Effect of limited warming on residual oil-gas tar

Abstract

The potential of limited soil warming (50 ᵒC) to function as a residual DNAPL phase remobilisation method, under the specific conditions of the ‘Amersfoort Vetgasfabriek’ site remediation project, is evaluated with this experimental study. The concept is based on the expected drop of NAPL-water interfacial tension with rising temperature. In order to maintain adequate correspondence of the experimental results to the actual field conditions, the materials used, i.e. oil-gas tar and sand, were collected directly from the particular site. Our measurements showed an approximate 40% drop of the tar-water interfacial tension with a rise of temperature from 15 to 50 ᵒC. However the new equilibrium state established was more unfavourable as the DNAPL-water density difference drop is more significant for the specific temperature rise. The column experiments came to verify this result. Limited warming was applied on soil carrying residual tar saturation, condition created by consecutive drainage and imbibition phases. The entrapped DNAPL maintained its position in the sand pores despite the increased flow velocity of water during flooding at the elevated temperature. Limited warming was proven inadequate to function as a residual phase remobilisation method. Nevertheless, valuable insight was gained on the behaviour of the particular oil-gas tar during the drainage and imbibition cycles.