Is it futile to measure relative permeability for heavy oil reservoirs?

The importance of relative permeability curves in calculations of reservoir performance can hardly be overstated. Both oil water and oil-gas two-phase relative permeability functions are crucial parts of the input data for heavy oil reservoir simulation studies of primary depletion and thermal recovery processes. The simulation results are often very sensitive to small changes in the relative permeability curves. Therefore, substantial effort and resources are spent in obtaining laboratory measurements of relative permeability. However, as is often the case, when the history match is unsatisfactory: the parameter that is most likely ro be adjusted is the relative permeability. is It, then, futile to measure relative permeability in heavy oil systems? This paper attempts to answer this question by examining the theoretical and experimental problems in applying conventional relative permeability concepts and methods to heavy oil systems. The experimental difficulties can start in the very first step of obtaining a representative core sample. The core damage occurring in coring and core handling operations can have significant effect on the measured relative permeability. A brief review of how heavy oil/water (or heavy oil/gas) relative permeability of unconsolidated sand formations is measured in the laboratory, is presented with focus on possible sources of errors. The role of viscous fingering in relative permeability measurements and the conditions under which the laboratory measurements fail to represent the field behaviour are discussed. It is shown that the laws governing simultaneous low of heavy oil and water (or heavy oil and gas) through porous media hare not yet been clearly formulated. The now description based on the relative permeability concept, although not as convenient and powerful as it is in the conventional oil systems, is still the best available alternative.