Log curve amplitude slicing: Visualization of well log amplitudes for paleogeographic reconstruction of the Middle Devonian Traverse Group, Michigan Basin

Well log curve shapes and amplitude trends are routinely used to correlate and map formations and reservoirs across petroleum basins or fields. The methods typically employed for correlation and mapping fail, however, to make full use of the vertical resolution of well log curves.{09}A new technique, log curve amplitude slicing (LCAS) facilitates correlation by generating a series of subhorizontal slices through the log curves using sample-by-sample analysis of log curve amplitudes in all wells between two correlative time-surfaces. The slices represent approximate time lines and are relative chronostratigraphic surfaces that can be gridded and contoured to show trends and patterns in log curve amplitudes in map view. When appropriate logs are used (e.g. gamma ray, photoelectric effect, resistivity), the slices show the inferred distribution of lithofacies at the time of deposition. Animation allows visualization of changes in the distribution of lithofacies between successive slices.{09}The log curves can be sliced through the interval of interest from the top-down, from the bottom-up, or proportionally depending upon the sequence stratigraphic interpretation.{09}Application of the LCAS technique facilitates correlation because it highlights trends in log curve amplitudes that are not apparent using traditional methods to display and compare log curves.; Gamma ray log data from 199 wells are used in this dissertation to identify the location, relative timing, and extent of significant fine-grained clastic influx into the carbonate/evaporite-dominated Michigan Basin during deposition of the Middle Devonian Traverse Group. LCAS maps are combined with outcrop stratigraphy to reconstruct the depositional history of the Traverse Group and to develop a relative water depth curve for the Michigan Basin during the Middle Devonian. Comparison of the relative water depth curve to a eustatic sea level curve suggests that although sea level fall may have resulted in formation of several Middle Devonian unconformities, sediment supply/production and subsidence/uplift were important factors influencing Middle Devonian deposition in the intracratonic Michigan Basin. Lithofacies patterns observed in LCAS maps at the basin scale coincide with productive Traverse Group carbonate trends and reveal potentially new areas for exploration and exploitation.