ABSTRACT

A Middle Miocene section (-9500 to -15,000 ft.) penetrated by numerous tests has been analyzed by a computer-aided mapping program within a 160 square-mile area of South Louisiana. The area is in the structurally low part of the well known "Five Islands" trend.

Seven resistivity features were picked on most of 136 electric logs, correlated, and used to make conventional (manually-contoured) structural maps of four horizons and one isochore map. The same data were then employed to generate computer maps by three different approaches: weighted-moving-average (contour maps), least-square-fits of polynomial surfaces up to the fifth order (trend maps), and residual maps. A large number of computer maps were generated on the high-speed printer and plotter, including structural maps, isochore maps, trend maps, and various residual maps. Some are useful and others do not appear to convey geologic sense; some, particularly high-order trend maps, may be of little or no significance.

The degree of similarity of the computer maps to manual maps varies widely with the map type and technique used. The computer drawn structural contour-type maps best serve as "quick-look" maps, bringing out the major structural elements and guiding the choice of horizons for hand-contouring. Isochore maps aid interpretation of growth-faults, growth structures, subsidence rates, and age interpretations. The polynomial surface maps depict regional trends which can be used for extrapolation away from the known area, suggest "highs" and "lows" of significance, and display meaningful thickness variations. The residual maps show promise of distinguishing structural traps, the locale of growth faulting, and typical tectonic and sedimentation patterns.

Computer maps do not supplant those made by conventional methods, but if used early in the mapping program, aid in picking key horizons and guiding the contouring. Computer and conventional maps, used together, suggest corrections in the structure and guide the final interpretation. Based on such considerations, tentative recommendations are made as to the most efficient application of computer-mapping techniques for exploration, specifically in the Gulf Coast region.