A B S T R A C TClay-and lithic-rich sandstones are difficult to characterize through uncored well sections in terms of their grain size, porosity, and mineralogy, all of which are required for assessing reservoir quality and production performance. This paper presents results from a study through one such interval and shows how a combination of different techniques can be used to better understand rock properties of complex reservoirs, thereby helping to reduce reservoir uncertainty.In this study, mean data from laser grain-size analysis are comparable to point-counted grain size, and both are considered as viable analytical methods. Automated quantitative evaluation of minerals by scanning electron microscopy (QEMSCAN ® ) provides a further useful and consistent grain-size measurement that can be applied to both core and cuttings samples. The QEMSCAN has also proved to be a valuable technique in the mineralogical analysis of sandstones that are lithic, clay-and feldsparrich, eliminating the subjective nature that is inherent with optical analysis.Results from the studied interval show that porosity measured by conventional core analysis (CA) and mercury injection capillary pressure (MICP) analysis are generally comparable with log-derived total porosity. Porosity measured from point-counting and QEMSCAN techniques is significantly lower than total porosity, with the QEMSCAN porosity locally equivalent to logderived effective porosity. Both point-count and QEMSCAN porosities show better correlations with permeability (r 2 = 0.90 and 0.94, respectively) than total porosity values (r 2 = 0.81 and 0.60 CA and MICP, respectively), suggesting that they might provide a measure of effective porosity in high-quality reservoir rocks.Karen Higgs is a reservoir sedimentologist working under contract for GNS Science, having previously worked as sedimentologist and sedimentology team leader at GNS. She has worked as lead geologist on a wide range of international projects and has 20 years of experience in clastic reservoir characterization. Her main research interests are clastic diagenesis, reservoir quality assessment, and prediction. M. J. Arnot ∼ GNS Science, 1 Fairway Drive, Avalon, P.O. Box 30 368, Lower Hutt, New Zealand; m.arnot@gns.cri.nz Malcolm Arnot is a petroleum geologist working for GNS Science. He specializes in sedimentology and has worked on a range of outcrop studies over the past 20 years. His main research interests are in the application of outcrop and subsurface analog data to exploration and reservoir characterization studies, with his current focus on deep-water clastic systems.Scott Brindle is a geoscientist working for Robertson UK, Ltd. He specializes in automated mineralogy in the oil and gas industry. He has contributed to the development of the technology for reservoir characterization in a wide range of reservoir types and locations. His main research interests are reservoir characterization in clastic, carbonate, and unconventional resources using automated mineralogy techniques.

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