When it comes to understanding the subsurface, very few direct measurements are available to us. We can capture values for pressure, temperature, conductivity, density, neutron energy levels, sound waves, mud weight, weight on bit. There might be a few more but not many. Everything else is a derivation from these data. These calculations are very sophisticated and serve the oil and gas industry quite well, but the further we get from the initial data, the more the combined effects of assumptions and data errors come into play.
This is part of the reason why understanding a basin's geothermics is so powerful. It uses a primary measurement from the formation; temperature. The Geothermal Gradient (GTG) calculation is straight-forward (GTG = (Formation Temperature - Surface Temperature)/Temperature Measurement Depth} and the data is relatively easy to QC. The primary path to enhancing the calculation is better understanding the Surface Temperature (ST) (as outlined in this LinkedIn post). And all it takes to create an Isotherm map is to convolve the GTG grid file with the grid for the TVD of the subject formation. It doesn't get much much closer to the basic measurements than that.
And the applications.of this data are powerful. Reliable Geochemistry data is, by its nature, widely spaced and discrete. Interpreting these data through the lens of a strong GTG/Isotherm map-set leads to a much stronger understanding of thermal maturity.
Another really cool application is the mapping oil viscosity at formation conditions. More on this in the next post. I believe this is what is known as a cliff hanger...