阅读说明：本技术 一种用于核磁共振两相流测量的传感器 (Sensor for nuclear magnetic resonance two-phase flow measurement ) 是由 李利品 韩瑞强 童美帅 袁景峰 陈欢 于 2019-09-29 设计创作，主要内容包括：一种用于核磁共振两相流测量的传感器,包括最里层的油水管道,其中油水管道为两相流体通道,在油水管道的外壁上绕有射频线圈,射频线圈的外部为磁体结构,磁体结构的外部为金属外壳；所述的磁体结构1由磁体Ⅰ、磁体Ⅱ、磁体Ⅲ在其同轴线上顺次连接,磁体Ⅰ、磁体Ⅱ、磁体Ⅲ组成三段式Halbach圆柱体阵列结构,本发明分别利用三段式磁体结构来实现均匀稳定磁场；采用分段式的绕线方式来提高射频线圈的信噪比、灵敏度,两者的性能直接决定核磁共振信号的质量,使得测量的自旋回波信号更为精确和稳定,也有利于后端一系列的数据处理。(a sensor for nuclear magnetic resonance two-phase flow measurement comprises an oil-water pipeline at the innermost layer, wherein the oil-water pipeline is a two-phase fluid channel, a radio frequency coil is wound on the outer wall of the oil-water pipeline, the outside of the radio frequency coil is of a magnet structure, and the outside of the magnet structure is of a metal shell; the magnetic structure 1 is formed by sequentially connecting a magnet I, a magnet II and a magnet III on a coaxial line thereof, and the magnet I, the magnet II and the magnet III form a three-section Halbach cylinder array structure; the signal-to-noise ratio and the sensitivity of the radio frequency coil are improved by adopting a sectional winding mode, and the performance of the radio frequency coil and the sensitivity directly determines the quality of a nuclear magnetic resonance signal, so that the measured spin echo signal is more accurate and stable, and a series of data processing at the rear end is facilitated.)

1. The sensor for nuclear magnetic resonance two-phase flow measurement is characterized by comprising an oil-water pipeline (4) at the innermost layer, wherein the oil-water pipeline (4) is a two-phase fluid channel, a radio frequency coil (2) is wound on the outer wall of the oil-water pipeline (4), the outside of the radio frequency coil (2) is a magnet structure (1), and the outside of the magnet structure (1) is a metal shell (3).

2. The two-phase flow sensor for NMR measurement according to claim 1, wherein the magnet structure 1 is formed by sequentially connecting a magnet I, a magnet II and a magnet III on a coaxial line, the magnet I, the magnet II and the magnet III form a three-section Halbach cylinder array structure, the inner diameter of each three-section cylinder is 20mm, the magnet II is located at the front end of the three-section magnet structure, the magnet III is located at the rear end of the magnet structure, and the magnet I is located between the magnet II and the magnet III.

3. A sensor for two-phase nuclear magnetic resonance measurement according to claim 2,

The magnet I consists of a magnet A, a magnet B and a magnet C, wherein each section of magnet is 40mm long, the inner diameter of each section of magnet is 20mm, and the outer diameter of each section of magnet is 40 mm;

In the magnet I, in the longitudinal direction, a magnet A, a magnet B and a magnet C are all composed of a magnet (I) and a magnet (II), and are sequentially arranged in an anticlockwise direction, and the magnetizing directions are also arranged in a clockwise direction which changes by 90 degrees every time, wherein the magnetizing direction of the magnet (I) is horizontally leftward, the magnetizing direction of the magnet (II) is vertically upward, the magnetizing direction of the magnet (III) is horizontally rightward, the magnetizing direction of the magnet (IV) is vertically downward, the magnetizing direction of the magnet (III) is horizontally leftward, the magnetizing direction of the magnet (III) is vertically upward, the magnetizing direction of the magnet (III) is horizontally rightward, the magnetizing direction of the magnet (III) is downward, and the assembling blocks, the magnetizing directions and the arrangement sequence of the magnet A, the magnet (B) and the magnet (C) are the same.

