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Modelling ultrasonic laboratory measurements of the saturation dependence of elastic modulus: New insights and implications for wave propagation mechanisms

Modelling ultrasonic laboratory measurements of the saturation dependence of elastic modulus: New insights and implications for wave propagation mechanisms
Modelling ultrasonic laboratory measurements of the saturation dependence of elastic modulus: New insights and implications for wave propagation mechanisms
Seismic time-lapse techniques are a valuable tool used to estimate the mobilization and distribution of stored CO2 in depleted reservoirs. The success of these techniques depends on knowing the seismic properties of partially saturated rocks with accuracy. It is commonplace to use controlled laboratory-scale experiments to determine how the fluid content impacts on their properties. In this work, we measure the ultrasonic P- and S-wave velocities of a set of synthetic sandstones of about 30% porosity. Using an accurate method, we span the entire saturation range of an air-water system. We show that the rocks’ elastic behaviour is consistent with patchy saturation and squirt flow models but observe a discontinuity at around 90% gas saturation which can be interpreted in two very different ways. In one interpretation, the responsible mechanism is frequency-dependent squirt-flow that occurs in narrow pores that are preferentially saturated. An equally plausible mechanism is the change of the mobile fluid in the pores once they are wetted. Extrapolated to seismic frequencies, our results imply that the seismic properties of rocks may be affected by the wetting effect with an impact on the interpretation of field data but would potentially be unaffected by the squirt flow effect. This provides strong motivation to conduct laboratory-scale experiments with partially saturated samples at lower frequency or, ideally, a range of frequencies in the seismo-acoustic range.
1750-5836
148-159
Amalokwu, Kelvin
a88bc1e5-5577-49a6-a503-fcd9ea12d8fe
Papageorgiou, Giorgos
8181cca9-12a0-4fa6-93a3-d5711132bc87
Chapman, Mark
087982f4-b96c-45d3-a773-3b54aad359dd
Best, Angus I.
cad03726-10f8-4f90-a3ba-5031665234c9
Amalokwu, Kelvin
a88bc1e5-5577-49a6-a503-fcd9ea12d8fe
Papageorgiou, Giorgos
8181cca9-12a0-4fa6-93a3-d5711132bc87
Chapman, Mark
087982f4-b96c-45d3-a773-3b54aad359dd
Best, Angus I.
cad03726-10f8-4f90-a3ba-5031665234c9

Amalokwu, Kelvin, Papageorgiou, Giorgos, Chapman, Mark and Best, Angus I. (2017) Modelling ultrasonic laboratory measurements of the saturation dependence of elastic modulus: New insights and implications for wave propagation mechanisms International Journal of Greenhouse Gas Control, 59, pp. 148-159. (doi:10.1016/j.ijggc.2017.02.009).

Record type: Article

Abstract

Seismic time-lapse techniques are a valuable tool used to estimate the mobilization and distribution of stored CO2 in depleted reservoirs. The success of these techniques depends on knowing the seismic properties of partially saturated rocks with accuracy. It is commonplace to use controlled laboratory-scale experiments to determine how the fluid content impacts on their properties. In this work, we measure the ultrasonic P- and S-wave velocities of a set of synthetic sandstones of about 30% porosity. Using an accurate method, we span the entire saturation range of an air-water system. We show that the rocks’ elastic behaviour is consistent with patchy saturation and squirt flow models but observe a discontinuity at around 90% gas saturation which can be interpreted in two very different ways. In one interpretation, the responsible mechanism is frequency-dependent squirt-flow that occurs in narrow pores that are preferentially saturated. An equally plausible mechanism is the change of the mobile fluid in the pores once they are wetted. Extrapolated to seismic frequencies, our results imply that the seismic properties of rocks may be affected by the wetting effect with an impact on the interpretation of field data but would potentially be unaffected by the squirt flow effect. This provides strong motivation to conduct laboratory-scale experiments with partially saturated samples at lower frequency or, ideally, a range of frequencies in the seismo-acoustic range.

PDF Modelling_paper_final_ack - Accepted Manuscript
Restricted to Repository staff only until 1 April 2018.

More information

Accepted/In Press date: 12 February 2017
Published date: 1 April 2017
Organisations: Geology & Geophysics, Ocean and Earth Science, Marine Geoscience, National Oceanography Centre

Identifiers

Local EPrints ID: 407922
URI: http://eprints.soton.ac.uk/id/eprint/407922
ISSN: 1750-5836
PURE UUID: 5724d3d9-1d6f-48b2-b4b8-20dea5be0cee

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Date deposited: 29 Apr 2017 01:02
Last modified: 17 Jul 2017 13:44

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Contributors

Author: Kelvin Amalokwu
Author: Giorgos Papageorgiou
Author: Mark Chapman
Author: Angus I. Best

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