Reactive, Multi-phase Behavior of CO2 in Saline Aquifers beneath the Colorado Plateau

The Colorado Plateau and adjacent Rocky Mountain region contain over 10,000 MW of coal-fired electricity emitting close to 100 million tonnes (Mt) of CO2 each year. This region also contains numerous natural CO2 fields in deep saline aquifers that are analogues for repositories of CO2 separated from flue gases of power plants. Several of these CO2 fields are presently in production, with most CO2 (25 Mt/year) being piped 800 km to enhanced oil recovery projects in west Texas.

The principal research goals are:

• Identification of the geochemical reactions that will be critical for CO2 sequestration in potential reservoirs of the Colorado Plateau;
  
• Quantification of the volume of CO2 that can be stored within typical reservoir geometries, and the factors controlling the volume;
  
• Evaluation of the consequences of permeability changes for well injectivity and CO2 containment as a result of CO2 sequestration;
  
• Investigation of the effects of hydrodynamic factors typical of saline aquifers of the Colorado Plateau on CO2 containment, including leakage to near-surface aquifers and the role of faulting;
  
• Assessment of the ultimate fate of injected CO2 and its distribution between a gas phase, dissolved CO2 and locally fixed CO2 (i.e. as carbonate) for typical representative reservoir and fluid geochemistry;
  
• Identification of environmental risks associated with CO2 leakage from repositories;
  
• Re-evaluation of the published CO2 reserve estimates for known CO2 reservoirs on the Colorado Plateau, the extent of depletion through CO2 production, and an estimate of the total storage possible if CO2 injection were to occur;
  
• Evaluation of the effect of other flue gas constituents, especially those containing sulfur.
  

Core from reservoir and seal rocks of several CO2 fields around the Colorado Plateau will be studied using petrographic and fluid-inclusion techniques to identify the alteration characteristics of late-stage CO2 flooding. This will be combined with a review of the physical and chemical information on the natural state of the fluid regimes, and will provide constraints for numerical simulation of the process of injecting large volumes of CO2 into such reservoirs.

The simulator CHEM-TOUGH2 will be used because of its ability to handle non-isothermal, multiphase reactive transport with full coupling between reactive chemistry and transport. Model scenarios will involve varying lithology and water chemistry, tight and leaky seal rocks, and hydrologic gradients at both reservoir depths and in the overlying unconfined groundwater zone.

Results will be compared with the characteristics of known CO2 reservoirs around the Colorado Plateau, allowing recommendations on their suitability for sequestration of separated CO2 flue gas. A cost-share component will be underwritten by the Energy and Geoscience Institute (University of Utah) Petroleum Exploration Corporate Associates research funds.