Natural CO2 Reservoirs on the Colorado Plateau and Southern Rocky Mountains, USA: A Numerical Model

Abstract

Gas reservoirs within the Colorado Plateau and Southern Rocky Mountains region are natural laboratories for studying the factors that promote long-term storage of CO2. They also provide sites for storing additional CO2 if it can be separated from the flue gases of coal-fired power plants in this part of the United States. These natural reservoirs are developed primarily in sandstones and dolomites. In many fields, stacked reservoirs are present, indicating that the gas has migrated up through the section. There is also evidence of geologically young travertine deposits at the surface and CO2-charged groundwater and springs in the vicinity of known CO2 occurrences. These near-surface geological and hydrological features also provide examples of the environmental effects of leakage of CO2 from reservoirs. The confidence in the predictions of numerical simulations by modeling a natural system of CO2 reservoirs and comparing the modeling results with a number of observations has been discussed in the chapter. A numerical model based on the Farnham Dome CO2 reservoir structure located in east-central Utah has been developed. This reservoir is typical of those found on the Colorado Plateau with stacked CO2 reservoirs contained within a Laramide, dome-like structure. Subsequent modeling of the chemical interactions between reservoir brine, CO2 gas and a simplified mineral assemblage using the simulator CHEMTOUGH2 produces results that are generally consistent with the water chemistry observed in basins of Eastern Utah.