Multiphase horizontal migration of BTEX in aquifers during in-situ oil shale exploitation

This study investigates the multiphase horizontal migration characteristics of benzene, toluene, ethylbenzene, and xylene (BTEX) in aquifers during in-situ oil shale pyrolysis. Through two-dimensional hydrodynamic dispersion experiments and numerical simulations, the main parameters, including the dispersion coefficient and residual saturation of the nonaqueous phase liquid (NAPL) phase were determined. The results indicated that in the same media, the dispersion coefficients and residual saturations of BTEX compounds differ. The longitudinal dispersivities decreased in the order of benzene (0.114 m) > ethylbenzene (0.053 m) > toluene (0.050 m) > xylene (0.046 m), whereas the transverse dispersivities decreased in the order of toluene (3.90 × 10⁻⁷m) > xylene (3.85 × 10⁻⁷m) > ethylbenzene (2.96 × 10⁻⁷m) > benzene (1.35 × 10⁻⁷ m). The calibrated residual saturation of the NAPL phase was highest for benzene (0.17), followed by toluene (0.15), ethylbenzene (0.14), and xylene (0.12). Numerical simulations were conducted to quantify interphase partitioning, revealing different equilibrium volume fraction ratios (gas: aqueous: NAPL) at the injection point and observation points. This study provides critical parameters and a numerical model for simulating BTEX multiphase migration, which can aid in predicting contamination plume evolution, assessing risks, and designing effective groundwater protection and remediation strategies during oil shale exploitation.