Failure Analysis of N80 Tubing Corrosion Perforation in a Shale Gas Well in South Sichuan

Abstract

In order to find out the cause of corrosion perforation failure of N80 tubing in a shale gas well in Sichuan basin, the causes of corrosion and perforation of N80 tubing were systematically analyzed by macroscopic observation, physical and chemical properties examination, tissue analysis, scanning electron microscope observation and energy spectrum analysis, combined with field service conditions. Results showed that the physical and chemical properties and materials of the oil pipe met the requirements, and there were a large number of loose and porous corrosion products on the surface of the oil pipe, which existed in the form of FeCO3, FeS and CaCO3. Moreover, the aggregate of SRB bacteria could be observed, and EDS results suggested the surface corrosion products contained more S elements. Hence, the corrosion perforation of the tubing was mainly caused by microbial corrosion. The coupling effect of CO2 and high Cl- in oil-based drilling fluid accelerated the local corrosion perforation, and adding fungicides could inhibit microbial corrosions of tubing.

Keywords

• n80 tubing|bacteria corrosion|perforation|failure analysis