1998 Volume 40 Issue 3 Pages 289-310
When a Dense Nonaqueous Phase Liquid (DNAPL) can penetrate into the saturated zone, two types of liquid form in either discrete drops or continuous flows will be observed. In order to understand their dynamics, the mechanism of formation of immiscible fluid drops in saturated pore space has to be enlightened. This study deals with the snap-off of immiscible drops in different constriction (pore) models. Snap-off experiments of DNAPL are carried out in models of (1) single capillary tubes; (2) single constrictions built of glass beads; and (3) successive constrictions built of glass beads. All models are submerged in pure water. According to the experimental results, the snap-off unconditionally occurs as the protruding DNAPL passes an equilibrium position below the neck of a single constriction owing to the effect of gravitational force. Dynamics of snap-off depend on both the properties of the fluids and geometry of the constriction. Structure and size of pore space under the constriction where the DNAPL is passing has a dominant influence on the possibility of snap-off formation. An unfavorable condition of the pore space can resist snap-off not to occur, and the DNAPL may achieve a filament flow in such a case. It is also observed that the snap-off-generated drops break again into two or more smaller drops as collision with solid phase in the successively underlying constrictions. This process results in different sizes of discrete drops flowing in the porous medium.
