CN109060861B - Permanent magnet device of nuclear magnetic resonance fluid metering instrument and metering method - Google Patents
Permanent magnet device of nuclear magnetic resonance fluid metering instrument and metering method Download PDFInfo
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Abstract
The invention provides a permanent magnet device of a nuclear magnetic resonance fluid metering instrument and a metering method, wherein the permanent magnet device comprises two sections of pre-polarized magnets and a section of main magnet which are coaxially arranged in sequence; the pre-polarized magnet and the main magnet are both of circular tubular structures, and a central cavity is a fluid flowing channel; equivalent models on axial sections of the pre-polarized magnet and the main magnet are both magnets with opposite N poles and S poles; the pre-polarizing magnet is rotatable along its central axis. The pre-polarizing magnet of the permanent magnet device can generate a certain magnetization effect on fluid with short longitudinal relaxation time no matter the direction of the magnetic field is the same or opposite, so that the length of the main magnet can not be too long. The change of the effective length of the pre-polarized magnet can be realized only by one layer of magnet structure, the overall length of the permanent magnet device is shortened, and the structure is more compact and simple.
Description
Technical Field
The invention belongs to the technical field of nuclear magnetic resonance, and particularly relates to a permanent magnet device of a nuclear magnetic resonance fluid metering instrument and a metering method.
Background
In the process of oil and natural gas production management, the proportion and the flow rate of oil, gas and water contained in the mixed fluid produced by the oil and gas well often change in real time along with time, and even indexes such as viscosity, temperature, pressure and the like of the oil and gas can also change along with the change. The conventional online detection multiphase fluid meter is a gamma ray-based radiodensity method, which utilizes the difference of absorption capacities of different substances to gamma rays, so as to calculate the proportion of each phase fluid in a mixed fluid. However, gamma fluid meters contain nuclear sources of radiation and present a safety hazard with leaks. In addition, the gamma ray fluid measuring instrument needs to calibrate the sample in a laboratory in advance before working, so that the oil gas property can not be identified timely, effectively and accurately under the condition that the oil gas property changes in real time. In order to replace the conventional gamma ray fluid meter, other multiphase fluid metering schemes have been proposed internationally, and the most typical one is multiphase fluid metering method based on the physical principle of nuclear magnetic resonance.
However, the permanent magnet device in the existing nuclear magnetic resonance fluid meter is long in length, large in magnet consumption and high in cost. In addition, the magnet is complex in structure, large in size and overweight, and is not beneficial to operation and use of the instrument.
Disclosure of Invention
Aiming at the defects in the prior art, the invention provides the permanent magnet device of the nuclear magnetic resonance fluid metering instrument, which has the advantages of compact and simple structure and shorter length.
Another object of the present invention is to provide a method for measuring the nuclear magnetic resonance fluid meter.
In a first aspect, a permanent magnet device of a nuclear magnetic resonance fluid meter comprises two sections of pre-polarized magnets and a section of main magnet which are coaxially arranged in sequence;
the main magnet also comprises a measuring antenna;
the pre-polarized magnet and the main magnet are both of circular tubular structures, and a central cavity is a fluid flowing channel; equivalent models on axial sections of the pre-polarized magnet and the main magnet are both magnets with opposite N poles and S poles; the pre-polarizing magnet is rotatable along its central axis.
Furthermore, the pre-polarized magnet and the main magnet both adopt a monopole cylindrical Halbach permanent magnet array structure.
Further, the two sections of pre-polarized magnets are the same in shape; and circular tube-shaped magnetic shielding layers are arranged outside the pre-polarized magnet and the main magnet.
