Emerging Proterozoic Unconventional Gas Plays in the Beetaloo Sub-Basin, Northern Territory, Australia

Abstract

Origin has completed exploration campaigns during 2015 and 2016 in the Beetaloo Sub-Basin (the Beetaloo) of the Northern Territory, drilling three vertical wells and one horizontal well targeting the Mesoproterozoic source rocks of the Velkerri (~1.4 Ga) and Kyalla formations (~1.2 Ga). Comprehensive wireline log and core data were acquired from the vertical wells and DFITs completed on three of the four wells. Although the Velkerri and Kyalla formations are both Proterozoic marine sources rocks, their distinct sedimentology, mineralogy and geochemistry illustrate a dynamic basin setting and environment of deposition in the Beetaloo. The differences in the formations also impact the technical risk and chance of success for each play.

The Velkerri and Kyalla reservoir intervals have similar characteristics to successful shale plays in North America, however, their uniqueness lies in the Mesoproterozoic age of the source rocks. Low atmospheric oxygen levels (~3% of modern atmospheric conditions) characteristic of the Precambrian Era hindered evolution of complex life forms but favoured the production of abundant prokaryotic (cyanobacteria) and possibly eukaryotic (primarily algae) organisms and facilitated the accumulation and preservation of thick, organic-rich source rock reservoirs over broad areas.

Legacy geochemical and mineralogical data from core acquired through over the Velkerri and Kyalla formations, in addition to wireline log data, allowed the extents of the Velkerri and Kyalla play fairways to be constrained with a reasonable level of confidence by the mid-1990s. These legacy data confirm the source rocks are high quality, marine (Type I and Type II) source rocks. Multiple operators have drilled exploration wells since 2009, however, it was not until 2015-16 that the first horizontal well was drilled, hydraulic fracture stimulated and production-tested by Origin (Amungee NW-1H), which has confirmed the potential of the Velkerri Play.

The Amungee NW-1H discovery has received substantial attention for an early stage exploration well, primarily due to the scrutiny on the Australian gas market and the timing of the discovery. There are significant technical and commercial challenges to resolve before a development project could be sanctioned in the Beetaloo; however, if technically successful and commercially competitive the resource is likely of sufficient scale to provide a flexible gas supply option for Australia’s domestic and export gas markets.

AAPG Datapages/Search and Discovery Article #90323 ©2018 AAPG Annual Convention and Exhibition, Salt Lake City, Utah, May 20-23, 2018