Oral Presentation Sub22 Conference

A search of open file data reveals 34 petroleum wells in Western Australian jurisdiction (excluding Barrow Island) that reported hydrogen (H₂) during drilling, or from subsequent laboratory analysis of gas samples (see Fig. 1, which includes several wells in Commonwealth jurisdiction). Most are in the NW Canning Basin and northern Perth Basin. Concentrations range from a trace up to 95.3% H₂ for a gas sample from DST 9 in Meda 1, NW Canning Basin. In most cases the source of H₂ was either not discussed, or considered an artefact (e.g., drilling mud reacting with steel liner, acid reactions with formation minerals or drill pipe). However, a number of observations, such as correlation with reservoirs, suggest that most occurrences could be natural H₂. Because many rigs were not equipped to detect H₂, occurrences are likely to be significantly under-reported. In addition to petroleum wells, H₂ has been reported from water bores in the southern Perth Basin, shallow drilling north of Perth, and from surface seeps (‘fairy circles’) in the northern Perth Basin and adjacent cratonic areas using hand-held monitoring equipment. Recent natural H₂ research at the Geological Survey of Western Australia has focused on Meda 1, including a fluid inclusion stratigraphy (FIS) study and search for surface H₂ seeps, and comparison of data from hand-held detection equipment (GA5000) with longer term autonomous monitoring of suspected surface seeps in the southern Perth Basin. The FIS study of Meda 1 cuttings and core shows high He and H₂ in fluid inclusions in the metamorphic basement and overlying Devonian reef carbonates below a basement tapping fault intersecting the well. Possible surface H₂ seeps, some associated with circular vegetation anomalies, were identified in the surrounding area. In the southern Perth Basin extended autonomous monitoring detected a weak diurnal H₂ flux in areas where significantly higher H₂ concentrations had been detected by spot readings.