A method and device for calculating magnetic field gradient distribution inside reservoir rock

Abstract

The present invention provides a method and device for calculating the magnetic field gradient distribution inside reservoir rocks, and belongs to the technical field of oil and gas exploration. The present invention uses a nuclear magnetic resonance logging instrument to measure multiple groups of echo train signal data under different echo measurement parameters in the well, performs inversion, and obtains a downhole T2-G spectrum and a downhole G spectrum; through a core nuclear magnetic experiment, the echo measurement parameters used in the downhole measurement are used to measure the echo train signal data, and then more echo measurement parameter groups are added to measure the echo train signal data to obtain an experimental T2-G spectrum and an experimental G spectrum. Combining the logging data with the experimental data, the obtained downhole T2-G spectrum is corrected to obtain a corrected downhole T2-G spectrum and a downhole G spectrum; the characteristic distribution value GLM of the corrected downhole G spectrum is calculated. The problem of continuous quantitative calculation of the magnetic field gradient inside the reservoir rock is realized, which provides a solid foundation for accurate measurement of reservoir parameters and effective evaluation of fluid properties by downhole nuclear magnetic resonance logging.

Description

Technical Field

[0001] The present invention relates to the technical field of hydraulic fracturing, and in particular to a method and a device for calculating the magnetic field gradient distribution inside reservoir rocks. Background Art

[0002] Conventional logging techniques and methods cannot effectively evaluate unconventional reservoirs. Nuclear magnetic resonance logging is one of the most important logging methods in the exploration and development of unconventional reservoirs. With the help of the measured reservoir T2 distribution spectrum, logging interpretation engineers can not only provide the porosity and pore size distribution characteristics of the reservoir, but also estimate physical property information such as permeability. Through the calibration of laboratory sampling parameters, nuclear magnetic resonance logging can also calculate the fluid proportion under different occurrence states (such as bound fluid saturation). In recent years, the development of two-dimensional nuclear magnetic resonance logging has provided a powerful means for the content and occurrence state standards of oil, gas, and water in unconventional reservoirs such as shale oil. It is the measurement technology that provides the richest reservoir information among all logging methods. At present, there are two commonly used nuclear magnetic resonance logging instruments, one is the gradient magnetic field nuclear magnetic resonance logging instrument represented by Halliburton's MRILP instrument, and the other is the local uniform field nuclear magnetic resonance logging instrument represented by Schlumberger's CMR series. The magnetic field strength (resonance frequency) and measurement parameters of the two types of instruments are different, resulting in large differences in the measured T2 spectrum information, which brings great difficulties to the subsequent data processing and analysis. The fundamental reason is that the internal gradient field generated by the reservoir in different magnetic field environments is very different. The magnetic field gradient inside the reservoir will cause nuclear magnetic resonance diffusion relaxation and accelerate the transverse relaxation rate, thereby affecting the distribution of the T2 spectrum. Therefore, how to calculate the internal magnetic field gradient of the continuous depth of the target reservoir is the key to solving this problem. Summary of the invention

[0003] In order to solve the problem that the existing downhole nuclear magnetic resonance logging technology cannot continuously and quantitatively calculate the magnetic field gradient inside the reservoir, the present invention is based on nuclear magnetic resonance logging data, clarifies the influencing factors of the internal magnetic field gradient, establishes a correction function and constructs a characterization model, and develops a set of technical processes for downhole nuclear magnetic resonance logging to continuously characterize the magnetic field gradient inside the reservoir. A method and device for calculating the magnetic field gradient distribution inside the reservoir rock based on nuclear magnetic resonance logging data are established, which solves the current problem that the magnetic field gradient inside the reservoir rock cannot be continuously and quantitatively calculated, and provides a solid foundation for downhole nuclear magnetic resonance logging to accurately measure reservoir parameters and effectively evaluate fluid properties.

