CN112710688B - Nuclear magnetic resonance longitudinal relaxation acquisition method and system - Google Patents
Nuclear magnetic resonance longitudinal relaxation acquisition method and system Download PDFInfo
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Abstract
The invention provides a nuclear magnetic resonance longitudinal relaxation acquisition method and a system, wherein the method comprises the following steps: setting a plurality of different waiting times; respectively collecting a plurality of groups of echo train signals corresponding to the different waiting times by using a CPMG pulse sequence; performing inversion processing on the multiple groups of echo string signals by adopting a mode smoothing method to obtain amplitude distribution data of transverse relaxation time; according to the amplitude distribution data, performing accumulation processing to obtain signal amplitudes of the echo strings at 0 moment; and inverting the signal amplitude of the echo string signals at the moment 0 to obtain the signal amplitude of the longitudinal relaxation time. Compared with the prior art, the method and the system have higher measurement precision and are more suitable for T1 extraction of reservoirs with compactness, low permeability, unconventional property and the like.
Description
Technical Field
The invention relates to the technical field of nuclear magnetic resonance data analysis, in particular to a nuclear magnetic resonance longitudinal relaxation acquisition method and system.
Background
Core analysis is a necessary means to recognize geologic features of hydrocarbon reservoirs. Compared with the conventional core analysis, the nuclear magnetic resonance core analysis has the characteristics of nondestructive testing, one machine with multiple parameters, as many parameters, rapid testing, no pollution, low cost, simple operation and the like, and is suitable for field application in oil fields.
Nuclear Magnetic Resonance (NMR) logging technology and core analysis for measuring transverse relaxation time T2 based on CPMG sequences are widely used at present, and the abundant information provided by the technology plays an important role in oil and gas resource exploration and development. With the development of horizontal wells and multi-branch wells and the continuous upgrading of logging hardware equipment, a measurement mode mainly used for measuring the longitudinal relaxation time T1 is more and more emphasized. The method for measuring the nuclear magnetic resonance longitudinal relaxation time T1 mainly comprises an inversion recovery method, a saturation recovery method and T1-T2 two-dimensional nuclear magnetic resonance, wherein the measured T1 signal contains information such as pore structure, fluid property, fluid content and the like.
In general, T1 is measured by a saturation recovery method and a reverse recovery method, and when a reservoir is densely packed, the signal-to-noise ratio of a measurement signal is lowered due to the lowered porosity, and the measurement accuracy of T1 is lowered. Although T1-T2 two-dimensional nuclear magnetic resonance can obtain T1 and T2 information at the same time, an acquisition method and a processing method are complex.
Therefore, there is a need for a longitudinal relaxation acquisition method with high calculation accuracy and high processing speed.
Disclosure of Invention
In order to solve the problems, the invention provides a nuclear magnetic resonance longitudinal relaxation method and a nuclear magnetic resonance longitudinal relaxation system, which can rapidly acquire the longitudinal relaxation time T1 in reservoir rock and remarkably improve the measurement accuracy of the longitudinal relaxation time.
In an embodiment of the present invention, a method for acquiring longitudinal relaxation of nuclear magnetic resonance is provided, which includes:
setting a plurality of different waiting times;
respectively collecting a plurality of groups of echo train signals corresponding to the different waiting times by using a CPMG pulse sequence;
performing inversion processing on the multiple groups of echo string signals by adopting a mode smoothing method to obtain amplitude distribution data of transverse relaxation time;
according to the amplitude distribution data, performing accumulation processing to obtain signal amplitudes of the echo strings at 0 moment;
and inverting the signal amplitude of the echo string signals at the moment 0 to obtain the signal amplitude of the longitudinal relaxation time.
Further, in the multiple sets of echo train signals, the number of echo signals of each set of echo train signals is the same, and all echo train signals are completely attenuated.
