A Comparative Study of Wettability Test Methods Based on Experimental Results From North Sea Reservoir Rocks

Abstract

ABSTRACT Three methods are widely accepted for evaluation of the wetting properties of a rock/fluid system: 1) The Amott test, 2) The USBM-test and 3) Contact angle measurements. In this work the Amott test and the USBM-test have been run in a combination procedure on reservoir rock samples, while contact angle measurements were performed on quartz surfaces. Nine core plugs from two reservoirs in the North Sea were tested in native state and then cleaned and retested. The experiments were run at 80°C with separator crude oil and synthetic formation water. The paper includes a detailed analysis of the experimental results and the experiences gained with respect to wettability testing, apparatus and procedures, core plug preparation techniques, cleaning methods and measurement reproducibility of wettability tests. The results from the wettability testing show that the Amott index and USBM-index coincide very well, and that a test procedure combining Amott and USBM is superior to single tests. The results also show that the cleaning procedure used in this work did not render the plugs completely water wet. This could be due to content of oil wetted minerals or remaining organic matter. The results from the contact angle measurements on clean quartz show that the system is more water wet than indicated by the Amott/USBM test. This contact angle behavior confirms the interpretations based on the cleaning and wettability tests.