Rheology and Transport of Improved EOR Polymers under Harsh Reservoir Conditions
- Erandimala Udamini Kulawardana (U. of Texas at Austin) | Heesong Koh | Do Hoon Kim (U. of Texas at Austin) | Pathma Jithendra Liyanage (U Of Texas At Austin) | Karasinghe Upamali (U. of Texas at Austin) | Chun Huh (U. of Texas at Austin) | Upali Weerasooriya (U. of Texas at Austin) | Gary Arnold Pope (U. of Texas at Austin)
- Document ID
- Society of Petroleum Engineers
- SPE Improved Oil Recovery Symposium, 14-18 April, Tulsa, Oklahoma, USA
- Publication Date
- Document Type
- Conference Paper
- 2012. Society of Petroleum Engineers
- 1.6.9 Coring, Fishing, 5.4.7 Chemical Flooding Methods (e.g., Polymer, Solvent, Nitrogen, Immiscible CO2, Surfactant, Vapex), 2.5.2 Fracturing Materials (Fluids, Proppant), 4.3.1 Hydrates, 5.6.5 Tracers, 4.1.2 Separation and Treating, 5.4.10 Microbial Methods, 1.8 Formation Damage, 5.1 Reservoir Characterisation
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New polymers that are stable in harsh environments (high salinity/hardness and high temperature) are in high demand because of the need for chemical EOR in oil reservoirs with these conditions. Commonly used partially hydrolyzed polyacrylamides (HPAM) have been successfully used in the field for decades, but they hydrolyze at high temperature and eventually precipitate in the presence of high concentrations of divalent cations. This paper mainly focuses on rheology and transport behavior of scleroglucan (non-ionic polysaccharide) and N-vinylpyrrolidone (NVP)-polyacrylamide (AM) co-polymer. The rigid, rod-like, triple helical structure of scleroglucan imparts exceptional stability and its non-ionic functionality makes it insensitivity to salinity and hardness. By a different mechanism, NVP in modified HPAM protects the polymer's amide group against thermal hydrolysis, i.e., by sterically hindering the amide group. This allows maintaining high viscosity even in high salinity brines at high temperature. Both scleroglucan and NVP co- or ter-polymers show good filterability and transport properties in sandstone and carbonate cores at high temperature and in brine with high salinity and hardness. Therefore, both polymers are promising candidates for polymer flooding, surfactant-polymer flooding and alkali-surfactant-polymer flooding in hard brine at high temperature, but must be evaluated under specific reservoir conditions.
Introduction and Background
A wide variety of polymers have been evaluated for their possible EOR application under high temperature and high salinity conditions (Askinsat, 1980). Incorporating monomer groups that are much resistant to hydrolysis, 2-Acrylamido-2-methylpropane sulfonic acid (AMPS), poly-vinylpyrrolidones (PVP), or N-vinylpyrrolidones (NVP), (Doe et al., 1987; Levitt and Pope, 2008; Vermolen et. al., 2011) significantly increased their tolerance to divalent ions and improved their resistance to precipitation. On the other hand, polysaccharides such as xanthan gum, scleroglucan, carboxymethylcellulose, and guar gum, have also been extensively investigated for EOR. These biopolymers are less sensitive towards high salinities, temperatures, and mechanical degradation due to their semi-rigid molecular structure (Kohler and Chauveteau, 1981). However, combinations of high temperature, high salinity and high divalent ion concentrations limit the performance of many of these polymers (Davison and Mentzor, 1982).
According to Davison and Mentzer (1982), polyacrylamides, cellulose-based polymers and guar gum showed limited thermal stability and poor sea water viscosification. PVP was a poor viscosifier when considering its molecular weight. Xanthan gum showed better performance but the content cell debris affected its thermal stability, filterability, and adsorption (Davison and Mentzor, 1982; Doe et. al., 1987). Also the upper limit of xanthan gum usefulness was identified as less than 70 oC (Ryles, 1983; Ash, et. al., 1983).
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