|Title||Geological and geochemical data from the Canadian Arctic Islands. Part XVI: Permafrost thickness determination from petroleum exploration wells|
|Author||Hu, K; Brent, T A; Dewing, K|
|Source||Geological Survey of Canada, Open File 7306, 2018, 243 pages, https://doi.org/10.4095/311129 (Open Access)|
|Publisher||Natural Resources Canada|
|Related||This publication is related to the following publications|
|File format||pdf (Adobe® Reader®); rtf; xls (Microsoft® Excel®)|
|Province||Nunavut; Northwest Territories; Northern offshore region|
|NTS||39; 48; 49; 58; 59; 68; 69; 78; 79; 88; 89; 97G; 97H; 98; 99; 340B; 340C; 560A; 560B; 560C; 560D|
|Area||Canadian Arctic Archipelago|
|Lat/Long WENS||-132.0000 -70.0000 82.0000 71.0000|
|Subjects||geochemistry; surficial geology/geomorphology; permafrost; ground ice; exploration wells; boreholes; ground temperatures; geophysical interpretations; geophysical logging; well logging; seismic
interpretations; seismic velocities; bedrock geology; lithology; sedimentary rocks; sandstones; siltstones; shales; conglomerates; carbonates; Pliocene; Miocene; Beaufort Formation; permafrost depth; ground ice depth; freezing depth; methodology;
Phanerozoic; Cenozoic; Mesozoic; Paleozoic|
|Illustrations||tables; geoscientific sketch maps; location maps; profiles; well logs; lithologic sections|
|Program||Western Arctic Project Management, GEM2: Geo-mapping for Energy and Minerals|
|Released||2018 09 13|
Permafrost occurrence is widespread in northern Canada and occurs continuously beneath the islands of the Canadian Arctic Archipelago (Fig. 1). This study was conducted to infer
depths to the base of ice-bearing permafrost (IBPF) at petroleum exploration wells located on these islands, and compile this alongside the directly measured depth to the 0° Celsius level, or true base of permafrost (PF). The depths to the 0° Celsius
isotherm were previously determined from 32 wells (one offshore and 31 onshore) by repeated shallow temperature surveys (Judge et al, 1979a, 1979b, 1981 and 1987). In this study area (Fig. 2), a determination was made for the base of IBPF for 140
onshore wells. Numerous data sets were consulted including suites of geophysical well logs, and well seismic surveys in conjunction with lithological analysis, and other data. Results at each well are provided graphically as composite borehole depth
plots with wireline logs, velocity surveys, shallow temperature data, drilling rate and lithology interpretations, to illustrate geophysical responses, and to provide multi-parameter evidence for integrated interpretations of the IBPF/PF zone.
IBPF/PF determinations are quality-assessed in terms of their reliability using a practical scale based on the type of methods used and the quality of data available.
The depths to the base of permafrost (0° Celsius) derived from temperature
surveys were used to corroborate the interpretations of correlative well log records and well seismic surveys, which were better able to discern ice in the pore spaces of sedimentary rocks and thus base of IBPF, rather than the zero degree Celsius
For most of the wells, the base of the interpreted fully frozen ice-bearing permafrost (IBPFF) may be constrained by a notable change in electrical and acoustic properties, borehole size, drilling rate and well seismic velocity.
For 106 wells, a transition zone below the base of IBPFF (between 9.5 m to 170 m in thickness) is interpreted to represent partially frozen ice-bearing permafrost (IBPFP), in which ice and unfrozen water may coexist. The base of permafrost (PF), or
the 0°C isotherm, as extrapolated from return-to- equilibrium calculations of repeat temperature surveys, ranges in depth from 143 m to 726 m below ground level (GL) in 31 onshore wells, and 40 m below sea floor (SF) in the only offshore well with a
temperature survey. Depth to the base of IBPFF and IBPFP defined by other geophysical methods varies from 37 m to 843 m below GL and 184 m to 779 m below GL respectively across the study area. For 93 of 143 wells total (> 65%), defined IBPFF/PF bases
occur in Mesozoic strata, distributed in sandstones, siltstones and shales, except one well in conglomerate. For 62 wells, IBPFF/PF bases are located in Cretaceous strata. IBPFF/PF bases are encountered in Paleozoic sandstone, siltstone, and
carbonates in 48 wells. Among the 106 wells with an interpreted ice transition zone, from fully frozen to unfrozen with depth, IBPFP base in 103 wells is predominantly confined to shale, siltstone, and sandstone. Both IBPFF and IBPFP bases occur
within highly porous sandstone of the Miocene-Pliocene Beaufort Formation in one well on Meighen Island, and one well on the northwest edge of Ellef Ringnes Island.
|Summary||(Plain Language Summary, not published)|
This OF re-examines permafrost thickness in petroleum exploration wells in Arctic Islands. The identified base of ice-bearing strata is cross checked
using multiple indicators. A transitional zone below the ice-bearing base from fully frozen zone to ice-free is also identified where it exists, to provide additional information on properties of the hosting rock and fluid.