Subsurface monitoring of anthropogenic CO2 injected in sedimentary basins: Results from the Frio-I brine test, Texas, USA

摘要

To investigate the potential for the long-term storage of CO2 in deep saline aquifers, 1600 t of CO2 were injected at 1500 m depth into a 24-m-thick "C" sandstone of the Frio Formation near Houston, Texas.Fluid samples obtained before CO2 injection from the injection well and an observation well 30 m updip showed a Na-Ca-Cl type brine with ～93,000mg/L TDS at saturation with CH4, but only 0.3% CO2. Following CO2 breakthrough, samples showed sharp drops in pH, pronounced increases in alkalinity and Fe, and significant shifts in the isotopic compositions of H2O, and DIC. These parameters, together with perfluorocarbon tracer gases were used for monitoring migration of injected CO2 into the overlying Frio "B", a 4-m-thick sandstone,separated from the "C" by ～15 m of shale and siltstone beds. Results from "B" 6 mo after injection show significant CO2 (2.9% vs. 0.3% CO2) migration into the "B" sandstone. Results of samples collected 15 mo after injection, however, show no indications of additional CO2 in the "B" sandstone.