[0004] The present invention provides a method for calculating the magnetic field gradient distribution inside reservoir rocks, comprising the following steps:

[0005] Using a nuclear magnetic resonance logging instrument to go down to a target layer, measuring multiple groups of echo string signal data under echo measurement parameters, wherein the multiple groups are at least three groups;

[0006] Invert the measured echo signal data to obtain the downhole internal magnetic field gradient distribution T2-G spectrum and downhole G spectrum;

[0007] Through core nuclear magnetic resonance experiments, the echo measurement parameters used in downhole measurements are used to measure echo train signal data, and more echo measurement parameter groups are added to measure echo train signal data to obtain experimental T2-G spectrum and experimental G spectrum;

[0008] Combining the logging data with the experimental data, the T2-G spectrum obtained by downhole measurement is corrected to obtain the corrected T2-G spectrum of the downhole internal magnetic field gradient distribution, and the corrected G spectrum of the downhole internal magnetic field gradient distribution is obtained;

[0009] Calculate the characteristic distribution value GLM of the corrected downhole internal magnetic field gradient distribution G spectrum.

[0010] Preferably, the echo measurement parameters include waiting time and echo spacing.

[0011] Preferably, adding more echo measurement parameter groups is adding shorter and longer echo interval measurement parameter groups.

[0012] Preferably, the calibration factor is obtained by combining the logging data with the experimental data, and the calibration factor is used to calibrate the T2-G spectrum of the magnetic field gradient distribution inside the well.

[0013] Preferably, the correction factor α is expressed as follows:

[0014]

[0015] In the formula: a, b, c are weight coefficients, Vsh is the mud content of the formation, %; Φ is the porosity, %; p is the relative content of paramagnetic minerals, %.

[0016] Preferably, the calculation formula of the underground internal magnetic field gradient distribution G spectrum before correction is as follows:

[0017]

[0018] In the formula, TE L TE S are long echo interval and short echo interval, ms respectively; T 2L 、T 2S are the geometric mean of long echo interval and short echo interval, ms respectively; G is the G spectrum of the magnetic field gradient distribution inside the well, G / cm; γ is the proton magnetic gyrometry ratio; and D is the fluid diffusion coefficient.

[0019] Preferably, the calculation formula of the corrected downhole internal magnetic field gradient distribution G spectrum is as follows:

[0020]

[0021] Where G' is the corrected internal magnetic field gradient distribution G spectrum.

[0022] Preferably, the characteristic distribution value GLM of the corrected downhole internal magnetic field gradient distribution G spectrum is calculated using the following formula:

[0023]

[0024] Where GLM is the corrected G spectrum characteristic value of the internal magnetic field gradient distribution in the well, ms; g 1 , g 2 and g 3 are the amplitudes of the first, second and third points of the corrected downhole internal magnetic field gradient G spectrum G', respectively, n-1 is the amplitude of the n-1th point of the G spectrum G' after correction of the internal magnetic field gradient in the well, g n is the amplitude of the nth distribution point of the G spectrum G' of the corrected downhole internal magnetic field gradient, and n is the total number of distribution points.

[0025] The present invention also provides a device for calculating the magnetic field gradient distribution inside reservoir rocks, including a processor, and the processor executes the above-mentioned method for calculating the magnetic field gradient distribution inside reservoir rocks.

[0026] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0027] (1) The present invention clarifies the influencing factors of the internal magnetic field gradient distribution through core nuclear magnetic field experiments, establishes a correction factor for the internal magnetic field gradient distribution, combines the experimental data with the downhole data to compensate the downhole echo data, uses the least squares method to fit the correction factor, and finally establishes a corrected calculation formula for the downhole continuous internal magnetic field gradient distribution.

[0028] (2) The present invention is the first to establish a method for continuously and quantitatively characterizing the magnetic field gradient inside the reservoir using T2-G spectrum and G spectrum by using nuclear magnetic resonance logging. It can continuously calculate the magnetic field gradient inside the reservoir when the resolution of the downhole echo string data is low, fully consider the influence of clay, pores and paramagnetic minerals, establish a calculation formula for the correction factor, and the inverted T2-G spectrum is closer to the experimental data. The present invention provides a basis for the accurate evaluation of the reservoir parameters and fluid state of nuclear magnetic resonance logging, and is of great significance to improving the application effect of nuclear magnetic resonance logging. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is a flow chart of a method for calculating the magnetic field gradient distribution inside reservoir rock according to an embodiment of the present invention.

