Nuclear magnetic resonance T2 spectrum inversion method considering baseline shifting under low signal-to-noise ratio

A baseline offset and nuclear magnetic resonance technology, which is applied in electric/magnetic exploration, acoustic wave reradiation, radio wave measurement system, etc., can solve low signal to noise, unavoidable terminal non-zero phenomenon, and does not consider baseline offset, etc. question

Inactive Publication Date: 2017-05-24
UNIV OF SCI & TECH OF CHINA
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Problems solved by technology

But at low signal-to-noise ratio, T 2 It is difficult to avoid the non-zero phenomenon at the end

Method used

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  • Nuclear magnetic resonance T2 spectrum inversion method considering baseline shifting under low signal-to-noise ratio
  • Nuclear magnetic resonance T2 spectrum inversion method considering baseline shifting under low signal-to-noise ratio
  • Nuclear magnetic resonance T2 spectrum inversion method considering baseline shifting under low signal-to-noise ratio

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Embodiment Construction

[0057] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

[0058] 1. SVD filtering method

[0059] The present invention aims at data with a low signal-to-noise ratio, so it is first necessary to perform a filtering operation on the data to improve the signal-to-noise ratio of the data. For matrix H of order n×m n×m Do singular value decomposition, that is, there are n×n-dimensional orthogonal matrix U and m×m-dimensional orthogonal matrix V, and n×m-dimensional diagonal matrix S, so that:

[0060] h n×m =U n×n diag[ω 1 ,ω 2 ,…,ω k ,0,…,0]V m×m

[0061] In the formula, ω is the singular value of the matrix H. In general, the rank of a matrix without noise is small, while a matrix with noise is a full rank matrix. Due to the influence of noise, the singular values ​​in the second half of the matrix will increase. The principle of SVD filtering is to set all the singular values ​​after a certai...

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Abstract

The invention discloses a nuclear magnetic resonance T2 spectrum inversion method considering baseline shifting under the low signal-to-noise ratio. Firstly filtering processing is performed on data by using a singular value decomposition (SVD) filtering method; then the area of the non-zero value of a target T2 spectrum is obtained by using an improved orthogonal matching pursuit (OMP) algorithm; and finally the target T2 spectrum is obtained in the determined non-zero value area by using an improved singular value decomposition (SVD) algorithm considering baseline shifting. The data are processed by introducing the SVD filtering method and the singular value decomposition algorithm considering baseline shifting so that the influence of noise and baseline shifting on the result can be reduced to a great extent and the computational accuracy of the algorithm can be enhanced.

Description

technical field [0001] The invention relates to signal processing, nuclear magnetic resonance logging T 2 The technical field of spectrum inversion, specifically related to a kind of nuclear magnetic resonance T 2 spectral inversion method. Background technique [0002] The method of using material nuclear magnetic resonance (NMR) properties to study rock properties in boreholes is called nuclear magnetic logging or nuclear magnetic resonance logging. The spatial distribution of rock formation porosity and fluid saturation can be obtained effectively by nuclear magnetic resonance logging technology. Therefore, it is widely used in natural gas and oil exploration fields at home and abroad. [0003] The nuclear magnetic resonance logging tool measures the rock pore fluid free induction attenuation echo signal, and the echo signal is the superposition of a series of pore fluid relaxation components, so it is necessary to invert the echo signal to obtain the pore Fluid Infor...

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Application Information

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IPC IPC(8): G01V3/38
CPCG01V3/38
Inventor 凌强张梦磊李峰
Owner UNIV OF SCI & TECH OF CHINA
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