Improved Quantification of Viscoelastic Effects during Polymer Flooding Using Extensional Rheology

  • Author / Creator
    Azad, Madhar Sahib
  • Polymer flooding is one of the traditional chemical enhanced oil recovery (EOR) methods with a high rate of success. Synthetic polymer such as hydrolyzed polyacrylamide (HPAM) characterized by flexible chain exhibits viscoelastic characteristics in porous media. Some of the implications of the polymer viscoelastic effects are reduced injectivity, enhanced residual oil saturation (Sor) reduction, and enhanced permeability reduction. Conventional shear rheology has been used for decades to screen the optimal polymers and simulate the in-situ rheological behaviour. Oscillatory shear rheology has also been used to characterize the viscoelastic properties of EOR polymers. Several research problems exist in the literature because of the existing characterization techniques. The research problems include the inability of the shear rheology to explain the different pressure behavior of HPAM and its similar shear associative polymer. Shear rheology fails to explain the typical flow behavior of associative polymer triggered by intermolecular hydrophobic association. Also, the inability of oscillatory rheology to honour the polymers’ viscoelastic effect on pressure drop and residual oil recovery is a limitation. The hypothesis regarding the polymer’s extensional rheological role on the permeability reduction remains unanswered. While the role of polymer’s viscoelastic effect on Sor reduction has been studied in detail, the extensional rheological role on the sweep efficiency and injectivity for heavy oil recovery conditions is unexplored. Viscoelastic polymers that show thinning in the shear field thickens in porous media after a critical onset rate. Existing viscoelastic models rely on the core flood data to predict viscoelastic behavior such as onset and shear thickening of synthetic polymers in porous media. Performing core flooding with respect to many pertinent EOR variables is a cumbersome process. Other limitations include the inability of the conventional capillary number calculated using apparent viscosity to explain the different residual oil recovery potential of viscoelastic polymers with varying level of elasticity. The rapid residual oil mobilization shown by viscoelastic polymers at the capillary number calculated using the shear/apparent viscosity well below the critical capillary number means that classical capillary theory becomes invalidated in the case of viscoelastic polymers. Also, contrasting opinion exists among leading EOR researchers about the polymer’s linear oscillatory viscoelastic effect on Sor reduction. Displacing polymer solutions propagating in porous reservoirs are subjected to both shear and elongational forces. Rotational rheometer has been used successfully to characterize the shear rheological properties of the EOR polymers. Characterizing the extensional properties of low viscous EOR polymer has been the challenge. In this thesis, capillary breakup extensional rheometer (CaBER) is used for the extensional characterization of EOR polymers. The special features of extensional rheology is its ability to distinguish the similar shear polymers based on elasticity. The higher pressure drop, due to higher permeability and mobility reduction and slightly higher recovery exhibited by the associative polymer over its similar shear HPAM, is due to its higher extensional resistance. Extensional rheology with its unique capability to probe the polymer’s structure clearly explains the typical behavior, triggered by different hydrophobic associations of associative polymer in porous media. Higher Sor reduction, shown by a higher saline polymer solution with a lower oscillatory Deborah number over the low saline polymer solutions with higher oscillatory Deborah numbers, is due to its higher extensional parameters indicative of higher stretch ability. Even though extensional rheology does not play a significant role in the sweep efficiency of heavy oil recovery, its role on injectivity cannot be overlooked. A novel viscoelastic model named Azad Trivedi (AT-VEM) is developed using the concept that viscoelastic polymer that thins in shear field will strain harden in the extensional field. The developed model could predict the viscoelastic onset and shear thickening regime, without any core flooding using direct extensional measurements. Extensional viscosity of viscoelastic polymers are significantly higher than shear viscosity during extensional flow. Modified capillary number developed using extensional viscosity validates the capillary theory and distinguishes the highly elastic polymer (with higher Sor reduction) from less elastic polymer. The correlation named the Azad Trivedi correlation (AT-C) is developed which predicts the Sor of various viscoelastic polymers. This dissertation emphasizes the need for incorporating extensional over shear/oscillatory parameters into polymer screening criteria. Furthermore, AT-VEM and AT-C can be incorporated into the commercial simulators for predicting injectivity and residual oil recovery during polymer flooding.

  • Subjects / Keywords
  • Graduation date
    Spring 2019
  • Type of Item
  • Degree
    Doctor of Philosophy
  • DOI
  • License
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