Understanding and Quantifying Corrosion of L80 Carbon Steel in Sour Environments

Prediction of carbon steel corrosion in sour acid gas systems is more challenging than that in sweet acid gas systems.  This is because in sour acid gas systems various iron sulfide scales form and result in different corrosion mechanisms.  To better understand such complex sour acid gas corrosion behavior, a unique approach was developed that combined long-term corrosion testing data, facility life predictions based on extreme value statistics method (EVS), and validation with long-term field caliper data.  This unique approach was implemented in this study to evaluate the applicability of carbon steel for downhole tubing in sour acid gas systems with an aim at optimum capital expenditure and long-term facilities integrity.

In the paper, the effects of three key parameters, H₂S concentration, chloride level, and test duration on L80 carbon steel tubing corrosion were investigated.  Laboratory data combined with EVS method was used to predict tubing life and compared with field caliper inspection data.  The comparison showed that laboratory data was consistent with the available field caliper data.  The results also indicated that field caliper inspection data provided reliable information for tubing life predictions and complemented mechanistic understanding from laboratory studies.