gravity drainage

[aeacfm]

hello buddies
i am oil field chemist , in my work i met some terms like gravity drainage but i cant imagine it !!!
could any one explain it please???
thanks in advance

[vinomarky]

Hard to know exactly without the context, but it could be referring to SAGD (Steam Assisted Gravity Drainage) scenarios - where you have two parallel (on top of one another) horizontal wells in a heavy oil reservoir - and you inject steam into one of the horizontal wells to create a 'steam chamber' which heats (hence reducing viscosity) the oil allowing it to trickle down (by gravity) into the other horizontal well for extraction.

If you can furnish more context we may be better able to give you an answer

[aeacfm]

If you can furnish more context we may be better able to give you an answer

ok i will

[aeacfm]

in shell manual of water flood this is the context:

"an important primary recovery mechanism is gravity drainage where either a primary gas cap is present or large amounts of gas are released from solution in the oil as the pressure declines "

so did he here mean gas drive reservoir or gravity drainage or both mixed ?
also i want to imagine gravity drainage : i mean what i know is that gravity make things go down by the force of gravity acceleration but here drainage make oil go up !!!!wow

[vinomarky]

I think they are talking about gravity stabilized drainage - essentially placing well perfs low in oil column (which lies beneath gas cap) and drawing down slow enough to avoid/minimize gas coning so that you get a stable GOC surface falling over time to maximize your oil recovery

[aeacfm]

I think they are talking about gravity stabilized drainage - essentially placing well perfs low in oil column (which lies beneath gas cap) and drawing down slow enough to avoid/minimize gas coning so that you get a stable GOC surface falling over time to maximize your oil recovery

so aimply he could have said gas drive !!!!

[vinomarky]

I think in this case they are more referring to the method of utilization of the available energy rather than the energy itself

[aeacfm]

thank you very much, but i still cant get that !!

also i want to imagine gravity drainage : i mean what i know is that gravity make things go down by the force of gravity acceleration but here drainage make oil go up !!!!wow

[vinomarky]

If they simply perfed the whole interval and produced hard then they'd get massive gas coning problems. The GOC would not be moving down (by gravity) as a stable interface, rather you'd have pockets of coning and essentially almost 100% gas production after a relatively short period. If they perf low and restrict drawdown they could get oil produced with gas at solution gas ratio, and get substantially better oil recovery.... Both scenarios get the majority of their drive energy from the gas cap, but the first scenario squanders that energy very quickly with little oil to show for it

[Chee Koh Peh]

Gravity Drainage is a phenomenon seen in reservoirs with high structural relief, that are relatively homogeneous, have large hydrocarbon columns and exhibit excellent permeability. It is of interest as it is associated with higher recovery efficiencies as compared to solution and water drive mechanisms. I have seen recoveries > 63% OOIP in reservoirs that exhibit this behavior.

Essentially these favorable properties promote the segregation of gas and oil under the influence of gravity, so that liberated gas in the reservoir (i.e. below Pb) tends to flow upwards into the gas cap or form a secondary gas cap (i.e it is not produced). In this way drive energy is conserved in the reservoir, that is the highly compressible gas which forms a significant portion of the reservoir depletion energy, remains in the reservoir, promoting higher recovery efficiencies.

Rgrds

Chee Koh Peh...

[DAH7542]

As it can be inferred from previous comments here, Gravity Drainage (G.D), been a primary recovery drive mechanism is very effective in steeply dipping reservoirs (and under some other conditions explained by Chee Koh Peh). Essley et al discusses very well this phenomenon for steeply dipping reservoirs (I strongly recommend this reading - attached paper), some conclusions are:

- The only additional recovery resulting from G.D will be that oil which is displaced by gas from within an expanding gas cap volume: this means that for G.D to be effective gas must accumulate updip in the reservoir.
- Fluid movement and recovery from G.D can be expressed by Darcy eq (analysis of the gravity term RHOxGxSintheta): authors show that ultimate recovery (to some assumed economic limit) is essentially independent of variations in the producing rate (graphically shown in fig. 6 of attached paper).

Regards.

[aeacfm]

good shot