CN107561113A - The method that nuclear magnetic resonance core analyzer searches for 90 degree of RF pulse widths automatically - Google Patents

Abstract

A kind of method that high-precision nuclear magnetic resonance core analyzer spectrometer searches for 90 degree of pulsewidths automatically.It is register and a comparator containing a counter, two data storage locations in pulse-series generator PLD.The pulse-series generator be altera corp of the U.S. EP3C80F780C8N devices, the minimum nanosecond of fire pulse width 6.25.Counter records search for the number of change pulsewidth during 90 degree of pulsewidths automatically, register is used to record signal amplitude initial value corresponding to radio frequency pulsed width actuation, during pulsewidth is continuously increased, when judging the adjacent initial value of signal amplitude twice from large to small by comparator, it just have found 90 degree of pulsewidths, then stop counting, record the pwm value of current setting.It is accurate to find 90 degree of pulsewidths and mean that 180 pulsewidths are also accurate, the more and more accurate measure of blowhole fluid content and species.

Description

The method that nuclear magnetic resonance core analyzer searches for 90 degree of RF pulse widths automatically

Art

A kind of method searched for the present invention relates to nuclear magnetic resonance core analyzer and determine 90 degree of RF pulse widths, especially It is that can search for the method for determining 90 degree of pulse widths of spectrometer automatically.

Background technology

Nuclear magnetic resonance core fluids analytic approach, it is a kind of technical method of important detection formation oil air water storage content. Nuclear magnetic resonance core fluids analytic approach, can not be by by means of hydrogen atom to magnetostatic field and the response pattern in radio-frequency pulse magnetic field Influenceed existing for mineral element and accurately detect the presence of oil.It is different according to the position of detection, nuclear magnetic resonance core fluids point Analysis method is divided into underground core fluids analysis and ground experiment room analysis method.According to detection when whether online real-time detection, core Magnetic resonance core analysis method can be divided into wireline logging and well logging again, and the former refers to break into well, after drilling well funeral affairs Fluid near palisades is detected and analyzed, and the latter is as the term suggests be rock core during the drilling well while around carrying out Analysis.

Nuclear magnetic resonance spectrometer is control electronic circuit unit important in nuclear magnetic resonance core analysis equipment, is carrying out rock core During fluid analysis, most commonly 90 degree of pulses and 180 degree pulse, i.e., by macroscopic magnetization intensity that may be present in pore-fluid 90 degree of deflection vector or 180 degree.If the inaccuracy that pulse width is set, it would not accurately obtain using 90 degree that excite fluid partially Turn or 180 degree deflects, when the relaxation time time spectrum that fluid is detected using spin echo string sequence CPMG, first 90 degree of pulsewidth Inaccuracy, follow-up some 180 degree pulses will be also inaccurate, and the error in this excitation can gradually add up, last total Error can be very big, causes test result data very inaccurate.

In Chinese utility model patent《A kind of SCM Based nuclear magnetic resoance spectrum instrument circuit》（Application number # 201320208893X）In, a kind of SCM Based nuclear magnetic resoance spectrum instrument circuit is disclosed, including：Frequency source module and frequency The pulses generation and reiving/transmitting state modular converter of rate source module connection, it is 90 ° for receiving the phase difference from frequency source module Sinusoidal signal and use high-speed microprocessor control analog switch break-make with produce the high-frequency impulse of a variety of pulse trains excitation Signal.The utility model realizes that a kind of circuit topological structure is simple, cheap, it is easy to accomplish miniaturization nuclear magnetic resonance spectrometer Circuit.But accurate excite in sample Spin System to turn 90 degrees partially not disclose, include how that search determines on how to realize 90 degree of pulsewidths etc..

