Paul Lyon

PhD Student



Telephone: +61 8 8303 4305
Facsimile: +61 8 8303 4345
E-mail: plyon@ncpgg.adelaide.edu.au

PhD Project:

The Modes of Fault Seal Breach in the Penola Trough, Otway Basin.

Commenced: 2002

Supervisors: Richard Hillis, Peter Boult (PIRSA)

Project support: Primary Industry Resources, South Australia; Origin Energy and University of Adelaide

Scholarship support: International post-graduate research scholarship (IPRS), University of Adelaide


Thesis Aims:

To undertake a full and systematic assessment of the fault seal breach mechanisms in the Penola Trough. Firstly the structural history of the study area will be re-evaluated using seismic data. Fault juxtaposition, fault sealing processes and reactivation will be assessed to investigate which of these control the presence of a hydrocarbon column in the Otway Basin. If fault seal is not the critical issue then the role of fracturing of top-seal will be assessed.

Backgroud:

Exploration interest in the Otway Basin has dropped considerably in recent years due to the frequent drilling of unsuccessful wells that have encountered only residual hydrocarbon columns (i.e. columns that have previously existed, but have since leaked away). Structurally, the Penola Trough shows a complex interaction of younger Early Cretaceous and older Late Cretaceous-Tertiary faulting. The petroleum play type is thus one of fault bound traps.

In at least some cases, it has been demonstrated that the sealing capacity of the cap seal rocks are sufficient to hold back hydrocarbon columns, hence leakage appears to primarily be a fault seal problem. Furthermore, again in at least some cases, both juxtaposition of units across the faults and shale smear/damage on the fault plane itself indicate that the faults should be sealing. Hence reactivation of trap-bounding faults subsequent to accumulation of hydrocarbon columns may be the key cause of breaching.

Fault Analysis Seals Technology (FAST) is a technique that can be used to quantitatively define the propensity of a fault plane to reactivate under the contemporary stress tensor. This tool has been successfully calibrated in the Timor Sea, but has not yet been properly tested in the Otway Basin. The inability to calibrate the technique has led to the development of a previously unconsidered mechanism of breach. Failure through reactivation may instead occur as natural fracturing within intact top seal.

The thesis will implement the FAST technique in the evaluation of seal breach due to reactivation of faulting using revised structural interpretation of fault geometries. Other causal mechanisms of unsuccessful trap accumulation due to unfavourable juxtaposition of reservoir against permeable units, or lack of development of sealing rock on the fault plane itself will also be determined.

If the analysis reveals that several traps bearing residual hydrocarbon columns are favourably juxtaposed and/or have a membrane seal, and are not predicted to have been breached by reactivation, then some type of cap seal breach must be inferred. In this case the project will investigate the likelihood of brittle failure of intact cap seal as a seal failure mechanism.


Biography

Paul graduated with a BSc (1st class honours) in Resource and Applied Geology from the University of Birmingham in 2001. As an undergraduate, Paul was involved in a structural mapping project of the Variscan suture zone, Beja, Portugal in collaboration with the University of Lisbon. Prior to his commencement of a Phd at the NCPGG in March 2002, Paul worked as a field geologist for the British Geological Survey.