A WAVELET BASED SIGNAL DENOISING AND HYDROCARBON PREDICTION ALGORITHM FOR A NEW MARINE CSEM ANTENNA DESIGN
In Marine Controlled Source Electromagnetics (MCSEM) surveys, signals are congested with noisy elements such as airwaves, direct waves, magneto telluric waves, and reflected waves. Airwaves data are known to create ambiguities during interpretation of the presence of hydrocarbon (HC). So do other...
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| Main Author: | |
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| Format: | Thesis |
| Language: | English |
| Published: |
2017
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| Subjects: | |
| Online Access: | http://utpedia.utp.edu.my/id/eprint/22034/1/Tadiwa%20Elisha%20Nyamasvisva%20%28PhD%29%20Thesis.pdf http://utpedia.utp.edu.my/id/eprint/22034/ |
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| Summary: | In Marine Controlled Source Electromagnetics (MCSEM) surveys, signals are
congested with noisy elements such as airwaves, direct waves, magneto telluric waves,
and reflected waves. Airwaves data are known to create ambiguities during
interpretation of the presence of hydrocarbon (HC). So do other noisy elements,
therefore there is a need to identify, quantify and eliminate these noises from the
receiver data for better prediction of HC. This research work proposes a modified
computational algorithm for decomposing and denoising the MCSEM data.
Subsequently a mathematical model is derived for shallow water with deep
hydrocarbon target environment. Currently MCSEM uses conventional horizontal
electrical dipole (HED) antenna for deep water and shallow to deep HC exploration.
This antenna lacks in directivity and focusing of the EM waves. The HED also
propagates the EM waves equally in all directions which is a major problem in
shallow water with air waves. In an attempt to explore deep HC in shallow waters, a
new curved electric dipole (CED) antenna was designed with the capabilities of
dispersing the airwaves by up to 77% in comparison with the conventional HED and
able to enhance the down going signals for better resolution of up to 125%. Massive
data sets are collected from extensive simulations of a geological model using the
CED and HED antennae. A modified denoising algorithm was designed based on
Johnstone and Donoho’s classical wavelet denoising protocol. The modified
algorithm uses Symlet wavelet with soft threshold rule and Fixed Form Threshold
(FFT) threshold technique, to decompose received signal Ex into single components
comprising guided waves Gw, direct waves Dw, air waves Aw and magneto telluric
wavesMT. Symlet 2 was taken as the base wavelet for decomposing MCSEM data on
the basis that it filters 28% more residual data and takes on average 13% less
computational time compared to other wavelets. |
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