Modeling CO₂ Sequestration in Underground Reservoirs

Carbon Dioxide released during fossil fuel consumption is a major source of greenhouse gases. In order to manage the future climatic changes, the CO₂ must be removed from the flue gas and be permanently stored. The Kyoto protocol has made reducing CO₂ emission in order to control the overall levels of carbon dioxide in the atmosphere an international priority. Several methods for CO₂ sequestration in the ocean floor and in geological formations have been proposed. The sequestration in geological formations including depleted oil and gas reservoirs, coal seams, and deep brine-fields have been studied. Among these, pumping CO₂ into reservoirs has been exploited commercially in the US for enhanced oil recovery. A schematic of the CO₂ sequestration for enhanced oil recovery is shown in Figure 1.

Figure 1. A schematic diagram of CO₂ sequestration and enhanced oil recovery

Recent studies of the use of CO₂ for oil recovery were reported by Hattenbach et al. (1999) and Holloway et al (1996). Lawrence Berkeley laboratory developed a general purpose reservoir simulator,TOUGH2 (1999), for solving subsurface flow using a finite volume method. Slattery (1972) and Kaviany (1995) described models for flow and heat transfer in porous media using volume-averaging techniques.

Objectives

The general objective of this project is to develop a computational tool for modeling the CO₂ sequestration processes in underground reservoirs. The specific objectives are:

1. To develop a realistic model for two-phase gas-liquid flows in underground reservoirs.
2. To develop a physical model for predicting the relative permeability in practical application.
3. To analyze process of CO₂ sequestration in depleted oil reservoirs.
4. To provide a detailed understanding of the enhanced oil recovery through CO₂ injection.
5. To predict the CO₂ sequestration and oil recovery enhancement for several realistic reservoir scenarios.

Preliminary Study

Preliminary results for gas flow in a fractured reservoir is obtained. It is assumed that the fractured regions in the reservoir have lower permeability. Sample results are shown in Figure 2.

Figure 2. Sample velocity field in a fractured reservoir.

Plan of Study

For the preliminary results shown in Figure 2 the FLUENT Code was used in the analysis. The treatment of porous media is rather elementary in the FLUENT Code. In addition, the code can not handle multiphase flows in porous media. We plan to make use of the TOUGH2 code for in the present study. This code which was developed at Lawrence Berkeley Laboratory is a multi-purpose reservoir simulator and can handle multiphase flows. The developed formulation will be incorporated in the TOUGH2 code. The modified code will then be used for studying CO₂ sequestration in underground reservoirs and oil recovery enhancement.

References

Hattenbach, R.P., Wilson, M., Brown, K. (1999), Capture Of Carbon Dioxide From Coal Combustion And Its Utilisation For Enhanced Oil Recovery, in Greenhouse Gas Control Technologies, Elsevier Science, New York.

Holloway, S., Heederik, J.P., van der Meer, L.G.H., Czernichowski-Lauriol, I., Harrison, R., Lindeberg, E., Summerfield, I.R., Rochelle, C., Schwarzkopf, T., Kaarstad, O., Berger, B. (1996), The Underground Disposal Of Carbon Dioxide, British Geological Survey, Keyworth, Nottingham, U.K.

Kaviany, M. (1995) Principles of Heat Transfer in Porous Media, Spring-Verlag, New York.

Lawrence Berkeley Lab., (1999) TOUGH2, Berkeley, CA.

Slattery, J.C. (1972) Momentum, Energy, and Mass Transfer in Continua, McGraw-Hill, New York.

Wong, S., Foy, C., Gunter, W. D., Jack, T. (1999), Injection Of CO₂ For Enhanced Energy Recovery: Coalbed Methane Versus Oil Recovery. in Greenhouse Gas Control Technologies, Elsevier Science, New York.

Funded by US Department of Energy, National Energy Technology Laboratory (NETL)