Influence of capillary-pressure models on CO2 solubility trapping |
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| Affiliation: | 1. Environmental Engineering and Earth Sciences Department, Clemson University, United States;2. Energy Resource Engineering Department, Stanford University, United States;3. Petroleum Engineering Department, Colorado School of Mines, United States;1. Peking University, Beijing 100871, China;2. The University of Texas at Austin, Austin, TX 78712, USA;1. Key Laboratory of Groundwater Resources and Environment, Ministry of Education, Jilin University, Changchun 130021, China;2. College of Construction Engineering, Jilin University, Changchun 130021, China;3. Liaoning Institute of Mineral Exploration, Shenyang 110032, China;1. Department of Earth and Environmental Sciences, Wright State University, 3640 Col. Glenn Hwy., Dayton, OH 45435, USA;2. Illinois State Geological Survey, Prairie Research Institute, University of Illinois at Urbana-Champaign, 615 East Peabody Drive, Champaign, IL 61820, USA;1. Massachusetts Institute of Technology, 77 Massachusetts Ave, Bldg. 48-319, Cambridge, MA 02139, USA;2. University of Oxford, Parks Road, Oxford OX1 3PJ, UK |
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| Abstract: | The typical shape of a capillary-pressure curve is either convex (e.g., Brooks–Corey model) or S-shaped (e.g., van Genuchten model). It is not universally agreed which model reflects natural rocks better. The difference between the two models lies in the representation of the capillary entry pressure. This difference does not lead to significantly different simulation results for modeling CO2 sequestration in aquifers without considering CO2 dissolution. However, we observe that the van-Genuchten-type capillary-pressure model accelerates CO2 solubility trapping significantly compared with the Brooks–Corey-type model. We also show that the simulation results are very sensitive to the slope of the van-Genuchten-type curve around the entry-pressure region. For the representative examples we study, the differences can be so large as to have complete dissolution of the CO2 plume versus persistence of over 50% of the plume over a 5000-year period.The cause of such sensitivity to the capillary-pressure model is studied. Particularly, we focus on how the entry pressure is represented in each model. We examine the mass-transfer processes under gravity-capillary equilibrium, molecular diffusion, convective mixing, and in the presence of small-scale heterogeneities. Laboratory measurement of capillary-pressure curves and some important implementation issues of capillary-pressure models in numerical simulators are also discussed. Most CO2 sequestration simulations in the literature employ one of the two capillary-pressure models. It is important to recognize that these two representations lead to very different predictions of long-term CO2 sequestration. |
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| Keywords: | Numerical simulation Brooks–Corey Van Genuchten Capillary entry pressure |
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