Modelling Sealing Potential within the Palaeozoic Sequence in the Fitzroy Trough, Canning Basin, Western Australia

Strand, Julian; Langhi, Laurent; Griffiths, Cedric
Earth Sciencs and Resource Engineering, CSIRO, Perth, WA, Australia.

The Fitzroy Trough / Gregory Sub-basin system contains significant Palaeozoic sediments, studies suggest these are >10km; according to some estimates >12km thick. The sub-basin contains sequences varying from the classic Frasnian reef complexes today exposed in the Kimberly to the thick Permo-Carboniferous glacial Grant Group. The units of the trough underwent a significant Mesozoic basin inversion event, the Fitzroy Transpression, resulting in the formation of anticlinal structures and locally significant erosion. Historically exploration drilling within the Fitzroy Trough has targeted these anticlinal structures.

As part of a review of the Canning Basin, Fault-seal potential has been estimated for the later Palaeozoic sequence in the NW of the basin. This study focussed upon identifying localities where the sequence will be prone to fault-seal given suitable reservoir geometry. The application for this study is for hydrocarbon exploration, but CO2 sequestration potential have accelerated impetus for the revaluation with the planning of the James Price Point (JPP) LNG facility, to service northern NW Shelf gas production.

The initial study analysed sequences directly from well data, which given the data sparsity, there are only 65 wells within 200km of JPP, limited the effectiveness of the modelling to the immediate vicinity of the wells. Additionally most of the wells are located on the trough's flanks rather than depocentres. Exploration targeting of anticlines has resulted in further under representation of the later parts of the sequence, due to significant, but localised, erosion on anticlinal crests, commonly including the significant top-sealing, Noonkanbah Formation. Prior to identifying suitable, fault-bound structures, identification of shale-rich, top-seal and fault-seal prone sequences is required.

As such the next stage goal of the project has been to produce a large-scale (1000 x 250km) sedimentological model of the Fitzroy Trough / Gregory Sub-basin. These sub-basins forming the northern flank of the Canning Basin have a similar tectonic history from the early Devonian to the Jurrasic which is not necessarily common to the rest of the basin. The stratigraphic forward modelling draws together data existing sedimentological models and the well data from the first phase. The output of the modelling will be used to additional estimates regarding seal potential and to provide a framework for hydrocarbon migration modelling studies.

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