Abstract
Scale inhibitor squeeze treatment is often used to prevent scaling in the oil field. However, some inhibitors show poor retention in the conventional squeeze treatment, where less than 50% of the inhibitors are retained in the formation. It has been shown that the addition of transition metal ions, such as Zn2+, and Cu2+ significantly increases inhibitor retention and effectiveness. In this study, calcite and oil field core material were used in laboratory squeeze simulations to test the squeeze efficiency of phosphonate and polymeric scale inhibitors. Three squeeze procedures, whereby transition metal ions are added into inhibitor pill, overflush solution, and preflush solution were compared. It was demonstrated that over 90% of BHPMP and PPCA were retained when Zn2+ and Cu2+ were added in the pill, overflush and preflush solution. Simulation indicates that squeeze life may be improved by a factor of 60 or greater if these new squeeze procedures are used. The mechanism of enhancing inhibitor retention is also discussed in the paper. It is probably due to the formation of transition metal-inhibitor and Ca-inhibitor co-precipitate, and more stable complex of transition metal ion with inhibitor. Zn2+ displacing Ca2+ from the calcium containing rock and forming a new solid phase ZnCO3 have been evidenced. This solid will enhance the inhibitor depositing in the formation and probably also serve as a sulfide scavenger to remove hydrogen sulfide from conate brine in the formation.