The document discusses surface tension and wettability as they relate to reservoir rock and fluid characterization. It defines surface tension and interfacial tension as the force exerted along the boundary between different phases. The surface tension can be measured using a tensiometer. Wettability refers to how fluids spread on solid surfaces in the presence of other immiscible fluids, and is quantified by the contact angle between the fluids. Contact angles are used to classify rocks as water-wet, oil-wet, or intermediately wetted.

1. RESERVOIRROCKANDFLUID
CHARACTERIZATION
SURFACE TENSION AND WETTABILITY

2. SURFACEANDINTERFACIAL
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. SURFACEANDINTERFACIAL
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. SURFACEANDINTERFACIAL
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. SURFACEANDINTERFACIAL
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
The density of air is negligible in comparison with the density of water.

6. SURFACEANDINTERFACIAL
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
• Tendency 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
1. 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.
2. If the upward force is 250 dynes assuming the same radius and
contact angle, what is the surface tension.