Matching between the diameter of the aggregates of hydrophobically associating polymers and reservoir pore-throat size during polymer flooding in an offshore oilfield

Abstract

Abstract In order to quantitatively study the matching between hydrophobically associating polymers (HAPs) and reservoir pore-throat size in offshore oilfields, the geological characteristics and fluid properties of the S area reservoir in the Bohai Oilfield were used as a research platform. After determining the matching of HAP solutions with different association degrees and core permeabilities using a seepage experiment at a constant flow rate, the matching between the diameter of the HAP aggregates (Dh) and the median pore-throat radius was quantified by combining the relationship between core permeability and median pore-throat radius. Finally, the importance of matching on the oil displacement effect of the HAP solution was demonstrated using homogeneous cores and heterogeneous cores with separate injection and production interlayers. The results showed that the diameter of the HAP aggregates, as well as their morphology and ability to increase viscosity, were highly related to the association degree of HAP. As the association degree of HAP was varied, the matching between cores with different permeabilities and the beta-cyclodextrin (β-CD)/HAP compound systems also changed. Under the experimental conditions used in this study, the ratio between the median pore-throat radius and Dh ranged from 4 to 7. During the process of HAP flooding, suitably increasing the Dh, i.e., increasing the association degree between HAP molecules, could allow control of the mobility of the HAP solution. The oil displacement effect of HAP was closely related to the matching between the HAP and reservoir pore-throat, rather than the viscosity of the HAP solution. Good matching between the HAP and reservoir pore-throat not only achieves fluid diversion but can also expand the swept volume in the low-permeability layer to ensure good oil displacement ability.