A comprehensive approach to studies of porous media (rocks) using a laboratory spectrometer and logging tool with similar operating characteristics

Abstract

The value of NMR spectrometry as a way to understand the porosity and permeability of rocks is well documented. Other more esoteric parameters, such as restrictive diffusion, grain size distribution, and fluid viscosities have received less notice but are also available from the NMR measurements as laboratory studies have shown. With the introduction of gradient field spin-echo NMR well logging, all of these parameters become available in a routine way. To accomplish the goal of having a well log that systematically provides this complete array of NMR answers requires consideration of the measurement principles that can be applied. Magnetic field strength and the relative merits of gradient versus homogeneous magnetic fields methods, as well as the limitations presented by the well bore and wireline systems are a few examples of the factors that must be considered. As important, to the end user, is being provided a definitive link between the well logging response and laboratory measurements on rock samples that prove the meaning of the log. This is ideally accomplished when the laboratory measurements are attained using an apparatus that has the same operating characteristics as the log. For most well logging systems this is seldom accomplished to the degree desired, but it is readily attainable with NMR technologies. The consideration of these factors and the features and benefits of having such a capability are the focus of this paper. The technical attributes of such a comprehensive system, the Numar Corporation's “MRIL ™” and “CoreSpec1000 ™”, plus actual examples of laboratory and well bore data are provided to show the value of such an approach.