On the behaviour of strongly oil wet and strongly water wet sands when contaminated by light hydrocarbons, and subsequent remediation thereof

ABSTRACT

The contamination of soil by light hydrocarbons is one of the most frequently encountered environmental problems. Leakage from underground storage tanks at refueling stations is the most common source, but others are refineries or production facilities. Research at the University of Calgary has been examining the application of proven petroleum reservoir engineering methods to address this issue. By use of horizontal boreholes, and cyclic water and gas injection, the contaminant can be recovered in situ.

Laboratory work has been ongoing to determine basic data on the contamination and remediation aspects of the process. In this paper, we report work that has been done to characterize the saturations during the contamination and remediation processes. Sand that typifies the grain shape and distribution of native soil was used. This sand was strongly water wet. To examine the impact of the humic acid from topsoil loam, humic acid was extracted and plated onto the sand. Characterization of the sand has been performed to demonstrate that the humic acid has bound to the surface of the sand grain, and has altered the surface wettability. Results of coreflooding also demonstrated that the performance of the organic coated sand, and the untreated sand, will lead to different contamination and remediation results. It appears that the treated sand exhibits hysteresis, for if it was originally in contact with water, it behaves as if water wet. If, instead, it was originally in contact with kerosene, it behaves as if oil wet.

Introduction

In our industrial world, one of the consequences of economic and technologic development is the discharge of undesirable materials into the environment. Of the many compounds released to the environment, the volume of petroleum related products released is very large. The importance of petroleum as the primary source of energy for our society is the main reason for this, reflecting the widespread usage of petroleum. The main discharge site for liquid hydrocarbons is at commercial refueling stations, from underground storage tanks (“UST”) that hold gasoline. Small holes in these tanks can result from corrosion or material stress. Further locations for possible leakage are at pipe connections or flanges, where shifting soil can lead to a compromise in the integrity of the connection.

It has been estimated (1) that of the roughly 1.6 million underground storage tanks in the United States, about 20% are or have discharged gasoline or diesel into the surroundings. Furthermore, conservative estimates of the cost to clean up these UST sites are around $37 billion U.S. dollars (year 2000 value). If all sites that have been contaminated by light hydrocarbons are included, such as refineries and airport tank farms, remediation is a multi-billion dollar per year industry. For Canada, scaling the $37 billion (U.S.) clean up cost estimate by population and currency differences leads to an estimate of $5 billion Canadian (year 2000 value) for the clean up of contaminated sites in Canada. A significant fiscal incentive therefore exists to improve both the cost effectiveness, and also the process efficiency, of remediation.

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