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Cementing 9-5/8" csg with long rathole below
02 April 2009
I'm currently working on a Geothermal land well project in Denmark. The well will TD in 12-1/4" hole but there are two targets, Gassum and Bunter sands. Before committing to 9-5/8" liner they need to evaluate which sand will give the greatest PI for producing water. Once it is determined which formation to produce from the 9-5/8" will be set above the reservoir and a gravel packed sand screen completion run. As such there will be a minimum of a 300m rathole beneath the shoe. I have spoken to a few people and the general consensus seems to be to just go ahead and cement conventionally, perhaps spotted a hi-vis pill first.

Anyone have any experience in doing this.

Adrian Todd
4 answer(s)
senior drilling engineer
Total Posts: 1
Join Date: 10/03/09

Not sure what inclination you proposed shoe is - but if high angle / horizontal take care when drilling out the shoe. I drilled a similar well with 2000 ft of rathole beneath it (we ran the 9-5/8" to top reservoir in the reservoir pilot hole) We had a pretty meaty composite shoe on the casing and when we drilled it out with an 8-1/2" cleanout assembly it fell off the end of the pipe (nothing to support it below, and no base to mill it up) and stuck the drillstring - had to use severance charges in the end. Main lesson here was to select a standard cement shoe if doing the same again.

As far as the cement job was concerned (Casing shoe at 17000 ft, TD 19000 ft at the end of an 80 deg tangent section) no problems.


Barry Fraser
SDE, bp
Total Posts: 93
Join Date: 10/04/08
You may end up with cement falling well below the 9.5/8" shoe if cemented well off bottom but if you plan to do a clean-out run this may not be an issue for you, however you may want to do the clean-out run with an underreamer to clean back to beyond the 12.25" OH you had below the 9.5/8"....depends on the needs of the installation and flow from below the 9.5/8" shoe.........however have you considered a packer stage collar at the bottom of the 9.5/8", these are reliable pieces of kit, you drop a device, inflate the packer, open ports about the packer, and cement above it........i have run many of them over the years, but not recently, but Davis Lynch have a very reliable one, they are used in the Middle East day in day out. Alternative, if you have time, run a swellable packer on the end with a ported joint above it, and the shoe blanked off, allow the swellable to swell and then cement through the ports above it. if you contact me on I'd be happy to talk and assist further.
Roc Oil Company Limited
Total Posts: 4
Join Date: 24/01/08
I have certainly done this both deliberately and unintentionally (when the casing has become stuck off bottom and had to use an emergency hanger system). I have never seen any issues whilst cleaning out beneath the cemented casing. You mention that you will be installing a 9 5/8" Liner. If it is a liner hanger system then you need to look at the emergency release mechanisms if the hanger doesn't set. On many systems you have to set the liner on bottom to release. If the bottom of the hole is 300m away then this becomes very difficult!!!

Andy Mellor
Roc Oil, Beijing
Total Posts: 28
Join Date: 09/03/08
No problem to set your 9.5/8" 300m off bottom, and cement above. Depending on formation strength below you could consider lightcrete for 9.5/8" casing cement and yes recomend viscos mud in open hole below.

Sandy Buchanan
Senior Drilling Supv
Shell, Brunei
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