In a second aspect, a metering method of a nuclear magnetic resonance fluid meter includes the steps of:
rotating the pre-polarized magnets in the permanent magnet device to enable the directions of the magnetic fields generated by the two pre-polarized magnets and the main magnet to be the same;
flowing fluid to be tested through a pre-polarized magnet and a main magnet, and defining a magnetization vector generated by magnetic field magnetization as a first magnetization vector; the fluid to be tested comprises two components: a first component and a second component;
a main magnet measuring antenna detects a nuclear magnetic signal of a fluid to be measured, and the nuclear magnetic signal is defined as a first nuclear magnetic signal;
keeping the directions of the magnetic fields generated by the second section of pre-polarized magnet and the main magnet the same, and rotating the first section of pre-polarized magnet to enable the directions of the magnetic fields generated by the two pre-polarized magnets to be opposite;
flowing fluid to be tested through a pre-polarized magnet and a main magnet, and defining a magnetization vector generated by magnetic field magnetization as a second magnetization vector;
the main magnet measuring antenna detects a nuclear magnetic signal of the fluid to be measured, and the nuclear magnetic signal is defined as a second nuclear magnetic signal;
and calculating the ratio of the two components in the fluid to be detected according to the first nuclear magnetic signal and the second nuclear magnetic signal.
Further, assume that the ratio of the first component in the fluid to be measured is λoThe ratio of the second component in the fluid to be measured is λw＝1-λo；
When the directions of the magnetic fields generated by the two pre-polarizing magnets and the main magnet are the same,
the fluid to be measured passes through the magnetization vector M generated by the first section of pre-polarized magnetz(t1) Comprises the following steps:
wherein, t1The time required for the fluid to be measured to pass through the first pre-polarizing magnet, T1 wIs the longitudinal relaxation time, T, of the second component1 oIs the longitudinal relaxation time of the first component, Mz o(t) is the magnetization vector of the first component in the fluid to be measured at the moment t,
the magnetization vector of a second component in the fluid to be measured at the time t;
is the saturation magnetization vector of the oil,
is the saturation magnetization vector of water;
pre-polarizing the fluid to be measured by a second stageMagnetization vector M generated by magnetz(t1+t2) Comprises the following steps:
wherein, t2The time required for the fluid to be measured to pass through the second section of pre-polarized magnet;
the magnetization vector produced by the fluid to be measured when it passes through the main magnet measuring antenna, i.e. the first magnetization vector Mz(t1+t2+t3) Comprises the following steps:
wherein, t3The time required for the fluid to be measured to pass through the measuring antenna from entering the main magnet;
the y function is obtained by:
the following equation was constructed:
will be provided with
And
and substituting the formula, and extracting a formula to obtain a y function.
Further, when the magnetic fields generated by the two pre-polarizing magnets are in opposite directions,
the fluid to be measured passes through the magnetization vector M generated by the first section of pre-polarized magnetz′(t1) Comprises the following steps:
flow to be measuredThe magnetization vector M of the body generated by the second segment of the pre-polarized magnetz′(t1+t2) Comprises the following steps:
the magnetization vector of the fluid to be measured, i.e. the second magnetization vector M, generated when it passes through the main magnet measuring antennaz′(t1+t2+t3) Comprises the following steps:
wherein the y' function is obtained by:
the following equation was constructed:
will be provided with
And
and (4) obtaining a y' function by inputting the formula and extracting the formula.
Further, the calculating the ratio of the first component and the second component in the fluid to be measured according to the first nuclear magnetic signal and the second nuclear magnetic signal specifically includes:
the following equation was constructed:
wherein S is a first nuclear magnetic signal, S/Is the second nuclear magnetic signal.
In a third aspect, a metering method of a nuclear magnetic resonance fluid meter includes the steps of:
rotating the pre-polarized magnets in the permanent magnet device to enable the directions of the magnetic fields generated by the two pre-polarized magnets and the main magnet to be the same;
flowing fluid to be tested through a pre-polarized magnet and a main magnet, and defining a magnetization vector generated by magnetic field magnetization as a first magnetization vector; the fluid to be tested comprises three components;
a main magnet measuring antenna detects a nuclear magnetic signal of a fluid to be measured, and the nuclear magnetic signal is defined as a first nuclear magnetic signal;
keeping the directions of the magnetic fields generated by the second section of pre-polarized magnet and the main magnet the same, and rotating the first section of pre-polarized magnet to enable the directions of the magnetic fields generated by the two pre-polarized magnets to be opposite;
flowing fluid to be tested through a pre-polarized magnet and a main magnet, and defining a magnetization vector generated by magnetic field magnetization as a second magnetization vector;
the main magnet measuring antenna detects a nuclear magnetic signal of the fluid to be measured, and the nuclear magnetic signal is defined as a second nuclear magnetic signal;
keeping the directions of the magnetic fields generated by the first section of pre-polarized magnet and the main magnet the same, and rotating the second section of pre-polarized magnet to enable the direction of the magnetic field generated by the second section of pre-polarized magnet to be opposite to the direction of the magnetic field generated by the main magnet;
flowing fluid to be tested through a pre-polarized magnet and a main magnet, and defining a magnetization vector generated by magnetic field magnetization as a third magnetization vector;
a main magnet measuring antenna detects a nuclear magnetic signal of the fluid to be measured, and the nuclear magnetic signal is defined as a third nuclear magnetic signal;
and calculating the proportion of the three components in the fluid to be detected according to the first nuclear magnetic signal, the second nuclear magnetic signal and the third nuclear magnetic signal.
