Corrosion Status of Shale Gas Wells and Application of Detection Techniques in Sichuan Basin, China

As an important component of unconventional oil and gas, shale gas has gradually become a hot spot in the world’s energy development in recent years. Sichuan Basin, with 44.39 trillion cubic meters gas amount, accounts for 51.3% of China's shale gas geological resources. However, the tubing corrosion such as perforation and fracture frequently occurred in the development of shale gas well. The tubing may even fail within 57 days, which seriously threatened wellbore safety. This paper summarized the downhole corrosion situation of typical shale gas blocks in Sichuan Basin. The main influencing factors and corrosion types were analyzed by scanning electron microscope (SEM), X-ray energy dispersive spectroscopy (EDS) and X-Ray Diffraction (XRD) technologies, and the corresponding corrosion mechanism was explained. In addition, the main detection technologies of wellhead/ wellbore corrosion and application effects in shale gas wells of Sichuan Basin were emphatically introduced. The application effect of ultrasonic energy spectrum leak detection technology was evaluated in the typical case well. The results showed that: (1) The main corrosion types of tubing in shale gas well were SRB corrosion and CO2 corrosion. Tubing corrosion mainly occured in the upper part (0–1000 m) and the middle part (2000–2500 m). The upper corrosion part of the tubing was mainly caused by the coupling effects of SRB corrosion and CO2 corrosion, while the middle and lower parts was mainly caused by CO2 corrosion. (2) The wellhead corrosion testing results showed that the overall wall thickness of each wellhead valve was uniform; (3) The source of B annulus sustained pressure in the Well X was identified by the ultrasonic energy spectrum leak detection technology. Through comprehensive analysis, for those wells that have been put into production with tubing in the early stage, it is necessary to regularly conduct wellhead and wellbore corrosion testing to get the service status of the well barrier; For those wells without tubing, further research on tubing material selection and anti-corrosion technology should be conducted to prevent tubing corrosion.