Thermal Regime of a Large Diameter Borehole: Instability of the Water Column and Comparison of Air‐ and Water‐filled Conditions

Diment, W.H.

doi:10.1190/1.1439885

Cited by 68 publications

(36 citation statements)

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“…This value of geothermal gradient is clearly surpassed by several orders of magnitude everywhere in Hole 504B. According to Diment (1967), small-diameter (2-3 cm) holes are usually stable, larger ones (6-8 cm) approach instability, and large-diameter wells (> 10 cm) are typically unstable. Thus, according to these criteria, convective fluid movement is likely to occur throughout the water column in Hole 504B.…”

Section: Convection Within the Boreholementioning

confidence: 99%

Geothermal State of Hole 504B: ODP Leg 111 Overview

Gable¹,

Morin²,

Becker³

1989

Proceedings of the Ocean Drilling Program

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Hole 504B in the eastern equatorial Pacific has been the focus of five scientific drilling expeditions since it was first drilled in 1979. During these five legs, a series of temperature logs has been obtained over a time span of almost 8 yr, documenting the geothermal and hydrologic state of the oceanic crust in this region. Immediately following reentry at the onset of ODP Leg 111 operations, a high-resolution temperature probe was lowered into the borehole and a precise record of temperature vs. depth in Hole 504B was recorded down to 1300 mbsf.As was observed during previous legs, the temperature gradient in the upper 400 m was reduced, indicating that downhole flow of cool ocean waters through the casing continued, though at a diminished rate. As subhydrostatic pressures in the upper basement have gradually diminished, the volume of flow has decayed from an estimated 6000-7000 L/hr in late 1979 to about 80 L/hr during Leg 111.At depths below 480 mbsf, a predominantly conductive heat transfer environment enabled the temperature gradient log to be analyzed with respect to lithology on both fine and broad scales. Anomalies in the gradient log in the cased section through the sedimentary column were found to correspond to biostratigraphic age markers and/or sharp changes in sediment composition and texture. Broad variations in temperature gradient within the basement correlated with large-scale porosity trends.Conductive heatflow estimates depict a systematic reduction with depth, ranging from approximately 196 mW/m 2 in the sediments to 120 ± 17 mW/m 2 at 1300 mbsf. Possible causes for this observation were examined from several perspectives, but none was suitably convincing. A fluid instability analysis indicated the likely existence of convection cells within the borehole and substantiated the hypothesis of mixing within the borehole postulated from isotopic and chemical studies of borehole waters. However, such mixing of borehole fluids does not provide an adequate explanation for the heatflow variations, and the disparity between surficial and deep values of heat flow remains unresolved.

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Section: Convection Within the Boreholementioning

confidence: 99%

Geothermal State of Hole 504B: ODP Leg 111 Overview

Gable¹,

Morin²,

Becker³

1989

Proceedings of the Ocean Drilling Program

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“…3). These small drifts in temperature may represent instances of transient fl uid exchange between the borehole and the formation (e.g., Drury et al, 1984;Ge, 1998;Šafanda et al, 2007) or localized intervals of fl uid convection within the borehole (e.g., Diment, 1967;Fisher and Becker, 1991). Substantial thermal anomalies appear at 647 mbsf, a consequence of circulation loss and drilling fl uid entering the surrounding formation within a fracture zone delineated by a thin lava fl ow (Falconer et al, 2007;Krissek et al, 2007).…”

Section: Temperature Logs and Geothermal Gradientmentioning

confidence: 99%

Heat Flow and Hydrologic Characteristics at the AND-1B borehole, ANDRILL McMurdo Ice Shelf Project, Antarctica

et al. 2010

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TheAntarctic Drilling Program (ANDRILL) successfully drilled and cored a borehole, AND-1B, beneath the McMurdo Ice Shelf and into a fl exural moat basin that surrounds Ross Island. Total drilling depth reached 1285 m below seafl oor (mbsf) with 98 percent core recovery for the detailed study of glacier dynamics. With the goal of obtaining complementary information regarding heat fl ow and permeability, which is vital to understanding the nature of marine hydrogeologic systems, a succession of three temperature logs was recorded over a fi veday span to monitor the gradual thermal recovery toward equilibrium conditions. These data were extrapolated to true, undisturbed temperatures, and they defi ne a linear geothermal gradient of 76.7 K/km from the seafl oor to 647 mbsf. Bulk thermal conductivities of the sedimentary rocks were derived from empirical mixing models and density measurements performed on core, and an average value of 1.5 W/mK ± 10 percent was determined. The corresponding estimate of heat fl ow at this site is 115 mW/m 2 . This value is relatively high but is consistent with other elevated heat-fl ow data associated with the Erebus Volcanic Province. Information regarding the origin and frequency of pathways for subsurface fl uid fl ow is gleaned from drillers' records, complementary geophysical logs, and core descriptions. Only two prominent permeable zones are identifi ed and these correspond to two markedly different features within the rift basin; one is a distinct lithostratigraphic subunit consisting of a thin lava fl ow and the other is a heavily fractured interval within a single thick subunit.

