Blocking geophysical borehole log data using the continuous wavelet transform

Gordon R. J. Cooper; Duncan R. Cowan

doi:10.1071/EG08127

RESEARCH ARTICLE

Previous Contents Vol 40(2)

Blocking geophysical borehole log data using the continuous wavelet transform

Gordon R. J. Cooper ¹ ³ Duncan R. Cowan ²

+ Author Affiliations

- Author Affiliations

¹ School of Geosciences, University of the Witwatersrand, Johannesburg, South Africa.

² Cowan Geodata Services, 12 Edna Road, Dalkeith, WA 6009, Australia.

³ Corresponding author. Email: cooperg@geosciences.wits.ac.za

Exploration Geophysics 40(2) 233-236 https://doi.org/10.1071/EG08127
Submitted: 22 September 2008 Published: 17 June 2009

Abstract

The interpretation of geophysical log data is frequently difficult due to the noisy downhole environment. Blocking algorithms attempt to smooth the log data while leaving the boundaries between different geological units sharp. This paper introduces a method for the determination of the boundaries based on the zero contour of the continuous wavelet transform (CWT) of the data. The amount of blocking can be controlled by the choice of the scale of the wavelet used. The method is compared with results from the median filter and with discrete wavelet transform (DWT) blocking methods, and is here applied to log data from Australia. The application of the new CWT method overcomes the rounding and shifting of boundaries inherent in median filtering, and provides greater flexibility by overcoming the power of two limitations in the DWT log blocking.

References

Cowan, D. R., and Cooper, G. R. J., 2003, Wavelet analysis of detailed drillhole magnetic susceptibility data, Brockman Iron Formation, Hamersley Basin, Western Australia: Exploration Geophysics 34, 87–92.
| Crossref | GoogleScholarGoogle Scholar | Harmsworth R. A. , Kneeshaw M. , Morris R. C. , Robinson C. J. , and Shrivastava P. K. , 1990, BIF-derived iron ores of the Hamersley Province. In F. E. Hughes, ed., Geology of the Mineral Deposits of Australia and Papua New Guinea, Monograph 14, The Australasian Institute of Mining and Metallurgy, 617–642.

Kerzner M. G. , 1986, Image Processing in Well Log Analysis, D. Reidel Publishing Company.

Krapez, B., Barley, M. E., and Pickard, A. L., 2003, Hydrothermal and resedimented origins of the precursor sediments to banded iron formation: sedimentological evidence of the Early Palaeoproterozoic Brockman Supersequence of Western Australia: Sedimentology 50, 979–1011.
| Crossref | GoogleScholarGoogle Scholar | Mallat S. , 1998. A Wavelet Tour of Signal Processing: Academic Press.

Strang G. , and Nguyen T. , 1996, Wavelets and Filter Banks, Wellesley-Cambridge Press.