An Elongational and Shear Evaluation of Polymer Viscoelasticity during Flow in Porous Media

Abstract

This paper uses a combination of approaches to evaluate the viscoelastic phenomenon in high-molecular-weight polymers (24–28 M Daltons) used for enhanced oil recovery (EOR) applications. Rheological data were cross-analyzed with single- and two-phase polymer flooding experiments in outcrop cores and micromodels, respectively. First, the impact of semi-harsh conditions (salinity, hardness, and temperature) was evaluated. Second, the impact of polymer degradation (sand face flow), focusing on the viscoelastic properties, was investigated. Finally, polymer viscoelastic properties were characterized, proposing a threefold rheological approach of rotational, oscillatory, and elongational behavior. Data from the rheological approaches were cross-analyzed with core flooding experiments and performed at a room temperature of 22 °C and at a higher temperature of 55 °C. The change in polymer viscoelastic properties were analyzed by investigating the effluents from core flooding experiments. Oil recovery experiments in micromodel helped our understanding of whether salinity or hardness has a dominating impact on in situ viscoelastic polymer response. These approaches were used to study the impact of mechanical degradation on polymer viscoelasticity. The brines showed notable loss in polymer viscoelastic properties, specifically with the hard brine and at higher temperature. However, the same polymer solution diluted in deionized water exhibited stronger viscoelastic properties. Multiple flow-behaviors, such as Newtonian, shear thinning, and thickening dominated flow, were confirmed through pressure drop analysis against interstitial velocity as already reported by other peer researchers. Turbulence-dominated excessive pressure drop in porous media was calculated by comparing core flood pressure drop data against pressure data in extensional viscometer–rheometer on a chip (eVROC®). In addition, a significant reduction in elastic-dominated flow was confirmed through the mechanical degradation that happened during core flood experiments, using various approaches. Finally, reservoir harsh conditions (high temperature, hardness, and salinity) resulted in a significant reduction in polymer viscoelastic behavior for all approaches.

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

“…So, as a consequence of the work of Hincapie et al [ 29 ], shear thickening is actually not an increase in fluid viscosity, but only an additional pressure. Similar observations have been made by Clarke et al [ 55 ], Tahir et al [ 20 , 63 ] and Galindo-Rosales et al [ 61 ].…”

“…It is important to mention that the critical shear rates shown in Figure 5 are only exemplary and can differ between different polymer types, solution properties as well as different porous media. The shear-thinning behavior was also experimentally investigated and extensively analyzed by Hincapie [ 8 ], Rock et al [ 30 ], Tahir et al [ 20 , 63 ] and Sheng [ 14 ] among many other researchers.…”

“…Shear-thickening behavior can be observed after the polymer flow has reached the second critical shear rate as shown in Figure 5 . A remarkable observation that can be made from this plot is that shear thickening is only encountered in porous media during polymer flooding and not in rotational rheometer measurements [ 8 , 20 , 26 , 27 , 63 , 65 , 66 , 67 , 68 ]. It is believed that the missing shear thickening is the result of the missing flow motion, since the viscosity increase is commonly explained with a distinctive stretching of the polymer molecule [ 27 , 69 ].…”