Glossary

Borehole ovalisation (elongation)

Boreholes rarely drill as perfect cylinders, but can become ovalised (or elongated) in cross-section during or after drilling. Inclined holes frequently are elongated in the direction of drilling as an effect of the tool string seeking the bottom of the hole (key seating). The effect of in-situ stress can also change hole shape through borehole breakout with the development of hole ovalisation in the direction of minimum horizontal stress (Shmin) and the orientation of borehole elongation can been interpreted as reflecting the orientation of Shmin. In the absence of borehole breakout and tension fractures, hole elongation may be used as a low confidence indicator of minimum horizontal stress (Shmin) direction.

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About the glossary
This listing is not exhaustive or definitive, do not expect Oxford English Dictionary standards; it is aimed at those who need to understand basic principles and those that read reports on dipmeters and borehole images requiring some technical help to get the most from such documents.

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Acknowledgements
This listing has been derived by Task Geoscientists. All external sources are fully acknowledged.