Bipolar pulse-based surface nuclear magnetic resonance transverse relaxation time measuring method

Abstract

The invention belongs to the nuclear magnetic resonance transverse relaxation time measuring field and relates to a bipolar pulse-based surface nuclear magnetic resonance transverse relaxation time measuring method. According to the method, bipolar spin echoes are adopted to measure transverse relaxation time T2; No. 1 positive-polarity 90-degree pulses and No. 1 positive-polarity 180-degree pulses are emitted, so that first actually-measured signals and second actually-measured signals are acquired; No. 2 negative-polarity 90-degree pulses and No. 2 positive-polarity 180-degree pulses are further emitted, so that third actually-measured signals and fourth actually-measured signals can be acquired; the second actually-measured signals and the fourth actually-measured signals are superposed, so that spin echo signals without free induction decay signal interference can be obtained; a time interval tau between the 90-degree pulses and the 180-degree pulses is changed, so that a plurality of times of repeated measurement can be carried out, and therefore, a plurality of spin echo signals can be obtained. With the bipolar pulse-based surface nuclear magnetic resonance transverse relaxation time measuring method of the invention adopted, the measurement accuracy of the ground nuclear magnetic resonance transverse relaxation time T2 can be improved, and the problem of the limitation of measurement precision caused by a situation that the number of spin echo signals acquired by a CPMG sequence is small when T2 is small can be avoided.

Description

technical field [0001] The invention relates to the field of measuring the transverse relaxation time of nuclear magnetic resonance, in particular to a method for measuring the transverse relaxation time of ground nuclear magnetic resonance based on bipolar spin echo. Background technique [0002] The characteristic parameter of the ground NMR (MagneticResonnanceSounding, MRS) signal is the transverse relaxation time T 2 The distribution includes very rich stratigraphic information, directly reflects the particle and pore size of the medium, and can be used to determine hydrogeological parameters such as porosity, irreducible water saturation, permeability, pore size distribution, and fluid properties and water content. However, the current international commercial ground NMR water finder generally uses a single pulse sequence to obtain the free induction decay FID signal, so it can only obtain the transverse relaxation time T 2 Approximate value of - mean relaxation time T...

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Problems solved by technology

[0007] The technical problem to be solved by the present invention is to provide a method for measuring the transverse relaxation time of terrestrial nuclear magnetic resonance based on bipolar pulses, so as to solve the problem of the average relaxation time T measured by conventional single pulses under the condition of inhomogeneous external magnetic field. 2 * The problem of large errors in estimating hydrological parameters, and the transverse relaxation time T 2 measurement conundrum

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