A Basic Primer on Hydrocarbon and Water Saturation (Sh-Sw)

Hydrocarbon Saturation is a major factor in the Volumetric equation
The pores are filled with fluid wither brine water, oil, natural gas or non hydrocarbon gases
The proportion of hydrocarbons in the pores is the hydrocarbon saturation, Sh
The portion of water in the pores is the water saturation, Sw
Sh = (1-Sw)
Higher Sh means that the pores contain more hydrocarbon
Water saturation is averaged for each layer in basic volumetrics
Water saturation in static models is generally modelled using saturation height functions for each rock type
In dynamic models water saturation changes with production - this can be history matched with data measurements - e.g. TDT logs
Water saturation is not measured by borehole logs directly but is calculated from other measurements
Water saturation is related to porosity and permeability - lower porosity rocks will have higher water saturations
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Also AAPG wiki and SPE Petro wiki

[@erbterb]

I have watched several videos on EOR, specifically steam flooding as a good way to change the viscosity. Others have shown CO2 injection as a way to normalise the hydrocarbons. Gas/heavy oil and gas/gas exchange.
So why does one not start each project with high temp CO2 injection? You flush the pores with gas, while still at pressure and get the benefits of viscosity changes. You also please the frequent flyer climate hypocrites by pumping down their emissions from cross continental flights.
Why start with just normal suction, when you can start with EOR directly?

[@AlanFoumGeophysicist]

It is probably a matter of cost vs return - A recovery method for an oilfield is determined in the initial development plan to give the maximum return for the money invested - EOR can be done from day one - but
a. you need a source of CO2 or steam and significant extra engineering which costs
b. the extra oil recovered by EOR needs to be worth more than the cost of the EOR
c. The operator needs to really understand EOR - the more complex a project (and EOR is complex to implement) the more scope there is for cost and time over runs
d. Most large oilfields for which EOR is suitable were first developed a long time ago (decades) when EOR was a mere glint in an engineers eye rather than a proven technology, hence late implementation
e. There is a not invented here mentality among some operators which can hinder progress