Abstract:

In order to explore the effect of fractures on oil displacement in low permeability reservoirs, the oil displacement effect of fractured reservoirs in different water cut stages was studied by a series experiments on glass model micro-oil displacement, micro core dissection and natural core oil displacement, and then the utilization status of various remaining oil under the action of fractures was obtained. The results showed that the saturation of cluster residual oil decreased with the increase of water cut, while the saturation of film, blind end, droplet and column residual oil increased. The residual oil saturation of the fractured models were higher than that of the non-fractured ones, the displacement fluid was channeling in the fractures, and the swept volume was reduced. When the model permeability increased, the cluster residual oil saturation increased, but the other types of residual saturation decreased. The distribution and variation rules of residual oil in micro core dissection experiments were generally consistent with that of the photolithographic glass model, thus proving the reliability of the photolithographic glass model. Seen from the core water flooding experiment, the water flooding law curve of low permeability core was an “S” curve. Water breaks through earlier in the fractured cores than that in the non-fracture ones. And the larger the permeability ratio of fracture to matrix（k_f /k_m） was, the smaller the anhydrous recovery would be.

Key words: water flooding curve, low permeability, oil displacement effect, microscopic residual oil, fracture, residual oil saturation