In Chinese utility model patent《The nuclear magnetic resonance rock core measurement apparatus of simulant bearing conditions of coal seam》（Application number # 2014201067396）In, there is provided one kind supported the use suitable for nuclear magnetic resonance rock core measuring instrument, can be in simulated formation temperature Under pressure state, the nuclear magnetic resonance rock core measurement apparatus of the simulant bearing conditions of coal seam of the Nuclear Magnetic Resonance Measurement of rock is realized.It is It is inserted in packing element in cylinder, the both ends of cylinder and packing element form the annular between cylinder and packing element after being blocked by blocking assembly Rock core storage chamber in space and packing element, the both ends of cylinder are communicated with connecing in toroidal cavity and outside thermal cycle respectively Mouthful, it is communicated with the closure assembly at packing element both ends in rock core storage chamber and outside displacement centre bore, cylinder is nonmagnetic Cylinder.The nuclear magnetic resonance rock core measurement apparatus of the simulant bearing conditions of coal seam of the present invention, design is simple, easy to use.But in rock core How 90 degree of pulse widths accurately determine in measurement, are not provided in the invention.

The content of the invention

The problem of in order to overcome existing 90 degree of pulsewidth inaccuracy of nuclear magnetic resonance core analyzer spectrometer, it is sometimes desirable to rely on Experience is randomly debugged repeatedly, and the present invention provides a kind of method that 90 degree of pulsewidths accurately test decision, and this method can be with 6.25ns precision come find and accurately set certain condition under 90 degree deflection angles corresponding to pulsewidth, and search it is most accurate The process of 90 degree of pulsewidths be it is a kind of rapidly, the process of Approach by inchmeal.

When exciting sample using spin echo series impulse sequence, nuclear magnetic resonance core analyzer spectrometer is first turned on, by journey Sequence design makes spectrometer start to search for and determine centre frequency automatically.Then, start to search for 90 degree of pulsewidths, pulsewidth hunting zone is 5 Microsecond is to 500 microseconds.After 90 degree of pulsewidths are found, the pulsewidth corresponding to 180 degree intensity of magnetization deflection angle is the 2 of 90 degree of pulsewidths Times.

The present invention solves its technical problem, and used technical scheme is：The FPGA produced using altera corp of the U.S. Chip EP3CF780C8N is as pulse-series generator, working clock frequency 160MHz.To any one caused radio-frequency pulse For, minimum pulse precision is 6.25ns.

The technical solution adopted for the present invention to solve the technical problems is：Test pulse width is set first as 5 microseconds, Ran Houguan The amplitude of the magnetic resonance signal of reception is examined, records the range value.Increase the microsecond of pulse width 1, if the initial value of signal amplitude increases Add, record the range value.It is further added by the microsecond of pulse width 1, and tracer signal amplitude initial value.It is wide so to increase pulse always Degree, and record the initial value of magnetic resonance free induction decay signal.After certain once increases by 1 microsecond of pulse width, at the beginning of signal amplitude Value diminishes, and illustrates first maximum point that have found nutating curve, the pwm value corresponding to the maximum point, is exactly approximately 90 degree of pulsewidths.Hereafter pulsewidth is continuously increased again, records a series of signal amplitude initial value, and draw amplitude initial value and pulsewidth according to this Curve, be exactly nutating curve.Each crest and trough on nutating curve, be corresponding in turn in 90 degree, 180 degree, 360 degree, 450 degree etc. of macroscopic magnetization strength vector deflection angle.In nuclear magnetic resonance core analyzer spectrometer control software, one is designed Counter, a comparator and two registers, counter are used for the increased number of recording impulse width, and two registers are used for Distinct pulse widths excite the amplitude initial value with its magnetic resonance signal twice before and after storage, and comparator is used for before and after comparing amplitude twice Size, in logic when previous amplitude is less than rear amplitude, then continue to increase pulsewidth, excitation sample simultaneously at the beginning of tracer signal amplitude Value, and when previous amplitude is more than rear amplitude, then stopping increases pulsewidth, and show first crest in nutating curve by Find, i.e., 90 degree of pulsewidths have been found.In the case where ensureing recovery time, when signal accumulative frequency is less, then signal Signal to noise ratio is not high, if accumulative frequency is more, Signal-to-Noise is preferable, then the feelings that can allow in pulse-series generator performance Under condition, shorten the increased step-length of pulsewidth, more accurately looked for 90 degree of pulsewidths.Accurate 90 degree of pulsewidths, it is meant that returning If individual 180 degree pulsed width actuation produces several echoes in wave train sequence, the phase coherence between several echo-signals is more Height, the detection of blowhole fluid content will be more accurate.

