METHOD FOR SEPARATING OIL-WATER TWO-PHASE NMR SIGNALS BY USING DYNAMIC NUCLEAR POLARIZATION

Abstract

A method for separating oil-water two-phase NMR signals by using dynamic nuclear polarization comprising: using a combination of a non-selective free radical and a selective relaxation reagent to selectively enhance an NMR signal of an oil phase or a water phase, the relaxation reagent being capable of selectively suppressing dynamic polarization enhancement of the water phase or oil phase, thus achieving the polarization enhancement of a single fluid phase in the mixed fluid phases and realizing separation of the two-phase signals; or using a selective free radical to selectively enhance the NMR signal of the oil phase or the water phase, thus achieving the polarization enhancement of a single fluid phase in the mixed fluid phases and realizing separation of the oil-water two-phase NMR signals. The method is simple and easy to operate, has a short test time, and can efficiently separate NMR signals of oil and water phases.

Claims

1. A method for separating oil-water two-phase NMR signals by using dynamic nuclear polarization, comprising: using a combination of a non-selective free radical and a selective relaxation reagent to selectively enhance an NMR signal of an oil phase or a water phase to separate NMR signals of the oil phase and the water phase; or using a selective free radical to selectively enhance the NMR signal of the oil phase or the water phase to separate the NMR signals of the oil phase and the water phase.

2. The method for separating oil-water two-phase NMR signals by using dynamic nuclear polarization according to claim 1, wherein the non-selective free radical is soluble in the oil phase and the water phase at the same time, which causes the simultaneous enhancement of the NMR signals of the oil phase and the water phase; and the selective relaxation reagent is used to selectively accelerate relaxation of the water phase or the oil phase, thereby suppressing the polarization enhancement of the NMR signal of the water-phase or oil-phase fluid; thus, only the NMR signal enhancement of the oil phase or the water phase fluid is obtained, so as to realize the separation of NMR signals of a two-phase fluid.

3. The method for separating oil-water two-phase NMR signals by using dynamic nuclear polarization according to claim 1, wherein the selective free radical is selectively soluble in the oil phase or the water phase, so the polarization enhancement of a single fluid phase is caused when the two phases coexist; if the NMR signal of the water phase needs to be separated, a selective free radical that is able to enhance the NMR signal of the water phase is added, and if the NMR signal of the oil phase needs to be separated, a selective free radical that is able to enhance the NMR signal of the oil phase is added.

4. The method for separating oil-water two-phase NMR signals by using dynamic nuclear polarization according to claim 1, wherein the non-selective free radical is tetramethylpiperidine oxynitride, and the selective relaxation reagent is Mn.sup.2+.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0015] FIG. 1 illustrates a diagram showing the effect of a relaxation reagent MnCl.sub.2 on relaxation of oil and water phases in an oil-water sample.

[0016] FIG. 2 illustrates a DNP enhancement effect diagram of oil and water phases in the pretense of both a relaxation reagent MnCl.sub.2 and a non-selective free radical TEMPO.

[0017] FIG. 3 illustrates a DNP enhancement effect diagram of an oil-water sample in the pretense of both a relaxation reagent MnCl.sub.2 and a non-selective free radical TEMPO.

[0018] FIG. 4 illustrates T2 diagrams of an oil-water sample with and without DNP enhancement in the pretense of both a relaxation reagent MnCl.sub.2 and a non-selective free radical TEMPO.

[0019] FIG. 5 illustrates a DNP enhancement effect diagram of oil-containing sandstone and oil-water-containing sandstone.

[0020] FIG. 6 illustrates T.sub.2 distribution diagrams measured simultaneously for oil-water-containing sandstone with and without DNP enhancement.

DETAILED DESCRIPTION OF THE INVENTION

[0021] The invention will be described in detail below with reference to specific embodiments.

[0022] 5# mineral oil and deionized water are used to prepare samples: equal volumes of 5# mineral oil and water are mixed and the mixture is rested for layering to obtain oil-water samples; TEMPO (tetramethylpiperidine oxynitride) is used as a non-selective free radical and MnCl.sub.2 is selected as a relaxation reagent to enhance the relaxation of the water phase. DNP-NMR analysis and detection of all samples are performed on a 0.06 T DNP spectrometer.

EXAMPLE 1

[0023] 1. T.sub.1 distributions of oil and water phases in the oil-water sample are tested at a 0.06 T static magnetic field.

