BAKER HUGHES - Drilling Fluids Reference Manual

CORROSION
7. Recommended Treatment
• NaOH and/or Ca(OH) 2 for pH 10.0 or above.
• MIL-GARD ® : 2 to 3 lb m /bbl (1 lb m /bbl = 500 mg/L sulfide)
or
MIL-GARD ® L: 55 gallons per 1000 bbls of drilling fluid to scavenge 50 – 80 ppm H 2 S.
or
MIL-GARD ® FE : 0.1 gal/bbl (0.24%) will treat approximately 100 ppm H 2 S.
Note:
MIL-GARD ® L should be used in clear fluids such as drillwater and brines, as
MIL-GARD ® will settle. Maintain excess MIL-GARD ® in the system when H 2 S
is suspected or known to be present. Use the Garrett Gas Train to monitor
excess MIL-GARD ® concentration.
In the event MIL-GARD ® is unavailable, the next best method to treat for H 2 S involves pH control
using lime, a filming amine to coat the pipe such as AMI-TEC , or KD–700, and SCALE-
BAN to prevent scale deposition. Control the pH at 10.5 or above using lime. Do not use caustic
soda alone, because caustic reacts to form sodium sulfide (Na 2 S) which is extremely soluble and
H 2 S may be released from the fluid if the pH drops. Lime is recommended instead because it forms
calcium sulfide (CaS) which is not as soluble and may precipitate from the system. Use AMI-
TEC or KD-700 to provide a film on the drillpipe to protect against sulfide corrosion.
Note:
The use of the Garrett Gas Train and sulfide indicating Dräger Tubes is
necessary to properly monitor the fluid system for quantitative information on
sulfides. Techniques utilizing lead acetate paper discs are used only to indicate
the presence of sulfides in relative concentration.
When testing for the presence of sulfides in a fluid, it is extremely important that the filtrate used
be as fresh as possible. In addition, the filtrate should be taken from a sample of fluid freshly
collected at the flowline. Minimize exposure of the fluid or filtrate to the atmosphere as this
reduces the accuracy of the test.
CORROSIVITY OF VARIOUS FLUIDS
• Non-dispersed – Oxygen entrapment and high dissolved oxygen contents caused by high gel
strengths and yield points cause these fluids to be regarded as corrosive. This is exacerbated by
these fluids often having a low pH.
• Low Solids – Corrosive due to the same rheological conditions as with Non-Dispersed fluids.
• Polymer Fluids – Usually have lower pH and may contain salts which increase the fluid
conductivity. Also, these fluids often have rheological properties which allow entrapment of
oxygen, resulting in high oxygen content. NEW-DRILL ® and PYRO-DRILL ® fluids routinely
have low corrosion rates. This phenomenon has been observed even when operating in the more
corrosive environments. Some polymers are natural O 2 scavengers; others are scale inhibitors,
etc.
BAKER HUGHES DRILLING FLUIDS
REVISION 2006 8-7
REFERENCE MANUAL