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Sedimentology and Stratigraphic Correlation |
1 University of Oslo and The Norwegian Computing Center, P.O. Box 114 Blindern, N-0314 Oslo 3, Norway
2 The Norwegian Computing Center, P.O. Box 114 Blindern, N-0314 Oslo 3, Norway
3 Norsk Hydro a/s, P.O. Box 200, N-1321 Stabekk, Norway
4 Statoil a.s, P.O. Box 300, N-4001 Stavanger, Norway
The problem addressed is whether a computer can be programmed to identify depositional facies from a set of wireline logs. The basic approach is to let the computer learn by itself the patterns to search for by feeding it log signatures that have already been assigned facies labels. Having gone through this training phase, it can make sedimentary predictions from new data. The underlying model is a mathematical formalization of the idea that sedimentary processes have deposited lithological sequences which influence the observed log traces. Stochastic descriptions are used for these relationships. Markov chains link the lithology to the underlying sedimentary facies. The upward transition probabilities of the Markov chain are the main features which discriminate sedimentary facies.
An efficient reconstruction algorithm permits probabilistic restoration of both lithology and sedimentology. This allows the uncertainty of the conclusions to be quantified, and more than one interpretation can be put forward where appropriate. Results of the tests are promising.