[0024] 2. MnCl.sub.2 is added to the oil-water sample and oscillated to be completely dissolved, and then rested for layering to obtain a mixed sample A. The concentration of MnCl.sub.2 in the mixed sample A is 10 mM. T.sub.1 distributions of oil and water phases in the mixed sample A are tested under a 0.06 T static magnetic field. The results of the two tests are shown in FIG. 1. From FIG. 1, it can be seen that before and after the addition of MnCl.sub.2, the relaxation time of the oil phase remains unchanged, and the relaxation of the water phase changes from 3.5 s to 3.2 ms.

[0025] 3. TEMPO is added to the mixed sample A and mixed evenly to obtain a mixed sample B. The concentration of TEMPO in the mixed sample B is 10 mM. The single pulse sequence with DNP is used to test the enhancement effects of the oil and water phases in the mixed sample B. The results are shown in the FIG. 2. From FIG. 2, it can be seen that the maximum DNP enhancement of the water phase is −0.5, that is, the signal intensity of the water phase is reduced. On the contrary, the DNP enhancement of mineral oil is much greater than that of the water phase, indicating that the coexistence of TEMPO and Mn.sup.2+ can effectively suppress the DNP enhancement of the water phase, while the oil phase still has a larger DNP enhancement.

EXAMPLE 2

[0026] 1. MnCl.sub.2 and TEMPO are added to an oil-water sample and oscillated until MnCl.sub.2 is completely dissolved, and then the resulting solution is rested for layering to obtain a mixed sample. The concentrations of MnCl.sub.2 and TEMPO in the mixed sample are both 10 mM. The DNP single pulse sequence is used to test the DNP enhancement effect of the mixed sample, and the DNP enhancement effect of mineral oil tested by the DNP single pulse sequence is used as a reference. Results are shown in FIG. 3. From FIG. 3, it can be seen that the DNP enhancement of the mixed sample is similar to that of mineral oil, indicating that the signal of the water phase is suppressed, and the signal of the mixed sample after the enhancement is basically an NMR signal of the oil phase.

[0027] 2. A CPMG sequence is used to test T.sub.2 distributions of oil and water phases in the mixed sample under a microwave power of 10 W, and the T.sub.2 distributions of the oil and water phases in the mixed sample without DNP enhancement are used as a reference. Results are shown in FIG. 4. From FIG. 4, it can be seen that the mixed sample exhibits oil-phase relaxation characteristics with the presence of DNP, which further indicates that the combination of TEMPO and Mn.sup.2+ can separate the NMR signal of the oil phase from the mixed sample and selectively enhance the NMR signal of the oil phase.

EXAMPLE 3

[0028] 1. MnCl.sub.2 and TEMPO are added to an oil-water sample and oscillated until MnCl.sub.2 is completely dissolved, and then the resulting solution is rested for layering to obtain a mixed sample. The concentrations of MnCl.sub.2 and TEMPO in the mixed sample are both 10 mM.

[0029] 2. Two pieces of sandstones with a permeability of 100 md and a porosity of 10.9% are taken and separately soaked in oil and water phases of the mixed sample for more than 12 hours. Then, the excess liquid on the surfaces of the two pieces of sandstones is wiped off and the sandstones are weighed. The weight of the sandstone soaked in the water phase increases from 1062 mg to 1118 mg, and the water content is 54 mg; the weight of the sandstone soaked in the oil phase increases from 715 mg to 747 mg, and the oil content is 32 mg.

[0030] 3. A DNP single pulse sequence is used to test the DNP enhancement effects of the oil-containing sandstone and the oil-water-containing sandstone (oil-containing sandstone and water-containing sandstone placed together) at the same time, and the DNP enhancement effect of the oil-containing sandstone tested by using the DNP single pulse sequence is used as a reference. Results are shown in FIG. 5. From FIG. 5, it can be seen that the DNP enhancement effects of the oil-containing sandstone and the oil-water-containing sandstone tested at the same time are similar to the DNP enhancement effect of the oil-containing sandstone. Even if the water content in the sandstone sample is higher than the oil content, it will have little influence on the enhancement of the oil-water-containing sandstone sample, which indicates that the NMR signal of the oil phase in the oil-water-containing sandstone sample can be directly separated by DNP-NMR.

[0031] 4. A CPMG sequence is used to test T.sub.2 distributions of oil and water phases in the oil-water-containing sandstone under a microwave power of 10 W, and the T.sub.2 distributions of the oil and water phases in the oil-water-containing sandstone without DNP enhancement are used as a reference. Results are shown in FIG. 6. From FIG. 6, it can be seen that without ODNP enhancement, the relaxation distributions of the oil and water phases can be seen, while, only the T.sub.2 distribution of the oil phase is obtained at the presence of microwave, which can further verify that the combination of DNP, a non-selective free radical, and a water-phase relaxation reagent can separate the NMR signal of the oil phase in the porous medium material.