Experimental imaging of a vertical vein using controlled-source seismic interferometry

Dias, Kriselle (2018) Experimental imaging of a vertical vein using controlled-source seismic interferometry. Masters thesis, Memorial University of Newfoundland.

[English] PDF - Accepted Version Available under License - The author retains copyright ownership and moral rights in this thesis. Neither the thesis nor substantial extracts from it may be printed or otherwise reproduced without the author's permission. Download (73MB)

Abstract

Seismic methods are desirably implemented in the imaging of economically viable hard rock mineral deposits, due to the technique's intrinsic higher resolution in comparison to tra- ditionally used geophysical methods. Conventional surface seismic methods are inadequate in the imaging of steeply dipping targets, due to unfavourable geometrical relationships between the surface sources, surface receivers, and the target. There is poor recovery of data when geological features have a dip approximately equal to, or greater than 65°, as the reflected wave propagates at an angle that reaches the surface outside the aperture of the receiver array, or does not reach the surface at all. Steep dips also cause the overall travel path to be much longer than the depth of the target, causing a loss of energy and associated amplitude and high frequency attenuation which results in a low signal to noise ratio and associated processing issues. This study investigates the viability of using a Vertical Seismic Profile (VSP) in com- bination with seismic interferometry as a new method of imaging thin and nearly-vertical veins, and develops techniques for the same, and for which a thin, nearly vertical barite vein at the Collier Point Barite property serves as a well constrained target for study. Seismic interferometry is a technique in which, a signal pair is cross-correlated to reproduce a vir- tual source-receiver pair and reconstruct the impulse response of a given medium. In using these methods, a source is virtually moved into a downhole location, which avoids issues associated with surface-seismic methods. The parameters of the experiment are optimized using ray-tracing analysis, finite-difference modelling and a study of the physical properties to ensure reflection detectability. The unprocessed dataset is highly contaminated by tube- waves which are removed using spiking deconvolution and F-K filtering. The pre-processed dataset is then subjected to seismic interferometry methods which theoretically results in the source and receiver placed in the same location, and is hence processed using standard CMP processing flows. It is noted that the seismic response to the barite target varies significantly through the profile. A 1-D synthetic seismogram modelling program is used to study the variations in the seismic response, and propose a geological interpretation for the same. The final processed image of the target is consistent with descriptions in prior geological reports. This thesis has demonstrated that with the appropriate experiment optimization and processing parameters, VSPs in combination with the seismic interferometry procedure has proven to be an appropriate tool towards detecting and imaging vertical to near-vertical subsurface bodies of economic importance which may otherwise not be imaged appropriately using surface-seismic methods.

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