procedures for analyzing pressure data from injectivity tests.