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Abstract: Statistical Curvature Analysis Techniques for Structural Interpretation of Dipmeter Data

C. A. Bengtson

Statistical curvature analysis provides guidelines for interpolation and extrapolation of Previous HitdipNext Hit data that make it possible to draw maps and cross sections for limited regions around a well using only the dipmeter data for the well. Five computer-derived displays are required: (1) angle of Previous HitdipNext Hit Previous HitversusNext Hit azimuth of Previous HitdipNext Hit, independent of depth; (2) L-direction Previous HitdipNext Hit component Previous HitversusNext Hit depth; (3) T-direction Previous HitdipNext Hit component Previous HitversusNext Hit depth; (4) azimuth of Previous HitdipNext Hit Previous HitversusNext Hit depth; and (5) angle of Previous HitdipNext Hit Previous HitversusNext Hit depth.

Previous HitDipNext Hit Previous HitversusNext Hit azimuth plots for any well (or parts of a well above or below an angular unconformity or certain kinds of faults) show one of five statistical patterns, each indicative of a specific structural setting. From each pattern (except for zero Previous HitdipNext Hit) mutually perpendicular directions of least and greatest structural change (the L- and T-directions) can be determined.

The L-direction parallels the Previous HitstrikeNext Hit in homoclinal Previous HitdipNext Hit settings and parallels the structural b-axis in fold and fault settings. L-direction Previous HitdipNext Hit component plots accordingly show simple patterns corresponding to nearly uniform apparent Previous HitdipNext Hit. T-direction Previous HitdipNext Hit-component plots, in contrast, show nine possible patterns (not counting discontinuities) that occur singly or in combination. Each pattern identifies a particular kind of bedding geometry or a specific kind of Previous HitdipNext Hit-slip fault. Azimuth Previous HitversusNext Hit depth plots show six patterns consistent with the L- and T-direction plots.

Cross-section construction begins by fitting internally consistent statistical trend lines to all five data displays. Previous HitDipNext Hit bars derived from the T-direction trend line are entered at convenient depths along the well. Crestal planes, axial planes, inflection planes, and faults, if present, are identified by "special points" on the T-direction trend line and entered at their appropriate depths. A freehand section now can be drawn, but better results are possible using auxiliary construction lines known as Previous HitdipNext Hit isogons. When the cross section is finished, structural elevations and analytically derived Previous HitdipNext Hit-Previous HitstrikeNext Hit symbols for any chosen horizon are projected perpendicular to the cross section in both directions, using the L-direction Previous HitdipTop component to raise or lower the elevations. This proce ure establishes a network of control for a contour map centered at the well.

AAPG Search and Discovery Article #90963©1978 AAPG/SEG/SEPM Pacific Section Meeting, Sacramento, California