Experimental and simulation determination of minimum miscibility pressure for a Bakken tight oil and different injection gases

Abstract

The effective development of unconventional tight oil formations, such as Bakken, could include CO₂ enhanced oil recovery (EOR) technologies with associated benefits of capturing and storing large quantities of CO₂. It is important to conduct the gas injection at miscible condition so as to reach maximum recovery efficiency. Therefore, determination of the minimum miscibility pressure (MMP) of reservoir live oil-injection gas system is critical in a miscible gas flooding project design. In this work, five candidate injection gases, namely CO₂, CO₂-enriched flue gas, natural gas, nitrogen, and CO₂-enriched natural gas, were selected and their MMPs with a Bakken live oil were determined experimentally and numerically. At first, phase behaviour tests were conducted for the reconstituted Bakken live oil and the gases. CO₂ outperformed other gases in terms of viscosity reduction and oil swelling. Rising bubble apparatus (RBA) determined live oil-CO₂ MMP as 11.9 MPa and all other gases higher than 30 MPa. The measured phase behaviour data were used to build and tune an equation-of-state (EOS) model, which calculated the MMPs for different live oil-gas systems. The EOS-based calculations indicated that CO₂ had the lowest MMP with live oil among the five gases in the study. At last, the commonly-accepted Alston et al. equation was used to calculate live oil-pure CO₂ MMP and effect of impurities in the gas phase on MMP change. The Bakken oil-CO₂ had a calculated MMP of 10.3 MPa from the Alston equation, and sensitivity analysis showed that slight addition of volatile impurities, particularly N₂, can increase MMP significantly.

Keywords

Enhanced oil recovery / CO₂ miscible flooding / Unconventional tight oil reservoirs / Bakken formation / Minimum miscibility pressure

Acknowledgments

The Authors acknowledge the financial support from the Petroleum Technology Research Centre (PTRC) and the participating oil companies in the PTRC's STEPS (Sustainable Technologies for Energy Production Systems) program. The Authors also wish to express their appreciation to Danie Subido, Kevin Rispler, and Rupan Shi for carrying out the experimental measurements, and to Brenda Tacik for editorial support.

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