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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 ${\displaystyle A1}$ and ${\displaystyle A2}$ to calculate the USBM index.

${\displaystyle USBM=log{\frac {A_{\mathit {1}}}{\ A_{\mathit {2}}}}}$

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

${\displaystyle USBM*={\frac {A_{\mathit {1}}-A_{\mathit {2}}}{\ A_{\mathit {1}}+A_{\mathit {2}}}}}$

USBM* varies from -1 to 1 for strongly oil-wet and strongly water-wet rocks, respectively.

See also

• Wetting
• Amott test
• Lak wettability index

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. doi:10.1016/j.engeos.2021.12.001. S2CID 245108452.

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