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Basin Screening for Seal Rock Quality, New Zealand Region

Abstract

This study provides the first New Zealand-wide assessment of the hydrocarbon seal rock potential of twenty sedimentary basins and is designed to help evaluate pre-drill seal risk assessment. Seal rock quality has been assessed using key petroleum wells and seismic lines. Deep-sea drilling research holes provide glimpses of the stratigraphy in some of the more distal basins. The Taranaki Basin is currently New Zealand's only producing basin — all others are frontier basins and many have no or few exploration wells and rather sparse seismic coverage. We have produced maps of inferred seal rock quality (extrapolated from selected wells) and rock property data such as XRD-derived mineralogy, mercury injection threshold pressure data and openfile hydrocarbon column heights, as well as drillhole montages, example seismic line panels, and photographs of outcrop analogues. Our results are compiled into an ArcGIS project and Geodatabase, allowing multiple layers of data, such as paleogeography and licence blocks, to be interrogated. We infer good seal quality to be widespread in Cretaceous to Neogene rocks in most basins. Most sample data are from the Taranaki Basin and the relationship of membrane entry pressures to key parameters such as maximum depth of burial and mineralogy are complex, with few trends apparent, though depositional setting and hydrothermal alteration appear to be key parameters in some cases. There appears to be a straightforward relationship between entry pressures and stratigraphic age in the East Coast Basin, based on a limited sample set. For the Canterbury Basin existing data indicates membrane seal quality is likely to be a key risk.