BAKER HUGHES - Drilling Fluids Reference Manual

CORROSION
Cathode
Anode
1st Step O 2 + 4H + + 4e – →2H 2 O Fe → Fe ++ + 2e −
2nd Step
Combined: 2Fe + O 2 + 4H + → 2Fe ++ + H 2 O
Fe ++ can be further oxidized:
4Fe ++ + O 2 + (4 + 2x) H 2 O → 2FeO 3 + H 2 O + 8H +
Note:
Oxygen is required to drive the reaction at the Cathode to supply (OH – ) for the
reaction at the Anode.
3. Attack Types – Pitting, localized (deep pits) or general (evenly distributed shallow pits are
characteristic). Oxygen results in an etching form of corrosion attack..
4. Treating Agents
• NOXYGEN TM L – Liquid ammonium bisulfite (NH 4 )HSO 3
• AMI-TEC TM – Film-forming amine (see CO 2 Treating Methods)
• KD-40 – Film-forming organophosphate corrosion inhibitor.
• KD-700 – Film-forming organophosphate corrosion inhibitor which also acts as a scale
inhibitor.
5. Treating Methods – Inject via chemical pump into the pump suction. Adjust injection
rates to maintain the sulfite at 75 to 125 mg/L sulfite residual (at the flowline). Where
filtrate calcium levels are untreatable, or excess lime is present, maintain only an
indication of sulfite residual.
Carbon Dioxide (CO 2 )
1. Source – Formations and bacterial degradation of certain fluid additives.
2. Reactions.
• CO 2 + H 2 O → H 2 CO 3 (Carbonic Acid)
• H 2 CO 3 + Fe ++ → FeCO 3 + H 2
3. Attack Type – Severe pitting (worm-eaten appearance).
4. Treating Agents.
• Caustic soda – NaOH.
• Lime – Ca(OH) 2.
• AMI-TEC – Film-forming amine.
BAKER HUGHES DRILLING FLUIDS
REVISION 2006 8-3
REFERENCE MANUAL