Porosity of the Bunter sandstone in the Southern North Sea basin based on selected borehole neutron logs

This report presents the results of a porosity study of the Bunter Sandstone (BNS) in the Southern North Sea Basin based primarily on the analysis of neutron logs. The Bunter Sandstone is a Triassic fluvial sandstone (Cameron et al 1992). It contains layers or lenses of varying thickness of shale and/or siltstone. The Prizm module from the GeoGraphix interpretation software suite (v. 2004.1), was used to display the borehole logs. Neutron logs were plotted alongside gamma, sonic and density logs. The gamma log was used to identify shales in the Bunter Sandstone to assist in averaging the neutron porosity over the sandy intervals only. Most porosities in the BNS had values in the interval of 10-22% but some extremes as low as 1% and as high as 27% were identified. Gas effect and salt cementation were also noted in some boreholes. Maps of the neutron and core porosities, depth to, and thickness of the sandstone, were produced in GeoAtlas, also from the GeoGraphix Interpretation suite 2004.1. In general the lowest porosities not linked with salt cementation coincided with the Sole Pit Trough, a major depocentre for the BNS.