A Novel Practical Method to Determine the Crude Oil Brine Rock System Wettability from Modified Amott Test

Wettability measurement of a crude oil–brine–rock (COBR) system is an integral part of the special core analysis (SCAL) since it influences the oil and water distribution and microscopic displacement of the former by the latter in a reservoir rock pore space. Wettability depends on several factors such as the type of rock, oil, and water properties, and the amount of time the pore space has been exposed to a given phase, i.e., oil, water, or both. Amott or its variant, the Amott-Harvey test, is perhaps the most time-honored and accepted method for wettability determination. Given the fundamental characteristics or definition of wettability, the Amott method is the most “logical” because wettability is determined based on the spontaneous and forced displacement of the oil by water and vice-versa. In a typical Amott test for a core sample, four different displacement cycles are required, which can be very time-consuming. We have recently designed a modified Amott method that is based only on the spontaneous displacement, which is carried out simultaneously on a pair of core samples originating from the same formation. Excellent, unambiguous wettability results have been obtained on the tested COBR system that proves the efficacy of our novel approach. Finally, the step-by-step methodology included in our paper demonstrates that it is not only practical and efficient, but also reliable, which can be easily implemented in the wettability determination of a given COBR system.