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The Neoproterozoic–Paleozoic Officer Basin, located in South Australia and Western Australia, remains a frontier basin for energy exploration, with significant uncertainty due to a paucity of data. As part of Geoscience Australia’s Exploring for the Future (EFTF) program, the objective of this study is to derive the petrophysical properties and to characterise potential reservoirs in the Neoproterozoic–Cambrian sedimentary succession in the Officer Basin through laboratory testing and well log interpretation using both conventional and neural network methods. Laboratory measurements of 41 legacy core samples provide the relationships between gas permeability, Klinkenberg corrected permeability, and nano-scale permeability, as well as grain density, effective and total porosity for various rock types. Conventional log interpretation generates the volume fraction of shale, effective and total porosity from gamma ray and lithology logs. A self-organising map (SOM) was used to cluster the well log data to generate petrophysical group/class index and probability profiles for different classes. Neural network technology was employed to approximate porosity and permeability from logs, conventional interpretation results and class index from SOM modelling. The Neoproterozoic−Cambrian successions have the potential to host both conventional and tight hydrocarbon reservoirs. Neoproterozoic successions are demonstrated to host mainly tight reservoirs with the range in average porosity and geometric mean permeability of 4.77–6.39% and 0.00087–0.01307 mD, respectively, in the different sequences. The range in average porosity and geometric mean permeability of the potential Cambrian conventional reservoirs is 14.54−26.38% and 0.341−103.68 mD, respectively. The Neoproterozoic shales have favourable sealing capacities. This work updates the knowledge of rock properties to further the evaluation of the resource potential of the Officer Basin.

A geochemical and biostratigraphic approach has been applied to investigate the spatial and stratigraphic variability of Palaeogene sandstones from key wells in Taranaki Basin, New Zealand. Chronostratigraphic control is predominantly based on miospore zonation, while differences in the composition of Paleocene and Eocene sandstones are supported by geochemical evidence. Stratigraphic changes are manifested by a significant decrease in Na2O across the New Zealand miospore PM3b/MH1 early Eocene zonal boundary, at approximately 53.5 Ma. The change in Na2O is associated with a decrease in baseline concentrations of many other major (MnO, CaO, TiO2) and trace elements, and is interpreted to reflect a significant change in sandstone maturity. Paleocene sandstones are characterized by abundant plagioclase (albite and locally Na–Ca plagioclase), significant biotite and a range of heavy minerals, while Eocene sandstones are typically quartzose, with K-feldspar dominant over plagioclase, low mica contents and rare heavy minerals comprising a resistant suite. This change could reflect a change in provenance from local plutonic basement during the Paleocene Epoch to relatively quartz- and K-feldspar-rich granitic sources during Eocene time. However, significant quartz enrichment of Eocene sediment was also likely due to transportation reworking/winnowing along the palaeoshoreface and enhanced chemical weathering, driven in part by long-term global warming associated with the Early Eocene Climatic Optimum. The broad-ranging changes in major-element composition overprint local variations in sediment provenance, which are only detectable from the immobile trace-element geochemistry.

Paleocene sandstones in the Kupe Field of Taranaki Basin, New Zealand, are subdivided into two diagenetic zones, an upper kaolinite–siderite (K-S) zone and a lower chlorite–smectite (Ch-Sm) zone. Petrographic observations show that the K-S zone has formed from diagenetic alteration of earlier-formed Ch-Sm sandstones, whereby biotite and chlorite–smectite have been altered to form kaolinite and siderite, and plagioclase has reacted to form kaolinite and quartz. These diagenetic zones can be difficult to discriminate from downhole bulk-rock geochemistry, which is largely due to a change in element-mineral affinities without a wholesale change in element abundance. However, some elements have proven useful for delimiting the diagenetic zones, particularly Ca and Na, where much lower abundances in the K-S zone are interpreted to represent removal of labile elements during diagenesis. Multivariate analysis has also proven an effective method of distinguishing the diagenetic zones by highlighting elemental affinities that are interpreted to represent the principal diagenetic phases. These include Fe-Mg-Mn (siderite) in the K-S zone, and Ca-Mn (calcite) and Fe-Mg-Ti-Y-Sc-V (biotite and chlorite–smectite) in the Ch-Sm zone. Results from this study demonstrate that the base of the K-S zone approximately corresponds to the base of the current hydrocarbon column. An assessment with 1D basin models and published stable-isotope data show that K-S diagenesis is likely to have occurred during deep-burial diagenesis in the last 4 Myr. Modeling predicts that CO2-rich fluids were generating from thermal decarboxylation of intraformational Paleocene coals at this time, and accumulation of high partial pressures of intraformational CO2 in the hydrocarbon column is considered a viable catalyst for the diagenetic reactions. Variable CO2 concentrations and residence times are interpreted to be the reason for different levels of K-S diagenesis, which is supported by a clear relationship between the presence or absence of a well-developed K-S zone and the present-day reservoir-corrected CO2 content.