A method for oil-water two-phase NMR signal separation using dynamic nuclear polarization

Abstract

The application discloses a method for separating oil-water two-phase NMR signals by dynamic nuclear polarization, and particularly relates to the following steps: adding free radicals for enhancing the NMR signals of water phase or oil phase into a sample containing oil and water to be detected, and then performing dynamic nuclear polarization enhanced nuclear magnetic resonance analysis and detection to obtain the NMR signals of the water phase or the oil phase. The method is simple and easy to operate, short in testing time, and can efficiently separate the NMR signals of the oil-water two phases.

Description

Technical Field

[0001] This invention belongs to the field of nuclear magnetic resonance application technology, specifically relating to a method for separating oil-water two-phase NMR signals using dynamic nuclear polarization. Background Technology

[0002] With the rapid development of the world economy and the rapid depletion of global oil and gas resources, the demand for oil and gas has surged dramatically, making the need to improve oil recovery rates and develop new, efficient methods for oil and gas exploration and extraction increasingly urgent. Geological reservoirs and other porous media materials are rich in oil and gas resources, offering new possibilities for resolving the increasingly tense supply-demand imbalance. Assessing reservoir content, extracting oil and gas resources from reservoirs, and methods to improve oil recovery rates require understanding reservoir structure, wettability, and the displacement and seepage patterns of different fluid phases within the reservoir. Research on these scientific issues relies on the differentiation of different fluid phases within the material.

[0003] As an important tool for analyzing the structure and properties of materials, NMR provides a new research method for studying oil, gas, and water in reservoir rocks. High-field chemical shift spectroscopy can effectively distinguish different fluids; however, its resolution is limited in the analysis of porous materials such as rock cores due to factors such as the internal magnetic field gradient caused by the difference in magnetic susceptibility between the solid and liquid phases and magnetic field inhomogeneity. To reduce the influence of the internal magnetic field gradient, the analysis and testing of porous materials are often carried out under low-field conditions, relying on the differences in relaxation and diffusion characteristics of different fluids to distinguish them. Due to the heterogeneity of porous material structures and the differences in fluid types and distributions, the relaxation or diffusion of different fluids exhibits similar distributions, and 1D (dimension) relaxation or diffusion characterization alone cannot effectively distinguish different fluid phases. Compared with 1D methods, 2D NMR methods, such as relaxation-relaxation, relaxation-diffusion, and relaxation-gradient, can provide more information and can distinguish different fluid phases with similar relaxation or diffusion characteristics. However, due to the lower sensitivity, low-field NMR testing time is long, and 2D NMR testing time can even be 3 to 4 hours.

[0004] Furthermore, NMR data obtained by 1D or 2D low-field NMR methods require data processing, such as Laplace inverse transformation, to obtain the corresponding relaxation distribution or diffusion characteristic trends. NMR signal processing is mathematically uncertain, and the low signal-to-noise ratio broadens the relaxation distribution, even making trace components invisible. To improve the reliability of core testing structures under low-field conditions and shorten the analysis cycle, new testing and analysis methods need to be developed. Summary of the Invention

[0005] In view of the problems existing in the prior art, the present invention provides a method for separating oil-water two-phase NMR signals using dynamic nuclear polarization. The method is simple and easy to operate, has a short testing time, and can efficiently separate oil-water two-phase NMR signals.

[0006] The technical solution adopted to achieve the above-mentioned objectives of this invention is as follows:

[0007] A method for separating NMR signals between oil and water phases using dynamic nuclear polarization involves adding free radicals to the oil-containing sample to enhance the NMR signal of either the aqueous or oil phase, followed by dynamic nuclear polarization-enhanced NMR analysis to obtain the NMR signal of either the aqueous or oil phase.

[0008] The free radicals mentioned are non-selective free radicals. Non-selective free radicals can simultaneously enhance the NMR signals of the aqueous phase and the oil phase. If only the NMR signal of the aqueous phase needs to be enhanced, a relaxation reagent that can enhance the relaxation of the oil phase is added.

[0009] The free radicals mentioned are selective free radicals, which can selectively enhance the NMR signal of the aqueous phase or the oil phase. If it is necessary to enhance the NMR signal of the aqueous phase, then a selective free radical that can enhance the NMR signal of the aqueous phase is added; if it is necessary to enhance the NMR signal of the oil phase, then a selective free radical that can enhance the NMR signal of the oil phase is added.

