Seepage Characteristics of a Low Permeability Sandstone Reservoir in Mobei Oilfield, Junggar Basin

The microscopic pore structure characteristics and the oil-water two-phase seepage law in the low permeability sandstone reservoir in Mobei oilfield in Junggar Basin were analyzed through laboratory experiments. The results of mercury pressure, constant velocity mercury pressure, thin slice of casting, and CT scan analyses showed that the reservoir had strong microheterogeneity with the presence of local large channels. The large channel had a small volume but considerably contributed to the permeability, which played a crucial role in the reservoir seepage. The relative permeability curve showed that with the increase of water saturation, the relative permeability of the oil phase decreased rapidly; the water phase relative permeability of glutenite, gravel-bearing sandstone, and coarse sandstone increased slightly; and the water cut increased rapidly. The relative permeability of the water phase of medium and fine sandstone increased, the water cut increased rapidly, and the residual oil saturation was high. In the process of core displacement, on-line CT scanning monitoring showed that before the breakthrough of the water drive front, the oil saturation decreased greatly along the way. After the breakthrough of the water drive front, the water cut increased rapidly and directly entered the ultrahigh water cut stage. Owing to the serious heterogeneity of the micropore structure, the fingering phenomenon was obvious in the process of displacement.