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.
Highlights
Polymer flooding is a well-established tertiary recovery mechanism and mature enhanced oil recovery (EOR) process
Viscoelastic phenomena of polymer solutions in porous media can be observed via a similar approach to that proposed by Heemskerk et al [81]
This approach measures the pressure drop approach to that proposed by Heemskerk et al [81]
Summary
Polymer flooding is a well-established tertiary recovery mechanism and mature enhanced oil recovery (EOR) process. As water flooding has been adopted in most mature fields, adding polymers to the injected water costs less than other chemical EOR methods, which require, for instance, the use of surfactants. Polymer flooding has been the most widely used chemical EOR process since the 1960s [1]. As the mode of action, polymer increases viscosity in the injected aqueous phase, Appl. Sci. 2020, 10, 4152 generating higher ultimate recovery due to better sweep efficiency and improved mobility control [2]
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