Monthly Luncheon Meeting
Thursday – November 15 2018
PanAm Building- Suite 1600
601 Poydras St, New Orleans, LA 70130
11:30 – 1:00 pm
RSVP: Elizabeth Tanis (Elizabeth.Tanis@shell.com)
Cost - $25
of Spectral Gamma Ray –
A Novel Technique for Easier Stratigraphic Correlation and
Presented By: Michael J. Sullivan -
Advisor, Chevron, Calgary
Spectral gamma ray data has long been recognized for its usefulness in clay typing and rock typing, including distinguishing organic rich shales and radioactive sands from conventional shales. The use of this data has not been widespread however, possibly because the analysis often involves point-based ternary diagrams and the results are not easily presented in a depth based log.
Colour cubing is a technique for turning the portion of the total gamma ray signal that is due to potassium, uranium, and thorium into distinct and meaningful colour patterns. Colour cubing uses the red-green-blue (RGB) colour axes to depict the changing proportions of three attributes (similar to how a colour TV can create any colour from RGB mixing). Using this colour shading on the total gamma ray curve results illustrates both the total gamma and its composition.
We have found this very useful for a variety of applications. It results in a step change improvement in our ability to recognize markers when doing inter-well stratigraphic correlation. Sediments from a common source will have a common mixture of radioactive elements, so layers of sediments rich in potassium, uranium, and thorium appear as distinct blue, red & green bands in cross sections, which greatly eases stratigraphic correlation. Whether diluted or concentrated, if the radioactive mixture does not change, the colour will remain the same, telling us the sediments are likely from the same source.
In addition, changing colour patterns in “shales” provide a quick indication when the shale properties have changed, which may call for different shale end-point parameters when doing petrophysical analysis. In unconventional reservoirs, since TOC rich sediments are often rich in uranium, the desirable zones are easily recognizable by their blue tint. The colour representation of shales is also useful for completion design for differentiating rock properties. Rocks with similar colour are likely to have similar properties. The colour patterns also make it possible to distinguish zones which are favorable for completion and fracturing, from others which are not favorable.