Oil Movement Investigation at Pore-Scale in Waterflood Fluvial Reservoir

In the process of fluvial reservoirs development, bottom water coning leads to the problem of increasing water cut and low oil production. There are still significant amount of remaining oil in the upper layers of reservoirs after long-term waterflood. Drilling one or more lateral drainholes near the top of the formation is the main acceptable enhance oil recovery techniques to unlock additional recoverable reserves, but the microscopic oil movement in pores of different sizes is unclear. Nuclear magnetic resonance (NMR) is an effective way for analyzing pore structures and quantifying oil saturation in the rock matrix. In this paper, three-dimension physical model experiment was performed to evaluate the distribution and movement of oil in pores. During the water flooding progress, oil in large-medium pores was displaced first. After further displacement, oil in small pores begin to be produced. The oil recovery of small pores was even larger than the medium and large pores in the later stage of waterflood because of imbibition effect. The ultimate recovery of large pore in both top and bottom formation was almost the same, while the ultimate recovery of small pores varied with the degree of displacement. Substantial amount of remaining oil existed in the upper layer and in the small-medium pore of bottom layer after long-term waterflood.