In this thesis, miscible CO2 water-alternating-gas (CO2-WAG) injection in the tight Bakken formation and the effectiveness of CO2-enhanced oil recovery (CO2-EOR) methods in the fractured Bakken formation were experimentally studied. First, the saturation pressure Psat, oil-swelling factor (SF), oil density, and CO2 solubility of CO2-saturated Bakken light crude oil were measured by using a PVT system. Second, the viscosities of CO2-saturated Bakken light crude oils with different CO2 concentrations were measured by using a capillary viscometer. Third, the vanishing interfacial tension (VIT) technique was applied to determine the minimum miscibility pressure (MMP) of the Bakken light crude oil and CO2 at the actual reservoir temperature. In addition, a total of nine coreflood tests were conducted through respective waterflooding, continuous miscible CO2 flooding, and miscible CO2-WAG injection in the tight Bakken formation. In the miscible CO2-WAG injection, different WAG slug sizes of 0.125, 0.250, and 0.500 pore volumes (PVs) and different WAG slug ratios of 2:1, 1:1, and 1:2 were used to examine their specific effects on the oil recovery factor (RF), cumulative water production (Qw), and average gas production rate (qg) in the tight Bakken formation. Last, four more coreflood tests were carried out to evaluate CO2-EOR processes in the fractured Bakken formation. Specifically, the first two tests were performed to examine CO2-soaking effect on miscible CO2 secondary flooding and the last two tests were undertaken to study the fracture effect on CO2-WAG injection in the fractured Bakken formation. The experimental results showed that saturation pressure Psat and oil SF of CO2-saturated Bakken light crude oil were increased respectively in the ranges of 2.01–9.29 MPa and 1.05–1.62 when CO2 concentration was increased in the range of 18.64–70.11 mol.%. The density was increased marginally at low CO2 concentrations and did not change appreciably by dissolving more CO2 into the Bakken light crude oil. The measured CO2 solubility was increased from 30.0 to 313.6 cm3 CO2/cm3 oil as the saturation pressure was increased from 2.01 to 9.29 MPa. The viscosities of CO2-saturated Bakken light crude oils with 18.64 and 70.11 mol.% CO2 concentrations were reduced to 56% and 28% of the original dead Bakken light crude oil viscosity at the same reservoir temperature. The measured equilibrium interfacial tension (IFT) was reduced almost linearly with the equilibrium pressure and the MMP was determined to be 10.0 MPa. The miscible CO2-WAG injection had the highest oil RF (78.8% in Test #3), in comparison with waterflooding (43.2% in Test #1), continuous miscible CO2 flooding (63.4% in Test #2), and miscible CO2 gas-alternating-water (CO2-GAW) injection (66.2% in Test #8). Furthermore, a smaller WAG slug size of CO2-WAG injection led to a higher oil RF and the optimum WAG slug ratio was approximately 1:1 for the tight Bakken formation. Over 60% of the light crude oil was produced in the first two cycles of the miscible CO2-WAG injection. The CO2 consumption in the optimum miscible CO2-WAG injection was much less than that in the continuous miscible CO2 flooding. The final oil RF of CO2 injection with a CO2-soaking period of 24 h was 9.7% higher than that of CO2 injection without CO2 soaking in the fractured Bakken formation. The CO2-WAG injection was less effective in the fractured Bakken formation than in the tight Bakken formation.