NMR on iron rich cores and cuttings - the importance of short TEs

Abstract

The moisture content of iron ore is a critical factor in determining its subsequent processing, transportation, quality and general handling. In particular, high moisture content can lead to extremely dangerous liquefaction of the ore during sea-transportation, with major financial and safety implications. NMR has long been used to measure moisture content in rocks but the presence of magnetic materials such as iron affects the NMR signal leading to data that cannot be interpreted by known methods.There has recently been interest in determining how the properties of the rock affect the NMR signal, particularly where there are different concentrations of magnetic materials or rocks with different mineralogical properties. There has, however, been less work in determining how the measurement techniques should be changed to accommodate these systems.In this work we measure iron rich rock cores and show the importance of selecting an appropriate echo time in the CPMG sequence. We show that longer echo times can lead to estimations of a T2 distribution that is not representative of the system. This in turn would lead to inaccurate measurements of the water content. We demonstrate the importance of short echo times and show that for the systems studied in this work, an upper limit of 0.4 ms should be imposed.