Integral Study of Internal Corrosion in the Managing of Crude Oil with Low Water Cut in Production Lines

The present study was carried out in the Production Unit Pirital, Eastern Venezuela. This unit handles 150 MBls/d (23,850 kL/d) of premium oil, with water cut below 2%, and an associated gas production of 350 MMCFD (9.9 MMm³/d). Since 1999 an increase has been observed in the frequency of failures due to internal corrosion in production lines at the Flow Station. Results from the failure analysis indicate that the CO₂ corrosion is the predominant mechanism. The work consisted on the determination of the corrosive potential at the production lines, by the characterization of the produced fluids, determination of corrosion rates with predictive models, and corrosion monitoring using weight loss coupons in static autoclave and coiled in line. Additionally the effect of the flow on CO₂ corrosion in the production lines was determined.

The results obtained show that the system is being affected by severe corrosion (Corrosion rates > 1.22 mm/yr), justifying the application of mitigation methods and control. The results of the field and laboratory evaluations for corrosion inhibition in multiphase flow, as alternative method for the control of internal corrosion, are also presented.

The implementation of anticorrosive treatment in this system has resulted in a considerable decrease in the frequency of failures, and in the associated cost of production delays for replacement of lines and other accessories, guaranteeing a continuous production at the unit.