Determining Safe Maximum Temperature Point (SMTP) for Polyacrylamide Polymer (PAM) in saline solutions

Abstract

Polyacrylamide (PAM) and partially hydrolysed polyacrylamide (HPAM) are the most used water soluble polymers in Enhanced Oil Recovery (EOR) applications because they represent a powerful means of increasing the viscosity of injection water and most importantly, improving mobility ratio. However, they exhibit limited stability in harsh reservoir conditions of elevated temperature and high salinity, which is a serious technical challenge. This paper describes a correlation analysis of the gradient of PAM hydrolysis and viscosity as a function of time, temperature (within the range of 25 to 93oC) and salinity, to determine the safe maximum temperature point (SMTP) during improved and enhanced oil recovery (IOR/EOR) applications. The results indicate that different saline solutions such as NaCl, CaCl2 and NaHCO3 contains different SMTPs. At 5% NaCl, the SMTP was about 71oC, while for a combined saline solution containing 9% NaCl and 1% CaCl2 the SMTP was 78oC while it was 65oC for 3% NaCl and 1% NaHCO3. However, the results indicate that a saline solution containing chemical properties of alkaline/acid behaviour, such as NaHCO3, hydrolysed more rapidly due to its lower SMTP value. Accordingly, this report provides insights into the chemistry behind PAM degradation and can help in predicting the maximum safe temperature point of polyacrylamide operations in the presence of brine at any ageing time of interest during chemical IOR/EOR techniques.