Further, inverting the signal amplitudes of the echo train signals at the time 0 to obtain signal amplitudes of the longitudinal relaxation time, wherein the equation of the signal amplitudes of the longitudinal relaxation time obtained by inversion is as follows:
wherein phi is 1 、φ 2 、…、φ x Signal amplitude as longitudinal relaxation time; a is that 1 、A 2 、…、A x For a plurality of different latencies; s is S 1 、S 2 、…、S x Signal amplitude at time 0 of the echo string signals of the plurality of groups; x is the number of waiting times set and the number of groups of echo train signals.
Further, the set plurality of different waiting times includes 9, respectively 2ms,10ms,30ms,100ms,300ms,1000ms,3000ms,6000ms and 10000ms.
Further, the method for respectively acquiring the multiple groups of echo train signals corresponding to the multiple different waiting times by using the CPMG pulse sequence further comprises the following steps:
and collecting echo string signals corresponding to each waiting time by adopting a mode of scanning and accumulating for a plurality of times for the CPMG pulse sequence of each waiting time, so that the signal-to-noise ratio of the collected echo string signals corresponding to each waiting time is larger than a preset signal-to-noise ratio threshold.
Further, inversion processing is performed on the multiple sets of echo train signals by a mode smoothing method to obtain amplitude distribution data of transverse relaxation time, including:
and respectively adopting the mode smoothing treatment to the echo string signals of the plurality of groups, and further utilizing singular value decomposition inversion treatment to obtain amplitude distribution data of transverse relaxation time.
Further, inverting the signal amplitudes of the echo train signals at time 0 to obtain signal amplitudes of longitudinal relaxation time, and further including:
according to the 9 waiting times and the signal amplitude of the corresponding 9 groups of echo train signals at the moment 0, the signal amplitude of the longitudinal relaxation time is obtained through inversion, and the formula is as follows:
wherein phi is 1 、φ 2 、φ 3 、…、φ 9 Signal amplitude for 9 longitudinal relaxation times; s is S 1 、S 2 、S 3 、…、S 9 Signal amplitude at time 0 for 9 sets of echo train signals.
In an embodiment of the present invention, there is also provided a nuclear magnetic resonance longitudinal relaxation acquisition system, including:
a waiting time setting module for setting a plurality of different waiting times;
the echo train signal acquisition module is used for respectively acquiring a plurality of groups of echo train signals corresponding to the different waiting times by using a CPMG pulse sequence;
the first inversion module is used for carrying out inversion processing on the multiple groups of echo train signals by adopting a mode smoothing method respectively to obtain amplitude distribution data of transverse relaxation time;
the accumulation processing module is used for carrying out accumulation processing according to the amplitude distribution data to obtain the signal amplitude of the echo string signals at the moment 0;
and the second inversion module is used for inverting the signal amplitude of the echo train signals at the time 0 of the plurality of groups to obtain the signal amplitude of the longitudinal relaxation time.
In an embodiment of the present invention, a computer device is also provided, including a memory, a processor, and a computer program stored on the memory and executable on the processor, where the processor implements a nuclear magnetic resonance longitudinal relaxation acquisition method when executing the computer program.
In an embodiment of the present invention, a computer-readable storage medium storing a computer program for performing the nuclear magnetic resonance longitudinal relaxation acquisition method is also presented.
The nuclear magnetic resonance longitudinal relaxation acquisition method and system provided by the invention acquire the signal intensity of each echo train at the 0 moment by using the CPMG pulse sequences with a plurality of waiting times, acquire the longitudinal relaxation time by using the signal intensity of the echo trains at the 0 moment with different waiting times, have higher measurement precision, and are more suitable for T1 extraction of reservoirs with compactness, low permeability, unconventional property and the like.
Drawings
FIG. 1 is a flow chart of a method for nuclear magnetic resonance longitudinal relaxation acquisition in accordance with an embodiment of the present invention.
Fig. 2 is a schematic diagram of 9 sets of echo trains with different latencies according to an embodiment of the present invention.
Fig. 3 is a schematic diagram of the signal amplitude of echo train 0 with 9 sets of different waiting times according to an embodiment of the present invention.
Fig. 4 is a schematic diagram of signal amplitudes of a longitudinal relaxation time T1 according to an embodiment of the present invention.
