Mudar Asks PERM:
I am thinking that to simulate saturation properly in the reservoir by SHF via Pc, it is more relevant to use vertical plugs rather than horizontal as common, because water is sucked up by capillarity force mainly vertically. Please provide your view with explanation.
Dr. Jonathan Bryan from PERM Answers:
Thank you for your question, it is an excellent one. The key to this test is that you want to be able to measure the capillary pressure curve for your system (Pc vs. Sw). The output from this measurement is the water saturation in the core for any given capillary pressure. So now we consider what controls capillary pressure. In general, we think of this as being set by the pore size distribution of your rock system. In that case, so long as you are sampling a section of rock that has the desired PSD to represent your formation, then it should not matter whether the core plug is horizontal or vertical.
There is a lot of discussion in petrophysics (and rightly so) around the concept of anisotropy (kv/kh is not equal to one). But this is a discussion of PERMEABILITY, i.e. it affects the rate at which fluids move through the system under a given pressure drop. In the case of a capillary pressure experiment, we are not measuring rate, but rather we measure equilibrium steps. In other words, we apply a given level of capillary pressure and wait until saturations are constant, and measure saturation at that time. So in that case, whether permeability is horizontal or vertical doesn’t matter, the only thing that matters is the arrangement of pores and how this will lead to trapping.
NOTE: This assumes that your capillary pressure test is something like an Amott system or a centrifuge, where flow can occur at all faces of the core. If you are running a core flood (linear displacement) and there is a permeability barrier to flow in the middle of the core, then fluids can’t move across this barrier. In that case then yes, horizontal vs. vertical plugs will change your answer. But aside from that, you should be okay with the plugs you already have.
Dr. Jonathan Bryan