Oil separator Temperature and Pressure Optimisation 1

[Coops]

It is understood that the 2 major properties affecting crude oil 3-phase separation are Temperature and Pressure. However I do not fully understand the rational of which way you might want to drive these for optimum production.

Temperature – ideally this would be high (?) because the density differential between water and oil is increased at higher temperatures because of different specific heat capacity of the fluids. Also the viscosity is increased at higher temperatures so the droplets separate easier. But what constrains this? Is it because more gas is retained within the oil at higher temperatures, which can cause problems with pumps?

Pressure – separator pressures are often lowered to increase the production rate, this increases the pressure differential between the well and the separators hence promoting more flow. However does it not mean that more gas is flashed off (?) also at lower pressure you actually have a lower mass/volume than at the higher pressure so is there actually more oil?

I would be grateful if somebody could clarify these points for me
Cheers

 

[bdog]

If you are trying to determine the optimum "flash" conditions (Presssure & Temperature) for OIL & GAS separation, run a flash calculation (available on the internet) from your known starting conditions (first separator pressure &temperature) and "flash" to the next separator pressure (variable). You will get a gas & liquid mixture @ the second separator. Depending on your start mixture components you may want to vary temperature by adding or subracting heat (coolers or heaters)to optimize the gas or liquid phases @ separator #2, again depending on what you want to sell or further process.

 

[d23]

Coops:

FYI:

Please don’t misunderstand this post. My goal is intended more as question than a statement.

I think maybe you were typing, not reading. Viscosity will decrease with higher temp. Heating crude will lower the viscosity making it easier to pump. The lower pressure will allow the liquids to break-out quicker.

Doing the molecule thing doesn’t heat affect the momentum of transfer between layers?

Once again please don’t misunderstand I'm not trying to make a statement, but doesn’t this explain the function of a heater-treater vessel?

 

[PDEBoss]

This one has a lot of factors to take into account and there isn't a simple one line answer. Separators are designed to meet certain specs e.g. BS&W and vapour pressure of the oil product, oil content of the water product and liquids content of the gas.

For BS&W, higher temperatures do assist separation but it is difficult to calculate. In oil fields, the temperature required is usually based on bottle separation lab tests for your oil ans water compositions. There is ususally a minimum temperature below which you will get no oil/water separation, after that it becomes a case of diminishing returns and you'll be putting in heat for the sake of tiny improvements.

For vapour pressure, for every pressure, there will be a corresponding temperatures that will meet the spec. High pressure will require higher temperatures which may not be practical with your heat source temperature. Low pressures will require lower temperatures but it makes the vessel bigger and you may need pumps & compressors to get the phases back up to a pressure suitable for their respective destinations.

For liquid content of the gas product, the vessel must essentially be sized for volumetric gas flowrate which will be higher at low pressures and high temperatures.

Operating temperature and pressure should have no effect on vapour entering pump provided the pump suction route is designed for the pump NPSH. Temperature will affect oil viscosity but unless you have a very viscous crude the effect isn't startling.