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Ultrasonic velocities of opaline rocks undergoing silica diagenesis
Author(s) -
Chaika Caren,
Dvorkin Jack
Publication year - 1997
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 - 10.1029/97gl01959
Subject(s) - porosity , diagenesis , quartz , geology , mineralogy , san joaquin , ultrasonic sensor , shear (geology) , petrology , geotechnical engineering , paleontology , soil science , physics , acoustics
Experimental results of laboratory measurements at ultrasonic frequencies on dry opaline rocks are documented from the Monterey Formation, a siliceous unit in the San Joaquin basin. In these samples the silica is primarily biogenic opal‐A in origin, but progressively alters to opal‐CT and then quartz with depth. The diagenetic transitions are accompanied by a marked porosity reduction. Compressional and shear wave velocities were measured on core plugs at effective reservoir pressure. Experimental results on samples from the opal‐A/opal‐CT transition and the opal‐CT/quartz transition show very little pressure‐dependence of elasticwave velocities. When their elastic moduli are normalized by those of the solid phase, the moduli‐porosity trend is very close to that of chalk and, in the lower‐porosity domain, of some clean sandstones.