Abstract:The water-soluble polymer PAM (polyacrylamide) is used in enhanced oil recovery (EOR) operations. It is pumped into water injection wells to increase the viscosity of the injected water and in turn to direct more oil towards production wells. This EOR process is proven to be sensitive to operational well conditions such as hydrocarbon reservoir temperature, as well as the salinity of the injected water and/or formation water. These operational conditions lead to technical challenges ranging from the solubility of PAM in injection water to the behaviour of PAM inside the reservoir. To gain a clear picture of the functionality of PAM in EOR applications, this report characterizes its behaviour of in terms of degree of hydrolysis and changes in solution viscosity determined using Perkin Elmer spectrum 100 Fourier transform infrared-Attenuated total reflection (FTIR)-ATR and nuclear magnetic resonance spectroscopy ( 1 H NMR) and a Fann model 35 Couette and Cole Parmer rotational viscometer, respectively. Different shear rates were investigated to determine the effect of shear on PAM gel stability. Experiments were performed for PAM mixed with formation brine at 50, 70, and 90 • C for ageing times of up to 30 days. The results indicate that the degree of hydrolysis achieved after 30 days is much higher in saline solutions than in pure water, and that this effect is more pronounced at higher temperatures. For example, after 30 days at 50 • C, the hydrolysis level was observed to be 53%, rising to 65% at 70 • C and 75% at 90 • C in PAM mixed with brines. Similar trends were observed with viscosity, where lower viscosity was observed for samples at higher temperatures and salinities. It is thus reasonable to conclude that the degree of hydrolysis causes changes in the viscosity of the polymer gel, leading to a decline in its performance as it ages.

Polyacrylamides (PAM) are widely used as water-soluble polymers producing gel in oil reservoirs to assist in oil extraction from reservoirs with high levels of heterogeneity. These gels are susceptible to degradation due to hydrolysis in harsh reservoir conditions such as elevated temperature and salinity. This study uses a polymer integration technique in attempting to optimize the performance of PAM in the enhanced oil recovery process for reservoirs with high temperature and salinity. The results show that, at high temperature, hydrolysis is suppressed and gel stability is maintained via the addition of Polyvinylpyrrolidone (PVP) to PAM solutions. The optimum composition was identified as being 20/80 wt% PAM: PVP for oilfield operations at 90 °C and a moderate salinity of 43,280 ppm. The degree of hydrolysis at 30 days was suppressed from 75% to 29.9%, with associated increases in viscosity from 11 to 38.2 mPa.s and from 18 to 44.3 mPa.s corresponding to rotational speeds of 30 and 10 rpm respectively. The issue of high salinity was considered by increasing the salinity of the optimised PAM: PVP mixture to 200,000 ppm. Under these conditions the degree of hydrolysis of the optimised solution increased from 29.9 to 46.9% and viscosity decreased from 38.2 to 28.6 and from 44.3 to 40.4 mPa.s for rotational speeds of 30 and 10 rpm respectively. 2-Acrylamido-2-MethylpropaneSulfonic acid (AMPS) was added to the mix to try to improve temperature stability. It was observed that, with an optimum composition of 18/72/10 wt% PAM:PVP:AMPS, the degree of hydrolysis decreased to 22% with viscosity levels of 30.6 and 22.8 mPa.s corresponding to rotational speeds of 10 and 30 rpm respectively.

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 93 o C) 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, CaCl 2 and NaHCO 3 contains different SMTPs. At 5% NaCl, the SMTP was about 71 o C, while for a combined saline solution containing 9% NaCl and 1% CaCl 2 the SMTP was 78 o C while it was 65 o C for 3% NaCl and 1% NaHCO 3 . However, the results indicate that a saline solution containing chemical properties of alkaline/acid behaviour, such as NaHCO 3 , 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.

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