adding the member volume_ratio_ for BlackOilFluidState

[GitPaean]

for OPM/opm-simulators#6957

[GitPaean]

jenkins build this opm-simulators=6957 please

[GitPaean]

jenkins build this opm-simulators=6957 failure_report please

[GitPaean]

jenkins build this opm-simulators=6957 failure_report please

[GitPaean]

This PR will also makes OPM/opm-simulators#7043 easier.

[GitPaean]

But since it is only used in the wellbore calculation. Maybe it is not good to add extra burden to the whole system, mostly the fluid state for the reservoir side.

[atgeirr]

Maybe it is not good to add extra burden to the whole system, mostly the fluid state for the reservoir side.

I agree with that, increasing the size of the fluid state for well usage only is not good. Can you instead use a separate class for the well usage, that contains both this fluid state and the extra data you need?

[GitPaean]

Maybe it is not good to add extra burden to the whole system, mostly the fluid state for the reservoir side.

I agree with that, increasing the size of the fluid state for well usage only is not good. Can you instead use a separate class for the well usage, that contains both this fluid state and the extra data you need?

That is a very helpful suggestion. I am closing the PR now based on the discussion.