Advanced Petrophysical Applications and Data Integration to Discriminate Primary and Secondary Pyritisation for Prospecting

A sedimentary complex from Bedout Basin in North West Shelf (NWS) of Australia has been analysed using petrophysical, geochemical, petrography and chemostratigraphy data to assess the occurrence of sulfidation process. Sandstone and clay layers are the dominant lithologies with thicknesses varying in the magnitude of meter scale from Lower to Upper Tertiary. The existence of pyritisation in sandstone sediment indicates correlation with porosity and permeability with higher contents in porous and permeable sandstones. The Lower Tertiary sandstones show porosities and permeabilities on the order of ~2 to 21 % and ~15 md to 5 d, respectively. We interpret the higher volume of pyritisation observed in sandstone units compared to claystone and shales is related to sediments burial processes, increased burial temperature and higher porosity and permeabilities of these units. Integrated Multi-Mineral petrophysical interpretation of Gamma Ray, Density, Neutron, Resistivity and Spectral Natural Gamma Ray logs show indications consistent with our observations from processed image log. These results can be used to identify and quantify the pyritisation in sandstone sediments. The discrimination between primary and secondary pyritisation can be inferred through petrography. Chemostratigraphy interpretation results integrated with petrophysical data also provide elemental and mineralogical boundaries which give insights into identifying the alteration and oxidation zones. This integrated approach can be applied to identify pyritisation processes which suggest the existence of iron, and more importantly within an environment of dissolved sulphides which can control the distribution of mineralisation - copper and gold for example.