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Inferring the lithology of borehole rocks by applying neural network classifiers to downhole logs: an example from the Ocean Drilling Program

Inferring the lithology of borehole rocks by applying neural network classifiers to downhole logs: an example from the Ocean Drilling Program
Inferring the lithology of borehole rocks by applying neural network classifiers to downhole logs: an example from the Ocean Drilling Program
In boreholes with partial or no core recovery, interpretations of lithology in the remainder of the hole are routinely attempted using data from downhole geophysical sensors. We present a practical neural net-based technique that greatly enhances lithological interpretation in holes with partial core recovery by using downhole data to train classifiers to give a global classification scheme for those parts of the borehole for which no core was retrieved. We describe the system and its underlying methods of data exploration, selection and classification, and present a typical example of the system in use. Although the technique is equally applicable to oil industry boreholes, we apply it here to an Ocean Drilling Program (ODP) borehole (Hole 792E, Izu-Bonin forearc, a mixture of volcaniclastic sandstones, conglomerates and claystones). The quantitative benefits of quality-control measures and different subsampling strategies are shown. Direct comparisons between a number of discriminant analysis methods and the use of neural networks with back-propagation of error are presented. The neural networks perform better than the discriminant analysis techniques both in terms of performance rates with test data sets (2–3 per cent better) and in qualitative correlation with non-depth-matched core. We illustrate with the Hole 792E data how vital it is to have a system that permits the number and membership of training classes to be changed as analysis proceeds. The initial classification for Hole 792E evolved from a five-class to a three-class and then to a four-class scheme with resultant classification performance rates for the back-propagation neural network method of 83, 84 and 93 per cent respectively.
artificial intelligence, borehole geophysics, drill cores, ocean drilling, sediments, statistical methods
0956-540X
477-491
Benaouda, D.
3626eb4e-bcaf-49dd-b3ab-ada8afb5dd9c
Wadge, G.
abe10fdf-f2a0-4fce-876c-574ae8902b65
Whitmarsh, R.B.
8a17394e-90a9-404a-a40c-f0099e9bfc1f
Rothwell, R.G.
fe473057-bf44-46d1-8add-88060037beb5
MacLeod, C.
13efff1d-97c5-424f-828a-66a9687ff6a2
Benaouda, D.
3626eb4e-bcaf-49dd-b3ab-ada8afb5dd9c
Wadge, G.
abe10fdf-f2a0-4fce-876c-574ae8902b65
Whitmarsh, R.B.
8a17394e-90a9-404a-a40c-f0099e9bfc1f
Rothwell, R.G.
fe473057-bf44-46d1-8add-88060037beb5
MacLeod, C.
13efff1d-97c5-424f-828a-66a9687ff6a2

Benaouda, D., Wadge, G., Whitmarsh, R.B., Rothwell, R.G. and MacLeod, C. (1999) Inferring the lithology of borehole rocks by applying neural network classifiers to downhole logs: an example from the Ocean Drilling Program. Geophysical Journal International, 136 (2), 477-491. (doi:10.1046/j.1365-246X.1999.00746.x).

Record type: Article

Abstract

In boreholes with partial or no core recovery, interpretations of lithology in the remainder of the hole are routinely attempted using data from downhole geophysical sensors. We present a practical neural net-based technique that greatly enhances lithological interpretation in holes with partial core recovery by using downhole data to train classifiers to give a global classification scheme for those parts of the borehole for which no core was retrieved. We describe the system and its underlying methods of data exploration, selection and classification, and present a typical example of the system in use. Although the technique is equally applicable to oil industry boreholes, we apply it here to an Ocean Drilling Program (ODP) borehole (Hole 792E, Izu-Bonin forearc, a mixture of volcaniclastic sandstones, conglomerates and claystones). The quantitative benefits of quality-control measures and different subsampling strategies are shown. Direct comparisons between a number of discriminant analysis methods and the use of neural networks with back-propagation of error are presented. The neural networks perform better than the discriminant analysis techniques both in terms of performance rates with test data sets (2–3 per cent better) and in qualitative correlation with non-depth-matched core. We illustrate with the Hole 792E data how vital it is to have a system that permits the number and membership of training classes to be changed as analysis proceeds. The initial classification for Hole 792E evolved from a five-class to a three-class and then to a four-class scheme with resultant classification performance rates for the back-propagation neural network method of 83, 84 and 93 per cent respectively.

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More information

Published date: February 1999
Keywords: artificial intelligence, borehole geophysics, drill cores, ocean drilling, sediments, statistical methods
Organisations: Marine Geoscience

Identifiers

Local EPrints ID: 355617
URI: http://eprints.soton.ac.uk/id/eprint/355617
ISSN: 0956-540X
PURE UUID: 38c5b0e4-070e-4b02-8a8c-42a3e9b5f791

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Date deposited: 09 Aug 2013 08:57
Last modified: 16 Jul 2019 21:26

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Contributors

Author: D. Benaouda
Author: G. Wadge
Author: R.B. Whitmarsh
Author: R.G. Rothwell
Author: C. MacLeod

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