[0030] Figure 2 This is a downhole T2-G spectrum obtained by inversion before correction according to an embodiment of the present invention.

[0031] Figure 3 This is a corrected downhole T2-G spectrum according to an embodiment of the present invention.

[0032] Figure 4 This is a T2-G spectrum measured in a laboratory according to an embodiment of the present invention.

[0033] Figure 5 The internal magnetic field gradient distribution G spectrum calculated downhole before correction in one embodiment of the present invention is compared with the experimental measurement result;

[0034] Figure 6 Comparison of the corrected downhole calculated internal magnetic field gradient distribution G spectrum and the experimental measurement result of one embodiment of the present invention;

[0035] Figure 7 This is a diagram showing the corrected internal magnetic field gradient distribution and eigenvalue calculation results according to an embodiment of the present invention. DETAILED DESCRIPTION

[0036] The specific implementation modes of the present invention are described in detail below in conjunction with the accompanying drawings.

[0037] The present invention provides a method for calculating the magnetic field gradient distribution inside reservoir rocks, comprising the following steps:

[0038] Using a nuclear magnetic resonance logging instrument to go down to a target layer, measuring multiple groups of echo string signal data under echo measurement parameters, wherein the multiple groups are at least three groups;

[0039] Invert the measured echo signal data to obtain the downhole internal magnetic field gradient distribution T2-G spectrum and downhole G spectrum;

[0040] Through core nuclear magnetic resonance experiments, the echo measurement parameters used in downhole measurements are used to measure echo train signal data, and more echo measurement parameter groups are added to measure echo train signal data to obtain experimental T2-G spectrum and experimental G spectrum;

[0041] Combining the logging data with the experimental data, the T2-G spectrum obtained by downhole measurement is corrected to obtain the corrected T2-G spectrum of the downhole internal magnetic field gradient distribution, and the corrected G spectrum of the downhole internal magnetic field gradient distribution is obtained;

[0042] Calculate the characteristic distribution value GLM of the corrected downhole internal magnetic field gradient distribution G spectrum.

[0043] Both T2-G spectrum and G spectrum represent the magnetic field gradient distribution inside the reservoir rock. T2-G is a two-dimensional spectrum, which reflects more comprehensive information. The G spectrum is obtained based on the T2-G projection. GLM represents the characteristic value of the magnetic field gradient distribution inside the reservoir rock, which is calculated from the G spectrum. GLM is to more intuitively represent the magnitude of the magnetic field gradient inside the reservoir rock.

[0044] In some specific embodiments of the present invention, the echo measurement parameters include waiting time and echo interval.

[0045] In some specific embodiments of the present invention, adding more echo measurement parameter groups is adding shorter and longer echo interval measurement parameter groups.

[0046] In certain specific embodiments of the present invention, a correction factor is obtained by combining logging data with experimental data, and the correction factor is used to correct the T2-G spectrum of the internal magnetic field gradient distribution downhole.

[0047] In some specific embodiments of the present invention, the correction factor α is expressed as follows:

[0048]

[0049] In the formula: a, b, c are weight coefficients, Vsh is the mud content of the formation, %; Φ is the porosity, %; p is the relative content of paramagnetic minerals, %.

[0050] In certain specific embodiments of the present invention, the calculation formula of the underground internal magnetic field gradient distribution G spectrum before correction is as follows:

[0051]

[0052] In the formula, TE L TE S are long echo interval and short echo interval, ms respectively; T 2L 、T 2S are the geometric mean of long echo interval and short echo interval, ms respectively; G is the G spectrum of the magnetic field gradient distribution inside the well, G / cm; γ is the proton magnetic gyrometry ratio; and D is the fluid diffusion coefficient.

