A Technique For Measuring Steam And Water Relative Permeabilities At Residual Oil In Natural Cores: CT Scan Saturations
Authors: Closmann Philip J. , Vinegar Harold J. 
Published: March 2010

A technique has been developed for measuring the relative permeabilities to steam and water in natural cores at steam drive residual oil saturation under in situ conditions. Liquid saturations were measured by means of CT scans on the natural cores t each equilibrium data point. The technique for pressure drop measurements is essentially the same as that used in previously published work on liquid-liquid systems. The measurement of temperature at the inlet and outlet on the cores permits an estimate of the heat losses during flow. The pressure data and inlet and outlet temperatures are used in calculating the steam and water permeabilities. Relative permeabilities to steam were found to be close to previously published values for gas flow in porous media, after allowance is made for scatter in the results. Relative permeabilityo water appeared to fall somewhat below the relative permeability urve measured by Leverett on coarse sands.The presence of clay mineral in the cores complicates boththe pressure measurement, due to swelling and particle movement, and also the saturation determination. Nevertheless, this technique appears to be a viable method for determining relative steam permeability in porous media in which the absolute permeability is stable.

Introduction

Since the relative permeability to steam plays a significant role in predicting and simulating steamflood performance, it is important to have reliable values for this parameter. The work described here on Peace River cores was initially undertaken as part of the laboratory effort in support of Shell's Peace River steam pilot(1). It was later extended to include core material from the Tulare formation in California. The intention in this work was to develop a method of steam permeability measurement which could be used on natural cores containing their original liquid saturation. Because of the nature of these unconsolidated cores and their tendency to undergo irreversible dimensional changes as the effective stress varies, it was necessary to design a procedure which permitted maintaining a constant overburden stress on the cores until testing was completed. The chief published data on relative permeability to steam are those those for geothermal systems(2, 3, 4, 5), where there is no oil phase presem, and of Trimble and Menzie(6) for stearn mobility In the presence of residual oil. Work at the University of Texas(7) has provided sorne measurements of permeability to steam in conjunction zith surfactant systems and has also produced results in essential agreement with those for steady state nitrogen/waterflow(8). Other published work (9) on external gas drive with vaporization present at various temperatures suggests that the gas phase permeability is only moderately sensitive to temperature. In our work, we made simultaneous measurements of the permeability to stearn and water in natural cores with residual oil present. The chief constraints affecting equipment design and operating procedures in these experiments were the following:Use of original core material containing original in situ fluids.Maintenance of overburden stress on the core during the entire run.Use of the CT scanner to measure saluration in the core.