How to calculate wettability index?
Wettability is determined in three ways:
- Measurement of the contact angle, or the product of the contact angle and the interfacial tension (the last term in Young’s equation)
- Measurement of the relative amounts of oil and water displaced under similar conditions.
How do you know if a rock is wettable?
There are several methods for determining wettability of a rock to various fluids. The main ones are: (i) Microscopic observation This involves the direct observation and measurement of wetting angles on small rock samples. Either a petrographic microscope or SEM fitted with an environmental stage is used.
How is wettability measured?
1 Wettability Analysis. Wettability is the ability of a liquid to spread over a surface. It can be measured by the contact angle between the liquid and the surface. There is a direct relationship between contact angle and surface energy—that is, the contact angle decreases with surface energy.
What is neutral wetting?
The intermediate state between water-wet and oil-wet can be caused by a mixed-wet system, in which some surfaces or grains are water-wet and others are oil-wet, or a neutral-wet system, in which the surfaces are not strongly wet by either water or oil.
How do you measure wetting angle?
In the tilting method, the droplet is placed on the substrate which is then gradually tilted. The advancing angle is measured at the front of the droplet just as the droplet starts to move. The receding contact angle is measured at the back of the droplet, at the same time point.
What makes a rock oil-wet?
Oil-wet rocks preferentially imbibe oil. Generally, polar compounds or asphaltenes deposited from the crude oil onto mineral surfaces cause the oil-wet condition. Similar compounds in oil-base mud also can cause a previously water-wet rock to become partially or totally oil-wet.
What makes a rock water-wet?
Rocks can be classified as water-wet, mixed-wet or oil-wet. When the rock is water-wet, water is preferentially in contact with the mineral when oil is the surrounding phase. The rock is said to be oil-wet when oil is the liquid in contact. The state in between is called intermediate- or mixed-wet.
What is rock wettability?
Wettability is a tendency of fluid to stick to the surface of formation when other types of fluid are present. Wettability of rock is measured by a core analysis in a laboratory and typically a laboratory measure contact angle between the fluid and the rock.
What is oil wet?
When the rock is water-wet, water is preferentially in contact with the mineral when oil is the surrounding phase. The rock is said to be oil-wet when oil is the liquid in contact. The state in between is called intermediate- or mixed-wet.
Can wettability be changed?
Wettability change is normally treated with mutual solvents to remove the rock-oil coating (asphaltene or paraffin precipitation), followed by a strong water-wet surfactant to reduce the tendency of further hydrocarbon precipitation.
How is the Amott-Harvey wettability index calculated?
The Amott procedure is then followed, but a combined index—the Amott-Harvey wettability index 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:
What is the difference between Amott method and neutral wettability indicator?
The most significant deviations occur near the neutral wettability region. The Amott method is more sensitive in this area and may be a better indicator. The Amott method can also be used to indicate mixed wettability if a sample spontaneously imbibes both oil and water.
What are the four basic measurements used in Amott method?
The Amott method uses four basic measurements: 1 Amount of oil spontaneously imbibed 2 Amount of oil forcibly imbibed 3 Amount of brine spontaneously imbibed 4 Amount of brine forcibly imbibed. More
Which is better USBM or Amott test?
Both the Amott and the USBM test are commonly used in the oil industry, but direct comparisons of the two techniques show only minimal correlation. The most significant deviations occur near the neutral wettability region. The Amott method is more sensitive in this area and may be a better indicator.