Using semi-analytic solutions to approximate the area of potential impact for carbon dioxide injection

Abstract

This study examines using the threshold critical pressure increase and the extent of the carbon dioxide (CO2) plume to delineate the area of potential impact (AoPI) for geologic CO2 storage projects. The combined area covering both the CO2 plume and the region where the pressure is greater than the threshold critical pressure increase is defined as the AoPI. The threshold critical pressure increase is defined as the pressure needed to lift formation brine up the length of an unplugged well to an underground source of drinking water. Using parameter values based on existing and planned CO2 injection sites, in combination with a simple conceptual model, semi-analytic solutions are used to find the radial pressure response and spread of the CO2 plume. A set of sensitivity analyses investigates the parameters that have the strongest impact on the size of the AoPI. The sensitivity analyses show that the injection formation salinity and the vertical distance between injection formation and drinking water source have a strong impact on the threshold critical pressure increase. In addition, the formation permeability has a strong impact on the radius at which the threshold critical pressure is reached, as does the amount of diffuse leakage into neighboring formations. The radius of the CO2 plume is mainly impacted by the available storage space (thickness and porosity), the formation permeability and the injection rate. The radius of the AoPI is determined by the threshold critical pressure increase in about half of 1458 sensitivity cases, the rest are determined by the maximum extent of the free phase CO2 plume. When brine leakage into and through the cap rock is considered, the size of the AoPI is determined by the threshold critical pressure increase for only about 29% of the cases.