A new exploration model with a claimed accuracy rate of 80% when tested against data in the Timor Sea could save oil and gas companies hundreds of millions of dollars. A team of CSIRO scientists in Perth has shown that combining several different geological techniques can more reliably predict where pools of oil and gas are trapped in the sub-surface. An understanding of a combination of factors including fault growth histories, trap geometry and hydrocarbon charge history can predict the distribution of preserved and breached traps.

Exploration is especially difficult in the Timor Sea because of the large amount of fault activity and associated earthquakes occurring over the last 10 million years. This can cause damage to the structures that trap hydrocarbons by allowing the oil and gas to seep out through fractures, and exploration companies have, as a consequence of this, spent millions of dollars drilling ‘dry’ wells. “Of the 64 Timor Sea prospects we investigated, our model would have advised against drilling 42 of them. This would have saved industry approximately $400 million dollars”, explained CSIRO Project Leader, Dr Anthony Gartrell. “Importantly, all of the commercial fields discovered in the area would have been high-graded by the model. These hold hydrocarbon accumulations worth billions of dollars.” In the cases where the model was at odds with the drilling data, other factors such as hydrocarbon charge and seismic resolution also need to be factored in.

Recently, it has been demonstrated that as fault systems evolve, movement tends to localise on to larger faults, while activity on smaller faults decreases and they may eventually become dormant. CSIRO said it has shown that this process resulted in partial protection of some fault-bound traps with favourable geometries from breach, but promoted breaching of others. The team claims to have developed a simple, but powerful, exploration model by using a range of techniques and expertise, including structural geology, fault seal assessment, and fluid inclusion analysis. By understanding a combination of factors such as fault growth histories, structural architecture ,and both past and present hydrocarbon fluid distributions, a set of characteristic high risk and low risk trap geometries was identified (Fig 1). These characteristic trap types can be used to predict the likelihood of encountering preserved hydrocarbons in the area with a relatively high degree of confidence.

The Fault Seal Team, which was part of the Australian Petroleum Cooperative Research Centre (APCRC) Consortium, believes that this model addresses many of the problems that existing techniques cannot deal with. “Previous models don’t take into account the way faults and stress fields evolve over time”, said Dr Gartrell, mentioning the range of skills, experience and expertise across CSRIO divisions as an advantage when addressing such complex issues. “By combining unique CSIRO techniques with standard industry methods, we have found an innovative solution in an area that has been explored for over 20 years.”

Dr Gartrell explained that the model does not officially have a name, but that they internally refer to it as ‘flogging a dead horst’ – “a bit of bad geologist humour there.” CSIRO has had a lot of interest in the model and feel that it “will be particularly useful for smaller and middle sized companies coming into the area and looking at some of the smaller structures yet to be drilled. However, there may be some large untested structures still out there to which the model could be applied”, added Dr Gartrell.

The model and the science behind it also apply to several other areas around Australia where fault reactivation represents a risk to exploration activities. “I should stress that although the model looks extremely simple, which it is, we have done a lot of work looking at the possible controls on hydrocarbon preservation, including several models and mechanisms that are already in the public domain”, he explained. “What we found is that this simple solution is the most consistent with the observational data that is available in the Timor Sea.”

CSIRO Petroleum Division Chief, Beverly Ronalds, added that “this is a prime example of how science based solutions are helping to maintain a globally competitive and sustainable energy industry for Australia.”

Reference

Gartrell, A., Bailey, W. R. and Brincat, M., 2005, Strain localisation and trap geometry as key controls on hydrocarbon preservation in the Laminaria High area: APPEA Journal, v. 45, p. 477-492.