4. A sensor for two-phase nuclear magnetic resonance measurement according to claim 2,

The length of the magnet II is 22mm, the inner diameter of the magnet II is 20mm, the outer diameter of the magnet II is 45mm, and the difference between the outer diameter of the magnet II and the outer diameter of the magnet I is 5 mm;

The magnet II and the magnet III are both composed of 8 magnetic blocks, the 8 magnetic blocks of the magnet II and the magnet III are also sequentially arranged in an anticlockwise direction, and the magnetizing direction is also in a clockwise direction which changes 90 degrees every time;

And the length, the inner diameter, the outer diameter, the magnetic block arrangement sequence and the magnetizing direction parameters of the magnetic blocks are all the same.

5. The sensor for two-phase nuclear magnetic resonance measurement according to claim 1, wherein the radio frequency coil (2) is composed of a coil D, a coil E, a coil F and a shielding layer G, the coil D is wound at the front end of the coil structure, the coil F is wound at the rear end of the coil structure, the coil E is wound at the middle position between the coil D and the coil F, and the shielding layer G is mainly distributed at the outer layers of the coil D, the coil E and the coil F, wherein the coil D has a wire diameter of 1mm and 4 turns, the turn pitch is 0.5mm, the coil F has a wire diameter of 1mm and 4 turns, the turn pitch is 0.5mm, and the coil E has a wire diameter of 1mm and 6 turns, and the turn pitch is 1 mm.

6. A two-phase nmr measurement sensor according to claim 1, wherein the metal housing (3) is made of aluminum, and has a total length of 165mm and a thickness of 3 mm.

7. The sensor for two-phase NMR measurement according to claim 1, wherein the oil/water pipe (4) is acrylic pipe material with an outer diameter of 20 mm.

Technical Field

the invention relates to the field of oil-water two-phase flow parameter measurement, in particular to a sensor for nuclear magnetic resonance two-phase flow measurement, which is used for measuring nuclear magnetic resonance two-phase flow parameters.

background

In oil exploitation, the variability and complexity of flow characteristics such as oil-water two-phase flow pattern, flow rate of each phase and the like make two-phase flow measurement still a great technical problem in the oil industry, and currently, common measurement methods include an electrical method, a tomography method and a nuclear magnetic resonance method. Because the electrical method belongs to contact measurement, the technical limitations which cannot be overcome, such as sensitivity reduction of the sensor, larger measurement error and the like, are easily caused; the tomography method is greatly influenced by the imaging speed and the data volume, and the effect of dynamic measurement in the two-phase flow is not ideal.

The two-phase flow measuring technology based on the nuclear magnetic resonance principle has the advantages that the measuring result is not influenced by macroscopic physical characteristics, the measuring precision is high, the limitation of the traditional measuring method can be effectively overcome, and the two-phase flow measuring technology is a new direction in the field of two-phase flow research at present. However, in the nuclear magnetic resonance two-phase flow measurement, generally, the sensor is affected by the uniformity of a static magnetic field, the detection sensitivity of a radio frequency coil and the like, and the oil-water two-phase flow parameter information cannot be accurately measured, so that the nuclear magnetic resonance sensor plays a decisive role in the two-phase flow measurement precision. At present, a nuclear magnetic resonance two-phase flow sensor mostly adopts a single structure, and has the following defects in practical application: (1) the permanent magnet structure has the defects of air gaps, low magnetic field intensity, uneven magnetic field, over-fast attenuation of air gap field and the like; (2) when the two groups of coils work, the two groups of coils are easy to be coupled with each other, the signal-to-noise ratio is reduced, the energy transfer error is caused and the like; (3) when the receiving coil and the transmitting coil are combined into a whole, the requirements of high strength and uniformity of a radio frequency magnetic field are difficult to meet at the same time, and meanwhile, the sensitivity and the signal to noise ratio of a received signal are obviously reduced.

