Analysis of borehole breakouts
Boreholes drilled into rock, which is subjected to stresses that amount to a significant fraction of the strength of the rock, may cause the rock to fail adjacent to the borehole surface. Often this results in the elongation of the cross section of the borehole in the direction of the minimum principal (compressive) stress orthogonal to the borehole axis. Such breakouts are valuable indicators of the direction of the minimum compressive stress orthogonal to the axis of the borehole. Their shapes may provide information about the magnitudes of both the maximum and minimum stresses relative to the strength of the rock. Borehole breakouts also may be impediments to drilling and to in situ measurement techniques, such as hydraulic fracturing. Observations and analyses of borehole breakouts raise three important questions. First, how does the shape of the borehole breakout evolve Second, why are breakout shapes stable despite the very high compressive stress concentrations that they produce Third, how is the shape of the breakout related to the magnitudes of the stresses in the rock In this paper, extensile splitting of rock in unconfined, plane strain compression is assumed to be the process of rock failure adjacent to the circumference of the borehole, by which a breakout forms. To simulate the evolution of a borehole breakout, this process is combined with a numerical boundary element analysis of the stresses around a borehole as its cross section evolves from the originally circular shape to that of a stable breakout.
- Research Organization:
- Earth Science Division, Lawrence Berkeley Laboratory, University of California, Berkeley(US)
- OSTI ID:
- 5875852
- Journal Information:
- J. Geophys. Res.; (United States), Vol. 94:B6
- Country of Publication:
- United States
- Language:
- English
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