Fault intersections as critical hydrocarbon leakage zones: integrated field study and numerical modelling of an example from the Timor Sea, Australia

Fault intersections are identified as important sites for hydrocarbon leakage from the Skua oil field in the Timor Sea, Australia. Integrated structural and fluid history data sets suggest that these fault intersections may be efficient and long-lived fluid conduits. Three-dimensional (3D) numerical modelling, based on fault patterns observed in the Skua Field, generated zones of high dilation in the vicinity of fault intersections during contraction, even at low bulk strain values. In nature, these dilational zones are likely to be sites of high structural permeability containing concentrated open fracture networks ideal for high fluid flux. The potential for fluid leakage from these zones may be further enhanced where low shear strain occurs due to mechanical locking at the fault intersection. Although not tested in the numerical experiments, fault gouge development is likely to be less extensive in these zones of low shear strain, reducing the probability of forming membrane seals. The modelling results support previously published charge and leakage history studies of the Skua Field and highlight the potential for large volumes of hydrocarbons to be lost where fault intersection zones breach the top seal. Fault intersections may therefore play a significant role in influencing trap integrity conditions in other areas.

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