A multi-dimensional nuclear magnetic resonance method and device for rapidly evaluating shale organic matter

Abstract

The present invention provides a multi-dimensional nuclear magnetic resonance method for rapidly evaluating organic matter in shale. The method includes the following steps: designing a nuclear magnetic resonance pulse sequence and collecting data to obtain nuclear magnetic resonance data; processing the nuclear magnetic resonance data to obtain T<subgt;1< / subgt>-T<subgt;2< / subgt;<supgt;*< / supgt> imaging; interpreting the nuclear magnetic resonance data and correlating it with organic matter. Further, a device for rapidly evaluating organic matter in shale is provided. This application can rapidly evaluate the distribution and overall content of organic matter in shale, and can provide rapid imaging for nuclear magnetic resonance instruments with different field strengths and different configurations, and is used to precisely measure the organic matter content and spatial distribution in samples of tight shale oil and gas reservoirs. This application can rapidly and non-destructively analyze to obtain the T<subgt;1< / subgt> and T<subgt;2* values and imaging results of tight shale samples, and further can characterize important information such as the internal structure, micropore characteristics, and occurrence status of saturated fluids in the samples, and has important application value in the analysis of complex samples in unconventional oil and gas reservoirs.

Description

Technical Field

[0001] This application relates to the field of nuclear magnetic resonance, and particularly to a multi-dimensional nuclear magnetic resonance method and device for rapidly evaluating shale organic matter. Background Art

[0002] As an advanced non-destructive detection means, nuclear magnetic resonance imaging technology has extremely wide applications in many fields such as medicine, biology, energy, materials, agriculture and forestry, food, safety monitoring, and chemical engineering. Taking biomedical as an example, due to the differences in the longitudinal relaxation times of different types of tissue fluids, nuclear magnetic resonance T1 imaging technology can provide the most direct and effective evidence for in-situ detection of the lesion mechanism of biological tissues, so it is a conventional nuclear magnetic resonance weighted imaging method. Nevertheless, since the conventional method has a long detection time for the longitudinal relaxation time T1, usually the hydrogen proton spin system in the tissue needs to reach thermal equilibrium before the next measurement can be carried out, so the overall measurement time of the T1 imaging technology for the sample to be measured is very long (for example, Chinese Patent CN112710688A). At the same time, T2* differences can also be used to a certain extent to distinguish sample components and identify fluid types and phases.

[0003] Therefore, providing a multi-dimensional nuclear magnetic resonance method for rapidly evaluating shale organic matter, improving the detection speed and efficiency of nuclear magnetic resonance imaging technology, and breaking through the dilemmas such as long test cycles and low accuracy of conventional organic matter content tests have become urgent problems to be solved by those skilled in the art. Summary of the Invention

[0004] The embodiments of this application provide a multi-dimensional nuclear magnetic resonance method for rapidly evaluating shale organic matter to improve the detection speed and efficiency of nuclear magnetic resonance imaging technology.

[0005] In a first aspect, a multi-dimensional nuclear magnetic resonance method for rapidly evaluating shale organic matter, the method includes the following steps:

[0006] S1: Design of nuclear magnetic resonance pulse sequence and data acquisition to obtain nuclear magnetic resonance data M(k z , NΔ, Sε);

[0007] S2: Process the nuclear magnetic resonance data M(k z , NΔ, Sε) to obtain T1-T2 * imaging

[0008] S3: Interpretation of nuclear magnetic resonance data and association with organic matter.

[0009] Further, step S1 includes the following steps:

[0010] S1.1: Apply a 90° radio frequency pulse to the hydrogen proton spin system of the sample under test on the TRS channel to rotate the macroscopic magnetization vector M0 to the transverse plane, obtaining the transverse plane magnetization vector;

[0011] S1.2: After waiting for a very short time τ, apply a 180° radio frequency pulse to the hydrogen proton spin system of the sample under test on the TRS channel again to refocus the dephased transverse plane magnetization vector;

[0012] S1.3: After waiting for a very short time τ again, apply a 90° radio frequency pulse to the hydrogen proton spin system of the sample under test on the TRS channel to rotate the refocused transverse plane magnetization vector 90° to the longitudinal axis;

[0013] S1.4: Apply a gradient pulse with a constant amplitude to the spin system on the GRD channel, and the gradient pulse is used to eliminate the magnetization vector still remaining in the transverse plane in the spin system;

[0014] S1.5: Then apply a small angle α radio frequency pulse to the spin system on the TRS channel, and then apply a phase encoding gradient pulse to the spin system on the GRD channel. The width of the phase encoding gradient pulse is δ, and the amplitude varies from -g max to +g max in m steps;

[0015] S1.6: After the application of the phase encoding gradient pulse is completed, apply a 180° radio frequency pulse to the spin system on the TRS channel again. After a certain time, a free induction decay signal FID is collected on the ACQ channel. The number of recording points of the free induction decay signal FID is S, and the time interval between the recording points is ε;

[0016] S1.7: After the collection of the free induction decay signal FID is completed, apply a 180° radio frequency pulse to the spin system on the TRS channel again to flip the magnetization vector remaining in the longitudinal direction; then apply a gradient pulse with a constant amplitude to the spin system on the GRD channel to eliminate the magnetization vector still remaining in the transverse plane in the spin system;

[0017] S1.8: Repeat steps S1.5 - S1.7 N times, and N free induction decay signals FID are sequentially collected on the ACQ channel. At the same time, the amplitude of the phase encoding gradient pulse on the GRD channel is changed m times. Finally, m * N free induction decay signals FID will be collected on the ACQ channel. Each free induction decay signal FID contains S data points, and finally a nuclear magnetic resonance data M(k z , NΔ, Sε) is obtained.

