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Abstract: Identification of Stratigraphic Patterns in Uncored Wells, Based on Quantification of Sedimentological Features from Formation Micro Image Logs (FMI)

FOLKESTAD, ATLE, IKU Petroleum Research, 7034 Trondheim Norway

Formation Micro Image logs (FMI), which are processed from resistivity measurements, show a promising potential for documenting bed-scale sedimentological features in uncored wells, thus aiding the identification of stratigraphic trends and patters in drilled successions.

997m of continuous FMI log and 174 m of cores from a well in the North Sea were used in this study. The FMI log was compared with the corresponding cored intervals in order to identify how different sedimentary structures observed in the cores are expressed in the FMI log. Four of these features were selected as parameters for measurement and quantification in a fixed interval: (1) number of sets, (2) angle of lamination (3) intensity of bioturbation and (4) number of erosional surfaces. The resulting four curves, showing how these parameters fluctuate throughout the log, were plotted and compared in order to identify possible patterns.

Two broad patterns emerge when moving upwards through the log: (1) Simultaneous increase of set density angle of lamination and erosion-surface density are accompanied by a decrease in bioturbation. (2) Simultaneous decrease of set density, angle of lamination and erosion-surface density are accompanied by an increase in bioturbation. The first pattern can be interpreted in terms of a shallowing and the second in terms of a deepening depositional setting. By systematizing these observations throughout the well, these data may be an important contribution in the construction of a sequence stratigraphic framework.

The study shows that it is possible to quantify sedimentological parameters from FMI logs in order to identify larger scale stratigraphic patterns, thus enhancing the interpretative resolution of well data.

AAPG Search and Discovery Article #90937©1998 AAPG Annual Convention and Exhibition, Salt Lake City, Utah