Implementation of Multirate Technique to Measure Relative Permeabilities Accounting

Abstract

Abstract A practical implementation of the multi-rate steady-state technique to determine relative permeabilities from steady- state floods and its comparison with the standard steady-state technique is the main subject of the paper. The multi-rate technique is based on the theory of two-phase flow, and facilitates analytical corrections of relative permeabilities to account for capillary end effect. This is especially of practical importance if the experiment is performed at low rates when the relative role of capillary forces increases. Normally, it is recommended to perform flooding experiments at high rates and/or on long cores to suppress capillary effects. Though this approach ensures simplicity in the interpretation procedure it disregards several factors one of which is that the relative permeabilities may depend on the rate. Proper account for capillary effects makes usage of long cores and high rates unnecessary. A number of steady-state core floods have been performed at different rates varying from a high rate typically used in the lab experiments to a low rate approaching the range of typical reservoir rates. The experimental results, i.e. a set of relative permeabilities depending on the rate, have been interpreted both without and with account for capillary end effect. The previously developed analytical corrections for capillary effects were implemented in the interpretation. The results of analytical interpretation are quality controlled by numerical simulation of the experiments. It is shown that much of the difference observed in relative permeability curves and residual saturations measured at different rates can be explained by the influence of capillary end effect. P. 901