Journal article

Improved scaling technique for two-phase pressure- saturation relationships

Current methods of scaling imbibition and drainage pressure- saturation data scale the capillary pressure head using ratios of surface tension, constant intrinsic contact angle, fluid density difference and bubbling pressure. These methods are applicable to scaling either the main drainage or imbibition curve for different fluid pairs. However, for a given fluid pair, scaling of the drainage to the imbibition curve is generally unsatisfactory. For the drainage to imbibition case, the maximum error in computed saturations typically occurs at saturations representative of the funicular zone. It is proposed that an empirical functional relationship between advancing and receding apparent contact angles for a specific porous medium can be used to improve the scaling of imbibition to drainage pressure-saturation data for organic liquid-water systems. The Leverett J scaling function is modified by including the ratio of the apparent contact angles as a new scaling term. In the term cos (φR)/cos(φA)p, the advancing apparent contact angle is first corrected for the combined effects of hysteresis and surface roughness by a constant exponent p. The exponent p is equal to the power of the fit of the advancing apparent contact angle, φA, to the receding apparent contact angle, φR. The magnitude of the correction appears to be a characteristic of the medium; however, more laboratory tests are needed for verification. The scaling procedure is tested for a limited series of fluid pairs in several porous media that are characterized by differing pore size distributions and granular compositions. The scaling technique is inadequate, however, for systems subjected to forced imbibition.


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