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Time‐lapse sonic logs reveal patchy CO 2 saturation in‐situ
Author(s) -
Caspari E.,
Müller T. M.,
Gurevich B.
Publication year - 2011
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/2011gl046959
Subject(s) - in situ , saturation (graph theory) , geology , remote sensing , geophysics , meteorology , physics , mathematics , combinatorics
Based on time‐lapse sonic and neutron porosity logs from the Nagaoka CO 2 sequestration experiment, a P‐wave velocity‐saturation relation at reservoir depth is retrieved. It does not coincide with either of the end‐member models of uniform and patchy saturation but falls in between even if realistic error estimates for the host rock properties are considered. Assuming a random distribution of CO 2 patches it is shown that the mechanism of wave‐induced flow can be evoked to explain this velocity‐saturation relation. Characteristic CO 2 patch size estimates range from 1 to 5 mm. Such mesoscopic heterogeneity can be responsible for attenuation and dispersion in the well logging frequency band.