An oil sample is pronounced “dead” when it has lost all its dissolved gases and volatile components. The gaseous components of crude oil are mainly methane, ethane, propane and butane. When these gaseous and volatile components are lost or absent from crude oil, then that oil is in a dead state.
If an oil sample is exposed long enough to the atmosphere, then the volatile components will escape from the oil. During crude oil production, as the oil is produced, pressure and temperature continue to drop until the oil gets to the surface.
This pressure reduction releases the dissolved gases, making them come out of solution. Furthermore, upon arrival at surface separators, more and more gases will be forced out of solution leaving the oil with little dissolved gases.
What Makes Crude Oil Dead?
After being produced to the surface, if all the gases and volatile components get stripped out of the crude oil eventually, then the remaining oil is termed dead oil. Under reservoir conditions, oil existing in a dead state will be difficult to produce from the reservoir.
This is because dissolved gases help in increasing fluid mobility, thus, the more “alive” the oil in a reservoir is, the easier it will be to initiate and sustain fluid flow. “Live oil” is a term used to represent oil with sufficient dissolved gases.
So the life or death of an oil sample is a function of the presence or absence of dissolved gases. In fluid characterization dead oil has zero solution-gas oil ratio and it is thicker and more viscous.
Producing From a Dead Oil Reservoir
Although oil can be made dead at the surface by mechanically stripping it of all gases and volatile components; some oils are found in a dead oil state right in the reservoir; for example bitumen or tar sands. These crude oil types flow with difficulty due to their very high viscosity.
One way to lighten the oil is by re-injecting gases and volatile compounds into the reservoir. This will make the oil less viscous and more pumpable. Another popular method is by steam injection which makes use of heat to reduce the oil viscosity leading to an increase in oil production.