Drainage

Drainage:.
Depending on the wetting properties of the fluids there are essentially two different types of displacement in two-phase flow in porous media. In this thesis we are considering drainage displacements where a non-wetting invading fluid displaces a wetting fluid. The opposite case, imbibition, occurs when a wetting fluid displaces a non-wetting fluid. The mechanisms of the displacements in drainage and imbibition are quite different and the two cases should not be confused. Typically, slow drainage is characterized by piston-like motion inside the pores where the invading non-wetting fluid only enters a pore if the capillary pressure is equal to or greater than the threshold pressure of that pore. The threshold pressure corresponds to the capillary pressure in the narrowest part of the pore. However, in imbibition at low injection rate the invading fluid will enter the most narrow pores before any other is considered.