Gas Injection

[rotanimod]

our reservoir guys were proposing to convert low oil producing well into gas injection well. Through this method, they were hoping to boost oil production from other wells. As a process/operation guy, I was assigned the task to review the design of this oil production to gas injection project. However, there couple of questions which need better clarification. I've gone through with the reservoir colleagues of mine, but they seemed not really convincing. The questions are:

1) Once we execute the gas injection, can we expect any oil to come out from that particular well if we were to stop the injection service and switch back to oil production mode??? I'm inclined to say that the well will no longer produce oil but rather we can expect gas to come out from the well. This gas can then be used for normal/start up purpose whenever more fuel gas is required on the platform.

2) On reservoir side, will you guys be needing to run a test using test separator on this particular well if it only produce gas?? If it is deemed not necessary, I planned to blind off the well production line from the test header hence simplifying the operation.

Hope you guys can give feedback on this concern. Cheers.

[Yengineer]

Wow! Before starting anything this questions needs to be answered:
What kind of gas do you plan to inject? (CO2, CH4 etc) they will react differently.
Do you plan to inject the gas to energise the reservoir, or to initiate any miscible production?
Is any free gas around the wellbore? if not, by presenting new gas you will definitely create Sgi.
What is the expected miscible pressure? What is the actual reservoir pressure?
What about hydraulic isolation (cement quality) and is the reservoir homogenous or not?

If you do not overpass miscible pressure then it is more likely that you will get the gas back to surface without any considerable increase on production.

Cheers and let us know how it will go

[thaicntech]

Thanks!

[rotanimod]

Answering to your question:-
1) Recovered CH4 (associated gas) will be used as the injection gas.
2) The gas injection is undertaken to boost oil production from other well i.e to re-energized the reservoir.
3) With high gas to oil ratio for this particular well, I believe there's a free gas around the wellbore. What is sgi by the way??
4) Regarding the miscible pressure etc....I will need to get back to you on that. However, for the sake of getting quick reply...I tend to say that the injection pressure which is a bit higher than reservoir pressure does not overpass the miscible pressure. can you elaborate further discussion based on this assumption please??

[Yengineer]

So you plan to inject produced gas to well "A" with the objective increase production in well "B".
I would prefer such a solution when the reservoir is still above the bubble point. In this case your gas goes again into solution lowering the viscosity and maintain reservoir pressure.
If you already have a gas cap, things get more complicated and economics needs to be run.
- gas can be reinjected right there (into gas cap) trying to balance fluid production and keep the reservoir pressure. BUT remember - gas is not sweeping efficient, you might bypass the oil and never get it back. By the way, Sgi is irreducible gas saturation.
- You can close gas producers and start pressure maintenace with water injection