Wettability

Reservoir rock properties

Professor Abdulla Ali Al-Dombi

Petroleum Production Engineer

مدونة بالعربية

https://aldambi.blogspot.com/

In English

https://aldambi2.blogspot.com/

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Wettability

• Wettability is defined as the tendency of one fluid to spread on or adhere to a solid surface in the presence of other immiscible fluids.
• The three droplets are then observed from one side as illustrated in below Figure. It is noted that the mercury retains a spherical shape, the oil droplet develops an approximately hemispherical shape, but the water tends to spread over the glass surface.

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Wettability(cont.)

• Wettability refers to the interaction between fluid and solid phases.
• In a reservoir rock the liquid phase can be water or oil or gas, and the solid phase is the rock mineral assemblage.
• This spreading tendency can be expressed more conveniently by measuring the angle of contact at the liquid-solid surface.
• This angle, which is always measured through the liquid to the solid, is called the contact angle(θ).

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Wettability(cont.)

• As shown in following Figure, as the contact angle decreases, the wetting characteristics of the liquid increase.
• Complete wettability would be evidenced by a zero contact angle, and complete non-wetting would be evidenced by a contact angle of 180°.
• There have been various definitions of intermediate wettability but, in much of the published literature, contact angles of 60° to 90° will tend to repel the liquid.

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Wettability(cont.)

• The wettability of reservoir rocks to the fluids is important in that the distribution of the fluids in the porous media is a function of wettability.
• Because of the attractive forces, the wetting phase tends to occupy the smaller pores of the rock and the non-wetting phase occupies the more open channels.

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Types of Wettability

• Water-wet: in this wettability state, the rock surface (large and small) has preference for the water phase rather than the hydrocarbon phase.
• Therefore, hydrocarbon phases (gas and oil) are contained in the centers of the pores and hence do not cover any of the rock surfaces as shown in Figure.

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Types of Wettability(cont.)

• Oil-wet: this wettability state is exactly the opposite of the water-wet state; the relative positions of the oil and water are reversed.
• Therefore, hydrocarbon phases (gas and oil) are covered of the rock surfaces as shown in Figure.

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Types of Wettability(cont.)

• Intermediate wet: in this wettability state, the rock surface has preference for both the oil and water phases.
• In neutral wettability, the rock surface has equal tendency for oil and water to wet the rock surface. intermediate wet if the contact angle is equal 90.
• The reservoir wetting state may further be divided into strongly-water-wet, weakly-water-wet, strongly-oil-wet and weakly-oil-wet.

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Types of Wettability(cont.)

• Mixed wettability: in this wettability state, the smaller pores are occupied by water and are water-wet, whereas the oil preferentially wets the interconnected larger pores.
• Water/ oil water is often the wetting fluid
• Water/ gas water is wetting fluid
• Oil/ gas oil is the wetting fluid

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Types of Wettability(cont.)

• The wettability of reservoir depends on the following factors:
• Oil composition.
• solid properties.
• Formation brine and its pH.
• Pressure and temperature.
• Thickness of the connate water layer.

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Wettability

Reservoir rock properties

Professor Abdulla Ali Al-Dombi

Petroleum Production Engineer

مدونة بالعربية

https://aldambi.blogspot.com/

In English

https://aldambi2.blogspot.com/

​

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