Petrophysical properties of greensand as predicted from NMR measurements

Nuclear magnetic resonance (NMR) is a useful tool in reser-voir evaluation. The objective of this study is to predict petrophysical properties from NMR T2 distributions. A series of laboratory experiments including core analysis, capillary pressure measurements, NMR T2 measure-ments and image analysis were carried out on sixteen greensand samples from two formations in the Nini field of the North Sea. Hermod Formation is weakly cemented, whereas Ty Formation is characterized by microcrystal-line quartz cement. The surface area measured by the BET method and the NMR derived surface relaxivity are associated with the micro-porous glau-conite grains. The effective specific surface area as calculated from Kozeny’s equation and as derived from petrographic image analysis of backscattered electron micrograph’s (BSE), as well as the estimated effective surface relaxivity, is associated with macro-pores. Permeability may be predicted from NMR by using Kozeny’s equation when surface relaxivity is known. Capillary pressure drainage curves may be predicted from NMR T2 distri-bution when pore size distribution within a sample is homogeneous.