According to the technical scheme, the pre-polarized magnet can generate a certain magnetization effect on fluid with short longitudinal relaxation time no matter the direction of the magnetic field of the pre-polarized magnet is the same or opposite, so that the length of the main magnet can be not too long. The change of the effective length of the pre-polarized magnet can be realized only by one layer of magnet structure, the overall length of the permanent magnet device is shortened, and the structure is more compact and simple.
According to the metering method provided by the invention, the proportion of each component in the mixed fluid can be calculated according to the nuclear magnetic signal difference under different pre-polarization conditions.
Drawings
In order to more clearly illustrate the detailed description of the invention or the technical solutions in the prior art, the drawings that are needed in the detailed description of the invention or the prior art will be briefly described below. Throughout the drawings, like elements or portions are generally identified by like reference numerals. In the drawings, elements or portions are not necessarily drawn to scale.
Fig. 1 is a schematic structural diagram of a permanent magnet device according to a first embodiment.
Fig. 2 is a flowchart of a method provided in the second embodiment.
Fig. 3 is a schematic structural diagram of the rotating pre-polarizing magnet in two cases provided in the second embodiment. Wherein (a) is a permanent magnet device in which the pre-polarized magnets produce magnetic fields in the same direction; (b) permanent magnet means for generating magnetic fields of opposite directions for the pre-polarizing magnets;
fig. 4 shows the static magnetic field intensity generated in the cavity by the pre-polarized magnet in two cases provided by the second embodiment, wherein the abscissa is distance and the ordinate is magnetic induction intensity. Wherein (a) is the static magnetic field intensity of the same direction magnetic field generated by the pre-polarized magnet; (b) static magnetic field strength to produce opposite magnetic fields for the pre-polarized magnet;
fig. 5 shows the magnetization vector change of oil and water for two cases as provided in example two. Wherein (a) the pre-polarized magnet generates magnetization vector changes of magnetic fields in the same direction; (b) generating magnetization vector changes of magnetic fields with opposite directions for the pre-polarized magnet;
fig. 6 is a flowchart of a method according to the fourth embodiment.
Detailed Description
Embodiments of the present invention will be described in detail below with reference to the accompanying drawings. The following examples are only for illustrating the technical solutions of the present invention more clearly, and therefore are only examples, and the protection scope of the present invention is not limited thereby. It is to be noted that, unless otherwise specified, technical or scientific terms used herein shall have the ordinary meaning as understood by those skilled in the art to which the invention pertains.
Spin is an intrinsic property of the microscopic particle, and the particle with non-zero spin is in the external magnetic field B0Under the magnetization of the magnetic field, a net magnetic moment is generated, and the magnetic moment performs Larmor precession along the direction of the external magnetic field. When a pulse radio frequency field B which is orthogonal to the direction of the external magnetic field and has the frequency consistent with the larmor precession frequency of the magnetic moment is applied1When the magnetic resonance is generated, a large number of spin particles are transferred from a low energy level to a high energy level, and resonance absorption occurs, which is called a nuclear magnetic resonance phenomenon. When the radio frequency field is removed, the spin particles at the high energy level release energy to return to the low energy state, and the evolution process is called relaxation process. At present, the most widely used and mature pulse NMR technique is used to detect the NMR relaxation process of various substances. The relaxation process of nuclear magnetic resonance is divided into two types: one is the longitudinal relaxation process, which represents the process by which a substance is magnetized in an external magnetic field, characterized by a longitudinal relaxation time T1(ii) a The other is transverse relaxation process, which represents the evolution process of the magnetization vector under the interaction of the spin particles and is characterized by transverse relaxation time T2。
The first embodiment is as follows:
a permanent magnet device of a nuclear magnetic resonance fluid meter is disclosed, referring to fig. 1, and comprises two sections of pre-polarized magnets 1 and a section of main magnet 3 which are coaxially arranged in sequence;
the main magnet also comprises a measuring antenna 5, and the coil structure of the measuring antenna 5 is in a solenoid shape;
in particular, the measurement antenna is used to detect nuclear magnetic signals of the fluid.
