Novel D-T2 pulse applying method based on pulse gradient magnetic field

Abstract

The invention discloses a novel D-T2 pulse applying method based on a pulse gradient magnetic field. Even magnetic field design is adopted in a main instrument magnetic field, the pulse gradient magnetic field is applied to a tested region through a gradient coil, and the pulse gradient and lasting time can be adjusted; a data acquisition pulse time sequence is divided into two windows on a time axis, the lasting time of the first window is fixed to be t0, and the shortest instrument echo interval is used for acquiring a CPMG pulse time sequence of the second window; spectrum unfolding is conducted on echo signals acquired in the two windows through an inversion algorithm so that a D-T2 two-dimensional distribution map of reservoir stratum pore fluid can be acquired. The method has the two unique advantages that firstly, a diffusion coefficient measurement range is large; secondly, the transverse relaxation resolution ratio is high, D-T2 two-dimensional nuclear magnetic resonance acquisition parameters are set more flexibly through unique double-variant design, and the method can well suitable for the changes of the nuclear magnetic resonance property of the reservoir stratum pore fluid.

Description

technical field [0001] The present invention relates to the field of low-field nuclear magnetic resonance rock core analysis, specifically D-T 2 A novel pulse acquisition timing design for 2D NMR. Background technique [0002] With the advantages of fast, non-destructive, non-invasive, non-toxic, and only sensitive to hydrogen-containing pore fluids, NMR technology has been introduced into the field of oil exploration since the 1950s. Since the first pulsed NMR logging tool was put into commercial service in the early 1990s, the one-dimensional NMR technology based on CPMG pulse sequence has been successful in porosity, permeability, saturation calculation, pore structure evaluation, fluid identification, etc. It provides important information for reservoir evaluation and productivity prediction. Due to one-dimensional T 2 However, the difference spectrum method (DSM), time domain method (TDA), shift spectrum method (SSM), diffusion analysis method (DIFAN), and enhanced d...

AI Technical Summary

Problems solved by technology

PFG and STE-PFG benefit from the variable pulsed magnetic field gradient, and have a large diffusion coefficient test range; but there is no echo signal in the pulse gradient action window, resulting in short relaxation components (clay bound water, heavy oil etc.) have lower resolution of transverse relaxation

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