FIG. 5 is a schematic diagram of a nuclear magnetic resonance longitudinal relaxation acquisition system according to an embodiment of the present invention.
FIG. 6 is a schematic diagram of a computer device according to an embodiment of the invention.
Detailed Description
The principles and spirit of the present invention will be described below with reference to several exemplary embodiments. It should be understood that these embodiments are presented merely to enable those skilled in the art to better understand and practice the invention and are not intended to limit the scope of the invention in any way. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art.
Those skilled in the art will appreciate that embodiments of the invention may be implemented as a system, apparatus, device, method, or computer program product. Accordingly, the present disclosure may be embodied in the following forms, namely: complete hardware, complete software (including firmware, resident software, micro-code, etc.), or a combination of hardware and software.
According to the embodiment of the invention, a nuclear magnetic resonance longitudinal relaxation acquisition method and system are provided. According to the method and the system, through nuclear magnetic resonance data analysis, data describing the hydrogen nuclear relaxation process are tested according to the relaxation process of the hydrogen nuclei in rock pore fluid, and the method is a nondestructive and environment-friendly analysis method. According to the data of nuclear magnetic resonance test, the information of porosity, permeability, irreducible water saturation, rock pore structure parameters and the like of the rock can be calculated. In the petroleum industry, a reasonable oil gas development scheme can be formulated according to nuclear magnetic resonance logging results, the oil gas development efficiency is improved, and the personnel and property safety in the oil gas development process is ensured.
The principles and spirit of the present invention are explained in detail below with reference to several representative embodiments thereof.
FIG. 1 is a flow chart of a method for nuclear magnetic resonance longitudinal relaxation acquisition in accordance with an embodiment of the present invention. As shown in fig. 1, the method includes:
step S1, setting a plurality of different waiting times.
Step S2, respectively acquiring a plurality of groups of echo train signals corresponding to the different waiting times by using a CPMG pulse sequence; the number of echo signals of each group of echo serial signals is the same, and all echo serial signals are completely attenuated.
And step S3, carrying out inversion processing on the multiple groups of echo string signals by adopting a mode smoothing method to obtain amplitude distribution data of transverse relaxation time.
And S4, according to the amplitude distribution data, carrying out accumulation processing to obtain the signal amplitudes of the echo string signals at the moment 0.
Step S5, inverting the signal amplitude of the echo string signals at the moment 0, and obtaining the signal amplitude of the longitudinal relaxation time through the following formula (1-1):
wherein phi is 1 、φ 2 、…、φ x Signal amplitude as longitudinal relaxation time; a is that 1 、A 2 、…、A x For a plurality of different latencies; s is S 1 、S 2 、…、S x Signal amplitude at time 0 of the echo string signals of the plurality of groups; x is the number of waiting times set and the number of groups of echo train signals.
In a specific embodiment, step S1 may set 9 different waiting times, and the collection time is from the smallest 2ms to the largest 10000ms, so that the collection range of T1 is ensured from 2ms to 10000ms, and oil, gas and water in the pore medium can be ensured to be obtained.
Correspondingly, in step S2, 9 sets of echo strings with waiting time of 2ms,10ms,30ms,100ms,300ms,1000ms,3000ms,6000ms and 10000ms are respectively acquired by using a CPMG (Carr-Purcell-meiboost-Gill) pulse sequence, the number of echoes of each set of echo strings is the same, and complete attenuation of all echo strings is ensured.
The CPMG pulse sequence of each waiting time can be scanned and accumulated for a plurality of times, and echo serial signals corresponding to each waiting time are collected, so that the signal to noise ratio of the collected echo serial signals corresponding to each waiting time is larger than a preset signal to noise ratio threshold.
According to step S3 and step S4, the 9 groups of echo strings are respectively processed by SVD (singular value decomposition) inversion processing by adopting a mode smoothing method, and the echo strings are processed by inversionThe obtained T2 distribution after deduction carries out accumulation processing on the amplitude, and determines the signal amplitude at the moment 0 of the echo string, which is S respectively 1 、S 2 、S 3 、S 4 、S 5 、S 6 、S 7 、S 8 、S 9 。
According to step S5, 9 0 time signal amplitudes S 1 、S 2 、S 3 、S 4 、S 5 、S 6 、S 7 、S 8 、S 9 Inversion is performed by the formula (1-2) to obtain the signal amplitude phi of 9 longitudinal relaxation times 1 、φ 2 、φ 3 、φ 4 、φ 5 、φ 6 、φ 7 、φ 8 、φ 9 Thereby obtaining a longitudinal relaxation time T1 distribution.
