Steady-State Interstitial Circulations in an Idealized Atoll Reef and Tidal Transients in a Deep Borehole by Computer Simulation

  1. G. F. Camoin4 and
  2. P. J. Davies5
  1. A.-M. Leclerc1,
  2. D. Broc2,
  3. Ph. Jean-Baptiste1 and
  4. J. Rancher3

Published Online: 27 MAY 2009

DOI: 10.1002/9781444304879.ch13

Reefs and Carbonate Platforms in the Pacific and Indian Oceans

Reefs and Carbonate Platforms in the Pacific and Indian Oceans

How to Cite

Leclerc, A.-M., Broc, D., Jean-Baptiste, Ph. and Rancher, J. (2009) Steady-State Interstitial Circulations in an Idealized Atoll Reef and Tidal Transients in a Deep Borehole by Computer Simulation, in Reefs and Carbonate Platforms in the Pacific and Indian Oceans (eds G. F. Camoin and P. J. Davies), Blackwell Publishing Ltd., Oxford, UK. doi: 10.1002/9781444304879.ch13

Editor Information

  1. 4

    CEREGE, Aix-en-Provence, France

  2. 5

    University of Sydney, Australia

Author Information

  1. 1

    CEA/SACLAY/DSM/LMCE, Orme des Merisiers, Bâtiment 709, 91191 Gif-sur-Yvette Cedex, France

  2. 2

    CEA/SACLAY/DRN/DMT/SEMT/TTMF, 91191 Gif-sur-Yvette Cedex, France

  3. 3

    CEA. B3/DSR/DTDS/SARI, B. P. 12, 91680 Brugères-le-Châtel, France

Publication History

  1. Published Online: 27 MAY 2009
  2. Published Print: 23 MAR 1998

ISBN Information

Print ISBN: 9780632047789

Online ISBN: 9781444304879

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Keywords:

  • steady-state interstitial circulations in atoll reef and tidal transients by computer simulation;
  • atoll carbonate platforms - time evolutive structures built on basaltic substrate;
  • computer simulation of interstitial water circulation;
  • numerical analysis of natural convection;
  • carbonate platforms and basaltic bedrock;
  • homogeneous atoll platform;
  • purely diffusive temperature field in homogeneous platform;
  • transition zone - exchange between interstitial water and ocean;
  • borehole response to tidal forcing

Summary

Hydraulic circulations induced by thermal convection inside the carbonate platform of atolls are still not well known. As part of a project aimed at modelling these circulations using the computer code TRIO/CASTEM, developed at the CEA/SEMT, we present preliminary simulations with simplifying assumptions. This numerical study is carried out with the objective of clarifying the basic physical phenomena responsible for pore-water motion within reefs and in deep boreholes.

In an entirely homogeneous carbonate body, inward and upward thermo-convective circulations are observed as a result of the oceanic thermal gradient and geothermal heating from the volcanic bedrock. However, the simulated thermal field inside the reef differs significantly from the field observations reported in the literature. Including a highly permeable zone at the base of the carbonate body, as is usually observed in atolls at the transition between carbonate and basalt, modifies the circulations. The velocities and the flow rate are greater, and the temperature gradients are in closer agreement with field data, pointing to the major role played by heterogeneities in shaping the velocity and temperature fields.

The numerical study of water motion in a deep borehole raises the question of interpreting the measurements made in such deep wells. If the borehole intersects the basal highly permeable zone, the system becomes an open hydraulic circuit in which the flow is mainly independent of the flow in the carbonate body. Our calculation of the borehole response to a simple sinusoidal tidal forcing shows that considerable hydraulic circulations develop in the borehole, leading to extensive temperature and velocity oscillations. These oscillations are comparable with those reported for the P7 well in Tahiti.