Disclosure of Invention

aiming at the problems of the existing nuclear magnetic resonance two-phase flow sensor, the invention aims to provide a sensor for measuring the nuclear magnetic resonance two-phase flow, which is used for constructing a three-section type magnet structure and a section type radio frequency coil and has the characteristics of high shimming, high sensitivity and high signal-to-noise ratio.

in order to achieve the purpose, the invention adopts the following technical scheme:

a sensor for nuclear magnetic resonance two-phase flow measurement comprises an innermost oil-water pipeline 4, wherein the oil-water pipeline 4 is a two-phase fluid channel, a radio frequency coil 2 is wound on the outer wall of the oil-water pipeline 4, a magnet structure 1 is arranged outside the radio frequency coil 2, a metal shell 3 is arranged outside the magnet structure 1,

Magnet structure 1 connect in order on its coaxial line by magnet I, magnet II, magnet III, three-section type Halbach cylinder array structure is constituteed to magnet I, magnet II, magnet III, and the internal diameter of three-section cylinder is 20mm, wherein magnet II is located the front end of three-section type magnet structure, magnet III is located the rear end of magnet structure, magnet I is located the centre of magnet II and magnet III.

The magnet I consists of a magnet A, a magnet B and a magnet C, wherein each section of magnet is 40mm long, the inner diameter of each section of magnet is 20mm, and the outer diameter of each section of magnet is 40 mm;

In the longitudinal direction of the magnet I, the magnet A, the magnet B and the magnet C are all composed of a first magnet and a second magnet which are sequentially arranged in an anticlockwise direction, and the magnetizing directions are also arranged in a clockwise direction which changes 90 degrees every time, wherein the magnetizing direction of the first magnet is horizontally leftward, the magnetizing direction of the second magnet is vertically upward, the magnetizing direction of the third magnet is horizontally rightward, the magnetizing direction of the fourth magnet is vertically downward, the magnetizing direction of the fifth magnet is horizontally leftward, the magnetizing direction of the sixth magnet is vertically upward, the magnetizing direction of the seventh magnet is horizontally rightward, the magnetizing direction of the fourth magnet is downward, and the number of assembling blocks, the magnetizing directions and the arrangement sequence of the magnets A, B, C are the same.

The length of the magnet II is 22mm, the inner diameter of the magnet II is 20mm, the outer diameter of the magnet II is 45mm, and the difference between the outer diameter of the magnet II and the outer diameter of the magnet I is 5 mm;

The magnet II and the magnet III are both composed of 8 magnetic blocks, the 8 magnetic blocks of the magnet II and the magnet III are also sequentially arranged in an anticlockwise direction, and the magnetizing direction is also in a clockwise direction which changes 90 degrees every time;

And the length, the inner diameter, the outer diameter, the magnetic block arrangement sequence and the magnetizing direction parameters of the magnetic blocks are all the same.

The radio frequency coil 2 constitute by coil D, coil E, coil F, shielding layer G, coil D coiling is at coil structure front end, coil F coiling is at coil structure rear end, coil E coiling is in coil D and coil F's intermediate position, shielding layer G mainly distributes at coil D, coil E, coil F's skin, wherein coil D, the diameter of a thread 1mm, 4 circles, the circle interval is 0.5mm, coil F, the diameter of a thread 1mm, 4 circles, the circle interval is 0.5mm, coil E, the diameter of a thread 1mm, 6 circles, the circle interval is 1 mm.

the metal shell 3 is made of aluminum, and has a total length of 165mm and a thickness of 3 mm.

The oil water pipeline 4 adopts an acrylic pipe material, and the outer diameter is 20 mm.

the invention realizes uniform and stable magnetic field by using three-section type magnet structures respectively; the signal-to-noise ratio and the sensitivity of the radio frequency coil are improved by adopting a sectional winding mode, and the performance of the radio frequency coil and the sensitivity directly determines the quality of a nuclear magnetic resonance signal, so that the measured spin echo signal is more accurate and stable, and a series of data processing at the rear end is facilitated.

drawings

fig. 1 is a schematic view of the structure of a nuclear magnetic resonance measurement sensor according to the present invention.

