Impact of CO2 Impurities on Storage Performance and Assurance - Report on Tasks 3 and 4 (Geochemistry) Prepared for: CO2 Capture Project (Phase III)

This document presents the results of Tasks 3 and 4 out of 5 tasks, focusing on the geochemical impacts of impurities in the CO2 stream. Tasks 1 and 2 were dedicated to examining the effects on flow behavior. The impurities primarily consist of N2, O2, and Ar, with several minor reactive species potentially added, including CO, H2, SOx, and other trace gases. The research methodology involved laboratory autoclave experiments combined with geochemical numerical modeling.

The autoclave utilized in the experiments is a 250-ml reactor capable of withstanding temperatures up to 150°C and pressures up to 400 bars, simulating conditions observed in reservoirs at depths of up to 12,000 ft. Pressure and temperature were automatically controlled by a computer, and the system allowed for water sampling during the experiments. Typically, 10 to 15 samples of the solution were collected during each experiment, which lasted 5 to 10 days.

Rock samples were exposed to either a supercritical mixture of CO2 and O2 (generally 3.5% molar) or pure supercritical CO2, filling approximately half of the reactor cell. The other half of the cell contained a single core fragment or several large fragments (~8g total) submerged in approximately 140 ml of synthetic brine (~1.88 mol NaCl, corresponding to a TDS of 100,000-110,000 mg/L).

The study analyzed three types of clastic rock samples:

1. A "dirty sandstone" of Miocene age obtained from a deep well in the shallow offshore region off the Texas coast.
2. A relatively clean sandstone from the Cretaceous-age Cardium Formation in Alberta.
3. A chlorite-rich sandstone from the Tuscaloosa Formation in Mississippi, sourced from the Cranfield site, which has been extensively studied by BEG for several years.