The thermal degradation of scale inhibitors poses a challenge for scale control and flow assurance in high temperature reservoirs. Targeting this problem, this study investigated the mitigation of scale potential of the most commonly used phosphonate diethylenetriamine penta (methylphosphonic acid) (DETPMP) before and after thermal aging at high temperature.
In this study, the DETPMP stock solution was oxygen removed and kept at 135°C for 7days. The performance of the aged and not aged DETPMP against CaCO3 and CaSO4 formation at high-temperature and high-hardness condition was investigated. The experimental results show the aged DETPMP presented similar inhibition efficiency for CaCO3 but less efficiency for CaSO4 formation prevention compared to the non-aged DETPMP at 105°C in high salinity waters. The chemical characterization of DETPMP using IR and NMR demonstrated that the product had characteristic signals of active materials, resulting from the breakdown of C-N and C-P bond. Compared with the original DETPMP molecules, the formed phosphorus acid compounds with shorter chains and fewer numbers of functional groups in the molecules presented less effectiveness in decreasing CaSO4 crystallization kinetics and lower scale inhibition efficiency. The smaller molecules did not show weaker inhibition of CaCO3 crystallization.