Lab and field corrosion testing was completed on materials commonly used downhole in Steam Assisted Gravity Drainage (SAGD) to evaluate general corrosion rates, and how they vary with well depth, and operating environment to determine a dominating mechanism.
Lab testing utilized autoclaves to allow for corrosion rate and characterization measurements under controlled conditions. Field coupon testing consisted of installing corrosion coupons at various elevations in the annulus of a producing SAGD well. Corrosion rate analysis consisted of weight loss and various electrochemical measurement techniques, visual inspections, and x-ray diffraction analysis to determine scale compositions. Materials tested included various carbon steels, alone and in combination, as well as steels with hard facing and galvanized finishes.
Field coupons showed corrosion rates decreasing from 0.0178mm/y at the bottom of the well to 0.0145mm/y at higher well elevations. This corresponded to a decrease in iron sulfide scale content from the well bottom upwards. Based on the scales composition, operating conditions, and fluids present, it is likely that the scales were formed through the well-known solid-state reaction between aqueous H2S and the metal. High average corrosion rates of 0.263mm/y were measured in the lab, compared to a low 0.0183mm/y in field studies.
Key words: SAGD, Corrosion, Well Integrity, Hydrogen Sulfide, Casing, Tubing, Operating, Aqueous