[0053] In certain specific embodiments of the present invention, the calculation formula of the corrected downhole internal magnetic field gradient distribution G spectrum is as follows:

[0054]

[0055] Where G' is the corrected magnetic field gradient distribution G spectrum inside the well.

[0056] In some specific embodiments of the present invention, the characteristic distribution value GLM of the corrected downhole internal magnetic field gradient distribution G spectrum is calculated using the following formula:

[0057]

[0058] Where GLM is the corrected G spectrum characteristic value of the internal magnetic field gradient distribution in the well, ms; g 1 , g 2 and g 3 are the amplitudes of the first, second and third points of the corrected downhole internal magnetic field gradient G spectrum G', respectively, n-1 is the amplitude of the n-1th point of the G spectrum G' after correction of the internal magnetic field gradient in the well, g n is the amplitude of the nth distribution point of the G spectrum G' of the corrected downhole internal magnetic field gradient, and n is the total number of distribution points.

[0059] The present invention also provides a device for calculating the magnetic field gradient distribution inside reservoir rocks, including a processor, and the processor executes the above-mentioned method for calculating the magnetic field gradient distribution inside reservoir rocks.

[0060] Example 1

[0061] According to a specific embodiment of the present invention, the method of calculating the magnetic field gradient distribution inside the reservoir rock of the present invention is described in detail below.

[0062] The present invention provides a method for calculating the magnetic field gradient distribution inside reservoir rocks, comprising the following steps:

[0063] Using a nuclear magnetic resonance logging instrument to go down to a target layer, measuring multiple groups of echo string signal data under echo measurement parameters, wherein the multiple groups are at least three groups;

[0064] Invert the measured echo signal data to obtain the downhole internal magnetic field gradient distribution T2-G spectrum and downhole G spectrum;

[0065] Through core nuclear magnetic resonance experiments, the echo measurement parameters used in downhole measurements are used to measure echo train signal data, and more echo measurement parameter groups are added to measure echo train signal data to obtain experimental T2-G spectrum and experimental G spectrum;

[0066] Combining the logging data with the experimental data, the T2-G spectrum obtained by downhole measurement is corrected to obtain the corrected T2-G spectrum of the downhole internal magnetic field gradient distribution, and the corrected G spectrum of the downhole internal magnetic field gradient distribution is obtained;

[0067] Calculate the characteristic distribution value GLM of the corrected downhole internal magnetic field gradient distribution G spectrum.

[0068] Example 2

[0069] According to a specific embodiment of the present invention, the method of calculating the magnetic field gradient distribution inside the reservoir rock of the present invention is described in detail below.

[0070] The present invention provides a method for calculating the magnetic field gradient distribution inside reservoir rocks, comprising the following steps:

[0071] Using a nuclear magnetic resonance logging instrument to go down to a target layer, measuring multiple groups of echo string signal data under echo measurement parameters, wherein the multiple groups are at least three groups;

[0072] Invert the measured echo signal data to obtain the downhole internal magnetic field gradient distribution T2-G spectrum and downhole G spectrum;

[0073] Through core nuclear magnetic resonance experiments, the echo measurement parameters used in downhole measurements are used to measure echo train signal data, and more echo measurement parameter groups are added to measure echo train signal data to obtain experimental T2-G spectrum and experimental G spectrum;

[0074] Combining the logging data with the experimental data, the T2-G spectrum obtained by downhole measurement is corrected to obtain the corrected T2-G spectrum of the downhole internal magnetic field gradient distribution, and the corrected G spectrum of the downhole internal magnetic field gradient distribution is obtained;

[0075] Calculate the characteristic distribution value GLM of the corrected downhole internal magnetic field gradient distribution G spectrum.

[0076] Among them, the echo measurement parameters include waiting time and echo interval.

[0077] Adding more echo measurement parameter groups means adding shorter and longer echo interval measurement parameter groups.

[0078] The correction factor is obtained by combining the logging data with the experimental data, and the correction factor is used to correct the T2-G spectrum of the magnetic field gradient distribution inside the well.