[0018] Further, the response formula of the nuclear magnetic resonance data M(k z , NΔ, Sε) is as follows:

[0019]

[0020] where k z is the wave function, N is the number of repetitions of steps S1.5 - S1.7, Δ is the time interval between two adjacent small-angle α radio frequency pulses in step S1.8, S is the number of recording points of the free induction decay signal FID, ε is the time interval between the recording points of the free induction decay signal FID, is the T1-T2 * imaging result, K1, K2, K3 are three kernel functions, z is the direction vector, T1 is the longitudinal relaxation time, is the transverse relaxation time;

[0021] The specific forms of the wave function k z and the three kernel functions K1, K2, K3 are:

[0022] k z = γg max δ / mπ

[0023] K1 = exp(i2πk z z)

[0024]

[0025]

[0026] where γ is the gyromagnetic ratio, g max is the maximum amplitude of the phase encoding gradient pulse, δ is the phase encoding gradient pulse width, m is the number of steps of the amplitude change of the phase encoding gradient pulse, and α is the angle of the small-angle radio frequency pulse.

[0027] Further, step S2 includes the following steps:

[0028] S2.1: Perform Fourier transform on the nuclear magnetic resonance data M(k z , NΔ, Sε), and decode the data in the imaging dimension to obtain m original attenuation data M(NΔ, Sε);

[0029] S2.2: Perform data fitting on the obtained original attenuation data M(NΔ, Sε) at any position in space to obtain the T1-T2 * distribution;

[0030] S2.3: Repeat step S2.2 continuously for m times, and perform ILT data processing on the data at each position in the space in sequence. Finally, obtain the continuous (T1 - T2 * ) distribution along the axial direction of the sample to be measured, and obtain the final T1 - T2 * imaging

[0031] Furthermore, the data fitting in step S2.2 includes single-exponential fitting, multi-exponential fitting, and Inverse Laplace inversion.

[0032] Furthermore, step S3 includes the following steps:

[0033] The homonuclear coupling and heteronuclear coupling effects of the hydrogen nuclei of organic matter in shale samples are completely different from those of the mobile fluid components, resulting in different T1 / T2 * ratios of organic matter and mobile fluid. By accumulating the signals shown in the (T1 - T2 * ) distribution within each rock slice, the relative contents of organic matter and mobile fluid in this layer are obtained;

[0034] Continuously identify and calculate the contents of organic matter and mobile fluid in m spectra along the axial direction, and the organic matter content profile and mobile fluid profile of the shale can be obtained.

[0035] In a second aspect, an apparatus for rapidly evaluating shale organic matter mainly includes the following modules:

[0036] A data acquisition module, configured to design a nuclear magnetic resonance pulse sequence and acquire data, and obtain nuclear magnetic resonance data M(k z , NΔ, Sε);

[0037] A data processing module, configured to process the nuclear magnetic resonance data M(k z , NΔ, Sε), and obtain T1 - T2 * imaging

[0038] A data interpretation module, configured to interpret nuclear magnetic resonance data and correlate it with organic matter.

[0039] In a third aspect, an electronic device includes:

[0040] A processor;

[0041] A memory, on which executable instructions are stored, and the executable instructions are executed by the processor, causing the electronic device to execute the steps of the multi-dimensional nuclear magnetic resonance method.

[0042] Fourthly, a computer-readable storage medium has executable instructions stored thereon, and when the instructions are executed, the steps of the multi-dimensional nuclear magnetic resonance method are implemented.

[0043] Based on the above technical solutions, the present application achieves the following technical effects.

[0044] (1) Starting from the perspective of quantum mechanics, by elaborating the basic theory, the corresponding pulses are reasonably arranged and optimized at different time periods of the pulse sequence, greatly shortening the operation time of the nuclear magnetic resonance T1 imaging technology; at the same time, the detection of the T2* parameter is increased in the fast T1 editing segment, and the organic matter content and movable fluid content of shale are quantitatively identified through T1 / T2* in the two-dimensional spectrum. The data collected by this technical solution is different from the conventional method and special attention needs to be paid in the actual data processing process.

[0045] (2) The present application proposes a data processing method and an interpretation workflow for the proposed fast nuclear magnetic resonance T1-T2* imaging technology, improving the detection speed and efficiency of the nuclear magnetic resonance imaging technology, and at the same time having the potential to solve problems such as long testing cycle and low accuracy of conventional organic matter content testing, and being able to be applied in the field of unconventional oil and gas reservoirs.

[0046] (3) The present application proposes a new type of multi-dimensional nuclear magnetic resonance technology. By correlating two characteristic relaxation times with the imaging editing segment, the organic matter content at the spatial imaging layer can be effectively obtained. At the same time, the spatial detection of the organic matter content can be completed with the help of the imaging technology, so it is an effective and fast detection method for detecting samples of unconventional tight oil and gas reservoirs. Description of the Drawings

[0047] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for the description of the embodiments will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments recorded in the present application. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0048] Figure 1 The nuclear magnetic resonance pulse sequence designed for a multi-dimensional nuclear magnetic resonance method for rapidly evaluating shale organic matter provided by the embodiment of the present application;

[0049] Figure 2 The data processing flow chart of a multi-dimensional nuclear magnetic resonance method for rapidly evaluating shale organic matter provided by the embodiment of the present application;

