SU802892A1 - Magnetic susceptibility sensor - Google Patents

Description

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The invention relates to well logging and may be used in magnetic susceptibility carrot devices or in well caps.

Magnetic susceptibility sensors for well equipment are known, which contain a ferrite rod with an inductance coil wound on it, which is connected to an AC measuring bridge fl. The magnitude of the inductive impedance of the coil and the measured signal are determined by the magnetic susceptibility of the medium in which the sensor is located.

The disadvantage of these sensors is that the signal taken from them is determined by the averaged magnetic susceptibility of the environment surrounding the sensor (as applied to measurements in wells with averaged magnetic susceptibility of the borehole walls at the measurement site). Measurement results are also obtained averaged and insufficiently detailed. By which it is impossible to estimate the distribution of magnetic minerals in the walls of the well.

As shown by the research core. and mine walls, the magnetic mineral in the ores (e.g., magnetite in magnetite ore or pyrrhotite in the popimetechic one.) are distributed unevenly and extreme, .. studying the patterns of this distribution under natural conditions, in 4acftioCTH in the walls of boreholes, represents a large scientific and practical interest as with

geological as well as technological. In addition, quantitative interpretation must take into account changes in the borehole diameter. This leads to large errors in determining the thickness of thin interlayers of magnetic ores intersected by a borehole at a right angle, since the width of the anomaly of magnetic susceptibility exceeds the maximum

reservoir due to the influence of the opposite walls of the well.

Also known is a magnetic susceptibility meter used for

examining specimens, outcrops and mine walls 2j. The sensor of this meter contains an H-shaped core with four exciting inductors placed

at its ends, and one measuring winding located on the middle part of the core. The sensor is in a housing of non-magnetic and non-conductive material. The excitation of the coils is connected to an alternating current source so that the magnetic fluxes in the middle part of the core are directed towards each other. The coils have the same number of turns and identical placement, therefore, when the sensor is in a nonmagnetic environment, the magnetic fluxes in the middle part of the core completely compensate each other, and the signal in the measuring winding is zero. If the working side of the sensor is applied to the sample with superior magnetic properties, then the magnetic resistance from this side of the sensor decreases, and the magnetic flux increases, and a differential magnetic flux appears in the middle of the core, which causes a signal in the measuring winding of the sensor. The signal is the measure of the magnetic susceptibility of the sample. With the help of this sensor it is possible to obtain more detailed research. However, it is not suitable for measurements in boreholes, because when the working side of the sensor is pressed against one of the walls of the well, the opposite wall affects the magnetic flux of the non-working side of the sensor and, therefore, the differential magnetic flux in the middle part of the core and the measured signal . The purpose of the invention is to increase the spatial resolution and accuracy of measurements. The goal is achieved by the fact that in the magnetic susceptibility sensor, containing an H-shaped serde from ferromagnetic material with four coils that excite uktivnosti placed at its ends, and a measuring winding placed at its middle part, the core is equipped with a plate of ferromagnetic material installed on the non-working side of the sensor with the ability to adjust the non-magnetic gap between the core and the plate. ; Due to this, the magnetic flux on the non-working side of the sensor is complete (It mimics through this plate and is not affected by the magnetic properties of the minerals located on this side of the sensor. The measured signal depends only on the magnetic properties of the borehole wall to which the working side of the sensor is pressed. Adjustable non-magnetic The gap between the core and the plate is necessary for balancing the sensor in a non-magnetic environment. The drawing shows a sensor, a partial longitudinal section is shown At the ends of an H-shaped core 1 made of ferromagnetic In total, four excitation coils 2–5 are placed, and measuring winding 6 is placed on the middle part of the core. On the non-working side of the sensor, the ends of the H-shaped core are clamped with a plate 7 made of ferromagnetic material installed with a non-magnetic gap. The plate is attached to the core with non-magnetic screws 8, on which in the non-magnetic gap between the core and the plate there are wound spiral springs 9 also of non-magnetic material. The sensor is housed in an airtight housing 10 of non-magnetic and non-conducting material, filled nnom transformer oil. The sensor can also be located in the remote unit of the wellbore, which presses the working side of the sensor to the test wall of the borehole 11. Exciting coils 2-5 are connected in series to an acoustic frequency AC source so that the magnetic fluxes Φ and generated by coils 2 and 4 and 3 and 5, respectively, are directed in the middle part of the core towards each other. The number of turns in these coils are equal in pairs. In a non-magnetic environment, the ratio between the number of turns in coils 2 and 4 and 3 and 5 and the size of the non-magnetic gap are chosen so that the magnetic flux F is equal and opposite in the direction of the flux Фз. in this case, the total magnetic flux in the middle part of the sisterch is zero, F F - O and the signal in winding 6 is absent. When the sensor is pressed against the working side, on which coils 2 and 4 are placed, against the wall of the borehole 11, having increased magnetic susceptibility, the magnetic resistance in the magnetic circuit of the flux Φ decreases, and, notOK Φ itself increases. In the middle part of the core, a differential magnetic flux occurs. - $ 1 O, and a measured signal appears in the winding. The opposite wall of the borehole .12 does not cause a change in the magnetic flux, since it is locked through the plate 7 made of ferromagnetic material, and its magnetic resistance is much less than the magnetic resistance of the rocks composing the borehole walls. The application of the proposed sensor ensures that the detailed study of the magnetic properties of the borehole walls increases, allows us to study the patterns of the distribution of magnetic minerals in the borehole walls and to avoid errors in determining the thickness of thin layers and seams with enhanced magnetic properties of 1m at

their intersection by the well is not at a right angle, and also simplifies the quantitative interpretation of the results, since it eliminates the operation of introducing a correction for the diameter of the well.

invention formula

Magnetic susceptibility sensor containing an H-shaped core of ferrous material with four exciting inductors placed at its ends and a measuring winding placed at its middle part, characterized in that, in order to increase the spatial resolution and accuracy of measurements, the core it is equipped with a plate made of ferromagnetic material mounted on the non-working side of the sensor with the ability to adjust the non-magnetic gap between the core and the plate.

Sources of information taken into account in the examination

1. Zeltzman, PA Constructing; equipment for geophysical research borehole. - M., Nedra, 1968, p. 91-93.

2.Methodical guidelines for determining the physical properties of rocks and minerals. Ed. N. B. Dortman and M. L. Ozerskaya,

M., Gosgeoltekhizdat, 19b2, pp. 36-43 j (prototype),

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Claims (1)

Claim Magnetic susceptibility sensor containing an H-shaped core made of ferromagnetic material with four exciting inductance coils located at its ends, and a measuring coil located on its middle part, characterized in that, in order to increase spatial resolution and accuracy of measurements, the core is equipped with a plate of ferromagnetic material mounted on the non-working side of the sensor with the possibility of adjusting the non-magnetic gap between the core and the plate.