6. Surface tension and wettability (1).pptx

Ingeniería en Petroleos

1. R eservoir rock and fluid characterization Surface tension and wettability

2. S urface and interfacial tension The surface tension is defined as the force exerted on the boundary layer between a liquid phase and a vapor phase per unit length. When the interface is between two liquids, the acting forces are called interfacial tension. All molecules are attracted one to the other in proportion to the product of their masses and inversely as the squares of the distance between them. The unbalanced attraction force between the molecules creates a membrane like surface with a measurable tension, i.e., surface tension

3. S urface and interfacial tension The surface or interfacial tension has the units of force per unit of length, e.g., dynes/cm, and is usually denoted by the symbol σ. It can be measured by using a tensiometer .

4. S urface and interfacial tension The water will rise in the tube until the total force acting to pull the liquid upward is balanced by the weight of the column of liquid being supported. Where: σgw = surface tension between air (gas) and water (oil), dynes/cm θ = contact angle r = radius, cm

5. S urface and interfacial tension where: h = height to which the liquid is held, cm g = acceleration due to gravity, cm/sec2 ρw = density of water, gm/cm3 ρair = density of gas, gm/cm3 T he density of air is negligible in comparison with the density of water.

6. S urface and interfacial tension Surface tension Interfacial tension Where: ρo = density of oil, gm/cm3 σοw = interfacial tension between the oil and the water, dynes/cm

7. WETTABILITY T endency of one fluid to spread on or adhere to a solid surface in the presence of other immiscible fluids. 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. Complete wettability would be evidenced by a zero contact angle, and complete nonwetting would be evidenced by a contact angle of 180°

8. WETTABILITY The contact angle between 60 and 90 degrees usually means intermediate wettability.

9. wettability Contact angle can be calculated with:

10. wettability Absolute water-wet Strongly water-wet Intermedier (neutral) Strongly oil-wet Absolute oil-wet

11. Wettability measurement Young-Laplace (drop fitting) method: the drop contour can be mathematically described by adapting the Young-Laplace equation for curved boundary areas. The contact angle is determined as the slope of the contour line at the three-phase contact point.

12. Wettability measurement

13. Problems A capillary of 2mm diameter is dipped in water container. The contact angle measured is 20 degrees and the surface tension is 50 dynes/cm. Determine the height of water inside the capillary. If the upward force is 250 dynes assuming the same radius and contact angle, what is the surface tension .