[0050] Figure 3 The schematic diagram of detecting rock samples and results of a multi-dimensional nuclear magnetic resonance method for rapidly evaluating shale organic matter provided by the embodiment of the present application;

[0051] Figure 4 Schematic diagram of a multi-dimensional nuclear magnetic resonance method for rapidly evaluating organic matter in shale to identify the content of organic matter and mobile fluid at a certain position in the shale space;

[0052] Figure 5 Schematic diagram of a cross-section of the content of organic matter and mobile fluid in the axial direction of the shale space identified by a multi-dimensional nuclear magnetic resonance method for rapidly evaluating organic matter in shale provided by an embodiment of the present application;

[0053] Figure 6 Schematic diagram of the structure of an electronic device provided by an embodiment of the present application;

[0054] Among them, TRS - Pulse emission channel; GRD - Gradient pulse emission channel; ACQ - Signal reception channel; 1 - First slice; 2 - Second slice; 3 - Third slice; 600 - Electronic device; 601 - Processor; 602 - Memory; 603 - Communication unit. Detailed implementation manners

[0055] In order to better understand the technical solution of the present application, the embodiments of the present application will be described in detail below with reference to the accompanying drawings.

[0056] It should be clear that the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present application without creative efforts shall fall within the protection scope of the present application.

[0057] The terms used in the embodiments of the present application are only for the purpose of describing specific embodiments, and are not intended to limit the present application. The singular forms of "a", "the" and "said" used in the embodiments of the present application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise.

[0058] First, the definitions and physical meanings of the relevant technical terms involved in the present application are introduced as follows.

[0059] Static magnetic field B0. The static magnetic field is provided by the magnet and determines the signal-to-noise ratio of the nuclear magnetic resonance signal. The sample to be measured is placed in the static magnetic field, and energy level splitting occurs in the spin system, and a macroscopic magnetization vector M0 will be generated along the direction of the static magnetic field. The macroscopic magnetization vector M0 is determined by parameters such as the static magnetic field strength B0 and temperature. The magnet materials usually include permanent magnets and superconductors. Permanent magnets are basically used for low-field nuclear magnetic resonance measurements; superconductors are usually used in medical imaging and chemical spectroscopy analysis of high-field instruments in laboratories, and liquid helium and liquid nitrogen are required to keep the magnet temperature constant.

[0060] RF Magnetic Field B1 and Pulses. RF pulses are electromagnetic signals, usually generated by coils. The magnetic field generated by RF pulses is the RF magnetic field. The direction of the RF magnetic field is perpendicular to the direction of the static magnetic field, achieving the rotation operation of the magnetization vector formed in the static magnetic field. The rotation angle θ is: θ = γB1t p . Where γ is the gyromagnetic ratio, B1 is the RF magnetic field strength, and t p is the duration of the RF pulse. Therefore, the purpose of changing the rotation angle can be achieved by controlling the amplitude or duration of the RF pulse. The nuclear magnetic resonance pulse sequence consists of RF pulses with different numbers and frequency attributes according to the set timing. By adjusting the time interval between pulses, the pulse angle, and the frequency selectivity of the pulses, measurements of relaxation, diffusion, etc. of the spin system can be realized.

[0061] Magnetic Field Gradient and Imaging. The pulsed magnetic field gradient is generated by the gradient coil. Usually, the eddy current effect between the pulsed gradient coil and the RF coil is considered during the application process, and attention is paid to the shielding effect. Through the relationship between the spatial magnetic field strength and the gradient value, corresponding spatial phase, frequency, and slice encoding can be performed on the measured sample to achieve spatial imaging in different dimensions. For a certain direction of the spatial position, taking z as an example, after applying a gradient pulse with an amplitude of g in this direction, the Larmor frequencies of protons at different spatial positions are:

[0062] ω(z) = γB0 + γgz

[0063] Therefore, the mutual relationship between the acquired echo signal and the imaging proton density sought in space is:

[0064] M(k) = ∫ε(z)e i2πkz dz

[0065] ε(z) = ∫M(k)e -i2πkz dk

[0066] Where k is the defined wave function, which is related to the parameters of the gradient pulse. When the system performs an imaging experiment in the frequency encoding mode, k = γg max δ / 2π; when using phase encoding, k = γg max δ / mπ. From the above formulas, it can be seen that M(k) and ε(z) are a Fourier transform pair. Therefore, performing a Fourier transform on the acquired echo signal can obtain the imaging result. By using the frequency gradient encoding and phase gradient encoding modes and methods in combination, the nuclear magnetic resonance imaging result in high dimensions can be obtained.

[0067] Free Induction Decay Signal FID. FID is one of the most common signals in nuclear magnetic resonance measurements. First, a 90° pulse is applied to the sample to be measured, and the magnetization vector M0 is rotated to the transverse plane perpendicular to the direction of the static magnetic field. Due to reasons such as molecular diffusion and the spatial inhomogeneity of the static magnetic field, the magnetization vector M0 undergoes dephasing. If the signal acquisition channel is opened to collect the signal during this period, a free decay signal can be obtained. During the acquisition process, by adjusting parameters such as the number of acquisition points and the time interval between acquisition points, the width of the acquisition window can be controlled. The decay rate of the FID signal is characterized by the parameter T2*, and it has the following important applications in nuclear magnetic resonance applications: (1) Complete the evaluation of magnetic field uniformity and shimming strategy through the duration of the FID signal; (2) Obtain the chemical spectrum through the FID signal to evaluate the components and contents of each functional group; (3) Obtain the difference in magnetic susceptibility through the decay of the FID signal to characterize the magnetic characteristics of the solid skeleton of the sample; (4) Obtain the phase difference through the decay of the FID signal to characterize the mobility and viscosity of the components.

