Miscible EOR Process Assessment for Unconventional Reservoirs: Understanding Key Mechanisms for Optimal Field Test Design
The objective of this study was to design an optimal Huff-n-Puff enhanced oil recovery (EOR) scheme for a field test in unconventional reservoirs. Using an integrated workflow for process assessment, our study indicates that carbon dioxide (CO2) Huff-and-Puff may be a technically feasible EOR method for unconventional reservoirs.
The main recovery mechanisms were: 1) vaporization of lighter oil components, and 2) interfacial tension (IFT) reduction at pressures above the minimum miscibility pressure (MMP). Moreover, the presence of hydraulic and natural fractures may provide a large contact area for injected gas to penetrate into the ultra-low permeability matrix. The effect of molecular diffusion was also investigated, but this did not appear to have a major impact on recovery for the modeled conditions at the field scale. The cycling scheme evaluation indicated that oil recovery is proportional to the mass of CO2 injected, and longer soak times do not greatly affect the amount of oil recovered from a Huff-and-Puff cycle.
This study found that the time to switch a well back to injection was when oil production returns to the pre-treatment base decline rate. The modeling also indicated that optimizing the cycles can result in a reasonable increase in oil production at acceptable utilization ratios.
These results suggest that miscible Huff-and-Puff could be a technically feasible EOR method for unconventional reservoirs.
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© Copyright 2018. 2018. Unconventional Resources Technology Conference
This paper was prepared for presentation at the Unconventional Resources Technology Conference held in Houston, Texas, USA, 23-25 July 2018.