Predicting brittle cap-seal failure of petroleum traps: An application of 2D and 3D distinct element method

Previous research shows the importance of understanding the relationship between fault geometry and current applied tectonic stresses in the prediction of critically stressed faults and their propensity for fluid flow via generated fracture networks along and/or around the fault plane. Data collected from the Penola Trough, onshore Otway Basin, South Australia shows that a more complex 3D failure mechanism may be active, whereby the cap-seal may fracture preferentially to fault failure. An emerging application for a two- and three-dimensional distinct element numerical modelling technique, at the play and prospect level, respectively, which assists in assessing pre-drill seal integrity, is presented by way of two case studies from the Penola Trough. Sensitivity studies at the prospect scale show how (1) fault rock strength, (2) fault zone width and (3) the interaction of two fault sets generates local perturbations in the regional stress field. At the play scale, the depth to which a younger active fault set propagates can be explained by the distribution of stress within the rock mass generated by the present-day far-field stress acting on older regionally significant faults. This work offers a workflow and an additional technique to predict cap-seal integrity prior to drilling. © 2009 EAGE/Geological Society of London.Bronwyn A. Camac, Suzanne P. Hunt and Peter J. Boul

Rapid, long-distance dispersal by pumice rafting

Pumice is an extremely effective rafting agent that can dramatically increase the dispersal range of a variety of marine organisms and connect isolated shallow marine and coastal ecosystems. Here we report on a significant recent pumice rafting and long-distance dispersal event that occurred across the southwest Pacific following the 2006 explosive eruption of Home Reef Volcano in Tonga. We have constrained the trajectory, and rate, biomass and biodiversity of transfer, discovering more than 80 species and a substantial biomass underwent a >5000 km journey in 7-8 months. Differing microenvironmental conditions on the pumice, caused by relative stability of clasts at the sea surface, promoted diversity in biotic recruitment. Our findings emphasise pumice rafting as an important process facilitating the distribution of marine life, which have implications for colonisation processes and success, the management of sensitive marine environments, and invasive pest species