Compared with the traditional T1 extraction method, the method has higher accuracy of results, and compared with the two-dimensional nuclear magnetic resonance, the method has higher processing speed and higher accuracy, and is more suitable for the T1 extraction of reservoirs with compactness, low permeability, unconventional property and the like.
It should be noted that although the operations of the method of the present invention are described in a particular order in the above embodiments and the accompanying drawings, this does not require or imply that the operations must be performed in the particular order or that all of the illustrated operations be performed in order to achieve desirable results. Additionally or alternatively, certain steps may be omitted, multiple steps combined into one step to perform, and/or one step decomposed into multiple steps to perform.
In order to more clearly explain the above-mentioned nuclear magnetic resonance longitudinal relaxation acquisition method, a specific embodiment will be described below, however, it should be noted that this embodiment is only for better illustrating the present invention and is not meant to limit the present invention unduly.
Taking an experiment as an example, the experiment adopts nuclear magnetic resonance experimental measurement technology, an experimental instrument adopts MARAN Ultra nuclear magnetic experimental instrument of oxford instrument company, and data acquisition, namely data inversion, is suggested to adopt SVD inversion algorithm. This particular embodiment is directed to 1 core experimental test data to obtain a T1 distribution.
The block core is a cylindrical core with the diameter of 2.54cm and the height of 3.81cm, the main components are quartz and feldspar, the helium porosity is 15.1%, and the air permeability is 10.38mD.
Before the experiment starts, the rock core is subjected to oil washing and salt washing treatment, and then the NaCl solution with the mineralization degree of 20000PPM is pumped out and then pressurized and saturated.
Next, performing CPMG pulse sequence measurement of 9 different waiting times (2 ms,10ms,30ms,100ms,300ms,1000ms,3000ms,600 ms,10000 ms), and respectively acquiring a plurality of groups of echo train signals corresponding to the different waiting times; as shown in fig. 2, there are 9 sets of echo trains with different waiting times. In order to ensure the precision of experimental data, each group of CPMG pulse sequences adopts a mode of scanning and accumulating for a plurality of times, so that the signal to noise ratio of the data is improved, and the signal to noise ratio of the experimental data is ensured to be at least more than 25.
Inversion processing is carried out on 9 groups of echo strings by adopting a Singular Value Decomposition (SVD) method to obtain T2 distribution, interval porosities corresponding to the T2 distribution are accumulated, so that signal amplitude at 0 moment is obtained, and the signal amplitude error at 0 moment is small because the signal-to-noise ratio of the original echo strings is high and SVD inversion precision is high, and the obtained 9 signal amplitudes S at 0 moment are small 1 、S 2 、S 3 、S 4 、S 5 、S 6 、S 7 、S 8 、S 9 The method comprises the steps of carrying out a first treatment on the surface of the As shown in fig. 3, the signal amplitude is shown at time 0 for 9 sets of echo trains with different waiting times.
Will 9 0 time signal amplitudes S 1 、S 2 、S 3 、S 4 、S 5 、S 6 、S 7 、S 8 、S 9 Inversion is carried out by adopting the method of the formula (1-2) to obtain the signal amplitude phi of 9 longitudinal relaxation times 1 、φ 2 、φ 3 、φ 4 、φ 5 、φ 6 、φ 7 、φ 8 、φ 9 Thereby obtaining a longitudinal relaxation time T1 distribution; as shown in fig. 4, a schematic diagram of the signal amplitude for the longitudinal relaxation time T1 is shown.
After experiments are carried out by using the existing saturation recovery method, inversion recovery method, T1-T2 two-dimensional nuclear magnetic resonance method and the method of the invention, the calculated accuracy of nuclear magnetic resonance porosity, acquisition time and inversion processing time are compared, and the specific results are shown in Table 1.
