Analysis of the Main Corrosion Controlling Factors of Shale Gas Tubing Based on Grey Relational Method

The shale gas resources in the Sichuan Basin rank first in the country, and the resource rich deep shale gas blocks in southern Sichuan will become the main area for shale gas production. The Carbon tubing corrosion poses a huge threat in development of shale gas wells. In this paper, the high temperature and high pressure (HTHP) corrosion weight loss experiments were conducted to study the corrosion behavior of N80 tubing. The uniform test design method was used to optimize the number of experimental groups and select adequately representative trials. And the main controlling factors affecting the tubing corrosion were analyzed based on grey relational analysis (GRA) method and experiment data. And the corrosion topography after corrosion was characterized by Scanning Electron Microscope (SEM) technology. The uniform test with four factors and six levels was optimized into six sets of typical experiments. The GRA results showed that the grey correlation coefficients of CO2 partial, SRB content, working medium flow rate, and working medium temperature are all greater than 0.6, indicating that the above four influencing factors are strongly related to corrosion inside the tubing. Among all the corrosion controlling factors, the influence of SRB concentration and CO2 partial pressure was slightly stronger than that of working medium temperature and flow rate. And the main CO2/SRB synergistic corrosion mechanism was revealed. The metabolic activity of SRB on the surface of steel promotes the occurrence of pitting corrosion of steel, and the interaction with CO2 aggravates the corrosion behavior of steel. The analysis research of the main tubing corrosion controlling factors of shale gas well and corrosion mechanism provides theoretical basis for corrosion prevention of shale gas well, which will grantee the safety of shale gas development.