Determination of relative wettability of porous sandstones by imbibition studies

Abstract

The effective wettability of consolidated sandstone rocks has been determined using the Washburn equation by measuring the rate of imbibition of water, ethanol and their mixtures into cores and thin rectangular sections. The rocks behaved as low energy surfaces with a critical surface energy of spreading, as defined by Zisman, of 28 mN m-I. This behaviour is believed to be caused by clay particles or organic material present on the pore surfaces. A discussion of the validity and limitations of the Washburn equation for obtaining effective wettabilities in consolidated porous media is presented. The general conclusion is that effective wettability depends on the preparation and general conditions of the samples.

On the Use of Washburn's Equation in the Analysis of Weight–Time Measurements Obtained from Imbibition Experiments

“…Among the experimental methods existing, two are the most commonly utilized: measurements of penetration distance (5, 10 -17, 19, 20, 22) or weight gain (4,6,9,18,20,21) and time spent on it. Both methods use Washburn's equation (23) as a basic model to analyze the experimental data, since although it neglects inertia effects, which can be especially important during the initial stage of the penetration process, and the viscous drag of the liquid due to dissipation near the contact line, some studies point out that this equation is valid at the macroscopic scale, despite its possible weakness at the porous level (24,25).…”

Influence of the Meniscus at the Bottom of the Solid Plate on Imbibition Experiments

“…This equation predicts a linear behavior when the square of the increase of weight of the porous solid due to the liquid imbibition is plotted as a function of the time. However, this straight-line relationship is not observed when the experimental results are analyzed (1,3,5,(10)(11)(12). In a previous paper, we proved that the change of the slope shown by the experimental curves was caused by the superposition of two physical phenomena: the penetration of the liquid and the effect of the liquid surface tension of the liquid on the solid when the solid is put in contact with the free surface of the liquid (14).…”

“…This technique was proposed in order to avoid the difficulties of measurement that arise when the liquid front was not visible or did not reflect the real progression of the fluid into the porous solid (1,3,5,(10)(11)(12)). Washburn's equation is the main tool for the analysis of the 1 To whom correspondence should be addressed.…”

Comparison of the Use of Washburn's Equation in the Distance–Time and Weight–Time Imbibition Techniques

“…This equation predicts a linear relationship between the square of the advanced distance, or the square of the increase of weight, and time, depending on the experimental technique employed. However, when the experimental data are plotted, the slope of the experimental lines is not a constant in the whole range (4,(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16). The changes of slope of the curves obtained from the height method are a consequence of the choice of the distance-time reference system (21), whereas those changes observed in the curves from the weight technique are caused by the superposition of the imbibition and the effect that appears when the contact between solid and liquid is established (22).…”