Microscopic Studies of Immiscible Displacement Behavior in Interconnected Fractures and Cavities

Carbonate rocks are generally highly heterogeneous that make it difficult to accurately assess the behavior of fluid flow and transport in them. In this paper, we experimentally investigate the oil-water displacement in carbonate reservoirs by mimicking the typical pore vugs of carbonates through fabricating glass micromodels. The micromodels were saturated completely with oil, and then water was injected continuously at a constant rate until a steady state was achieved. After that, the injection rate was increased in steps. For each injection rate, water was continuously injected until a steady state was achieved and then increased to the next injection rate. For each injection rate, the displacement process of oil and water in the micromodel was captured by a digital video camera. Experimental results show that water breakthrough occurs in pure-fracture channels earlier than that in fracture-cavity channels. The wettability and pore networks of fractures and vugs have a significant impact on the distribution of trapped oil. Oil is preferential to be trapped in the oil-wet zone and the zone where deviation from the mainstream line starts. Residual oil saturation shows no noticeable change with relatively low injection rates. However, when the injection rate exceeds a critical value, residual oil saturation decreases with an increase in the injection rate.