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H2S effect on PDM elastomers
01 December 2008
I am trying find out the effects of H2S on downhole tools and in
particularly on mud motors (PDM's). I am aware of the Hydrogen
Embrittlement effect on the steel, but was looking for some
guidelines as to the effects on the elastomers.

Does anyone have any data, recommendations or comments please?
8 answer(s)
shangkarnaidu
Engineer
Halliburton
Total Posts: 1
Join Date: 04/09/08
Hi Hendo,

The content of this discussion draws heavily on a report submitted
to NACE in 1988 on the Effect of Dimethyl Disulphide (DMDS) on Oil
Field Elastomers. Its intent was to investigate the effects of a
sour well environment both alone and in combination with two
different concentrations of DMDS sulphur solvent on elastomers which
included NBR (Acrylonitrilebutadiene rubber, commonly referred to as
Nitrile), FKM (Fluorocarbon elastomers, commonly referred to as
Viton), HNBR (Hydrogenated nitrile rubber), TFE/P
(Tetrafluoroethylenepropylene rubber, commonly referred to Aflas)
and FFKM (Perfluoroelastomers, commonly referred to as Chemraz,
KalrezÆ’nand Zalak).

The attached document illustrates the limitations and effects of
common oil field elastomers.

Shankar

Documents uploaded by user:
1.pdf
hendo
Directional Driller
SPREADAssociates
Total Posts: 125
Join Date: 27/02/08
Nick,

Thanks for the information.

I don't think TFE/P is offered as an option, but I take on board
your comments - thanks again.
hendo
Directional Driller
SPREADAssociates
Total Posts: 125
Join Date: 27/02/08
Edwin,

Many thanks for the information.

I find the idea of putting the float in the rotating bit sub on the
motor to be very interesting.

Take care and again many thanks
edwin.damasena
Drilling Superintendent
Vestigo
Total Posts: 14
Join Date: 31/10/07
Hendo
Inteq did a 3 1/8" M1XL PDM run in Russia in 6% H2S with good
result. The mud system was treated with Petrolite scavengers. Check
on teh PDM after the run did not reveal any problems.
Could you not treat the mud in your case in the same way to protect
not only the elastomer but the rotor and other drillstring
components as well?
If feasible a solid drillstring float (e.g placed in a rotating sub
above the bit) could be used also to prevent formation fluid to
contact your pdm elastomer?
Edwin
NickAtkins
Managing Director
Rubberatkins Ltd
Total Posts: 5
Join Date: 01/12/08
The simplest checks are to check the hardness of the material to
identify any change from the original material spec and to visually
ispect the ID for surface cracking of the elastomer. Best Regards
Nick Atkins

www.rubberatkins.com
NickAtkins
Managing Director
Rubberatkins Ltd
Total Posts: 5
Join Date: 01/12/08
From the testing and experience at Rubberatkins we would not
recommend using Nitrile (NBR) elastomers within H2S environment.
This is mainly due to the attack from the free sulphur radicals from
the H2S at the unsaturation points (double bonds) within the Nitrile
polymer chain network. This will be visible as embrittlement of the
material and cracking of the surface.

Our recommended elastomer would be a Hydrogenated Nitrile (HNBR)
elastomer where the level of unsaturation is minimal and can be used
in lower levels of H2S.

For higher levels of H2S Rubberatkins would recommend Aflas (TFE/P).
However it should be noted that Aflas has poor aromatic hydrocarbon
resistance as well as poor low temp flexibility and relatively poor
physical properties which would not probably suit a high torque
application as a PDM. I hope this is of some help.
hendo
Directional Driller
SPREADAssociates
Total Posts: 125
Join Date: 27/02/08
Milap,

Many thanks for your kind response.

Are there are checks or tests (non-destructive) you know about that
can be done on the elastometer materials to;

1) Indicate any possible future reduction in perofrmance due to
exposure to H2S.

2) Be performed on motros received from other areas, where [email protected]
exposure may have been a factor.
MilapG
Drilling
Reliance Industries Ltd.
Total Posts: 14
Join Date: 28/11/05
The effect of H2S on elastomers depend upon the type of rubber of
which they are made up of.

Normally Nitrile rubber parts are considered safe for harsh
environment. H2S being acidic in nature will not have severe adverse
impact on HTHP proof type of elastomers which have degree of
resistance towards alkalinity/acidity which can take care of H2S
protection.
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