An Investigation of Residual Hydrocarbon Dissolution by Micromodels

M. Y. Corapcioglu, S. Chowdhury, S. Roosevelt, K. Bullock, R. Kukreja, and D. Hodko

NAPLs trapped by capillary forces in subsurface environments pose a longterm contamination source as they dissolve in groundwater. An understanding and quantification of the NAPL dissolution process at the pore-scale is important in estimating the source of contaminants and performance of remediation schemes. The dissolution kinetics of residual hydrocarbons in porous media was investigated by conducting micromodel studies. Micromodels are artificial glass models that simulate the complexities of natural porous media. Various micromodels with patterns representing a range of geologic formations were employed to show the effect of pore structure and heterogeneity on NAPL dissolution. The micromodels with an initial residual saturation were injected with surfactant solution at constant flow rates till all residuals were removed. Changes in residual hydrocarbon surface areas were measured and mass transfer rates between residual NAPLs and various surfactant solutions were calculated by processing the recorded images with an image analyzer. Dissolution kinetics depends on the distribution of the residual NAPL, i.e., total interfacial area available for mass transfer, as well as NAPL and aqueous phase properties. The effects of porous medium properties, distribution of residual NAPL saturation, velocity, and surfactant concentration were studied Experiments were conducted with NAPLs such as toluene, TCE and various surfactants, both anionic and nonionic, to provide a benchmark for selecting the most efficient NAPL-surfactant combinations for remedial design.

AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California