AVA seismic reflectivity analysis in carbon dioxide accumulations: Sensitivity to CO2 phase and saturation |
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| Authors: | Claudia L Ravazzoli Julián L Gómez |
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| Institution: | 1. Department of Kinesiology, Indiana University, Bloomington, IN, USA;2. Department of Kinesiology, Auburn University, Auburn, AL, USA;3. Department of Kinesiology and Health Sciences, Augusta University, Augusta, GA, USA;4. Department of Cell Biology and Physiology, Edward Via College of Osteopathic Medicine—Auburn Campus, Auburn, AL, USA;1. Finnish Museum of Natural History (Geological Museum), University of Helsinki, P.O. Box 44, 00014, Finland;2. Geological Survey of Finland, P.O. Box 1237, 70211 Kuopio, Finland;3. Geological Survey of Finland, P.O. Box 96, 02151 Espoo, Finland;1. School of Natural Sciences, Black Hills State University, Spearfish, SD 57799, USA;2. Department of Nuclear Engineering, University of California-Berkeley, CA 94720, USA;3. Physics Division, Lawrence Berkeley National Laboratory, CA 94720, USA;4. Department of Physics, University of California- Berkeley, CA 94720, USA;5. Department of Physics, South Dakota School of Mines and Technology, Rapid City, SD 57701, USA;6. Department of Physics and Astronomy, University of North Carolina, Chapel Hill, NC 27514, USA;7. Triangle Universities Nuclear Laboratory, Durham, NC 27708, USA;8. Department of Physics, University of South Dakota, Vermillion, SD 57069, USA;9. Department of Physics, Duke University, Durham, NC 27708, USA;10. Department of Chemistry and Applied Biological Sciences, South Dakota School of Mines and Technology, Rapid City, SD 57701, USA;11. Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA;1. Veterinary Research Institute, Department of Chemistry and Toxicology, Hudcova 296/70, 62100 Brno, Czech Republic;2. Institute of Scientific Instruments of the CAS, Královopolská 147, 612 64 Brno, Czech Republic;3. Veterinary Research Institute, Department of Pharmacology and Immunotherapy, Hudcova 296/70, 62100 Brno, Czech Republic;4. Institute for Environmental Studies, Faculty of Science, Charles University, Benátská 2, 12801 Prague 2, Czech Republic;1. School of Resources and Geosciences, China University of Mining & Technology, Xuzhou 221116, China;2. School of Safety Science and Engineering, Henan Polytechnic University, Jiaozuo 454000, China |
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| Abstract: | Seismic monitoring of sequestered carbon dioxide (CO2) in underground deposits is a matter of growing importance. The subsurface monitoring of this greenhouse gas is possible due to the marked contrast between the physical properties of natural reservoir fluids and those of carbon dioxide after the injection. This technique makes necessary the investigation of appropriate seismic indicators to link seismic attributes to petrophysical properties, composition and state of the rock as well as pore-fluid type and in-situ physical conditions. With this motivation in mind, we use a Biot–Gassmann formulation to model the theoretical P-wave amplitude reflection coefficients vs. angle of incidence in the seismic range when a planar P-wave strikes the interface between a caprock and a porous sandstone which has its pore space saturated by a mixture of CO2 with brine or oil at different states (supercritical, liquid and gas). The effects of dissolution of CO2 in oil and the existence of a saturation threshold, above which a free CO2 phase develops, are included in the computations. Attention is particularly focused on the sensitivity of the classic best-fit amplitude variations with angle coefficients, to different degrees of CO2 saturation. We conclude from this analysis that the changes in seismic AVA attributes between 30 and 40 degrees can be useful to infer bounds on the CO2 saturation degree, to detect the presence of immiscible CO2 phase and, in some cases, to infer the physical state of the accumulations. |
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