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“…Using this equation, it can be shown that for normal geothermal gradients (approximately 25 °C/km), convection can be expected in boreholes with diameters greater than about 5 cm. However, several field investigations by Urban et al (1978), Diment (1967), Gretener (1967), and Wisian et al (1998), as well as the observations by this author, have shown that although convection cells do form, they rarely extend vertically more than a few borehole diameters before dying out. Thus, the general effect of convection within boreholes is to decrease the signal-to-noise ratio of a temperature log without interfering with broader temperature trends.…”

Section: Thermal Gradientmentioning

confidence: 63%

“…Since, generally, borehole temperatures increase with depth, it would appear that the warmer waters deeper within the borehole would tend to rise up through the cooler fluids higher in the borehole, producing convection cells. Hales (1937), Auld (1948), and Diment (1967) investigated this phenomenon and developed, and refined, an equation to describe convection in boreholes relating fluid properties and the radius of the borehole to a critical thermal gradient, above which convection would be expected. Using this equation, it can be shown that for normal geothermal gradients (approximately 25 °C/km), convection can be expected in boreholes with diameters greater than about 5 cm.…”

Section: Thermal Gradientmentioning

confidence: 99%

Temperature Profiles and Hydrologic Implications from the Nevada Test Site

Gillespie¹

2005

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Groundwater temperature is sensitive to the competing processes of heat flow from below and the advective transport of heat by groundwater flow. Because groundwater temperature is sensitive to conductive and advective processes, groundwater temperature may be utilized as a tracer to further constrain the uncertainty of predictions of advective radionuclide transport models constructed for the Nevada Test Site (NTS). Since heat transport, geochemical, and hydrologic models for a given area must all be consistent, uncertainty can be reduced by excluding those models that do not match estimated heat flow.The initial objective of this study was to identify the quantity and quality of available heat flow data at the NTS. Although thousands of temperature logs have been conducted at the NTS, most are recorded on paper and not easily examined. Therefore, only those temperature logs in digital format were considered. During the course of an earlier investigation, 145 temperature logs from 63 boreholes on the NTS were examined. Of these, 13 boreholes were found to have temperature profiles suitable for the determination of heat flow values from one or more intervals within the boreholes. The successful analysis of the initial 13 temperature profiles led to the acquisition of an additional 21 temperature profiles from boreholes at the NTS, during fiscal year (FY) 2003. Five of these 21 temperature profiles were obtained in boreholes that had been previously profiled and were collected to ensure the previously collected profiles were representative of ambient conditions. The other 16 profiles were obtained in boreholes that had not been previously profiled. Additionally, a previously measured temperature profile (borehole UE-18t) that was overlooked in the initial investigation of existing temperature profiles from the NTS was discovered, and borehole PM-1 was relogged during an operational check of a new wireline for DRI's geophysical logging unit. During FY04, an additional 15 temperature profiles were obtained. Five of the temperature profiles were obtained in boreholes that had been previously profiled. The other 10 profiles were measured in boreholes from which previous stabilized temperature profiles had not been obtained. Interpretation of a temperature profile in a lithology without major variations in thermal conductivity may be fairly straightforward; interpretation of a temperature profile crossing several hydrostratigraphic units requires accurate knowledge of the thermal properties of the corresponding hydrostratigraphic units, and is complicated if advective heat transport is occurring.Heat flow values for intervals contained within the boreholes ranged from a low of 5.0 mW m -2 to a high of 181.6 mW m -2 . Vertical variations in heat flow values, within individual boreholes, were readily explained by the advection of heat by groundwater flow. Horizontal consistencies and variations in heat flow values between various boreholes were dependent upon the geologic setting of the borehole, and the effect o...

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Thermal Regime of a Large Diameter Borehole: Instability of the Water Column and Comparison of Air‐ and Water‐filled Conditions

Cited by 68 publications

References 0 publications

Geothermal State of Hole 504B: ODP Leg 111 Overview

Geothermal State of Hole 504B: ODP Leg 111 Overview

Heat Flow and Hydrologic Characteristics at the AND-1B borehole, ANDRILL McMurdo Ice Shelf Project, Antarctica

Temperature Profiles and Hydrologic Implications from the Nevada Test Site

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