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Nuclear time in resonance2/18/2023 ![]() In addition to laboratory research, these investigations included proposals for logging devices and the development of well-logging methods to permit formation evaluation in situ. In the early 1950s, several companies-particularly California Research (Chevron), Magnolia (Mobil), Texaco, Schlumberger, and Shell-began extensive investigations to understand the NMR properties of fluids in porous media for the purpose of characterizing reservoir rocks (porosity, permeability, and fluid content). Within a few years after the first successful observations of NMR in 1946, and the demonstration of free-precession NMR in the earth’s magnetic field in 1948, the petroleum industry recognized the potential of NMR measurements for evaluating: However, NMR logs are the most complex logging service introduced to date and require extensive prejob planning to ensure optimal acquisition of the appropriate data needed to achieve the desired objectives. Whether used as a standalone service or in combination with other logs and core data, NMR logs can provide an improved understanding of reservoir petrophysics and producibility. In the past few years, logging-while-drilling (LWD) devices and downhole NMR spectrometers have also been introduced. During the past decade, a new generation of wireline-logging devices has been introduced into commercial service. Whether run independently as a standalone service or integrated with conventional log and core data for advanced formation and fluid analyses, NMR logging has significantly contributed to the accuracy of hydrocarbon-reservoir evaluation. NMR logging provides measurements of a variety of critical rock and fluid properties in varying reservoir conditions (e.g., salinity, lithology, and texture), some of which are unavailable using conventional logging methods ( Fig.1) and without requiring radioactive sources ( Table 1). NMR-log data also provide information concerning pore size, permeability, hydrocarbon properties, vugs, fractures, and grain size. Differences in relaxation times and/or fluid diffusivity allow NMR data to be used to differentiate clay-bound water, capillary-bound water, movable water, gas, light oil, and viscous oils. NMR porosity is independent of matrix minerals, and the total response is very sensitive to fluid properties. Type and quantity of fluid hydrocarbonsįig.1 – NMR logging-tool response compared to conventional logging tools.The volume (porosity) and distribution (permeability) of the rock pore space.From this information, it is possible to infer or estimate ( Fig.1): NMR logs provide information about the quantities of fluids present, the properties of these fluids, and the sizes of the pores containing these fluids. Because these protons primarily occur in pore fluids, NMR effectively responds to the volume, composition, viscosity, and distribution of these fluids, for example: Unlike conventional logging measurements (e.g., acoustic, density, neutron, and resistivity), which respond to both the rock matrix and fluid properties and are strongly dependent on mineralogy, NMR-logging measurements respond to the presence of hydrogen protons. NMR logging, a subcategory of electromagnetic logging, measures the induced magnet moment of hydrogen nuclei (protons) contained within the fluid-filled pore space of porous media (reservoir rocks).
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