The use of X-ray CT in various geological disciplines such as petroleum geology, soil science, paleontology and sedimentology began in the early 1980s. CT applications in petroleum engineering are classified into two important categories: static (rock characterization) and dynamic (fluid flow studies); Among these applications, we can mention the estimation of porosity and porosity distribution, heterogeneity, electrical resistance, bulk density, mineralogy, absolute permeability, saturation and saturation distribution, pore compressibility, etc. These parameters play an important role in the calculations of multiphase flow characteristics such as resistance index, capillary pressure and relative permeability.
Due to much higher resolution, X-ray micro-tomography or micro-CT was introduced in the 1980s, and images of rock samples were generated in 1987. The difference between CT and micro CT is in the resolution that they provide. At best, clinical CTs provide a resolution of about 200 to 400 micrometers, but the resolution achieved by micro-CT is below 5 microns. Therefore, due to the high resolution and non-destructive nature of micro-CT, its use in geological sciences has grown rapidly in the last three decades and it has been recognized as a powerful tool for digital core analysis, pore-scale imaging and modeling. Micro-CT also eliminates the process of sectioning, which is damaging, costly and time-consuming.