M. Baviere, SPE member, C. Bocard, J. Ducreux, N. Monin, Institut Francais du Petrole, and P. Muntzer and O. Razakarisoa, Institut Franco-Allemand de Recherche sur l'Environnement (IMF-CNRS) Copyright 1997, Society of Petroleum Engineers, Inc.
A surfactant-flooding technique is described for the remediation of soils contaminated by semivolatile and nonvolatile petroleum products, such as crudes and diesel oils. It consists of injecting a surfactant slug into contaminated areas to mobilize oil trapped in both vadose (unsaturated) and capillary-fringe zones, and of depleting the groundwater level to collect this oil.
To deal with contamination by diesel oil, a procedure to select a surfactant formulation was applied, based on (1) the phase behavior of the water-oil-surfactant system, (2) an appraisal of surfactant-soil interactions, namely ion exchange with clays and surfactant adsorption, and (3) the measurement of the surfactant efficiency for extracting the contaminant from 1D and 2D sandpacks. With a mixture of anionic and nonionic surfactants more than 90% of the residual oil was recovered.
The process was implemented in a large-scale experimental site of 900 m3, packed with slightly clayey sand and locally contaminated by a spill of 476 L of diesel oil. Two successive surfactant injections were performed in order to treat: first, the vertical oil-migration zone; secondly, the horizontal oil-extension zone in the capillary fringe. Based on soil-core sampling after the surfactant flood, the high displacement efficiency was confirmed: about 80% after the first injection. However, it appeared that the mobilized oil was not entirely recovered at the pumping well: about 50% of the residual oil, probably due to insufficient hydraulic confinement. The same observations were made after the second injection. The removal of diesel oil and surfactants from the effluents was performed on-site, before sewage disposal, by centrifuging, precipitation and finally by biodegradation.
The remediation of soils and aquifers contaminated by petroleum products is now proving increasingly essential in the protection of human health. To palliate the poor efficiency of conventional pump-and-treat processes, due in particular to capillary trapping and the low water solubility of contaminants, alternative in-situ restoration strategies have been developed, such as venting, biodegradation, and surfactant flooding. The latter is particularly promising when semivolatile and nonvolatile contaminants are involved.
The use of surfactants is investigated here in the framework of a modular process: the DHBP (Drainage HydroPneumatique Bioactif). It consists of implementing one stage of surfactant flooding and one stage of surfactant-enhanced biodegradation. P. 481