The pre-polarized magnet 1 and the main magnet 3 are both of circular tubular structures, and a cavity in the center is a fluid flowing channel 2; equivalent models on axial sections of the pre-polarized magnet 1 and the main magnet 3 are magnets with opposite N poles and S poles; the pre-polarizing magnet 1 is able to rotate along its central axis.
Specifically, the pre-polarized magnet magnetizes a fluid, and the fluid evolves according to a longitudinal relaxation law to generate a magnetization vector M, which is detected in the main magnet and has a magnitude proportional to the nuclear magnetic signal intensity. The pre-polarizing magnet is capable of rotating along its central axis, changing the direction of the magnetic field of the pre-polarizing magnet.
The pre-polarizing magnet in the permanent magnet device can generate a certain magnetization effect on fluid with short longitudinal relaxation time no matter the direction of the magnetic field is the same or opposite, so that the length of the main magnet can not be too long. The change of the effective length of the pre-polarized magnet can be realized only by one layer of magnet structure, the overall length of the permanent magnet device is shortened, and the structure is more compact and simple.
Further, the pre-polarized magnet 1 and the main magnet 3 both adopt a monopole cylindrical Halbach permanent magnet array structure.
Specifically, the Halbach permanent magnet array structure comprises a series of magnetic blocks arranged according to a specific magnetization direction and a nonmagnetic metal framework required by the fixation of the magnetic blocks. The unipolar cylindrical Halbach array can generate a uniform static magnetic field in a channel where fluid flows, and the Halbach array is the key for generating a uniform magnetic field.
Further, the two sections of pre-polarized magnets 1 are the same in shape; and the external parts of the pre-polarized magnet 1 and the main magnet 3 are respectively provided with a tubular magnetic shielding layer 4.
Specifically, the magnetic shield layer is a substance of high magnetic permeability, such as soft iron. The magnetic shielding layer can block the interference of static magnetic field to external equipment and can play the role of internal shimming. Example two:
the second embodiment provides a method for testing a fluid to be tested with two components by using the nuclear magnetic resonance fluid meter.
A method of metering a nuclear magnetic resonance fluid meter, see fig. 2, comprising the steps of:
s1: referring to fig. 3(a), the pre-polarized magnets in the permanent magnet device are rotated so that the directions of the magnetic fields generated by the two pre-polarized magnets and the main magnet are the same;
s2: flowing fluid to be tested through a pre-polarized magnet and a main magnet, and defining a magnetization vector generated by magnetic field magnetization as a first magnetization vector; the fluid to be tested comprises two components: a first component and a second component;
s3: a main magnet measuring antenna detects a nuclear magnetic signal of a fluid to be measured, and the nuclear magnetic signal is defined as a first nuclear magnetic signal;
specifically, the fluid to be measured may be a fluid containing two components whose longitudinal relaxation times are greatly different. Such as a fluid containing both oil and water components. Both oil and water are rich in hydrogen atoms, the hydrogen nuclei are particles of spin 1/2, and are also the most common subject of nmr studies. The hydrogen atoms in the two substances have distinctly different longitudinal relaxation times due to the difference of molecular structures and chemical environments. Typical T of, among others, underground mineralized water1Values of about 1-2 s are typical for mobile oils1The value is generally about 100 to 300 ms.
