Performance Evaluation of Polyacrylamide Polymer to be Applied in Water-Based EOR Methods at High Salinity/High Temperature Condition; Polymer Rheology and Adsorption Studies

Performance evaluation of polymers with different chemical structure considering temperature and salinity tolerance and adsorption on rock surface, is one of key step through the design of a water-based EOR project. The aim of this paper is to evaluate the performance of polyacrylamide-based polymers to be applied in water-based EOR methods in a reservoir with high salinity/high temperature condition. To do so, based on the results of previous researches, four different polymers with distinguished chemical structure were selected, and a series of rheology measurements, thermal stability and static adsorption tests were performed using the selected polymers. Based on the results of rheology measurements, the viscosity (at the equivalent reservoir shear rate) of 2000 ppm HPAM solution prepared in seawater was 25 cp, while HPAM was insoluble in formation water. However, addition of sulfonate (SPAM), sulfonate and acrylic acid (SAPAM) and sulfonate and polyvinylpyrrolidone (SVPAM) polymer chains to HPAM structure increased the HPAM tolerance to salinity of makeup water, in a way that the viscosity retention of SPAM and SAPAM polymer was 35.3% and 44.3%, respectively. However, the maximum viscosity retention due to increase in makeup water salinity from seawater to formation water was obtained in the case of SVPAM with 55% of viscosity retention. Moreover, the viscosity retention as the result of 120 days aging in reservoir temperature was 2% in the case of HPAM, while in the case of SPAM, SAPAM and SVPAM the viscosity retention is improved to 25%, 31% and 73%, respectively. Furthermore, due to the lowest polymer molecular weight, the minimum of polymer adsorption on the rock surface was obtained in the case of SVPAM. According to static adsorption measurement tests, for 2000 ppm polymer solutions, adsorption of SVPAM on reservoir rock surface was 765 micro gr of polymer/gr rock, while the adsorption of HPAM, SAPAM and SPAM was 1475, 1265 and 1134 micro gr polymer/gr rock. Also, adsorption data reported in this article was in agreement with Langmuir’s adsorption isotherm. The results of this paper approve the potential of SVPAM polymer to be considered in the studies related to design of polymer flooding projects for high temperature/high salinity oil reservoirs, and also shed light on the importance of the selection of polymer chemical structure and molecular weight through EOR polymer studies.