Vulcan Sub-Basin Fault Styles — Implications for Hydrocarbon Migration and Entrapment

Abstract

Several structural domains are recognised within the Vulcan Sub-basin, Timor Sea. These domains developed during the Jurassic rifting phase and are separated by major transfer zones which trend in a northwest-southeast direction. Within each domain are frequent third order transfers which sub-divide the main northeast trending fault blocks into numerous compartments. These enable structural hydrocarbon traps to be formed, despite a predominant regional dip. They also affect migration pathways.Jurassic fault styles include detached rotational blocks, salt-associated features, tilted fault blocks and 'hourglass' horsts and grabens. These generally have a northeast-southwest orientation. The transfer faulting complicates these features and forms zones of structural complexity with associated poor seismic data quality. A separate fault episode in the north of the sub-basin during the Tithonian resulted in an east-west fault set overprinting the earlier structuring.Intra-Cretaceous fault movement is also recognised and has an important role in early hydrocarbon entrapment.Structural reactivation during the Late Miocene/Early Pliocene of the earlier fault sets modified the geometry of many existing traps. Numerous new traps may also have formed as a result of this tectonism. In many places the resulting geometry is complex, particularly where the younger fault orientation is at an angle to the main Oxfordian fault set. The late-stage movement is primarily extensional, manifested by predominantly normal faults; overall, however, a varying component of strike slip is likely. A divergent strike-slip zone is recognised at the southwest end of the Cartier Trough.The effects of the late stage tectonism tend to mask the seismic expression of Mesozoic hydrocarbon traps resulting in many wells being drilled off-structure at the target horizon. An understanding of the deeper structuring should result in further discoveries in this prospective basin.

Structural style in a young flexure-induced oblique extensional system, north-western Bonaparte Basin, Australia

“…This is consistent with minimum horizontal compressive stress ( Fig. 3; Woods, 1992;De Ruig et al, 2000), which is orthogonal to the present-day maximum principal horizontal stress direction (S Hmax ) modelled in the Timor Sea ( Fig. 17; Hillis et al, 1998;Castillo et al, 2000;Reynolds et al, 2003;Hillis et al, 2008), and along the AustraliaBanda Arc collision margin (Dyksterhuis et al, 2005).…”

“…18 and 19). In the study area, soft and hard-linkages have been described by many researchers (Woods, 1992;De Ruig et al, 2000;Keep et al, 2002;Gartrell et al, 2006;Langhi et al, 2011;Çiftçi and Langhi, 2012). Our results suggest that both the pre-existing structural style and the obliqueness of Neogene-Recent extension direction are critical for the type of linkage between two fault systems (Figs.…”

“…9 and 18). This phenomenon is more characteristic of the Nancar Trough/Laminaria High region, although hour-glass geometry has also been described for the Jabiru and Challis structures (Woods, 1992;Chen et al, 2002). The mean orientation of the young faults measured along the Base Miocene (063 ) is 27 oblique to the EeW set of faults (090 ) mapped along the Valanginian Unconformity (Fig.…”

“…It has been proposed that an NNW trending transfer zone (the Paqualin Transfer Zone) is bounding these structures to the northeast ( Fig. 6; Woods, 1992). To the northeast, a prominent NE-trending horst and graben architecture is present (Fig.…”

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

“…A number of deformation events occurred during the post-rift history of the region in association with plate-scale reorganisations and collision on the northern margin of the Australian Plate (Etheridge, Mcqueen, & Lambeck, 1991;Gartrell et al, 2002;O'Brien et al, 1998;O'Brien & Woods, 1995;Veevers, Powell, & Roots, 1991;Woods, 1992Woods, , 1994. Pulses of folding and uplift throughout the Late Cretaceous and into the early part of the Tertiary are observed along the length of the Skua Fault.…”