Artificial Gas Lift

[dhenderson2014]

Hi there,

I was hoping that someone could describe the process of artificial gas lift for me as I am slightly confused. I understand that by introducing gas, it has the effect of reducing the density of the fluid and hence the hydrostatic pressure which is acting on the well - does this act as a back pressure effectively? Does artificial gas lift increase the total available pressure drop between the well and the platform i.e. does it’s introduction increase the bottom hole pressure?

Thanks

 

[georgeverghese]

No , bottom hole pressure remains the same. All it does is to reduce the hydrostatic pressure head in the production tubing, as a result of reduced bulk density, thereby increasing forward flow. But lift gas flow should be optimised. Beyond an upper limit, there is no benefit in increasing lift gas injection, oil flow starts to tail off after that, due to high pressure drop resulting from high lift gas flow.

 

[LittleInch]

well the flow and lift etc are all finely balanced and interdependent.

As you inject gas it has two impacts
One to reduce overall density and two the gas bubbles rise faster than the liquid but essentially "drag" the fluid with them.

however as the pressure falls from bottom to top these bubbles get bigger and bigger and reduce the space available for the liquid and increase overall pressure drop. So too much gas the overall liquid rate goes down. Not enough and the flow also drops off. So gas flow vs liquid will be a game of trial and error to establish the optimum gas flow rate.

Given that the aim is to increase liquid flow then then this will reduce the bottom hole pressure as more liquid is flowing out of the rocks at the bottom and hence BHP will reduce. Too much gas and the flow goes down so the BHP would increase ( maybe only a little)

now sometimes the hydrostatic head of the well will be similar to the BHP, so gas lift is one cheap way to get flow.

A submersible pump, nodding donkey or PCP pump are also used commonly for low pressure wells.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[chicopee]

For a better understanding of the material, research air lift pumps on the internet or in Mechanical and Chemical Engineering handbooks which you'll find in city libraries.