[0079] The expression of the correction factor α is as follows:

[0080]

[0081] In the formula: a, b, c are weight coefficients, Vsh is the mud content of the formation, %; Φ is the porosity, %; p is the relative content of paramagnetic minerals, %.

[0082] Among them, the calculation formula of the underground internal magnetic field gradient distribution G spectrum before correction is as follows:

[0083]

[0084] In the formula, TE L TE Sare long echo interval and short echo interval, ms respectively; T 2L 、T 2S are the geometric mean of long echo interval and short echo interval, ms respectively; G is the G spectrum of the internal magnetic field gradient distribution downhole, G / cm; γ is the proton magnetic gyrometry ratio; and D is the fluid diffusion coefficient.

[0085] Among them, the calculation formula of the corrected underground internal magnetic field gradient distribution G spectrum is as follows:

[0086]

[0087] Where G' is the corrected magnetic field gradient distribution G spectrum inside the well.

[0088] The characteristic distribution value GLM of the corrected downhole internal magnetic field gradient distribution G spectrum is calculated using the following formula:

[0089]

[0090] Where GLM is the corrected G spectrum characteristic value of the internal magnetic field gradient distribution in the well, ms; g 1 , g 2 and g 3 are the amplitudes of the first, second and third points of the corrected downhole internal magnetic field gradient G spectrum G', respectively, n-1 is the amplitude of the n-1th point of the G spectrum G' after correction of the internal magnetic field gradient in the well, g n is the amplitude of the nth distribution point of the G spectrum G' of the corrected downhole internal magnetic field gradient, and n is the total number of distribution points.

[0091] Example 3

[0092] According to a specific embodiment of the present invention, the method of calculating the magnetic field gradient distribution inside the reservoir rock of the present invention is described in detail below.

[0093] The present invention does not require the modification of the existing hardware of the nuclear magnetic resonance logging instrument, but needs to set its measurement parameters according to the requirements of the present invention. Taking the MRILP instrument (frequency is 1 MHZ) as an example, after the instrument is debugged and lowered into the target reservoir, the first group of echo data ECHO1 is measured according to the performance index of the instrument, and the measurement parameters used are as follows: TE = 0.6 milliseconds, TW = 12000 milliseconds; NECH = 2000.

[0094] Then, the diffusion relaxation component is changed by increasing the echo interval TE, and the second group of echo train data ECHO2 is measured, and the measurement parameters are as follows: TE = 2.4 milliseconds, TW = 12000 milliseconds; NECH = 500. The diffusion relaxation component is changed by increasing the echo interval TE, and the third group of echo train data ECHO3 is measured, and the measurement parameters are as follows: TE = 7.2 milliseconds, TW = 12000 milliseconds; NECH = 166. In this way, multiple groups of echo data are obtained by setting multiple groups of different echo intervals and waiting times.

[0095] Through experiments, multiple groups of echo measurement parameters such as ECHO1, ECHO2, and ECHO3 were measured, and shorter and longer echo interval measurement groups were added (as shown in Table 1 below) to compensate for the information loss caused by the limitation of downhole parameters, and the experimental T2-G two-dimensional spectrum ( Figure 4 shown).

[0096] Table 1 Experimental measurement of 14 groups of different echo interval parameters

[0097]

[0098]

[0099] The uncorrected downhole T2-G spectrum is obtained by inverting the echo string data measured downhole using formula (2). Figure 2 ).

[0100] The T2-G spectrum measured in the laboratory is used as a label to fit the uncorrected T2-G spectrum downhole. The three coefficients a, b, and c in the correction factor α in formula (1) are fitted using the least squares method to obtain the specific values ​​of a1, b1, and c1.

[0101] Formula (3) is used to invert the downhole echo train at continuous depth segments, thus obtaining the internal magnetic field gradient distribution (T2-G spectrum) after downhole correction, as shown in Figure 3 By projecting T2-G in the G direction, the projected G spectrum is obtained, as shown in Figure 5 As shown, this is a comparison chart of the G spectrum calculated at a certain depth point in a certain well. It can be seen that the G spectrum after correction and calculation is more consistent with the G spectrum measured under laboratory conditions.