FIG. 2 is a schematic view of the magnetizing direction of a three-section Halbach magnet in the sensor.

FIG. 3 is a schematic distribution diagram of a magnet A, a magnet B and a magnet C in a magnet I.

Fig. 4 is a schematic diagram of a structure of a radio frequency coil in the sensor.

Fig. 5 is a schematic diagram of axial magnetic flux density mode change of a three-section Halbach magnet, where fig. 5(a) is a magnetic field change rule of a magnet i, fig. 5(b) is a magnetic field change rule of a magnet with two ends stretched by 20mm, fig. 5(c) is a magnetic field change rule of a magnet with two ends stretched by 22mm, fig. 5(d) is a magnetic field change rule of a magnet with two ends stretched by 25mm, fig. 5(e) is a magnetic field change rule of an optimized magnet with two ends stretched, fig. 5(f) is a magnetic field change rule of a magnet with an outer diameter stretched by 42mm, fig. 5(g) is a magnetic field change rule of a magnet with an outer diameter stretched by 45mm, and fig. 5(h) is a.

FIG. 6 is a graph of the number of turns of the RF coil versus the signal-to-noise ratio for different wire diameters.

Fig. 7 is a graph showing the variation of the axial magnetic induction of the rf coil with respect to the length and the number of turns, in which fig. 7(a) is a dot diagram and fig. 7(b) is a line diagram.

detailed description of the preferred embodiments

the present invention will be described in further detail with reference to the accompanying drawings.

Referring to fig. 1, 2, 3 and 4, the sensor for nuclear magnetic resonance two-phase flow measurement comprises an innermost oil-water pipeline 4, wherein the oil-water pipeline 4 is a two-phase fluid channel, a radio frequency coil 2 is wound on the outer wall of the oil-water pipeline 4, a magnet structure 1 is arranged outside the radio frequency coil 2, a metal shell 3 is arranged outside the magnet structure 1, and the metal shell 3 is fixed outside the magnet, so that the position of the magnet is fixed, and magnetic leakage of the magnet is prevented from generating.

Magnet structure 1 connect in order on its coaxial line by magnet I, magnet II, magnet III, three-section type Halbach cylinder array structure is constituteed to magnet I, magnet II, magnet III, and the internal diameter of three-section cylinder all is 20mm, wherein magnet II is located the front end of three-section type magnet structure, magnet III is located the rear end of magnet structure, magnet I is located the centre of magnet II and magnet III. When magnet I and II are connected with magnet III at both ends respectively, because there is repulsion between magnet I and II and magnet III and I, so two end kneck must zonulae occludens, avoids the magnet position to take place the skew, influences final experimental result.

The magnet I consists of a magnet A, a magnet B and a magnet C, wherein each section of magnet is 40mm long, the inner diameter of each section of magnet is 20mm, and the outer diameter of each section of magnet is 40 mm;

in the magnet I, in the longitudinal direction, a magnet A, a magnet B and a magnet C are all composed of a magnet (I) and a magnet (II), and are sequentially arranged in an anticlockwise direction, and the magnetizing directions are also arranged in a clockwise direction which changes by 90 degrees every time, wherein the magnetizing direction of the magnet (I) is horizontally leftward, the magnetizing direction of the magnet (II) is vertically upward, the magnetizing direction of the magnet (III) is horizontally rightward, the magnetizing direction of the magnet (IV) is vertically downward, the magnetizing direction of the magnet (III) is horizontally leftward, the magnetizing direction of the magnet (III) is vertically upward, the magnetizing direction of the magnet (III) is horizontally rightward, the magnetizing direction of the magnet (III) is downward, and the assembling blocks, the magnetizing directions and the arrangement sequence of the magnet A, the magnet (B) and the magnet (C) are the same.

