Study on Self-repairing Annulus Protection Fluid in Underground Gas Storage Wells

There is a packer located in every underground gas storage (UGS) well to protect casing from corrosive media and high pressure. Although there is protection fluid in the annulus, it is found some tubing failed of corrosion resistance on the outer surfaces. The casing and tubing are not protected by annulus protection fluid very well. A self-repairing annulus protection fluid is invented. The main agent and promoters are designed. The NaCl is selected to be the main agent because of low fluid density (1.0–1.05 g/cm3). The promoters are corrosion inhibitor, oxygen scavenger, bactericide, scale inhibitor, and pH regulator. The high-performance promoters are selected in laboratory. The pH regulators are the most important. The various combinations of pH regulators are studied to select the best one and the combination. The scale inhibition rate for CaCO3 was 93.5%. The rate of deoxidation was 99.5%. The bactericidal rate was 99.97%. The corrosion rate was far lower than 0.076 mm/a. They were better than the ones used in the field. The pH was about 9. The protection fluid could absorb far more corrosive medium than the other ones, and the pH would keep stable or decrease a little. The protection fluid was applied in two wells in Dagang Underground Gas Storage. The application effect is very well. The conventional properties of self-repairing annulus protection fluid are much better. Once the corrosive media coming into annulus from tubing, the pH regulator reacts with them. The corrosive media will be transformed into soluble inorganic salt, and the pH of fluid is still maintained. The tubing is protected from corrosion, which comes from corrosive media or the pH decreasing to 7 or lower.