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lidge (Petroleum)
11 Sep 03 7:08
Hi,
Does anyone know if there is a rule of thumb to calculate the minimum flow rate (bullheading) required to fully displace a tubing volume of gas?

More specifically we have a 5500 m gas condensate well with 4" ID tubing (s - shaped well). The density of the gas/condensate is 463 kg/m3. Surface pressure is 440 bars shut -in. We have previously successfully partially killed this well with water pumping at an initial rate of 2.5 Bbls/min. The well can be easily bullheaded, +30bar will start to push the fluids back into formation. This well is now on production and the maximum pump rate available is 1.68 Bbls/min (positive displacement pumps) and the only fluid available is water. Hence would this rate (or a lower rate) be sufficient to leave a full column of water in the tubing after partial kill, consequently reducing the surface pressure?
nonAPI (Petroleum)
17 Sep 03 23:58
Lidge,

I don't know a rule of thumb but I can tell you from experience that the rate you have will be sufficient.  Yes, it will take longer and a larger volume of fluid to evacuate the gas from the tubing but you will be successful.  Simply overdisplace to compensate for the lower rate.

Out of curiosity, what is it that you are contemplating doing that a lower pressure will help you do?

Cliff

lidge (Petroleum)
24 Sep 03 10:49
Cliff,
Thanks for your reply.

We may have a potential integrity problem in the production annulus. Being able to reduce the surface pressure by immediately bullheading will reduce the pressure that this production annulus will see ( in the event of a tubing leak)
and if the potential integrity problem is real then the intermediate annulus is designed to take this reduced pressure.

The issue arose out of a risk review, although it is very much a what if - what if - what if type scenario.
DrillEng (Petroleum)
7 Oct 03 13:39
You can't rule of thumb well killing but having had to kill numerous gas wells in preparation for workover operations I can offer some advice.
First you cannot kill it with water alone (presuming water is of sufficient hydrostatic pressure to kill the well). You have to pump a large HEC pill ahead of the water to stop gas migration. You stated your well is S shaped which will mean that you could flip the gas out so you need to pump a big pill. I would suggest 2000 ft equivalent or more depending on well geometry.
Your pump rates again will depend on what your injection rate is. You only know this by trying a rate.
Also you have to pump a the maximum rate you can so that your gas does not bypass the pill.
If you cannot get all the gas injected or you flip the HEC pill you have another option which is to lubricate the well. Which if you need to do I will email at length at how to achieve this if needed.
Any questions drop me a line,

Regards

Dave
DrillEng (Petroleum)
7 Oct 03 13:45
To follow on from what I have just written. I suspect that you only partially killed the well previously because you did not pump at sufficient rates. I would suggest 10 bbl/min + if you can. It seems that your pump is too small for the job if you are to kill without something to isolate the water from the gas. So, pump a 50 bbl HEC pill, the pump at your max pump rate that you can. This should isolate the gas from the water, stop gas migration ( no such thing as a partial kill, the well is either dead or not ), and enable you to kill the well in one try.
If the first pass fails, try more HEC. If this fails get a bigger pump, if another pump is not available, then lubricate the well.

Regards

dave

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