Effect of Biological Gas Generation on Oil Sand Fine Tailings

CIM Edmonton 2004
Rick J. Chalaturnyk, J. Don Scott, Mike MacKinnon,
Abstract The Mildred Lake Settling Basin (MLSB) is the largest disposal site for tailings at the Syncrude Canada Ltd oil sands plant containing 216,000,000 cubic meters of mature fine tailings (MFT). Over the past years (since 1997), there has been a marked change in the consolidation behaviour of MFT in the MLSB, which is attributed to microbial activity. Methane-producing microorganisms, known as methanogens, have become very active, and large amounts of biogas (mainly methane) have been produced. In certain regions within the MLSB, gas bubbles are released to the water surface of the tailings pond. Continued field monitoring of the MLSB has provided convincing evidence of the rapid densification process (rapid water drainage from the tailings). This phenomenon contradicts the consolidation models for MFT developed over the past 20 years. The above phenomenon has also been reported at the oil sands tailings ponds operated by Suncor Energy Ltd. in Fort McMurray. This rapid densification has caused pumping challenges in the transfer of fine tailings from the Mildred Lake Settling Basin for the creation of composite tailings. The rapid densification of the MFT may also have potential positive effects in accelerating the reclamation of the oil sands fine tailings.

A field and laboratory research program is underway to study the mechanism leading to the rapid densification phenomenon. Systematic field investigations were performed to determine the distribution and characteristics of the rapidly densified MFT. Gas bubble distribution on the water surface was mapped to determine the zones of different biological activities in the pond. These field investigations provided solid ground for further experimental and theoretical research. A number of small-scale column tests were carried out to observe the gas evolution and to measure the changes of some geotechnical parameters under different microbial activity. Also, a series of large-scale densification tests are being conducted to study the mechanism of the rapid densification of the MFT under microbiological activity. A review and discussion of the research program is given and some preliminary research results
Keywords: Densification, Biological gas, Microbial activity, mature fine tailings, Gassy soil
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