When the magnetization directions of the two sections of pre-polarized magnets are the same, the fluid is always polarized along the same magnetization direction, the pre-polarized magnets are in a completely effective condition, the oil and the water are simultaneously magnetized, and finally the measured nuclear magnetic signal is a mixed signal containing the oil and the water, which not only depends on the proportion of the oil and the water, but also depends on the degree of magnetization of the oil and the water. The strength of the static magnetic field generated in the cavity by the pre-polarized magnet is shown in fig. 4 (a); magnetization vector generating Process of oil and Water referring to FIG. 5(a)
S4: referring to fig. 3(b), keeping the direction of the magnetic field generated by the second pre-polarized magnet and the main magnet the same, rotating the first pre-polarized magnet to make the direction of the magnetic field generated by the two pre-polarized magnets opposite;
s5: flowing fluid to be tested through a pre-polarized magnet and a main magnet, and defining a magnetization vector generated by magnetic field magnetization as a second magnetization vector;
s6: the main magnet measuring antenna detects a nuclear magnetic signal of the fluid to be measured, and the nuclear magnetic signal is defined as a second nuclear magnetic signal; the strength of the static magnetic field generated in the cavity by the pre-polarized magnet is shown in fig. 4 (b). Magnetization vector generating Process of oil and Water referring to FIG. 5(b)
Specifically, when the magnetization directions of the two sections of pre-polarized magnets are opposite, the fluid is polarized in one magnetization direction and then polarized in the opposite magnetization direction. When the magnetization directions are opposite, the oil can be slightly magnetized, the water can be slightly magnetized, and the nuclear magnetic signal of the water is relatively small.
S7: and calculating the ratio of the two components in the fluid to be detected according to the first nuclear magnetic signal and the second nuclear magnetic signal.
According to the method, the proportion of oil and water in the mixed fluid can be calculated according to the nuclear magnetic signal difference under different pre-polarization conditions. Example three:
the third embodiment is added with the following contents on the basis of the second embodiment:
for hydrogen-rich species, it follows the static magnetic field B0Magnetization vector M of directionzStrictly satisfies bloch's equation:
Mz(t)＝Mz(0)e-t/T+M0(1-e-t/T)；
wherein M isz(0) Representing the magnetization vector at time zero, M0Representing the saturation magnetization vector, T is the longitudinal relaxation time of the substance.
Assuming that the volume occupied by the fluid to be measured is 1, and assuming that the proportion of the first component in the fluid to be measured is lambdaoThe ratio of the second component in the fluid to be measured is λw＝1-λo；
1. When the directions of the magnetic fields generated by the two pre-polarizing magnets and the main magnet are the same,
the fluid to be measured passes through the magnetization vector M generated by the first section of pre-polarized magnetz(t1) Comprises the following steps:
wherein, t1The time required for the fluid to be measured to pass through the first pre-polarizing magnet, T1 wIs the longitudinal relaxation time, T, of the second component1 oIs the longitudinal relaxation time of the first component,
the magnetization vector of the first component in the fluid to be measured at the time t,
the magnetization vector of a second component in the fluid to be measured at the time t;
is the saturation magnetization vector of the oil,
is the saturation magnetization vector of water.
The fluid to be measured passes through the magnetization vector M generated by the second-stage pre-polarized magnetz(t1+t2) Comprises the following steps:
wherein, t2The time required for the fluid to be measured to pass through the second section of pre-polarized magnet;
the magnetization vector produced by the fluid to be measured when it passes through the main magnet measuring antenna, i.e. the first magnetization vector Mz(t1+t2+t3) Comprises the following steps:
wherein, t3The time required for the fluid to be measured to pass through the measuring antenna from entering the main magnet;
the y function is obtained by:
the following equation was constructed:
will be provided with
And
and substituting the formula, and extracting a formula to obtain a y function.
2. When the magnetic fields generated by the two pre-polarizing magnets are in opposite directions,
the fluid to be measured passes through the magnetization vector M generated by the first section of pre-polarized magnetz′(t1) Comprises the following steps:
the fluid to be measured passes through the magnetization vector M generated by the second-stage pre-polarized magnetz′(t1+t2) Comprises the following steps:
the magnetization vector of the fluid to be measured, i.e. the second magnetization vector M, generated when it passes through the main magnet measuring antennaz′(t1+t2+t3) Comprises the following steps:
wherein the y' function is obtained by:
the following equation was constructed:
will be provided with
And
and (4) obtaining a y' function by inputting the formula and extracting the formula.
