GEOSCAN, résultats de la recherche


TitreThermal modelling and massive ground ice investigations at Parsons Lake, NWT
AuteurAngelopoulos, M; Fox, D; Pollard, W; Couture, N; Riseborough, D; Gowan, R
Source41st International Arctic Workshop, abstracts; 2011 p. 28-29
Séries alt.Secteur des sciences de la Terre, Contribution externe 20100458
Réunion41st International Arctic Workshop; Montreal; CA; mars 2-4, 2011
ProvinceTerritoires du Nord-Ouest
Lat/Long OENS-134.0000 -133.0000 69.0000 68.7500
Sujetscongélation du sol; glace fossile; températures au sol; pergélisol; climat arctique; analyses thermiques; géologie des dépôts meubles/géomorphologie
Programmepipeline nordiques, Géoscience de l'environnement
Résumé(disponible en anglais seulement)
Mapping ground ice distribution is an enormous challenge facing land management and resource development related to oil and gas in the Arctic. The melting of ice within permafrost destabilizes the ground, leading to extensive thaw subsidence called thermokarst, which could result in the destruction of infrastructure. Traditional methods for identifying ground ice involve drilling, but these techniques are expensive, destructive, and only provide point samples. Nondestructive geophysical methods, however, can survey a large area in a cost-effective manner. Our research currently integrates two tools for the detection and assessment of ground ice at Parsons Lake (68°59' N, 133°33' W), a natural gas field in the Northwest Territories. Instruments include capacitively-coupled resistivity (CCR) and ground-penetrating radar (GPR). The primary objective of our work is to use CCR and GPR to interpolate ice contents between boreholes at Parsons Lake. In July 2009 and 2010, 5 CCR and GPR (50 MHz, 100 MHz, 250 MHz) transects intersecting a total of 10 boreholes were conducted. In addition, CCR surveys at 2 of the transects were carried out in March 2010 to examine seasonal changes in electrical resistivity. Although geophysical outputs are affected by ice content, they are also influenced by ice structure, salinity, temperature, and unfrozen water content. Hence, 1D thermal modelling at the examined boreholes has been conducted to estimate vertical changes in temperature and unfrozen water contents during fieldwork campaigns. The models are validated by borehole temperature logs from March/April and September 2004. Although a few studies have correlated electrical resistivity data with permafrost properties such as ice content and unfrozen water content (e.g. Fortier et al., 2008, Fortier et al., 1994), no attempt has been made to do so using a capacitively-coupled system. Preliminary results suggest that empirical relationships between electrical resistivity and these permafrost properties can be derived using the capacitively-coupled system. In addition, GPR surveys have successfully mapped the top and in certain cases the base of massive ground ice structures (Figure 1). Hence, CCR and GPR is being used to generate 2D maps of excess ice content and potential taliks (which preliminary findings suggest could exist in disturbed areas characterized by previous excavations and gravel infillings, as well as freezing point depressions associated with nearby sump leakages). Geochemical ground ice investigations conducted at a nearby retrogressive thaw slump suggest that the ground ice is of intrasedimental origin, which implies a known stratigraphy that can aid in geophysical interpretations. The results of this study form part of an Indian and Northern Affairs Canada (INAC) GIS land management database.