Optimization of a High Temperature Low Corrosivity Acid Fluid for Application at 180℃ High Temperature

A new high temperature corrosion inhibitor has been developed though molecular structure design and synthesis to deal with problems encountered in high temperature deep well acidification, such as high bottom hole temperature and corrosion of downhole string and downhole tools. The corrosion inhibitor, which can be used at 180℃, was used with other optimized additives to formulate 2 sets of low corrosivity acid fluids for operation at 180℃. Laboratory experimental results showed that:1) the corrosion rate N80 steel in the presence of the corrosion inhibitor at 180℃ was 70 g/m²·h, indicating that the corrosion inhibitor developed has very good corrosion inhibiting capacity. 2) precipitation and stratification were not observed in the acid fluids formulated with the corrosion inhibitor, meaning that the additives used to formulate the acid fluids have good compatibility and filtration control capacity. 3) at 180℃, the average corrosion rates of N80 steel plate in 0.4% and 0.8% gel acids were 87.3 g/(m²·h) and 95.8 g/(m²·h), respectively. In high temperature deep well acid fracturing operation, the high temperature low corrosivity acid fluids had almost no negative effect on downhole strings and downhole tools; tubing strings pulled out of hole after operation had smooth inner walls. The acid fluids had good properties before and after acid fracturing operation, and the well was in safe conditions throughout the operation.