Amott test

The two Amott indices are often combined to give the Amott–Harvey index. It is a number between −1 and 1 describing wettability of a rock in drainage processes. It is defined as:

${\displaystyle AI=I_{w}-I_{o}}$

Figure 1: Amott–Harvey index and USBM number calculation.

These two indices are obtained from special core analysis (SCAL) experiments (porous plate or centrifuge) by plotting the capillary pressure curve as a function of the water saturation as shown on figure 1:

${\displaystyle I_{w}={\frac {S_{spw}-S_{cw}}{S_{or}-S_{cw}}}}$

with ${\displaystyle S_{spw}}$ is the water saturation for a zero capillary pressure during the imbibition process, ${\displaystyle S_{cw}}$ is the irreducible water saturation and ${\displaystyle S_{or}}$ is the residual oil saturation after imbibition.

${\displaystyle I_{o}={\frac {S_{or}-S_{spo}}{S_{or}-S_{cw}}}}$

with ${\displaystyle S_{spo}}$ is the oil saturation for a zero capillary pressure during the secondary drainage process, ${\displaystyle S_{cw}}$ is the irreducible water saturation and ${\displaystyle S_{or}}$ is the residual non-wetting phase saturation after imbibition.

A rock is defined as:

• Water wet when the Amott–Harvey index is between 0.3 and 1,
• Weakly water wet when the Amott–Harvey index is between 0 and 0.3,
• Weakly oil wet when the Amott–Harvey index is between −0.3 and 0,
• Oil wet when the Amott–Harvey index is between −1 and −0.3.

• Capillary pressure
• Imbibition
• Leverett J-function
• Multiphase flow
• Relative permeability
• TEM-function
• Rise in core – An alternate Reservoir Wettability Characterization Method
• Lak wettability index

• Dake, L.P., "Fundamentals of Reservoir Engineering", Elsevier Scientific Publishing Company, Amsterdam, 1977.
• Amott, E., "Observations relating to the wettability of porous rock", Trans. AIME 219, pp. 156–162, 1959.

• Fluid flow in porous media : facts
• Fundamentals of Wettability
• Multi-phase Saturated Rock Properties: Wettability: Laboratory Determination