Horizontal drilling and hydraulic fracturing have enabled production from Bakken tight oil reseroirs. However, since the primary recovery is very low, it is important to use enhanced oil recovery methods to unlock part of the remaining oil in the reservoir. In this study, the CO2 injection as a huff-n-puff EOR process is studied. Numerical simulation was used for coupling the reservoir fluid flow with geomechanics to study the stress and deformation of reservoir rock in a CO2-EOR process. The simulation was performed through porosity and permeability relationships with pressure, temperature, and mean total stress for iterative coupling of stress and flow to account for the effect of geomechanics in CO2-EOR.