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The Baker Hughes MR eXplorer™ (MReX™) instrument responds to hydrogen protons in the pore fluids present in the formation. The MReX instrument uses static and pulsed radio frequency (RF) magnetic fields to make downhole spin-echo magnetic resonance measurements. Initially, the MReX instrument aligns, or polarizes, the hydrogen protons in the formation fluid to its static magnet. The MReX instrument then applies an RF magnetic field to rotate or “tip” the protons. The initial, or α, pulse “tips” the protons perpendicular to the static field. The instrument then applies a secondary, or β, pulse to rephase the protons, generating a measurable signal called a spin echo at a time designated as TE. The MReX instrument continues to apply a series of secondary pulses at equal time intervals, with each pulse generating a spin echo. The important information measured by the MReX instrument is contained in the echoes.
The amplitude of each echo and the time at which the echo was generated is measured and recorded. The initial amplitude of the train of echoes is related to the volume of fluid present in the formation and is used to determine formation porosity. The echo amplitudes decrease, or decay, with time. The decay rate of the echo train (T2) provides information about pore sizes and the types of fluid present in the pores.
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