Chapter 3 - Comparative analysis between CO2-EOR mechanisms in conventional reservoirs versus shale and tight reservoirs

Abstract

Abstract This chapter discusses how the recovery mechanisms of CO2 injection differ between unconventional and conventional reservoirs. A methodology which combines real production data with the outputs of reservoir numerical simulation is introduced to diagnose the mechanisms of CO2-EOR huff-n-puff in conventional versus shale and tight oil reservoirs. Two reverse engineering approaches have been integrated to produce a unique type of curve for the performance of CO2-EOR huff-n-puff in shale-oil reservoirs. First, numerical simulation methods were used to upscale the reported experimental outcomes to the field conditions. As a result, forward diagnostic plots have been generated by combining different physical and chemical mechanisms of CO2 with different shale-reservoir conditions. Second, different backward diagnostic plots have been produced from the history match with the CO2 performances of pilot tests conducted in some portions of the Bakken formation in North Dakota and Montana. Finally, the backward and forward diagnostic plots were fitted to produce another unique type of curve, which agrees with the typical general simulation solutions curve, to represent CO2-EOR performance in shale-oil reservoirs. This chapter clearly reports that the CO2-EOR mechanisms in unconventional reservoirs are different from those in conventional reservoirs. Also, the performance behavior of CO2-EOR in the puff stage is totally different in conventional reservoirs. This chapter provides a thorough explanation of how CO2-EOR performance differs at the field scale of conventional reservoirs versus shale formations.