NATURAL OCCURRENCES AS ANALOGS FOR THE GEOLOGICAL DISPOSAL OF CARBON-DIOXIDE

It is now generally accepted that anthropogenic CO2 emissions are cont ributing to the global rise in atmospheric CO2 concentrations. One pos sibility for reducing carbon dioxide emissions is to remove it from th e flue gases of coal-fired power stations and dispose of it in undergr ound geological reservoirs, possibly offshore in the North Sea. The fe asibility of this option has been studied in detail by a consortium of European partners. As part of this study, natural occurrences of carb on 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 dioxid e reserves occur in geological structures and lithologies which are si milar to those present in the North Sea. As such, these fields offer a n ideal natural analogue for the disposal of carbon dioxide, since the interactions with groundwaters and reservoir lithologies have occurre d on both spatial and temporal scales relevant to geological processes . Those carbon dioxide fields currently being exploited have already b een studied to a limited extent by the oil companies involved. However , further study is required to provide information on the potential ef fects that disposing of large quantities of carbon dioxide might have on groundwaters and reservoir quality. In addition, more detailed info rmation will be obtained on the interactions which occur during EOR us ing carbon dioxide. This paper presents data on some of the natural ca rbon dioxide fields, and compares the effects of these natural fluid-r ock interactions with those observed in laboratory experiments perform ed to establish what reactions occur during the geological disposal of carbon dioxide.