Table 1 comparison of the effects of the acquisition methods
In terms of accuracy, the method has higher porosity accuracy, and the method is used for acquiring echo train information with higher signal-to-noise ratio although the acquisition time is longer than that of a saturated recovery method and an inverse recovery method; in the aspect of inversion processing, the method provided by the invention is equivalent to a 'saturation recovery method' and a 'inversion recovery method', the acquisition time is obviously shortened compared with that of 'T1-T2 two-dimensional nuclear magnetic resonance', the data processing speed is high, and the field requirement can be better met.
Based on the same inventive concept, the invention also provides a nuclear magnetic resonance longitudinal relaxation acquisition system, as shown in fig. 5, comprising:
a latency setting module 510 for setting a plurality of different latencies;
the echo train signal acquisition module 520 is configured to acquire multiple sets of echo train signals corresponding to the multiple different waiting times by using a CPMG pulse sequence;
a first inversion module 530, configured to perform inversion processing on the multiple sets of echo train signals by using a mode smoothing method, so as to obtain amplitude distribution data of transverse relaxation time;
the accumulation processing module 540 is configured to perform accumulation processing according to the amplitude distribution data to obtain signal amplitudes of the echo train signals at time 0;
and a second inversion module 550, configured to invert the signal amplitudes of the multiple sets of echo train signals at time 0, to obtain signal amplitudes of the longitudinal relaxation time.
It should be noted that while several modules of a nuclear magnetic resonance longitudinal relaxation acquisition system are mentioned in the above detailed description, this partitioning is merely exemplary and not mandatory. Indeed, the features and functions of two or more modules described above may be embodied in one module in accordance with embodiments of the present invention. Conversely, the features and functions of one module described above may be further divided into a plurality of modules to be embodied.
In an embodiment of the present invention, as shown in fig. 6, a computer apparatus 600 is further provided, including a memory 610, a processor 620, and a computer program 630 stored in the memory 610 and capable of running on the processor 620, where the processor 620 implements the aforementioned nuclear magnetic resonance longitudinal relaxation acquisition method when executing the computer program 630.
In an embodiment of the present invention, a computer-readable storage medium storing a computer program for performing the nuclear magnetic resonance longitudinal relaxation acquisition method is also presented.
The method and the system for acquiring the longitudinal relaxation of the nuclear magnetic resonance firstly acquire the signal intensity of each echo train at the 0 moment by using the CPMG pulse sequences with 9 waiting times, and acquire the longitudinal relaxation time by using the signal intensity of the echo trains at the 0 moment with 9 different waiting times, and compared with the traditional T1 extraction method, the method has higher precision, and compared with the two-dimensional nuclear magnetic resonance, the method has higher processing speed and higher precision, and is more suitable for T1 extraction of reservoirs with compactness, low permeability, unconventional property and the like.
The invention can effectively improve the signal-to-noise ratio of the nuclear magnetic resonance logging while drilling signal, and better reflect the aperture distribution information by using the longitudinal relaxation signal which is not influenced by the magnetic field gradient and the diffusion coefficient, so that the invention can more accurately identify the fluid and has more profound significance for the analysis and evaluation of the characteristics of the complex lithology reservoir.
While the spirit and principles of the present invention have been described with reference to several particular embodiments, it is to be understood that the invention is not limited to the disclosed embodiments nor does it imply that features of the various aspects are not useful in combination, nor are they useful in any combination, such as for convenience of description. The invention is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.
