Modeling of CO2 Flooding and Huff and Puff Considering Molecular Diffusion and Stress-Dependent Deformation in Tight Oil Reservoir

Abstract

Abstract Recently, the potential of enhanced oil recovery (EOR) with CO2 injection in tight oil reservoir has drawn attention. Most of previous studies for CO2 injection in tight oil reservoir have considered only huff-and-puff process. However, CO2 flooding could show further improvement depending on the fracture-reservoir system. To investigate the effects of CO2 flooding and huff-and-puff processes in tight oil reservoir, numerical models incorporating molecular diffusion and stress-dependent deformation mechanisms were generated. In order to model the realistic tight oil reservoir, core and reservoir models were constructed with data from Bakken shale field. Coand counter-diffusive transport is depicted by Sigmund and Wilke correlation. Stress-dependent deformation in tight reservoir is considered by exponential correlation coupled with linear-elastic model. The developed models were used to investigate major factors affecting CO2 injection process such as molecular diffusion, stress-dependent compaction, and conductivity of fracture system. In the proposed model, about 8% of hydrocarbon was recovered during the primary production. Recoveries with CO2 flooding and huff-and-puff following primary production are increased to 18 and 15%, respectively. The main factor which facilitates CO2 flooding is the fracture conductivity of unstimulated zone. Because the middle Bakken formation shows relatively higher permeability and fracture conductivity than other ultra-tight reservoirs, the CO2 displaces the oil between wells with flooding. In case of the reservoir with lower fracture conductivity, on the ther hand, huff-and-puff process is better than flooding process for EOR. In addition, CO2 flooding process showed higher CO2 storage than huff-and-puff process. CO2 flooding method stores 1.7 times higher CO2 than huff-and-puff method. About 91% of injected CO2 is stored for CO2 flooding and about 54% of injected CO2 is stored for huff-and-puff. Therefore, the need to develop CO2 flooding techniques is evident in order to improve not only the oil recovery but the CO2 storage. The investigation of CO2 flooding and huff-and-puff with comprehensive numerical model suggests better understanding and design of CO2 injection in order to improve the efficiency of CO2 EOR and storage in tight oil reservoirs.