If you are interested in the efficiency from a research point of view, i.e. using outcrop rocks similar to the reservoir. This is possible to perform 2D experiments to capture areal and vertical efficiency. 

If you only have 25-50 mm core plugs (1D flow) you can only get the microscopic efficiency. and the others can only be estimated from mathematical models.

However, I will be very interested if someone  have a different point of view.

Thanks Dr. Carlos for sharing your views.

I still have some clarifications – regarding – securing the details of microscopic efficiency at the laboratory scale.

It’s known that the contact angle (theta), which decides, whether, which fluid-phase has a larger wetting – plays a crucial role in deciding the nature of wettability. While the theoretical definitions are based - with reference to a smooth flat surface, I am not sure whether the same smooth flat solid surface could be expected in a core-plug as well? Or at least, does it remain, nearly flat??  OR,  Are we assuming that the surface of the solid grains tend to remain flat and smooth?

In other words, while contact angle depends on crude oil composition, amount of dissolved gas in solution, pH and salinity of the wetting-phase fluid, and mineralogy of the rock surface, does it still depend on the degree of flatness / smoothness of the solid grain surfaces??

In addition, what is generally encountered in the field is to do with the “Dalmation wetting”, if I am right. In such cases, I am not sure how does the laboratory-scale study, which is either based on strongly water-wet or strongly oil-wet – be translated – to the field scale investigations?

In addition, laboratory-deduced capillary pressure values depend on pore-geometry as well – in addition to the nature of wettability. In this context, Could I assume that the pore-network geometry of the core plugs – before and after drilling – remain the same?

In case, if drilling induces a significant change in pore-network geometry, then, how does the concept of microscopic efficiency at the laboratory scale work out – (as the maximum water saturation during imbibition is going to decide the degree of residual oil saturation to water-flooding) ? In fact, the changes in pore geometry will also influence the profiles of spontaneous and forced imbibition.

Further, given the fact that mixed-wettability favors the phase-continuity of non-wetting phase (oil) fluid as against the water-wet conditions (associated with the discontinuous non-wetting phase), whether the water-wet based laboratory results – be extrapolated to represent the actual field conditions?

I would be glad whoever enlightens me.

Thanks in anticipation.

Suresh Kumar.

 http://www.doe.iitm.ac.in/gskumar/

For contact angle measurement, we must polish the surface because surface roughness adds to uncertainty and creates issues with contact angle measurement. This way, we will have fluid and rock interaction. Some people may say with polishing we are exposing fresh cut minerals which is true. But, we try to age the rock slabs and let the rock and fluids reach to chemical and surface charge equilibrium. In the pores however, we have sharp angle pore edges which is different from polished rocks. Thus, I prefer wettability measurement on cores and have contact angle measurement as a proof. As I said, contact angle measurement will give us information about rock-fluid interaction and it is very valuable. But the angle is not necessarily the same in the pores. 

If you crush the cores you will definitely change the pore geometry, and if you have unconsolidated rocks you may not be able to maintain pore geometry. But, rocks which are well consolidated such as carbonates will maintain their pore geometry after drilling. I worked with carbonates and tight unconventional rocks and they are hard enough to stay tight even under high confined pressure and under huge centrifugal forces.