In the first part of this thesis we introduce a new numerical method that combines a numerical method with an analytical method. We model the seismic wave propagation in fractured rock using the pseudospectral method. The fractures are treated as planes of weakness using the concept of the linear slip deformation or displacement discontinuity model. The implementation of fractures with a vanishing width in the finite difference grid is done using an equivalent medium theory. The objective is to investigate the effects of lengthscale (size) and spatial distributions of fractures on the characteristics of propagating waves. We demonstrate that the waveforms can be significantly affected by the presence of fractures with different lengthscales reltive to the wavelength, and we also show that different spatial distributions of fractures can give characteristic features on the wavefields, implying that information about fracture distributions in natural rock may be obtained directly from seismic data. In the second part of the thesis, we deal exclusively with scattering attenuation. Synthetic modelling studies with and without intrinsic attenuation show that the contribution of scattering attenuation is significant. Scattering involves no energy loss, but produces a more extended, lower amplitude wavetrain by the resulting interference. It is dependent on the nature of small-scale fluctuations in the earth parameters and is found to be frequency dependent. For the numerical simulation, we use the method introduced in the thesis that can accurately model the effects of scattering. The various fracture patterns examined are patterns of development of a population of fractures involving nucleation, growth, branching, interaction and coalescence created by a multiscale cellular automaton model. The objective is to examine the behaviour of scattering attenuation at different fracture patterns characterised by different statistical properties, fracture population geometry and criticality. We examine scattering attenuation in a range of frequencies for each one of the fracture patterns and demonstrate the frequency dependence. The comparison of the pattern of scattering attenuation with frequency between different fracture patterns shows that there is a change that can be attributed to the changes in the statistical properties of the fracture population. We conclude by examining the existence of direct links between fracture properties and scattering attenuation patterns, which can be used for the characterisation of fractured reservoirs.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:663297 |
| Date | January 2005 |
| Creators | Vlastos, Serafeim |
| Publisher | University of Edinburgh |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/1842/11507 |
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