Hyperspectral Midwave and Longwave Infrared Spectroscopy as an XRD Proxy for Fracture Stimulation in Unconventional Hydrocarbon Exploitation

Abstract

Characterizing mineralogy is important in determining “sweet spots” in drill cores for fracture stimulation in the exploitation of unconventional hydrocarbon resources. The XRD tomography scanning system OreExplore (Swick Mining) and XRF core loggers such as TruScan (Boart Longyear) and Minalyse are examples of systems that attempt to map mineralogy in a quantitative manner. XRF and XRD solutions are expensive and more cumbersome than the new generation of hyperspectral thermal cameras now available. Lightweight tripod mounted devices image core in the midwave infrared spectrum from 3 to 5 microns [MWIR] and longwave region, from 7.7 to 12 microns [LWIR]. To determine their effectiveness for mapping mineralogy, we considered the Holdfast-1 well drilled in the southern Cooper Basin of South Australia. The Cooper Basin is Australia’s leading onshore hydrocarbon-producing province and hosts a range of unconventional oil and gas plays. The well has been logged by the Hylogger-3 system in the range 6 to 14.5 microns at 25nm spectral resolution. 101 downhole XRD measurements were used to express the thermal spectra at the XRD sample locations as the product of a spectral library and matrix of spectral abundances using a novel non-negative matrix factorization algorithm. This linear mixing model may be used to infer calibrated mineral abundances for the whole core log at 0.8mm spatial resolution and hence flag suitable fracture stimulation sweet spots within appropriate stratigraphy. To simulate corelogs for commercially available MWIR and LWIR cameras, we resampled JPL library spectra for the five XRD minerals present (Quartz, Kaolinite, Siderite, Muscovite and Illite) to the camera bandpasses. If XRD calibration samples had been available, we would have used their thermal spectra instead of the JPL reference spectra. The laboratory spectra were then mixed together using the XRD abundances to produce simulated corelogs which were then inverted using the same procedure as applied to the Hylogger-3 data. Good reconstruction of the MWIR and LWIR spectra and abundances was achieved for all minerals with the exception of Illite, which was confused with Kaolinite by the LWIR systems. This study indicates that lightweight and relatively inexpensive thermal cameras may be used to map mineralogy in drill cores, allowing zones suitable for fracture stimulation to be identified in unconventional hydrocarbon plays.

AAPG Datapages/Search and Discovery Article #90332 © 2018 AAPG International Conference and Exhibition, Cape Town, South Africa, November 4-11, 2018