the length of the magnet II is 22mm, the inner diameter of the magnet II is 20mm, the outer diameter of the magnet II is 45mm, and the difference between the outer diameter of the magnet II and the outer diameter of the magnet I is 5 mm;

The magnet II and the magnet III are both composed of 8 magnetic blocks, the 8 magnetic blocks of the magnet II and the magnet III are also sequentially arranged in an anticlockwise direction, and the magnetizing direction is also in a clockwise direction which changes 90 degrees every time;

And the length, the inner diameter, the outer diameter, the magnetic block arrangement sequence and the magnetizing direction parameters of the magnetic blocks are all the same.

the radio frequency coil 2 comprises a coil system and an insulating layer, the coil system is wound on the outer wall of the oil-water pipeline 4 by adopting an enameled wire, and the insulating layer is positioned on the outer layer of the coil system.

The radio frequency coil 2 constitute by coil D, coil E, coil F, shielding layer G, coil D coiling is at coil structure front end, coil F coiling is at coil structure rear end, coil E coiling is in coil D and coil F's intermediate position, shielding layer G mainly distributes at coil D, coil E, coil F's skin, wherein coil D, the diameter of a thread 1mm, 4 circles, the circle interval is 0.5mm, coil F, the diameter of a thread 1mm, 4 circles, the circle interval is 0.5mm, coil E, the diameter of a thread 1mm, 6 circles, the circle interval is 1 mm.

the radio frequency coil device comprises a coil D, a coil E, a coil F and a shielding layer G, wherein the coil is wound in a winding mode according to simulation parameters, and the shielding layer also needs to cover the outside of the whole enameled wire, so that the external electromagnetic interference is avoided.

The metal shell 3 is made of aluminum, and has a total length of 165mm and a thickness of 3 mm.

The oil water pipeline 4 adopts an acrylic pipe material, and the outer diameter is 20 mm.

Referring to fig. 5, the working principle of the present invention includes the following steps:

(1) In the nuclear magnetic resonance multiphase flow experiment, the requirement on the strength of the magnet is lower, so that a ferrite material with lower remanence is selected.

(2) The number of the assembly blocks adopts an 8-subblock Halbach array structure, and the design optimization is mainly carried out on a Halbach cylinder structure with the height of 120mm, the inner diameter of 20mm and the outer diameter of 40 mm.

(3) Under the condition that the inner diameter is determined to be constant and the outer diameter is increased to 45mm, the lengths of the superposed magnets at the two ends are respectively 20mm, 22mm and 25mm, and the optimized length parameter is obtained. The outer diameter is fixed to be 45mm and is not changed, and compared with magnetic flux density mode images between 0mm and 80mm in the axial direction of four Halbach array structures with different stretching lengths, the magnetic flux density mode images are respectively the original Halbach magnet magnetic field change rule, the magnet magnetic field change rule of 20mm stretched at two ends, the magnet magnetic field change rule of 22mm stretched at two ends and the magnet magnetic field change rule of 25mm stretched at two ends, as shown in figure 5. Through observation and analysis, the axial magnetic fields of the three structures (b), (c) and (d) all change at about 243mT, the change range of the flux density mode of the Halbach structure axial magnetic field with the two ends stretched by 22mm is the minimum within 0-80 mm, the change range is within 243 mT-244.1 mT, namely the difference is only 1.1mT, and finally the three-section type magnet with the two ends stretched by 22mm is the structure with the best magnetic field uniformity.

(4) in the case where the inner diameter is constant and the magnet length is 22mm, the outer diameter is changed to 42mm, 45mm, and 47mm, respectively, to obtain an optimized outer diameter parameter. The stretching length of the additional magnet is fixed to be 22mm and is unchanged, compared with the magnetic flux density mode change rule between 0-80 mm in the axial direction of four Halbach array structures, as shown in (e), (f), (g) and (h) of figure 5, the two-end stretching optimization magnet magnetic field change rule, the outer diameter stretching optimization magnet magnetic field change rule and the outer diameter stretching optimization magnet magnetic field change rule are shown in figure 5, wherein the outer diameter stretching optimization magnet magnetic field change rule is shown in figure 5, and. Through observing and analyzing the images (f), (g) and (h), the Halbach structure with the outer diameter stretched by 45mm has the smallest change amplitude of the axial magnetic field and changes between 243mT and 244.1mT, namely, the phase difference is only 1.1mT, the magnetic field uniformity is the best, and finally the Halbach structure with the two ends stretched by 20mm can be obtained as the structure with the best simulation effect.

