Fluid Migration and Diagenetic Homogeneity in the Amadeus Basin, Australia

This study investigates the diagenetic homogeneity of the Ordovician Pacoota and Stairway sandstone reservoir rocks throughout the basin. By analysing in what way diagenesis is controlled by depositional environment (e.g. grain size, sorting), by varying burial depth and by varying fluid migration pathways this study aims at predicting cementation pattern in frontier basin with limited existing data. Pacoota and Stairway sandstone samples of 4 wells have been studied using image analysis, SEM, CL, XRD and fluid inclusion thermometry. Preliminary data indicate extensive quartz cementation (10-15% cement) occurring at ca. 90°C in a highly saline NaCl-CaCl2 fluid system. The saline brines are likely to be originating from evaporites of the underlying Bitter Springs Formation. Hydrocarbons were encountered along microfractures and styolites but not found in fluid inclusions. It indicates that oil and gas migration may have occurred subsequent to extensive quartz cementation.