Relative permeability is perhaps the most important parameter in describing underground flow behavior of immiscible fluids. In recent years, thermal recovery methods have gained in importance. This requires an understanding of temperature effects on flow characteristics of reservoir fluids.
This paper presents an experimental study dealing with temperature effects on relative permeabilities of oil-water systems. Results indicate that the curves are independent of temperature as are the end point saturations. There is a decrease in "practical" residual oil with temperature saturation due to a change in the shape of the fractional flow curve.
Relative permeability curves basically represent multiphase flow of fluids as controlled by the interaction of viscous and capillary forces within a porous medium. Altering temperature can cause changes in the relative levels of these two forces. This, in turn, may affect the flow characteristics of the different fluids within the porous medium.
Temperature effects on relative permeabilities were first studied by Wilson who observed no temperature dependence. Following that, a number of studies were conducted that showed distinct changes in end point saturations. All these studies observed a decrease in the residual oil saturation, , with an increase in temperature. Those that studied changes in irreducible water saturation, , found it to increase with temperature. One reason given for these changes was an increase in water-wetness of the porous media with an increase in temperature. Lo and Mungan conducted steady state runs to determine relative permeabilities. They observed that if the viscosity ratio remained constant, relative permeability curves were independent of temperature. permeability curves were independent of temperature. The purpose of this study was to determine the effect of temperature on relative permeabilities and to provide explanations for any observed effects. Further, dependence of or on initial water saturation was also studied.
The schematic diagram of the equipment is shown in Fig. 1. The system consists of a Ruska constant-rate, positive-displacement pump that can independently flow oil from on cylinder and water from the other. Lines from both these cylinders enter an air bath that is capable of maintaining a constant temperature (+/- 0.4F) up to 650F. Once inside the air bath, both lines flow through heating coils and capillary tube viscometers, the latter to measure fluid viscosities at temperature and pressure. After the viscometers, the lines flow into a four-way switching valve that is controlled from outside the air bath. This valve is capable of withstanding temperatures up to 750F and pressures up to 500 psia. One of the outlets from this valve goes out of the air bath, through a condenser and a back-pressure regulator, and into a collection vessel. The other outlet goes into the core which is composed of Ottawa sand packed in a stainless steel tube. Bypassing is prevented by applying a confining pressure on the sand through a movable end plug. The core holder itself is pressure on the sand through a movable end plug. The core holder itself is capable of withstanding 10,000 psia confining pressure. On leaving the core, the fluid is cooled in a condenser, then flows through a thick-walled glass capillary metering tube and finally into a pressure bomb.
The porous medium used in this study was unconsolidated Ottawa sand (mesh size 170–200). The pack has a diameter of 1 in. and a length of 7 in. The sand was subjected to a confining pressure of 2000 psi. A pore pressure of 200 psi was used in the runs to keep the fluids in liquid phase pressure of 200 psi was used in the runs to keep the fluids in liquid phase at high temperatures.
Figure 2 shows a schematic of the glass tube that is used to determine the oil produced. The metering technique assumes that the oil and water flow as independent slugs. This is true for pure systems that do not contain emulsion-forming agents. A light emitting diode (LED) source is used to provide light from one side of the tube and a photoelectric cell receives the light on the other side after it has passed through the tube walls and the fluid flowing within.