Abstract: Computer Approach to Vertical-Variability Mapping

T. Leo Broin, Dan R. Schenck

Conventional facies maps portray lateral changes in rock type over an area without regard to where the changes are taking place within the formation being mapped. In contrast, vertical-variability maps take into account individual beds and their position in the formation and so make possible better interpretation of environments of deposition.

Though vertical-variability maps have been in the literature for more than 20 years, examples are rare because of the great amount of manpower required to make them. With computerized procedures they now can be made with a reasonable expenditure of manpower. Procedures involve the proper marking of mechanical logs by a geologist so that clerical help can use digitizer tables to code the log depths of the tops and bases of beds of a selected lithology. The data are stored on a magnetic tape and computer-retrieved for machine-plotting and/or contouring. Formation tops may be captured either during the bed-digitizing process or by being entered on data sheets and are stored in a separate file. Formation tops can be changed in the tops file without redigitizing the positions of beds.

Conventional facies maps such as isolith and percentage maps, as well as the following types of vertical-variability maps, can be made from data in the vertical-variability file: number of beds of any lithology, average thickness of lithologic units, number of reservoirs, tripartite distribution, multipartite distribution, D-function vertical variability, center of gravity, relative center of gravity, average dispersion, and relative average dispersion.

AAPG Search and Discovery Article #90968©1977 AAPG-SEPM Annual Convention and Exhibition, Washington, DC