RU2372478C1 - Electromagnetic borehole defectoscope - Google Patents

Abstract

FIELD: oil and gas production.

SUBSTANCE: invention relates to geophysical investigations in wells and can be used for exposure and classification of defects of operational and protecting strings, oil-well tubing in oil and gas wells. Electromagnetic borehole defectoscope contains casing, electronics block, exciter coil of probe inductance, axis of which match to axis of well, and not less than three exploring inductance coils, located by perimetre of probe with magnetic axis, directed perpendicularly to axis. Magnetic axis of exciter inductance coil, excited by feeding of recurrent pulses with specified duration, directed lengthwise probe. Electronics block is implemented with ability of digital recording of electromotive difference of transients of exploring coils, as functions of time in range 1÷100 ms, that provides azimuthal and radial resolution.

EFFECT: increasing informativity of measurements ensured by ability of discharge of defects by different walls of strip, separation of defects on inner and external surface, and also increasing of sensitiveness to little defects.

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Description

The invention relates to geophysical research in wells and can be used to identify and classify defects in production and technical columns, tubing in oil and gas wells.

Known electromagnetic module (MTT) company Sondex W.L.E. to identify defects in tubing. (Magnetic thickness tools-MTT. Leding Oilfield technology. Sondex, p.10, http://www.sondex.com). The MTT probe consists of one generator coil and twelve miniature magnetic sensors mounted on the inside of the springs. The generator operates at three frequencies. The amplitude and phase of the signal on the measuring coil depend on the amount of metal surrounding the sensor.

The known probe allows you to identify defects on one tubing string or the casing interval after exiting the tubing and does not allow to separate defects on the inner and outer columns.

A device is known for detecting defects in columns and perforations. An electromagnetic well detector contains a housing, a generator coil, the magnetic axis of which is oriented along the axis, and the magnetic axis of the measuring coil is oriented perpendicular to the axis of the detector. (Pat. RF №2215143, publ. 10/27/2003, bull. No. 30).

In the known device, an alternating current is passed through the generator coil, exciting circular eddy currents in the surrounding steel pipe, which induce the emf in the measuring coils. When the measuring coils pass past defects in the column wall, characteristic changes in the magnetic field are noted.

The disadvantage of this device is the inability to separate defects on the inner and outer surfaces of the pipe.

The closest in technical essence to the claimed invention is an electromagnetic flaw detector, which eliminates the mixing of signals from the "front" and "back" pipe walls. (Pat. RF №2250372, publ. 04/20/2005, bull. No. 11).

Known flaw detector contains a non-magnetic body, an electronic unit. The transverse probe has at least three inductors located along the perimeter of the central ferromagnetic core.

Flaw detector works as follows.

The generator windings, whose magnetic axis is perpendicular to the axis of the device (transverse probe), pass a current pulse that excites eddy currents in the studied column. The signals received in the receiving windings are in the form of exponential decays, which carry information about the presence or absence of defects.

The known device has the following disadvantages.

Transverse probes in a given diameter have dimensions that do not ensure the creation of a uniform magnetic field in the pipe. Therefore, the readings are strongly influenced by the magnetic inhomogeneity of the metal, which reduces the sensitivity to small defects.

The probe readings are also significantly affected by a change in the electrical conductivity of the metal.

The present invention solves the problem of increasing the information content of measurements due to the possibility of isolating defects on different walls of the column, separating defects on the inner and outer surfaces, as well as increasing sensitivity to small defects.

This problem is solved in that in an electromagnetic borehole flaw detector containing a housing, an electronics unit, a probe generator inductor, the axis of which coincides with the axis of the well, and at least three measuring inductors located along the perimeter of the probe with magnetic axes perpendicular to its axis, the magnetic axis of the generator inductor, excited by the supply of periodic current pulses with a given duration, is directed along the probe, and the electronics unit is configured to Frova registration emf transients measuring coils as a function of time in the range of 1 ÷ 100 ms that provides radial and azimuthal resolution.

Figure 1 presents a schematic diagram of the location of the probes in the inventive flaw detector.

Figure 2 - section of the probe along aa.

Figure 3 shows the decline in the excited current.

Figure 4 is a structural diagram of a flaw detector.

Figure 5 shows an example of a measurement in a pipe with anomalies on the outside.

Figure 6 shows an example of azimuthal sounding.

