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The Petroleum Potential of the West Timor Trough, Indonesia

Tripathi, Anand; Jones, William; Rajagopal, Rajesh
Reservoir Multi Client, Petroleum Geo Sevices, Perth, WA, Australia.

The West Timor Trough lies southeast of the Indonesian part of Timor Island and separates it from the Australian continental shelf, reaching depths of 2500m in the Indonesian waters. Timor Island consists of slices of Australian continental crust thrust backwards to the southeast as a result of collision with the Asian fore-arc since 4 Ma. The Timor Trough formed by buckling of the Australian continental crust as it was overridden by the thrust complex.

The West Timor Trough covers an area of 40,000 km 2 but has been only lightly explored. With four wells close to the Australian/Indonesian boundary, all of which were dry, the perception has arisen that the region is non-prospective. However interpretation of 4300 km of new 2D seismic has improved the picture considerably. The data were recorded in 2010 with dual streamer sensors and a record length of 10 seconds.

The geology visible on the seismic data is very different on the two sides of the trough. On the southeast an older section of Permian to Triassic fluvio-deltaic shales, sandstones and minor limestones is faulted into a pattern of northeast trending horsts, grabens and tilted fault blocks. This is truncated by a ‘break-up' unconformity overlain by thin Jurassic and Cretaceous clastics, in turn overlain by a succession of Cenozoic carbonates. The northwestern side is obscured by an accretionary prism comprising imbricate thrust sheets overlying a detachment surface. Below this there are hints of major southeast-verging thrusts of Permian to Jurassic sediments.

The prospectivity of the area has been upgraded by the recognition of a graben underneath the axis of the trough which appears to contain Jurassic sediments buried to a depth at which source rocks could be mature. A possible secondary source horizon is Lower Triassic shales deeply buried in a depocentre in the southwest of the region. Traps are provided by the Permotriassic horsts over a dome in the southeast and associated onlapping Jurassic sands and Triassic tilted fault blocks in the southwest. Another possible trapping mechanism on the northwest side of the trough is within reservoirs in the major thrusts sealed by the detachment surface.

 

AAPG Search and Discovery Article #90155©2012 AAPG International Conference & Exhibition, Singapore, 16-19 September 2012