[0068] Relaxation. The process by which a spin system returns from the resonance state to the thermal equilibrium state. This process is characterized by the longitudinal relaxation time T1 or the transverse relaxation time T2 in different directions. T1 is also called the spin-lattice relaxation time, which reflects the energy exchange between the spin system and the external environment. T2 is also called the spin-spin relaxation time, which reflects the internal energy loss of the spin system. The relaxation process of the spin system can be described by the Bloch equation. The longitudinal relaxation time T1 can be measured using a saturation recovery pulse sequence. By changing the time interval T W between two pulses and recording the signal amplitude, the evolution process of the longitudinal magnetization vector at different editing times can be reflected:

[0069]

[0070] The above method takes a long time. At each step of T W , the proton spin system needs to wait for a long time and reach the thermal equilibrium state before the next experiment can be carried out. Therefore, the acquisition process is extremely slow.

[0071] Example 1

[0072] This embodiment of the present application provides a multi-dimensional nuclear magnetic resonance method for quickly evaluating shale organic matter, and the method includes the following steps:

[0073] S1: Design of nuclear magnetic resonance pulse sequence and data acquisition to obtain nuclear magnetic resonance data M(k z , NΔ, Sε);

[0074] S2: Process the nuclear magnetic resonance data M(k z , NΔ, Sε) to obtain T1-T2 * imaging

[0075] S3: Interpretation of nuclear magnetic resonance data and correlation with organic matter.

[0076] Among them, refer to Figure 1 The nuclear magnetic resonance pulse sequence designed according to a multi-dimensional nuclear magnetic resonance method for rapidly evaluating shale organic matter provided by an embodiment of the present application as shown. Step S1 may include the following steps.

[0077] S1.1: Apply a 90° radio frequency pulse to the hydrogen proton spin system of the sample to be measured on the TRS channel to rotate the macroscopic magnetization vector M0 to the transverse plane, obtaining a transverse plane magnetization vector;

[0078] S1.2: After waiting for a very short time τ, apply a 180° radio frequency pulse to the hydrogen proton spin system of the sample to be measured on the TRS channel again to refocus the dephased transverse plane magnetization vector;

[0079] S1.3: After waiting for a very short time τ again, apply a 90° radio frequency pulse to the hydrogen proton spin system of the sample to be measured on the TRS channel to rotate the refocused transverse plane magnetization vector 90° to the longitudinal axis, and the rotated magnetization vector is in the same direction as the static magnetic field direction;

[0080] S1.4: Apply a gradient pulse with a constant amplitude to the spin system on the GRD channel, and the gradient pulse is used to eliminate the magnetization vector remaining in the transverse plane in the spin system;

[0081] S1.5: Then apply a small angle α radio frequency pulse to the spin system on the TRS channel, and then apply a phase encoding gradient pulse to the spin system on the GRD channel. The width of the phase encoding gradient pulse is δ, and the height varies from -g max to +g max for m steps;

[0082] S1.6: After the phase encoding gradient pulse is applied, apply a 180° radio frequency pulse to the spin system on the TRS channel again. After a certain time, a free induction decay signal FID is collected on the ACQ channel. In practice, it is necessary to record the full waveform of the FID. The number of recording points is S, and the time interval between points is ε;

[0083] S1.7: After the signal acquisition on the ACQ channel is completed, apply a 180° radio frequency pulse to the spin system on the TRS channel again to flip the magnetization vector remaining in the longitudinal direction. Then, apply a gradient pulse with a constant amplitude to the spin system on the GRD channel again, which is used to eliminate the magnetization vector remaining in the transverse plane in the spin system;

[0084] S1.8: From the first small-angle α radio-frequency pulse on the TRS channel to the last gradient with a constant amplitude on the GRD channel, the entire timing duration is Δ. The acquisition system continuously loops through this part of the timing N times, and N FID signals are acquired in one go in the ACQ channel. The phase-encoding gradient amplitude value in the GRD gradient is changed m times, and finally m*N FID signals are acquired in the ACQ channel. Each FID signal contains S data points. By performing nuclear magnetic resonance data processing on the acquired echo train signals, we can obtain the desired fast nuclear magnetic resonance T1-T2* imaging results.

[0085] Further, the length range of the extremely short time τ is 10 - 30 us, preferably 1 - 3 times the width of the radio-frequency pulse.

[0086] Further, the amplitude range of the gradient pulse with a constant amplitude is 0.5 - 10 mT / m, which is to be determined according to the actual situation.

[0087] Further, the angle range of the small angle α is 3 - 10 degrees, which is to be determined according to the actual situation.

[0088] The imaging technique of this application is based on a fast T1 editing method, and the final measurement result is obtained by collecting a train of small-angle α radio-frequency pulses. By applying this train of pulses containing N small-angle radio-frequency pulses, the components of the magnetization vector of the spin system of the measured sample itself can be expressed as:

[0089]

[0090]

[0091] where M xy is the magnetization vector in the transverse plane, M z is the longitudinal magnetization vector, Δ is the time interval between two adjacent small-angle α radio-frequency pulses, T1 is the longitudinal relaxation time, M0 is the macroscopic magnetization vector, and α is the angle of the small-angle radio-frequency pulse.

