It is very difficult to estimate the performance of water flooding on the sweep efficiency and oil recovery for a fractured reservoir, especially for a basement fractured reservoir. Understanding the two-phase flow behavior of oil and water and the mechanism of oil residue in a fracture is, therefore, required for the improvement of water flooding performance to the fractured reservoir.

In this study, some cases of water flooding simulation using lattice Boltzmann method (LBM) have been conducted for a single fracture in order to investigate the effects of viscous ratio (water/oil) and positions of inlet and outlet on the oil recovery and the condition of oil residue in detail. The inlet and outlet positions are actually determined from the positions where the other two single fractures cross the now considering single fracture in a fractured reservoir.

The results show that the oil recovery increases as the viscous ratio increases in every case. This is because the difference of flow velocity depending on the aperture becomes smaller as the viscous ratio increases, and consequently the sweep efficiency is improved. In addition, the increment of oil recovery strongly depends on the inlet and outlet positions, and the oil displacement area expands to the other relatively large aperture regions as the viscous ratio increases even when the injected water is more difficult to flow into a main flow pass due to the blocking by contact regions. It is also found that the cross-sectional shape of injected water front is changed by changing the viscous ratio and affects to the residual condition of oil on the fracture surface. These results are difficult to obtain from a conventional reservoir simulation study and useful to develop a new effective method of improved oil recovery (IOR) from the fractured basement reservoirs.

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