Corrosion Analysis of Shale Gas Downhole Tubing Under the Synergistic Action of Multiple Factors

Abstract

Abstract The downhole tubing of a shale gas block in our southwest region has been corroded to varying degrees, which has led to perforation failure, seriously affecting the normal production of gas wells, and at the same time, there are great potential safety hazards. To clarify the corrosion type and corrosion mechanism, the corrosion analysis research of downhole tubing was carried out. The research methods mainly include corrosion morphology observation, corrosion product analysis, and fluid mechanics calculation. The results show that the corrosion under the synergistic effect of scouring-CO2-SRB (Sulfate-Reducing Bacteria)-Cl-is the main corrosion type of downhole tubing in shale gas and scouring that causes damage to the pipe wall in the early stage of operation. These locations are suitable for SRB growth and enrichment, and SRB corrosion causes local corrosion: with the addition of the bactericide, the SRB corrosion stops. At this time, CO2 corrosion continues to develop at the local corrosion position that has been formed. Although it is in the CO2 corrosion insensitive range and the corrosion inhibitor is added, the formed corrosion pit makes the pre-film difficult, it is difficult to guarantee the corrosion inhibition effect. Therefore, SRB corrosion is the main corrosion in the downhole pipe section in the early stage, and CO2 corrosion is the main corrosion in the later stage. Fluid scouring such as liquid sand and gas sand and Cl- promote the occurrence and development of related corrosion.