--> Exploring for Unconventional Plays in the McArthur Basin, Northern Territory, Australia: The Application of an Integrated Regional Evaluation in a Data-Sparse Frontier Basin

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Exploring for Unconventional Plays in the McArthur Basin, Northern Territory, Australia: The Application of an Integrated Regional Evaluation in a Data-Sparse Frontier Basin

Abstract

In the greater McArthur Basin, Northern Territory, Australia, the Mesoproterozoic Velkerri and Kyalla Formations of the Roper Group contain sequences of fine-grained, organic–rich sedimentary rocks that are attracting interest as potential shale gas and shale oil targets. In 2011 and 2012 Santos, in partnership with FROGTECH, conducted a regional assessment to help understand the tectonic and sedimentary evolution of the McArthur Basin and identify and highgrade prospective exploration plays. The evaluation, assisted by FROGTECH's SEEBASETM technology, integrated regional geology, sparse well and seismic data and potential fields data. During this evaluation it became apparent that a depression, named the OT Downs Sub-basin, represented a possibly significant easterly extension to the prospective Beetaloo Sub-basin. However, at that time, neither seismic nor well data had been acquired in the OT Downs Sub-basin and the subsurface stratigraphy and structure was unknown. Utilising the SEEBASETM methodology, the interpretation of the geometry of the OT Downs Sub-basin was refined to postulate a NW/SE trending foredeep-style depression with a basin fill, potentially containing the Roper Group prospective intervals, developed to a significant thickness in the axis of the trough and abutting the Mallapunyah High to the east and north-east. Guided by the review, Santos farmed in to EP161, the license that covered much of the OT Downs Sub-basin. Seismic data, acquired in 2013, was of high quality and confirmed for the first time the presence of sedimentary fill in the basin. The continuity of seismic reflections confirmed the overall lack of tectonic disturbance away from basin margins. Subsequently, exploration well Tanumbirini-1, drilled in 2014 to a total depth of just under 4km, confirmed the presence of Roper Group organic-rich intervals. The results of seismic and Tanumbirini-1 confirmed the effectiveness of the integrated approach utilising the SEEBASETM methodology in understanding the basin evolution and identifying prospective trends. As a result of this approach, a significant easterly development of the prospective McArthur Basin Roper Group shale plays is now proven in the OT Downs sub-Basin.