A Comparison Of Steady-State And Unsteady-State Relative Permeabilities Of Viscocities Oil And Water In Ottawa Sand
Authors: Maini Brij , Coskuner Gokhan , Jha Kamal 
Published: March 2010

Relative permeabilities have a central role in numerical simulation of oil recovery processes. Reliable relative permeability data for heavy oil reservoirs are scarce because of the experimental difficulties involved in working with heavy oil systems at reservoir conditions. Often, in computer simulation studies, the laboratory measured relative permeabilities fail to provide satisfactory history march of field operation. While there are several reasons for such failures, including the difficulties in obtaining a representative sample of the reservoir material and differences between hydrodyna1n1e conditions used in the laboratory measurements and the actual reservoir conditions, the experimental errors in relative permeability measurements may be a principal cause.

There appears to be lack of consensus among different laboratories on how relative permeabilities should be measured in heavy oil systems. The measurement techniques currently being used were developed for light oil systems and fail to address experimental problems which are peculiar to heavy oil systems. For example, viscous fingering is rarely a concern in light oil systems but becomes extremely difficult to eliminate when heavy oils are involved. Because of its speed and convenience, the unsteady-state technique is favoured by most laboratories. In light oil systems there appears to be good agreement between relative permeabilities measured by the steady-state method and those obtained by the unsteady-stare technique. However, the equivalence of steady-state and unsteady-state measurements has not been confirmed in viscous oil systems.

Steady-state measurements of relative permeability are generally free from viscous fingering effects. Therefore relatively high flow rates can be used to eliminate capillary end effects. The unsteady-states technique, in viscous oil systems, is likely to suffer from capillary end effects at low rates and from viscous fingering at high flow rates.

The objective of this work was to compare steady-state and unsteady-state relative permeabilities in a viscous oil-water-Ohawa sand system. Both types of measurements were obtained at two temperatures (room temperature and 100 °C). Displacement were carried out at several different flood velocities to determine the effect of flow rate. The results show that in this system the two techniques provide different results. Moreover, the unsteady-state relative permeability was found to vary with flood velocity. The results appear to show that the unsteady-state technique may not be reliable when very adverse viscosity ratios are involved.

Introduction

Production of oil and gas from petroleum reservoirs usually involves flow of two or more immiscible fluids through a porous rock. Multi-phase now in porous media is it complex process that depends on a number of factors, including the absolute permeability; pressure drop; capillary pressure; fluid viscosities; and relative permeability of each phase. Of these the relative permeability is probably the most important parameter in determining the reservoir performance.

Relative permeability, by definition, is a measure or the ability of a porous medium to conduct a given fluid when one or more other immiscible fluids are present. The resistance lo now or a given phase in a multi-phase situation depends primarily on how this phase distributes itself within the porous medium in the presence of other fluids.