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Cement spacer contact time?
21 November 2019
10mins spacer contact time?
Should this not change with a function of hole size?
Cement gurus comments please?
Thanks.
8 answer(s)
ianpetitt
(retired) Well Fluids Team leader
SPREAD Associates
Total Posts: 47
Join Date: 14/06/06
Hello Peter,
 
I had written a story but then I see John North has cover it all in response 4 !! 

Regards Ian 
 


Ohara
Cementing Advisor
Beach Energy
Total Posts: 2
Join Date: 16/09/19
John's comment is true. Contact time doesn't mean anything basically, if it is not in turbulent flow.
Because that in most of cases spacer/cement  will not be in turbulent all around pipe due to poor casing stand off, thus laminar flow has been chosen for many years.
Laminar flow is nothing to do with contact time and there is no proof.
Cementing service providers have their own minimum  spacer volume requirement and run mud removal modeling to see cement placement, however casing stand off is main key factor for achieving good mud removal.
Johnn
Consultant
SPREAD Associates
Total Posts: 7
Join Date: 21/09/10
Pumping in turbulent was old advice but it is not always possible, practical or desirable to pump in turbulent flow and turbulent flow is difficult to achieve especially in the narrow side of eccentric annuli which covers most situations. Mud Erodability was a concept which was developed by Halliburton and Amoco which can be used to determine how to remove mud. There are quite a few SPE papers on the subject please read for a better understand of how to ensure best mud removal. For example at a 70% stanfoff often regarded, sometimes wrongly, as being a "good" standoff you can have a velocity ratio of 2:1 between the narrow and wide side of the annuluar gap depending on the fluid properties.. This would make turbulent flow unacheivable with anything apart from low density newtonian fluids which may not be desirable. Rules of thumb are ok if you do not have anything better, but we have much better tools today for analysis of mud removal which should be used.
Ohara
Cementing Advisor
Beach Energy
Total Posts: 2
Join Date: 16/09/19
Contact time definition should be cleared. SPE 742 clearly defined contact time. 
Contact time is defined as the period of time that a particular point in the annular space remains in contact with cement slurry being displaced in turbulent flow.
I would say spacer should be considered as same, however the fluid has to be in turbulent flow regime all around pipe. Fluid to be turbulent flow in wider side and narrow side  is  different obviously,so pipe centralisation is also key factor. Laminar flow with contact time may not mean anything.
Johnn
Consultant
SPREAD Associates
Total Posts: 7
Join Date: 21/09/10

The rule of thumb that I am aware of is 1000 ft of annular fill and 10 mins contact time. Need to fulfil both criteria. That should take care of hole size and also pump rate issues. Low pump rate still 1000 ft of fill and 10 mins contact time. High pump rate achievable 10 mins contact time and 1000 ft of fill. This came from a number of experiments on simulated cores in large scale experiments and field evaluation. Of course this is not the whole story with regards to spacer design. For OBM need to have water wetting additives in the spacer system and materials to ensure compatibility between the cement spacer system and mud. As mentioned chemical washes are also effective at breaking up certain mud types. Along with these materials it is also desirable to have density and rheology hierarchy to maximise mud removal. The mud can be tested to determine how hard it can be to remove and the spacer rheology designed to maximise mud removal in the eccentric annulus. So the rheology and density profile of the cement should be greater than the spacer system and the spacer system rheology and density should be greater than the mud system. All of this course within the allowable ECD of the well. So there is much more to spacer systems than 10mins contact time (which is desirable to allow for mud breakup and water wetting the surfaces if OBM is used). The old school idea of pumping in turbulent flow is not always possible within ECD limits and mud systems may not always be easily removed by turbulent flow which may not be achievable anyway. Lab testing and computer simulation in eccentric annuli is the only way to design spacer system to maximise mud removal and maximise the successful isolation required in the well.

Johnn
Consultant
SPREAD Associates
Total Posts: 7
Join Date: 21/09/10

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PaulHowlett
CEO
Sudelac
Total Posts: 109
Join Date: 10/04/08
10 minutes contact time, if specified for a given spacer design with a given mud type accounts for all open hole sizes and therefore you have to adjust volume at a given displacement rate to achieve it, or adjust displacement rate for a given volume!
Dan
Workover Engineer
SPREAD Associates
Total Posts: 16
Join Date: 01/08/18

Hi Peter,

I am not a cement guru :) but I know the chemical washer has to allow at least 8 minutes contact time across zone of interest, when in turbulent flow, or a combination of chemical washer and spacer to be used if well control issue do not allow such contact time. 

Dan

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