Performance evaluation and oil displacement mechanism of special viscoelastic fluid in high salinity media

Key words:  enhanced oil recovery  crosslinking polymer gel  intramolecular crosslinking  viscoelasticity  the first normal-stress difference  molecular aggregated state structure  crosslinking mechanism

Abstract:

The viscosity, molecular aggregated state structure, molecular coil dimensions, viscoelasticity and influence factors of the partially hydrolyzed polyacrylamide (HPAM) and the Cr³⁺ crosslinking polymer solution were studied by using Bush viscometer, rheometer, dynamic light scattering and scanning electron microscope. The flow characteristics and profile modification of crosslinking polymer were evaluated using core flow and flooding experiments. The results show that intramolecular crosslinking reaction and intermolecular crosslinking reaction both could take place by adjusting the solvent salinity and crosslinking agent mass concentration. The intramolecular crosslinking would make the system viscoelasticity increase obviously, but the intermolecular crosslinking has a little influence on the viscoelasticity. The intramolecular crosslinking reaction occurs first, and then intermolecular crosslinking reaction occurs. And the viscoelasticity not only could improve cleaning efficiency, but also could expand the microcosmic sweep coefficient. Compared with the same concentration polymer solution, the viscosity of intramolecular crosslinking polymer gel is similar, but the molecular coil dimensions, viscoelasticity, drag coefficient and residual drag coefficient of intramolecular crosslinking polymer gel are greater, so high oil displacement efficiency can be obtained.