Specifically, when the magnetization directions are opposite, the magnetization vector increases from zero in one direction and then in the opposite direction, see fig. 5 (b). Due to the longitudinal relaxation time T of the oil1 oThe time is short, and the time is short,
close to the value of zero is obtained,
close to unit 1. While the longitudinal relaxation time T of water1 wThe time is long, and the time is long,
close to the value of 1, the number of the channels,
it is close to zero. This shows that when the magnetization direction is opposite, the magnetization to water of pre-polarization magnet has greatly reduced, but still has certain magnetization to oil, and this has increased the contrast of profit signal undoubtedly, can further shorten the length of main magnet simultaneously, practices thrift more volume, weight, cost.
Further, the calculating the ratio of the first component and the second component in the fluid to be measured according to the first nuclear magnetic signal and the second nuclear magnetic signal specifically includes:
the following equation was constructed:
wherein S is a first nuclear magnetic signal, S/Is the second nuclear magnetic signal.
Specifically, Mz、Mz' are both defined expressions, so f is also a defined functional expression. Thus, under two pre-polarized magnet working modes, the oil-water ratio is brought into an equation set, and the magnetization vector is proportional to the nuclear magnetic signal intensity. Thus, the division of the measured signals in the two modes yields a signal containing only one unknown number λoThe equation of (a) is given,solving it obtains the fluid proportion of each phase of the mixed fluid.
For the sake of brief description, the method provided by the embodiment of the present invention may refer to the corresponding contents in the foregoing method embodiments.
Example four:
example four provides a method of testing a fluid comprising three components using the nmr fluid meter described above.
A method of metering a nuclear magnetic resonance fluid meter, see fig. 6, comprising the steps of:
s11: rotating the pre-polarized magnets in the permanent magnet device to enable the directions of the magnetic fields generated by the two pre-polarized magnets and the main magnet to be the same;
s12: flowing fluid to be tested through a pre-polarized magnet and a main magnet, and defining a magnetization vector generated by magnetic field magnetization as a first magnetization vector; the fluid to be tested comprises three components;
s13: a main magnet measuring antenna detects a nuclear magnetic signal of a fluid to be measured, and the nuclear magnetic signal is defined as a first nuclear magnetic signal;
s14: keeping the directions of the magnetic fields generated by the second section of pre-polarized magnet and the main magnet the same, and rotating the first section of pre-polarized magnet to enable the directions of the magnetic fields generated by the two pre-polarized magnets to be opposite;
s15: flowing fluid to be tested through a pre-polarized magnet and a main magnet, and defining a magnetization vector generated by magnetic field magnetization as a second magnetization vector;
s16: the main magnet measuring antenna detects a nuclear magnetic signal of the fluid to be measured, and the nuclear magnetic signal is defined as a second nuclear magnetic signal;
s17: keeping the directions of the magnetic fields generated by the first section of pre-polarized magnet and the main magnet the same, and rotating the second section of pre-polarized magnet to enable the direction of the magnetic field generated by the second section of pre-polarized magnet to be opposite to the direction of the magnetic field generated by the main magnet;
s18: flowing fluid to be tested through a pre-polarized magnet and a main magnet, and defining a magnetization vector generated by magnetic field magnetization as a third magnetization vector;
s19: a main magnet measuring antenna detects a nuclear magnetic signal of the fluid to be measured, and the nuclear magnetic signal is defined as a third nuclear magnetic signal;
s20: and calculating the proportion of the three components in the fluid to be detected according to the first nuclear magnetic signal, the second nuclear magnetic signal and the third nuclear magnetic signal.
Specifically, when measuring a fluid to be measured containing three components, the component ratio of the fluid to be measured can be measured by rotating the direction of the pre-magnetized magnet to form 3 magnetization processes.
For the sake of brief description, the method provided by the embodiment of the present invention may refer to the corresponding contents in the foregoing method embodiments.
Finally, it should be noted that: the above embodiments are only used to illustrate the technical solution of the present invention, and not to limit the same; while the invention has been described in detail and with reference to the foregoing embodiments, it will be understood by those skilled in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; such modifications and substitutions do not depart from the spirit and scope of the present invention, and they should be construed as being included in the following claims and description.
