USBM wettability index explained

The U.S. Bureau of Mines (USBM), developed by Donaldson et al. in 1969, is a method to measure wettability of petroleum reservoir rocks. In this method, the areas under the forced displacement Capillary pressure curves of oil and water drive processes are denoted as

A 1 and A 2 to calculate the USBM index.^{[1] [2]} USBM = log (A _{1})/(A _{2}) USBM index is positive for water-wet rocks, and negative for oil-wet systems.

Bounded USBM (or USBM*)

The USBM index is theoretically unbounded and can vary from negative infinity to positive infinity. Since other wettability indices such as Amott-Harvey, Lak wettability index and modified Lak are bounded in the range of -1 to 1, Abouzar Mirzaei-Paiaman highlighted the bounded form of USBM (called USBM*) as a replacement of the traditional USBM as ^[3]

USBM* = (A _{1} - A _{2})/(A _{1} + A _{2}) USBM* varies from -1 to 1 for strongly oil-wet and strongly water-wet rocks, respectively.

See also

• Wetting
• Amott test
• Lak wettability index

Notes and References

1. Donaldson. E.C.. Thomas. R.D.. Lorenz. P.B.. 1969. Wettability determination and its effect on recovery efficiency. SPE Journal . 9. 1. 13–20.
2. Sharma. M.M.. Wunderlich. R.W.. 1987. The alteration of rock properties due to interactions with drilling fluid components. J. Petrol. Sci. Technol.. 1. 127–143.
3. Mirzaei-Paiaman. A.. 2022. Analysis of the bounded and unbounded forms of USBM wettability index. Energy Geoscience . 3. 1. 94–102. 10.1016/j.engeos.2021.12.001. 245108452. free.