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Geological Society, London, Special Publications; 1992; v. 65; p. 157-168;
DOI: 10.1144/GSL.SP.1992.065.01.11
© 1992 Geological Society of London

Fractures and Stress

Borehole breakouts and stress analysis in the Timor Sea

R. R. Hillis1 & A. F. Williams2

1 School of Earth Sciences, The Flinders University of South Australia, GPO Box 2100, Adelaide, SA 5001, Australia
Department of Geology and Geophysics, University of Adelaide, GPO Box 498, Adelaide, SA 5001, Australia
2 CSIRO Division of Geomechanics, PO Box 54, Mt Waverley, VIC 3149, Australia

Boreholes drilled in the search for oil in the Vulcan Sub-basin (Timor Sea, Northwest Shelf, Australia) commonly exhibit an elliptical cross section believed to be the result of wellbore failure known as borehole breakout. The azimuths of the long axes of breakouts identified in 13 wells in the Vulcan Sub-basin show a reasonably consistent 130–170°N trend implying that maximum horizontal compressive stress (SHmax) is oriented 040–080°N.

This NE-ENE SHmax orientation in the Vulcan Sub-basin does not coincide with the direction of absolute plate velocity, nor is it consistent with compression transmitted from the nearby Australia/Banda Arc collision zone. However, it is in agreement with theoretical models of stress distribution based on the plate-driving forces throughout the Indo-Australian plate.

The breakout analyses, in conjunction with structural interpretations, suggest that the instabilities observed in vertical wells will be exacerbated by orienting horizontal wells 040–080°N, and that drilling in the 130–170°N direction may enhance both stability and production rates.





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S. F. Rogers
Critical stress-related permeability in fractured rocks
Geological Society, London, Special Publications, 2003; 209: 7 - 16.
[Abstract] [PDF]