Claims (1)
1. A metering method of a nuclear magnetic resonance fluid meter is characterized by comprising the following steps:
rotating the pre-polarized magnets in the permanent magnet device to enable the directions of the magnetic fields generated by the two pre-polarized magnets and the main magnet to be the same; the permanent magnet device comprises two sections of pre-polarized magnets and a section of main magnet which are coaxially arranged in sequence; the main magnet also comprises a measuring antenna; the pre-polarized magnet and the main magnet are both of circular tubular structures, and a central cavity is a fluid flowing channel; equivalent models on axial sections of the pre-polarized magnet and the main magnet are both magnets with opposite N poles and S poles; the pre-polarizing magnet is rotatable along its central axis;
flowing fluid to be tested through a pre-polarized magnet and a main magnet, and defining a magnetization vector generated by magnetic field magnetization as a first magnetization vector; the fluid to be tested comprises two components: a first component and a second component;
a main magnet measuring antenna detects a nuclear magnetic signal of a fluid to be measured, and the nuclear magnetic signal is defined as a first nuclear magnetic signal;
keeping the directions of the magnetic fields generated by the second section of pre-polarized magnet and the main magnet the same, and rotating the first section of pre-polarized magnet to enable the directions of the magnetic fields generated by the two pre-polarized magnets to be opposite;
flowing fluid to be tested through a pre-polarized magnet and a main magnet, and defining a magnetization vector generated by magnetic field magnetization as a second magnetization vector;
the main magnet measuring antenna detects a nuclear magnetic signal of the fluid to be measured, and the nuclear magnetic signal is defined as a second nuclear magnetic signal;
calculating the ratio of two components in the fluid to be detected according to the first nuclear magnetic signal and the second nuclear magnetic signal;
let λ be the ratio of the first component in the fluid to be measuredoThe ratio of the second component in the fluid to be measured is λw＝1-λo；
When the directions of the magnetic fields generated by the two pre-polarizing magnets and the main magnet are the same,
the fluid to be measured passes through the magnetization vector M generated by the first section of pre-polarized magnetz(t1) Comprises the following steps:
wherein, t1The time required for the fluid to be measured to pass through the first pre-polarizing magnet, T1 wIs the longitudinal relaxation time, T, of the second component1 oIs the longitudinal relaxation time of the first component,
the magnetization vector of the first component in the fluid to be measured at the time t,
the magnetization vector of a second component in the fluid to be measured at the time t;
is the saturation magnetization vector of the first component,
is the saturation magnetization vector of the second component;
the fluid to be measured passes through the magnetization vector M generated by the second-stage pre-polarized magnetz(t1+t2) Comprises the following steps:
wherein, t2The time required for the fluid to be measured to pass through the second section of pre-polarized magnet;
the magnetization vector produced by the fluid to be measured when it passes through the main magnet measuring antenna, i.e. the first magnetization vector Mz(t1+t2+t3) Comprises the following steps:
wherein, t3The time required for the fluid to be measured to pass through the measuring antenna from entering the main magnet;
the y function is obtained by:
the following equation was constructed:
will be provided with
And
substituting the formula, and extracting a formula to obtain a y function;
when the magnetic fields generated by the two pre-polarizing magnets are in opposite directions,
magnetization vector M 'generated by passing fluid to be tested through first-segment pre-polarized magnet'z(t1) Comprises the following steps:
the fluid to be measured passes through the magnetization vector M generated by the second-stage pre-polarized magnetz′(t1+t2) Comprises the following steps:
the magnetization vector generated when the fluid to be measured passes through the main magnet measuring antenna, i.e. the second magnetization vector M'z(t1+t2+t3) Comprises the following steps:
wherein the y' function is obtained by:
the following equation was constructed:
will be provided with
And
inputting the formula, extracting a formula to obtain a y' function;
the calculating the ratio of the first component to the second component in the fluid to be measured according to the first nuclear magnetic signal and the second nuclear magnetic signal specifically comprises:
the following equation was constructed:
wherein S is a first nuclear magnetic signal, S/Is the second nuclear magnetic signal.
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| CN107525819A (en) * | 2017-07-17 | 2017-12-29 | 中国石油大学(北京) | Nuclear magnetic resonance analysis of fluid instrument probe and nuclear magnetic resonance analysis of fluid instrument |
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