Introduction

The problems and processes of sequestering CO₂ in geologic formations must be analyzed from several viewpoints. There are several well constrained aspects to the process of CO₂ sequestration, such as the number of point sources, the mass of CO₂ emitted by the point sources, and the pipelines that will have to be built to move the CO₂ from the point source to the sequestration site. However, the typical approach to CO₂ sequestration assessments involves estimating the sequestration capacity of a geologic formation, i.e. the volume or mass of CO₂ that can be stored in a geologic formation, such as saline reservoirs, coal beds, or petroleum reservoirs (Hendriks and Blok, 1993; van der Meer, 1995, 1996; Bachu et al., 1994; Law and Bachu, 1996; Ennis-King and Paterson, 2001). One recent study took a different view of CO₂ sequestration assessments; Bachu (2001) proposed considering the subsurface space of geologic formations in terms of CO₂ phase relations, categorizing regions within the stratigraphic units of Alberta where CO₂ would be gas, liquid, or a supercritical fluid, based on measured temperatures and pressures.

The approach outlined in this paper differs from previous work in that here we calculate the sequestration volumes, i.e. the amount of geologic formation needed to sequester a given mass of CO₂, by converting the mass of CO₂ emitted by point sources into volumes of geologic formations needed to sequester CO₂ based on realistic geologic conditions. The term of specific sequestration volume (SSV) is defined herein as the factors necessary to convert the mass of CO₂ emissions to geologic storage volume. If CO₂ emissions are recalculated as units of specific volume, i.e. volume per unit mass, then the volumes of geologic reservoirs necessary to store CO₂ emissions from large point sources can be estimated. The SSV's, as defined in this study, can be reported in units of cubic meters, cubic feet, and petroleum barrels to establish a framework that fits reference volumes common to ground-water hydrogeology and the oil and gas industry. In this paper, we convert the mass of CO₂ emitted annually by a single 1100 megawatt power plant into volumes of geological formations needed for sequestration over annual and decadal intervals.