Capillary Forces Flashcards
True or False: Buoyancy tends to drive relatively low-density fluids downwards.
False: it drives it upwards
Surface Tension - ST
forces between liquid and a gas (water and air)
Interfacial Tension - IFT
forces between two different liquids (oil and water)
What are the 3 interfaces possible in reservoirs:
- oil - gas (ST)
- water - gas (ST)
- oil - water (IFT)
The angle between the liquid and solid phases is called the __ __
contact angle
True or False: Contact angles are always measured in the denser fluid phase
true
Cohesive forces are at the fluid - ___ interface
fluid
Adhesive forces are at the ___ - fluid interface
solid
Non-wetting
Contact Angle > 90°
*WATER WET
Wetting
Contact Angle < 90°
- OIL WET
What are the parameters which distinguish between strongly water-wet, to intermediate, to strongly oil-wet: (degree range)
0° - 70° strongly water-wet
70° - 110° inter. wettability
110° - 180° strongly oil-wet
True or False: A oil-wet system will exhibit greater oil recovery under water flooding.
FALSE
Why: a water-wet system would be more beneficial as the water molecules would adhere to the mineral grains and force the oil to other void spaces (hopefully creating flow towards producer)
Capillary Seal
the seal for a reservoir that is usually water-wet with a low (but finite) permeability
*typically a shale
Capillary Pressure
the effect of IFT which creates a finite pressure between immiscible fluids
- Pc = Poil -Pwater
Drainage
process of decreasing the wetting phase saturation
Imbibition
process of decreasing the non-wetting phase
saturation
*caused by trapping of non-wetting phase
Hysteresis
the effect of having different drainage and imbibition curves
Irreducible Water Saturation - Swi
asymptotic min value of water saturation.
- when there is no connected water in pore space
- residual water exists only as droplets or films coating grains, depending on wettability
Irreducible Oil Saturation - Soi
asymptotic min value of oil saturation on imbibition curve
- oil phase become discontinuous
- residual oil exists only as droplets or films coating grains, depending on wettability
- oil can no longer be driven out of rock by hydraulic means
