Trapping magnetisable particulates upstream of magnetic resonance apparatus

摘要

Nuclear magnetic resonance apparatus for measuring properties of a fluid stream which is flowing within a pipeline 10 and which may be hydrocarbon from an underground reservoir will comprise one or more magnet systems for applying one or more magnetic fields to the fluid stream and means for inducing and observing magnetic resonance within the fluid stream as it passes through a said magnetic field. The apparatus may include a polarizing magnetic field (magnets 13, polarizing section B) upstream of the magnetic field in which resonance is observed (magnets 11, section A). These magnetic fields are potentially vulnerable to the accumulation of magnetisable iron debris particles entrained in the fluid flow. To guard against this, the apparatus comprises one or more upstream traps (trapping section C) having a magnetic field to attract and hold solid magnetizable material and an exit path for the removal of the solid magnetizable material so that it does not continue towards any polarizing field and the field where resonance is observed. The trap(s) may comprise a branch pipe from the pipeline (fig. 2); a magnetic pole piece extending into the pipeline (figs. 4-7), traps in parallel (fig. 3) or magnets supported on pivoted arms (fig. 8).