Natural occurrences as analogues for the geological disposal of carbon dioxide

It is now generally accepted that anthropogenic CO2 emissions are contributing to the global rise in atmospheric CO2 concentrations. One possibility for reducing carbon dioxide emissions is to remove it from the flue gases of coal-fired power stations and dispose of it in underground geological reservoirs, possibly offshore in the North Sea. The feasibility of this option has been studied in detail by a consortium of European partners. As part of this study, natural occurrences of carbon dioxide were identified and preliminary information from these was obtained. The best characterised are found in the United Stales where the carbon dioxide reserves are exploited for use in tertiary enhanced oil recovery (EOR) programs in the Texas oilfields. The carbon dioxide reserves occur in geological structures and lithologies which are similar to those present in the North Sea. As such, these fields offer an ideal natural analogue for the disposal of carbon dioxide, since the interactions with groundwaters and reservoir lithologies have occurred on both spatial and temporal scales relevant to geological processes. Those carbon dioxide fields currently being exploited have already been studied to a limited extent by the oil companies involved. However, further study is required to provide information on the potential effects that disposing of large quantities of carbon dioxide might have on groundwaters and reservoir quality. In addition, more detailed information will be obtained on the interactions which occur during EOR using carbon dioxide. This paper presents data on some of the natural carbon dioxide fields, and compares the effects of these natural fluid-rock interactions with those observed in laboratory experiments performed to establish what reactions occur during the geological disposal of carbon dioxide.