Evaluation of Spectral Proxies in Unconventional Hydrocarbon Plays: A Case Study From the Southern Georgina Basin, Australia

Abstract

The Georgina Basin is a Neoproterozoic–Paleozoic basin in northern Australia, covering approximately 325,000km² and straddling the Queensland and Northern Territory border. A thick Cambro-Ordovician succession of marine carbonates in the southern part of the basin hosts several prospective source units that are associated with shales. The main unconventional target is the middle Cambrian Arthur Creek Formation (ACF). In this study, we examine the utility of HyLoggerTM data for the characterisation of unconventional hydrocarbon source rocks and reservoirs in the southern Georgina Basin. We also evaluate whether spectral proxies can be developed for key data types (e.g. total organic carbon (TOC) and total gamma response) by integrating the HyLoggerTM data with existing well log, mineralogical and geochemical data. The automated HyLoggerTM technologies use reflectance spectroscopy to map relative changes in key mineral species in drill core and cuttings. Three spectrometers in the HyLoggerTM instrument measure spectral responses across the visible-near-infrared (VNIR), short-wave infrared (SWIR), and thermal infrared (TIR) wavelengths for oxide, hydroxide and carbonate, and anhydrous silicates respectively. Previous use of HyLoggerTM data has largely been restricted to mapping mineral alteration assemblages for mineral exploration; however, the data have excellent potential for petroleum applications. Initial results are promising: there is an apparent relationship between gamma intensity, core SWIR albedo (mean SWIR reflectance), aspectral SWIR response and quartz content in the lower ACF. Peaks in gamma intensity broadly align with troughs in SWIR albedo, suggesting that the reduced albedo is a result of increased TOC content. This has been confirmed by Rock-Eval 6 measurements of organic content in the lower ACF, thus developing a HyLoggerTM TOC spectral proxy appears possible. The HyLoggerTM data also illustrate distinct mineralogical variations associated with sedimentary cyclicity in the middle ACF in the Toko Syncline. Peaks in gamma intensity appear driven by an increase in anoxic, quartz-rich sediments and a decrease in carbonate contribution, and are also associated with decreased core SWIR albedo and spectral contrast. Thus HyLoggerTM data support log-derived paleo-environmental interpretations, and illustrate the excellent potential of HyLoggerTM mineralogical and spectral data for characterising unconventional hydrocarbon reservoirs.

AAPG Datapages/Search and Discovery Article #90217 © 2015 International Conference & Exhibition, Melbourne, Australia, September 13-16, 2015