Nuclear magnetic resonance T2 spectrum inversion method based on orthogonal matching pursuit algorithm

Abstract

The invention discloses a nuclear magnetic resonance T2 spectrum inversion method based on an orthogonal matching pursuit algorithm. A T2 spectrum non-zero value range is determined by utilizing the orthogonal matching pursuit algorithm and then a T2 spectrum is solved in the non-zero value range by adopting a following singular value decomposition algorithm improved by a regularization method; firstly, a problem initial solution is calculated by adopting the regularization method and then the singular value decomposition algorithm is used for carrying out non-negative iteration. The nuclear magnetic resonance T2 spectrum inversion method comprises the following steps: (1): reading original well logging data Y; (2): carrying out median filtering processing on the data and calculating a signal matrix A; (3): calculating a T2 spectrum non-zero zone by utilizing the orthogonal matching pursuit algorithm; (4): calculating the T2 spectrum of a problem in the T2 spectrum non-zero zone by utilizing the singular value decomposition algorithm improved by the regularization method; (5): calculating whether an error is in an allowable range or not; if so, outputting the final T2 spectrum; otherwise, taking the calculated T2 spectrum as the initial solution and returning back to STEP 4 for recalculating; and (6): outputting the final T2 spectrum. The regularization method is introduced and the initial solution is provided, so that the calculation precision of the algorithm can be improved to the great extent.

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] Nuclear magnetic resonance (NMR) logging technology is a very effective method to measure the porosity and fluid saturation of rock formations. It has a particularly wide range of applications in the field of oil and gas exploration at home and abroad. The inverse interpretation of spin echo signals measured by NMR logging tools is a key part of NMR logging theory. [0003] The data obtained by NMR logging are free induction attenuation signals, which usually need to be inverted to obtain the T of the transverse relaxation component of the echo train. 2 spectral distribution, and then use the obtained T 2 The spectrum analyzes the fluid properties. Therefore T 2 Spectrum inversion is very important for...

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Problems solved by technology

But at low signal-to-noise ratio, T 2 It is difficult to avoid the terminal non-zero phenomenon when the number of spectral distribution points is large

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