A Green's function approach for assessing the thermal disturbance caused by drilling deep boreholes in rock or ice

Geophysical Journal International
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Abstract

A knowledge of subsurface temperatures in sedimentary basins, fault zones, volcanic environments and polar ice sheets is of interest for a wide variety of geophysical applications. However, the process of drilling deep boreholes in these environments to provide access for temperature and other measurements invariably disturbs the temperature field around a newly created borehole. Although this disturbance dissipates over time, most temperature measurements are made while the temperature field is still disturbed. Thus, the measurements must be ‘corrected’ for the drilling-disturbance effect if the undisturbed temperature field is to be determined. This paper provides compact analytical solutions for the thermal drilling disturbance based on 1-D (radial) and 2-D (radial and depth) Green's functions (GFs) in cylindrical coordinates. Solutions are developed for three types of boundary conditions (BCs) at the borehole wall: (1) prescribed temperature, (2) prescribed heat flux and (3) a prescribed convective condition. The BC at the borehole wall is allowed to vary both with depth and time. Inclusion of the depth dimension in the 2-D solution allows vertical heat-transfer effects to be quantified in situations where they are potentially important, that is, near the earth's surface, at the bottom of a well and when considering finite-drilling rates. The 2-D solution also includes a radial- and time-dependent BC at the earth's surface to assess the impact of drilling-related infrastructure (drilling pads, mud pits, permanent shelters) on the subsurface temperature field. Latent-heat effects due to the melting and subsequent refreezing of interstitial ice while drilling a borehole through ice-rich permafrost can be included in the GF solution as a moving-plane heat source (or sink) located at the solid–liquid interface. Synthetic examples are provided illustrating the 1-D and 2-D GF solutions. The flexibility of the approach allows the investigation of thermal drilling effects in rock or ice for a wide variety of drilling technologies. Numerical values for the required radial GFs GR are available through the Advanced Cooperative Arctic Data and Information Service at doi:10.5065/D64F1NS6.

Additional publication details

Publication type Article
Publication Subtype Journal Article
Title A Green's function approach for assessing the thermal disturbance caused by drilling deep boreholes in rock or ice
Series title Geophysical Journal International
DOI 10.1093/gji/ggv415
Volume 203
Issue 3
Year Published 2015
Language English
Publisher Blackwell Science
Publisher location Oxford, England
Contributing office(s) Geosciences and Environmental Change Science Center
Description 19 p.
First page 1877
Last page 1895
Online Only (Y/N) N
Additional Online Files (Y/N) N