Quantifying physical properties of Weyburn oil via molecular dynamics simulation

• Developed a generalized MD compositional model for the Weyburn CO2-EOR process.
• Quantified CO2 mixing under long term CO2-EOR application.
• Captured the existence of fluid microstructures which impact CO2 mixing processes.
• Captured CO2-asphaltene interactions and gas exsolution as pressure declines.

Weyburn and Bakken reservoirs represent two medium gravity tight oil reservoirs who are currently utilizing CO2 injection as an EOR recovery process. To properly establish the CO2 recovery potential, extensive data are required to characterize CO2-oil mixing characteristics. Such data include compositional changes on oil density and oil viscosity as well as component diffusion coefficients. Additional effects of fluid-rock (sand and clay) interactions are also of importance especially due to the tight oil characteristics of such reservoirs.The necessary laboratory data are currently not available to build a reliable field prediction model. Laboratory experiments are costly and time consuming and often show wide variability, especially for non-equilibrium properties for binary and ternary mixtures. This implies significant uncertainties in the previously employed Weyburn 7 component compositional model used for field simulations.Here, we build a 15 component molecular dynamics (MD) model for the Weyburn oil and its mixing with CO2 to quantify these essential equilibrium and non-equilibrium process parameters. Via MD simulation, we established these parameters for the Weyburn oil at two different field conditions. These property results can be used in future CO2-EOR field simulation for Weyburn. A similar MD strategy can be used for other tight oil reservoirs (e.g. Bakken reservoir). This work establishes that MD simulation can be used as a cost-effective tool, along with laboratory experiments and field simulation, in an integrated approach to proper analysis of an EOR development strategy.