Extraction method for relaxation time spectrum of nuclear magnetic resonance detection signal for underground water by utilizing multi exponent fitting technology

Abstract

The invention relates to an extraction method for a relaxation time spectrum of a nuclear magnetic resonance detection signal for underground water, wherein the method is realized by utilizing a multi exponent fitting technology. According to the method, a spectrum analysis is carried out on a free induction decay (FID) signal that is obtained by testing by a nuclear magnetic resonance underground water detection system; a normalization digital quadrature detection technology is utilized to decompose the signal into a homonymous component X and a quadrature component Y; and filtering and denoising processing is carried out to improve a signal to noise ratio; And a low pass filter is utilized to filter and remove a high-frequency component and multi exponent fitting operation is carried out, so that a minimal solution of an objective function equation is solved; that is, a corresponded relaxation time spectrum and a corresponded amplitude as well as a relaxation time spectrum and an amplitude of an ith kind of an aperture of a magnetic resonance sounding (MRS) signal can be extracted. According to the invention, occupied shares of rocks with all sizes of particles of an aquifer with a certain depth can be distinguished in detail; and a permeability and an occurrence situation of an underground aquifer can be explained accurately. Moreover, a coastal zone or an interference of underground salt water and underground fresh water can be indirectly determined; and the relaxation time spectrum that is extracted by the multi exponent fitting technology can also be popularized and applied to estimation of an interference of a top plate and a bottom plate of a water bearing layer, so that a reliable scientific basis is provided for exploitation of underwater.

Description

technical field [0001] The invention relates to a method for extracting characteristic parameters in the process of geophysical detection, in particular to a method for extracting relaxation time spectrum of nuclear magnetic resonance signals measured in underground aquifers used in nuclear magnetic resonance groundwater detection instruments. Background technique [0002] MRS (Magnetic Resonance Sounding, Magnetic Resonance Sounding) groundwater detection method is a geophysical method for directly exploring groundwater. Compared with traditional geophysical groundwater exploration methods, it has high resolution, high efficiency, rich information and unique solution. And other advantages, the depth, thickness, water content and average porosity of the aquifer can be determined without drilling. Pan Yuling and Zhang Changda edited "Surface Nuclear Magnetic Resonance Theory and Method for Finding Water" (2000.8, Wuhan, China University of Geosciences Press ISBN 7-5625-1551-4...

AI Technical Summary

Problems solved by technology

[0011] The purpose of the present invention is to address the above-mentioned deficiencies in the prior art, to provide a method for extracting the relaxation time spectrum of nuclear magnetic resonance signals using multi-exponential fitting technology, so as to solve the data processing of groundwater detection signals in heterogeneous and anisotropic regions and explain the problem

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