Method for obtaining NMR (nuclear magnetic resonance) echo strings for ringing elimination

Abstract

The invention provides a method for obtaining NMR (nuclear magnetic resonance) echo strings for ringing elimination, which comprises the following steps of: sequentially acquiring a plurality of No.1 spin echoes by using a No.1 spin echo pulse sequence; emitting a No.1 180-degree radio-frequency pulse and a No.1 90-degree radio-frequency pulse, and turning a macroscopic magnetization vector plate to the direction of a Z axis; sequentially acquiring a plurality of No.2 spin echoes by using a No.2 spin echo pulse sequence; sequentially emitting a plurality of No.2 180-degree radio-frequency pulses on an X axis so as to sequentially obtain positive-negative alternately No.3 spin echoes with a number corresponding to that of the No.2 180-degree radio-frequency pulses; carrying out cross phase superposition on the No.1 spin echoes and the No.2 spin echoes; and multiplying negative echo signals in the No.3 spin echoes by minus 1 so as to obtain No.4 spin echoes, then, carrying out inter-echo superposition and filtration on each echo signal in the No.4 spin echoes. By using the method above, the measuring efficiency can be ensured, and a spin echo string with a high SNR (signal to noise ratio) and a high longitudinal resolution can be obtained.

Description

technical field [0001] The invention relates to the technical field of nuclear magnetic resonance logging, in particular to a method for acquiring nuclear magnetic resonance echo trains for eliminating ringing. Background technique [0002] During the nuclear magnetic resonance measurement of oil wells, since the antenna of the nuclear magnetic resonance instrument surrounds the magnet, when the radio frequency pulse is emitted, the current flowing through the radio frequency coil interacts with the magnetic field formed by the magnet, and a net torque will be formed on the nuclear magnetic resonance instrument . Since the emission is alternating current, the torque changes, which will cause the NMR instrument to vibrate, and the vibration of the NMR instrument will also generate additional electronic noise on the antenna, that is, "ringing". Ringing usually decays quickly, but it still exists during echo detection, and the smaller the echo spacing, the more pronounced the ...

AI Technical Summary

Problems solved by technology

In this method the transverse relaxation time T 1 Relatively small formations work well, but the disadvantage of this method is that when the formation's T 1 When it is relatively large, due to the non-uniformity of the radio frequency magnetic field, stimulated echoes will be generated

And the ringing cancellation method requires additional acquisition of ringing information after the normal spin echo pulse sequence, thus reducing the efficiency of the measurement

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