Decrease in viscosity of partially hydrolyzed polyacrylamide solution caused by the interaction between sulfide ion and amide group

Costa

J of Applied Polymer Sci

et al. 2019

Partially hydrolyzed polyacrylamide (HPAM) is the water-soluble polymer most often used in flooding applications in the petroleum industry. However, in aqueous solutions at high temperatures, HPAM undergoes hydrolysis of the lateral amide groups, and the presence of salts in the solution can lead to precipitation of this polymer. Therefore, a method was developed to monitor the thermal stability of HPAM solutions in different saline environments and varying temperatures. The proposed test method involved measurements of intrinsic viscosity as a function of time and determination of the degree of hydrolysis of the HPAM by elemental analysis. The results obtained indicated that the presence of divalent cations (Ca +2 and Mg +2 ) negatively influenced the intrinsic viscosity of the solutions and in some systems led to precocious precipitation of the polymer in environments with higher concentrations of these cations. The hydrolysis reaction of the amide groups to the acrylate groups of the HPAM chain was significantly affected by rising temperature: at 50 C, hydrolysis occurred, but not as significantly as at 70, 85, 90, and 95 C. Hydrolysis up to 84% was observed for solutions processed at 90 C. The results also indicated limits of hardness for the brine at some temperatures: 1353 ppm for 95 C and 2867 ppm for 70 C. For brine containing 13,610 ppm or more of divalent cations, hydrolysis and precipitation of the polymer were not observed at 50 C.

Section: Introductionmentioning

confidence: 99%

Hydrolysis and thermal stability of partially hydrolyzed polyacrylamide in high‐salinity environments

Costa

J of Applied Polymer Sci

et al. 2019

“…The most accepted mechanism proposes that the presence of cations interferes in the water double layer and reduces the repulsion between the acrylate monomers which shrink the polymer structure reducing the viscosity obtained . Also, the cations interact with the charged group of HPAM, which affects the inter-polymer interaction and avoids the creation of the viscoelastic network. ,, The effect of anions was also studied, but with the exception of S 2– , the viscosity degradation is negligible . However, several species of ions can be present in the brines, and also new species can appear in the interaction with the reservoir brine, each of them with different effects over HPAM.…”

Section: Introductionmentioning

confidence: 99%

Effect of the Cations (Na⁺, Ca²⁺, Fe²⁺, and Fe³⁺) on the Partially Hydrolyzed Polyacrylamide Shrinking by Molecular Dynamics Simulations

2022

The presence of cations on injection fluids used during polymer flooding leads to viscosity losses of the polymeric solution and reduces its drag capacity. Thus, understanding the mechanisms of this chemical degradation is crucial to improving the efficiency of these treatments. This study focused on obtaining physical insights into the mechanisms involved in chemical degradation by molecular dynamics simulations. To do this, the interaction energies between a variety of cations present at polymer flooding (Na + , Ca 2+ , Fe 2+ , and Fe 3+ ) and partially hydrolyzed polyacrylamide (HPAM) were calculated. First, several potentials for ion description were evaluated to guarantee a proper description of the ion hydration. Then, multiple simulations were carried out to understand the effect of each ion individually and the synergic effect of a mixture of ions (brine) on the HPAM chain shrinking. The radius of gyration of the HPAM chain was used as an evaluation parameter of the chain shrinking. The results indicate that multivalent cations have a stronger interaction with the polymer than the monovalent cations, exhibiting smaller interaction distances and higher interaction energies. These interaction energies are related to the ionic radius of the cations and their charge. Smaller cations get close enough to avoid the repulsion between charged monomers, being the Coulombic interactions the most important (two-third of the total interaction energy). Thus, the strongest interaction energies with the HPAM correspond to multivalent cations, which reduce the radius of gyration of the HPAM since they can interact with two carboxylate oxygen simultaneously. Interestingly was found a high dependence of the concentration of Fe 3+ cations in the interaction with HPAM; at high concentrations, the cations cannot get close enough to interact with the polymer, but in low concentrations, the cations present the strongest interaction. These findings contribute to understanding the mechanisms that macroscopically are related to viscosity losses in the solution by the cation effect.

“…This knowledge is essential to improve polymer performances in reservoirs with sulfide. Since the flow mechanisms of polymers are initially obtained from microscopic seepage experiments [16], it is of great significance to observe the flow field of HPAM and to analyze the mechanisms affecting recovery [17][18][19][20]. However, instead of accurate pore scale flow fields, a traditional microscopic seepage experiment only provided results on multiphase morphology and saturation [21].…”

Section: Introductionmentioning

confidence: 99%

Pore-Scale Flow Fields of the Viscosity-Lost Partially Hydrolyzed Polyacrylamide Solution Caused by Sulfide Ion

Niu

et al. 2022

Energies

The rheology of a partially hydrolyzed polyacrylamide (HPAM) solution plays an important role in its oil recovery during polymer flooding. However, multiple factors in brine, such as sulfide ions, cause a dramatic loss in the viscosity and oil recovery. To better understand the sulfide-induced viscosity loss and the consequent flow mechanisms in pore networks, the morphology of polymer solutions with and without sulfide ion was observed by scanning electron microscopy; and the variations of the pore scale flow fields were demonstrated by a microscopic visualization seepage experiment combined with Micro-PIV (Microscale Particle Image Velocimetry). The results showed that, with the presence of sulfide ion, the microstructure of the polymer changed from a uniform three-dimensional network structure to loose and uneven floccules, which resulted in viscosity loss (over 70% with 5-mg/L sulfide ion). Moreover, higher concentrations of sulfide ions (5 mg/L and 10 mg/L) resulted in earlier shear thinning characteristics than those with lower sulfide concentrations. Due to viscosity loss, the average flow velocity in the main stream of the microscopic seepage experiment increased more significantly than that without sulfide. However, the viscosity loss alone cannot independently explain the severe viscous fingering during the subsequent post-water flooding, which was about five times greater than that of the primary water flooding in terms of the velocity ratio between the mainstream and margin. A further pore-scale flow field analysis exhibited an eccentric and a bimodal velocity distribution in the throat along the radial and axial directions, respectively. The former distribution indicated that the adsorbed polymer on the pore wall was broken through by hydraulic shear due to the collapsed structure caused by sulfide ion. The latter suggested that another sulfide-induced impact was an earlier-occurring non-Newtonian characteristic with a low shear rate. Therefore, instead of viscosity loss, elastic loss is the dominant mechanism affecting the characteristics of the aggregate flow field under the action of sulfide. Microscopic flooding combined with Micro-PIV is a feasible and essential method to reveal pore scale flow mechanisms.