A Comprehensive Model for Investigation of CO2-EOR with Nanopore Confinement in the Bakken Tight Oil Reservoir

Abstract

Abstract CO2 injection is an effective enhanced oil recovery (EOR) method in unconventional oil reservoirs. However, the investigation of CO2 Huff-n-Puff in tight oil reservoirs with nanopore confinement is lacking in the petroleum industry. The conventional models need to be modified to consider the nanopore confinement in both phase equilibrium and fluid transport. Hence, we develop an efficient model to fill this gap and apply it in the field production of the Bakken tight oil reservoir. Complex fracture geometries are also handled in this model. First, we revised the phase equilibrium calculation and evaluated the fluid properties with nanopore confinement. An excellent agreement between this proposed model and the experimental data is obtained considering nanopore confinement. Afterwards, we verified the calculated minimum miscibility pressure (MMP) using this model against the experimental data from rising-bubble apparatus (RBA). We analyzed the MMP and well performance of CO2-EOR in the Bakken tight oil reservoir. Based on the prediction of the field data, the MMP is 5.4% lower than the MMP with bulk fluid when the pore size reduces to 10 nm. Subsequently, we examined the impacts of key parameters such as matrix permeability and CO2 molecular diffusion on the CO2 Huff-n-Puff process. Results show that both CO2 diffusion and capillary pressure effect improve oil recovery factor from tight oil reservoirs, which should be correctly implemented in the simulation model. Finally, we analyzed well performance of a field-scale horizontal well from the Bakken formation with the non-planar fractures and natural fractures. Contributions of CO2 diffusion and capillary pressure effect are also examined in depth in field scale with the complex fracture geometries. The oil recovery factor of CO2 Huff-n-Puff process with both CO2 diffusion and capillary pressure effect increases by as much as5.1% in the 20-year period compared to the case without these factors. This work efficiently analyzes the CO2 Huff-n-Puff with complex fracture geometries considering the CO2 diffusion and nanopore confinement in the field production from Bakken tight oil reservoir. This model can provide a strong basis for accurately predicting the long-term production with complex fracture geometries in the tight oil reservoirs.