Figure 7 presents an example of the operation of the device in a model well.

The inventive flaw detector contains a longitudinal generator inductor 1 of the probe, the axis of which coincides with the axis of the well and with a magnetic axis directed along the probe, measuring inductors 2 located along the perimeter of the probe, with magnetic axes perpendicular to its axis. The flaw detector is installed inside the column 3 (figure 1). The longitudinal generator inductor has an elongated shape along the axis of the probe. The number of measuring coils located around the perimeter of the probe is determined by the diameter of the probe and the dimensions of each coil (figure 2). Pos.4 - the location of the eddy currents excited by the generator inductor.

According to the structural diagram of the flaw detector (Fig. 4), a stabilizer 7 with a power source of the generator coil 8 and a secondary power source 9, as well as a transmitter 10, a communication controller 11 (containing a set of standard microcircuits selected for solving specific tasks) having a two-way communication of control and reception of signals with a measuring unit 12 (including an amplifier, ADC - an analog-to-digital converter) connected to measuring inductors 2.

Flaw detector works as follows.

A magnetizing current pulse of amplitude J with the same duration and frequency τ ₀ in the range 1 ÷ 100 ms is passed through the generator inductor 1, which excites eddy currents 4 in the surrounding steel pipe 4. The transient emfs are recorded in the receiving coils 2 (13, 14) as function of time (figure 3). The measuring unit 12, under the control of the communication controller 11, separates the signals from the measuring inductors in time, amplifies and digitizes them and transfers them to the transmitter 10 via the signal receiving lines through the controller 11, which transmits data to the surface via a wireline 5.

Temporal separation of the signal allows to obtain measurements as a function of the radius of the study. In the early days, an unsteady signal is determined only by the properties of the inner surface; with increasing time, the electromagnetic field penetrates into the metal.

The use of a solenoid of a certain length (approximately equal to the diameter of the studied pipe) with a magnetic axis (magnetic moment) directed along the axis of the column (along the probe) as a generator coil, as well as the location of the magnetic axes of the receiving coils perpendicular to the column walls, provides the maximum ratio of anomalies against defect to the magnitude of the background anomalies caused by the electromagnetic inhomogeneities of the metal (electrical conductivity σ and magnetic permeability μ), since the signal in this measurement system proportional to the difference between the longitudinal and transverse electromagnetic properties. That is, in the resulting signal, anomalies caused by the heterogeneity of the electromagnetic properties are subtracted.

Figure 4 shows an example of a measurement in a pipe having a smooth inner surface, grooves of 4.5 mm (15), 1 mm (16), 0.5 mm (17) deep were made on the outer surface of the 5.5 mm thick column 200 mm wide. At a time t = 1 ms, the electromagnetic field has not yet penetrated to a depth of 2 mm, only coupling joints of columns are marked on the curves (18). At t = 2 ms, the curves show anomalies of small amplitude against the boundaries of the groove (15), which indicates the penetration of the electromagnetic field to a depth of 2 mm. At t = 5 ms, the curves show anomalies against all grooves (15, 16, 17), which indicates the penetration of the electromagnetic field to a depth of 5.5 mm.

Figure 5 shows an example of azimuthal sounding. The module simulates a horizontal crack 19. The boundaries of violations are marked on two of the four measuring coils. Against the whole wall, anomalies are absent.

Figure 6 shows an example of the operation of the device in a model well in the early 3 ms and late 7 ms times. Various defects stand out confidently.

The proposal facilitates the interpretation of the information received, allows you to isolate and qualify defects substantially smaller than their counterparts. Using a powerful generator winding of a longitudinal probe, creating a uniform field in the tube under study, each of the additional receiving coils located along the perimeter of the probe only works with its sector of the tube under study. During repeated recordings, turning the device will only lead to the transition of the anomaly from the defect to another sector, which is not difficult for perception.

Since the size of the receiving coils is much smaller than that of a powerful generator coil, the detection of small defects becomes more real.

Claims (1)

An electromagnetic well detector containing a housing, an electronics unit, a generator inductor and at least three measuring inductors located along the perimeter of the probe with magnetic axes perpendicular to its axis, characterized in that the magnetic axis of the generator inductor excited by the supply of periodic current pulses with predetermined duration, directed along the axis of the well, and the electronics unit is configured to digitally register emf transient measuring coils as a function of time in the range of 1 ÷ 100 ms.

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