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Geological Society, London, Special Publications; 2003; v. 216; p. 369-379;
DOI: 10.1144/GSL.SP.2003.216.01.24
© 2003 Geological Society of London

Deep Subsurface Sediment Mobilization

Pore pressure/stress coupling in Brunei Darussalam — implications for shale injection

Mark R. P. Tingay1, Richard R. Hillis1, Christopher K. Morley2, Richard E. Swarbrick3 & Eugene C. Okpere4

1 National Centre for Petroleum Geology and Geophysics, Adelaide University, South Australia, Australia mtingay{at}ncpgg.adelaide.edu.au
2 University of Brunei Darussalam, Bandar Seri Begawan, Negara Brunei Darussalam
3 Durham University, Durham, UK
4 Brunei Shell Petroleum, Seria, Negara Brunei Darussalam

Shale dykes, diapirs and mud volcanoes are common in the onshore and offshore regions of Brunei Darussalam. Outcrop examples show that shale has intruded along both faults and tensile fractures. Conventional models of overpressure-induced brittle failure assume that pore pressure and total stresses are independent of one another. However, data worldwide and from Brunei show that changes in pore pressure are coupled with changes in total minimum horizontal stress. The pore pressure/stress-coupling ratio ({Delta}{sigma}h/{Delta}Pp) describes the rate of change of minimum horizontal stress magnitude with changing pore pressure. Minimum horizontal stress measurements for a major offshore field where undepleted pore pressures range from normal to highly overpressured show a pore pressure/stress-coupling ratio of 0.59. As a consequence of pore pressure/stress coupling, rocks can sustain a greater increase in pore pressure prior to failure than predicted by the prevailing values of pore pressure and stress. Pore pressure/stress-coupling may favour the formation of tensile fractures with increasing pore pressure rather than reactivation of pre-existing faults. Anthropogenically-induced tensile fracturing in offshore Brunei supports this hypothesis.





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 Geological Society, London, Special PublicationsHome page
R. R. Hillis
Pore pressure/stress coupling and its implications for rock failure
Geological Society, London, Special Publications, 2003; 216: 359 - 368.
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 Geological Society, London, Special PublicationsHome page
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