[0092] By using the relevant adapted radio-frequency pulse phase cycling and the amplitude of the acquired signal, the magnetization vector under each small-angle α radio-frequency pulse can be obtained as:

[0093]

[0094] where M(NΔ) is the magnetization vector under each small-angle α radio-frequency pulse, M0 is the macroscopic magnetization vector, α is the angle of the small-angle radio-frequency pulse, N is the number of small-angle α radio-frequency pulses, Δ is the time interval between two adjacent small-angle α radio-frequency pulses, and T1 is the longitudinal relaxation time.

[0095] Compared with the conventional T1 measurement method, since only one operation is performed on the longitudinal magnetization vector, the above method can complete the T1 measurement in a shorter time.

[0096] For T2 * measurement, this parameter can be obtained by processing each acquired FID signal. Its mathematical correlation can be expressed as:

[0097]

[0098] where M(Sε) is the magnetization vector corresponding to the time point Sε, M0 is the macroscopic magnetization vector, S is the number of recording points of the free induction decay signal FID, ε is the time interval between the recording points of the free induction decay signal FID, is the transverse relaxation time.

[0099] The tight shale sample in this application is a tight pore material. Due to the different spin system environments of the movable fluid and the hydrogen-containing components in the organic matter, the longitudinal relaxation time T1 and the transverse relaxation time T2 * exhibited by different components are relatively obvious. Therefore, in this application, by combining weighted information with imaging technology, cross-scale observation of the macro and micro aspects of the sample to be measured is achieved. If conventional T1 and T2 * measurement methods are combined with imaging, the actual measurement time is relatively long, which is not conducive to quickly dynamically observing the information of the sample itself. Therefore, in this application, the fast longitudinal relaxation time T1 measurement and the fast transverse relaxation time T2 * measurement methods are integrated with relevant imaging technologies. Under the step of optimizing and adjusting relevant parameters, a feasible solution for fast multi-dimensional nuclear magnetic resonance T1-T2 * imaging technology is given.

[0100] According to the mutual relationship between measuring the longitudinal relaxation time T1, the transverse relaxation time T2 * of the sample to be measured and spatial gradient encoding, this embodiment designs a fast nuclear magnetic resonance T1-T2 Figure 1 imaging pulse sequence as shown in * and obtains the following response formula by collecting signals:

[0101]

[0102] where k z is the wave function, N is the number of small-angle α radio frequency pulses, Δ is the time interval between two adjacent small-angle α radio frequency pulses, S is the number of recording points of the free induction decay signal FID, ε is the time interval between the recording points of the free induction decay signal FID, is the T1-T2 * imaging result, K1, K2, K3 are three kernel functions, and z is the direction vector.

[0103] The specific forms of the three kernel functions K1, K2, and K3 are as follows:

[0104] K1 = exp(i2πk z z)

[0105]

[0106]

[0107] where k z is the wave function, z is the direction vector, α is the angle of the small-angle radiofrequency pulse, N is the number of small-angle α radiofrequency pulses, Δ is the time interval between two adjacent small-angle α radiofrequency pulses, T1 is the longitudinal relaxation time, S is the number of recording points of the free induction decay signal FID, ε is the time interval between the recording points of the free induction decay signal FID, and is the transverse relaxation time.

[0108] For the phase encoding mode as shown in Figure 1 in this application, k z = γg max δ / mπ, where δ is the width of the phase encoding gradient pulse, g max is the highest amplitude of the phase encoding gradient pulse, and m is the number of steps of the amplitude change of the phase encoding gradient pulse.

[0109] This application obtains multi-dimensional data by changing the number of steps of the gradient amplitude m, the number of small-angle α radiofrequency pulses N in T1 editing, and the number of acquisition points S in each FID signal. The obtained data is processed using subsequent data inversion steps to obtain the T1-T2 * imaging result of the sample to be measured.

[0110] Example 2

[0111] There are relatively more spatial dimensions and data dimensions involved in this method. Therefore, targeted processing is required during the actual operation process. On the basis of Example 1, this example refers to Figure 2 the data processing flow chart of a multi-dimensional nuclear magnetic resonance method for rapidly evaluating shale organic matter provided in the embodiments of this application as shown. Step S2 may include the following steps.

[0112] Arrange the dimensions of the nuclear magnetic resonance data M(k z , NΔ, Sε) collected, and determine that the final data size is m * N * S, where m is the number of phase encoding steps, N is the number of FID signals collected in each phase encoding step, and S is the number of acquisition points in each FID signal;

[0113] S2.1: For M(k z,NΔ,Sε) data is first Fourier-transformed, and the data is decoded in the imaging dimension to obtain m original M(NΔ,Sε) attenuation data. The Fourier transform is a linear transform and is a non-ill-posed problem, which will not be elaborated in this embodiment.

[0114] S2.2: Perform data fitting on the decoded two-dimensional data at each position in the obtained space to obtain the T1-T2 * distribution. Specific data fitting algorithms are divided into multiple types, including single-exponential fitting, multi-exponential fitting, and Inverse Laplace inversion, to obtain the T1-T2 at different spatial positions finally * distribution. Since the Inverse Laplace inversion is an ill-posed problem, the Inverse Laplace transform will be briefly described here. A regularization term will be introduced to invert this data matrix. To obtain a stable and accurate solution F, the Tikhonov regularization method is usually adopted, and a smoothing term is introduced to solve this problem:

[0115]

[0116] where s is the regularization factor, which is related to the signal-to-noise ratio of the acquired data, and the ||·|| term represents the Frobenius norm of the matrix. The introduced regularization term determines the stability and accuracy of the solution. If the regularization factor is selected too large, although the obtained distribution is more stable, the accuracy of the solution is worse, that is, the so-called over-smoothing; if the regularization factor is selected too small, the solution is more accurate, but the stability of the solution is reduced, and more pseudo signals appear, that is, under-smoothing. Therefore, considering the authenticity and stability of the solution comprehensively and using a reasonable regularization factor is the key point of this method. Through the non-negativity constraint step, the non-negativity constraint solution F(T1,T2 * ) at each spatial layer under a specific regularization factor s can be obtained.