Claims (9)
1. A method for nuclear magnetic resonance longitudinal relaxation acquisition, the method comprising:
setting a plurality of different waiting times;
respectively collecting a plurality of groups of echo train signals corresponding to the different waiting times by using a CPMG pulse sequence;
performing inversion processing on the multiple groups of echo string signals by adopting a mode smoothing method to obtain amplitude distribution data of transverse relaxation time;
according to the amplitude distribution data, performing accumulation processing to obtain signal amplitudes of the echo strings at 0 moment;
inverting the signal amplitude of the echo string signals at the moment 0 to obtain the signal amplitude of the longitudinal relaxation time; the formula for obtaining the signal amplitude of the longitudinal relaxation time through inversion is as follows:
wherein phi is 1 、φ 2 、…、φ x Signal amplitude as longitudinal relaxation time; a is that 1 、A 2 、…、A x For a plurality of different latencies; s is S 1 、S 2 、…、S x Signal amplitude at time 0 of the echo string signals of the plurality of groups; x is the number of waiting times set and the number of groups of echo train signals.
2. The method of claim 1, wherein the number of echo signals in each set of echo train signals is the same, and all echo train signals are completely attenuated.
3. The method of claim 1, wherein the set plurality of different waiting times includes 9, 2ms,10ms,30ms,100ms,300ms,1000ms,3000ms,6000ms and 10000ms, respectively.
4. A nuclear magnetic resonance longitudinal relaxation acquisition method according to claim 3, wherein inverting the signal amplitudes of the echo train signals at time 0 to obtain the signal amplitudes of the longitudinal relaxation time further comprises:
according to the 9 waiting times and the signal amplitude of the corresponding 9 groups of echo train signals at the moment 0, the signal amplitude of the longitudinal relaxation time is obtained through inversion, and the formula is as follows:
wherein phi is 1 、φ 2 、φ 3 、…、φ 9 Signal amplitude for 9 longitudinal relaxation times; s is S 1 、S 2 、S 3 、…、S 9 Signal amplitude at time 0 for 9 sets of echo train signals.
5. The method of claim 1, wherein the plurality of sets of echo train signals corresponding to the plurality of different waiting times are acquired respectively using a CPMG pulse sequence, further comprising:
and collecting echo string signals corresponding to each waiting time by adopting a mode of scanning and accumulating for a plurality of times for the CPMG pulse sequence of each waiting time, so that the signal-to-noise ratio of the collected echo string signals corresponding to each waiting time is larger than a preset signal-to-noise ratio threshold.
6. The method of claim 1, wherein inverting the echo train signals in multiple sets by a mode smoothing method to obtain amplitude distribution data of transverse relaxation time comprises:
and respectively adopting the mode smoothing treatment to the echo string signals of the plurality of groups, and further utilizing singular value decomposition inversion treatment to obtain amplitude distribution data of transverse relaxation time.
7. A nuclear magnetic resonance longitudinal relaxation acquisition system, the system comprising:
a waiting time setting module for setting a plurality of different waiting times;
the echo train signal acquisition module is used for respectively acquiring a plurality of groups of echo train signals corresponding to the different waiting times by using a CPMG pulse sequence;
the first inversion module is used for carrying out inversion processing on the multiple groups of echo train signals by adopting a mode smoothing method respectively to obtain amplitude distribution data of transverse relaxation time;
the accumulation processing module is used for carrying out accumulation processing according to the amplitude distribution data to obtain the signal amplitude of the echo string signals at the moment 0;
the second inversion module is used for inverting the signal amplitude of the echo train signals at the moment 0 to obtain the signal amplitude of the longitudinal relaxation time; the formula for obtaining the signal amplitude of the longitudinal relaxation time through inversion is as follows:
wherein phi is 1 、φ 2 、…、φ x Signal amplitude as longitudinal relaxation time; a is that 1 、A 2 、…、A x For a plurality of different latencies; s is S 1 、S 2 、…、S x Signal amplitude at time 0 of the echo string signals of the plurality of groups; x is the number of waiting times set and the number of groups of echo train signals.
8. A computer device comprising a memory, a processor and a computer program stored on the memory and executable on the processor, characterized in that the processor implements the method of any of claims 1 to 6 when executing the computer program.
9. A computer readable storage medium, characterized in that the computer readable storage medium stores a computer program for executing the method of any one of claims 1 to 6.
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| 廖广志 ; 肖立志 ; 谢然红 ; 付娟娟 ; .孔隙介质核磁共振弛豫测量多指数反演影响因素研究.地球物理学报.2007,(第03期),全文. * |
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