Terrestrial heat flow near Alberta, Virginia

Abstract

Temperatures were measured to a depth of 312 m in a hole cored in granite at 36ø52.15'N, 77ø54.15'W (elevation 116 m), near Alberta, Virginia. The temperature gradient in the lower half of the hole is uniformly 18øC/km. The cause of a variable gradient in the upper half of the hole is thought to be movement of groundwater within the hole. The average thermal conductivity determined from measurements on 0.64-cm-thick disks is 7.8 mcal/cm sec øC, but the average conductivity computed by summing the thermal resistivities of the constituent minerals is 6.2. The corresponding values of heat flow are 1.4 and 1.1 vcal/cm" sec, respectively. The average heat flow in eastern North America is 1.0, and the previously published high in this region is 1.3 tzcal/cm 2 sec. Introduction. Determinations of terrestrial heat flow on the continents number about 100 [Lee, 1963]. 0nly five measurements have been published for the metamorphic zone of the Appalachian Mountains of eastern North America [references in Dimen• and Werre, 1964]. In view of this paucity of data, any borehole that is free from strong thermal perturbations, and from which rock samples have been retrieved, represents an opportunity to supplement knowledge of an important but poorly known geophysical parameter. Site and drilling details. During 1909 and 1910 a hole was cored to a depth of 480 m in granite at 36ø52.15•N, 77ø54.15'W (elevation 116 m above mean sea level), about 1.8 km west of Alberta, Virginia, on the right-of-way of the Norfolk and Western Railway Company, 60 m east of mile post 99 and 5 m north of the track.

Convective Flow and Its Effect on Temperature Logging in Small‐diameter Wells

“…However, amplitudes of temperature oscillation at these gradients apparently are no greater than a few hundreths of a degree C, and in reports in which consideration is given to the convective transfer of heat (e.g., Diment and Robertson, 1963;and Diment et al, 1965), it is generally concluded that, in view of the larger uncertainties that enter into such estimates, convective instability has a negligible effect on the determination of the earth' s thermal gradient or rate of heat flow. On the other hand, my investigations have confirmed the findings of others that under some conditions, temperature gradients become very large, and temperature oscillations of several tenths of a degree may occur in some wells (Diment et al, 1965;Diment, 1967;and Gretner, 1967). Thermal disturbances of this magnitude would seriously impair the accuracy of temperature measurements required to estimate groundwater velocities, for example, in a method suggested by Stallman (1963).…”

“…The temperature gradient between X.6 and 9.3 m was 5.5X10-20C m, a value just on the unstable side of the calculated critical cur\' c for this well. The water column at and below 9.d m appeared to be completely stable and thermal gradients were positive upward.AsDiment (1967) also observed in his experiments, the temperature fluctuations did not seem to be periodic, but rather to reflect complex superposition of many small movements. The intervals between peaks of the major oscillations showed only small correlation, if any, with the observed thermal gradients although the amplitudes of the fluctuations could be' related fairly well to the-%J&x FIG.…”