Experimental Study of Recovery from a 2-D Layered Sandmodel

摘要

The effect of flow rate on the recovery of oil by waterflooding is studied, using a two-dimensional, layered sand model allowing visual observation. The model consists of three communicating layers of equal thickness of water-wet sand with the permeability ratio of 2:4:1 from top to bottom. Three white mineral oils of viscosity 15, 30, and 150 centipoise have been used for immiscible liquid/liquid displacement under constant pressure drops covering a range of flow rates. The changes in flow regimes in the various layers are observed with respect to the variations in pressure drop across the model. The effects of capillary imbibition, gravity segregation and viscous pressure gradient are observed and an attempt is made to quantify the crossflow. Crossflow of oil from the tight layers to the most permeable layer increases the intermediate recovery of oil for a given volume of water injected. Oil recovery increases with a decrease in flow rate and also with a decrease in oil viscosity. Slow flow rates produce higher recovery but may not be feasible in the field for economic reasons. Most of the crossflow of oil into the permeable layer occurs just behind the flood front and produces a secondary oil bank soon after breakthrough. A sequence of slow flow rate followed by a fast flow rate is shown to improve the recovery of oil for a given volume of water injected. The effect of variation in interfacial tension on the displacement behavior is also studied. Interfacial tension is reduced from 45.0 to 0.5 dyne/cm by the addition of a surfactant to the injected flood-water. These ranges of interfacial tension are not sufficiently low to increase oil recovery from interfacial effects. 29 refs., 75 figs., 14 tabs. (ERA citation 11:039678)