Numerical Analysis of Thermal Remediation in 3D Field‐Scale Fractured Geologic Media

Abstract

Thermal methods are promising for remediating fractured geologic media contaminated with volatile organic compounds, and the success of this process depends on the coupled heat transfer, multiphase flow, and thermodynamics. This study analyzed field-scale removal of trichloroethylene (TCE) and heat transfer behavior in boiling fractured geologic media using the multiple interacting continua method. This method can resolve local gradients in the matrix and is less computationally demanding than alternative methods like discrete fracture-matrix models. A 2D axisymmetric model was used to simulate a single element of symmetry in a repeated pattern of extraction wells inside a large heated zone and evaluate effects of parameter sensitivity on contaminant recovery. The results showed that the removal of TCE increased with matrix permeability, and the removal rate was more sensitive to matrix permeability than any other parameter. Increasing fracture density promoted TCE removal, especially when the matrix permeability was low (e.g., <10(-17) m(2)). A 3D model was used to simulate an entire treatment zone and the surrounding groundwater in fractured material, with the interaction between them being considered. Boiling was initiated in the center of the upper part of the heated region and expanded toward the boundaries. This boiling process resulted in a large increase in the TCE removal rate and spread of TCE to the vadose zone and the peripheries of the heated zone. The incorporation of extraction wells helped control the contaminant from migrating to far regions. After 22 d, more than 99.3% of TCE mass was recovered in the simulation.

Steam-Enhanced Extraction Experiments, Simulations and Field Studies for Dense Non-Aqueous Phase Liquid Removal: A Review

“…The DNAPL removal rate is higher in coarse sand compared to fine sand [21,25]. In fractured geologic media, the DNAPL removal rate is influence by matrix permeability and fracture density [22]. In addition, the distance between point of compliance and upgradient domain face directly affect the pore water concentration of fracture geologic media which consequently affect the DNAPL removal [26].…”

“…The results show that higher removal rate for coarse sand compared to fine sand. Chen, et al [22] has study TCE removal in 3-D fractured geologic media using thermal remediation. The study was aim to investigate the heat transfer behavior and evaluate the sensitivity of parameter through numerical simulation using TMVOC TOUGH2 program.…”

Strategies for Managing Risk due to Back Diffusion

“…After 28 days, temperatures reached 103°C and the heat was turned off, but extraction continued for an additional 7 days, at which time 28% of the pore water and >99% of the contaminant mass were removed. In the simulation reported by Chen et al (2015), the contaminant was TCE at an initial aqueous concentration of 7.28 mg/l. Heat was uniformly applied to the saturated zone at a rate of 200 W/m 3 for 30 days to induce boiling, and sensitivity of contaminant removal by a multiphase extraction well to matrix K , fracture spacing and aperture, and extraction well pressure was evaluated.…”

“…Related modeling work was reported by Chen et al (2012Chen et al ( , 2015, who modeled the laboratory experiments dealing with fractured rock and field-scale thermal remediation in fractured rock. For the field-scale simulations, a 2D radially symmetric domain 20-m deep by 8-m radius was used with the groundwater table 4.5 m below ground surface.…”

Effect of fracture distribution on extraction efficiency in low-permeability NAPL-contaminated formations

“…This provides comprehensive evidence for the effectiveness of fracturing-enhanced extraction. To further investigate the enhancement mechanisms of fracturing on extraction, numerical simulation analysis revealed that the permeabilities of the fractures and matrix have a greater impact on the removal efficiency of NAPL than the extraction pressure, fracture length, thickness, and spacing [15][16][17] . Although the effectiveness of fracturing collaborative extraction has been demonstrated through experiments and numerical simulations, existing research has mainly focused on attempts to adopt the pollutant removal rate as the main evaluation indicator.…”