The invention has the advantages that 90 degree of pulsewidths can determine with higher pulsewidth precision, using soft in console The logic module and memory module realized in part, can automatically be quickly found out 90 degree of pulsewidths, and algorithm is simple.

Brief description of the drawings

The present invention is further described with reference to the accompanying drawings and examples.

Fig. 1 is the logic schematic diagram of the present invention 90 degree of pulsewidths of search.

1. counter in figure, 2. registers, 3. comparators.

Embodiment

In Fig. 1, the counter of pulse-series generator（1）Pulsewidth step-length increases during being recorded in 90 degree of pulsewidths of search The number added, works as counter（1）Often increase by 1 time, register（2）With regard to updating once, register（2）In simultaneously store before and after twice Magnetic resonance signal initial amplitude value, register（2）Often update once, comparator（3）Also can be updated under clock control once, That is comparand register（2）In when the size of the first two magnetic resonance signal initial value, when comparative result is true, what previous pulsewidth Signal initial value is less than the initial value of the signal corresponding to rear excitation pulsewidth, then counter continues to increase.

In the embodiment shown in fig. 1, pulse-series generator uses the PLD of altera corp of the U.S. EP3C80F780C8N designs realize that the working clock frequency of the device is 160MHz, the pulse sequence realized using the logical device The nanosecond of row minimum pulse width 20, the most short increase nanosecond of step-length 6.25, i.e. pulsewidth precision was 6.25 nanoseconds.Open nuclear magnetic resonance rock core point Analyzer spectrometer, after finding and setting central resonance frequency, present invention invention starts 90 degree of pulsewidths of search automatically, counter （1）Electrification reset count value zero setting, counter after a clock cycle（1）1 is put, nuclear magnetic resonance core analyzer spectrometer transmitting one Individual pulsewidth is the radio-frequency pulse of 5 microseconds, and spectrometer records the amplitude initial value of magnetic resonance signal by magnetic resonance signal receiving circuit, And it is stored in register（2）, then counter（1）Numerical value be further added by 1, RF pulse width excites rock again after increasing by 1 microsecond Heart pore-fluid, records the amplitude initial value of corresponding magnetic resonance signal, and is stored in register（2）Second storage location, pass through After one clock cycle, comparator（3）It is triggered, to register（2）Two currently stored initial values are compared, if compared Device（3）Output result be 1, then mean that previous signal initial value is less than the signal initial value of rear time, then should continue to increase Pulse width finds 90 degree of pulsewidths, if comparator（3）Output result be 0, then after meaning that previous signal initial value is more than Secondary signal initial value, i.e., should stop search, pulsewidth when corresponding 90 degree of pulsewidths are exactly previous excitation.

Claims (2)

1. a kind of method that nuclear magnetic resonance core analyzer searches for 90 degree of RF pulse widths automatically, in nuclear magnetic resonance core analysis In the pulse-series generator of instrument spectrometer, comprising a counter, a data register and a comparator, it is characterized in that： The number that counter records test pulsewidth changes from small to large, there is provided believed with adjacent magnetic resonance twice in comparator comparand register Number initial amplitude, when initial amplitude occurs from large to small, corresponding previous pwm value is exactly 90 degree of arteries and veins pulled down corresponding to angle It is wide.

2. the method that nuclear magnetic resonance core analyzer according to claim 1 searches for 90 degree of RF pulse widths automatically, its It is characterized in：The pulse-series generator of the nuclear magnetic resonance core analyzer spectrometer is the FPGA of altera corp of the U.S. Device EP3C80F780C8N.