Close-Range Hyperspectral Imaging for Mapping Outcrop Composition

Kurz, Tobias H.¹; Buckley, Simon J.¹; Howell, John A.¹
(1)Geosciences, Uni CIPR, Bergen, Norway.

Mineralogy is a principal control on the petrophysical properties that control fluid flow in reservoirs. Outcrops provide the opportunity to study the textural distribution of mineralogy and petrography in systems that are analogous to reservoirs. Until now mapping and quantification of mineralogy in outcrops has only been possible using the labour-intensive collection of spot samples. Close-range hyperspectral imaging offers a new, efficient and high resolution solution for analysing the composition and distribution of outcrop mineralogy. This method measures the interaction of electromagnetic energy (from the sun) on rocks and minerals, with each unique material having identifying features at different wavelengths. In contrast to conventional digital cameras that measure three bands in the visible spectrum, the hyperspectral sensor records 240 bands in the near-infrared, giving the potential for classifying many common mineral types. Hyperspectral imaging has been applied in geological applications from airborne and spaceborne platforms for many years, but the equipment needed for field usage is only now becoming suitable for outcrop work.

Here, we use a portable hyperspectral sensor to acquire images of carbonate and siliciclastic outcrop surfaces. The sensor offers a high resolution, with pixel sizes of 3 cm at 50 m distance, allowing small-scale variations in outcrop content to be distinguished. Imagery is calibrated and processed to result in thematic maps of the outcrop composition, with mineral content given per image pixel. Results are ground-truthed and integrated with existing geological knowledge to support interpretation. Additionally, we combine the classifications with photorealistic models derived from terrestrial laser scanning (lidar) and conventional digital photos. This fusion allows the 3D outcrop geometry to be supplemented with the material composition from the hyperspectral output. Visualisation of the thematic maps as different layers on the 3D model greatly improves the interpretation and validation of results, as well as allowing spatial analysis (such as material areas and extents). We show case studies highlighting the potential accuracy of the method, with applications such as plotting the spread of carbonate nodules in a clastic system, and mapping multiphase dolomitisation. Hyperspectral imaging is expected to become a valuable tool in field-based geoscience studies as technology improves and more applications are found.

AAPG Search and Discovery Article #90135©2011 AAPG International Conference and Exhibition, Milan, Italy, 23-26 October 2011.