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Velocity anisotropy and attenuation in shale in under and over pressured conditions

Velocity anisotropy and attenuation in shale in under and over pressured conditions
Velocity anisotropy and attenuation in shale in under and over pressured conditions
Ultrasonic compressional- and shear-wave attenuation measurements have been made on 40, centimetre-sized samples of water- and oil-saturated oolitic limestones at 50 MPa effective hydrostatic pressure (confining pressure minus pore-fluid pressure) at frequencies of about 0.85 MHz and 0.7 MHz respectively, using the pulse-echo method. The mineralogy, porosity, permeability and the distribution of the pore types of each sample were determined using a combination of optical and scanning electron microscopy, a helium porosimeter and a nitrogen permeameter. The limestones contain a complex porosity system consisting of interparticle macropores (dimensions up to 300 microns) and micropores (dimensions 5–10 microns) within the ooids, the calcite cement and the mud matrix. Ultrasonic attenuation reaches a maximum value in those limestones in which the dual porosity system is most fully developed, indicating that the squirt-flow mechanism, which has previously been shown to occur in shaley sandstones, also operates in the limestones. It is argued that the larger-scale dual porosity systems present in limestones in situ could similarly cause seismic attenuation at the frequencies of field seismic surveys through the operation of the squirt-flow mechanism.
0016-8025
359-392
Domnesteanu, P.R.
7317c046-d7e4-4878-aeab-2b9419aa4bcb
McCann, C.
e3bec51c-7d04-47f4-a7bd-1865963e8599
Sothcott, J.
71ab4088-7b13-46d6-9e28-67538a02d595
Domnesteanu, P.R.
7317c046-d7e4-4878-aeab-2b9419aa4bcb
McCann, C.
e3bec51c-7d04-47f4-a7bd-1865963e8599
Sothcott, J.
71ab4088-7b13-46d6-9e28-67538a02d595

Domnesteanu, P.R., McCann, C. and Sothcott, J. (1999) Velocity anisotropy and attenuation in shale in under and over pressured conditions. Geophysical Prospecting, 47 (3), 359-392. (doi:10.1046/j.1365-2478.1999.00136.x).

Record type: Article

Abstract

Ultrasonic compressional- and shear-wave attenuation measurements have been made on 40, centimetre-sized samples of water- and oil-saturated oolitic limestones at 50 MPa effective hydrostatic pressure (confining pressure minus pore-fluid pressure) at frequencies of about 0.85 MHz and 0.7 MHz respectively, using the pulse-echo method. The mineralogy, porosity, permeability and the distribution of the pore types of each sample were determined using a combination of optical and scanning electron microscopy, a helium porosimeter and a nitrogen permeameter. The limestones contain a complex porosity system consisting of interparticle macropores (dimensions up to 300 microns) and micropores (dimensions 5–10 microns) within the ooids, the calcite cement and the mud matrix. Ultrasonic attenuation reaches a maximum value in those limestones in which the dual porosity system is most fully developed, indicating that the squirt-flow mechanism, which has previously been shown to occur in shaley sandstones, also operates in the limestones. It is argued that the larger-scale dual porosity systems present in limestones in situ could similarly cause seismic attenuation at the frequencies of field seismic surveys through the operation of the squirt-flow mechanism.

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Published date: 1999

Identifiers

Local EPrints ID: 58409
URI: http://eprints.soton.ac.uk/id/eprint/58409
ISSN: 0016-8025
PURE UUID: 15e5b557-da20-473e-a65f-60f617e277c0

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Date deposited: 13 Aug 2008
Last modified: 13 Mar 2019 20:32

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Contributors

Author: P.R. Domnesteanu
Author: C. McCann
Author: J. Sothcott

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