Investigation of phase behavior and reservoir fluid properties in support of enhanced oil recovery of Alaska North Slope (ANS) viscous oils

Abstract

Declining light oil production on Alaska North Slope (ANS) has attracted oil producers to develop viscous oil resources of ANS that range between 20 to 25 billion barrels. These oils are viscous, flow sluggishly in the formations, and are difficult to transport through unconsolidated formations and are hard to produce by conventional methods. Viscous oil recovery entails neatly designed enhanced oil recovery processes and the success of these processes is critically dependent on accurate knowledge of phase behavior and fluid properties of these oils under variety of pressure and temperature conditions. An experimental study was conducted to quantify the phase behavior and physical properties of viscous oils from ANS. The oil samples were compositionally characterized by simulated distillation technique, constant composition expansion and differential liberation tests were conducted on these samples. Experimentally studied phase behavior and reservoir fluid properties were modeled by using the Peng-Robinson Equation-of-State (EOS). The Peng-Robinson EOS was tuned with experimental data to predict the phase behavior, accurately. Widely used corresponding state viscosity model predictions deteriorate when applied to heavy oil systems due to use of ultra-light methane as a reference compound. Therefore, a semi empirical approach (Lindeloff model) was adopted for modeling the viscosity behavior. Viscosity behavior of degassed ANS viscous oils was correlated to their temperature and molecular weight. Integration of this correlation into the Lindeloff model resulted in accurate viscosity predictions for viscous oils under reservoir conditions.