Characterization of residual LNAPL and effect of LNAPL entrapment configuration on water flow in a single fracture

The mechanism becomes very difficult to realize when light non-aqueous phase liquid (LNAPL) migrates with residue in the variable-aperture fracture. The immiscible liquids in the 'fracture-water-LNAPL' system can affect and interact with one another. Meanwhile, these liquids are confined and controlled by the fracture surfaces and the aperture. We performed a toulene migration experiment with the use of a transparency replica fracture with a length of 27.4 cm and a width of 20.0 cm. Some LNAPL migration images and entrapment configuration were first acquired. We then analyzed the geometric characteristics of the LNAPL entrapment configuration and clogged aperture. We also compared the water flow in the fracture before and after LNAPL entrapment through numerical modeling. Results show that free phase LNAPL invaded the fracture through a gallery with large aperture, and some isolated LNAPL blobs were entrapped at a tight aperture area. The location of the LNAPL migration and residue is closely related to the aperture, and the frequency of the clogged aperture followed a normal distribution. The range of the clogged aperture is from 0.01 mm to 1.40 mm, whereas the distribution centered at 0.20 mm to 0.30 mm. As the water flow resistance was increased in the entrapment configuration, the pressure difference between the inlet and outlet increased after the entrapment. Residual LNAPL caused water flow velocity redistribution, and changed the distribution and amount of channel flow.