(5) In the analysis and comparison of two parameters of comprehensive stretching length and stretching outer diameter, the Halbach magnet structure with the length stretching of 22mm and the outer diameter stretching of 45mm can meet the requirement that the axial uniform length is 80 mm.

(6) According to the simulation experiment result parameters, the sizes of the magnet shell and the magnet are actually customized, and a novel magnet structure meeting the requirements can be obtained.

Referring to fig. 6 and 7, the design principle of the invention is as follows:

In the process of designing the solenoid radio frequency coil, the main parameters comprise the number of turns N of the coil, the distance g/2 between turns of the coil, the length L of the coil, the diameter D of the coil and the like. The signal-to-noise ratio is the main basis in the design of the solenoid coil, and for the convenience of calculation, the constant in the formula is simplified, and the expression of the relative signal-to-noise ratio is obtained as follows:

The main optimization direction is to obtain the best relative signal-to-noise ratio by maximizing the coil sensitivity and minimizing the effective resistance.

In the low-field nuclear magnetic resonance multiphase flow measurement, a test tube with the diameter of 20mm is used for containing samples in a multi-selection mode, the coil driving emission power and the current carrying capacity are considered, enamelled copper wires are selected according to 2.5-3A per square millimeter, the wire diameter is controlled to be 0.6-1.5 mm in the manufacturing process of the nuclear magnetic resonance multiphase flow sensor coil, and the rule of influence of the number of turns of the coil under different wire diameters on the signal to noise ratio is researched through simulation analysis and is shown in figure 6. It can be seen that when the wire diameter is 0.5mm, the signal-to-noise ratio of the 24-turn coil is the highest, when the wire diameter is 1mm, the signal-to-noise ratio of the 12-turn coil is the highest, and when the wire diameter is 1.5mm, the signal-to-noise ratio of the 5-turn coil is the highest.

the quality factor Q is an important parameter representing the quality of the coil. The quality factor Q is defined as the ratio of the inductive reactance exhibited by the coil when the coil is operated at an ac voltage of a certain frequency to the dc resistance of the coil:

The higher the quality factor Q, the lower the energy loss of the loop and the higher the performance of the coil. The influence of the coil turn pitch on the quality factor is obtained by a simulation method as shown in table 1: as can be seen from table 1, the value of the coil quality factor reaches a maximum when the turn pitch g/2 is equal to the wire diameter, i.e., g — d, for different wire diameters.

TABLE 1

According to the law of the Biot-Safa method, the magnetic field intensity generated by any point on the axis of a single circular coil is as follows:

and (3) completing the integration of Z' on the solenoid coil with the length L to obtain the magnetic induction intensity of any point on the axis:

As can be seen from fig. 7, the dual effects of the magnetic field uniformity and the signal-to-noise ratio must be considered comprehensively, and on the basis of ensuring the optimal signal-to-noise ratio under the condition that the number of turns and the length of the coil are not changed, the magnetic field uniformity is improved by adopting a winding manner of density combination. The parameters finally determined are: the diameter of the wire is 1mm, the number of turns is 14, the middle part is 6, the turn interval is 1mm, the two ends are respectively 4, and the turn interval is 0.5 mm.

The uniformity of the radial magnetic field of the optimized coil structure is good, the uniformity range of the axial magnetic field is increased to-40 mm compared with the uniformity range of-20 mm before optimization, the uniformity space is greatly improved, and the error allowable range of the magnetic resonance device is met.