Study on gelling effect of Cr3+ polymer gel and its influence factors

Key words:  polymer gel  orthogonal experiment  intramolecular cross-link  seepage characteristics  viscoelasticity  oil displacement efficiency

Abstract:

Although high-concentration polymer has strong viscoelasticity, there exist the compatibility problems between polymer molecules aggregate size and reservoir rock pore size during its practical application. According to the geological characteristics and fluid properties of Daqing Oilfield reservoir, the viscoelasticity and oil displacement efficiency of the intramolecular cross-link polymer gel system were investigated after it was selected by orthogonal experiment through evaluating seepage characteristics, with core flow experiment and oil displacement experiment. It was found that intramolecular cross-link polymer gel system with smaller molecular aggregate, higher resistance coefficient and residual resistance coefficient can be obtained by regulating polymer concentration, water solution salinity and polymer/Cr³⁺. Once intramolecular cross-link reacted in polymer solution, on the one hand, transmission migration ability of polymer molecular clew is enhanced, and its rigidity is also improved. In this way, deformation ability of the polymer molecular clew is weakened when it flows through core pore, which can enhance the retention ability, increase the injection pressure and enlarge sweep volume effectively. On the other hand, the viscoelasticity and first normal stress difference of polymer gel system are improved, as well as the washing oil efficiency. The above two aspects insure jointly Cr³⁺ polymer gel has higher oil displacement efficiency.