CN101294493A - Probe permanent magnet for central nuclear magnetic resonance logging tool - Google Patents

Abstract

The invention relates to a medium-duty permanent magnet for the nuclear magnetic resonance logging instrument probe, in particular to a permanent magnet for generating the gradient magnetic field underground, which is arranged on a nuclear magnetic resonance logging instrument. The permanent magnet is characterized in that the permanent magnet is formed by 10 to 50 numbers of small magnetic pillar bodies which are provided with identical cross sections and stuck together with strong adhesive after being radially charged with magnetism; the total length of the small magnetic pillar bodies after being stuck is between 1800 to 2500 mm. The small magnetic pillar bodies are made of ferrite material. Through-holes are arranged at the centers of the small magnetic pillar bodies. The cross section of each small magnetic pillar body is the middle part of the two symmetrical chords of a circle. The outer surfaces of the small magnetic pillar bodies form symmetrical planes. The two symmetrical planes of the small magnetic pillar bodies are S pole and N pole respectively. The outer diameter of the circle is between 50 to 70 mm; the length of the longest vertical line of the chords to the edge of the circle is between 5 to 30 mm. A titanium steel wire is arranged in the center hole of the medium-duty permanent magnet for the nuclear magnetic resonance logging instrument probe, and both ends of the titanium steel wire are 5 to 15 mm higher than the cross sections of the small magnetic pillar bodies. The permanent magnet has the advantages that a 360 DEG gradient magnetic field can be generated in peripheral formation of the well bore, and a detection blind area is arranged in the peripheral formation of the well bore.

Description

Probe permanent magnet for central nuclear magnetic resonance logging tool

technical field

The invention relates to the technical field of petroleum logging, and mainly relates to a key component of a nuclear magnetic resonance logging tool, which is a magnet of the probe part of a centered nuclear magnetic resonance logging tool, which is arranged on the nuclear magnetic resonance logging tool and can generate gradient magnetic field.

technical background

The probe magnet of the nuclear magnetic resonance logging tool generates a gradient magnetic field in the formation, which polarizes the hydrogen atoms in the formation in the longitudinal direction. In this way, hydrogen atoms in the formation are polarized with different magnetic field strengths at different radial depths. In order to achieve the measurement of petroleum physical information on formations of different depths.

At present, the magnets used in nuclear magnetic resonance logging tools mainly include the following types: the cylindrical magnet of Halliburton Company in the United States, which is a piece of cylindrical magnetic steel, with N poles or S poles on both sides of the circular surface. The gradient magnetic field distribution is formed by the closed magnetic field lines between the N pole and the S pole. The magnet has the advantages of simple structure, easy processing, and easy magnetization, and is suitable for making with ferrite magnetic material, which has a low level of magnetic energy and can be magnetized as a whole. The early CMR three-piece uniform magnetic field magnet of Schlumberger Company in the United States is composed of three rectangular parallelepiped magnetic steels with axial magnetic field. The front and rear of each rectangular parallelepiped magnetic steel are N poles or S poles. The magnetic lines of force generate a uniform magnetic field in the detection area. The system can only detect in a small range in one direction at a time, and the uniform field debugging and environmental requirements are very strict. Its later improved type is the samarium-cobalt gradient magnetic field magnet, which adopts the method of sticking to the well wall, and the shape of the magnet is approximately trapezoidal. The magnetic energy product of the magnet is not too high, the volume of the magnet is large, the process of the probe is complicated, and the production cost is increased. The double-cylindrical magnet of Oxford Company in the United Kingdom is composed of two rings of cylindrical magnetic steel, with an axial magnetic field, and the two ends of each cylinder are N poles or S poles. The distribution of the magnetic field is a uniform magnetic field generated by the closed magnetic field lines of the cylinder in the detection area, and the system can only detect in a small range in one direction at a time. Chinese Patent Announcement No. 1088791 provides a permanent magnet for nuclear magnetic resonance logging tools. It consists of four or more pieces of permanent magnetic steel bonded with superglue to form a cylinder. The inner circle in the cylinder is hollow, and the inner circle and the outer circle The polarity is opposite, the inside is the S pole, and the outside of the circle is the N pole. The invention has simple structure and no pole blind zone. But one pole is inside and one pole is outside. In addition, the short length of the invented magnet cannot change the length of the magnet according to the needs of the site, making it difficult to match the instrument, and is not suitable for nuclear magnetic resonance logging tools.

Contents of the invention

The object of the present invention is to provide a permanent magnet for the probe of a central nuclear magnetic resonance logging tool, which is made of non-conductive ferrite material. The magnet is a stacked cylinder with two magnetic poles on two symmetrical planes. Generate the gradient magnetic field required by the design in the 360-degree formation around the wellbore, measure the petroleum physical information of the formation at different depths, and there is no detection blind zone in the formation around the wellbore.

The technical scheme adopted in the present invention is: the permanent magnet of the central nuclear magnetic resonance logging instrument probe is formed by bonding 10-50 radially magnetized small magnetic cylinders with the same cross-section with superglue, and the total length after bonding is Between 1800-2500 mm. The small magnetic cylinder is made of ferrite material. There is a through hole in the center of the small magnetic cylinder. The cross section of the small magnetic cylinder is the middle part of two symmetrical chords of a circle, that is, a circle has two symmetrical chords, and the middle part of the two symmetrical chords is the cross-sectional shape of the small magnetic cylinder. The outer surface of the small magnetic cylinder forms a symmetrical plane. The two symmetry planes of the small magnetic cylinder are S pole or N pole, which generate a 360-degree gradient magnetic field in the formation around the wellbore, and there is no detection blind zone in the formation around the wellbore. The outer diameter of the circle is between 50-70 mm; the length of the longest vertical line from the chord to the edge of the circle is between 5-30 mm. A titanium steel wire is arranged in the central hole of the probe permanent magnet of the central nuclear magnetic resonance logging tool, and the two ends of the titanium steel wire grow out of the end faces of the two small magnetic cylinders (1) by 5-15 mm.

