The challenges of polymer application to the low cretaceous limestone reservoir in Al Shaheen field, offshore Qatar, are low permeability (~10 mD) and high salinity (~50,000ppm). This study aims to investigate the injectivity and recovery mechanisms of polymer flooding by experimental study, including polymer rheological properties, core heterogeneity evaluation, resistance factor determination and core floods for oil recovery monitored by CT scan. The main conclusions are: The incremental oil recovery of polymer floods in very low permeability (~10 mD) Al Shaheen field cores ranges from 12.8% to 25.4% accompanied by large pressure drops. The polymer flooding in field cores appears to be very effective under the current conditions and warrants further study. Conversely, the incremental oil recovery of tertiary polymer floods in medium permeability (~100-200 mD) limestone cores is small and continues the trend of water floods. CT scan is essential for understanding the displacement results influenced by core heterogeneity.