Abstract Three-dimensional coupled deformation and fluid-flow numerical modeling, charge-history analysis, and seismic imaging of inferred leakage-related geobodies are integrated to investigate the response of a complex set of Jurassic trap-bounding normal faults to extensional reactivation and to assess hydrocarbon upfault seepage on the Laminaria High (Timor Sea, Australian North West Shelf). Fluid inclusion data are consistent with the presence of paleo-oil columns below the current accumulations in the Laminaria and Corallina fields. Evidence for other partially breached (current and paleo-oil column) as well as breached (dry with paleo-oil column) closures across the region implies that active and widespread seepage took place after the time of initial oil charge. The distribution of current and paleo-oil zones, and the location of inferred hydrocarbon leakage indicators defined on 3D seismic data, correlates with the prediction of fault-seal effectiveness based on modeled strain distribution. Within the geologic framework of the Laminaria High area, this distribution suggests that when sufficient reactivation shear strain is accumulated by reservoir faults, ductile deformation might give way to brittle failure in the top seal, allowing active flow pathways to develop and upfault seepage to take place from the reservoir to thief zones or the seafloor. The observations emphasize that strain and upfault fluid-flow partitioning is constrained by prereactivation fault size, lateral fault-tip distributions, and the presence of fault jogs inherited from successive episodes of growth processes. These elements can explain the complex distribution of paleo- and preserved oil columns in the study area and further support Cenozoic tectonic activity as being the first-order control on trap breaching and hydrocarbon seepage in this region.

ABSTRACT Hydrodynamics-based approaches were used to characterise and analyse the present-day pressure and fluid-flow conditions in the Permian Rotliegend reservoirs in the Netherlands. These approaches involve the use of multi-well pressure– depth plots, regional all fluid overpressure maps, salinity maps, and hydraulic-head maps. The maps and plots revealed a general regional trend of, often stepwise, decreasing fluid overpressures from northeast towards the south. Values of fluid overpressure vary between hard geopressures (P excess > 40 MPa in block L2) and near-hydrostatic pressures (P excess < 1 MPa in southern offshore). The highest overpressures occur in a zone following the northern limit of the Permian Rotliegend reservoirs. The width of the zone of high overpressures extends southward into the onshore Netherlands in the area of the Lauwerszee Trough. The hydraulic-head map of the Rotliegend reservoir demonstrates the potential for a general southward dewatering direction. The hydrodynamic evaluation identified that there are distinct regional differences between the southern and the northern part of the area with respect to important factors influencing both pressure generation (such as sedimentary loading and gas generation) and dissipation (by fluid flow) in the Rotliegend reservoir. The distribution of observed overpressures and hydraulic heads reflect these regional differences. We show that because the vertical and lateral dewatering of the Rotliegend reservoirs is controlled by the permeability framework, the regional variations therein exert a major influence on the observed distribution of fluid overpressure. Relatively high fluid overpressures are maintained in zones where dewatering of the Rotliegend is severely restricted. This is especially apparent in the southern part of the Dutch Central Graben and also in the northern part of the Lauwerszee Trough.