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Geofysikk
Masterprosjekt

Microstructures of carbonate rocks from velocity and attenuation measurements: Implications for CO2 storage

Project description
With applications to seismic reservoir characterisation and monitoring in mind, geoscientists study the acoustic properties of rocks using a combination of experimental and theoretical methods (Jakobsen et al., 2019).
The acoustic properties of sandstones are relatively well understood, but there is an important need for a better understanding of the acoustic properties of carbonate rocks; both in applications to petroleum and CO2 storage (Siqueira et al., 2017).
The velocity and attenuation of acoustic waves in carbonate rocks depends on the parameters of the microstructure (e.g., permeability, porosities, scales, pore shapes and orientations) as well as the parameters of the saturating fluid(s).
This implies that one can potentially determine the parameters of the microstructure from measurements of velocity and attenuation of acoustic waves under different saturation conditions (Jakobsen et al., 2003).
Carbonate rocks are characterised by more complicated microstructures than sandstones. Carbonate rocks are often characterised by dual porosity (Agersborg et al., 2009).
The number of unknown rock physics parameters involved in a seismic characterisation of a carbonate rock formation is often relatively large, suggesting that it can be difficult to determine these parameters by manual tuning of the parameters of the microstructure (Agersborg et al., 2009).
In this project, the student shall employ a global optimisation method called simulated annealing to perform an automatic search for the best-fitting parameters of the microstructure (Jakobsen et al., 2019; https://en.wikipedia.org/wiki/Simulated_annealing)

The student should perform numerical experiments on synthetic data contaminated with random noise as well as to analyse real measurements of velocity and attenuation at different frequencies. The student should also discuss effects of fractures and implications for CO2 storage (Siquiera et al., 2017).

References
Agersborg, R., Johansen, T.A. and Jakobsen, M., 2009, 57, 81-98. Velocity variations in carbonate rocks due to dual porosity and wave-induced fluid flow. Geophysical Prospecting, 57, 81-98.
Jakobsen, M., McCann, C. and Johansen, T.A., 2003. The acoustic signature of fluid flow in complex porous media. Journal of Applied Geophysics, 54, 219-246.
Jakobsen, M., McCann, C.. and Sothcott, J. 2019. Microstructures of limestones from velocity and attenuation data at sonic and ultrasonic frequencies.
Expanded abstract, Annual SEG meeting.Technology, 0, 1-14.

Proposed course plan during the master's degree (60 ECTS):
PTEK218 Rock physics.
GEOV219 Computational methods in solid earth physics.
GEOV274 Reservoir geophysics.
GEOV276 Theoretical seismology.

Prerequisites
Some programming skills are required for this project.

External data
Felt- lab- og analysearbeid
Experimental data are available for this project.