[0117] S2.3: Continuously repeat the above steps m times, perform ILT data processing on the data at each point in the space in turn, and finally obtain the continuous (T1-T2 * ) distribution along the axial direction of the sample to obtain the final T1-T2 * imaging

[0118] Embodiment III

[0119] On the basis of Embodiment II, this embodiment further proposes specific steps for interpreting nuclear magnetic resonance data and associating it with organic matter.

[0120] Refer to Figure 3Schematic diagram of a rock sample and its results detected by a multi-dimensional nuclear magnetic resonance method for rapidly evaluating shale organic matter according to an embodiment of the present application. Among them, the three bands in the left figure are the first slice 1, the second slice 2, and the third slice 3, respectively representing the positions of local rock slices after spatial imaging editing. Layers 1, 2, and 3 in the right figure respectively represent the (T1-T2 * ) distribution inside the corresponding rock slices.

[0121] Furthermore, the (T1-T2 * ) distribution inside each rock slice is as Figure 4 shown. Due to the homonuclear coupling and heteronuclear coupling effects of the hydrogen nuclei of the organic matter in the shale sample being completely different from those of the mobile fluid components, the T1 / T2 * ratios of these two components are different. Therefore, this parameter difference can be used to quickly and non-destructively identify the organic matter components. By accumulating the signals shown in the spectrum, the relative contents of the organic matter and the mobile fluid at this horizon can be obtained.

[0122] Furthermore, continuously, by continuously identifying and calculating the contents of the organic matter and the mobile fluid in m spectra along the axial direction, the organic matter content profile and the mobile fluid profile of the shale can be obtained, as Figure 5 shown.

[0123] Conventional methods for detecting shale organic matter require grinding and destroying the samples, and performing multiple pyrolysis and pickling on the processed samples to obtain the shale organic matter content. Therefore, the conventional methods have low working efficiency and poor detection accuracy. At the same time, only the volume organic matter content of the samples can be obtained, and the spatial distribution of the organic matter cannot be obtained. The present application proposes a new type of multi-dimensional nuclear magnetic resonance technology. By correlating two characteristic relaxation times and imaging editing segments, the organic matter content at the spatial imaging horizon can be effectively obtained. At the same time, with the help of imaging technology, the spatial detection of the organic matter content can be completed. Therefore, it is an effective and rapid detection method for detecting samples of unconventional tight oil and gas reservoirs.

[0124] Example 4

[0125] Corresponding to Examples 1 to 3, the present application also provides a device for rapidly evaluating shale organic matter. The device mainly includes the following modules:

[0126] A data acquisition module, used for designing a nuclear magnetic resonance pulse sequence and acquiring data to obtain nuclear magnetic resonance data M(k z ,NΔ,Sε);

[0127] A data processing module, used for processing the nuclear magnetic resonance data M(k z ,NΔ,Sε) to obtain T1-T2 * imaging

[0128] A data interpretation module for nuclear magnetic resonance data interpretation and association with organic matter.

[0129] It should be noted that the specific content involved in this embodiment can be referred to the description of the above method embodiment. For the sake of brevity, it will not be repeated here.

[0130] See Figure 6 , which is a schematic structural diagram of an electronic device provided by an embodiment of the present application. As Figure 6 shown, the electronic device may specifically include a processor 601, a memory 602, and a communication unit 603. These components communicate through one or more buses. Those skilled in the art can understand that the structure of the electronic device shown in the figure does not constitute a limitation to the embodiment of the present application. It can be a bus structure, a star structure, and may also include more or fewer components than shown in the figure, or combine some components, or different component arrangements.

[0131] Among them, the communication unit 603 is used to establish a communication channel so that the electronic device can communicate with other devices.

[0132] The processor 601 is the control center of the electronic device, connecting various parts of the entire electronic device through various interfaces and lines. By running or executing software programs and / or modules stored in the memory 602, and calling data stored in the memory, to execute various functions of the electronic device and / or process data. The processor may be composed of an integrated circuit (IC). For example, it may be composed of a single packaged IC, or composed of multiple packaged ICs with the same or different functions connected. For example, the processor 601 may only include a central processing unit (CPU). In the embodiment of the present application, the CPU may be a single operation core or may include multiple operation cores.

[0133] The memory 602 is used to store the execution instructions of the processor 601. The memory 602 can be implemented by any type of volatile or non-volatile storage device or a combination thereof, such as static random access memory (SRAM), electrically erasable programmable read-only memory (EEPROM), erasable programmable read-only memory (EPROM), programmable read-only memory (PROM), read-only memory (ROM), magnetic memory, flash memory, magnetic disk or optical disk.

[0134] When the execution instructions in the memory 602 are executed by the processor 601, the electronic device 600 can execute some or all of the steps in the above method embodiment.

