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IS cavitation in drilling tools a real thing?
19 January 2019

I have heard the word “Cavitation” in the context of affecting the performance of downhole drilling tools.

My understanding of cavitation is limited to pumps and ships propellers.

But I wonder if the phenomenon can occur in a downhole environment?

I am thinking that under downhole temperatures, pressure and to a fluid containing viscosifiers it would not be likely.

But as this is out of my usual arena I felt the need to poll the community for advice and education.

10 answer(s)
Scott_McNeil
Consultant
SPREAD Associates
Total Posts: 137
Join Date: 05/03/08
Hendo,

One more thing is that if there is any evidence of cavitation on a Rig location these days, it is far more likely to be downstream of the choke after a well kill operation, or possibly downstream of the choke on a well test package.

All the best!

Scott
learning.lifewayne@g
D&C Project Coordinator / Decommissioning
Society of Petroleum Engineers
Total Posts: 27
Join Date: 25/01/16
Cavitation would be a phenomena that could occur where there are impellers and fluid displacement.  One can design for the phenomena using cross flow with nozzles in a bit with extended nozzles and diverse sizes to where cutting can be swept up and pushed into the flow stream.  Where I've seen problems is with "centrifugal forces" that occur around diameter changes and the solids get removed from the fluid stream and build up and prevent seals like in float areas and back pressure valves.  The hazards on drilling fluids with solids in them for density management.  
JDDrouin
Project Quality
SPREAD Associates
Total Posts: 108
Join Date: 06/05/09
There was a significant error in that video ... valves don't regulate pressure, they only regulate flow.
hendo
Mentor to the youth of our industry
OILSERV
Total Posts: 132
Join Date: 27/02/08
Thanks Neil.
I just viewed the YouTube video and found it clear and professional.
What I am saying is that (a) cavitation is a real thing, but (b) not likely in a downhole environment.
For the fluid to be "nozzled down" to an extent that the vapour pressure will be breached (considering the additional hydrostatic), I am thinking the extra pressure drop would be obvious on surface pressures.
Thanks again Neil and all the best to you Sir.

nbergstrom
Senior Wellbore Positioning Advisor
Helmerich & Payne
Total Posts: 36
Join Date: 03/07/08
I found a good example and discussion of cavitation on YouTube - search for "Cavitation in a Water Pump".  The video shows a centrifugal pump with inlet and outlet tubes all made of clear acrylic as the inlet pressure is gradually reduced below the vapor pressure of the clear water being pumped.  Visual and audio effects!
Scott_McNeil
Consultant
SPREAD Associates
Total Posts: 137
Join Date: 05/03/08
Hi Hendo,

Ahh yes, they were good days in Erbil!

Keeping well, thanks - just wanting to get back to work to get the brain cells working and cash flow direction reversed!

How about yourself?

Unfortunately I don't have any proof - this was many, many Moons ago and any reports I had have long since disappeared.

It's just occurred to me that it might be worth talking to one of the old Turbine hands (if there are any still around!) to see if there was any evidence of cavitation in the power section vanes when they were taken apart.

All the Best!

Scott
JDDrouin
Project Quality
SPREAD Associates
Total Posts: 108
Join Date: 06/05/09
Chris,

Just my opinion, but I suspect that cavitation happens far more frequently in the downhole environment than most realize ... back in the 'old days' when I used to service mud motors, there was a constant problem with the chrome failing on the rotors and pits developing.  As chrome plating was (even then) old tech, really old tech, the attribubation of 'poor' chrome plating as the failure mode always struck me as convenient rationalization.  Cavitation would certainly explain the localized failures on the chrome.

Dominic
SimonKlampfer
Drilling Manager
OMV
Total Posts: 3
Join Date: 25/12/15

Hi Chris

I never came across this during my long career - could have been that - as mentioned in Scott's remark - MWD pulser failures (we had pulsers that were completely eroded) were wrongly attributed to mud properties (as it is usually the case ;-)  ) instead of being caused by mud cavitation.

We actually asked the vendor to look at it for some proper explanation, but did not receive any.

hendo
Mentor to the youth of our industry
OILSERV
Total Posts: 132
Join Date: 27/02/08
Thanks Scott - your opinion is always highly valued in my book.

Do you have, or can you point me in the direction of the proof.

I want to be able to prove it happens.

Hope you are keeping well, and all the best mate (Kurdistan seems like a liftime ago eh?).

Cheers.............Chris
Scott_McNeil
Consultant
SPREAD Associates
Total Posts: 137
Join Date: 05/03/08
Hi Hendo,

Yes, it can occur downhole and used to be relatively common in MWD / LWD tools that used pulsers (as opposed to turbine vanes) to get the signal back to surface.

Over time, the design of the pulser has improved and I can't honestly recall the last time I saw it in that location.

The main indication is several small, deep, pits in a localised area.

Cavitation is incredibly destructive and can very quickly lead to a washout or even the string parting.

All the best!

Scott
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