Migration behaviour of LNAPL in fractures filled with porous media: Laboratory experiments and numerical simulations.

With the increasing requirement of maintaining world energy security and strategic reserves, oil storage and transportation facilities are being built at a large scale. Taking the safe and efficient operation of petroleum storage projects as the goal, a set of experimental apparatus to investigate the migration of contaminants in fractures filled with media was developed to predict and evaluate the environmental risk of oil contaminants leakage. A multiphase numerical flow model based on COMSOL was built based on the laboratory experimental model. Specifically, the migration behaviour of Light Non-aqueous Phase Liquid (LNAPL) through a sand-filled fractured medium was studied by laboratory experiments and numerical simulations. Image and chemical analyses methods were used to monitor and study LNAPL migration behaviour for varying grain sizes of porous medium filling the fractures and varying groundwater table elevations. Laboratory experimental results showed that the LNAPL migration velocity in filled fracture network was significantly faster than that in adjoining porous media during the initial stage of infiltration. The migration velocity increased with the relative permeability of filled sand, which was closely related to the Van Genuchten (VG) model parameters α and n. LNAPL migrated downward with the falling groundwater table and became entrapped with the rising groundwater table, and the amount of entrapment depended on VG model parameters. Hydrogeological parameters were calibrated and LNAPL migration in filled fractured media was predicted using the calibrated numerical model. Simulation results revealed that fracture inclination had an important influence on LNAPL migration in filled fractured media and its migration velocity decreased with a decrease in fracture inclination. These research results can be applied to the control and remediation of oil-contaminated sites in fractured rock settings, such as at underground oil storage tanks and caverns, as well as at underground oil pipelines.

Experimental investigation of light non-aqueous phase liquid mobilization in filled fractured network media.

With the increasing requirement of international energy security, oil storage projects have been constructed in large numbers, but leaking petroleum-based contaminants are threatening the soil and groundwater environment. In order to assess the environmental risk of petroleum-based contaminants, an experimental apparatus was designed and developed to monitor the concentration and pressure variations of light non-aqueous phase liquid (LNAPL) in filled fractured network media. The mobilization mechanism of LNAPL was investigated by theoretical analysis and laboratory experiments; the pressure balance relationships at different interfaces were investigated. When the experimental model was unsaturated, the dynamic processes of concentration and pressure at different locations in filled fractures were explored. When the groundwater level was raised to 35 cm, the cumulative height of LNAPL (HL) was a function of the density of LNAPL, interfacial tension, interfacial contact angle, aperture of fracture, porosity, and particle diameter of filling and HL21 > HL22. The final concentrations of H21, H22, H25, H26, and H27 were 0.467, 0.458, 0.026, 0.062, and 0.041 mg/mL, respectively. Subsequently, the effect of the particle diameter of filling sand on LNAPL mobilization was further discussed, the concentration of each point in the fractures increased with the increase of the particle diameter of filling sand, and its peak decreased with the increase of the burial depth. The response time of pressure at each point was advanced and the peak of pressure dynamic curve increased as the particle diameter of filling sand increased. The peak pressure heads of H12 and H13 were 22.360 cm and 25.332 cm respectively when the particle diameter of filling was 0.5-1.0 mm. The Spearman analysis results between LNAPL concentration and time showed a significant correlation (≥ 0.879, [Formula: see text]). Research results characterized the existence and mobilization of LNAPL in filled fractured network media from the perspectives of concentration and pressure, which could provide a reference for the study of the leakage and migration mechanism of LNAPL.