Experimental Study of Groundwater Contamination By Phenol From Water/Heavy Oil Emulsion
Authors: Tang J.S. 
Published: March 2010

A leaching experiment was conducted at 4 ° C to study the transport of phenol and chloride from a quiescent, viscous Cold Lake W/O emulsion into flowing fresh water. Test results indicated that phenol and chloride were transferred through different mechanisms. The rate-determining step for phenol transport was the slow molecular diffusion of phenol in emulsion. This was successfully modelled by a de-coupled second order diffusion equation from which the diffusion coefficient of phenol in emulsion was determined to be 2.2 x?10−8 cm2/s. Chloride was transported through direct contact of the emulsified water droplets with the leaching water in an 82 µm thick coalescence layer. The transport was essentially complete in less than two days and no further leaching was observed for the rest of the experiment. The bulk emulsified water was stable with no coalescing or segregation with time. The phenol/chloride transport model can be readily scaled to predict the mass transfer of these two chemicals from a contaminated zone into a flowing aquifer as shown in a subsequent paper. No appreciable air oxidation or biological degradation of phenol was detected within the experiment time frame of 61 days.

Introduction

Similar to coal gasification, the Cold Lake steam stimulation process also generates highly toxic by-products in the formation. These by-products, including various types of phenols, carboxylic acids and other high molecular weight acidic compounds generically classified as humic acids(1), are weak acids. Being soluble both in bitumen and especially in the high pH steam condensate, these compounds are brought to the surface by the produced water and bitumen. Cold Lake bitumen tends to form a stable, highly viscous water in oil emulsion with the produced water under minimal stress. The water content in the emulsion(2) can be as high as 40%. After separation, part of the produced water is softened and re-cycled for steam generation and the excess produced water, together with other harmful waste streams, are injected through a disposal well into an isolated zone to avoid aquifer contamination.

In 1988, a leaky seal in the abandoned well C7-13 at Cold Lake caused an accidental spill of bitumen in the form of a water-in-oil emulsion and produced water into a near-surface aquifer zone where the bitumen and the produced water were in a danger of being contacted by the flowing aquifer(3). Although the W/O emulsion was practically immobile at the formation temperature of 4 ° C due to its high viscosity, the toxic phenolic compounds could still be expected to leach slowly into the flowing stream, posing a threat of potential groundwater contamination. To assess the environmental impact of phenol contamination on groundwater, water was produced from a newly drilled well and continuously monitored for chloride and phenol levels. In the meantime, experiments were designed and conducted in the lab to study the rate and mechanism of the release of phenol into fresh water. Experiments were also carried out to quantify the extent of natural degradation of phenol via air oxidation and biological pathways.