The length of the small magnetic cylinder is between 50-200 mm. The diameter of the through hole in the center of the small magnetic cylinder is between 2-5 millimeters.

Beneficial effects of the present invention Effects of the invention: the permanent magnet of the central nuclear magnetic resonance logging instrument probe adopts the central mode, and uses non-conductive ferrite material as the magnet, and the two magnetic poles are on a plane symmetrical on both sides, so the eddy current can be reduced It can generate the gradient magnetic field required by the design in the 360-degree formation around the wellbore, and there is no detection blind zone in the formation around the wellbore. At the same time, the design difficulty of the resonant circuit is reduced, the structure of the probe is simplified, and the overall load-bearing capacity of the probe is increased. While strengthening the length of the prepolarized magnet, it can effectively improve the speed measurement. The centering method has no blind area around the wellbore, and the generated gradient magnetic field can realize multi-dimensional well logging.

Description of drawings

Fig. 1 is a top view of the permanent magnet of the probe of the central nuclear magnetic resonance logging tool of the present invention.

Fig. 2 is a front view of the permanent magnet of the central nuclear magnetic resonance logging tool probe of the present invention, which is a half-section schematic diagram.

In the figure, 1. small magnetic cylinder, 2. titanium steel wire.

Detailed ways

Embodiment 1: refer to accompanying drawing 2. The permanent magnet of the central nuclear magnetic resonance logging tool probe is made of 10 small magnetic cylinders with the same cross-section after radial magnetization, bonded with super glue, and the total length after bonding is 2000 mm. Refer to accompanying drawing 1. The small magnetic cylinder is made of ferrite material. There is a through hole in the center of the small magnetic cylinder, and the diameter of the central through hole is 3 mm. The cross section of the small magnetic cylinder is the middle part of two symmetrical chords of a circle, that is, a circle has two symmetrical chords, and the middle part of the two symmetrical chords is the cross-sectional shape of the small magnetic cylinder. The outer surface of the small magnetic cylinder forms a symmetrical plane. The two symmetry planes of the small magnetic cylinder are S pole and N pole, which generate a 360-degree gradient magnetic field in the formation around the borehole, and there is no detection blind zone in the formation around the borehole. The sintering and magnetization of the small magnetic cylinders do not belong to the scope of the present invention and will not be described in detail. The outer diameter of the outer circle of the small magnetic cylinder is 50 millimeters; the length of the longest vertical line from the chord to the edge of the circle is 15 millimeters. Refer to attached drawing 2. A titanium steel wire is arranged in the center hole of the permanent magnet of the center type NMR logging instrument probe, and the two ends of the titanium steel wire grow 10 millimeters from the end faces of the small magnetic cylinders (1) at both ends.

During the test, the N pole of the permanent magnet of the central NMR logging tool probe generates a gradient magnetic field toward the formation around the wellbore, and the magnetic field lines return to the S level, which can generate a 360-degree gradient magnetic field in the formation around the wellbore.

Embodiment 2: refer to accompanying drawing 3. It is basically the same as Embodiment 1, except that one end surface of the small magnetic cylinder is a concave conical surface; the other end surface is a convex conical surface. The degree of the apex angle of the conical surface is between 110-170 degrees. The apex angle of the conical surface in this embodiment is 120 degrees.

Claims (3)

1, a kind of type permanent magnet for NMR logging instrument probe placed in the middle, it is characterized in that: be to form with the seccotine bonding by the small magnetic rod body (1) behind the identical radial magnetizing in 10-50 cross section, small magnetic rod body (1) bonding back total length is between the 1800-2500 millimeter, small magnetic rod body (1) adopts Ferrite Material to make, there is through hole at small magnetic rod body (1) center, the cross section of small magnetic rod body (1) is the mid portion of two symmetrical strings of circle, i.e. circle, two symmetrical strings are arranged, two shape of cross sections that symmetrical string mid portion is the small magnetic rod body, the external surface of small magnetic rod body (1) forms the plane of symmetry, two symmetrical planes of small magnetic rod body (1) are respectively the S utmost point or the N utmost point, produce the gradient magnetic of 360 degree in the wellbore stratum, do not have detection blind area in the wellbore stratum, the external diameter of described circle is between the 50-70 millimeter; Described string arrives the longest vertical line length in round edge between the 5-30 millimeter, in the centre bore of type permanent magnet for NMR logging instrument probe placed in the middle a titanium steel silk (2) is arranged, and the two ends of titanium steel silk (2) grow magnetic cylinder small in ends (1) end face 5-15 millimeter.

2, type permanent magnet for NMR logging instrument probe placed in the middle according to claim 1 is characterized in that: the length of described single small magnetic rod body (1) is between the 50-200 millimeter, and the diameter of small magnetic rod body (1) central through hole is between the 2-5 millimeter.

3, type permanent magnet for NMR logging instrument probe placed in the middle according to claim 1 and 2 is characterized in that: an end face of described small magnetic rod body is the taper seat of depression; Another end face is the taper seat of projection, and the number of degrees of taper seat drift angle are between the 110-170 degree.

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