Magnet design of nuclear magnetic resonance system for well logging and geoscience applications

Nuclear magnetic resonance measurement (NMR) is an important technology to assess the characteristics of oil reservoirs which provides information on the type of fluid in the formation. The analysis by logging tool is based on using relaxation time measurements to understand the structure of the reservoir. In this research, the Computer Simulation Technology (CST) software is used to design a typical permanent magnet for NMR device and simulate it for different types of materials and different dimensions. The effects of temperature inside the well along with the magnetic response of the magnet which is a very important and effective parameter in well logging were considered. In addition, the effects of the cement wall on the field were studied. Due to the fact that the relative magnetic coefficient of ferrite material is in the range of 1.45 to 1.65, the effects of this parameter in the field of magnets have been investigated. Increasing the relative magnetic permeability coefficient reduces the amount of magnetic field in the considered depth. The influence of the magnet radius in the produced field has also been analyzed which indicates that, with a 6-inch diameter device, the penetration depth was greater than that using a similar 4.5-inch tool, thus making it an efficient tool for investigating the depth of the formation.