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Surface Forces and Capillary Pressure

Surface Forces and Capillary Pressure

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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Fluid Rock Interaction

• The study of fluid rock interaction is of fundamental importance to reservoir engineering. Not only does such interaction influence fluid flow through the reservoir, it also plays a dominant role in the distribution of fluids within the reservoir’s pore space and, more importantly, it dictates the maximum amount of a fluid that can be withdrawn from the reservoir.
• We shall start with the simplest form of such interaction and then move up to more complex ones.

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Surface and Interfacial Tension

• In dealing with multiphase systems, it is necessary to consider the effect of the forces at the interface when two immiscible fluids are in contact.
• When these two fluids are liquid and gas, the term surface tension is used to describe the forces acting on the interface.
• When the interface is between two liquids, the acting forces are called interfacial tension.

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Surface and Interfacial Tension(cont.)

• Consider the two immiscible fluids, air (or gas) and water (or oil) as shown schematically in following Figure.
• A liquid molecule, which is remote from the interface, is surrounded by other liquid molecules, thus having a resulting net attractive force on the molecule of zero.

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Surface and Interfacial Tension(cont.)

• A molecule at the interface, however, has a force acting on it from the air (gas) molecules lying immediately above the interface and from liquid molecules lying below the interface.
• Resulting forces are unbalanced and give rise to surface tension. The unbalanced attraction force between the molecules creates a membrane like surface with a measurable tension, i.e., surface tension.

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Surface and Interfacial Tension(cont.)

• The following figure can be defined in terms of an immiscible fluids, oil and water, in which case the resulting unbalanced forces at the surface give rise to interfacial tension.
• The unbalanced attraction force between the molecules creates a membrane like surface with a measurable tension such as surface or interfacial tension.

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Surface and Interfacial Tension(cont.)

• Therefore, the interfacial or surface tension has the dimensions of force per unit length usually expressed as dynes/cm, and is usually denoted by the symbol σ.
• The interfacial tension or surface tension entirely fluid property and not a petroleum reservoir rock property.
• High IFT indicates immiscible fluids and Low IFT indicates miscible fluids..

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Surface and Interfacial Tension(cont.)

• If a glass capillary tube is placed in a large open vessel containing water, the combination of surface tension and wettability of tube to water will cause water to rise in the tube above the water level in the container outside the tube as shown in following Figure.

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Surface and Interfacial Tension(cont.)

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Surface and Interfacial Tension(cont.)

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Surface and Interfacial Tension(cont.)

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Effect of Pressure and Temperature on IFT

• Since gas, oil, and water coexist at a variety of high-pressure and high-temperature conditions in petroleum reservoirs, it is important to understand the effect of these variables on IFT or ST.
• The variation of IFT or ST with temperature and pressure strongly influences the transport of fluids in a reservoir and therefore are fundamental to the understanding of the role of interfacial forces in oil recovery.
• Surface tension generally decreases with an increase in pressure and temperature. As temperature increases, the kinetic agitation of the molecules and the tendency of the molecules of fly outward increases, resulting in a decrease in ST values as shown in Figure

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Effect of Pressure and Temperature on IFT

• The effect of pressure on ST is also somewhat similar to the temperature effect. The high-pressure gas phase tends to develop miscibility toward the companion liquid phase thereby reducing ST as pressure increases.

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Capillary Pressure

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Capillary Pressure

• Capillary phenomena occur in pours media when two or more immiscible fluids are present in the pore space.
• A difference in the pressure across the interface due to interfacial energy between two immiscible phases results in a curvature of the interface.
• The capillary forces in a petroleum reservoir are the result of the combined effect of the surface and interfacial tensions of the rock and fluids, the pore size and geometry, and the wetting characteristics of the system.
• The rise or depression of fluids in fine bore tubes is a result of the surface tension and wetting preference and is called capillarity.

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Capillary Pressure(cont.)

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Capillary Pressure(cont.)

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Capillary Pressure(cont.)

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Capillary Pressure(cont.)

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Capillary Pressure(cont.)

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Surface Forces and Capillary Pressure

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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