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Sedimentology |
University of Trondheim, The Norwegian Institute of Technology, Division of Petroleum Engineering and Applied Geophysics, The Petroleum Centre, N-7034 Trondheim-NTH, Norway
The sedimentary sequence as recorded in vertical section, i.e. by boreholes and logged sections, is a very uneven representation of the passage of time. Thick sand sequences may be deposited instantaneously with respect to geological time, whereas thin shales may represent either millions or hundreds of years, depending on their environment of deposition. This uncertainty concerning the relative time values of sedimentary units and the breaks between them adds a certain spice to attempts to correlate rather than match well sequences. Consideration of Gressly’s original facies concept, and the formal application of ‘Walthers Law’ suggests the basis of a sequence analysis tool that can be used to correlate adjacent wells. The syntactic pattern recognition technique demonstrated here is based on the development of a grammar of unit associations, and the parsing of logderived lithology units. The development of stratigraphic syntax is shown for both wireline log and grain-size data, with example taken from the North Sea.
