Injection of C02 into an Unconfined Aquifer Located Beneath the Colorado Plateau, Central Utah

Abstract

Some geothermal fields, for example Ohaaki and Ngawha in New Zealand, contain significant amounts of C02. In a post Kyoto protocol world it may be financially advantageous to capture and dispose of the C02 in a permanent manner rather than releasing it to the atmosphere. C02 sequestration in geological formations is an active area of investigation at present and techniques developed in non-geothermal situations may be applicable in geothermal situations. While this paper is not concerned with disposal of C02 in a geothermal setting the methods are applicable in such a case. We have developed a regional scale, two-dimensional numerical model of a non-dome-shaped such structure on the Colorado Plateau that includes the major physical and chemical processes induced by injection of C02. Ignoring water-rock reactions, C02 returns to the surface after about 250 years and about 40% remains sequestered after 1000 years. However, coupling water-rock reactions to transport calculations shows significantly more C02 is sequestered, with dawsonite and calcite being the most important sequestration minerals.