Changes

A modification of the test in general use first prepares the sample by centrifuging it in brine. This is followed by centrifuging in oil to [http://petrowiki.org/Glossary%3AIrreducible_water_saturation irreducible water saturation]. The Amott procedure is then followed, but a combined index—the Amott-Harvey wettability index<ref name=pt05r26>Boneau, D. F., Clempett, R. L., 1977, A surfactant system for the oil wet sandstone of the North Burbank unit: Journal of Petroleum Technology, v. 29, p. 501–506., 10., 2118/5820-PA</ref> is calculated by subtracting the displacement by oil ratio from the displacement by water ratio. Figure 2 shows these volumes, and Equation 2 gives the calculation:

A modification of the test in general use first prepares the sample by centrifuging it in brine. This is followed by centrifuging in oil to [http://petrowiki.org/Glossary%3AIrreducible_water_saturation irreducible water saturation]. The Amott procedure is then followed, but a combined index—the Amott-Harvey wettability index<ref name=pt05r26>Boneau, D. F., Clempett, R. L., 1977, A surfactant system for the oil wet sandstone of the North Burbank unit: Journal of Petroleum Technology, v. 29, p. 501–506., 10., 2118/5820-PA</ref> is calculated by subtracting the displacement by oil ratio from the displacement by water ratio. Figure 2 shows these volumes, and Equation 2 gives the calculation:

:<math>\mbox{Index} = \overline{BC}/\overline{BD} - \overline{DE}/\overline{DB}</math>

:<math>\mbox{Index} = \frac{\overline{BC}}{\overline{BD}} - \frac{\overline{DE}}{\overline{DB}}</math>

The range of values and the corresponding wettability characteristics are listed in Table 1.

The range of values and the corresponding wettability characteristics are listed in Table 1.