Short-Wave Infrared (SWIR) Spectroscopy as Geothermal Well Logging Tool in the Maibarara Geothermal Field, Batangas

Abstract

Hydrothermal mineral identification and characterization during the drilling of geothermal wells typically involves the use of microscopic, petrographic, fluid inclusion, and X-ray diffraction (XRD) techniques. While useful, these methods can be time-consuming and expensive, considering the high volume of samples retrieved during geothermal drilling. Reflectance spectroscopy is presented as a fast, cost-effective, and reproducible analytical technique for identifying hydrothermal minerals and, consequently, assessing formation competency and estimating reservoir temperature while drilling. Short-Wave Infrared (SWIR) spectra were generated from drill cutting samples of a geothermal well in the Maibarara Geothermal Field, Batangas. Spectral identification was conducted through comparison of generated mineral spectra with published data within the spectral range of 1000-2500nm. Montmorillonite, illite, kaolinite, chlorite, and goethite were identified and verified against results from microscopic analysis. Information derived from SWIR Spectroscopy was successfully used to interpret subsurface hydrothermal alteration and infer the location of the borehole with respect to the geothermal system.