Bruce N. Carpenter
Target Reservoir Analysis
Craig Peck
The GHK Company
ABSTRACT
Certain log features have become commonly associated with marine environments, but less commonly employed in mapping, Large-scale features are transitional variations reflecting the prograding of clastic material into marine shales such as in pro-delta environments. Smaller-scale features are implied fining or coarsening-upward trends within clastic bodies and unusual gamma ray or other characteristics near or above their top and/or base.
A number of log features were parameterized for use in computer generated maps and evaluated for the deep Upper Morrow clastics in the western Anadarko Basin. These maps were compared to conventional structure and isopachous maps reflecting the results of a study of representative cores and logs.
Resistivity and neutron log gradients and their extreme values in marine environments appear to predict the direction and proximity to the shoreline by a progressive increase in silica diluting marine shales. These same logs and the gamma ray log appear to reflect areas in which shales with unusually high organic content accumulated contemporaneously or subsequent to deposition of coarser clastics. Parameters such as the minimum resistivity value, maximum gamma ray value, and thickness of these organic-rich shales result in maps which indicate the positions of swamps and near-shore environments consistent with the interpretation of the core and log studies.
Other more complicated parameters, such as the results of computer-derived log curve frequency analysis, appear to easily distinguish between marine and fluvial deposits. The computer was also used in an interactive mode to detail correlation to assure correspondence between mapped intervals, and to pick many of the map parameters.