Chronostratigraphic diagrams revisited - Zoltan Sylvester

Описание: Chronostratigraphic diagrams are often viewed and used as tools to illustrate basic concepts in stratigraphy, and, with the exception of a couple of seismic interpretation packages, rarely considered useful in applied stratigraphic correlation and interpretation. Yet the Wheeler diagram is an invaluable tool for (1) understanding and analyzing stratigraphy when time-elevation data is available, for example in flume experiments and numerical models; and (2) to create a stratigraphic correlation framework when only stratigraphic data is available, e.g., reflection seismic surveys and geophysical well logs. We use experimental data from the ‘Jurassic Tank‘ flume (St. Anthony Falls Laboratory) to create three-dimensional chronostratigraphic diagrams, compute stratigraphic completeness, and test several sequence stratigraphic concepts. While these might seem to be fairly academic pursuits, the Wheeler diagram is also useful as a key output of a quasi-automated workflow for correlating well logs. To create a three-dimensionally consistent correlation framework, we use a Python implementation of the Wheeler and Hale (2014) approach, which is based on the idea of stretching-an-squeezing all logs into a chronostratigraphic diagram that has relative geologic time (RGT) on its y-axis. The depth shifts needed for the RGT transformation are computed by translating the outputs of a large number of pairwise dynamic-time-warping correlations into a least-squares optimization problem. The resulting chronostratigraphic diagram provides an overview of the overall stratigraphy and its variability. To create geologically intuitive well-log cross sections, we use a multi-scale blocking method that relies on the continuous wavelet transform to identify stratigraphic units of a certain scale in a type log. This type log is obtained through averaging all the logs in the time domain. The RGT approach is not a simple lithologic correlation, as the global optimization often places different lithologies into the same time-stratigraphic unit. Using this technique in data-rich parts of the Permian Basin in West Texas makes it possible to quickly map linear submarine channel bodies in the deepwater Spraberry Formation.