Some basic questions of the RE about the relative permeability

[typndvd1979]

Hello everybody.

Pls help to answer, Tks

Why the Krw@Sor is low, compared to the Kro @ Swi ? What is the basic of theory ?

[vinomarky]

Think about it in terms of how the fluids sit in the pore throats. At Swi - assuming water wet - a water film lines the grains and pore throats but otherwise presents minimal obstruction to oil globules sliding through. At Sor, you have some left over / snapped off oil globules that are immobile and in some cases sit in the flow pathways, obstructing mobile water trying to get through pore throats.

It's going to be case specific depending on your rock and surface tensions, but this is the sort of mechanism that could be occurring.

[DAH7542]

The explanation given by vinomarky covers water-wet rocks, but the "basic" question by typndvd1979 can go beyond: Why do we observe "Krw at Sor" less than "Kro at Swir" even for oil-wet rocks? I'll let this question for further discussion of all of us here and I'll also provide my point of view. Based on what has been published in the literature, fluids (lets say oil and water) in oil-wet rocks are located in a partly reversed form than in the water-wet case. In oil-wet rocks, water still fills the smallest pores since oil is not able to enter them due to capillary forces higher than buoyancy during hydrocarbon migration. But in the largest pores, the water is present in the middle of the pores while the oil contacts the grain surfaces; although the water doesnt contact the rock surfaces in the largest pores, the literature says "it is usually present in small amounts", this probably being the reason why "Krw at Sor" is less than "Kro at Swir" even for oil-wet rocks.

I'm not fully satisfied with this reasoning, that's why I would invite you all to share your points of view here.

PS: attached extract of Cobb's manual on Waterflooding where I found most of the previous statement.

[vinomarky]

One would imagine that in oil wet rocks, the scenario I sketched out for water wet rocks is simply magnified.

Initially, with oil wet rocks, the initial charge would be practically 100% oil - in effect single phase fluid flow yielding Kro = 1. Every pathway to oil flow no matter how tortuous has in effect negligible capillary pressure impediment to flow

As water floods the rock, the larger pathways become flooded with water, leaving the narrower (oil filled) pathways somewhat isolated, with oil emerging into the prevailing water flow paths needing to overcome capillary pressures to enter.