[0102] In order to more intuitively display the internal magnetic field gradient distribution characteristics of the rock, the internal magnetic field gradient distribution characteristics GLM are calculated using formula (4). Figure 6 The figure shows the internal magnetic field gradient distribution and characteristic value calculation results of continuous depth in a certain well section. The last track in the figure shows the T2-G spectrum of the continuous depth section underground, and the third track shows the internal magnetic field gradient distribution G spectrum of the continuous depth section underground, as well as the internal magnetic field distribution characteristic value GLM.

[0103] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention are included in the protection scope of the present invention.

Claims

1. A method for calculating the magnetic field gradient distribution inside reservoir rock, characterized in that: The following steps are involved: Using a nuclear magnetic resonance logging instrument to go down to a target layer, measuring multiple groups of echo string signal data under echo measurement parameters, wherein the multiple groups are at least three groups; Invert the measured echo signal data to obtain the downhole internal magnetic field gradient distribution T2-G spectrum and downhole G spectrum; Through core nuclear magnetic resonance experiments, the echo measurement parameters used in downhole measurements are used to measure echo train signal data, and more echo measurement parameter groups are added to measure echo train signal data to obtain experimental T2-G spectrum and experimental G spectrum; Combining the logging data with the experimental data to obtain a correction factor, using the correction factor to correct the internal magnetic field gradient distribution T2-G spectrum obtained by downhole measurement, to obtain a corrected downhole internal magnetic field gradient distribution T2-G spectrum, and to obtain a corrected downhole internal magnetic field gradient distribution G spectrum; Calculate the characteristic distribution value GLM of the corrected downhole internal magnetic field gradient distribution G spectrum; The expression of the correction factor α is as follows: In the formula: a, b, c are weight coefficients, Vsh is the mud content of the formation, %; Φ is the porosity, %; p is the relative content of paramagnetic minerals, %.

2. The method for calculating the magnetic field gradient distribution inside reservoir rock according to claim 1, characterized in that: Echo measurement parameters include waiting time and echo interval.

3. The method for calculating the magnetic field gradient distribution inside reservoir rock according to claim 1, characterized in that: Adding more echo measurement parameter groups means adding shorter and longer echo interval measurement parameter groups.

4. The method for calculating the magnetic field gradient distribution inside reservoir rock according to claim 1, characterized in that: The calculation formula of the G spectrum of the underground internal magnetic field gradient distribution before correction is as follows: In the formula, TE L TE S are long echo interval and short echo interval, ms respectively; T 2L 、T 2S are the geometric mean of long echo interval and short echo interval, ms respectively; G is the G spectrum of the magnetic field gradient distribution inside the well, G / cm; γ is the proton magnetic gyrometry ratio; and D is the fluid diffusion coefficient.

5. The method for calculating the magnetic field gradient distribution inside reservoir rock according to claim 4, characterized in that: The calculation formula of the corrected underground internal magnetic field gradient distribution G spectrum is as follows: Where G' is the corrected magnetic field gradient distribution G spectrum inside the well.

6. The method for calculating the magnetic field gradient distribution inside reservoir rock according to claim 5, characterized in that: The characteristic distribution value GLM of the corrected downhole internal magnetic field gradient distribution G spectrum is calculated using the following formula: Where GLM is the corrected G spectrum characteristic value of the internal magnetic field gradient distribution in the well, ms; g 1、 g2 and g3 are the amplitudes of the first, second and third points of the corrected downhole internal magnetic field gradient G spectrum G', respectively. n-1 is the amplitude of the n-1th point of the G spectrum G' after correction of the internal magnetic field gradient in the well, g n is the amplitude of the nth distribution point of the G spectrum G' of the corrected downhole internal magnetic field gradient, and n is the total number of distribution points.

7. A device for calculating the magnetic field gradient distribution inside a reservoir rock, characterized in that: It includes a processor, which executes the method for calculating the magnetic field gradient distribution inside the reservoir rock as described in any one of claims 1-6.

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