Impact of Mechanical Degradation on Polymer Injectivity in Porous Media

Abstract

Polymer flooding is an established enhanced oil recovery (EOR) method, still many aspects of polymer flooding are not well understood. This study investigates the influence of mechanical degradation on flow properties of polymers in porous media. Mechanical degradation due to high shear forces may occur in the injection well and at the entrance to the porous media. The polymers that give high viscosity yields at a sustainable economic cost are typically large, MW > 10 MDa, and have wide molecular weight distributions. Both MW and the distributions are altered by mechanical degradation, leading to changes in the flow rheology of the polymer. The polymer solutions were subjected to different degrees of pre-shearing and pre-filtering before injected into Bentheimer outcrop sandstone cores. Rheology studies of injected and produced polymer solutions were performed and interpreted together with in-situ rheology data. The core floods showed a predominant shear thickening behavior at high flow velocities which is due to successive contraction/expansion flow in pores. When pre-sheared, shear thickening was reduced but with no significant reduction in in-situ viscosity at lower flow rates. This may be explained by reduction in the extensional viscosity. Furthermore, the results show that successive degradation occurred which suggests that the assumption of the highest point of shear which determines mechanical degradation in a porous media does not hold for all field relevant conditions.

On the Role of Polymer Viscoelasticity in Enhanced Oil Recovery: Extensive Laboratory Data and Review

“…Because of this stretching and the high shear rate, the polymer molecule has no sufficient time to re-coil itself. By that, the polymer flow is dominated by elongational forces and the viscosity increase is referred to as elongational viscosity or extensional viscosity [ 14 , 58 , 62 , 70 , 71 , 72 ].…”

“…Mechanical degradation can be understood as the break-up of polymer chains or rather molecules due to mechanical forces caused by the high shear stress [ 13 , 17 , 43 , 70 , 71 ]. Usually those conditions are encountered in the near-wellbore region and in the equipment such as pumps and valves.…”

Laminar flow-induced scission kinetics of polymers in dilute solutions

“…For example, polymers used for drag reduction purposes or in enhanced oil recovery fluids are mechanically degraded over time (Seright 1983; Al-Shakry et al. 2018; Soares 2020). Large biopharmaceuticals can break or lose their activity when processed through narrow channels (Lengsfeld & Anchordoquy 2002; Rathore & Rajan 2008; Cook, Wang & Derby 2010; Hawe et al.…”

The seepage flow characteristics of hydrophobically associated polymers with different aggregation behaviours in porous media

“…[4,5]. Mechanical shear will inevitably occur in the process of polymer flooding, which will lead to a significant reduction in the performance of polymer solutions and subsequently affect polymer flooding [6]. Therefore, improving the shear resistance of polymer solutions for oil displacement is the main direction of scientific researchers at present.…”