Multiphase flow of fluid through porous media and recovery efficiency are controlled by the relative permeability of each phase, fluid viscosity, pressure drop, capillary pressure and permeability. Among these, relative permeability is about the least understood. Moreover, obtaining representative relative permeability data is often difficult because of the uncertainties in the measurements and wettability of the rock.

Here we discuss the uncertainties in the choice of the commonly used relative permeability test methods and also evaluate the performance and quality of data provided by different special core analysis laboratories. All tests were performed at very well controlled ambient laboratory conditions and with lab oil to simplify the measurements.

Commercial laboratories that provide core analysis services to the industry were each given a set of carbonate plugs with similar properties. The grouping criteria included hydraulic unit zonation and petrophysical rock-typing. Each set of samples was further divided into three subsets to examine three different measurement methods. The methods investigated were steady state, unsteady state and centrifuge water-oil relative permeability. Each laboratory followed the same detailed procedures designed to reduce uncertainties. To allow for better comparison between laboratories, the procedures also specified oil-water viscosity ratios for use in each test, as well as water injection rates and Bond number criteria.

Furthermore, we emphasize the importance of establishing robust QC/QA protocols for special core analysis data and level of engagement required between clients and lab vendors throughout the data acquisition program. There was wide variability in the relative permeability data obtained.