Active field nuclear magnetic resonance logging probe with adjustable detection area and detection method thereof

Abstract

The invention belongs to the research field of geophysical exploration technology, and relates to an active field nuclear magnetic resonance logging probe with an adjustable detection area and a detection method thereof. The probe comprises a cylindrical probe shell, wherein layout of components in the probe is specified by a cylindrical structure with a specific diameter, the size requirement ofa well logging borehole is met, and the components in the probe are protected; two axially magnetized permanent magnets, which are oppositely arranged in polarity, an annular magnetic field which is strengthened firstly and then weakened is generated outside the probe, and the external hydrogen protons can be magnetized to form a detection area; a moving unit consisting of a speed reducing motor,a worm gear and a rack, which can change the distance between the two permanent magnets, thereby changing the position of the detection area outside the probe. The layout mode of the permanent magnetsin the invention can generate a detection area with larger space outside the probe, and the signal-to-noise ratio of nuclear magnetic signals can be enhanced. The invention also utilizes the characteristic of self-locking of worm transmission, and changes the distance between the permanent magnets by controlling the speed reducing motor, thereby changing the position of the detection uniform areaand obtaining the detection capability of more radial detection depths.

Description

Technical field [0001] The invention belongs to the research field of geophysical prospecting technology, and relates to an active field nuclear magnetic resonance logging probe with an adjustable detection area and a detection method thereof. Background technique [0002] Nuclear magnetic resonance detection technology is a method that can detect groundwater directly and non-destructively in the field of geophysics. However, the detection depth of ground nuclear magnetic resonance detection technology is limited, and the limit detection depth is 150 meters. The use of nuclear magnetic resonance logging technology can break through the depth limit of ground nuclear magnetic resonance. For nuclear magnetic resonance logging technology, increasing its radial detection range and enhancing signal-to-noise ratio are new challenges. The magnetization direction of the permanent magnets of traditional logging tools is radial magnetization, and the magnetic field strength decays as the ...

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But its disadvantage is that its effective detection area is small, resulting in low signal-to-noise ratio

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