[0010] Compared with the prior art, the beneficial effects and advantages of the present invention are as follows:

[0011] 1. This invention addresses the need for NMR signal separation in oil-water two-phase systems by combining free radicals and relaxants. Free radicals enhance the NMR signal of the fluid phase, while relaxants enhance the relaxation of the unselected fluid phase. This selectively enhances the NMR signal of the desired fluid phase and suppresses the NMR signal of the unselected fluid phase, thereby achieving the separation of the desired fluid phase NMR signal.

[0012] 2. Since DNP enhancement is related to the leakage factor of the observed nucleus, the presence of relaxant reagents can weaken the relaxation effect of free radicals on the unselected fluid phase, thereby reducing the leakage factor related to DNP and inhibiting DNP enhancement of the unselected fluid phase. Thus, when the free radicals are non-selective, relaxant reagents can effectively inhibit DNP enhancement of the unselected fluid phase, ensuring the enhancement and separation of the NMR signal of the desired fluid phase.

[0013] 3. In addition to achieving the separation of NMR signals between oil and water phases, this invention can further improve the signal-to-noise ratio of NMR signals. Moreover, the testing time is short, no inversion calculation is required, and data processing is simple and easy. Attached Figure Description

[0014] Figure 1 The figure shows the effect of the relaxant MnCl2 on the relaxation of the oil and water phases in the oil-water sample.

[0015] Figure 2 The image shows the DNP enhancement effect of the oil and water phases in an oil-water sample when the relaxant MnCl2 and the non-selective free radical TEMPO are present simultaneously.

[0016] Figure 3 The image shows the DNP enhancement effect of oil-water samples in the presence of both relaxant MnCl2 and non-selective free radical TEMPO.

[0017] Figure 4 T2 plots are shown for oil-water samples with or without DNP enhancement when the relaxant MnCl2 and the non-selective free radical TEMPO are present simultaneously.

[0018] Figure 5 The image shows the DNP enhancement effect of oil-bearing sandstone and oil-water-bearing sandstone.

[0019] Figure 6 This is a T2 distribution map of oil-bearing sandstone and water-bearing sandstone measured simultaneously with and without DNP enhancement. Detailed Implementation

[0020] The present invention will now be described in detail with reference to specific embodiments.

[0021] Samples were prepared by mixing No. 5 mineral oil with deionized water. Equal volumes of No. 5 mineral oil and water were mixed and allowed to stand to separate into layers, resulting in an oil-water sample. Tetramethylpiperidine nitride (TEMPO) was selected as a non-selective free radical, and MnCl2 was selected as a relaxor to enhance the relaxation of the aqueous phase. DNP-NMR analysis of all samples was performed on a 0.06T DNP spectrometer.

[0022] Example 1

[0023] 1. Test the T1 of the oil and water phases in the oil-water sample under a static magnetic field of 0.06T;

[0024] 2. Add MnCl2 to the oil-water sample, shake until the MnCl2 is completely dissolved, allow to stand and separate into layers to obtain mixed sample A. The concentration of MnCl2 in mixed sample A is 10 mM. Test the T1 of the oil and water phases in mixed sample A under a static magnetic field of 0.06 T. The results of two T1 tests are as follows: Figure 1 As shown, by Figure 1 It can be seen that the relaxation time of the oil phase remains unchanged before and after the addition of MnCl2, while the relaxation time of the aqueous phase changes from 3.5s to 3.2ms.

[0025] 3. TEMPO was added to mixed sample A and mixed thoroughly to obtain mixed sample B. The concentration of TEMPO in mixed sample B was 10 mM. The DNP enhancement effect of the oil-water two-phase mixture in mixed sample B was tested using a DNP single-pulse sequence. The results are as follows: Figure 2 As shown, by Figure 2 It can be seen that the maximum DNP enhancement in the aqueous phase is -0.5, meaning the signal intensity in the aqueous phase decreases. Conversely, the DNP enhancement in mineral oil is much greater than that in the aqueous phase, indicating that TEMPO and Mn... 2+ When coexisting, they can effectively suppress the enhancement of DNP in the aqueous phase, while the oil phase still has a large enhancement of DNP.

