Muhammed Asks PERM:
When a wetting phase is displacing a non wetting phase, snapping off occurs as the potential gradient in the wetting phase across the flow segment is lower than the capillary pressure across the same flow segment;
I can’t understand how can capillary pressure oppose the flow of a wetting phase; we are always concerned with spontaneous imbibition (capillary pressure is always with not against).
Hope this finds you well.
All of the appreciation and respect.
Dr. Jonathan Bryan from PERM Answers:
Thank you for your question.
Snap off only occurs in certain cases:
- Strongly water wet, ie the rock needs a water film completely separating the rock from oil.
- High aspect ratio, ie large pore bodies with very small associated pore throats.
When this happens, it is easy for oil to stay in the bodies, where Pc forces are small. So water wants to come in, but it is really hard to get oil out of the bodies. In that case, because water is continuous over the whole rock surface, the water films thicken is the small throats and become continuous. At that point the pore body is snapped off, and oil is trapped because now it is discontinuous and surrounded by water. But this only happens when the two criteria above are met.
Does this make sense?
Dr. Jonathan Bryan