STRATIGRAPHIC ARCHITECTURE OF A PROTEROZOIC SHALE PLAY: INSIGHTS FROM WELL CORRELATION IN THE VELKERRI FORMATION (BEETALOO SUB-BASIN, NORTHERN TERRITORY, AUSTRALIA)

For more than 20 years, the oil and gas industry has been exploring for and producing hydrocarbons from unconventional targets. In self-sourced reservoirs, the main challenge lies in finding “sweet spots” that are a combination of liquid- or gas-rich rocks with good reservoir characteristics. In unconventional exploration, understanding the distribution of organic carbon and its thermal maturity, as well as variations in the porosity, permeability and brittleness of the host formation, assists in identifying sweet spots and determining their distribution. These features are mainly controlled by sedimentary facies, mineralogy, and thermal history. The Beetaloo Sub-Basin in northern Australia presents tremendous potential for unconventional hydrocarbon exploration. However, exploration of the 1.4 Gyr old Velkerri Formation in this area is challenging because of the complex geological history and lack of laterally continuous data required to accurately map key elements of the unconventional petroleum system.

The aim of the present work is to improve our understanding of the stratigraphic architecture of the Velkerri Formation in order to understand and predict sedimentary heterogeneities. Based on well correlations, we present the facies distribution and sequence stratigraphic architecture of the Velkerri Formation along two regional transects. We discuss the different geological controls that have impacted the evolution of the stratigraphic architecture and propose different regional paleogeographic maps to illustrate the evolution of the basin during the Mesoproterozoic. By integrating geochemical analyses (e.g., Rock-Eval, ICP-OES-MS) into this stratigraphic framework, we lay the foundation for understanding the accumulation of organic matter in this shale play. The results from this study are currently being incorporated into a process-based stratigraphic forward- model to predict in 3D the distribution of sedimentary heterogeneities and organic richness of the entire basin. The findings will advance the understanding of the complex distribution of sweet spots present in this unique Mesoproterozoic shale play.