Relating have been determined between wettability and the two-phase relative permeability saturation properties of three consolidation intergranular cores. Wettability was defined by the contact angel (θ), measured external to the porous medium, and by the ability of a fluid to spontancously imbibe into the porous system. Close control over the wettability was achieved in these tests by using synthetic cores composed of polytetrafluoroethylene (PTPE) and various pure fluid paris which displayed essencially uniform wetting behaviour with the solid. The PTPE media, which were of widely differing porousity and permeability, provided systems of fixed pore geometry which were ideal for systematic studies of the wettability variable. Certain comparisons with published work suggested that the PTPE cores were representative models of naturally occurring intergranular porous media. Results determined during the study suggested that wettability effects may predominate over influences from the detailed pore structure.
Relative permeability test results indicated that the most efficient immiscible displacement was obtained with fluids capable of spontaneously imbibing into the porous media. Relative permeability saturation relations were media. Relative permeability saturation relations were virtually independent of (θ) for displacements with imbibing fluids. As (θ) was increased through values for which imbibitions did not occur, a consistent shift in the relative permeability properties of both phases was found when the media contained an initial irreducible saturation of the displacing phase. For drainags or forced displacements from a core initially saturated with one fluid, relative permeability curves were little affected when the system contact angel through the displacing phase was varied over the range of 180 to 90 degrees. The sensitivity of the relative permeability relations to contact-angel changes was strongly influenced by the saturation history of a core.
THE EFFECT of wettability on immiscible displacement has been studied by many investigators over the past few decades(1). It is well recognized that the relative wetting preference displayed by oil and water for the reservoir rock has a strong influence on the behaviour of a waterflood or natural water drive. Wettability has, in fact, been described as the single most important variable affecting the recovery history of a Waferflood(2,3). Reservoir performance calculations and estimates of residual oil saturation are often based on laboratory flow tests with representative core samples believed to possess the wetting characteristics of the reservoir. An accurate assessment of the residual oil saturation is also very important for the evaluation of tertiary recovery processes(4). The influence that wettability has on the microscopic distribution and configuration of residual oil within the pore spaces of the rock could be important in the design and application of surfactant or micro-emulsion floods.
Despite the large past effort that has been devoted to studies of wettability effects in porous media, the large number of recent reports on this subject indicate that many aspects are still not well understood. Rathmell et al.(4) have recently summarized some of the areas of conflict.