[0135] Corresponding to the above embodiments, an embodiment of the present application further provides a computer-readable storage medium, where the computer-readable storage medium may store a program, and when the program runs, it can control the device where the computer-readable storage medium is located to execute some or all of the steps in the above method embodiments. In a specific implementation, the computer-readable storage medium may be a magnetic disk, an optical disk, a read-only memory (ROM for short), a random access memory (RAM for short), or the like.

[0136] Corresponding to the above embodiments, an embodiment of the present application further provides a computer program product, which includes executable instructions. When the executable instructions are executed on a computer, the computer is enabled to execute some or all of the steps in the above method embodiments.

[0137] Those of ordinary skill in the art can realize that the various units and algorithm steps described in the embodiments disclosed herein can be implemented by a combination of electronic hardware, computer software, and electronic hardware. Whether these functions are executed in a hardware or software manner depends on the specific application and design constraints of the technical solution. Professional technicians can use different methods to implement the described functions for each specific application, but such implementation should not be considered to exceed the scope of the present application.

[0138] Those skilled in the art can clearly understand that for the convenience and simplicity of description, the specific working processes of the systems, devices, and units described above can refer to the corresponding processes in the foregoing method embodiments, and will not be elaborated herein again.

[0139] In several embodiments provided by the present application, if any function is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on such an understanding, the technical solution of the present application, in essence, or the part that contributes to the prior art or a part of the technical solution can be embodied in the form of a software product. The computer software product is stored in a storage medium and includes several instructions for causing a computer device (which may be a personal computer, a server, or a network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of the present application. The foregoing storage medium includes: various media such as a USB flash drive, a mobile hard disk, a read-only memory (ROM for short), a random access memory (RAM for short), a magnetic disk, or an optical disk that can store program codes.

[0140] The above are only specific embodiments of the present application. Any person skilled in the art within the technical scope disclosed in the present application can easily think of changes or substitutions, which should all be covered within the protection scope of the present application. The protection scope of the present application shall be subject to the protection scope of the claimed rights.

Claims

1. A multi-dimensional nuclear magnetic resonance method for rapidly evaluating organic matter in shale, characterized in that The method includes the following steps: S1: Designing a nuclear magnetic resonance pulse sequence and collecting data to obtain nuclear magnetic resonance data M; S2: Process the nuclear magnetic resonance data M to obtain a T1-T2 * imaging F; T1 is the longitudinal relaxation time, and T2 is the transverse relaxation time; S3: Interpreting the nuclear magnetic resonance data and correlating it with organic matter; Step S1 includes the following steps: S1.1: Applying a 90° radio frequency pulse to the hydrogen proton spin system of the sample to be measured on the TRS channel to rotate the macroscopic magnetization vector M0 to the transverse plane, obtaining a transverse plane magnetization vector; S1.2: After waiting for a very short time τ, applying a 180° radio frequency pulse to the hydrogen proton spin system of the sample to be measured on the TRS channel again to refocus the dephased transverse plane magnetization vector; S1.3: After waiting for a very short time τ again, applying a 90° radio frequency pulse to the hydrogen proton spin system of the sample to be measured on the TRS channel to rotate the refocused transverse plane magnetization vector 90° to the longitudinal axis; S1.4: Applying a gradient pulse with a constant amplitude to the spin system on the GRD channel, and the gradient pulse is used to eliminate the magnetization vector still remaining in the transverse plane in the spin system; S1.5: Then, apply a small-angle α radio frequency pulse to the spin system on the TRS channel, and then apply a phase encoding gradient pulse to the spin system on the GRD channel. The width of the phase encoding gradient pulse is δ, and the amplitude varies from -g max to +g max in m steps; S1.6: After the phase encoding gradient pulse is applied, applying a 180° radio frequency pulse to the spin system on the TRS channel again. After a certain time, a free induction decay signal FID is collected on the ACQ channel. The number of recording points of the free induction decay signal FID is S, and the time interval between recording points is ε; S1.7: After the free induction decay signal FID is collected, applying a 180° radio frequency pulse to the spin system on the TRS channel again to flip the magnetization vector remaining in the longitudinal direction; then applying a gradient pulse with a constant amplitude to the spin system on the GRD channel to eliminate the magnetization vector still remaining in the transverse plane in the spin system; S1.8: Repeat steps S1.5 - S1.7 for N times, and successively acquire N free induction decay signals FID in the ACQ channel. At the same time, change the amplitude of the phase encoding gradient pulse on the GRD channel for m times. Finally, m * N free induction decay signals FID will be acquired on the ACQ channel. Each free induction decay signal FID contains S data points, and finally a nuclear magnetic resonance data M with a data size of m * N * S is obtained. The nuclear magnetic resonance data M includes k z , NΔ, and Sε, where k z is the wave function, and Δ is the time interval between two adjacent small angle α radio frequency pulses in step S1.8; The response formula of the nuclear magnetic resonance data M is as follows: Among them, F is from T1 to T2 * For imaging, K1, K2, and K3 are three kernel functions, z is the direction vector, T1 is the longitudinal relaxation time, and T2 is the transverse relaxation time; Wave function k z and the specific forms of the three kernel functions K1, K2, and K3 are as follows: k z = γg max δ / mπ K1 = exp(i2πk z z) where γ is the gyromagnetic ratio, g max is the maximum amplitude of the phase-encoding gradient pulse, δ is the width of the phase-encoding gradient pulse, m is the number of steps of the amplitude change of the phase-encoding gradient pulse, and α is the angle of the small-angle radiofrequency pulse.