[0026] Example 2

[0027] 1. Add MnCl2 and TEMPO to the oil-water sample, shake until MnCl2 is completely dissolved, allow to stand and separate into layers to obtain a mixed sample. The concentrations of MnCl2 and TEMPO in the mixed sample are both 10 mM. The DNP enhancement effect of the mixed sample was tested using a DNP single-pulse sequence, and the DNP enhancement effect of mineral oil tested using a DNP single-pulse sequence was used as a control. The results are as follows: Figure 3 As shown, by Figure 3 It can be seen that the DNP enhancement of the mixed sample is similar to that of the mineral oil enhancement, indicating that the aqueous phase signal is suppressed and the enhanced signal of the mixed sample is basically the oil phase NMR signal.

[0028] 2. The T2 distribution of the oil-water two-phase mixture in a mixed sample at a microwave power of 10W was tested using a CPMG sequence, with the T2 distribution of the oil-water two-phase mixture in a mixed sample without DNP enhancement used as a control. The results are as follows: Figure 4 As shown, by Figure 4 As shown, with DNP enhancement, the mixed sample exhibits oil phase relaxation characteristics, further indicating that TEMPO and Mn... 2+ The combination can separate the oil phase NMR signal from the mixed sample and selectively enhance the oil phase NMR signal.

[0029] Example 3

[0030] 1. Add MnCl2 and TEMPO to the oil-water sample, shake until MnCl2 is completely dissolved, let stand to separate into layers, and obtain a mixed sample. The concentration of MnCl2 and TEMPO in the mixed sample is 10mM.

[0031] 2. Take two sandstones with a permeability of 100 md and a porosity of 10.9%. Immerse the two sandstones in the oil phase and water phase of the mixed sample, respectively, for more than 12 hours. After immersion, wipe off the excess liquid on the surface of the two sandstones and weigh them. The sandstone immersed in the water phase increased from 1062 mg to 1118 mg, with a water content of 54 mg. The sandstone immersed in the oil phase increased from 715 mg to 747 mg, with an oil content of 32 mg.

[0032] 3. The DNP enhancement effect of oil-bearing sandstone and water-bearing sandstone was simultaneously measured using a DNP single-pulse sequence, with the DNP enhancement effect of oil-bearing sandstone measured using the DNP single-pulse sequence as a control. The results are as follows: Figure 5 As shown, by Figure 5 It can be seen that the DNP enhancement measured simultaneously in oil-bearing sandstone and water-bearing sandstone is similar to that in oil-bearing sandstone. Even if the water content in the sandstone sample is higher than the oil content, it has little effect on the enhancement of the oil-water mixed sandstone sample. This indicates that the NMR signal of the oil phase in the oil-water mixed sandstone sample can be directly separated by DNP-NMR.

[0033] 4. The T2 distribution of oil and water phases in oil-bearing and water-bearing sandstones was tested using a CPMG sequence at a microwave power of 10W. The T2 distribution of oil and water phases in oil-bearing and water-bearing sandstones without DNP enhancement was used as a control. The results are as follows: Figure 6 As shown, by Figure 6 It can be seen that the relaxation distribution of both oil and water phases can be observed without ODNP enhancement, while only the T2 distribution of the oil phase is obtained when the microwave power is 10W. This further verifies that the NMR signal of the oil phase in porous media can be separated by using a combination of DNP, non-selective free radicals and aqueous phase relaxants.

Claims

1. A method for separating oil-water two-phase NMR signals using dynamic nuclear polarization, characterized in that: By adding free radicals and selective relaxation reagents to the oil-water sample to enhance the NMR signal of the aqueous or oil phase, and then performing dynamic nuclear polarization-enhanced NMR analysis, the enhanced NMR signal and separation of the oil phase can be obtained. The free radicals mentioned are non-selective free radicals. Non-selective free radicals can simultaneously cause NMR signal enhancement in both oil and water phases. Selective relaxants are used to selectively suppress the polarization enhancement of the NMR signal in the unselected aqueous phase fluid, thereby obtaining only the desired NMR signal enhancement in the oil phase fluid, thus achieving NMR signal separation between the two phase fluids. The non-selective free radical is tetramethylpiperidine nitride, and the selective relaxant is a Mn-containing free radical. 2+ Salt.

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