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Potassium Brine Compatibility
29 April 2019

Hi

I am looking for any industry experience in using potassium formate brine as a completion fluid. The specific query is the long term effects of the brine in the A annulus which will remain in place below the Orifice valve of a gas lifted producer well. Potassium formate brine is naturally buffered and has been buffered further with bi-carbonate to give a pH of 9.5 - 10. The exposed tubing is L80 13Cr and the gas lift fluid has up to 3% CO2 but we think the interface with the top of the formate in the A annulus will not be exposed to new gas lift gas over time as the formate level will fall. The completion brine fluid weight could be 10.8ppg, therefore is not neat formate at 13.1ppg but diluted with about 70% fresh water. The BHT is 90 deg C.

There is lots of information in one of the brine providers website and the occasional SPE paper but nothing specific to our situation. 

I would be interested to hear what experience is out there.

Grant


3 answer(s)
dr2019
CWI Engineer
SPREAD Associates
Total Posts: 8
Join Date: 11/05/19
Hi Grant,

Some years back I have been involved in a project that used potassium,sodium or a combination of the two formates in 20 plus wells completions at weights comparable to yours and as far as I remember slightly higher DHTs. 

Our tubulars were SM 13Cr 95 and we had a similar concern. 

The position was based on the concern of formates long term stability at temperature, and/or in case acid gases percolate into the annuli (in case of a completion leak).

The feedback was that 13Cr80 is usually immune to SCC, but there is a question mark whether the same would apply to 13Cr95 for which at the time ( 2007) was very little prior usage history.

We did go ahead with potassium formate and as far as I know there were no failures related to this  for the next 10 yrs. 

At that time ( 2007) there was an API JIP that looked into this issue and since they must have come back with a RP.

The tubulars specialized consultancy that we're using at the time was S&L Consulting SA out of Switzerland.

One more thing I'd like to mention here is the long term incompatibility of formates with Viton. Short term could be used for days/weeks by playing with the ph.

Hope it helps.

Daniel 


grant00
Senior Completion Engineer
CNOOC International
Total Posts: 2
Join Date: 11/03/16

Hi Ian

Thanks for the reply, we are actually going to test the completion tubulars with the range of potassium formate completion brine weights we need. Potential SPE paper could be written after if I had time.

Regards

Grant


ianpetitt
(retired) Well Fluids Team leader
SPREAD Associates
Total Posts: 44
Join Date: 14/06/06
Grant, We did a North Sea coiled tubing completion well drilled and completed with potassium formate fluid about 25 years ago. Don't remember any issue of annular gas during production. And do not remember any issue if/when completion was removed.  We did have some completion corrosion issues with inappropriate calcium completion brine during the same period used on other wells. 
About 10 years ago I had a student intern working in our laboratory for six months who's project was cesium formate and corrosion or formate break down at high temperature . We had done a long HTHP workover ( BHCT 150C +) with cesium formate and had observed some H2 gas during operations contrary to completion fluid company claims.   
The lady's laboratory work did actually prove some minor breakdown of formate in these HTHP well conditions and some minor corrosion of completion coupons (including H2 generation).  As these conditions were much severe than yours I would not expect you to have an issue with your completion fluid selection and metallic choice.   

Regards Ian 



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