ABSTRACT: Interpretation of Structural and Stratigraphic Features with Steep Dips

Robert L. Langley, Don Lee, Robert A. Young

Steep (>60°) bedding dips commonly are associated with large geological features, such as salt domes and faults, and with smaller scale features caused by compaction and slumps. In highly deviated boreholes, high apparent dips are encountered even when bedding dips are low, the extreme case being a horizontal well where horizontal beds become vertical with respect to the borehole. Recognition of high dips from dipmeter data is difficult in wells where bed resistivity contrast is low.

Recognition of steeply dipping beds is possible on high-resolution (1.25-cm or 0.5-in.) borehole images from microresistivity measurements. Confidence in the dip calculation is significantly increased because the interpreter is able to see images of the geologic features used to compute the dips.

Structurally deformed bedding in a highly deviated well and in a well near a salt dome is used to compare steep dips measured from images with dipmeter images. In both instances, dips from images provided the most reliable dip analysis. Comparison of steep dips in cores taken from distorted beds caused by sediment loading with dips from images and dipmeter in the same interval also shows how images provide the best means of interpreting the geologic significance of high local dips. Finally, analysis of a horizontal well drilled through horizontal beds indicates image-based dips are the only practical means of recognizing near-vertical apparent dips.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990