1 Tutorial T 1 NMR Relaxation and Petrophysical Properties

T1 NMR Relaxation and Petrophysical Properties Marc Fleury 1 1 IFP Energies Nouvelles NMR relaxation is routinely used in the field of geosciences to give basic petrophysical properties such as porosity, pore size distribution, saturation etc. In this tutorial, we will give the basic principle used in the interpretation of the NMR signal and compare the results with other standard petrophysical techniques such as mercury pore size distribution, BET specific surface measurements, thin sections analysis and visualizations, etc. Porosity seems a very obvious measurement. However, it relies heavily on the sample preparation and is affected by manipulation as well. When dealing with nanoporous media (coal, clays), porosity depends strongly on the instrument capabilities and mobile/non mobile protons must be distinguished. The NMR pore size distribution is a unique information available on water saturated porous media. We will show that it can differ substantially from the distribution obtained by mercury injection for many reasons that will be detailed. In addition, transforming relaxation time (s) into pore sizes (mm) requires the knowledge of the surface relaxivity (mm/s) and we will present different methodology for its determination. The NMR pore size resolution will be discussed together with the inverse Laplace transform data processing. We will also explore the lower limit of the NMR method when considering nanometer scales encountered in clays, coals, catalysis support. Finally, we will introduce briefly recent techniques sensitive to the pore to pore diffusional exchange, providing new information on the connectivity of the pore network, but showing another possibility of discrepancy in the determination of pore size distribution with standard techniques.