SCAT Dip Analysis and Isogon-Controlled Sections improve 3-D Seismic

James D. Morse, C. A. Bengtson, and Duane Dopkin

SCAT, isogon-controIIed cross sections, and plunge-projection contour maps provide valuable constraints for testing and improving 3-D seismic, especially where 3-D seismic doesn't image structure completely or properly (in complex structures, beneath major faults, beneath salt, etc.).

SCAT, a system for 3-D dip analysis, fits mutually consistent trend line to multiple data displays, thereby providing more (and more accurate) stuctural control than conventional analysis, which uses just a single display (tadpol plots). Locally, nearly all structures have mutually perpendicularTransverse and Longitudinal directions of greatest and least stmctural change. SCA determines these directions, makes separate T and L plots of apparent dip versus depth, and fits trend lines to these plots. L trend-lines show plunge and how plunge changes with depth. T trend-lines exhibit mathematical special points that locate and orient special surfaces (crestal, trough, axial, inflection, fault, detachment, etc.), which greatly aid interpretation and make isogon controlled sections possible

SCAT results are then converted into isogon-controlled sections and plunge-projection contour maps. First, the deviated wellbore, apparent-dip barbs, and special points are drawn on T and L sections. Second, isogons (line connecting points of equal dip) are drawn through each of the dip barbs. This secondary control is then used to complete the sections. Finally, the sections are projected according to the L trend-line to generate contour maps. These sections and maps (local, near-3-D depth models) can be compared directly with 3-D depth seismic or converted to time for evaluating time seismic.

AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California