Long Term Corrosion Risk Evaluation of Load Bearing High Power Electrical Submersible Pump Cable

Abstract Fit-for-purpose Electrical Submersible Pump (ESP) load bearing power cable is deployed inside the production tubing of a sour oil well for an extended period of service. As the highest cost component of a novel ESP deployment system, project economics requires the power cable metallurgy to survive long term exposure reliably for up to 15% H2S and high salinity production fluids. Furthermore, due to the metallurgy discrepancy, galvanic corrosion between the cable metal armor and the production tubing pauses a significant risk of premature failure of either the cable armor or the tubing. Lab tests simulating varying sour well and extended galvanic corrosion conditions have been devised and carried out to determine the adequacy of the selected armor metallurgy in the downhole corrosive environments. The power cable consists of a load bearing armor (mechanical) and an electrical core. All cable metallurgy needs to maintain the required tensile strength and corrosion resistance for up to 15% H2S. A fit-for-purpose, computer-modeled finite element analysis (FEA) was carried out to identify potential showstoppers, followed by two independent empirical tests. Various cable armor strands simulating downhole tensile and bending conditions were enclosed inside two sets of Autoclaves (5% and 15% H2S) and tested for 90 days. Visual, microscopic, weight loss and tensile strength inspections were then carried out and yearly corrosion rates computed. Cable long term integrity was then determined with various metallurgy. Furthermore, a complete section of cable was enclosed inside a typical production tubing joint with 150,000 ppm water for 11 months. The pipe and cable were inspected before and after the tests to determine any damage to either the cable or the tubing. Both higher and lower NACE rated cable armor metallurgies were tested. The NACE rated cable armor metallurgy yearly corrosion rates proved to be adequate to meet the required cable life inside the production tubing. The galvanic corrosion testing confirmed negligible damage to both cable and tubing inner wall. The lower NACE rated armor metallurgy had a hardness closer to the tubing metal, and thus limiting the galvanic corrosion. The decision was made to manufacture the lower NACE rated, lower cost armor metallurgy cable. The novel and rigorous corrosion testing in varying sour well and galvanic conditions achieves multiple objectives simultaneously. These include fit-for-purpose metallurgy selection, cable mechanical and electrical reliability as well as project financial risk reduction.