2. A multi-dimensional nuclear magnetic resonance method for rapidly evaluating shale organic matter according to claim 1, characterized in that, Step S2 includes the following steps: S2.1: Performing Fourier transform on the nuclear magnetic resonance data M and decoding the data in the imaging dimension to obtain m original decay data; S2.2: Perform data fitting on the original attenuation data at any position in the obtained space to obtain the T1-T2 * distribution; S2.3: Repeat step S2.2 continuously for m times, and perform ILT data processing on the data at each position in the space in sequence, finally obtaining continuous T1-T2 along the axial direction of the measured sample, and obtaining the final T1-T2 * distribution, and obtaining the final T1-T2 * imaging F.

3. A multi-dimensional nuclear magnetic resonance method for rapidly evaluating shale organic matter according to claim 2, characterized in that, The data fitting in step S2.2 includes single-exponential fitting, multi-exponential fitting, and Inverse Laplace inversion.

4. A multi-dimensional nuclear magnetic resonance method for rapidly evaluating shale organic matter according to claim 2, characterized in that Step S3 includes the following steps: The homonuclear coupling and heteronuclear coupling effects of the organic matter hydrogen nuclei in the shale samples are completely different from those of the mobile fluid components, resulting in different T1 / T2 * ratios between the organic matter and the mobile fluid. By accumulating the signals shown in the T1-T2 * distribution within each rock slice, the relative contents of the organic matter and the mobile fluid in this layer can be obtained. Continuously identifying and calculating the organic matter and movable fluid content in m spectra along the axial direction, and the organic matter content profile and movable fluid profile of the shale can be obtained.

5. An apparatus for rapidly evaluating organic matter in shale, characterized in that, The device mainly includes the following modules: A data acquisition module, used for designing a nuclear magnetic resonance pulse sequence and collecting data to obtain nuclear magnetic resonance data M; A data processing module for processing the nuclear magnetic resonance data M to obtain a T1-T2 * imaging F; T1 is the longitudinal relaxation time, and T2 is the transverse relaxation time; A data interpretation module, used for interpreting nuclear magnetic resonance data and correlating it with organic matter; Designing a nuclear magnetic resonance pulse sequence and collecting data to obtain nuclear magnetic resonance data M, including the following steps: S1.1: Applying a 90° radio frequency pulse to the hydrogen proton spin system of the sample to be measured on the TRS channel to rotate the macroscopic magnetization vector M0 to the transverse plane, obtaining a transverse plane magnetization vector; S1.2: After waiting for a very short time τ, applying a 180° radio frequency pulse to the hydrogen proton spin system of the sample to be measured on the TRS channel again to refocus the dephased transverse plane magnetization vector; S1.3: After waiting for another extremely short time τ, apply a 90° radio frequency pulse to the hydrogen proton spin system of the sample under test on the TRS channel to flip the refocused transverse plane magnetization vector by 90° to the longitudinal axis; S1.4: Apply a gradient pulse with a constant amplitude to the spin system on the GRD channel, and the gradient pulse is used to eliminate the magnetization vector still remaining in the transverse plane of the spin system; S1.5: Then, apply a small-angle α radiofrequency pulse to the spin system on the TRS channel, and then apply a phase-encoding gradient pulse to the spin system on the GRD channel. The width of the phase-encoding gradient pulse is δ, and its amplitude varies from -g max to +g max in m steps; S1.6: After the phase encoding gradient pulse is applied, apply a 180° radio frequency pulse to the spin system on the TRS channel. After a certain time, a free induction decay signal FID is collected on the ACQ channel. The number of recording points of the free induction decay signal FID is S, and the time interval between recording points is ε; S1.7: After the free induction decay signal FID is collected, apply a 180° radio frequency pulse on the TRS channel to flip the magnetization vector remaining in the longitudinal direction; then apply a gradient pulse with a constant amplitude on the GRD channel to eliminate the magnetization vector still remaining in the transverse plane of the spin system; S1.8: Repeat steps S1.5 - S1.7 for N times, and sequentially acquire N free induction decay signals FID in the ACQ channel. At the same time, change the amplitude of the phase encoding gradient pulse on the GRD channel for m times. Finally, m * N free induction decay signals FID will be acquired on the ACQ channel. Each free induction decay signal FID contains S data points, and finally a nuclear magnetic resonance data M with a data size of m * N * S is obtained; the nuclear magnetic resonance data M includes k z , NΔ, and Sε, where k z is the wave function, and Δ is the time interval between two adjacent small - angle α radio frequency pulses in step S1.8; The response formula of the nuclear magnetic resonance data M is as follows: where F is T1 - T2 * imaging, K1, K2, and K3 are three kernel functions, z is the direction vector, T1 is the longitudinal relaxation time, and T2 is the transverse relaxation time; Wave function k z and the specific forms of the three kernel functions K1, K2, and K3 are as follows: k z = γg max δ / mπ K1 = exp(i2πk z z) where γ is the gyromagnetic ratio, g max is the maximum amplitude of the phase-encoding gradient pulse, δ is the width of the phase-encoding gradient pulse, m is the number of steps of the amplitude change of the phase-encoding gradient pulse, and α is the angle of the small-angle radiofrequency pulse.

6. An electronic device, characterized in that, The device includes: A processor; A memory, on which executable instructions are stored. The executable instructions are executed by the processor, causing the electronic device to execute the steps of the multi-dimensional nuclear magnetic resonance method according to any one of claims 1 to 4.

7. A computer-readable storage medium, characterized in that, On which executable instructions are stored, and when the instructions are executed, the steps of the multi-dimensional nuclear magnetic resonance method according to any one of claims 1 to 4 are implemented.

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