Our objective was to determine the effects of frequently used core-cleaning liquids on water surface tension.  It is common practice to clean core samples in order to remove residual oil, water, or salt in a sample before making effective porosity, permeability or capillary pressure measurements in the laboratory. These laboratory measurements, however, depend on the amount of liquid bound to the core’s granular surfaces which, in turn, is governed by the surface tension of the sample.  Therefore, by cleaning a sample with a liquid that has a different surface tension than the in situ liquid, the surface tension of the sample is changed, leading to laboratory measurements of transport properties that may not be characteristic of those in situ.

We performed two different experiments to characterize the changes in surface tension due to the presence of the following common cleaning agents: hexane (C₆H₁₄), methanol (CH₄O), toluene (C₇H₈), and trichloroethylene (C₂HCl₃).  The first set of experiments involved measuring surface tensions using capillary tubes. Initially, we measured the surface tension of (1) each contaminant, (2) distilled water, and (3) tap water and compared our values to those published in order to verify our measurement procedure. We then measured the surface tensions of distilled water in capillary tubes that were “contaminated” with each of the four cleaning agents mentioned above. The second set of experiments involved measuring capillary pressures in a sintered glass bead core using a capillary pressure apparatus. We first measured the capillary pressure of distilled water in the glass bead plug to serve as our reference. We then measured the capillary pressure of distilled water in the same plug after “contaminating” the plug with a single cleaning agent, repeating the experiment for each cleaning agent.  Our results suggest that the cleaning agents do change the surface tension of the samples. The change in surface tension that is due to the presence of the contaminant decreases with the amount of time water is flowed through the sample.  Therefore, we conclude that before transport properties are measured in the laboratory, it is important that the core sample be at the in situ wetting phase.

This project was possible because of support provided by Prof. Hartmut Spetzler, University of Colorado, Boulder.