Ground nuclear magnetic resonance inversion method containing variable frequency deviator
A ground nuclear magnetic resonance and changing frequency technology, which is applied in the direction of electronic magnetic resonance/nuclear magnetic resonance detection, can solve the problems of being unable to be used, and achieve the effect of improving accuracy
Inactive Publication Date: 2020-04-10
JILIN UNIV
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However, when the frequency offset varies with space, resonance and off-resonance exist at the same time, that is, compound resonance, which cannot be corrected by this method
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[0045] In order to make the object, technical solution and advantages of the present invention more clear, the present invention will be further described in detail below in conjunction with the examples. It should be understood that the specific embodiments described here are only used to explain the present invention, not to limit the present invention.
[0046] see figure 1 As shown, a ground-based NMR inversion method involving varying frequency offsets, including,
[0047] Step 1: First, perform Hilbert transform and low-pass filtering on the field measurement data to obtain the measurement data envelope matrix do bs = d R +id I (R and I represent real and imaginary parts, respectively), see Figure 2a and Figure 2b shown. Secondly, the nonlinear fitting method is used to extract the characteristic parameters of the measurement data matrix, and the variation of the frequency offset with the pulse moment q Δf is obtained q =[Δf(q 1 ), Δf(q 2 ),…,Δf(q Q )] (where...
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The invention relates to a ground nuclear magnetic resonance inversion method containing a variable frequency deviator, and the method comprises the steps: firstly carrying out the Hilbert transform and low-pass filtering of field measurement data, and obtaining a measurement data envelope matrix; carrying out characteristic parameter extraction on the measurement data envelope matrix by utilizinga nonlinear fitting method to obtain a variable quantity of a frequency offset along with a pulse moment, carrying out preliminary correction, and carrying out preliminary inversion to obtain a preliminary change of water content and relaxation time along with depth, and a system phase; carrying out ground nuclear magnetic resonance preliminary inversion with the frequency deviator changing alongwith the depth to obtain the change of the water content and relaxation time of the first iteration along with the depth z and the change of the Larmor frequency along with the depth; establishing ground nuclear magnetic composite resonance inversion containing the frequency offset changing along with the depth to obtain wz and delta fz of the second iteration; and repeatedly executing until an error condition is met. According to the method, the accuracy of a ground nuclear magnetic resonance inversion result under the condition that the Larmor frequency changes along with space is improved.
Description
technical field [0001] The invention belongs to the field of geophysical data processing and inversion interpretation, and specifically relates to a ground nuclear magnetic resonance inversion method including variable frequency offset. Background technique [0002] Surface nuclear magnetic resonance method is a geophysical method based on the principle of nuclear magnetic resonance, which directly detects groundwater and quantitatively evaluates the intrinsic properties of aquifers. However, in field experiments, due to the uneven distribution of the geomagnetic field and the influence of metal magnetic anomalies, the Larmor frequency of ground NMR varies with space, which affects the accuracy of detection results. Therefore, it is of great significance to study ground-based NMR inversion methods that include varying frequency offsets. [0003] Patent CN106019393A invented a ground nuclear magnetic off-resonance detection method with unknown Larmor frequency. This method ...
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IPC IPC(8): G01V3/14
CPCG01V3/14
Inventor 王琦蒋川东杜海龙田宝凤易晓峰
Owner JILIN UNIV