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A computer-aided subsurface mapping program of the middle Miocene section (-9,500 to -15,000 ft) was attempted for a 160-sq mi tract in the structurally "low" part of the famous "Five Islands" trend of Louisiana.
Seven resistivity features were picked from most of 136 electric logs and were correlated and used to make one isopach map, and conventional (manually contoured) structural maps of 4 zones. The same data were then employed to generate computer maps by 2 different approaches: weighted-moving-average (contour maps) and least-square-fits of polynomial surfaces up to the fifth order (trend maps). Numerous computer maps were generated on the high-speed printer and plotter, including structural maps, isopach maps, trend maps, and various residual maps. However, all of them do not appear to convey geologic sense, and some, particularly high-order trend maps, may be of little use.
The degree of similarity the computer maps bear with the manual maps varies widely with the map type and technique used. The contour-type maps may best serve as "quick-look" maps, bringing out the major structural elements and guiding the choice of horizons for hand contouring. Others, such as the isopach maps, yield the growth-fault effect and can guide later interpretations. The polynomial surface maps depict regional trends which can be used to make predictions away from known areas, to suggest "highs" and "lows" of significance, and to display meaningful thickness variations. The residual maps show promise of distinguishing structural traps, the locale of growth faulting, and typical tectonic and sedimentational patterns.
Computer maps do not supplant manually contoured maps. Some of them, if used early in a mapping program, could aid in picking horizons for hand contouring and could be used as a guide for contouring. Others should be used to suggest corrections in the structure, and still others as guides to the final interpretation.
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