Detection of small amounts of N2 in CO2-rich high-density fluid inclusions from mantle xenoliths

Fluid inclusions (FIs) (n = 34) in spinel lherzolite xenoliths derived from the subcontinental lithospheric mantle from Jeju Island (S. Korea), the Rio Grande Rift (New-Mexico, USA) and Mt. Quincan (Australia) were analysed using confocal Raman spectroscopy. Despite the significant geographical distances, the studied rocks and their FIs show similar petrographic features. We show evidence for the presence of small amounts of nitrogen in extreme high density (≥1 g/cm3 ) FIs from the deep lithospheric mantle using Raman spectroscopy with a spectral resolution between 0.6 and 0.7 cm-1 . The only nitrogen-bearing species found in the inclusions was N2. The N2 Raman signal appeared as two adjacent, partially overlapping bands. The band at higher Raman shift is identical with the nitrogen-in-air (N2 air) band. The band at lower Raman shift is therefore nitrogen within the FIs (N2 fluid). The relative amounts of CO2 and N2 within the FIs were calculated using the integrated band areas. In the studied ultramafic xenoliths, N2 concentrations varied between 0.2 and 1.8 mol%, with one exceptionally high concentration of 3.1 mol%. We believe that microthermometric measurements and/or Raman spectroscopy with an inferior spectral resolution may leave N2 undetected in CO2- rich upper mantle FIs. Based on our observations, we propose that N2 may be a minor but common component in subcontinental lithospheric upper-mantle fluids

The relevance of dawsonite precipitation in CO2 sequestration in the Mihályi-Répcelak area, NW Hungary

A natural CO2 reservoir system with sandstone lithology has been studied in NW Hungary due to similarities with a large saline reservoir formation widespread in the whole of the Pannonian Basin (Central Europe), suggested to be one of the best candidates for industrial CO2 storage. A range of analytical techniques has been used on core samples from the CO2-containing sandstone layers representing a wide pressure (90-155 bar), temperature (79-95°C) and pore fluid composition range (TDS between 18 000 – 50 700 mg/l) to identify the mineralogy and textural characteristics of the natural reservoir. The only clear CO2-related feature in the studied lithology was the occurrence of dawsonite (NaAlCO3(OH)2) always in close textural relation with albite. This is in clear agreement with our geochemical modelling results, which also underline the presence of albite as a precondition for the crystallization of dawsonite at the given p-T-X conditions. Our results suggest that, at least in the Pannonian Basin, dawsonite may be an important mineral to safely sequester industrial CO2 in the subsurface

The relevance of dawsonite precipitation in CO2 sequestration in the Mihályi-Répcelak area, NW Hungary

A natural CO2 reservoir system with sandstone lithology has been studied in NW Hungary due to similarities with a large saline reservoir formation widespread in the whole of the Pannonian Basin (Central Europe), suggested to be one of the best candidates for industrial CO2 storage. A range of analytical techniques has been used on core samples from the CO2-containing sandstone layers representing a wide pressure (90-155 bar), temperature (79-95°C) and pore fluid composition range (TDS between 18 000 – 50 700 mg/l) to identify the mineralogy and textural characteristics of the natural reservoir. The only clear CO2-related feature in the studied lithology was the occurrence of dawsonite (NaAlCO3(OH)2) always in close textural relation with albite. This is in clear agreement with our geochemical modelling results, which also underline the presence of albite as a precondition for the crystallization of dawsonite at the given p-T-X conditions. Our results suggest that, at least in the Pannonian Basin, dawsonite may be an important mineral to safely sequester industrial CO2 in the subsurface