A hierarchical application of 20+ years of learnings from North American unconventional exploration and appraisal activities to delineate a 1MM-acre ‘sweet spot’ in the Beetaloo Basin shale gas play, Northern Territory, Australia

Abstract

The definition of a ‘sweet spot’ in unconventional shale plays varies from person to person, operator to operator, and analyst to analyst. More importantly, it varies with respect to the maturity of the play itself. Early in the life of a play, a sweet spot usually refers to an area where the properties of the target formation result in the highest performing wells, but a mature play may have a sweet spot associated with the lowest well costs, proximity to important infrastructure, or the highest return on investment. For a frontier basin in a remote setting like the Beetaloo, having only 15 vertical exploration wells and eight horizontals drilled to date, the definition is necessarily the former, and could be more appropriately termed the ‘first spot.’ High-rate well tests attract important investment dollars that allow appraisal to continue towards pilot development and first sales. Without these tests, the play concept quickly loses momentum. Exploration by Tamboran Resources and others in the Beetaloo Sub-basin suggests the presence of a world-class shale gas play. The key self-sourcing reservoir is the Mesoproterozoic aged Velkerri Formation (~1.4 Ga), which may be the oldest productive petroleum system in the world. Delineating the play boundaries of an unconventional shale is a relatively easy task, as the area is defined by meeting certain rock property thresholds (e.g. total organic content, depth, thickness, thermal maturity). Defining the sweet spot is much more involved, requiring an understanding of how to appropriately weight rock and reservoir properties at the basin scale of observation.