Bronwyn Camac, University
of Adelaide, Australian
School of Petroleum, Adelaide, S.A., Australia,
[email protected]
The understanding of the geomechanical behaviour of cap rock in the Penola
Trough, South Australian Otway Basin is in its earliest stages. Due to its
thickness, lithotype and regional extent, the main sealing unit of the gas
bearing sands of the Pretty Hill Formation, the Laira Formation, has been
considered to have a low risk of cap rock failure in the past. The observation
of an open conductive fracture network throughout the seal on FMI logs and
associated perturbations in the regional stress field, as analysed from dipmeter
data, led to the question: Can these perturbations be modelled using distinct
element code and ‘ground truthed’ against field data, where these perturbations
correlate with brittle seal failure. If so, can this technique be developed into
a risking tool for seal evaluation, ahead of the bit?”
This research concentrates on these questions and is showing that using
existing tools and data routinely collected in the petroleum and mining
industries, a more comprehensive and integrated risking analysis can be
undertaken for hydrocarbon seals, incorporating both cap and fault seal.
The selection of modelling parameters is critical to the success of the
outcomes of the models. Much of the research has been directed towards the more
confident determination of fault parameters, such as friction angle, stiffness
and orientation.
The developed techniques have also been applied to other areas within
Australia and New Zealand. These modelling techniques have direct application to
risk assessment in other highly faulted regions throughout Australia and
internationally.
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