Fundamentals of Fluid Flow in Porous Media

Chapter 2

Multi-phase Saturated Rock Properties:

Phase Trapping

As the capillary pressure is reduced to zero, the value of S_nw does not decrease to zero, but reach to the non-wetting residual phase saturation, S_nwr. As a result, the complete recovery of oil from water-wet oil bearing reservoirs by imbibition capillary forces is impossible.  The same can be said with regard to the wetting phase, i.e., complete removal of the wetting phase from the porous medium by drainage displacement mechanism is impossible. Capillarity plays a very important role in the displacement of one immiscible fluid by another immiscible fluid. The detailed pore structure of the porous medium (pore geometry and pore topology) governs the fluid-fluid interfaces established within the porous medium, i.e. the way they interact with one another and the manner of hierarchy of advancement.  Entrapment of one fluid by another immiscible fluid during the course of an immiscible displacement is the net result of the interaction of capillary forces at the microscopic pore level.  Because pores differ in size and geometry, the presence of a given number of fluid-fluid interfaces does not give rise to the same capillary pressure value.

There are different trapping mechanisms: Snap-Off, Bypassing and Jamin Effect.