PARASEQUENCE-SCALE STRATIGRAPHIC CORRELATIONS IN DEEP-MARINE SEDIMENTS USING BOREHOLE IMAGES
NEIL F. HURLEY, 1996. "PARASEQUENCE-SCALE STRATIGRAPHIC CORRELATIONS IN DEEP-MARINE SEDIMENTS USING BOREHOLE IMAGES", Stratigraphic Analysis Utilizing Advanced Geophysical, Wireline and Borehole Technology for Petroleum Exploration and Production, Jory A. Pacht, Robert E. Sheriff, Bob F. Perkins
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Modified Fischer plots can be used in subsurface reservoirs for parasequence-scale correlations. Although the technique is applied to deep-marine sediments, it is not restricted to such sediments. The approach is based on high-resolution bedboundary detection using borehole-imaging logs such as FMS (Formation MicroScanner, Trademark of Schlumberger, Inc.), FMI (Formation Microlmager, Trademark of Schlumberger, Inc.), or any of the other electrical or acoustic dipmeter devices. The operator interactively selects dips at the top of every clay-sand and clay-chalk interbed while viewing images on a computer workstation. A spreadsheet is prepared which lists the depths to the top of each selected bed boundary. From all contiguous cycles, one calculates a mean-cycle thickness and the departure of each cycle thickness from the mean. Dimensionless cycle thickness is then calculated by dividing mean-cycle thickness into departure from mean-cycle thickness. Interpretations are made on a cross plot of cycle number (a function of depth) vs. cumulative dimensionless departure from mean cycle thickness. The curve that results has a distinctive shape which is based on changes in cycle thickness. This curve can be used like a well-log trace to correlate cycles between wells, look for missing section, and hypothesize about changes in sea level, channel migration, and lateral continuity of facies.