During thermal heating of rocks, how do we measure or calculate the porosity and permeability in non-standard samples or powders?

By non-standard, I mean the ones which are not 54-mm NX sized cores.

Is there any imaging-based method to calculate the porosity and permeability from Scanning Electron Microscopy (SEM) images?

If yes, then,

• What is the procedure to calculate pore size distribution using SEM images?
• What should be the magnification range for this method?
• How to calculate permeability?
• Is it mandatory to use thin-section samples of rock for SEM or the powders from the thermally influenced regions can be used?
• Will the non-usage of thin-section sample affect the results and influence standardization?