D20 Report : Soil Gas surveys in the Weyburn oil field (2001-2003)

Beaubien, S.; Strutt, M.H.; Jones, D.G.; Baubron, J.C.; Cardellini, C.; Lombardi, S.; Quattrochi, F.; Penner, L.. 2004 D20 Report : Soil Gas surveys in the Weyburn oil field (2001-2003). Nottingham, UK, British Geological Survey, 62pp. (CR/04/030N) (Unpublished)

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The International Energy Agency (IEA) Weyburn project is an international project that is studying the feasibility of long-term geological storage of carbon dioxide (CO2), allied to an enhanced oil recovery operation, by Encana, in the Weyburn oilfield, south-eastern Saskatchewan, Canada. CO2 is being injected into the oil reservoir to improve oil production, whilst at the same time the process should lead to long term geological storage of large volumes of CO2. Soil gas studies are being undertaken as part of an EU-funded component of this project, with the primary objectives of measuring the natural background concentrations and to ascertain if there is a leak of CO2, or associated tracer gases, as a direct result of the solvent flood presently occurring at the Encana Weyburn oil field. This report describes the results from three sampling periods conducted between July of 2001 and October of 2003. Sampling of the large 360 point grid above the injection area over the last three years showed CO2, O2 and CO2 flux values in the range of natural soils, and these observed levels can be explained by standard metabolic pathways that normally occur in the shallow soil horizon. The spatial anomaly distributions of these gases are reasonably reproducible from year to year and season to season, despite the fact that the range of values vary from high concentrations in the hot wet summer of 2001 to the low values found in the fall of 2002 and 2003. In contrast to these biologically active species, the statistical and spatial distribution of radon and thoron is very similar from one sampling season to the next. This provides support for the idea that leakage is not taking place, as one would expect to see high radon during the periods of high CO2 if the latter was acting as carrier for the more trace former gas. Hydrocarbon values were found to be within normal ranges in October of 2003, however the previous two seasons showed elevated values which were not fully expected. In fact ethylene and propane show a statistical distribution over the three years which is quite similar to that of CO2, whereas methane and ethane have relatively constant values except for more concentrated outliers during the first and second seasons. As the heavier hydrocarbons do not normally originate via shallow biological reactions it is difficult to reconcile these results with those of the other gases. A comparison of the grid data with that of the background site, located in similar surface geology but outside the Weyburn oil field, shows a very similar statistical distribution for all monitored parameters. This result supports the interpretation that the observed gas concentrations are not due to deep leakage. In particular, both sites have a very similar CH4 / (C2H6 + C3H8) ratio. This value is low and in the range of thermo-catalytic regime, however the fact that such a value was found both within and outside the oil field implies that the origin of these gases are not necessarily from a deep oil reservoir.

Item Type: Publication - Report
Programmes: BGS Programmes > Sustainable and Renewable Energy
Funders/Sponsors: European Commission
Additional Information. Not used in RCUK Gateway to Research.: This item has been internally reviewed but not externally peer-reviewed
Date made live: 06 Feb 2015 12:30 +0 (UTC)

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