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Raman Spectroscopy for Detection of CO2, SOx and NOx in Precipice Sandstone


Raman spectroscopy is an analytical technique for characterization of the chemistry of substances using lasers and optical detectors. WellDog’s proprietary Reservoir Raman System (RRS) is the world’s only self-contained Raman spectrometer system capable of deployment downhole for the in situ geochemical characterization of reservoir fluids. The RRS has been used commercially to characterize dissolved gases such as methane and carbon dioxide in oil and gas formations such as coal seams and shales. In this project, we investigate the adaptation of this tool to detecting reaction products resulting from the injection of a green-house gas stream captured from a coal-fired power station into a saline aquifer. This research, funded by Australian National Low-Emissions Coal Research & Development (ANLEC R&D) and in collaboration with the University of Queensland, supports the CTSCO Surat CO2 Storage Demonstration Project, in which a locally-sourced post-combustion capture stream will be injected into the Precipice Sandstone formation.

Thirteen reaction products of a CO2/SOx/NOx mixture combined with both Precipice brine and sandstone were identified in batch-reactor studies with results including sulfate, nitrate and carbonate as major products. Calibrations of the Raman response of the RRS for each of the products were determined, along with instrument limits of detection. Additionally, the ability of the tool to differentiate and quantify the species in a mixture was investigated. Finally, a reservoir simulation apparatus was designed and implemented to simulate the reaction of Precipice brine and a simulated greenhouse gas stream with a sample of Precipice sandstone under reservoir temperature and pressure conditions while monitoring in real-time the geochemical composition of fluids with the RRS.

The RRS was successful in differentiating the major classes of reaction products. For example, SOx-derived species are easily distinguished from NOx and CO2 products. Limits of detection for carbonate, sulfate and nitrate were shown to be sufficient for detection of the expected concentrations of those species from batch-reactor studies. In the reservoir simulation experiments, the concentration of dissolved CO2 was easily quantified. This project clearly demonstrates the immediate applicability of WellDog’s RRS platform, and provides a clear path for continued advancement of the unique, in-situ geochemical sensing required for successful and safe CCS projects.