Determination of permafrost thickness in wells in northern Canada

Abstract

Accurate interpretation of geophysical data, design of safe casing strings for drilling and production operations, and determination of the potential for existence of gas hydrates in and immediately below the permafrost zone are only possible if the thickness of the permafrost zone can be accurately determined.Freezing of interstitial water in soils has little effect on many of the physical properties of the soil, however, large changes in elastic properties and electrical resistivity do result. This makes it feasible to determine the thickness of the permafrost zone using techniques which measure changes in acoustic and electrical properties of the soils adjacent to the wellbore. This paper discusses the characteristic response which occurs as the borehole logging tool passes upwards from unfrozen sediments into the permafrost zone. It is this response which indicates the base of the permafrost zone and allows determination of permafrost thickness.Conclusive evidence of permafrost thickness and confirmation of permafrost thickness inferredfrom acoustic and electrical data is obtained from temperature data obtained subsequent to well suspension. Techniques utilized to obtain these temperature data are outlined in this paper.L'interpretation precise des donnees geophysiques, le calcul de tubages securitaires pour les operations de forage et de production, et l'examen de la presence possible d'hydrates gazeux dans la zone de pergelisol ou immediatement en dessous ne sont possibles que si on peut determiner l'epaisseur de la zone de pergelisol avec precision.Le gel de I'eau interstitielle dans les sols n'a que peu d'effets sur plusieurs des proprietes physiques du sol, mais, par contre, des changements importants de proprietes elastiques et de resistivite electrique se produisent. Ce fait rend possible la determination de l'epaisseur de la zone de pergelisol en utilisant des techniques qui mesurent les changements de proprietes acoustiques et electriques des sols au voisinage d'un forage. Cet article discute la reponse caracteristique qu'on observe dans un forage lorsqu'une sonde remonte des sediments non geles vers la zone de pergelisol. C'est cette rkponse qui indique la base de la zone de pergelisol et permet d'en determiner l'epaisseur.Les releves de temperature apres la completion d'un forage apportent des donnees concluantes sur l'epaisseur de pergelisol et sur sa verification par les methodes acoustiques et electriques. On decnt aussi les techniques utilisees pour obtenir ces mesures de temperature.

CVPM 1.1: a flexible heat-transfer modeling system for permafrost

“…10). This leads to zones with relatively high ice contents in coarse-grained sediments as is often observed in electrical resistivity geophysical logs (Hnatiuk and Randall, 1977;Osterkamp and Payne, 1981). An interesting facet of this behavior is that a pocket of icerich sandstone can occur below a fine-grained unit that has little or no ice (e.g., the silty claystone above the sandstone at 450 m in Fig.…”

Well drilling in permafrost regions: dynamics of the thawed zone

“…It is known that the electric resistivity of frozen sediments is affected by the freezing-thawing transition to a greater extent than the seismic velocities. Seismic velocities may increase by 2-10 times in transition to a frozen state, whereas the electrical resistivity may increase by 30 to 300 times in the same temperature interval ( Hnatiuk & Randall 1977;Dobinski 2011). The dynamics of the thawed zone (the radius of thawing, Eqn.…”

Importance of Deep Permafrost Soil Characterization for Accurate Assessment of Thaw Subsidence Impacts on the Design and Integrity of Arctic Wells

“…Since thicker permafrost intervals typically imply more individual soil layers will be subject to thaw, stress changes and resultant deformations, permafrost thickness represents a key parameter with respect to the potential for thaw subsidence to impact the loading and integrity of production wells and surface facilities. Permafrost thickness in the southern (older) portions of the delta ranges from zero to a maximum of about 100 m, while the northern (modern) delta region is known to contain relict permafrost up to 400 m thick [DeGeer and Cathro 1992, Hnatiuk and Randall 1976, Taylor et al 1997]. complex history of sea level transgressions and regressions in some areas), the exposure and temperature conditions during the freezing period, freezing period duration, the presence of deep lakes and rivers, and the local geothermal gradient.…”

“…The temperature also varies substantially with depth at many locations as shown in Figure 4 which presents the insitu ground temperature profiles measured through the permafrost interval at a number of different onshore and offshore arctic locations [Hnatiuk and Randall 1975, Weaver and Stewart 1982, Taylor et al 1998]. The temperature also varies substantially with depth at many locations as shown in Figure 4 which presents the insitu ground temperature profiles measured through the permafrost interval at a number of different onshore and offshore arctic locations [Hnatiuk and Randall 1975, Weaver and Stewart 1982, Taylor et al 1998].…”