Permeability-Dependent Retention of Polymer in Heterogeneous Reservoirs

Abstract

Polymer retention occurring in porous media induces significant mobility reduction as well as poor sweep efficiency. In the heterogeneous reservoir, it is very complicated and difficult to analyze performance of polymer due to permeability-dependent retention. Among various mechanisms of retention, mechanical entrapment of polymer affects mainly the propagation of injected polymer solution by forming macromolecular polymer plugging into pore throats, especially occurring in low permeability zone. Besides, polymer adsorption contributes to mobility reduction and polymer retention. The influence of heterogeneity on polymer retention has been not investigated accurately in the reservoir scale and limited to experimental studies, even though both mechanisms are highly dependent on permeability. In this paper, extensive numerical simulations incorporating mathematical modeling on the retention mechanisms have been performed to examine polymer propagation and flow behavior at various heterogeneous reservoir models. All reservoir models have same average permeability and different Dykstra-Parsons' coefficients (V DP ) to represent wide range of reservoir heterogeneity.The results show the amount of polymer adsorption is at high level in low permeability zone. The mechanical entrapment also exhibits same trend with adsorption. Most of polymer retention is accumulated in the low permeability zone, which causes a substantial increase resistance factor in the area. After polymer flooding, total amount of polymer accumulated by retention in the reservoir with V DP =0.72 is 2.5 times more than that of homogeneous reservoir. Furthermore, flow path of polymer solution is restricted to only high permeability zone in the highly heterogeneous reservoir. Thus, the polymer propagates through small pores at a lower rate, giving very poor sweep and irregular propagation path. Sweep efficiency of polymer flooding in the case of V DP =0.72 is reduced about 33% compared to the case of V DP =0.14. This paper could be helpful for an accurate assessment of polymer retention during polymer floods in the heterogeneous reservoirs.

Integrated Analysis of Permeability Reduction Caused by Polymer Retention for Better Understanding Polymer Transport

“…Heterogeneities in petrophysical properties, especially in permeability, can result in these adsorption properties varying significantly within a reservoir system. For example, the adsorbed polymer induces greater resistance to flow in the low permeability layers than in the high permeability layer [14,19,20]. According to the Jewett and Schurz experimental works [9], they found that no accurate correlations between residual resistance factors and permeability were available.…”

Investigating the Effect of Water Softening on Polymer Adsorption onto Carbonates through Single-Phase and Two-Phase Experiments

“…Polymer retention is the phenomenon of losing polymer molecules into the porous medium by various mechanisms, including the adsorption of polymer molecules onto the rock due to dominant binding forces, mechanical entrapment of polymer molecules in small pores, and hydrodynamic retention due to the varying flow rates (Grattoni et al 2004;Choi et al 2014;Zhang and Seright 2015). Several factors influence polymer adsorption, including polymer type, rock surface properties, and connate/injection water properties (Afolabi et al 2019;Ahsani et al 2021).…”