David from Calgary Asks PERM:
What methodology would you propose for measuring drainage capillary pressure vs. wetting phase saturation? Typical plug perm is
Dr. Jonathan Bryan from PERM Answers:
For tight core plugs our best bet for measuring drainage capillary pressure is through centrifugation. In this approach, we would saturate the core wetting phase (water?) and then displace it with the non-wetting phase (oil or gas). The approach generally taken is to spin at different rpm settings, and at each setting we measure how much production has come out of the core, and by difference how much wetting phase is still present. From there, we know the average saturation in the core. There are different models that can be applied (things like the Hassler-Brunner, Ruth-Wong, Ruth-Forbes, etc) to then estimate the inlet wetting phase saturation.
In an oil-water system, this is pretty much the only way we have for doing the tests (i.e. run the centrifuge and use models to estimate Sw at the inlet). But if you are looking at a gas-water system, then we have other options. If we were to spin at a high centrifuge setting, this would extract maximum water out of the core, i.e. bring the system to Swirr at that centrifuge setting. Then we could take a CT scan of the core, and compare it to a CT scan of the original dry core. From there, we could actually determine a saturation profile within the core. And in fact, since we also know Pc vs. length along the core, it may even be possible to extract a full capillary pressure curve from the single spin.
Dr. Jonathan Bryan